HK1120600B - Parallel-flow evaporators with liquid trap for providing better flow distribution - Google Patents

Description

Parallel flow evaporator with liquid trap to provide better flow distribution

Technical Field

The present invention relates to a parallel-flow evaporator (parallel-flow evaporator) in which a liquid trap is placed upstream of the inlet manifold to provide better flow distribution in the parallel channels, improve heat transfer and enhance system reliability.

Background

Refrigerant systems are utilized to control the temperature and humidity of air in various indoor environments that are conditioned. In a typical refrigeration system operating in a cold state, a refrigerant is compressed in a compressor and delivered to a condenser (or an outdoor heat exchanger in this case). In the condenser, heat is exchanged between the outside atmosphere and the refrigerant. From the condenser, the refrigerant passes to an expansion device, where it is expanded to a lower pressure and temperature, and then to an evaporator (or to an indoor heat exchanger if the system is operating in a cold state). Within the evaporator, heat is exchanged between the refrigerant and the indoor air to condition the indoor air. When the refrigeration system is operating in a cooling state, the evaporator cools and typically dehumidifies the air provided to the indoor environment.

One type of evaporator that may be utilized in a refrigeration system is a parallel flow evaporator. Such evaporators have parallel channels for communicating refrigerant between an inlet manifold and an outlet manifold. Typically, each channel has a plurality of parallel internal channels of various cross-sectional shapes separated by internal walls. Corrugated fins are disposed between the channels for enhanced heat transfer and structural rigidity. Typically, the channels, manifolds and fins are constructed of similar materials, such as aluminum, and are interconnected by furnace brazing. Recently, parallel flow evaporators have attracted much attention and are advantageous in the air conditioning field due to their superior performance, compactness, rigid construction and enhanced corrosion resistance. However, one concern with parallel flow evaporators is maldistribution of refrigerant among their channels. Maldistribution problems in parallel flow evaporators typically result from the separation of the liquid phase from the vapor in the inlet manifold due to gravity combined with insufficient refrigerant velocity and thus manifest themselves as unequal amounts of vapor and liquid refrigerant passing through the evaporator passages. Additional phenomena affecting maldistribution may be attributed to different distances that refrigerant must flow to and drain from the various channels, unequal pressure impedances, and variations in heat transfer rates between channels, among others.

Known parallel flow evaporators typically have cylindrical inlet and outlet manifolds. The channels are typically extruded from the same aluminum that forms the flat tubes. When two-phase refrigerant enters the inlet manifold, the gas phase often separates from the liquid phase. Whereby the two phases move independently of each other after separation, resulting in a frequent refrigerant maldistribution problem.

When such maldistribution occurs, the heat exchanger performance degrades significantly, often resulting in liquid refrigerant leaving the outlet manifold, which can lead to serious reliability problems and permanent compressor damage. This is clearly undesirable.

Disclosure of Invention

In a disclosed embodiment of the invention, the parallel flow evaporator is provided with a liquid trap upstream of its inlet manifold. In this manner, the refrigerant will move at a rate such that the liquid phase will not separate from the vapor phase, and it can flow through the trap, into the manifold, and into the evaporator channels in a generally uniform distribution. However, the refrigerant will move at a reduced speed, so that separation of liquid may occur, and then the liquid will separate and accumulate in the liquid trap. As liquid accumulates in the liquid trap, the cross-sectional flow area for the remaining flow of refrigerant becomes smaller. As the cross-sectional flow area becomes smaller, the refrigerant velocity will increase, creating a jetting effect that will carry liquid droplets into the inlet manifold and will limit further phase separation. This phenomenon will be self-regulating to ensure that sufficient refrigerant velocity is achieved so that refrigerant liquid will not separate from vapor.

In one embodiment, a serpentine channel provided by a plurality of such U-shaped structures is utilized, rather than a serpentine channel having a single U-shaped trap.

In another disclosed embodiment, a refrigeration system is provided with an economizer circuit and utilizes a liquid trap on a line directing a two-phase refrigerant mixture to be separated into an economizer heat exchanger. Such an embodiment provides the same benefits and effects as the first disclosed embodiment.

These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.

Drawings

FIG. 1 is a cross-sectional view of an integrated evaporator of the present invention.

Fig. 2 shows the evaporator of fig. 1 in different flow states.

Fig. 3 shows another embodiment.

Fig. 4 shows a further embodiment.

Detailed Description

In fig. 1, a refrigeration system 20 having a parallel flow evaporator 22 is shown. As is known, refrigerant moves from downstream of the evaporator 22 to the compressor 24, the condenser 26, through the expansion device 28, and back to the evaporator 22. The refrigerant leaving the expansion device 28 is a mixture of vapor and liquid. The evaporator 22 has a plurality of parallel channels 32 spaced along an inlet manifold 34. The channels 32 and the inlet manifold 34 are in fluid communication with each other. Further, the passages 32 are similarly disposed and in communication with an outlet manifold 35. The fins 30 are disposed between the channels 32. Typically, the channels 32, fins 30, inlet manifold 34 and outlet manifold 35 are interconnected by furnace brazing. As is known, air passes through the fins 30 and the channels 32 to be conditioned. The refrigerant evaporates in the channels 32 due to heat transfer interaction with the air supplied to the conditioned space.

As discussed above, the velocity of the refrigerant entering the inlet manifold 34 is not sufficiently low, which may result in separation of liquid refrigerant from vapor. This may result in poor distribution of the two refrigerant phases in the channels 32. As shown in fig. 1, the refrigerant moves at a sufficient speed, and almost no refrigerant phase separation occurs.

The tubes 36 leading into the inlet manifold 34 are disposed downstream of the liquid trap 38. As shown, the liquid trap 38 extends generally vertically in a U-shape. Thus, any liquid that tends to separate will collect in the liquid trap 38.

As shown in fig. 2, the refrigerant velocity is not low enough in fig. 2 compared to the condition of fig. 1 preventing phase separation, and a significant amount of liquid refrigerant 40 collects in the trap 38, and therefore the remaining cross-sectional area 42 for refrigerant flow is significantly reduced. This in turn increases the refrigerant velocity through the inlet manifold 34. As the velocity of the refrigerant flow increases, the vapor refrigerant will tend to carry its liquid phase to the channels 32 in a uniform manner to ensure generally equal distribution. In effect, the sparging zone is formed to increase the velocity and limit additional phase separation. Thus, by including the liquid trap 38 upstream of the manifold 34, the present invention automatically adjusts the refrigerant velocity and ensures that the remaining liquid refrigerant does not separate in the vapor phase, except for the initial separation of a small amount of liquid refrigerant 40, thereby creating a uniform flow condition in the inlet manifold 34. Of course, the inlet manifold 34 should have a suitable cross-sectional area and length to maintain such flow uniformity. Also, the liquid trap 38 should be located in close proximity to the inlet manifold 34. Preferably, the liquid trap 38 should be positioned within 5 inches from the inlet to the inlet manifold 34 and extend vertically below it. Thereby improving the performance of the evaporator. This will also result in no liquid refrigerant in the evaporator outlet manifold 35 and enhanced system reliability.

Although this invention is disclosed in a conventional evaporator, other heat exchangers, such as economizer heat exchangers (or so-called brazed plate heat exchangers) that also function as evaporators, may equally benefit from the present invention.

Further, while the liquid trap 38 is shown in its simplest configuration, other arrangements (e.g., multiple U-shaped segments connected together, local flow impedance, etc.) are possible.

FIG. 3 shows another embodiment 100 having a plurality of successive U-shaped traps 102 upstream of a portion 104 of the intake manifold 34. Each liquid trap 102 may collect a small amount of liquid refrigerant to increase gas phase velocity and improve uniformity at the inlet of the inlet manifold 34.

Another embodiment of a refrigeration system 110 is shown in fig. 4. In this embodiment, the compressor 112 supplies compressed refrigerant to the condenser 114. Line 116 branches from the main refrigerant flow line 126 and passes through an economizer expansion device 118. The liquid trap 120 conditions refrigerant passing through an inlet 122 to an economizer heat exchanger 124. The liquid trap 120 will function as provided by and operate as described for the embodiment of fig. 1 and 2. It is to be understood that the economizer heat exchanger 124 has a structure of adjacent passages, whereby heat exchange is performed between the refrigerant of the branch line 116 and the refrigerant of the main flow line 126. A main flow line 126 supplies refrigerant to an outlet 128 and passes through a main expansion device 130 to an evaporator 132. The present invention may utilize a liquid trap with an economizer heat exchanger 124 and an evaporator 132. From the evaporator 132, the refrigerant returns to the compressor 112. Downstream of line 134 of the economizer heat exchanger 124, the separated refrigerant is returned to an intermediate compression point in the compressor 112.

It must be noted that although all the inlet manifolds are shown in a horizontal configuration, the maldistribution phenomenon is more pronounced in the longitudinal direction. In this case, the benefits of the present invention will become more apparent.

Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims (15)

1. A refrigeration system comprising:

a compressor supplying compressed refrigerant to a condenser, refrigerant passing from the condenser to an expansion device, and from the expansion device to an evaporator, the evaporator including an inlet manifold, an outlet manifold, a plurality of channels receiving refrigerant from the inlet manifold and supplying refrigerant to the outlet manifold, and fins disposed between the channels; and

a conduit connecting the expansion device and the evaporator, the conduit being provided with a first liquid trap to collect liquid separated from vapor refrigerant flowing from the expansion device to the evaporator.

2. The refrigerant system as set forth in claim 1, wherein said first liquid trap extends vertically below said inlet manifold.

3. The refrigerant system as set forth in claim 1, wherein said first liquid trap is provided by a U-shaped downward extension of said conduit.

4. The refrigerant system as set forth in claim 1, wherein said first liquid trap is disposed within 5 inches of said inlet manifold.

5. A refrigeration system as set forth in claim 1 and further provided with an economizer circuit having an economizer heat exchanger with a branch line connecting the main flow line through an economizer expansion device, said branch line returning to an intermediate compression point in said compressor downstream of said economizer heat exchanger, and a second liquid trap for collecting liquid separated from vapor refrigerant flowing from said economizer expansion device to said economizer heat exchanger.

6. The refrigerant system as set forth in claim 1, wherein said first liquid trap includes a plurality of sequentially spaced U-shaped liquid trap sections.

7. A method of operating a refrigeration system comprising the steps of:

providing an evaporator having a plurality of tubes that receive refrigerant from an inlet manifold and convey the refrigerant to an outlet manifold and from the outlet manifold to a compressor, the compressor conveying refrigerant to a condenser, and the refrigerant passing from the condenser to an expansion device and then back to the evaporator, and providing a fluid line connecting the expansion device to the evaporator, the fluid line being provided with a first liquid trap to collect liquid that has separated from vapor refrigerant; and

passing refrigerant through the refrigeration system and causing the first liquid trap to automatically adjust the velocity of the refrigerant as liquid separates from vapor refrigerant, thereby delivering refrigerant to the inlet manifold in a predominantly uniform state.

8. The method as set forth in claim 7, wherein the refrigerant system is further provided with an economizer circuit including an economizer heat exchanger, tapping refrigerant and passing tapped refrigerant through an economizer expansion device into said economizer heat exchanger, and a second liquid trap for collecting liquid that has been separated from vapor passing through said economizer expansion device into said economizer heat exchanger, and further including the step of passing refrigerant through said economizer expansion device and to said economizer heat exchanger such that when liquid is separated from vapor refrigerant, said second liquid trap automatically adjusts the velocity of the refrigerant to deliver refrigerant to said economizer heat exchanger in a substantially uniform state.

9. A system comprising a heat exchanger and a fluid circuit, comprising:

a fluid line leading to an inlet manifold;

a liquid trap on the fluid line; and

a heat exchanger having a plurality of channels receiving fluid from the inlet manifold.

10. The heat exchanger and fluid line system as set forth in claim 9, wherein said heat exchanger is an evaporator of a refrigeration system.

11. The system comprising a heat exchanger and a fluid line of claim 9, wherein the heat exchanger is an economizer heat exchanger of a refrigeration system.

12. The system comprising a heat exchanger and a fluid line of claim 9, wherein the liquid trap extends vertically below the inlet manifold.

13. The system comprising a heat exchanger and a fluid line of claim 9, wherein the liquid trap is provided by a U-shaped downward extension of the fluid line.

14. The system comprising a heat exchanger and a fluid line of claim 9, wherein the liquid trap is disposed within 5 inches of the inlet manifold.

15. The system comprising a heat exchanger and a fluid line of claim 9, wherein the liquid trap is provided by a plurality of sequentially spaced U-shaped structures.