U.S. patent application number 13/297481 was filed with the patent office on 2012-05-17 for thin film evaporator.
Invention is credited to Adnan Hussain Ayub, Zahid Hussain Ayub.
Application Number | 20120118545 13/297481 |
Document ID | / |
Family ID | 46046746 |
Filed Date | 2012-05-17 |
United States Patent
Application |
20120118545 |
Kind Code |
A1 |
Ayub; Zahid Hussain ; et
al. |
May 17, 2012 |
THIN FILM EVAPORATOR
Abstract
A thin film evaporator has a shell with tubes extending through
the shell in at least one pass. The shell has a top and a bottom.
Process fluid flows through the tubes. A suction from a compressor
is applied to the top of the shell at a refrigerant outlet.
Refrigerant is introduced into the shell at the bottom and is
distributed across the bottom region of the shell. The refrigerant
flows up and contacts the tubes, exchanging heat therewith before
flowing out of the shell top. Oil in the refrigerant contacts the
shell wall and drains into a sump.
Inventors: |
Ayub; Zahid Hussain;
(Arlington, TX) ; Ayub; Adnan Hussain; (Arlington,
VA) |
Family ID: |
46046746 |
Appl. No.: |
13/297481 |
Filed: |
November 16, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61414059 |
Nov 16, 2010 |
|
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Current U.S.
Class: |
165/159 |
Current CPC
Class: |
F28D 3/02 20130101; F28D
7/06 20130101; F28D 2021/0071 20130101; F25B 2339/0242 20130101;
F28D 3/04 20130101; F25B 39/02 20130101 |
Class at
Publication: |
165/159 |
International
Class: |
F28D 7/00 20060101
F28D007/00 |
Claims
1. A thin film evaporator, comprising: a) a shell having two ends,
a top and a bottom; b) a plurality of tubes located in the shell
and extending between the two ends, the tubes forming a path
through the shell, the path comprising at least one pass through
the shell; c) at least one refrigerant inlet located in the bottom
of the shell; d) a refrigerant distributor connected to the
refrigerant inlet and located between the shell bottom and the
tubes, the distributor having openings facing the shell bottom; e)
a perforated plate between the distributor and the tubes; f) at
least one refrigerant outlet located in the shell top; g) a suction
applied to the refrigerant outlet.
2. The thin film evaporator of claim 1, wherein the distributor
openings are sized so as to produce a spray of refrigerant.
3. The thin film evaporator of claim 1, further comprising a thin
film of liquid refrigerant on the tubes, with vapor refrigerant in
between the tubes.
4. The thin film evaporator of claim 1, further comprising a
demister located in the shell between the tubes and the refrigerant
outlet.
5. The thin film evaporator of claim 4, wherein the tubes comprise
a main body of tubes, further comprising a super heat body of tubes
located between the demister and the refrigerant outlet.
6. The thin film evaporator of claim 1, further comprising a sump
located in the bottom of the shell.
7. A method of heat exchange using a thin film evaporator having a
shell with two ends, a top and a bottom, a plurality of tubes in
the shell and extending between the ends, comprising the steps of:
a) flowing a process fluid through the tubes; b) flowing
refrigerant into the bottom of the shell; c) distributing the
refrigerant across a bottom region of the shell; d) providing a
film of refrigerant around the tubes and affecting heat transfer
between the process fluid and the refrigerant; e) allowing the
refrigerant to exit the top of the shell through a refrigerant
outlet; f) applying a suction at the refrigerant outlet.
8. The method of claim 7, wherein the step of distributing the
refrigerant across a bottom region of the shell further comprising
spraying the refrigerant against the shell.
9. The method of claim 8, wherein the step of distributing the
refrigerant across a bottom region of the shell further comprising
passing the refrigerant spray through a perforated member before
flowing the refrigerant around the tube.
10. The method of claim 7, further comprising the step of providing
a resistance to flow in the shell between the tubes and the
refrigerant outlet.
11. The method of claim 10, further comprising the step of
coalescing liquid at the top of the shell before exiting through
the refrigerant outlet.
12. The method of claim 10, wherein the tubes comprise a main body
of tubes, further comprising the step of providing a super heat
body of tubes between the resistance and the refrigerant
outlet.
13. The method of claim 7, wherein the refrigerant comprises oil,
wherein: a) the step of flowing refrigerant into the shell further
comprises spraying the refrigerant against the shell before flowing
the refrigerant to the tubes; b) draining the oil into a sump in
the shell.
Description
[0001] This application claims the benefit of provisional patent
application Ser. No. 61/414,059 filed Nov. 16, 2010.
FIELD OF THE INVENTION
[0002] The present invention relates to heat exchangers and
refrigeration systems and in particular to evaporators.
BACKGROUND OF THE INVENTION
[0003] In a typical refrigeration cycle there is an evaporator or
chiller that cools the process fluid at the expense of boiling the
refrigerant that is at lower saturation temperature and pressure, a
compressor that compresses the vaporized refrigerant to an elevated
pressure and temperature, a condenser that condenses the high
pressure refrigerant to liquid phase at the expense of heating the
cooling medium, and an expansion device that reduces the pressure
of the condensed refrigerant back to the low side, thus entering
the evaporator or chiller to repeat the above cycle again. This
cycle is called the reverse Rankine cycle.
[0004] Such refrigeration systems are found in a variety of
installations, such as food processing plants.
[0005] Refrigerants are typically synthetic and/or natural, such as
ammonia, carbon dioxide, or hydrocarbons such as propane. Synthetic
refrigerants are falling out of favor due to environmental
concerns. However, even natural refrigerants have drawbacks; for
example, ammonia is toxic and propane is flammable.
[0006] It is desirable to design an evaporator that would use a
reduced amount of refrigerant, thus minimizing any danger from an
accidental refrigerant release. In addition, a more efficient
evaporator would be physically smaller, thus saving money.
SUMMARY OF THE INVENTION
[0007] A thin film evaporator comprises a shell having two ends, a
top and a bottom. A plurality of tubes is located in the shell and
extends between the two ends. The tubes form a path through the
shell. The path comprises at least one pass through the shell.
There is at least one refrigerant inlet which is located in the
bottom of the shell. A refrigerant distributor is connected to the
refrigerant inlet and is located between the shell bottom and the
tubes. The distributor has openings facing the shell bottom. A
perforated plate is between the distributor and the tubes. There is
at least one refrigerant outlet located in the shell top. A suction
is applied to the refrigerant outlet.
[0008] In accordance with one aspect, the distributor openings are
sized so as to produce a spray of refrigerant.
[0009] In accordance with still another aspect, the evaporator
further comprises a thin film of liquid refrigerant on the tubes,
with vapor refrigerant between the tubes.
[0010] In accordance with one aspect, the thin film evaporator
further comprises a demister located in the shell between the tubes
and the refrigerant outlet.
[0011] In accordance with another aspect, the tubes comprise a main
body of tubes. They further comprise a super heat body of tubes
located between the demister and the refrigerant outlet.
[0012] In accordance with another aspect, a sump is located in the
bottom of the shell.
[0013] There is also provided a method of heat exchange using a
thin film evaporator having a shell with two ends, a top and a
bottom, and a plurality of tubes in the shell and extending between
the ends. A process fluid flows through the tubes. Refrigerant is
flowed into the bottom of the shell. The refrigerant is distributed
across a bottom region of the shell. A film of refrigerant is
provided around the tubes and affects heat transfer between the
process fluid and the refrigerant. The refrigerant is allowed to
exit through a refrigerant outlet in the top of the shell. A
suction is applied at the refrigerant outlet.
[0014] In accordance with one aspect, the step of distributing the
refrigerant across a bottom region of the shell further comprises
spraying the refrigerant against the shell.
[0015] In accordance with another aspect, the step of distributing
the refrigerant across a bottom region of the shell further
comprises passing the refrigerant spray through a perforated member
before flowing the refrigerant around the tubes.
[0016] In accordance with one aspect, a resistance to flow in the
shell is provided between the tubes and the refrigerant outlet.
[0017] In accordance with another aspect, the method further
comprises the step of coalescing liquid at the top of the shell
before exiting through the refrigerant outlet.
[0018] In accordance with another aspect, the tubes comprise a main
body of tubes. A super heat body of tubes is provided between the
resistance and the refrigerant outlet.
[0019] In accordance with another aspect, the refrigerant comprises
oil. The step of flowing refrigerant into the shell further
comprises spraying the refrigerant against the shell before flowing
the refrigerant to the tubes. The oil is drained into a sump in the
shell.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a side cross-sectional view of the proposed thin
film evaporator, in accordance with a preferred embodiment.
[0021] FIG. 2 is a top cross-sectional view showing the
distribution pipes and baffles.
[0022] FIG. 3 is a cross-sectional view, taken along lines III-III
of FIG. 2.
[0023] FIG. 4 is a bottom view of one of the distribution
pipes.
[0024] FIG. 5 is a side view of the distribution pipes of FIG.
4.
[0025] FIG. 6 is a block diagram of a refrigeration system with the
evaporator.
[0026] FIG. 7 is a cross-sectional view of some of the tubes,
showing a thin film of refrigerant.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] Referring to the Figs., the evaporator 11 has a cylindrical
shell 13. Tubes 15, which carry the process fluid, are located in
the shell. The evaporator shown in the drawings has two passes of
tubes 15, with a lower pass 15L of tubes and an upper pass 15U of
tubes. The tubes are not touching one another and are spaced apart
to allow the refrigerant to flow around each tube. Baffle plates 17
support the tubes inside of the shell. The ends of the tubes are
coupled to tube sheets 19, located at the ends of the shell. Thus,
the tubes 15 extend between the tube sheets 19 inside of the shell
13. (The tubes 15 are not shown in FIGS. 1 and 2 so that other
details can be shown; however the location of the tube passes 15U,
15L are shown in FIG. 1.)
[0028] At one end of the shell, an end bonnet 20 (see FIG. 1) has
an inlet chamber 21 communicating with the upper pass 15U of tubes
and an outlet chamber 23 that communicates with the lower pass 15L
of tubes. A respective inlet 25 and outlet 27 are connected to the
inlet and outlet chambers. A divider plate 29 separates the inlet
and outlet chambers.
[0029] At the opposite end of the shell is another end bonnet 31
with a single chamber so that fluid exiting the upper pass 15U of
tubes enters the lower pass 15L of tubes.
[0030] The chiller can have a single pass of tubes or more than two
passes of tubes. FIG. 3 shows an imaginary horizontal center line
which visually separates the upper pass 15U from the lower pass
15L.
[0031] The process fluid 30, such as water, brine, gas, etc., flows
through the inlet 25 (see FIG. 1) into the inlet chamber 21 and
then flows through the upper pass 15U of tubes into the opposite
end bonnet 31 and then enters the lower pass 15L of tubes where it
then flows into the outlet chamber 23 and through the outlet
27.
[0032] The refrigerant enters the shell at the bottom and moves up,
where it exits at the top of the shell. The refrigerant flows into
the shell by way of distribution pipes 37. The distribution pipes
37 are arranged in assemblies 33. In the preferred embodiment,
there are two distribution pipe assemblies 33, arranged end-to-end
along the bottom portion of the shell. Each distribution pipe
assembly 33 is shaped like an elongated "H" (see FIG. 4). Each
distribution pipe assembly has a center feed section 35 that is
transverse to parallel outlet distribution pipes 37. Each
distribution pipe 37 has openings 39 along the bottom of the pipes.
The openings 39 are located along the length of the outlet pipes
37. The openings 39 are oriented straight down. However, the
openings could be oriented at some angle relative to straight down.
The openings 39 are sized so that the refrigerant exits the
distribution pipes 37 as a spray. As shown in FIGS. 3 and 5, a
vertical riser pipe 41 depends from each center feed section 35.
The riser pipes 41 are the refrigerant inlets. The distribution
pipes 33 are located in the bottom portion in the shell 13 and are
spaced above the bottom by the vertical riser pipe 41 so that a gap
43 is formed between the distribution pipes and the shell bottom. A
perforated plate 45 is located above the distribution pipes. If
need be, the distribution pipes 33 can be secured to the perforated
plate 45 for support. The perforated plate is located below the
lower pass 15L of tubes.
[0033] The distribution pipe assemblies 33 can be in various
configurations. If the shell is short enough, only a single
distribution pipe assembly 33 need be used. Conversely, a longer
shell may require more than two distribution pipe assemblies.
Likewise, each distribution pipe assembly can have one or more
pipes 37. For example, a single pipe can be used, which pipe can be
of a larger inside diameter than the pipes 37 shown in FIG. 3. With
such a single pipe, some of the openings can be oriented to spray
vertically down, while other of the openings can be oriented to
spray at an angle to vertical. Alternatively, more than one or two
pipes 37 can be used. The number and size of pipes 37 will depend
somewhat on the size of the shell. The distribution pipe assemblies
33 are designed so as to provide a distribution of the refrigerant
across the bottom of the shell, so that the refrigerant contacts
all of the tubes 15. The perforated plate 45 assists in evenly
distributing the refrigerant among the tubes 15.
[0034] A demister pad 47 is located above the upper pass 15U of
tubes. The demister pad is, in one embodiment, a 1'' thick pad of
stainless steel wool wire. One or more refrigerant outlets 49 are
at the top of the shell, located above the demister pad 47. Between
the demister pad 47 and the outlets 49 a single or multiple rows of
tubes 15D are located. These tubes 15D are part of the upper pass
15U. The tubes in this section could be the same diameter or type
as the tubes in the other sections or passes, or the tubes could be
different. For example, the tubes 15D could be of a smaller
diameter so as to provide more tubes above the demister 47. The
tubes 15D impart super heat to the refrigerant. These tubes 15D act
as the final barrier to stop any liquid refrigerant carry-over into
the compressor 63 (FIG. 6).
[0035] The shell 13 is provided with a sump 51 in its bottom. The
bottom wall of the shell at the sump periphery is curved into the
sump so as to facilitate drainage into the sump.
[0036] The evaporator is installed in a refrigerant system 61 as
shown in FIG. 6. The refrigerant outlets 49 are connected to the
inlet of the compressor 63. The compressor is connected to a
condenser 65. The condenser outlet is connected to an expansion
device or valve 67, which in turn is connected to the refrigerant
inlets 41 of the evaporator 11. No refrigerant pump is needed to
provide refrigerant for the evaporator 11.
[0037] The expansion device 67 is provided at the refrigerant
inlets to control the flow of refrigerant into the evaporator.
Sensors 69 are located at the refrigerant outlets 49. The sensors
can be pressure transducers or temperature sensors. As the demand
for refrigerant increases, as sensed at the outlets 49, the
expansion device 67 can allow more refrigerant into the evaporator,
and vice versa.
[0038] In operation, the process fluid 30 (FIG. 1) is circulated
through the tubes 15 while the refrigerant 70 is circulated through
the shell, although exterior to the tubes. The liquid-vapor
refrigerant mixture enters by way of the inlets 41, flows into the
distribution pipes 37 and passes through the openings 39 as a spray
70 (in FIG. 3, only one side of the distribution pipe assembly 33
is shown as spraying for illustrative purposes). The refrigerant is
distributed evenly by the distribution pipes 33 into the bottom
shell at the shell wall. The refrigerant impacts the shell wall
below the distribution pipe assemblies 33. This action serves to
create a homogeneous two-phase (liquid and vapor) refrigerant
mixture, which mixture is then evenly distributed across the bottom
region of the shell. The perforated plate 45 further helps to
evenly distribute the refrigerant mixture across the bottom region
of the shell. The compressor 63 suction as applied to the outlets
49 draws the refrigerant up inside of the shell into the tube
regions (FIG. 3). The refrigerant forms a thin liquid film 71 on
the outside of the tubes 15 (FIG. 7). The refrigerant film has
excellent heat transfer characteristics, particularly when compared
to a flooded evaporator. As the refrigerant is boiled off of the
tubes, the process fluid 75 cools and the refrigerant flows up as a
vapor 73. The spaces between the tubes 15 contain the refrigerant
in both liquid and vapor phases, with the liquid refrigerant being
the size of droplets. This is in contrast with a flooded evaporator
where the spacing between the tubes is filled with a pool of
refrigerant. The refrigerant vapor first passes through the
demister pad 47, then the last batch of tubes 15D and finally out
through the refrigerant outlets 49.
[0039] At the upper end of the shell, the refrigerant in the spaces
between the tubes 15 is mostly vapor and may contain some liquid.
The demister pad 47 coalesces any liquid refrigerant and thereby
prevents liquid from entering the compressor 63. The coalesced
liquid drops back down onto the tubes 15 below the demister 47. The
demister pad also applies a back pressure across the refrigerant
outlets 49, which serve to evenly distribute the refrigerant across
the tube bundle.
[0040] As the refrigerant vapor exits the evaporator 11 (FIG. 6),
it is super heated. Thus, it will not return to a liquid state
prior to being compressed by the compressor. The interaction
between the sensor 69 and the expansion device 67 maintains a fixed
superheat level.
[0041] The sump 51 (FIG. 1) captures oil in the refrigerant and
keeps the tubes 15 clean. The refrigerant picks up oil from the
compressor. As the refrigerant is sprayed out of the distribution
pipes, the oil adheres to the shell wall more readily than does the
refrigerant. The oil drains into the sump 51, where it collects and
can be removed. Removal of the oil is discussed in U.S. Pat. No.
7,082,774, the entire disclosure of which is incorporated herein by
reference.
[0042] The thin film evaporator has advantages over other types of
heat exchangers. Where a flooded evaporator requires the shell to
be flooded with refrigerant, the thin film evaporator requires a
much smaller charge of refrigerant. For example, for a 130
Ton-Refrigeration capacity system, a flooded evaporator would
require approximately 1200 pounds of ammonia, while the thin film
evaporator would require only about 35 pounds. Thus, there is less
toxic refrigerant to potentially leak into the atmosphere.
[0043] On the other hand, conventional spray evaporators require a
pump to spray the refrigerant down onto the tubes. Refrigerant
pumps are expensive as they must have special seals and maintenance
costs are high due to moving parts in a system. Furthermore, in
order to ensure reliability of the refrigeration system, typically
a backup pump is called for. The use of two special pumps
significantly increases the cost of the refrigeration system.
Furthermore, the refrigerant charge is still higher in the spray
evaporator as compared to thin film evaporator. However, with the
thin film evaporator described herein, no pump is needed as the
compressor suction is used to draw the refrigerant up through the
evaporator.
[0044] The foregoing disclosure and showings made in the drawings
are merely illustrative of the principles of this invention and are
not to be interpreted in a limiting sense.
* * * * *