US20140208784A1

US20140208784A1 - Refrigeration system with isentropic expansion nozzle

Info

Publication number: US20140208784A1
Application number: US13/753,595
Authority: US
Inventors: Lakhi Nandlal Goenka
Original assignee: Visteon Global Technologies Inc
Current assignee: Hanon Systems Corp
Priority date: 2013-01-30
Filing date: 2013-01-30
Publication date: 2014-07-31

Abstract

A refrigeration system is provided that comprises a compressor, condenser, a thermal expansion valve, an isentropic expansion nozzle, and an evaporator. An isentropic expansion nozzle includes an inlet and an outlet with the isentropic expansion nozzle inlet fluidly coupled to a thermal expansion valve outlet. The evaporator includes an inlet and an outlet, wherein the evaporator inlet is fluidly coupled to the isentropic expansion nozzle outlet and the evaporator outlet is fluidly coupled to the compressor inlet. Using the system, a fluid can be modified prior to evaporation. The fluid is passed through the thermal expansion valve to decrease a pressure and decrease a temperature of the fluid. The fluid is then passed through the isentropic expansion nozzle to increase a velocity of the fluid without substantially changing the temperature of the fluid. The fluid is thereafter passed into the evaporator.

Description

FIELD OF THE INVENTION

The present technology relates to using a thermal expansion valve coupled to an isentropic expansion nozzle to drop the pressure of a refrigerant and increase its flow velocity.

BACKGROUND OF THE INVENTION

This section provides background information related to the present disclosure which is not necessarily prior art.
Heat transfer is useful for many purposes. For example, it is employed in refrigerators, air conditioning systems, vehicle HVAC systems, and the like, and can be used to liquefy gases for repeated distillation or rectification, or for storage in the liquified state. Heat transfer is further used in various devices that operate more efficiently at low temperatures. Such devices include, for example, superconductive electrical cables, cryogenic comminuting devices which embrittle a material before the milling thereof, among others. In addition, various heat transfer machines are employed to maintain materials at low temperatures to protect against degradation or as part of a process or treatment; e.g., lyophilization or freeze drying a material.
One means employed to transfer heat is through the use of a refrigeration cycle, which generally comprises a compressor, a cooler or condenser for the refrigerant downstream of the compressor, an expansion valve or throttle downstream of the cooler or condenser, and a heat exchanger or evaporator in which heat is transferred by the phase change of a refrigerant. The heat exchanger or evaporator is connected to the upstream or inlet side of the compressor to complete the refrigerant cycle.
The expansion valve is a flow-restricting device that causes a pressure drop of the working fluid. For example, the expansion valve may be configured with a needle that remains open during steady state operation. The size of the opening or the position of the needle can be related to the pressure and temperature of the evaporator. As operation of such expansion valves can be dependent on temperatures, they are also referred to as thermal expansion valves.
In some configurations, the expansion valve can include various components to regulate the position of the needle. A sensor bulb at the end of the evaporator can monitor the temperature change of the evaporator. A change in temperature creates a change in pressure on a diaphragm. For example, if the temperature in the evaporator increases, the pressure in the diaphragm increases causing the needle to lower. Lowering of the needle subsequently allows more of the working fluid into the evaporator to absorb heat. The pressure at the inlet of the evaporator affects the position of the needle and prevents the working fluid from flowing back into the compressor. Since the pressure before the valve is higher than the pressure after the valve, the working fluid flows into the evaporator. The pressure at the inlet of the evaporator acts on the diaphragm.
The expansion valve can further include a spring providing a force towards closing the valve needle. The spring can therefore restricts the amount of working fluid entering the evaporator. The pressure spring can be adjusted to increase or decrease pressure based on temperature needs. The pressure created by the spring acts on the opening of the valve. When the pressure of the sensor bulb acting on the diaphragm is greater than the combined pressure of the evaporator and spring, the valve opens to increase the flow of the working fluid. An increase of flow lowers the temperature of the evaporator and allows for more heat absorption.
One problem with the throttling process involving the expansion valve is that mechanical energy is wasted in reducing the refrigerant pressure. Accordingly, it is desirable to provide an improved refrigeration system with more efficient energy utilization.

SUMMARY OF THE INVENTION

The present technology includes systems, processes, articles of manufacture, and compositions that relate to the use of an isentropic expansion nozzle positioned downstream of a thermal expansion valve to reduce a refrigerant pressure by accelerating the refrigerant (two-phase) and increasing its flow velocity into an evaporator. The result serves the same purpose as throttling with the expansion valve alone, but minimizes the loss of energy in the process.
In some embodiments of the present technology, a refrigeration system is provided that comprises a compressor, condenser, a thermal expansion valve, an isentropic expansion nozzle, and an evaporator. The compressor includes an inlet and an outlet. The condenser includes an inlet and an outlet with the condenser inlet fluidly coupled to the compressor outlet. The thermal expansion valve includes an inlet and an outlet where the thermal expansion valve inlet is fluidly coupled to the condenser outlet. The isentropic expansion nozzle includes an inlet and an outlet with the isentropic expansion nozzle inlet fluidly coupled to the thermal expansion valve outlet. The evaporator includes an inlet and an outlet, wherein the evaporator inlet is fluidly coupled to the isentropic expansion nozzle outlet and the evaporator outlet is fluidly coupled to the compressor inlet.
Other embodiments of the present technology include using the refrigeration system in a method where a refrigerant passing through the compressor is compressed. The refrigerant passing through the condenser is condensed. A pressure of the refrigerant passing through the thermal expansion valve is decreased. A velocity of the refrigerant passing through the isentropic expansion nozzle is increased. And the refrigerant passing through the evaporator is evaporated.
In certain embodiments of the present technology, a method of modifying a fluid prior to evaporation is provided. The method includes passing a fluid through a thermal expansion valve to decrease a pressure and decrease a temperature of the fluid. The fluid having the decreased pressure and decreased temperature is then passed through an isentropic expansion nozzle to increase a velocity of the fluid without substantially changing the temperature of the fluid. The fluid having an increased velocity and substantially unchanged temperature is subsequently passed into an evaporator.
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

FIG. 1 is a schematic flow diagram of a refrigeration system according to one embodiment of the present technology.

FIG. 2 is a schematic flow diagram of a refrigeration system according to another embodiment of the present technology.

FIG. 3 is a schematic flow diagram of a refrigeration system according to yet another embodiment of the present technology.

FIG. 4 is a fragmentary schematic plan view of a portion of a refrigeration system according to an embodiment of the present technology showing aspects of an evaporator.

FIG. 5 is a fragmentary schematic plan view of a portion of a refrigeration system according to an another embodiment of the present technology showing aspects of an evaporator

DETAILED DESCRIPTION

The following description of technology is merely exemplary in nature of the subject matter, manufacture and use of one or more inventions, and is not intended to limit the scope, application, or uses of any specific invention claimed in this application or in such other applications as may be filed claiming priority to this application, or patents issuing therefrom. Regarding the methods disclosed, the order of the steps presented is exemplary in nature, and thus, the order of the steps can be different in various embodiments. Except in the examples, or where otherwise expressly indicated, all numerical quantities in this description are to be understood as modified by the word “about” in describing the broadest scope of the technology.
A non-limiting discussion of terms and phrases intended to aid understanding of the present technology is provided at the end of this Detailed Description.
The present technology includes refrigeration systems and methods of using such systems where a thermal expansion valve is coupled to an isentropic expansion nozzle to drop the pressure of a refrigerant and increase a flow velocity of the refrigerant as the refrigerant enters an evaporator. As a result, less energy is lost in the throttling process of the thermal expansion valve. The coupled thermal expansion valve and isentropic expansion nozzle can include a heat exchanger positioned therebetween or thereafter to further control and manage the refrigerant. The evaporator can also be configured in ways to accommodate the increased flow velocity of the refrigerant.
With reference to FIGS. 1-3, a refrigeration system 100 is shown. The refrigeration system 100 includes a compressor 105, a condenser 110, a thermal expansion valve 115, an isentropic expansion nozzle 120, and an evaporator 125. The compressor 105 has an inlet 130 and an outlet 135. The condenser 110 has an inlet 140 and an outlet 145, the inlet 140 fluidly coupled to the outlet 135 of the compressor 105. The thermal expansion valve 115 has an inlet 150 and an outlet 155, the inlet 150 fluidly coupled to the outlet 145 of the condenser 110. The isentropic expansion nozzle 115 has an inlet 160 and an outlet 165, the inlet 160 of the isentropic expansion nozzle 115 fluidly coupled to the outlet 155 of the thermal expansion valve 115. The evaporator 125 has an inlet 170 and an outlet 175, the inlet 170 fluidly coupled to the outlet 165 of the isentropic expansion nozzle 115 and the outlet 175 fluidly coupled to the inlet 130 of the compressor 105.
The refrigeration system 100 can employ one or more refrigerants or working fluids and various blends thereof. The refrigerant can exhibit a reversible phase transition between a liquid phase and a gas phase. Examples of refrigerants include various hydrocarbons and halogenated hydrocarbons. Other refrigerants include ammonia, sulfur dioxide, and carbon dioxide.
The compressor 105 can comprise one or more various devices or systems that increase the pressure of the refrigerant by reducing its volume. The compressor 105 can be hermetically sealed, open, or semi-hermetic. Examples of various compressors include centrifugal, diagonal or mixed flow, axial flow, reciprocating, rotary screw, rotary vane, scroll, and diaphram types.
The condenser 110 can comprise one or more various devices or systems that are used to condense the refrigerant from its gas phase to its liquid phase, typically by cooling the refrigerant. In so doing, latent heat is given up by the refrigerant. In certain embodiments, the condenser 110 can be a heat exchanger that transfers heat from the refrigerant to another fluid.
The thermal expansion valve 115 can include one or more various devices or systems that operate to restrict refrigerant flow and cause a pressure drop of the refrigerant. The thermal expansion valve 115 can include one or more remote sensing elements (not shown) so the valve 115 is responsive to a temperature at a particular location in the system 100. In use, the thermal expansion valve 115 can control the amount of refrigerant flow into the evaporator 125, thereby controlling superheating at the outlet 175 of the evaporator 125.
The isentropic expansion nozzle 120 can take the form of a tube that is pinched in the middle, making a carefully balanced, asymmetric hourglass-shape. The isentropic expansion nozzle 120 can be used to accelerate pressurized refrigerant passing therethrough to a higher speed, and upon expansion of the refrigerant, the isentropic expansion nozzle 120 shapes the exhaust flow so the heat energy propelling the flow is maximally converted into directed kinetic energy. In this manner, the entropy of the refrigerant is nearly constant, so that while the temperature and pressure of the gas may drop, the flow velocity increases accordingly. An example of an isentropic expansion nozzle 120 is a de Laval nozzle, also known as a convergent-divergent nozzle, CD nozzle or con-di nozzle.
The evaporator 125 can include one or more various devices used to turn the liquid phase of the refrigerant into the gas phase. An increase in volume and/or a lower pressure within the evaporator 125 can cause the refrigerant to evaporate into the gas phase and absorb heat. One or more tubes (not shown) can be included in the evaporator 125 for the refrigerant to pass through. Another fluid stream, such as an air stream, can contact the evaporator 125 and the evaporator tube(s) to transfer heat from the air stream to the refrigerant. In this way, the cooled air stream can be used to condition air as part of an HVAC system, for example.
Various additional components can be included in the refrigeration system 100. For example, an optional drier or liquid separator 180 can be positioned within the refrigeration system 100. As shown in FIGS. 1-3, the liquid separator 180 can be fluidly coupled to the outlet 145 of the condenser 110 and fluidly coupled to the inlet 150 of the thermal expansion valve 115. A heat exchanger 185 can also be employed, where the heat exchanger 185 is configured to transfer heat between a fluid upstream of the compressor 105 and a fluid downstream of the condenser 110. In this way, refrigerant heated from compression via the compressor 105 and condensed by the condenser 110 can exchange heat with cooler refrigerant that has yet to enter the compressor 105 and be compressed. The heat exchanger 185 is sometimes referred to as an internal heat exchanger in the refrigeration system 100.
With reference to FIG. 2, another embodiment of the refrigeration system 100 is shown that further includes a heat exchanger 190 configured to transfer heat between a fluid upstream of the evaporator 125 and a fluid upstream of the compressor 105. In this way, for example, cooler refrigerant located between the outlet 175 of the evaporator 125 and the inlet 130 of the compressor 105 can receive heat from warmer refrigerant located between the outlet 165 the isentropic expansion nozzle 120 and the inlet 170 of the evaporator 125. A conduit 195 can also be used to fluidly couple the outlet 155 of the thermal expansion valve 115 and the inlet 160 of the isentropic expansion nozzle 120. The conduit 195 can allow for flow equalization of the refrigerant after leaving the thermal expansion valve 115.
With reference to FIG. 3, yet another embodiment of the refrigeration system 100 is shown that further includes a heat exchanger 200 configured to transfer heat between a fluid upstream of the isentropic expansion nozzle 120 and a fluid upstream of the compressor 105. In this way, for example, cooler refrigerant located between the outlet 175 of the evaporator 125 and the inlet 130 of the compressor 105 can receive heat from warmer refrigerant located between the outlet 155 of the thermal expansion valve 115 and the inlet 160 of the isentropic expansion nozzle 120. A conduit 205 can also be used to fluidly couple the outlet 165 of the isentropic expansion valve 120 and the inlet 170 of the evaporator 125. The conduit 205 can optionally be configured with another heat exchanger, such as heat exchanger 190 as shown in FIG. 2, thereby providing heat exchangers 190, 200 on each side of the isentropic expansion nozzle 120.
As the flow velocity of the refrigerant passing through the isentropic expansion nozzle 120 is substantially increased, aspects of the evaporator 125 can modified to accommodate the increased flow velocity of the refrigerant. For example, the high speed of the refrigerant flow within the evaporator 125 can provide a significantly higher refrigerant-side heat transfer, thereby enabling a downsizing of the evaporator with a resulting decrease in size and weight, as compared to other evaporators. For example, the overall length of the evaporator 125 can be shortened and/or the number of tubes within the evaporator 125 can be reduced.
With reference now to FIG. 4, a portion of the refrigeration system 100 is shown that includes the thermal expansion valve 115, the isentropic expansion nozzle 120, and a multi-tube evaporator 210. It should be noted that although the thermal expansion valve 115 and isentropic expansion nozzle 120 are shown as configured in FIG. 1, these components may be configured as shown in FIGS. 2 and 3, with the conduits 195, 205 and heat exchangers 190, 200 as shown therein. As such, the front end of the multi-tube evaporator 210 can include the various configurations shown in FIGS. 1-3.
The multi-tube evaporator 210 includes an inlet manifold 215 fluidly coupled to a plurality of tubes 220 that are fluidly coupled to an outlet manifold 225. The refrigerant having an increased velocity exiting the outlet 165 of the isentropic expansion nozzle 120 therefore enters the inlet manifold 215 of the multi-tube evaporator 210 and is divided amongst the several tubes 220, where the tubes 220 can be contacted with another fluid stream, such as an airflow, in order to transfer heat from the fluid stream to the refrigerant. The warmed refrigerant then exists the tubes 220 into the outlet manifold 225 where the refrigerant exits the multi-tube evaporator 210 as a single stream.
With reference now to FIG. 5, another portion of the refrigeration system 100 is shown that includes the thermal expansion valve 115, the isentropic expansion nozzle 120, and a single-tube evaporator 230. It should be noted that although the thermal expansion valve 115 and isentropic expansion nozzle 120 are shown as configured in FIG. 1, these components may be configured as shown in FIGS. 2 and 3, with the conduits 195, 205 and heat exchangers 190, 200 as shown therein. As such, the front end of the single-tube evaporator 230 can include the various configurations shown in FIGS. 1-3.
The single-tube evaporator 230 includes a single, continuous evaporator tube running from the inlet 170 of the evaporator 125 to the outlet 175 of the evaporator 125. As shown, the single-tube evaporator 230 can include at least one radiused portion 235 separating a plurality of substantially parallel portions 240. The refrigerant having an increased velocity exiting the outlet 165 of the isentropic expansion nozzle 120 therefore enters the inlet 170 of the evaporator 125 and passes through the single, continuous evaporator tube running to the outlet 175 of the evaporator 125. The linear flow of the refrigerant can be redirected by the one or more radiused portions 235 so that the refrigerant passes through several parallel portions 240, thereby affording a single, continuous evaporator tube of significant length but reducing the exterior dimensions of the single-tube evaporator 230.
The present technology further includes various methods of using the various refrigeration systems 100 described herein. One method includes compressing the refrigerant passing through the compressor 105. The refrigerant passing through the condenser 110 is condensed. The pressure of the refrigerant passing through the thermal expansion valve 115 is decreased. A velocity of the refrigerant passing through the isentropic expansion nozzle 120 is increased. The refrigerant passing through the evaporator 125 is evaporated.
The method of using the refrigeration system 100 can include further aspects. For example, liquid in the refrigerant can be separated using the liquid separator 180 fluidly coupled to the outlet 145 of the condenser 110 and fluidly coupled to the inlet 150 of the thermal expansion valve 115. Various heat exchange operations can also be performed. Heat can be exchanged between the refrigerant upstream of the compressor 105 and the refrigerant upstream of the condenser 110 using the heat exchanger 185. Heat can be exchanged between the refrigerant upstream of the evaporator 125 and the refrigerant upstream of the compressor 105 using the heat exchanger 190. And heat can be exchanged between the refrigerant upstream of the isentropic expansion nozzle 120 and the refrigerant upstream of the compressor 105 using the heat exchanger 200.
Other methods of the present technology include ways to modify a fluid prior to evaporation. In certain embodiments, a method of modifying a fluid prior to evaporation includes passing a fluid through a thermal expansion valve 115 to decrease a pressure and decrease a temperature of the fluid. The fluid having the decreased pressure and decreased temperature is then passed through an isentropic expansion nozzle 120 to increase a velocity of the fluid without substantially changing the temperature of the fluid. The fluid having an increased velocity and substantially unchanged temperature is further passed into an evaporator 125.
Such methods for modifying a fluid prior to evaporation can include additional aspects. In one aspect, the method can further include removing heat from the fluid having an increased velocity and substantially unchanged temperature prior to the fluid entering the evaporator 125. In another aspect, the method can further include passing the fluid having the decreased pressure and decreased temperature through a length of conduit 195 prior to the fluid entering the isentropic expansion nozzle 120. In yet another aspect, the method can further include removing heat from the fluid having the decreased pressure and decreased temperature prior to the fluid entering the isentropic expansion nozzle 120.
The present technology affords several benefits and advantages. The systems and methods presented herein minimize the loss of mechanical energy by the thermal expansion valve in the throttling process used to reduce refrigerant pressure. The resulting isentropic expansion of the refrigerant can results in a substantially unchanged entropy and an increase in flow velocity of the refrigerant. Thus, pressure is reduced prior to the refrigerant entering the evaporator 125, but the increased speed of the refrigerant serves to substantially offset any energy lost. As the refrigerant is generally at a higher speed than other systems, new high-speed evaporator designs can be used to accept the high-velocity fluid. These designs have significantly higher refrigerant-side heat transfer, thereby enabling a downsizing of the evaporator 125, with a resulting decrease in size and weight. The improvements described herein can provide overall efficiency improvements in the refrigeration system, as well as a reduction in HVAC airside pressure drop and package space.
Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms, and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail. Equivalent changes, modifications and variations of some embodiments, materials, compositions and methods can be made within the scope of the present technology, with substantially similar results.

Claims

What is claimed is:

1. A refrigeration system comprising:

a compressor including an inlet and an outlet;

a condenser including an inlet and an outlet, the inlet of the condenser fluidly coupled to the outlet of the compressor;

a thermal expansion valve including an inlet and an outlet, the inlet of the thermal expansion valve fluidly coupled to the outlet of the condenser;

an isentropic expansion nozzle including an inlet and an outlet, the inlet of the isentropic expansion nozzle fluidly coupled to the outlet of the thermal expansion valve; and

an evaporator including an inlet and an outlet, the inlet of the evaporator fluidly coupled to the outlet of the isentropic expansion nozzle and the outlet of the evaporator fluidly coupled to the inlet of the compressor.

2. The system of claim 1, further comprising a refrigerant within at least one of the compressor, the condenser, the thermal expansion valve, the isentropic expansion nozzle, and the evaporator.

3. The system of claim 1, further comprising a liquid separator fluidly coupled to the outlet of the condenser and fluidly coupled to the inlet of the thermal expansion valve.

4. The system of claim 1, further comprising a heat exchanger configured to transfer heat between a fluid upstream of the compressor and a fluid upstream of the condenser.

5. The system of claim 1, further comprising a heat exchanger configured to transfer heat between a fluid upstream of the evaporator and a fluid upstream of the compressor.

6. The system of claim 5, wherein the thermal expansion valve outlet is fluidly coupled to the inlet of the isentropic expansion nozzle via a conduit.

7. The system of claim 1, further comprising a heat exchanger configured to transfer heat between a fluid upstream of the isentropic expansion nozzle and a fluid upstream of the compressor.

8. The system of claim 7, wherein the isentropic expansion nozzle and the evaporator are fluidly coupled via a conduit.

9. The system of claim 1, wherein the evaporator further comprises:

an inlet manifold fluidly coupled to the inlet of the evaporator;

an outlet manifold fluidly coupled to the outlet of the evaporator; and

a plurality of evaporator tubes, each tube having an inlet and an outlet, wherein the inlet of each evaporator tube is fluidly coupled to the inlet manifold and the outlet of each evaporator tube is fluidly coupled to the outlet manifold.

10. The system of claim 1, wherein the evaporator comprises a single, continuous evaporator tube running from the inlet of the evaporator to the outlet of the evaporator.

11. The system of claim 10, wherein the single, continuous evaporator tube comprises at least one radiused portion separating a plurality of substantially parallel portions.

12. A method of using a refrigeration system comprising:

providing a refrigeration system comprising:

a compressor including an inlet and an outlet;

an evaporator including an inlet and an outlet, inlet of the evaporator fluidly coupled to the outlet of the isentropic expansion nozzle and the outlet of the evaporator fluidly coupled to the inlet of the compressor;

compressing a refrigerant passing through the compressor;

condensing the refrigerant passing through the condenser;

decreasing a pressure of the refrigerant passing through the thermal expansion valve;

increasing a velocity of the refrigerant passing through the isentropic expansion nozzle; and

evaporating the refrigerant passing through the evaporator.

13. The method of claim 12, further comprising separating liquid in the refrigerant using a liquid separator fluidly coupled to the outlet of the condenser and fluidly coupled to the inlet of the thermal expansion valve.

14. The system of claim 12, further comprising exchanging heat between the refrigerant upstream of the compressor and the refrigerant upstream of the condenser using a heat exchanger.

15. The system of claim 12, further comprising exchanging heat between the refrigerant upstream of the evaporator and the refrigerant upstream of the compressor using a heat exchanger.

16. The system of claim 12, further comprising exchanging heat between the refrigerant upstream of the isentropic expansion nozzle and the refrigerant upstream of the compressor using a heat exchanger.

17. A method of modifying a fluid prior to evaporation comprising:

passing a fluid through a thermal expansion valve to decrease a pressure and decrease a temperature of the fluid;

passing the fluid having the decreased pressure and decreased temperature through an isentropic expansion nozzle to increase a velocity of the fluid without substantially changing the temperature of the fluid; and

passing the fluid having an increased velocity and substantially unchanged temperature into an evaporator.

18. The method of claim 17, further comprising removing heat from the fluid having an increased velocity and substantially unchanged temperature prior to the fluid entering the evaporator.

19. The method of claim 18, further comprising passing the fluid having the decreased pressure and decreased temperature through a length of conduit prior to the fluid entering the isentropic expansion nozzle.

20. The method of claim 17, further comprising removing heat from the fluid having the decreased pressure and decreased temperature prior to the fluid entering the isentropic expansion nozzle.