EP2097701B1

EP2097701B1 - Refrigerant distribution improvement in parallel flow heat exchanger manifolds

Info

Publication number: EP2097701B1
Application number: EP06839399.0A
Authority: EP
Inventors: Michael F. Taras; Alexander Lifson
Original assignee: Carrier Corp
Current assignee: Carrier Corp
Priority date: 2006-12-15
Filing date: 2006-12-15
Publication date: 2013-11-20
Anticipated expiration: 2026-12-15
Also published as: EP2097701A4; HK1137803A1; WO2008073108A1; US20100095688A1; EP2097701A1; CN101563577A; ES2440241T3; CN101563577B

Abstract

A method and apparatus are presented to ensure adequate distribution of a two-phase refrigerant flowing through a plurality of heat transfer tubes of a parallel flow heat exchanger in a generally parallel manner. In several embodiments of this invention, predominantly single-phase refrigerant (liquid for condensers and vapor for evaporators) is tapped and delivered downstream to a location where a predominantly single-phase refrigerant phase is already present, bypassing at least some of the heat transfer tubes. In this manner, the remaining single-phase refrigerant (vapor for condensers and liquid for evaporators) flowing through the heat exchanger core is uniformly distributed amongst a plurality of heat transfer tubes in the next downstream pass.

Description

BACKGROUND OF THE INVENTION

This application relates to multi-pass parallel flow heat exchangers in refrigerant systems, wherein liquid and vapor refrigerant phases are undesirably separated in one or more intermediate manifolds, resulting in refrigerant maldistribution amongst downstream heat transfer tubes and consequent heat exchanger performance degradation. In particular, this application relates to re-routing one of the refrigerant phases (the liquid phase for the condensers and the vapor phase for the evaporators) from at least one intermediate manifold to one or more downstream locations, bypassing one or more banks of heat transfer tubes within the parallel flow heat exchanger and subsequently allowing for uniform distribution of remaining predominantly single refrigerant phase (the vapor phase for the condensers and the liquid phase for the evaporators) among parallel heat transfer tubes that are positioned downstream and are in fluid communication with this at least one intermediate manifold. Heat exchanger and overall refrigerant system performance is thus enhanced.
Refrigerant systems utilize a refrigerant to condition a secondary fluid, such as air, delivered to a climate-controlled space. In a basic refrigerant system, the refrigerant is compressed in a compressor, and flows downstream to a condenser, where heat is typically rejected from the refrigerant to an ambient environment, during heat transfer interaction with this ambient environment. Then refrigerant flows through an expansion device, where it is expanded to a lower pressure and temperature, and to an evaporator, where during heat transfer interaction with another secondary fluid (e.g., indoor air), the refrigerant is evaporated and typically superheated, while cooling and often dehumidifying this secondary fluid.
In recent years, much interest and design effort has been focused on the efficient operation of the heat exchangers (condensers and evaporators) in the refrigerant systems. One relatively recent advancement in the heat exchanger technology is the development and application of parallel flow, or so-called microchannel or minichannel, heat exchangers (these two terms will be used interchangeably throughout the text), as the condensers and evaporators.
These heat exchangers are provided with a plurality of parallel heat transfer tubes, typically of a non-round shape, among which refrigerant is distributed and flown in a parallel manner. The heat transfer tubes are orientated generally substantially perpendicular to a refrigerant flow direction in inlet, intermediate and outlet manifolds that are in flow communication with the heat transfer tubes. The primary reasons for the employment of the parallel flow heat exchangers, which usually have aluminum furnace-brazed construction, are related to their superior performance, high degree of compactness, structural rigidity and enhanced resistance to corrosion.
When utilized in many condenser and evaporator applications, these heat exchangers are normally designed for a multi-pass configuration, typically with a plurality of parallel heat transfer tubes within each refrigerant pass, in order to obtain superior performance by balancing and optimizing heat transfer and pressure drop characteristics. In such designs, the refrigerant that enters an inlet manifold (or so-called inlet header) travels through a first multi-tube pass across a width of the heat exchanger to an opposed, typically intermediate, manifold. The refrigerant collected in a first intermediate manifold reverses its direction, is distributed among the heat transfer tubes in the second pass and flows to a second intermediate manifold. This flow pattern can be repeated for a number of times, to achieve optimum heat exchanger performance, until the refrigerant reaches an outlet manifold (or so-called outlet header). Typically, the individual manifolds are of a cylindrical shape (although other shapes are also known in the art) and are represented by different chambers separated by partitions within the same manifold construction assembly.
Heat transfer corrugated and typically louvered fins are placed between the heat transfer tubes for outside heat transfer enhancement and construction rigidity. These fins are usually attached to the heat transfer tubes during a furnace braze operation. Furthermore, each heat transfer tube preferably contains a plurality of relatively small parallel channels for in-tube heat transfer augmentation and structural rigidity.
However, there have been some obstacles to the use of the parallel flow heat exchangers in a refrigerant system. In particular, a problem, known as refrigerant maldistribution, typically occurs in the microchannel heat exchanger manifolds when the two-phase flow enters the manifold. A vapor phase of the two-phase flow has significantly different properties, moves at different velocities and is subjected to different effects of internal and external forces than a liquid phase. This causes the vapor phase to separate from the liquid phase and flow independently. The separation of the vapor phase from the liquid phase has raised challenges, such as refrigerant maldistribution in parallel flow heat exchangers. This phenomenon takes place due to unequal pressure drop inside the channels and in the inlet and outlet manifolds, as well as poor manifold and distribution system design. In the manifolds, the difference in length of refrigerant paths, phase separation and gravity are the primary factors responsible for maldistribution. Inside the heat exchanger channels, variations in the heat transfer rate, airflow distribution, manufacturing tolerances, and gravity are the dominant factors. Furthermore, a recent trend of heat exchanger performance enhancement promoted miniaturization of its channels, which in turn negatively impacted refrigerant distribution. Since it is extremely difficult to control all these factors, along with the complexity and inefficiency of the proposed techniques or prohibitively high cost of the solutions, many of the previous attempts to manage refrigerant distribution, have failed.
On the other hand, refrigerant maldistribution may cause significant heat exchanger and overall system performance degradation over a wide range of operating conditions. Therefore, it would be desirable to reduce or eliminate refrigerant maldistribution in parallel flow heat exchangers.
EP 0886113 A2 discloses a system as set out in the precharacterising portion of claim 1.

SUMMARY OF THE INVENTION

The invention provides a refrigerant system as defined in claim 1 and a method of operating a refrigerant system as defined in claim 14.
In disclosed embodiments of this invention, one of the phases of a two-phase refrigerant mixture, which is the liquid phase for condensers and the vapor phase for evaporators, is tapped from a location within a parallel flow heat exchanger, where a liquid phase is likely to separate from a vapor phase and accumulate, causing refrigerant maldistribution in downstream heat transfer tubes that are in fluid communication with this upstream location. Tapped, predominantly single-phase refrigerant, which is, once again, liquid for the condensers and vapor for the evaporators, is redirected into a downstream location in a parallel flow heat exchanger, where refrigerant is already in a predominantly single phase (the liquid phase for condensers and the vapor phase for evaporators). by passing at least some of the downstream heat transfer tube banks (or passes). Therefore, the remaining predominantly single phase refrigerant (vapor for the condensers and liquid for the evaporators) flowing through the next pass of the parallel flow heat exchanger can be uniformly distributed among parallel heat transfer tubes that are positioned downstream of the redirection (or tap) location and are in fluid communication with this location. As a result, both heat exchanger and overall refrigerant system performance are improved.
In one embodiment, a predominantly single-phase refrigerant is tapped from an intermediate manifold and redirected to another downstream intermediate manifold. In another embodiment, a predominantly single-phase refrigerant is tapped from an intermediate manifold and redirected to an outlet manifold. Although manifold locations are preferred and the most convenient tapping and bypass return points, other positions in the parallel flow heat exchangers are also feasible and within the scope of the invention. Moreover, if for instance, the manifold locations are utilized as the tapping points, a predominantly liquid bypass refrigerant flow in the condenser applications is taken from a location close to the bottom of the manifold of manifold chamber and a predominantly vapor bypass refrigerant flow for the evaporator applications is taken from a location close to the top of the manifold or manifold chamber.
Furthermore, in some embodiments, a single-phase refrigerant is tapped from a single location within a parallel flow heat exchanger, and in other embodiments, multiple tapping points are used. Also, although a single bypass return point is the most feasible, multiple bypass return points may be driven by design and space limitations and are within the scope of the invention.
The bypass line can be placed in the path of the secondary media, such as air, to obtain additional heat transfer and further improve the heat exchanger and overall system performance. Also, the bypass line may have internal and external heat transfer enhancement elements to further improve heat transfer between a predominantly single-phase bypass refrigerant and a secondary fluid. Since a counterflow arrangement is desired, the bypass line is preferably placed upstream of the parallel flow heat exchanger for both condenser and evaporator applications, with respect to the secondary fluid flow.
The invention is applicable for any multi-pass parallel flow heat exchanger shape and configuration, with any number of passes, and with a general upward or downward refrigerant flow direction. Further, the invention is beneficial for any parallel flow heat exchanger orientation, including horizontal, vertical and inclined.
In various embodiments, the tapped refrigerant bypass is arranged by various methods. In some embodiments, there is a hole in a separation plate between the manifold chambers that may be controlled by a float device (for the liquid phase bypass), check valve or solenoid valve. Of course, other methods of control known in the art are also applicable and within the scope of the invention. In other embodiments, an actual bypass return line is utilized to return refrigerant to a downstream location and a valve may be placed on this bypass return line to control the flow of a predominantly single-phase bypass refrigerant.
As stated above, the disclosed invention can be implemented in parallel flow heat exchanger installations functioning as condensers as well as evaporators.
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.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows a refrigerant system incorporating the present invention.
Figure 2A shows a first schematic.
Figure 2B shows a heat transfer tube design feature.
Figure 3 shows a second schematic.
Figure 4 shows a third schematic.
Figure 5 shows a fourth schematic.
Figure 6 shows a fifth schematic.
Figure 7 shows a sixth schematic.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A basic refrigerant system 20 is illustrated in Figure 1 and includes a compressor 22 delivering refrigerant into a discharge line 23 heading to a condenser 24. The condenser 24 is a parallel flow heat exchanger, and in one disclosed embodiment is a microchannel heat exchanger. The heat is transferred in the condenser 24 from the refrigerant to a secondary fluid, such as ambient air. The high pressure, but desuperheated, condensed and typically subcooled, refrigerant passes into a liquid line 25 downstream of the condenser 24 and through an expansion device 26, where it is expanded to a lower pressure and temperature. Downstream of the expansion device 26, refrigerant flows through an evaporator 28 and back to the compressor 22. An evaporator 28 may also be a parallel flow heat exchanger. In the evaporator 28, the heat is transferred from another secondary fluid, such as air delivered to the conditioned environment, to the refrigerant that is evaporated and typically superheated during heat transfer interaction with this secondary fluid. Although a basic refrigerant system 20 is shown in Figure 1, it is well understood by a person of ordinarily skill in the art that many options and features may be incorporated into a refrigerant system design. All these refrigerant system configurations are well within the scope and can equally benefit from the invention. Also, although all the embodiments are described in the relation to the condenser applications, it is well understood by a person skilled in the art that a similar approach can be utilized for evaporators, where a predominantly vapor phase (instead of a liquid phase in the condenser applications) is bypassed, allowing remaining liquid phase (instead of the vapor phase in the condenser applications) to be uniformly distributed among the downstream heat transfer tubes.
As shown in Figure 2A, the multi-pass condenser 24 has a manifold structure 30 that consists of multiple chambers 30A, 30B and 30C. An inlet manifold chamber 30A receives the refrigerant, typically in a vapor phase, from the discharge line 23. The refrigerant flows into a first bank of parallel heat transfer tubes 32, and then across the condenser core to a chamber 34A of an intermediate manifold structure 34. It should be noted that, in practice, there may be more or less refrigerant passes than the four illustrated passes 32, 36, 38, and 40. Further, it should be understood that, although for simplicity purposes each refrigerant pass is represented by a single heat transfer tube, typically there are many heat transfer tubes within each pass amongst which refrigerant is distributed while flowing within the pass, and, in the condenser applications, a number of the heat transfer tubes within each bank (or pass) typically decreases in a downstream direction with respect to a refrigerant flow. For instance, there could be 12 heat transfer tubes in the first bank, 8 heat transfer tubes in a second bank, 5 heat transfer tubes in a third bank and only 2 heat transfer tubes in the fourth bank. A separator plate 42 is placed within the manifold 34 to separate the chamber 34A from a chamber 34B positioned within the same manifold structure 34.
As shown in the Figure 2A, at chamber 34A, the refrigerant is starting to condense while flowing through the first pass along the tubes 32 (due to heat transfer interaction with a secondary fluid) and is in a two-phase thermodynamic state, although typically with a relatively small liquid amount in a two-phase mixture. Also, at this location, liquid phase may be starting to separate from the vapor refrigerant, as shown by 35, since liquid and vapor phases have different thermophysical properties and are affected differently by external forces such as gravity and momentum sheer. Separation of liquid and vapor phases may create maldistribution conditions, while the refrigerant flows from the chamber 34A of the intermediate manifold structure 34 back across the core of the condenser 24 through a second bank of parallel heat transfer tubes 36 into a chamber 30B of the manifold structure 30.
Since, in some cases, a somewhat insignificant amount of liquid refrigerant is accumulated within the chamber 34A, refrigerant maldistribution may not have a profound effect on the performance of the condenser 24 yet. Still, a float valve 52 and drain orifice 50 are shown to discharge liquid refrigerant into the adjacent chamber 34B, bypassing the downstream second and third banks of heat transfer tubes 36 and 38 respectively. As a result, favorable conditions are created for uniform distribution of a predominantly single-phase vapor refrigerant among the second bank of heat transfer tubes 36. The refrigerant entering the second bank of heat transfer tubes 36 is predominantly in a vapor phase and is flowing in generally parallel (although counterflow) direction to the refrigerant flow in the first bank of heat transfer tubes 32. As shown in the Figure 2A, a separator plate 42 prevents refrigerant mixing or direct flow communication between the manifold chambers 30A and 30B. In the chamber 30B, the refrigerant is also in a two-phase thermodynamic state but containing lower vapor quality and potentially promoting the conditions for liquid refrigerant accumulation, as shown at 144, at the bottom of the chamber 30B.
In such circumstances, vapor refrigerant will predominantly flow into the upper portion of the heat transfer tubes of the third pass 38 with liquid refrigerant flowing through the lower portion of the third bank 38 of heat transfer tubes. Therefore, refrigerant maldistribution may have a profound effect on performance of the condenser 24. Another float valve 52 and drain orifice 50 assembly discharges that liquid refrigerant downstream into the adjacent chamber 30C, bypassing the third and forth banks of heat transfer tubes 38 and 40 respectively. Consequently, the uniform distribution of a predominantly single-phase vapor refrigerant among the third bank of heat transfer tubes 38 can be achieved.
The predominantly single phase vapor refrigerant flows, for further condensation, from the intermediate chamber 30B of the manifold structure 30 into a third bank of parallel heat transfer tubes 38 generally positioned in parallel arrangement to the first and second banks of heat transfer tubes 32 and 36, across the condenser 24 and into an intermediate chamber 34B of the manifold structure 34. The liquid refrigerant level in the manifold chamber 34B, as shown at 244, may be even higher than levels 35 and 144, since liquid refrigerant from the intermediate manifold chamber 34A directly enters intermediate manifold chamber 34B through the orifice 50. It should be understood that the liquid levels 35, 144 and 244 may be somewhat exaggerated to illustrate the concept of the present invention as well as may vary with operating and environmental conditions.
The refrigerant flowing through the chamber 34B has even lower vapor quality and potentially creating similar maldistribution conditions for the fourth (and last) bank of heat transfer tubes 40. Again, the orifice 50 in the separator plate 42 positioned between the chambers 30B and 30C allows the flow of liquid refrigerant to enter from the intermediate manifold chamber 30B into the intermediate manifold chamber 30C and mix with the refrigerant flow leaving the forth bank of heat transfer tubes 40, while the float valve 52 prevents vapor refrigerant flow between the same chambers.
From the chamber 30C, the liquid refrigerant exits condenser 24 through the line 25. As known, corrugated, and typically louvered, fins 33 are located between and attached to the heat transfer tubes (typically during a furnace brazing process) to extend the heat transfer surface and improve structural rigidity of the condenser 24.
As shown in Figure 2B, the heat transfer tubes within the tube banks 32, 36, 38, and 40 may consist of a plurality of parallel channels 100 separated by walls 101. The Figure 2B is cross-sectional view of the heat transfer tubes shown in Figure 2A. The channels 100 allow for enhanced heat transfer characteristics and assist in improved structural rigidity. The cross-section of the channels 100 may take different forms, and although illustrated as a rectangular in Figure 2B, may be, for instance, of triangular, trapezoidal or circular configurations.
In the present invention, liquid refrigerant is tapped from the liquid accumulation locations within the two-phase flow portion of the condenser 24 (that may or may not be directly associated with the separator plates 42 dividing the manifold chambers) and directed to the locations downstream where a predominantly single-phase liquid refrigerant is flowing, thus bypassing the region where a two-phase refrigerant is present and avoiding maldistribution conditions for the downstream heat transfer tube bank. Therefore, the parallel flow heat exchanger and overall refrigerant system performance is improved. Alternatively, a heat exchanger of a smaller size can be allowed, if no performance enhancement is required.
Although the float valve 52 is illustrated having a spherical shape, it also may have other configurations such as conical, cylindrical, etc. Further, other type valves, such as a solenoid valve or a check valve, can be employed instead. Although an internal bypass between the manifold chambers is convenient, it may not always be feasible (e.g., when the manifold chambers are positioned at the opposite ends of the heat exchanger) or desired from a manufacturing complexity point of view. In such circumstances, an external bypass may be established instead, such a bypass line 53 tapping liquid refrigerant from a location 244 close to the bottom of the manifold chamber 34B to a downstream location 54 within the outlet manifold chamber 30C. In the outlet manifold chamber 30C, the three liquid refrigerant flows (leaving the forth bank of heat transfer tubes 40, bypassed from the chamber 30B to the chamber 30C and bypassed from the chamber 34B to the chamber 30C) are mixed. A flow control device, such as valve 49, may be positioned on the bypass line 53 and associated with a control 10 to allow the flow of this liquid refrigerant to be pulsed, modulated or completely shutdown. In this manner, a refrigerant system designer can achieve additional precise control over the desired amount of the bypassed liquid refrigerant flow, which can be tailored, for instance, to specific operating conditions, to provide even more uniform distribution of liquid and vapor refrigerant phases amongst the heat transfer tubes. Analogously, in case the float valves 52 are replaced by solenoid valves, a similar type of control can be executed for these valves as well. Additionally, level measurement devices installed with the liquid refrigerant flow control devices can be positioned in the manifold chambers, if desired or required for proper operation of these liquid refrigerant flow control devices. Lastly, other locations, rather than intermediate manifold chambers, can be selected for tapping of liquid refrigerant.
The bypass line 53 may have internal and external heat transfer enhancement elements and be placed into the path of the secondary media, such as ambient air, flowing across the condenser 24. Further, in order to maintain overall counterflow configuration, the bypass line 53 is preferably placed upstream of the heat transfer core of the condenser 24, in relation to the airflow.
Figure 3 shows another embodiment 124 of the parallel flow condenser having three passes and inlet and outlet tubes 23 and 153 respectively positioned on opposite sides of the heat exchanger core, wherein a fixed orifice of a predetermined size 54 replaces the float valve 52 and orifice 50 assembly of the first intermediate manifold chamber 34A shown in Figure 2A. The size of the orifice 54 is to be selected to maintain a liquid seal between the intermediate manifold chambers 34A and 34B at all operating conditions. Similarly to the Figure 2A embodiment, an orifice 50 and float valve 52 assembly is included to pass the liquid refrigerant from an intermediate manifold chamber 30B into a bypass return line 56, and back to a location 51 and to an outlet tube 153. In all other aspects the Figure 3 embodiment is similar to the Figure 2A embodiment.
Figure 4 shows yet another embodiment 224 of a parallel flow condenser having two passes, wherein a single bypass return line 53 redirects predominantly liquid refrigerant from an intermediate manifold 34 to the downstream point 160 and into an outlet manifold chamber 30B, to be combined with the refrigerant exiting a second bank of heat transfer tubes 36. In all other aspects the Figure 4 embodiment is similar to the Figure 2A embodiment.
Figure 5 shows another embodiment 324 of a parallel flow condenser having four passes, wherein bypass return lines 58 and 62 redirect the predominantly liquid refrigerant from an intermediate manifold chamber 30B into an outlet tube 25 and from an intermediate manifold chamber 34B into an outlet manifold chamber 30C respectively, or to the locations 60 and 64 where a predominantly single-phase liquid refrigerant is already present. Once again, in the absence of active flow control devices associated with the bypass lines, maintenance of a liquid seal at all operating conditions is essential. In this embodiment, the refrigerant flow is generally upward but in all other aspects it is similar to the Figure 2A embodiment.
Figure 6 shows yet another embodiment 424 of the parallel flow condenser having three refrigerant passes, inlet and outlet manifold chambers on opposite sides of the condenser core and generally upward refrigerant direction, wherein a bypass return line 62 is utilized to redirect liquid refrigerant from an intermediate manifold chamber 30B to an outlet manifold chamber 34B. Once again, liquid seal maintenance at all operating conditions is critical. Also, in both Figure 5 and 6 embodiments, where the refrigerant flow is generally upward, the pressure drop through the bypassed bank of heat transfer tubes (e.g., bank 40 in the Figure 5 embodiment and bank 38 in the Figure 6 embodiment) should be less than the pressure drop through the bypass return line 58 plus hydrostatic head between the chambers 30B and 30C in the Figure 5 embodiment and through the bypass return line 62 plus hydrostatic head between the chambers 30B and 34B in the Figure 6 embodiment.
Figure 7 shows another embodiment 524 of a parallel flow condenser having two passes where a bypass return line 70 leads to a point 68 in the outlet manifold chamber 30A where it mixes with the refrigerant exiting the second bank of the heat transfer tubes 36, and includes a float valve 80 and orifice 66. In all other aspects, this embodiment is similar to the Figure 5 and Figure 6 embodiments.
In summary, in the present invention, one of the phases of a two-phase refrigerant mixture, which is liquid phase for the condensers and vapor phase for the evaporators, is tapped from a location within a parallel flow heat exchanger where a liquid phase is likely to separate from a vapor phase and accumulate, causing refrigerant maldistribution in downstream heat transfer tubes that are in fluid communication with this upstream location. Tapped, predominantly single-phase refrigerant (once again, liquid for the condensers and vapor for the evaporators), is redirected into a downstream location in a parallel flow heat exchanger, where refrigerant is already in a predominantly single phase (the liquid phase for condensers and vapor phase for the evaporators), bypassing at least some of the downstream heat transfer tube banks (or passes). Therefore, the remaining predominantly single-phase refrigerant (vapor for the condensers and liquid for the evaporators) flowing through the next pass of the parallel flow heat exchanger can be uniformly distributed among parallel heat transfer tubes that are positioned downstream of the redirection (or tap) location and are in fluid communication with this location. As a result, both heat exchanger and overall refrigerant system performance are improved.
A predominantly single-phase refrigerant is tapped from an intermediate manifold and redirected to another downstream intermediate manifold, or to an outlet manifold, or to outlet refrigerant line. Although manifold locations are preferred and the most convenient tapping and bypass return points, other positions in the parallel flow heat exchangers are also feasible and within the scope of the invention. The redirection method can be internal to the heat exchanger design, such as redirection through the plates separating the manifold chambers, or external, such as bypass refrigerant lines. Active flow control devices, such as solenoid or float valves, or passive bypass devices, such as orifices or check valves, can be used.
Furthermore, a single-phase refrigerant may be tapped from a single location within a parallel flow heat exchanger or from multiple tapping points. Also, although a single bypass return point is the most feasible, multiple bypass return points may be driven by design and space limitations and are within the scope of the invention.
It has to be noted that the bypass line can be placed in the path of a secondary media, such as air, to obtain additional heat transfer and further improve the heat exchanger and overall system performance. The bypass line may have internal and external heat transfer enhancement elements to further improve heat transfer between a predominantly single-phase bypass refrigerant and a secondary fluid. Since a counterflow arrangement is desired, the bypass line is preferably placed upstream of the parallel flow heat exchanger core for both condenser and evaporator applications, with respect to the secondary fluid flow.
The invention is applicable for any multi-pass parallel flow heat exchanger shape and configuration with any number of passes and with a general upward or downward refrigerant flow direction. In an upward condenser configuration, the pressure drop through the bypass return line and hydrostatic head should not exceed the pressure drop through the bypassed tube bank for the desired amount of the bypass refrigerant flow. Also, in many cases, as stated above, a good liquid seal is important for proper operation and functionality, in the absence of active flow control devices. Further, the invention is beneficial for any parallel flow heat exchanger orientation, including horizontal, vertical and inclined.
The tapped single-phase refrigerant may be actively controlled to maintain the liquid seal for improved functionality or to adjust thermodynamic conditions of refrigerant at the heat exchanger exit. Also, sensors, such as a liquid level sensor, can be employed in conjunction with these flow control devices. While the main discussion in the invention is focused on condenser applications, refrigerant system evaporators can also benefit from the invention. In the evaporator applications, a predominantly single-phase vapor refrigerant is bypassed around some of the heat transfer tube banks (instead of liquid in condenser applications). Also, if for instance, the manifold locations are utilized as the tapping points, a predominantly vapor bypass flow for the evaporator applications is to be taken from the location close to the top of the manifold or manifold chamber (a predominantly liquid bypass flow in condenser applications is to be taken from the location close to the bottom of the manifold or manifold chamber). In most other aspects, the invention concept is similar for condenser and evaporator applications.
While the invention is disclosed for parallel flow heat exchangers, it does have applications for other heat exchanger types, for instance, for the heat exchangers having intermediate manifolds in the condenser applications. Also, the number of passes shown is purely exemplary, and a heat exchanger with any number of passes can equally benefit from the present invention. Further, the manifold constructions 30 and 34 encompassing a number of chambers may have many different design shapes and configurations. Also, the manifold chambers may not necessarily be positioned within the same manifold construction.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in the 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

A refrigerant system (20) comprising:
a condenser (24; 124;224;324;424;524);

a compressor (22);

an expansion device (26); and

an evaporator (28),

the compressor for delivering a compressed refrigerant to the condenser, refrigerant from said condenser passing through the expansion device, and from said expansion device through the evaporator, and from said evaporator being returned to said compressor; and

at least one of said condenser and said evaporator having a plurality of heat transfer tubes (32,36,38,40) which pass a refrigerant downstream in a generally parallel manner; and

at least one location (30B,34A,34B,34) within said evaporator (28) being likely to receive separated vapor and liquid phases of refrigerant mixture as the refrigerant flows through the plurality of heat transfer tubes, characterised by at least a portion of a separated vapor phase being tapped from said location and delivered to a downstream location (30C,34B;30;25) bypassing at least some of the heat transfer tubes to Improve distribution of a remaining refrigerant flowing through the bypassed heat transfer tubes that are in direct fluid communication with this location.
The refrigerant system (20) as set forth In Claim 1, comprising
at least one location (30B,34A,34B,34) within said condenser being likely to receive separated vapor and liquid phases of refrigerant mixture as the refrigerant flows through the plurality of heat transfer tubes, and at least a portion of a separated liquid phase being tapped from said location and delivered to a downstream location (30C,34B;30;25) bypassing at least some of the heat transfer tubes to improve distribution of a remaining refrigerant flowing through the bypassed heat transfer tubes that are in direct fluid communication with this location
The refrigerant system (20) as set forth in Claim 1 or 2, wherein said at least one of said condenser (24;124;224;324;424;524) and said evaporator (28) has at least one manifold structure (30,34) in fluid communication with said plurality of heat transfer tubes (32,36,38,40), said at least one manifold structure being provided with at least one separation member providing at least two chambers (30A,30B,30C,34A,34B) within said at least one manifold structure, and at least one of said chambers being said tap location.
The refrigerant system (20) as set forth in Claim 3, wherein said separation member is one of a separation plate (42), a check valve, a float valve (52;80), a solenoid valve, an orifice with a liquid seal and a combination thereof.
The refrigerant system (20) as set forth In Claim 1 or 2, wherein said at least one of said condenser (24;124;224;324;424;524) and said evaporator (28) has at least one manifold structure (30,34) in fluid communication with said plurality of heat transfer tubes (32,36,38,40), said at least one manifold structure being provided with at least one separation member providing at least two chambers (30A,30B,30C,34A,34B) within said at least one manifold structure, and at least one of said chambers being said downstream location (30C,34B;30;25).
The refrigerant system (20) as set forth in Claim 1 or 2, wherein said at least one of said condenser (24;124;224;324;424;524) and said evaporator (28) has an outlet refrigerant tube (25) and said outlet refrigerant tube being said downstream location (30C;34B;30;25).
The refrigerant system (20)as set forth in any preceding Claim, wherein said separated refrigerant Is at least partially carried by a bypass line (53;56;62;78).
The refrigerant system (20) as set forth in Claim 7, wherein said bypass line (53;56;62;78) has at least one of external and internal heat transfer enhancement elements.
The refrigerant system (20) as set forth in Claim 7, wherein said bypass line (53;56;62;78) associated with at least one of said condenser (24;124;224;324;424; 524) and said evaporator (28) Is positioned in the airflow path moving over at least one of said condenser and said evaporator.
The refrigerant system (20) as set forth in Claim 9, wherein said bypass line (53;56;62;78) associated with at least one of said condenser (24;124;224;324;424; 524) and said evaporator (28) is positioned upstream at least one of said condenser and said evaporator, in relation to the airflow.
The refrigerant system (20) as set forth in any preceding Claim, wherein each of said plurality of heat transfer tubes (32,36,38,40) have a plurality of small parallel Internal channels (100) carrying refrigerant in parallel paths within said heat transfer tubes, and wherein said parallel internal channels create a microchannel heat transfer tube or a minichannel heat transfer tube.
The refrigerant system (20) as set forth in any preceding Claim, wherein there are multiple tap locations.
The refrigerant system (20) as set forth in any preceding Claim, wherein there are multiple downstream locations.
A method of operating a refrigerant system comprising the steps of:
(1) providing a compressor (22) for delivering a compressed refrigerant to a condenser (24;124;224;324;424;524), refrigerant from said condenser passing through an expansion device (26), and from said expansion device through an evaporator (28), and from said evaporator being returned to said compressor; and

(2) providing at least one of said condenser and said evaporator having a plurality of heat transfer tubes (32,36,38,40) which pass a refrigerant downstream in a generally parallel manner;
characterised by the step of:

(3) identifying at least one location (34A,34B,30B;34) within said evaporator (28) likely to receive separated vapor and liquid phases of refrigerant mixture as the refrigerant flows through the plurality of heat transfer tubes, and at least a portion of a separated vapor phase being tapped from said location and delivered to a downstream location (30C,34B;30;25) bypassing at least some of the heat transfer tubes to improve distribution of a remaining refrigerant flowing through the bypassed heat transfer tubes that are In direct fluid communication with this location.
The method as set forth In claim 14, comprising the step of (4) identifying at least one location (34A,34B,30B;34) within said condenser (24;124;224;324;424;524) likely to receive separated vapor and liquid phases of refrigerant mixture as the refrigerant flows through the plurality of heat transfer tubes, and at least a portion of a separated liquid phase being tapped from said location and delivered to a downstream location (30C,34B;30,25) bypassing at least some of the heat transfer tubes to improve distribution of a remaining refrigerant flowing through the bypassed heat transfer tubes that are In direct fluid communication with this location.