U.S. patent application number 14/347521 was filed with the patent office on 2014-08-14 for refrigerant management in hvac systems.
This patent application is currently assigned to TRANE INTERNATIONAL INC.. The applicant listed for this patent is TRANE INTERNATIONAL INC.. Invention is credited to Ronald Maurice Cosby II, Michael William Groen, Jonathan Phillip Hartfield, Stephen Anthony Kujak, Harry Kenneth Ring.
Application Number | 20140223936 14/347521 |
Document ID | / |
Family ID | 47996359 |
Filed Date | 2014-08-14 |
United States Patent
Application |
20140223936 |
Kind Code |
A1 |
Hartfield; Jonathan Phillip ;
et al. |
August 14, 2014 |
REFRIGERANT MANAGEMENT IN HVAC SYSTEMS
Abstract
Generally, management of refrigerant in an evaporator of an HVAC
chiller is described. Methods, systems, and apparatuses to manage
refrigerant in an evaporator can include one or combination of the
following approaches: (1) by use of a refrigerant displacement
array to physically prevent refrigerant from residing where the
array is positioned; (2) by control of the interstitial velocity of
refrigerant flow within the volume of the shell of an evaporator;
(3) by a phase biased distribution of the refrigerant mixture, so
that a gaseous portion is uniformly distributed into the evaporator
shell, while liquid refrigerant and oil is distributed into the
evaporator shell at a designated area; and (4) by preventing or
reducing the occurrence of foaming inside the evaporator through
anti-foaming surfaces, such as by the use of refrigerant phobic and
lubricant phobic material(s). Refrigerant management can in turn
improve the thermal performance and overall efficiency of the
evaporator.
Inventors: |
Hartfield; Jonathan Phillip;
(La Crosse, WI) ; Ring; Harry Kenneth; (Houston,
MN) ; Groen; Michael William; (La Crosse, WI)
; Kujak; Stephen Anthony; (Onalaska, WI) ; Cosby
II; Ronald Maurice; (La Crosse, WI) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TRANE INTERNATIONAL INC. |
PISCATAWAY |
NJ |
US |
|
|
Assignee: |
TRANE INTERNATIONAL INC.
PISCATAWAY
NJ
|
Family ID: |
47996359 |
Appl. No.: |
14/347521 |
Filed: |
September 26, 2012 |
PCT Filed: |
September 26, 2012 |
PCT NO: |
PCT/US2012/057287 |
371 Date: |
March 26, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61674601 |
Jul 23, 2012 |
|
|
|
61539325 |
Sep 26, 2011 |
|
|
|
Current U.S.
Class: |
62/115 ;
165/133 |
Current CPC
Class: |
F25B 39/02 20130101;
F28D 3/04 20130101; F28D 3/02 20130101; F25B 39/028 20130101; F28F
13/182 20130101; F28F 9/0131 20130101; F25B 2339/0242 20130101;
F28F 13/02 20130101; F28D 21/0017 20130101 |
Class at
Publication: |
62/115 ;
165/133 |
International
Class: |
F28F 13/02 20060101
F28F013/02; F28F 13/18 20060101 F28F013/18; F25B 39/02 20060101
F25B039/02 |
Claims
1-6. (canceled)
7. A method of refrigerant management in an evaporator of a HVAC
chiller, comprising: causing refrigerant to enter a volume present
inside a shell of an evaporator; wetting outer surfaces of tubes in
a tube bundle with the refrigerant, the step of wetting comprises
attaining a mist or spray flow of a refrigerant mixture through the
interstitial volume of the shell including between outer surfaces
of the tubes of the tube bundle, the step of attaining a spray flow
of the refrigerant comprises maintaining a target interstitial
velocity of refrigerant flow suitable to attain the spray flow of
refrigerant above a threshold interstitial velocity that does not
attain the spray flow of refrigerant; and evaporating refrigerant
inside the shell by way of heat transfer with a process fluid
traveling through the tubes of the tube bundle and releasing
evaporated refrigerant from the shell.
8-9. (canceled)
10. A method of refrigerant management in an evaporator of a HVAC
chiller, comprising: causing refrigerant to enter a volume present
inside a shell of an evaporator, wetting outer surfaces of tubes in
a tube bundle with the refrigerant; evaporating refrigerant inside
the shell by way of heat transfer with a process fluid traveling
through the tubes of the tube bundle; reducing the formation of
foam by one or more of the refrigerant and lubricant during the
evaporating step, the step of reducing formation of foam comprises
causing the refrigerant to interact with anti-foaming surfaces
present within the shell; and releasing evaporated refrigerant from
the shell.
11. The method of claim 10, wherein the step of causing the
refrigerant to interact with the anti-foaming surfaces comprises
causing the refrigerant to interact with refrigerant phobic
surfaces and causing lubricant present with the refrigerant to
interact with lubricant phobic surfaces, the refrigerant phobic and
lubricant phobic surfaces being present within the shell.
12. The method of claim 11, wherein the refrigerant phobic and
lubricant phobic surfaces being present on one or more of spacers
arranged and configured within the shell and of baffles having
openings through which the tubes are inserted.
13. The method of claim 11, wherein the refrigerant phobic and
lubricant phobic surfaces being present on one or more of inner
surfaces of the shell and of outer surfaces of the tube bundle.
14. The method of claim 11, wherein the refrigerant phobic and the
lubricant phobic surfaces being present on a mesh placed within the
shell of the evaporator.
15. The method of claim 11, wherein the anti-foaming surfaces being
both refrigerant phobic and lubricant phobic.
16. A refrigerant management system for an evaporator of an HVAC
chiller, comprising: a shell having a volume to receive a
refrigerant mixture therein; a tube bundle disposed inside the
shell, the tube bundle including tubes extending within the shell
to pass a process fluid therethrough and to undergo heat transfer
with the refrigerant; and anti-foaming surfaces disposed within the
volume of the shell, the anti-foaming surfaces are arranged and
configured inside the shell to interact with the refrigerant
mixture.
17. The refrigerant management system of claim 16, wherein the
anti-foaming surfaces comprise: refrigerant phobic surfaces
disposed within the volume of the shell; and lubricant phobic
surfaces disposed within the volume of the shell, wherein the
refrigerant phobic surfaces and the lubricant phobic surfaces are
arranged and configured inside the shell to interact, respectively,
with refrigerant and lubricant present in the refrigerant
mixture.
18. The refrigerant management system of claim 17, wherein the
refrigerant phobic and lubricant phobic surfaces including thereon
one or more of materials being a polymeric plastic, a galvanized
material, an aluminum iron material, an inorganic coating, and an
integral surface enhancement created on the surfaces.
19. The refrigerant management system of claim 17, wherein the
refrigerant phobic and lubricant phobic surfaces being present on
one or more of spacers arranged and configured within the shell and
of baffles having openings through which the tubes are
inserted.
20. The refrigerant management system of claim 17, wherein the
refrigerant phobic and lubricant phobic surfaces being present on
one or more of inner surfaces of the shell and of outer surfaces of
the tube bundle.
21. The refrigerant management system of claim 17, wherein the
refrigerant phobic and the lubricant phobic surfaces being present
on one or more a mesh surfaces and placed within the shell of the
evaporator.
22. The refrigerant management system of claim 16, wherein the
anti-foaming surfaces being both refrigerant phobic and lubricant
phobic.
23. A method of refrigerant management in a refrigerant and/or oil
tank of a HVAC chiller, comprising: causing one or more of
refrigerant and lubricant to enter a volume present inside a shell
of a tank; flashing one or more of refrigerant and lubricant inside
the shell by way of pressure loss; and reducing the formation of
foam by one or more of the refrigerant and lubricant during the
refrigerant flashing step, the step of reducing formation of foam
comprises causing one or more of the refrigerant to and lubricant
to interact with anti-foaming surfaces present within the
shell.
24. The method of claim 23, wherein the step of causing one or more
of the refrigerant and lubricant to interact with the anti-foaming
surfaces comprises causing the refrigerant to interact with
refrigerant phobic surfaces and causing lubricant present to
interact with lubricant phobic surfaces, the refrigerant phobic and
lubricant phobic surfaces being present within the shell.
25. The method of claim 23, wherein the refrigerant phobic and
lubricant phobic surfaces being present on one or more of inner
surfaces of the shell or baffles within the shell.
26. The method of claim 23, wherein the refrigerant phobic and
lubricant phobic surfaces being present on a mesh placed within the
shell of an evaporator.
27. The method of claim 23, wherein the anti-foaming surfaces being
both refrigerant phobic and lubricant phobic.
28. A refrigerant management system for a refrigerant and/or oil
tank of a HVAC chiller, comprising: a shell having a volume to
receive a refrigerant mixture therein; and anti-foaming surfaces
disposed within the volume of the shell, the anti-foaming surfaces
are arranged and configured inside the shell to interact with the
refrigerant mixture.
29. The refrigerant management system of claim 28, wherein the
anti-foaming surfaces comprise: refrigerant phobic surfaces
disposed within the volume of the shell; and lubricant phobic
surfaces disposed within the volume of the shell, wherein the
refrigerant phobic surfaces and the lubricant phobic surfaces are
arranged and configured inside the shell to interact, respectively,
with refrigerant and lubricant present in the refrigerant
mixture.
30. The refrigerant management system of claim 28, wherein the
refrigerant phobic and lubricant phobic surfaces including thereon
one or more of materials being a polymeric plastic, a galvanized
material, an aluminum iron material, an inorganic coating, and an
integral surface enhancement created on the surfaces.
31. The refrigerant management system of claim 28, wherein the
refrigerant phobic and lubricant phobic surfaces being present on
one or more of baffles arranged and configured within the
shell.
32. The refrigerant management system of claim 28, wherein the
refrigerant phobic and lubricant phobic surfaces being present on
one or more of inner surfaces of the shell.
33. The refrigerant management system of claim 28, wherein the
refrigerant phobic and lubricant phobic surfaces being present on
one or more mesh surfaces within the shell.
34. The refrigerant management system of claim 30, wherein the
anti-foaming surfaces being both refrigerant phobic and lubricant
phobic.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/674,601 filed on Jul. 23, 2012 and titled
REFRIGERANT MANAGEMENT IN HVAC SYSTEMS and claims the benefit of
U.S. Provisional Application No. 61/539,325 filed on Sep. 26, 2011
and titled REFRIGERANT EVAPORATOR, the entirety of both the
above-identified provisional applications are incorporated by
reference herewith.
FIELD
[0002] The disclosure herein relates to heating, ventilation, and
air-conditioning ("HVAC") systems, and more particularly to
evaporators used in HVAC systems. Generally, methods, systems, and
apparatuses are described that are directed to refrigerant
management in an evaporator such as may be used in HVAC
chillers.
BACKGROUND
[0003] Flooded and falling-film evaporators generally are known and
often have a construction of a tube bundle within a shell. Such
evaporators are typically used in HVAC chillers to cool a process
fluid (e.g., water) which, in turn, is typically used in connection
with a heat exchanger coil or air-handling unit to cool air moving
through the coil or air-handling unit. Due to the interstitial
spacing within the volume of the shell, such as between the tubes
of the tube bundle, through which the process fluid flows, a
relatively large quantity of liquid refrigerant may be required to
wet the outside of all the tubes with refrigerant in order to
achieve maximized efficiency of the evaporator. Excess liquid
refrigerant between or adjacent the tubes next to the evaporator
shell does not contribute to the overall efficiency of the HVAC
chillers, and can be a burden on the cost of operating and
maintaining chillers.
SUMMARY
[0004] Improvements may be made to the refrigerant management in
evaporators used in HVAC chiller systems, which in turn can reduce
refrigerant charge significantly without sacrificing thermal
performance and the overall efficiency of the evaporator and, in
some instances, can improve the thermal performance and the overall
efficiency of the evaporator, such as at operation modes that may
be at reduced or less than full load. Generally, methods, systems,
and apparatuses to manage refrigerant in an evaporator are
described, and which can include any one or combination of the
following approaches.
[0005] In one approach, a refrigerant displacement array is used,
which can include a number of spacers and/or baffles. The
refrigerant displacement array physically prevents refrigerant from
residing where the array is positioned.
[0006] In another approach, refrigerant management can be achieved
by the distribution of the refrigerant mixture that enters the
evaporator. The term "refrigerant mixture" herein generally refers
to but is not limited to one or more refrigerants, which may be
present in one or more phases, e.g. liquid, gaseous, solid, and can
include other non-refrigerant material(s) in one or more phases.
For example, the refrigerant mixture can include a liquid
refrigerant present in gaseous and liquid form, as well as a
lubricant material such as oil or another refrigerant serving also
as a lubricant material. For example, the refrigerant mixture can
be distributed into the shell of an evaporator, such as by using a
distributor to distribute the gaseous portion of the refrigerant
mixture in a manner of flow that is different relative to the
distribution and manner of flow of the liquid portion of the
refrigerant mixture. For example, the manner of flow of the gaseous
portion may be optimized to achieve a desired flow to facilitate
heat transfer, such as in a uniform flow through the distributor,
while the manner of flow of the liquid portion may be concentrated,
and distributed by the distributor from a designated area. Such
phase biased distribution of the liquid versus the gaseous portion
of the refrigerant mixture can be achieved.
[0007] In yet another approach, refrigerant management may be
achieved by controlling the interstitial velocity of refrigerant
flow within the volume of the shell of an evaporator.
[0008] In yet another approach, refrigerant management can be
achieved by preventing or at least reducing the occurrence of
foaming inside the evaporator. Surfaces within the evaporator can
be made to be anti-foaming, for example by having one or more
refrigerant phobic and lubricant phobic materials applied, formed,
or otherwise put on surfaces within the evaporator.
[0009] In the approach of using a refrigerant displacement array,
one embodiment of a method of refrigerant management in an
evaporator of a HVAC chiller includes causing refrigerant to enter
a volume present inside a shell of an evaporator. A portion of the
volume present inside the shell is displaced with a refrigerant
displacement array including spacers that physically extend from an
inner surface of the shell at a lower portion thereof toward outer
surfaces of tubes arranged in a tube bundle. The step of displacing
a portion of the volume present inside the shell includes
physically preventing refrigerant from residing in the portion of
the volume where the spacers reside, such that no refrigerant is
present in the portion of the volume displaced by the spacers. The
outer surfaces of the tubes in the tube bundle are wetted with the
refrigerant. The step of wetting in some embodiments includes
attaining a mist or spray flow of the refrigerant through the
interstitial volume within the shell including between outer
surfaces of the tubes of the tube bundle and between outer surfaces
of the tubes and outer surfaces of the spacers. The refrigerant
inside the shell is evaporated by way of heat transfer with a
process fluid traveling through the tubes of the tube bundle and
the evaporated refrigerant is released from the shell.
[0010] One embodiment of a refrigerant management system for an
evaporator of a HVAC chiller has the refrigerant displacement
array. The system includes a shell having a volume to receive
refrigerant to be evaporated therein, and a tube bundle disposed
inside the shell. The tube bundle includes tubes extending within
the shell to pass a process fluid therethrough and to undergo heat
transfer with the refrigerant. The refrigerant displacement array
includes a number of spacers to displace a portion of the volume of
the shell. The spacers are disposed within the shell to physically
extend from an inner surface of the shell at a lower portion
thereof and toward outer surfaces of tubes of the tube bundle. The
spacers physically prevent refrigerant from residing in the portion
of the volume where the spacers reside.
[0011] In some examples, the refrigerant displacement array
includes a number of baffles to displace a portion of the volume in
the shell, the portion of the volume being a portion of the
interstitial volume between the tubes of the tube bundle. The
baffles include openings, such as through holes, through which the
tubes are insertable. In some embodiments, the openings have an
inner diameter that is larger than an outer diameter of the tubes,
and the baffles physically prevent refrigerant from residing in the
portion of the interstitial volume where the baffles reside.
[0012] In the approach of using a certain distribution of the
refrigerant mixture that enters the evaporator, for example by
using a phase biased distributor, a method of refrigerant
management in an evaporator of a HVAC chiller includes causing a
refrigerant mixture to enter a distributor present on a lower
portion of a shell that has a volume therein, and causing the
refrigerant mixture to enter the volume present inside the shell.
The step of causing the refrigerant mixture to enter the volume
inside the shell can include, for example, distributing the
refrigerant mixture into the shell, such as by using a distributor
to distribute the gaseous portion of the refrigerant mixture in a
manner of flow that is different relative to the distribution and
manner of flow of the liquid portion of the refrigerant mixture.
For example, the manner of flow of the gaseous portion may be
optimized to achieve a desired flow to facilitate heat transfer,
such as in a uniform flow through the distributor, while the manner
of flow of the liquid portion may be concentrated, and distributed
by the distributor from a designated area. A phase biased
distribution of the liquid versus the gaseous portion of the
refrigerant mixture can thus be achieved.
[0013] In one embodiment, phased biased distribution can include
feeding a liquid portion of the refrigerant mixture from one end of
the distributor into the volume inside the shell, and feeding a
gaseous portion present in the refrigerant mixture into the volume
inside the shell from injection apertures disposed along a length
portion of the distributor.
[0014] The outer surfaces of tubes in a tube bundle within the
shell are wetted with refrigerant in the refrigerant mixture. The
refrigerant inside the shell is evaporated by way of heat transfer
with a process fluid traveling through the tubes of the tube
bundle, and the evaporated refrigerant is released from the
shell.
[0015] One embodiment of a refrigerant management system for an
evaporator of a HVAC chiller has a phase biased distributor. The
system includes a shell having a volume to receive a refrigerant
mixture therein. The shell has an inlet to receive the refrigerant
mixture inside the volume of the shell, and an outlet to release
from the shell refrigerant evaporated from the refrigerant mixture.
A tube bundle is disposed inside the shell. The tube bundle
includes tubes that extend within the shell to pass a process fluid
therethrough and to undergo heat transfer with the refrigerant. The
distributor is disposed at a lower portion of the shell, such as
for example, proximate the bottom or on a lower side of the shell.
The refrigerant mixture can be distributed into the shell of the
evaporator using a flow conditioner and apertures of the
distributor, so as to distribute the gaseous portion of the
refrigerant mixture in a manner of flow that is different relative
to the distribution and manner of flow of the liquid portion of the
refrigerant mixture. For example, the manner of flow of the gaseous
portion may be uniform through the apertures of the distributor,
while the manner of flow of the liquid portion may be concentrated,
and distributed by the distributor from a designated area. A phase
biased distribution of the liquid versus the gaseous portion of the
refrigerant mixture can thus be achieved. In some embodiments, the
distributor includes a flow conditioner therein and injection
apertures. The flow conditioner can be configured to feed a liquid
portion of the refrigerant mixture from a designated location, such
as at one end of the distributor into the volume inside the shell.
The injection apertures are configured to feed a gaseous portion
present in the refrigerant mixture into the volume inside the
shell, such as for example along a length portion of the
distributor.
[0016] In the approach of controlling the interstitial velocity of
refrigerant flow within the volume of the shell of an evaporator,
such as the interstitial two-phase velocity of known low pressure
refrigerants, one embodiment of a method of refrigerant management
includes causing refrigerant to enter a volume present inside a
shell of an evaporator, and wetting outer surfaces of tubes in a
tube bundle with the refrigerant. The step of wetting includes
attaining a mist or spray flow of the refrigerant, which may be in
the form of both gaseous and liquid refrigerant, through the
interstitial volume of the shell including between outer surfaces
of the tubes of the tube bundle. The step of attaining a mist or
spray flow of the refrigerant includes maintaining a target
interstitial velocity of refrigerant flow suitable to attain the
spray flow of refrigerant at or above a threshold interstitial
velocity that does not attain the spray flow of refrigerant. The
refrigerant inside the shell is evaporated by way of heat transfer
with a process fluid traveling through the tubes of the tube bundle
and evaporated refrigerant is released from the shell. In this
approach, either or both of the refrigerant displacement array and
the phase biased distributor can be used to facilitate attaining
desired interstitial velocity of the refrigerant flow.
[0017] In the approach of using anti-foaming surfaces, one method
of refrigerant management in an evaporator of an HVAC chiller
includes causing refrigerant to enter a volume present inside a
shell of an evaporator, and wetting outer surfaces of tubes in a
tube bundle with the refrigerant. Refrigerant inside the shell is
evaporated by way of heat transfer with a process fluid traveling
through the tubes of the tube bundle. The formation of foam by one
or more of the refrigerant and lubricant during the evaporating
step is reduced. The step of reducing formation of foam includes
causing the refrigerant to interact with anti-foaming surfaces
present within the shell. The evaporated refrigerant is released
from the shell.
[0018] One embodiment of a refrigerant management system for an
evaporator of an HVAC chiller has the anti-foaming surfaces. The
system includes a shell having a volume to receive a refrigerant
mixture therein, and a tube bundle disposed inside the shell. The
tube bundle includes tubes extending within the shell to pass a
process fluid therethrough and to undergo heat transfer with the
refrigerant. Anti-foaming surfaces are disposed within the volume
of the shell. The anti-foaming surfaces are arranged and configured
inside the shell to interact with the refrigerant mixture and are
suitable to prevent or at least reduce foaming that may occur.
[0019] It will be appreciated that anti-foaming surfaces may be
created through use of known or novel materials, coatings, surface
enhancements, novel mesh material, and combinations thereof. In
some embodiments, the anti-foaming surfaces can be one or both of
refrigerant phobic surfaces and lubricant phobic surfaces disposed
within the volume of the shell. It will also be appreciated that
the use of anti-foaming surfaces is not limited to evaporators as
other apparatuses, devices, and components of HVAC systems
including but not limited to chillers may employ such anti-foaming
surfaces. For example, such refrigerant management approach may be
employed in an oil and/or refrigerant tank or source of HVAC
chillers.
[0020] Other features and aspects of the refrigerant management
approaches will become apparent by consideration of the following
detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Reference is now made to the drawings in which like
reference numbers represent corresponding parts throughout.
[0022] FIG. 1 is an end view inside a shell and tube flooded
evaporator.
[0023] FIG. 2A is a schematic side view of a tube bundle.
[0024] FIG. 2B is a schematic end view of a tube bundle showing
interstitial volume between outer surfaces of tubes and a
representation of interstitial velocity of a refrigerant mixture
flow through the tube bundle.
[0025] FIG. 3 is a schematic side view of a tube bundle with one
embodiment of a refrigerant displacement array having spacers and
baffles connected thereto.
[0026] FIG. 4 is a schematic side view of a tube bundle with
another embodiment of a refrigerant displacement array with spacers
and baffles.
[0027] FIG. 5 is a schematic side view of a tube bundle with
another embodiment of a refrigerant displacement array with spacers
and baffles.
[0028] FIG. 6 is an end view of a tube bundle with tubes inserted
through holes of one embodiment of a baffle that shows an
embodiment of projections within one of the holes.
[0029] FIG. 7 is a side view of one embodiment of a spacer for a
refrigerant displacement array.
[0030] FIG. 8 is a picture of a spacer used as a split spacer
assembled to one embodiment of a baffle.
[0031] FIG. 9 is a side view of another embodiment of a spacer and
baffle shown alone, the baffle is a partial height baffle.
[0032] FIG. 10 is a side view of one embodiment of a spacer and
baffle shown alone, the baffle is a full height baffle.
[0033] FIG. 11 is a perspective view of another embodiment of a
refrigerant displacement array, which includes alternating spacers
and spacers with full height baffles.
[0034] FIG. 12 is a side view of another embodiment of a
refrigerant displacement array, which includes a series of spacers,
and spacers with full and partial height baffles.
[0035] FIG. 13A is a picture of an evaporator in operation without
a refrigerant displacement array and showing "bubbly" flow or
non-mist/spray flow.
[0036] FIG. 13B is a picture of an evaporator in operation with a
refrigerant displacement array having a series of full height
baffles and that shows the spray/mist flow during heat
transfer.
[0037] FIG. 14 is an example of a falling film flooded evaporator,
within which a refrigerant displacement array can be
implemented.
[0038] FIG. 15 is a schematic side view of one embodiment of a
distributor within an evaporator.
[0039] FIG. 16A is a schematic side view of the distributor from
FIG. 15 shown alone.
[0040] FIG. 16B is a schematic side view of another embodiment of a
distributor shown alone.
[0041] FIG. 17A is a partial side sectional view of another
embodiment of a distributor.
[0042] FIG. 17B is a sectional view taken from line 17B-17B in FIG.
17A.
[0043] FIG. 18A is a side view of one embodiment of the top
distributor plate from FIGS. 17A-B.
[0044] FIG. 18B is an end view of the top distributor plate of FIG.
18A.
[0045] FIG. 19A is a side view of one embodiment of the bottom
distributor plate from FIGS. 17A-B.
[0046] FIG. 19B is an end view of the bottom distributor plate of
FIG. 19A.
[0047] FIG. 20 is a side sectional view of one embodiment of an
evaporator in which one embodiment of a refrigerant displacement
array and the distributor of FIGS. 17A-B are implemented.
[0048] FIG. 21 is a schematic representation of one embodiment of a
phased biased flow pattern from a distributor.
DETAILED DESCRIPTION
[0049] Improvements may be made to the refrigerant management in
evaporators used in HVAC chiller systems, which in turn can reduce
refrigerant charge significantly without sacrificing thermal
performance and the overall efficiency of the evaporator and, in
some instances, can improve the thermal performance and the overall
efficiency of the evaporator. Generally, methods, systems, and
apparatuses to manage refrigerant in an evaporator are described,
and which can include any one or combination of the following
approaches: (1) use of a refrigerant displacement array to
physically prevent refrigerant from residing where the array is
positioned; (2) control of the interstitial velocity of refrigerant
flow within the volume of the shell of an evaporator; (3) use of
phase biased distribution of the refrigerant mixture, so that a
gaseous portion is distributed into the evaporator shell in manner
of flow that is different from the distribution and manner of flow
of liquid refrigerant and oil into the evaporator shell, for
example where the gaseous portion is distributed to achieve uniform
flow and interstitial velocities and the liquid portion is
distributed from a designated and/or concentrated location; and (4)
using foam abatement with anti-foaming surfaces, such as by the use
of refrigerant phobic and/or lubricant phobic material(s) to
prevent or reduce the occurrence of foaming inside the evaporator.
Refrigerant management using such approach(es) can reduce
refrigerant charge significantly without sacrificing thermal
performance and the overall efficiency of the evaporator and, in
some instances, can improve the thermal performance and the overall
efficiency of the evaporator.
[0050] As to the basic design of a flooded evaporator which is
referred to throughout the descriptions herein, FIG. 1 shows an end
view of a basic flooded evaporator 10. The evaporator 10 has a
shell 12 where a mixture of refrigerant 14 is on the outside of the
tubes 16 and is vaporized by heat transfer from the process fluid
on the inside of the tubes 16. In many cases, the mixture of
refrigerant 14 is present in two phases of a gaseous and liquid
portion, and enters a lower portion of the shell 12, such as at the
bottom of the shell 12. The shape of the tube 16 arrangement at the
bottom 18 is to allow room for a distributor (not shown in FIG.
1).
[0051] The distributor, which is further described below in FIGS.
15-19, is designed to introduce the gaseous portion of the
refrigerant mixture 14 in a manner of flow that is different from
the distribution and manner of flow of the liquid portion. In some
instances, the gaseous portion may be distributed from the
distributor along a length portion or direction of the evaporator
shell and sometimes in uniform manner as may be needed for desired
and/or certain performance. For example, gas can be distributed
relatively evenly along the length of the shell 12, but the liquid
distributed from a designated location, such as toward an end. By
placing more liquid at a concentrated location, such as at one end
of the shell relative to the other, for example, the place where
the highest oil concentration exists can be controlled. The
description of FIGS. 15-19 hereinbelow provide further details of
such a distributor. Also, U.S. Pat. No. 6,516,927 describes the
issues with management of liquid phase and pool migration, and the
entirety of which is herewith incorporated by reference.
[0052] In FIG. 1, twelve rows of tubes 16 are shown, but this is
meant as one example only, as it will be appreciated that the
number of rows can vary as well as the number of tubes in a row.
Gas and liquid enter the tube bundle from the bottom of the shell.
If the amount of gas flow is low enough so that the velocity upward
between the tubes is low, then the interstitial area around the
bottom tube rows of the evaporator are essentially a pool of liquid
with bubbles rising through the liquid, somewhat like bubbles
rising from the bottom of a boiling pan of water, or bubbles from a
scuba diver rising to the top of the lake. This is referred to as
"bubbly flow" for this discussion. Bubbly flow is not desired for
minimizing refrigerant charge in an evaporator and for achieving
suitable thermal management, which may be reduced due to head
pressure raising the liquid refrigerant boiling point.
[0053] It will be appreciated that as the refrigerant flows through
the tubes 16, each row up from the bottom has a larger volume of
gas that flows through it. For example, gas from the lower rows
enters the spaces in the upper rows. Gas generated by the lower
rows is added to the volume flow of upper rows, so that the gas
entering the upper rows is greater than the amount of gas entering
lower rows, and so on up the tube bundle. As the volume of gas flow
increases up through the tube bundle, the velocity can increase so
that there is no longer a liquid pool with bubbles floating up
through the pool. In this manner, there can be a change in the
basic two-phase flow pattern to a "spray flow" where droplets of
liquid are carried up through the tube bundle to wet the tubes, and
where gas flow entrains the liquid droplets.
[0054] Bubbly flow has a much higher percent of liquid in the space
between tubes than spray flow, so spray flow has been determined to
be more desired for minimizing refrigerant charge in the
evaporator. The quality of the spray flow can adequately wet the
tubes to achieve efficient thermal transfer, while requiring less
refrigerant charge or inventory in the evaporator relative to
bubbly flow which as described above has more liquid and is subject
to pooling at various locations in the evaporator, such as at the
bottom of the shell. If the quality of the spray flow can be
attained throughout the tube bundle of the evaporator, desirable
refrigerant management can be achieved, to thereby minimize
refrigerant charge or inventory, which can reduce parasitic loss
due to pressure differences in the tube bundle, and to thereby
maintain or increase efficiency of the evaporator.
[0055] Referring to the lower left of FIG. 1, "wasted space" 20
near the perimeter of the shell 12 is usually present in many
evaporators. This volume adjacent to the lower part of the shell 12
can be completely displaced without adversely affecting the
performance of the evaporator.
[0056] As mentioned above, a refrigerant mixture entering the
evaporator can typically have two phases of refrigerant, as well as
other materials. There can be cases where only liquid enters, but
this may be a less frequent operating condition. If the velocity
V.sub.i between the tubes 16 (interstitial velocity) is greater
than a minimum threshold, then "spray flow" can be developed. If
the velocity V.sub.i is below the threshold, then "bubbly flow"
occurs. See e.g. FIGS. 2A and 2B respectively for a representation
of the tube bundle alone and the interstitial velocity through the
tubes (see arrows through between tubes 16 in FIG. 2B).
[0057] Bubbly flow is not wanted, so if a refrigerant displacement
array is added, such as a series of spacers and/or baffles, the
effective interstitial velocity can be increased. However, in
operating conditions where interstitial velocity is above the
threshold required to obtain the spray flow, then a series of
spacers and/or baffles needed may be less or may not be
required.
[0058] In one approach to facilitate attaining the spray flow
condition, the refrigerant displacement array displaces volume that
would otherwise be taken up by the refrigerant mixture including
the "wasted space" 20 described earlier. If there is little or no
gas entering the bottom rows of tubes, the addition of the
refrigerant displacement array can displace liquid at the bottom of
the tube bundle, but can still serve to help increase the
interstitial flow regime to a spray flow that minimizes or
otherwise reduces interstitial volume that could be subject to
"bubbly flow".
[0059] For example, by introducing the refrigerant displacement
array, it is possible for the gaseous portion of the refrigerant
mixture to exceed the threshold velocity by reducing the length of
the interstitial area between the tubes, e.g. along the axial
length of the tubes. Since the flow area is reduced, the upward gas
velocity can be increased to attain the spray flow and avoid bubbly
flow.
Refrigerant Displacement Array FIGS. 1-14
[0060] FIGS. 3-5 show examples of refrigerant displacement arrays,
that can include a series of spacers and baffles that physically
reside within a shell of an evaporator. For example, spacers are
meant to refer to the portion used at a lower portion of the shell,
such as toward the bottom of the shell and toward the lower part of
the tube bundle. The spacers can butt up against the evaporator
shell wall. Baffles are meant to refer to the portion used in an
upper portion of the shell and around the tubes of the tube bundle.
It will be appreciated that baffles may include a "spacer" portion
at the bottom of the baffle, but for ease of description they are
hereafter referred to as baffles.
[0061] FIG. 3 is a side view of a tube bundle 36 with one
embodiment of a refrigerant displacement array 30 having spacers 32
and baffles 34 connected thereto. FIG. 3 shows a baffle side that
is substantially vertically straight, but it will be appreciated
that the side profile can vary as desired and/or suitable.
[0062] For example, FIG. 4 is a side view of a tube bundle 46
showing another embodiment of a refrigerant displacement array 40
with baffles 44 having a varied side profile. Although bottom
spacers are not shown, it will be appreciated that spacers may be
included with the baffles 44. Baffles 44 are shown with a side
profile that tapers outward from the top toward the bottom, for
example as variable width baffles. It will be appreciated that the
side profile as desired and/or necessary can vary from the profile
specifically shown.
[0063] FIG. 3 shows full height baffles 34 extending the height of
the tube bundle 36, and FIG. 4 shows partial height baffles 44 that
extend partially up the tube bundle 46. It will be appreciated that
full, partial, or a combination of both can be used in either of
the arrays 30, 40 of FIGS. 3 and 4.
[0064] For example, FIG. 5 shows a side view of a tube bundle 56
with another embodiment of a refrigerant displacement array 50 with
spacers 52 and baffles 54. As shown, the baffles 54 are of varied
height.
[0065] Generally, the refrigerant displacement array, with the
series of spacers and/or baffles, is positioned to displace
refrigerant causing the amount of refrigerant charge in the
evaporator to be reduced. In addition to displacing refrigerant,
the presence of and spacing of the spacers and/or baffles can
maintain interstitial velocities between the tubes in a range
whereby two phase spray flow of the refrigerant is achieved rather
than bubbly flow of the refrigerant, e.g. bubbles of refrigerant
gas rising through a pool(s) of refrigerant liquid. In some
embodiments, the thickness of a baffle or a spacer can be about
0.25 to about 0.5 inches. It will be appreciated that the thickness
can vary and may be somewhat larger or smaller than the above
range, but there may be a limit to how thick a baffle may be so as
to allow the refrigerant mix to freely move through the baffle,
such as through the openings or through holes of the baffle (see
e.g. FIGS. 7 to 12 below for further description of the
openings.
[0066] To insert the tubes through baffles of the refrigerant
displacement array, openings such as for example through holes can
be used. FIG. 6 is an end view of part of a tube bundle with tubes
16 inserted through holes 62 of one embodiment of a baffle 60. It
will be appreciated that a space or gap 64 is present between tubes
16 and the baffle 60, e.g. inner diameter of the holes 62. FIG. 6
also shows one embodiment for maintaining an annular gap by using
projections 66 within one of the holes. The projections 66 can be
disposed on the inner diameter of the holes 62 to provide a
standoff for the tubes 16 to avoid contact with the inner diameter.
It will be appreciated that any of the spacers/baffles described
herein can have the projections 66 within the through holes. The
clearance, e.g. diametral clearance, between the inner diameter of
the hole and the outer diameter of the tube can depend upon tube
diameter, for example for larger diameter tubes, e.g. 1 inch tubes,
a higher clearance may be desired and/or needed, but for smaller
diameter tubes, e.g. 3/4 inch tubes, a lower clearance may be
desired and/or needed. In some examples, about 0.1875 inch
diametral clearance can be used for 1 inch diameter tubes, and
about 0.125 inch diametral clearance can be used for Y, inch
diameter tubes. In some instances, there may be a clearance between
the outermost projecting surface of the projections 66 and the
outer diameter of the tubes. Such clearance may be for example
about 1/32 inch.
[0067] FIGS. 7 to 10 show various embodiments of spacers and
baffles (partial and full height) that can be used alone or in some
combination to construct a refrigerant displacement array.
[0068] FIG. 7 is a side view of one embodiment of a spacer 70 for a
refrigerant displacement array. The spacer 70 has grooves or
cutouts 72 proximate a top on which to allow tubes of a tube bundle
to rest, and can also include the projections or standoffs as shown
in FIG. 7. The spacer 70 has portions 74, 76 that can displace
volume within the shell of the evaporator, such as between a lower
portion of the shell and the tubes toward the bottom portion of the
bundle (e.g. at 74), and between a distributor and tubes toward the
bottom of the bundle (e.g. at 76). FIG. 8 shows a picture of the
spacer 70 that may be used as a split spacer assembled to one
embodiment of a baffle 80, which may be partial or full height. The
baffle 80 has through holes 82 with an opening 84 through which
tubes can be inserted. The baffle 80 can also have projections 86,
such as already described above. FIG. 9 is a side view of the
baffle 80 (with a bottom spacer portion) shown alone, the baffle is
a partial height baffle.
[0069] FIG. 10 is a side view of another embodiment of a baffle 100
(with bottom spacer portion) shown alone. The baffle 100 is a full
height baffle, and includes through holes 102 with an opening 104
through which tubes can be inserted. The baffle 100 can also
include projections 106 as similarly described above.
[0070] FIGS. 11 and 12 show partial views of additional examples
for a construction of a refrigerant displacement array. FIG. 11 is
a perspective view of another embodiment of a refrigerant
displacement array 110. The refrigerant displacement array is
constructed to include a series of alternating spacers 112 and full
height baffles 114 (with bottom spacer portions). As one example
only, the array of FIG. 11 could be used along the length inside an
evaporator shell, and the baffle/spacer alternating arrangement
could repeat at about 1 inch intervals, where along a 70 inch long
evaporator, there may be about 70 baffles and 70 spacers. Depending
on the longitudinal spacing (lengthwise within the evaporator
shell) of the baffles/spacers, the need for certain traditional
tube supports could be reduced or eliminated. FIG. 12 is a side
view of another embodiment of a refrigerant displacement array 120,
which includes a series of spacers 122, and full and partial height
baffles, 124, 126, which can also include bottom spacer portions to
connect to adjacent spacers 122.
[0071] FIGS. 13A and 13B show pictures that illustrate operation of
an evaporator without a refrigerant displacement array (FIG. 13A)
compared to operation of an evaporator with a refrigerant
displacement array having a series of full height baffles (FIG.
13B). As described above, if the amount of gas flow is low enough
so that the velocity upward between the tubes is low, then the
interstitial area around the bottom tube rows of the evaporator can
be subject to pooling of liquid with bubbles rising through the
liquid, i.e. "bubbly flow". As seen in the pictures, bubbly flow
would be expected to have a much higher percent of liquid in the
space between tubes than spray flow (FIG. 13B). The quality of the
spray flow adequately wets the tubes to achieve efficient thermal
transfer, while requiring less refrigerant charge or inventory in
the evaporator relative to bubbly flow which, as described above,
has more liquid and is subject to pooling at various locations in
the evaporator, such as at the bottom of the shell or other areas
that may be subject to low velocity without the use of the
refrigerant displacement array. FIG. 13A shows a velocity that is
less than the threshold velocity which results in the bubbly flow,
whereas FIG. 13B shows velocity at or above a threshold velocity to
attain the desired spray flow.
[0072] FIG. 14 is an example of a falling film flooded evaporator
140, within which any of the refrigerant displacement array
described herein could be implemented. In some instances, falling
film evaporators have different refrigerant flow characteristics
and can have different flow velocity issues. The falling film
evaporator 140 can be known to have a falling film region 142,
where liquid flows downward from tube to tube of the bundle (e.g.
top to bottom via gravity). Vapor can more easily escape upward and
outward, so there may not be an advantage to have full height
baffles. However, a pool zone 144 may be present in the evaporator
140 during operation, and so spacers and partial height baffles
could be used to displace such liquid pooling to help facilitate
efficient evaporation through high vapor velocity and to limit
refrigerant charge. For example, baffles and/or spacers could be
implemented in the pool zone 144 and into a portion of the middle
height of the tube bundle within the falling film region 142.
[0073] FIGS. 15 and 16A and B show embodiments of a phase biased
distributor. Generally, the phase biased distributors described
herein are designed for bottom feed from the bottom of the
evaporator shell, by introducing the gas of the refrigerant into
the evaporator shell as needed for certain or optimum performance,
for example by distributing gas evenly along a length portion of
the shell 12. It will be appreciated that the distributors
described herein are not limited to bottom mount configurations,
but may be disposed at other portions, e.g. relatively upper or
lower or side portions of the shell as may be desired and/or
needed, or example depending on the particular implementation.
[0074] Through the distributor, liquid is distributed from a
localized part of the distributor, such as toward an end(s) or
otherwise dedicated location(s) thereof. By placing more liquid,
for example at one end of the shell relative to the other, the
location where the highest oil concentration exists can be
controlled, which can be desirable for lubricant management and
recovery.
[0075] FIG. 15 is a side view of one embodiment of a distributor
150 within an evaporator 158. FIG. 16A is a side view of the
distributor 150 from FIG. 15 shown alone. The distributor 150 has a
main body that houses a flow conditioner 152 and has apertures 154,
where in the embodiment shown are disposed for example along the
length of the main body. The flow conditioner 152 in some
embodiments can be a turning vane that directs the flow of the
refrigerant mixture as it enters the distributor 150. In the case
of the flow conditioner 152 being a turning vane, flow can enter
the distributor 150 and the manner of flow of the liquid portion of
the refrigerant mixture can be directed or phase biased by the flow
conditioner 152 to flow down the majority of the main body inside
the distributor and be exited at or proximate the other end. This
can provide a concentrated or localized flow of the liquid phase
refrigerant, such as at a side(s), other outlet(s), or certain
apertures of the distributor. The apertures or orifices 154 are
sized to promote gas flow out of the distributor 150, such as for
example along the length thereof and in an even, uniform
manner.
[0076] FIG. 16B is a side view of another embodiment of a
distributor 160 shown alone. The distributor 160 also includes a
main body that houses a flow conditioner 162, such as a turning
vane, and apertures 164 disposed for example along a length portion
or length direction of the main body. In the case of the flow
conditioner 162 being a turning vane, flow can enter the
distributor 160 at one end and be phase biased by the flow
conditioner 162 to have liquid be exited at or proximate the same
end. The apertures or orifices 164 are sized to promote gas flow
out of the distributor 160, such as for example along the length
thereof and in an even, uniform manner. This configuration may be
useful where the flow entering the distributor 160 is mainly
liquid. In such an embodiment as shown in FIG. 16B, the gaseous and
liquid portions of the refrigerant mixture can exit the far right
end of the distributor 160 and change direction around the end of
the flow conditioner 162 and flow toward the left between the flow
conditioner 162 and the upper part of the distributor with the
apertures. The apertures at the far right begin after the gaseous
portion and liquid portion have made this turn around the flow
conditioner 162, and accelerated to the left.
[0077] The distributors described herein are designed to provide a
desirable injection of the gaseous portion of the refrigerant
mixture to achieve suitable heat transfer while reducing
refrigerant charge. For example, gaseous distribution from the
distributor into the shell can be a relatively uniform injection of
gas along the length of a shell and tube evaporator, while
injecting the majority of liquid at localized positions, e.g. at
one end or both ends. In operation, the distributors have an inlet
that can accept a refrigerant mixture, usually in two phase gas and
liquid forms. A flow conditioner 152, 162, e.g. turning vane or
other flow director or contour, within the distributor wall can
allow for a suitable momentum to be imparted to the liquid phase of
the refrigerant mixture so that it can be forced down toward
terminal end(s) thereof. At such location(s), the liquid can be
injected out of the distributor and into the volume within the
shell of the evaporator. This biased liquid feed of the refrigerant
can facilitate operation of a flowing pool associated with
excellent oil management and recovery, while providing suitable
distribution of the refrigerant.
[0078] It will be appreciated that the flow conditioner may not be
a turning vane and can be constructed as any suitable flow director
or contour that would achieve the phase biased distribution, e.g.
of separating or concentrating the liquid portion of the
refrigerant mixture from the gaseous portion and allowing for
balanced distribution of the gaseous portion into the volume of the
shell. It will also be appreciated that the liquid portion can be
distributed at various desired locations, for example at one or
both ends of the distributor, and in some embodiments where
appropriate distribution of the liquid portion can be concentrated
toward the center, for example where momentum of the refrigerant
mixture may come from the end(s). It will also be appreciated that
distribution location of the liquid portion can be at non-centered
location(s) but away from the ends. One or more flow conditioners
may be implemented in order to achieve the desired refrigerant
flow/distribution.
[0079] In terms of the gas which enters the distributor through the
inlet, the distributors herein can in some instances relatively
uniformly inject the gas phase along the length of the evaporator
through the apertures, e.g. apertures 154, 164. It will be
appreciated that the placement, sizing, and quantity of holes can
vary to facilitate and help achieve the desired distributed
injection. The distributors herein are directed to leveraging the
different properties of gas and liquid, e.g. density, in order to
provide the phase biased effect. For example, refrigerant gas is
less dense than refrigerant liquid. The flow conditioner can
leverage this property to create momentum to force the liquid to
the desired exit location, such as toward the other end from the
inlet, if needed. The gas has significantly less momentum and can
be fed through the apertures of the distributor. Injection of the
gas relatively evenly or balanced can result in a desired operation
and thermal performance, for example in a flooded evaporator, to
better distribute the refrigerant mixture by avoiding relatively
higher localized loft of liquid droplets above the tube bundle
(e.g. higher velocities) compared to other areas that may be
subject to lower localized loft (e.g. lower velocities), which may
not be suitable for adequate wetting of the tubes. Likewise,
excessive loft can introduce droplets or liquid into the suction
stream which is not desired.
[0080] FIGS. 17A through 19B show views of another embodiment of a
distributor 170 disposed at a bottom of an evaporator shell 180.
The distributor 170 includes a flow conditioner 172 which is
disposed within a main body of the distributor 170. In some
embodiments, the flow conditioner 172 can be constructed as a
turning vane. The main body can be composed of two plates, a top
plate 174 and a bottom plate 176, each of which has apertures that
allow for refrigerant distribution, e.g. gas therethrough. The
distributor 170 can have an overall triangle shaped pitch when
viewed from an end thereof, but this is merely exemplary as other
geometries may be used. An opening 178 from the flow conditioner
172 into the space defined within the bottom plate 176 allows for
the direction of liquid refrigerant to exit the area within the
flow conditioner 172, turn around the flow conditioner 172 and be
directed toward the other end of the distributor 170. Gas can exit
the apertures of the top and bottom plates 174, 176, which in some
embodiments can have their apertures positioned relatively offset
from one another and have relatively different sizes (see FIGS.
18A-19B). It will be appreciated that the size and geometry the
apertures of the top and bottom plates 174, 176 can be varied as
appropriate to achieve desired and/or needed distribution.
[0081] FIG. 20 is a side sectional view of one embodiment of an
evaporator 200 in which one embodiment of a refrigerant
displacement array 202 and the distributor 170 of FIGS. 17A-B are
implemented. As shown, the refrigerant displacement array can have
solid material, e.g. spacers and bottom of baffle near the shell,
but where there is an alternative pattern of full and partial
height baffles to allow for the refrigerant mixture to freely move
in this volume in the shell and through openings, through holes of
the baffles. As shown, the distributor in some cases may have two
flow conditioners that receive refrigerant mixture from two inlets
and can direct the refrigerant flow.
[0082] FIG. 21 is a schematic representation of one embodiment of a
phased biased flow pattern from a distributor. The upward arrow
lines represent gaseous refrigerant flow/distribution leaving a
distributor such as from its apertures. The solid profile line
rising from left to right represents one example of the liquid
refrigerant flow/distribution from the distributor. It will be
appreciated that the liquid refrigerant flow/distribution can vary
depending upon the configuration of the flow conditioner, such as a
turning vane, and the desired location at which liquid refrigerant
concentration is desired.
[0083] In the approach of controlling the interstitial two-stage
velocity of refrigerant flow within the volume of the shell of an
evaporator, either or both of the refrigerant displacement array
and the phase biased distributor can be used to facilitate
attaining desired or target interstitial velocity of the
refrigerant flow. In some embodiments, a target interstitial
velocity may be about 5 ft/s, but may be higher or lower depending
upon system operation, load and depending on certain oil
management/recovery goals. In some embodiments, the threshold
interstitial velocity may be about 3 ft/s, under which bubbly flow
may occur. It will be appreciated that a row by row analysis of the
tube bundle could be tested to determine the threshold and target
velocities, and perhaps to assess whether a refrigerant
displacement array could be used, is desired and/or is needed. In
other instances, the tube pitch of the tube bundle may be modified
to help obtain the target interstitial velocity. For example, for
low pressure refrigerants the tube pitch and lanes can be modified,
for example by decreasing the available volume or space in the
shell so that the interstitial velocity can be obtained. As one
example only, the tube pitch could be reduced to allow for about as
low as 3/16 inch spacing/distance between the outer surfaces of the
tubes, for example, while still being suitable for typical tube
sheet/support assembly. In some examples, a ratio of tube pitch (P)
and tube diameter (D) can be used to determine the tube bundle
design. As one example only, a ratio of about 1.16<P/D<about
1.375 may be used to determine the tube bundle configuration. The
tube pitch could be locally enlarged, for example, toward the top
of the bundle, where the tube pitch may not be constant throughout.
Likewise, it will be appreciated that the tube openings of a baffle
array, if used, could be modified as needed to accommodate
different tube spacing and pitch among tube bundles.
[0084] Generally, one embodiment of a method of refrigerant
management includes causing refrigerant to enter a volume present
inside a shell of an evaporator, and wetting outer surfaces of
tubes in a tube bundle with the refrigerant. The step of wetting
includes attaining a spray flow of the refrigerant through the
interstitial volume of the shell including between outer surfaces
of the tubes of the tube bundle. The step of attaining a spray flow
of the refrigerant includes maintaining a target interstitial
velocity of refrigerant flow suitable to attain the spray flow of
refrigerant above a threshold interstitial velocity that does not
attain the spray flow of refrigerant. For example, maintaining a
target interstitial velocity includes maintaining an interstitial
two-phase velocity above a threshold, below which a relatively
higher liquid, i.e. bubbly flow, can exist which is not desired.
The refrigerant inside the shell is evaporated by way of heat
transfer with a process fluid traveling through the tubes of the
tube bundle and evaporated refrigerant is released from the
shell.
Anti-Foaming Surfaces
[0085] In the approach of using anti-foaming surfaces, one method
of refrigerant management in an evaporator of a HVAC chiller
includes causing refrigerant to enter a volume present inside a
shell of an evaporator, and wetting outer surfaces of tubes in a
tube bundle with the refrigerant. Refrigerant inside the shell is
evaporated by way of heat transfer with a process fluid traveling
through the tubes of the tube bundle. The formation of foam by one
or more of the refrigerant and lubricant during the evaporating
step is reduced, such as by reducing a height of a foam layer that
may be present above the refrigerant mixture. The step of reducing
formation of foam includes causing the refrigerant to interact with
anti-foaming surfaces present within the shell. The evaporated
refrigerant is released from the shell.
[0086] One embodiment of a refrigerant management system for an
evaporator of an HVAC chiller has the anti-foaming surfaces. The
system includes a shell having a volume to receive a refrigerant
mixture therein, the mixture of which may include a lubricant. A
tube bundle is disposed inside the shell. The tube bundle includes
tubes extending within the shell to pass a process fluid
therethrough and to undergo heat transfer with the refrigerant.
Anti-foaming surfaces are disposed within the volume of the shell.
The anti-foaming surfaces are arranged and configured inside the
shell to interact with the refrigerant mixture and are suitable to
prevent or at least reduce foaming that may occur.
[0087] In some embodiments, the anti-foaming surfaces can be one or
both of refrigerant phobic surfaces and lubricant phobic surfaces
disposed within the volume of the shell. In some embodiments, such
surfaces can be created through use of certain materials, and may
be applied for example as a coating, surface enhancement, mesh, or
combinations thereof, that can still allow for refrigerant vapor
flow and that is phobic enough to not coat the material used.
[0088] Generally, use of refrigerant and/or oil phobic materials,
such as on surfaces inside of an evaporator of a water chiller in
an HVAC system, can be used to reduce or prevent foaming of the
refrigerant mixture. For example, such surfaces may be applied on
surfaces of other structures inside the shell of the evaporator
including for example displacement baffles, or can be applied on
the copper tubes inside the tube/shell evaporator. Additionally,
such surfaces may be in the form of a mesh that can be used to
disrupt and destabilize bubble formation.
[0089] The refrigerant phobic and lubricant phobic surfaces can be
present on one or more of spacers arranged and configured within
the shell and of baffles having openings through which the tubes
are inserted. In general, the refrigerant phobic and lubricant
phobic surfaces can be present on one or more of inner surfaces of
the shell and of outer surfaces of the tube bundle.
[0090] Materials that can be used to make such surfaces include
polymeric plastics such as polypropylene, polyethylene, or Teflon;
galvanized or aluminum iron materials; inorganic coatings; or a
combination of such materials. The use of such materials
destabilizes bubbles that may form during the evaporation process,
and reduces the amount of foam in the refrigerant/lubricant
mixture.
[0091] It will be appreciated that anti-foaming surfaces may be
created through use of known or novel materials, coatings, surface
enhancements, novel mesh material, and combinations thereof. In
some embodiments, the anti-foaming surfaces can be one or both of
refrigerant phobic surfaces and lubricant phobic surfaces disposed
within the volume of the shell. It will be appreciated that
materials may also utilize surface enhancements that have been
created to create a refrigerant phobic and/or lubricant phobic
surface. The use of such surface enhancement, which may include but
are not limited to milli-, micro-, and/or nano-scale structures,
destabilizes bubbles that may form during the evaporation process,
and reduces the amount of foam in the refrigerant/lubricant
mixture.
[0092] It will also be appreciated that the use of anti-foaming
surfaces is not limited to evaporators as other apparatuses,
devices, and components of HVAC systems including but not limited
to chillers may employ such anti-foaming surfaces. For example,
such refrigerant management approach may be employed in an oil
and/or refrigerant tank or source of HVAC chillers.
[0093] For example, another method of refrigerant management in an
oil and/or refrigerant tank of a HVAC chiller includes causing
refrigerant to enter a volume present inside a shell of a tank.
Refrigerant inside the shell is flashed to vapor by way of pressure
equalization. The formation of foam by one or more of the
refrigerant and lubricant, such as for example during the flashing
step, is reduced. Foam may occur through agitation and flashing of
the refrigerant. The step of reducing formation of foam includes
causing the refrigerant to interact with anti-foaming surfaces
present within the shell of the tank.
[0094] In another embodiment of a refrigerant management system, an
oil/refrigerant tank of an HVAC chiller has the anti-foaming
surfaces. The system includes a shell having a volume to receive a
refrigerant/oil mixture therein. Anti-foaming surfaces are disposed
within the volume of the shell. The anti-foaming surfaces are
arranged and configured inside the shell to interact with the
refrigerant mixture and are suitable to prevent or at least reduce
foaming that may occur.
[0095] In some embodiments, the anti-foaming surfaces can be one or
both of refrigerant phobic surfaces and lubricant phobic surfaces
disposed within the volume of the shell. These surfaces may be
created through material usage, coatings, surface enhancements, or
mesh.
[0096] Generally, the use of refrigerant and/or oil phobic
materials, such as on surfaces inside of a refrigerant and/or
lubricant source or tank of a water chiller in an HVAC system, can
reduce or prevent foaming of the refrigerant mixture. For example,
such surfaces may be applied on surfaces of other structures inside
the tank, including for example tank baffles or tank internal
surfaces. Additionally, such surfaces may be in the form of a mesh
that can be used to disrupt and destabilize bubble formation.
[0097] Materials that can be used to create such surfaces include
polymeric plastics such as polypropylene, polyethylene, or Teflon;
galvanized or aluminum iron materials; inorganic coatings; or a
combination of such materials. The use of such materials
destabilizes bubbles that may form during the refrigerant flashing
process, and reduces the amount of foam in the
refrigerant/lubricant mixture. Materials may also utilize surface
enhancements that have been created to create a refrigerant phobic
and/or lubricant phobic surface. The use of such surface
enhancement, whether they are milli, micro, or nano scale
structures, destabilizes bubbles that may form during the
refrigerant flashing process, and reduces the amount of foam in the
refrigerant/lubricant mixture.
[0098] With regard to the foregoing description, it is to be
understood that changes may be made in detail, without departing
from the scope of the present invention. It is intended that the
specification and depicted embodiments are to be considered
exemplary only, with a true scope and spirit of the invention being
indicated by the broad meaning of the claims.
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