ES2511036T3 - Heat exchanger with microchannels with improved refrigerant distribution - Google Patents

Abstract

A microchannel heat exchanger (30), comprising: a plurality of heat transfer tubes (36); a header (34) for communicating coolant into said plurality of heat transfer tubes; and a distributor insert (32) connectable to a coolant source and having a plurality of holes (42) on an outer periphery of said distributor insert, characterized by dividing elements (44) in an outer wall of said distributor insert such that a plurality of distribution chambers (46) are defined and associated with said plurality of heat transfer tubes, wherein the plurality of holes are arranged to evenly distribute heat two-phase refrigerant inside the plurality of distribution chambers.

Description

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DESCRIPTION

Heat exchanger with microchannels with improved refrigerant distribution

Background of the invention

This application is related to heat exchangers with microchannels of refrigerating systems that use a distributor insert part mounted inside a manifold, and more particularly with heat exchangers that incorporate dividing elements that separate the manifold into a plurality of chambers, each one associated with at least one heat exchange tube. JP-6-159983 describes a heat exchanger as defined in the preamble of claim 1.

In recent years, much of the interest and design effort has focused on the efficient operation of heat exchangers (and condensers and evaporators in particular) of cooling systems. A relatively recent advance in heat exchanger technology is the development and application of parallel flow heat exchangers, or so-called microchannels or mini-channels, (these two terms are used interchangeably in the text), such as condensers and evaporators. In addition, throughout the text, reference will be made to a heat exchanger by heat rejection as a condenser, with the understanding that the heat exchanger by heat rejection can function as a gas cooler, at least part of the time.

This type of heat exchangers with microchannels are provided with a plurality of parallel heat exchange tubes, between which the refrigerant is distributed and flows in parallel. Heat exchange tubes are generally oriented substantially perpendicular to the flow direction of the refrigerant in the inlet, outlet and intermediate manifolds that are in flow communication with the heat exchange tubes. When used in condenser and evaporator applications, these heat exchangers can be designed with a multi-step configuration, typically with a plurality of parallel heat exchange tubes within each refrigerant passage, in order to obtain superior performance by the balancing and optimization of heat transfer and pressure drop characteristics. Mono-step configurations are typically more desirable in evaporator applications, since refrigerant pressure drop plays a dominant role in evaporator performance.

However, there have been some obstacles to the use of microchannel heat exchangers in a cooling system. In particular, a problem, known as poor refrigerant distribution, 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 speeds and is subjected to different effects of internal and external forces than in a liquid phase. This causes the vapor phase to separate from the liquid phase and flow independently. The separation of the vapor phase and the liquid phase has posed challenges, such as the poor distribution of refrigerant in parallel flow heat exchangers.

In certain refrigerant systems it is known to use a distributor insert to deliver refrigerant to an evaporator manifold (see, for example, JP 6-159983). Such systems have been used in refrigerated trading systems, such as refrigeration cabinets. The proposed input distributor insert used in refrigerant showcases would not solve the problem of the poor distribution of refrigerant mentioned above.

Another proposed heat exchanger is constructed with a plurality of plates. The heat exchange refrigerant channels are formed of spaced plates, and remote ends of those spaced plates provide inlet chambers (plenums) for each refrigerant channel. The plates separate adjacent chambers (plenums), and an insert piece tube extends through the plates and into the chambers (plenums). This tube includes a plurality of holes that direct the refrigerant into the individual chambers (plenums). This arrangement would not be practical for heat exchangers with microchannels, and would only be a practical construction for the type of heat exchanger formed by spaced plates.

Compendium of the invention

The present invention provides a microchannel heat exchanger comprising: a plurality of heat transfer tubes; a manifold for communicating the refrigerant within said plurality of heat transfer tubes; and a distributor insert that can be connected to a refrigerant source and that has a plurality of holes in an outer periphery of said distributor insert, characterized by dividing elements in an outer wall of said insert insert distributor such that a plurality of distribution chambers are defined and associated with said plurality of heat transfer tubes, wherein the plurality of holes are arranged to uniformly direct the refrigerant from within the plurality of distribution chambers.

In one embodiment, the heat exchanger manifold is an inlet manifold of an evaporator and, in another embodiment, the heat exchanger manifold is an intermediate manifold of a condenser or an evaporator.

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While all separation chambers can have an identical size and the distributor divider elements are evenly spaced, in one embodiment, they have a variable size to further refine the refrigerant distribution. Although the invention is described in relation to a two-phase refrigerant, it is also applicable to a single-phase refrigerant and refrigerant-oil mixtures.

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

Brief description of the drawings

Figure 1 schematically shows a basic example of a refrigerant system.

Figure 2 shows a part of an input manifold of an inventive heat exchanger.

Figure 3 shows a part of an intermediate manifold of an inventive heat exchanger.

Figure 4 shows an example design of a distributor insert.

Figure 5A shows a cross-sectional view of an example heat transfer tube.

Figure 5B shows a cross-sectional view of an example of a dividing element.

Figure 5C shows a side view of an example of a dividing element of Figure 5B.

Figure 5D shows a cross-sectional view of another example of a dividing element.

Figure 5E shows a side view of an example of a dividing element of Figure 5D.

Detailed description of a preferred embodiment

A basic example of a refrigerant system 20 is illustrated in Figure 1, which includes a compressor 22 that compresses a refrigerant and delivers it downstream to a condenser 24. From the condenser 24 the refrigerant passes through an expansion device 26 to a Inlet refrigerant pipe 28 leading to an evaporator 30. From the evaporator 30, the refrigerant is returned to the compressor 22 to complete the closed refrigerant circuit.

A portion of the evaporator 30 is illustrated in Figure 2, which includes a refrigerant inlet manifold 34 incorporating the present invention. The evaporator 30 is a heat exchanger with microchannels, such heat exchangers particularly benefit from this inventive design and construction. The benefits of this invention can be extended to other applications, such as, for example, condenser applications.

Although the benefits of the invention will be described by referring to a two-phase refrigerant flow that passes through the heat exchanger, the single-phase refrigerant flows and the refrigerant oil mixtures are also within range and can benefit from the invention.

As shown in Figure 2, the inlet refrigerant pipe 28 has fluid communication with a distributor insert 32, which provides a refrigerant flow path along its longitudinal axis. An inlet manifold 34 of the evaporator 30 receives the distributor insert 32, and in turn has a fluid communication with a plurality of heat exchange tubes 36, generally perpendicular and downstream with respect to the flow direction of refrigerant, from the inlet manifold 34. The inlet refrigerant pipe 28 may be placed at the end of the inlet manifold 34, in the middle of the inlet manifold 34 or in some intermediate location in between. In addition, the inlet refrigerant pipe 28 may comprise two inlet refrigerant pipes connected at opposite ends of the inlet manifold 34 or in some intermediate locations. Obviously, more than two inlet coolant pipes can be used, but all must have fluid communication and provide coolant paths within the distributor insert 32.

As is known, a plurality of heat transfer fins 38 can be disposed between the heat exchange tubes 36 and rigidly connected thereto, usually by a furnace welding process, in order to increase the external heat transfer and provide structural rigidity for the heat exchanger

30. Also, as is known, each heat exchange tube 36 of a heat exchanger (evaporator) 30 with microchannels typically has a plurality of small internal channels 41 that provide multiple parallel coolant flow paths along the longitudinal axis of each heat exchange tube 36 (see Figure 5A). The internal channels 41 improve the internal heat transfer and also provide structural rigidity for the heat exchanger 30.

As also illustrated in Figure 2, a plurality of small size coolant distribution holes 42 is formed to protrude through the walls of the distributor insert 32 and to provide the coolant paths from an internal cavity of the distributor insert 32 for the inlet manifold 34. The distribution holes 42 may have, for example, round, rectangular,

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oval form or any other form. On the other hand, the distributor insert 32 has divider elements 44 located at its periphery and rigidly connected to the outer walls of the distributor insert 32. By placing the distributor insert 32 in the inlet manifold 34 of the evaporator 30, the divider elements 44 form a refrigerant separation chambers 46 within the internal cavity of the inlet manifold 34, each chamber communicates the downstream refrigerant with at least one heat exchange tube 36. Typically, each separation chamber would have fluid communication with several coolant distribution holes 42 and several heat exchange tubes 46.

As mentioned above, a plurality of small coolant distribution holes 42 are provided to direct the coolant from the distributor insert 34 to a plurality of separation chambers 46 defined by adjacent divider elements 44 of the insert Distributor 32 within the cavity of the inlet manifold 34. The distance between the dividing elements 44 can be uniform or can be adjusted to control the final size of the separation chambers 46 associated with any particular grouping of heat transfer tubes 36. This distance between the dividing elements 44 may vary from one group of heat transfer tubes 36 to another, or, in an extreme case, from one heat transfer tube 36 to another. As an example, for a single inlet refrigerant pipe 28 located at the end of the inlet manifold 34, the size of the chambers 46 may be uniform along the longitudinal axis of the manifold 34 or, for example, may decrease from the end of collector inlet at its remote end, in which the refrigerant speed is expected to be lower. Any particular configuration of the dividing elements 44 could depend on operating parameters and the particular application.

The distributor insert 32 receives the two-stage refrigerant from the inlet refrigerant pipe 28 and delivers this refrigerant, through a plurality of small distribution holes 42, to the heat exchanger manifold 34 which has been divided into the separation chambers 46 by the dividing elements 44 of the distributor insert 32. A relatively small size of the distributor insert 32 provides a significant time for the flow of refrigerant that prevents phase separation of the refrigerant into two phases. The plurality of the distribution holes 42 uniformly directs the refrigerant in two phases to the plurality of separation chambers 46 of the manifold 34 defined by the spaced divider elements 44 of the distributor insert 34. Since the size of the separation chambers 46 is relatively small, the liquid and vapor refrigerant phases do not have conditions or time to separate, as in the prior art, when the two-phase refrigerant expanded throughout the collector cavity input Even in cases where some separation of the refrigerant phases occurs, it would be within a relatively small manifold chamber 46, and, on average, the refrigerant distribution would still be predominantly uniform throughout the heat exchanger 30. Therefore, the inventive concept of distributor having a plurality of small distribution holes 42 and dividing elements 44 prevents poor distribution of refrigerant and ensures uniform distribution of refrigerant in the heat exchange tubes

36. In this manner, the refrigerant that is delivered to the heat exchange tubes 36 through the holes 42 of the distributor insert and the separation chambers 46 of the inlet manifold 34 will not have different amounts of phases of steam and liquid flowing through different heat exchange tubes and groups of heat exchanger tubes.

An outer periphery of the dividing elements 44 is tightly received within an inner wall of the inlet manifold 34. Similarly, an inner periphery of the dividing elements 44 is closely received in an outer wall of the insert 32. In this way , adjacent separation chambers 46 remain predominantly isolated from each other, which prevents the migration of refrigerant from one separation chamber 46 to another. Therefore, the general characteristics of the refrigerant flow to the heat exchange tubes 36 can be controlled in such a way that the effects of phase separation and / or refrigerant migration can be eliminated or minimized.

Figure 3 shows another embodiment 300, wherein the manifold 301 is an intermediate manifold, downstream of heat exchange tubes 302, and which feeds the refrigerant to heat exchange tubes 312. As shown, the piece of Distributor insert 306 has holes 308, an upper separator plate 304 and intermediate separator plates 310. This embodiment functions as in the previous embodiment to reduce refrigerant phase separation and poor distribution. In this embodiment, the heat exchanger could be a condenser, or an evaporator.

The dividing elements 44 may have any shape, such as, for example, flat plates (see Figure 5B), provided that they do not drastically block coolant flow to the heat exchange tubes 36 and do isolate a separation chamber 46 from another (e.g. through a small clearance or mechanical / chemical adhesion). On the other hand, the dividing elements 44 may have cut-outs 200, in case the heat exchange tubes 36 penetrate into the intake manifold 34 (see Figures 5B and 5C). The dividing elements 44 can be mechanically connected to the distributor insert 32 (eg snapped into place in small grooves made in the outer wall of the distributor insert 32), or by strong welding , fusion welding or soft welding. The dividing elements 44 can also be connected to the inner wall of the inlet manifold 34 (eg by oven welding). Both connection processes can be carried out, for example during furnace welding of the entire heat exchanger 30.

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Figures 5D and 5E show another embodiment, wherein the dividing elements 44 do not include the cutout 200, but include a groove or notch 202. The purpose of this notch is to provide a holding cavity for the welding flow, such that The distributor insert can be inserted into a manifold and welded onto the entire heat exchanger construction.

In general, each of the described embodiments teaches a distributor insert that will receive refrigerant, and will distribute the refrigerant through a plurality of holes to defined separation chambers between dividing elements. Since the insert and the dividing elements are connected together as a rigid subset, the entire assembly can be inserted into a manifold. This will allow the use of this feature without requiring a specific heat exchanger design, as has been the case in the

10 prior art.

Although an embodiment of this invention has been described, one skilled in the art will recognize that certain modifications fall within the scope of this invention, which is defined by the claims. For that reason, the following claims must be studied to determine the scope of the invention.

Claims (14)

5 10 fifteen twenty 25 30 35 40 Four. Five E09747084 09-30-2014 1. A heat exchanger (30) with microchannels, comprising: a plurality of heat transfer tubes (36); a manifold (34) for communicating the refrigerant within said plurality of heat transfer tubes; Y a distributor insert (32) that can be connected to a refrigerant source and that has a plurality of holes (42) on an outer periphery of said distributor insert, characterized by dividing elements (44) in an outer wall of said distributor insert in such a way that a plurality of distribution chambers (46) is defined and associated with said plurality of heat transfer tubes, wherein the plurality of holes are arranged to distribute the refrigerant evenly in two phases within the plurality of distribution chambers.

2.

The heat exchanger according to claim 1, wherein said distributor insert and said dividing elements improve the distribution of refrigerant in said heat exchanger.

3.

The heat exchanger according to claim 1, wherein said dividing elements are evenly spaced along a length of said distributor insert.

Four.

The heat exchanger according to claim 1, wherein said dividing elements are connected to said distributor insert by a mechanical connection or chemical adhesion.

5.

The heat exchanger according to claim 1, wherein the distributor insert has a round cross-sectional shape.

6.

The heat exchanger according to claim 1, wherein said manifold has an internal caliber with a round cross-sectional shape.

7.

The heat exchanger according to claim 1, wherein the refrigerant passing through said distributor insert is a two phase refrigerant.

8.

A refrigerant system comprising:

a compressor, said compressor is to compress a refrigerant and deliver said refrigerant downstream to a condenser, the refrigerant from said condenser passes through an expansion device and then to an evaporator, at least one of said condenser and said evaporator is a heat exchanger according to claim 1.

9.

The refrigerant system according to claim 8, wherein said distributor insertion piece extends from an upstream end of said manifold to an downstream end of said manifold, and the size of said defined separation chambers between the adjacent of said elements Dividers are determined to optimize the flow of refrigerant within the plurality of heat transfer tubes.

10.

The cooling system according to claim 8, wherein said plurality of heat transfer tubes, each including a plurality of channels, are generally spaced perpendicular to an upstream to downstream direction of said distributor insert.

eleven.

The heat exchanger or the cooling system according to claim 1 or 8, wherein the heat exchanger is an evaporator, and said manifold is an inlet manifold.

12.

The heat exchanger or the cooling system according to claim 1 or 8, wherein said manifold is an intermediate manifold.

13.

The heat exchanger or the cooling system according to claim 1 or 12, wherein said distributor insertion piece extends only along a part of said manifold, and does not align with the heat transfer tubes that communicate inside said collector, but it is aligned with the heat transfer tubes that communicate outside said collector.

14.

The heat exchanger or the cooling system according to claim 1 or 8, wherein said dividing elements are flat plates having a cutout part on an outer periphery to provide a clearance for said heat transfer tubes.

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