U.S. patent application number 12/933729 was filed with the patent office on 2011-01-27 for methods and systems for injecting liquid into a screw compressor for noise suppression.
This patent application is currently assigned to CARRIER CORPORATION. Invention is credited to Vishnu M. Sishtla.
Application Number | 20110016895 12/933729 |
Document ID | / |
Family ID | 41417344 |
Filed Date | 2011-01-27 |
United States Patent
Application |
20110016895 |
Kind Code |
A1 |
Sishtla; Vishnu M. |
January 27, 2011 |
Methods and Systems for Injecting Liquid Into a Screw Compressor
for Noise Suppression
Abstract
A screw compressor for use in a chiller assembly includes
cooperating screw rotors configured to increase the pressure of a
vaporized refrigerant flowing through the compressor, a venturi
tube arranged in a flow path of the refrigerant in the compressor
downstream of the rotors, and an inlet port in fluid communication
with a throat of the venturi tube and configured to deliver liquid
refrigerant from a condenser of the chiller assembly to the flow
path of the refrigerant in the compressor. The venturi tube is
configured to cause a pressure drop in the refrigerant in the
compressor. The liquid refrigerant delivered from the condenser
reduces pulsations in the pressure of the refrigerant discharged
from the compressor.
Inventors: |
Sishtla; Vishnu M.;
(Manlius, NY) |
Correspondence
Address: |
Cantor Colburn LLP - Carrier
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
CARRIER CORPORATION
Farmington
CT
|
Family ID: |
41417344 |
Appl. No.: |
12/933729 |
Filed: |
May 19, 2009 |
PCT Filed: |
May 19, 2009 |
PCT NO: |
PCT/US09/44567 |
371 Date: |
September 21, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61128467 |
May 21, 2008 |
|
|
|
Current U.S.
Class: |
62/115 ;
418/201.1; 62/498 |
Current CPC
Class: |
F04B 41/06 20130101;
F04C 29/06 20130101; F04C 18/165 20130101; F04C 29/12 20130101;
F04F 5/54 20130101; F04C 29/0035 20130101; F04C 29/042 20130101;
F04C 2270/13 20130101; F04C 29/0007 20130101 |
Class at
Publication: |
62/115 ;
418/201.1; 62/498 |
International
Class: |
F25B 1/00 20060101
F25B001/00; F01C 1/16 20060101 F01C001/16 |
Claims
1. A screw compressor for use in a chiller assembly, the compressor
comprising: a plurality of cooperating screw rotors configured to
increase the pressure of a vaporized refrigerant flowing through
the compressor; a first venturi tube arranged in a first flow path
of the refrigerant in the compressor downstream of the rotors for
causing a pressure drop in the refrigerant; and a first inlet port
in fluid communication with a throat of the first venturi tube and
configured to deliver liquid refrigerant from a condenser of the
chiller assembly to the flow path of the refrigerant in the
compressor for reducing pulsations in the pressure of the
refrigerant discharged from the compressor.
2. The compressor of claim 1, wherein the first venturi tube is
located in a bearing housing of the compressor.
3. The compressor of claim 1, wherein the first venturi tube is
located in a discharge housing of the compressor.
4. The compressor of claim 1 further comprising: a second venturi
tube arranged in a second flow path of the refrigerant in the
compressor; and a second inlet port in fluid communication with a
throat of the second venturi tube and configured to deliver liquid
refrigerant from the condenser to the second flow path of the
refrigerant in the compressor.
5. The compressor of claim 1, wherein the first venturi tube
reduces the pressure of the refrigerant in the compressor below a
pressure of the refrigerant in the condenser.
6. A chiller assembly comprising: a screw compressor; a condenser
coupled to the screw compressor; a first venturi tube arranged in a
first flow path of a refrigerant passing through the compressor,
wherein the first venturi tube comprises a convergent portion
connected to a divergent portion at a throat; and a first conduit
coupled between the throat of the first venturi tube and the
condenser and configured to deliver liquid refrigerant from the
condenser to the first flow path of the refrigerant in the
compressor for reducing pulsations in the compressed refrigerant
exiting the compressor.
7. The assembly of claim 6, wherein the screw compressor comprises:
a plurality of cooperating screw rotors configured to increase a
pressure of the refrigerant flowing through the compressor, wherein
the first venturi tube is arranged downstream of the screw
rotors.
8. The assembly of claim 7, wherein the first venturi tube is
located in a bearing housing of the compressor.
9. The assembly of claim 7, wherein the first venturi tube of the
discharge chamber is located in a discharge housing of the
compressor.
10. The assembly of claim 6 further comprising: a second venturi
tube arranged in a second flow path of the refrigerant in the
compressor, wherein the second venturi tube comprises a convergent
portion connected to a divergent portion at a throat; and a second
conduit coupled between the throat of the second venturi tube and
the condenser is configured to deliver liquid refrigerant from the
condenser to the second flow path of the refrigerant in the
compressor.
11. The assembly of claim 6, wherein the first venturi tube reduces
a pressure of the refrigerant in the compressor below a pressure of
the refrigerant in the condenser.
12. A screw compressor for use in a chiller assembly, the
compressor comprising: a screw rotor bearing housing; a first
venturi tube disposed in the bearing housing and arranged in a
first flow path of a refrigerant carried through the bearing
housing for decreasing the pressure of the refrigerant; and a first
inlet port in fluid communication with a throat of the first
venturi tube and configured to deliver liquid refrigerant from a
condenser of the chiller assembly to the first flow path of the
refrigerant in the bearing housing.
13. The compressor of claim 12 further comprising: a second venturi
tube disposed in the bearing housing and arranged in a second flow
path of the refrigerant carried through the bearing housing; and a
second inlet port in fluid communication with a throat of the
second venturi tube and configured to deliver liquid refrigerant
from the condenser to the second flow path of the refrigerant in
the bearing housing.
14. The compressor of claim 12, wherein the venturi tube reduces a
pressure of the refrigerant in the bearing housing below a pressure
of the refrigerant in the condenser.
15. A screw compressor for use in a chiller assembly, the
compressor comprising: a discharge housing; a first venturi tube
disposed in the discharge housing and arranged in a first flow path
of the refrigerant carried through the discharge housing for
decreasing the pressure of the refrigerant; and a first inlet port
in fluid communication with the throat of the venturi tube and
configured to deliver liquid refrigerant from a condenser of the
chiller assembly to the first flow path of the refrigerant in the
discharge housing.
16. The compressor of claim 15 further comprising: a second venturi
tube disposed in the discharge housing and arranged in a second
flow path of the refrigerant carried through the discharge housing;
and a second inlet port in fluid communication with a throat of the
second venturi tube and configured to deliver liquid refrigerant
from the condenser to the second flow path of the refrigerant in
the discharge housing.
17. The compressor of claim 15, wherein the first venturi tube
reduces a pressure of the refrigerant in the discharge housing
below a pressure of the refrigerant in the condenser.
18. A method of suppressing noise in a screw compressor of a
chiller assembly, the method comprising: introducing a liquid
refrigerant from a condenser of the chiller assembly into a
compressed gas refrigerant flowing through the screw compressor to
reduce pulsations in the refrigerant; and reducing, without adding
work, a pressure of the gas refrigerant in the compressor below a
pressure of the liquid refrigerant in the condenser to facilitate
introduction of the liquid refrigerant into the gas
refrigerant.
19. The method of claim 18, wherein the pressure of the gas
refrigerant is reduced by passing the gas refrigerant through one
or more venturi tubes.
20. The method of claim 18, wherein the pressure of the gas
refrigerant is reduced in one of a bearing housing or a discharge
housing of the compressor.
Description
BACKGROUND
[0001] The present invention relates to suppressing noise generated
in mechanical systems. In particular, the present invention relates
to noise suppression in screw compressors used in commercial and
industrial air conditioning and refrigeration systems.
[0002] The use of compression type water-cooled chillers is the
most common method of cooling air in medium or large commercial,
industrial and institutional buildings. Compression type
water-cooled chillers are usually electrically driven, but may also
be driven by a combustion engine or other power source. There are
several types of compressors employed in water-cooled chillers. One
common compressor is a screw compressor, which uses a rotary type
positive displacement mechanism to compress a working fluid, such
as a refrigerant.
[0003] Water cooled chillers used in air conditioning and
refrigeration systems are required to meet stringent noise level
requirements, such as those prescribed by the Occupational Safety
and Health Association (OSHA). However, screw chillers have a
tendency to generate significant noise during operation. The
primary source of noise generated in these types of chillers is
pressure pulsations originating from the compressor, which
generates noise, as well as vibration of adjoining components. In
addition to the screw compressor, there is a multitude of secondary
sources of noise, such as the evaporator, the condenser, and the
economizer.
[0004] Prior screw compressor designs have employed various devices
and methods to suppress the noise generated by the compressor, such
as mufflers and baffle plates arranged in the discharge chamber.
Additionally, prior chillers have injected liquid refrigerant from
the condenser into the gas refrigerant flow discharged from the
compressor to suppress noise generated from pressure pulsations.
However, under many operating conditions, these prior chiller
designs have required a pressure application device, such as a
pump, to compensate for a negative pressure differential between
the condenser and the compressor. The addition of a pump, or other
device, increases the cost and complexity of the system.
SUMMARY
[0005] A screw compressor for use in a chiller assembly includes
cooperating screw rotors configured to increase the pressure of a
vaporized refrigerant flowing through the compressor, a venturi
tube arranged in a flow path of the refrigerant in the compressor
downstream of the rotors, and an inlet port in fluid communication
with a throat of the venturi tube and configured to deliver liquid
refrigerant from a condenser of the chiller assembly to the flow
path of the refrigerant in the compressor. The venturi tube is
configured to cause a pressure drop in the refrigerant in the
compressor. The liquid refrigerant delivered from the condenser
reduces pulsations in the pressure of the refrigerant discharged
from the compressor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] FIG. 1 is a perspective view of a screw chiller assembly
according to the present invention.
[0007] FIG. 2 is an axial section view of the screw compressor
included in the chiller assembly of FIG. 1.
[0008] FIG. 3 is a schematic of the screw chiller assembly of FIG.
1 illustrating refrigerant flow through the system.
[0009] FIGS. 4A and 4B are schematics of two embodiments of the
compressor from the chiller assembly of FIG. 1.
DETAILED DESCRIPTION
[0010] FIG. 1 is a perspective view of screw chiller assembly 10
including screw compressor 12, variable frequency drive 14,
condenser 16, and evaporator 18. In FIG. 1, the inlet of compressor
12 is fluidly connected to evaporator 18 and the outlet of
compressor 12 is fluidly connected to condenser 16. Condenser 16 is
fluidly connected to evaporator 18. Variable frequency drive 14 is
mounted on condenser 16.
[0011] FIG. 2 is an axial section view of screw compressor 12 of
FIG. 1, which compressor 12 includes compressor housing 20, drive
screw 22, two opposed screws 24, 26, bearing housing 28, discharge
housing 30, discharge chamber 32, discharge ports 34, and motor 48.
Housing 20 receives central drive screw 22 and two opposed screws
24 and 26. Housing 20 is connected to motor 48, which is configured
to drive screws 22, 24, 26. Bearing housing 28 receives screw
bearings 28a that facilitate low friction rotation of drive screw
22 and opposed screws 24, 26. Bearing housing 28 also receives
compressed refrigerant from compression chambers 36 and delivers
this compressed refrigerant through discharge ports 34 in the
bearing housing 28 to discharge chamber 32 in discharge housing 30.
The size of the discharge chamber 32 necks down with the inner
peripheral surface 38 of the discharge housing 30.
[0012] FIG. 3 is a schematic of chiller assembly 10 illustrating
flow of refrigerant through the system. Chiller assembly 10 is a
closed loop system through which refrigerant is cycled in various
states, such as liquid and vapor. As a somewhat arbitrary starting
point in chiller assembly 10 of FIGS. 1-4, a low temperature, low
pressure superheated gas refrigerant is sucked into screw
compressor 12 through fluid conduit 42, such as a steel pipe, or
other conduit from evaporator 18. Compressor 12 is driven by motor
48 under the control of variable frequency drive 14. Variable
frequency drive 14 controls the frequency of the alternating
current (AC) supplied to motor 48, thereby controlling the speed of
motor 48 and the output of compressor 12. Refrigerant is sucked
into compressor 12 through inlet ports 40, and compressed between
screws 22, 24, and 22, 26 and carried towards discharge ports 34 in
bearing housing 28. The compressed refrigerant enters discharge
chamber 32 through discharge ports 34. After the refrigerant is
compressed, the high temperature, high pressure superheated gas is
discharged from compressor 12 through fluid conduit 42 to condenser
16. Chiller assembly 10 may also include an oil separator (not
shown) between compressor 12 and condenser 16, which separates
compressor lubricant from the refrigerant before delivering the
refrigerant to condenser 16. In condenser 16, the gaseous
refrigerant condenses into liquid as it gives up heat. The
superheated gas refrigerant enters condenser 16 and is
de-superheated, condensed, and sub-cooled through a heat exchange
process with, for example, water flowing through condenser 16 to
absorb heat. The liquid refrigerant is discharged from condenser 16
to metering device 44, which may convert the higher temperature,
high pressure sub-cooled liquid to a low temperature saturated
liquid-vapor mixture. The low temperature saturated liquid-vapor
refrigerant mixture enters evaporator 18 from metering device 44
through fluid conduit 42. The low pressure environment in
evaporator 18 causes the refrigerant to change states to a
superheated gas and absorbs the required heat of vaporization from
the chilled water, thus reducing the temperature of the water. The
low pressure superheated gas is then drawn into the inlet of
compressor 12 and the cycle is continually repeated. The chilled
water is then circulated through a distribution system to cooling
coils for providing air conditioning, or for other purposes.
[0013] Chiller assembly 10 may commonly be located in relatively
close proximity to people and as such may be designed to suppress
noise production and radiation as much as possible. Screw
compressor 12 is a significant contributor to noise generation,
because of pressure pulsations created when the refrigerant is
compressed. Pressure pulsations in compressor 12 result from
unsteady mass flux caused by the refrigerant compression process
performed within compressor 12. The pressure pulsations in
compressor 12 produce undesirable noise, which noise in turn is
radiated from chiller assembly 10. Additionally, the pressure
pulsations may generate mechanical vibrations in components of
chiller assembly 10 such as piping, heat exchangers, or compressor
housing 20 itself. Mechanical vibrations propagating through
chiller assembly 10 may themselves result in further noise
generation and radiation.
[0014] In order to suppress noise generated from the pressure
pulsations in compressor 12, chiller assembly 10 includes liquid
refrigerant conduit 46 shown in FIG. 3. Conduit 46 is configured to
deliver liquid refrigerant from condenser 16 to the superheated gas
refrigerant flow in compressor 12. In particular, conduit 46 is
configured to deliver liquid refrigerant from condenser 16 to
compressor 12 downstream of compression chambers 36 shown in FIG.
2. For example, conduit 46 may deliver liquid refrigerant to
channels in bearing housing 28, which channels deliver the
superheated gas refrigerant from compression chambers 36 to
discharge chamber 32 through discharge ports 34. Noise in the gas
refrigerant flow in compressor 12 is caused by pressure pulsations
at frequencies in the audible range, which may range from
approximately 20 to 20,000 Hz. Noise levels can be reduced by
reducing the magnitude of such pressure pulsations. The objective
of introducing liquid refrigerant from condenser 16 into gas
refrigerant flow in compressor 12 is to reduce the strength of the
pressure pulsations by transferring energy from the gas to liquid
phase. Three mechanisms contribute to reduce pressure pulsations
when liquid refrigerant droplets are injected into the gas
refrigerant flow: a) viscous drag between liquid and gas
refrigerant; b) heat transfer between liquid and gas refrigerant;
and c) mass transfer from vaporization of liquid refrigerant to
gas. Generally speaking, the magnitude of noise attenuation depends
on the mass flow rate and droplet size of liquid refrigerant
delivered from condenser 16. Noise suppression due to viscous drag
and heat transfer are both functions of droplet size. Noise
suppression due to mass transfer is a function of mass flow rate.
Viscous drag and heat transfer are particularly effective to reduce
noise at frequencies above 10,000 Hz, while vaporization, i.e. mass
transfer, is effective at lower frequencies.
[0015] In order to deliver the liquid refrigerant from condenser 16
to the superheated gas refrigerant flow in compressor 12, the
pressure in the condenser 16 must be greater than in the compressor
12. However, downstream of compression chambers 36 the superheated
gas refrigerant often has a higher pressure than the pressure of
the liquid refrigerant in condenser 16. Embodiments of the present
invention therefore provide methods of and systems for inducing a
pressure drop in the superheated gas refrigerant flow in compressor
12 sufficient to reduce the pressure in compressor 12 below the
pressure in condenser 16 without the addition of work to the
system.
[0016] FIGS. 4A and 4B are schematics of two embodiments of
compressor 12 configured to induce a pressure drop in the
superheated gas refrigerant flow discharged from compressor 12
through bearing housing 28 and discharge chamber 32. In FIGS. 4A
and 4B, compressor 12 includes compressor housing 20, bearing
housing 28, discharge housing 30, motor 48 and venturi tubes 50.
Arranged in compressor housing 20 is compression chamber 36, which
chamber 36 includes drive screw 22 and two opposed screws 24, 26
(shown in FIG. 2). Venturi tubes 50, also referred to as
convergent-divergent or De Laval nozzles, include, in the direction
of flow, a converging portion and diverging portion connected at a
throat. The throat of venturi tubes 50 defines a location of
minimum cross-sectional area and is in fluid communication with
condenser 16 through conduit 46, which may be, for example, a steel
pipe. In the embodiment of FIG. 4A, venturi tubes 50 are arranged
in bearing housing 28 and are configured to direct refrigerant flow
52 from compressor 12 to discharge chamber 32 in discharge housing
30.
[0017] As refrigerant flow 52 passes through venturi tubes 50, the
velocity of flow 52 increases while the pressure of flow 52
decreases. The throat of venturi tubes 50 defines not only the
location of minimum cross-sectional area, but also the location of
minimum pressure of refrigerant flow 52. Venturi tubes 50 thereby
induce a pressure drop in refrigerant flow 52 being discharged from
compressor 12 through bearing housing 28 and discharge chamber 32
to condenser 16. In embodiments of the present invention, venturi
tube 50 is configured to induce a pressure drop in refrigerant flow
52 sufficient to reduce the pressure of flow 52 at the throat of
venturi tube 50 below the pressure of liquid refrigerant directed
through conduit 46 from condenser 16. Therefore the liquid
refrigerant from condenser 16 used to suppress noise in compressor
12 may freely flow from condenser 16 to compressor 12 without
adding work to the system, e.g., without the use of a pressure
applicator like a pump.
[0018] In some applications, space constraints in compressor 12 may
not permit venturi tubes 50 to be disposed in bearing housing 28.
In an alternative embodiment (FIG. 4B), venturi tubes 50 are
arranged within discharge chamber 32 of discharge housing 30. In
the embodiment of FIG. 4B, refrigerant flow 52 passes through
bearing housing 28 into venturi tubes 50 in discharge chamber 32
through discharge ports 34. A pressure drop is induced in
refrigerant flow 52 as the refrigerant passes through venturi tubes
50, which pressure drop enables liquid refrigerant from condenser
16 to freely flow from condenser 16 through conduit 46 to
compressor 12 without adding work to the system.
[0019] Embodiments of the present invention provide methods of and
systems for inducing a pressure drop in the superheated gas
refrigerant flow in a screw compressor of a chiller assembly
sufficient to reduce the pressure in the compressor below the
pressure in a condenser without the addition of work to the system.
Inducing a pressure drop in the compressor refrigerant flow enables
liquid refrigerant from the condenser to freely flow to the
compressor without the use of a pressure application device, such
as a pump. Embodiments of the present invention thereby suppress
noise generated from pressure pulsations in the screw compressor by
injecting liquid from the condenser into the gas refrigerant flow
in the compressor without significantly increasing the cost and
complexity of the chiller assembly.
[0020] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention.
* * * * *