MX2007009252A

MX2007009252A - Parallel flow heat exchangers incorporating porous inserts.

Info

Publication number: MX2007009252A
Application number: MX2007009252A
Authority: MX
Inventors: Michael F Taras; Mikhail B Gorbounov; Igor B Vaisman; Parmesh Verma; Robert A Chopko; Allen C Kirkwood; Raymond A Rust Jr; Thomas D Radcliff
Original assignee: Carrier Corp
Priority date: 2005-02-02
Filing date: 2005-12-29
Publication date: 2007-09-04
Also published as: CN101111734B; AU2005326711B2; JP2008528938A; AU2005326711A1; HK1117224A1; CN101111734A; WO2006083443A2; EP1844290A4; KR20070100785A; US20080099191A1; WO2006083443A3; CA2596365A1; EP1844290B1; BRPI0519907A2; EP1844290A2

Abstract

A parallel flow (minichannel or microchannel) evaporator includes a porous member inserted at the entrance of the evaporator channels which provides refrigerant expansion and pressure drop controls resulting in the elimination of refrigerant maldistribution and prevention of potential compressor flooding.

Description

THERMOINTERCAMBIADOEFES OF PARALLEL FLOW THAT INCORPORATE POROUS INSERTIONS DESCRIPTION OF THE INVENTION This invention relates generally to air conditioning, heat pump and cooling systems and, more particularly, to parallel flow evaporators thereof, A definition of a so-called parallel flow heat exchanger is widely used in the air conditioning and refrigeration industry and designates a heat exchanger cc n a plurality of parallel passages, between which the refrigerant is distributed and flows in 1 < General direction and substantially perpendicular to the direction of flow (ie refrigerant in the inlet and outlet hoses) This definition is well adapted within the technical community and will be used throughout the text, The maldistribution of the refrigerant in evaporators of The refrigerant system is a well-known phenomenon, it causes a significant degradation of the evaporator and the overall system performance over a wide range of operating conditions.The poor distribution of the refrigerant can or does not occur due to differences in the flow impedances within the evaporator channels, the non-uniform air flow distribution on external caliper transfer surfaces, inadequate orientation of the heat exchanger or poor design of the collector and the distribution system. The maldistribution is particularly pronounced in parallel flow evaporators due to its specific design with respect to the routing of the refrigerant to each refrigerant circuit. Attempts to eliminate or reduce the effects of this phenomenon on the performance of parallel flow evaporators have been made with little or no success. The main reasons for such failures have generally been related to the cost and flexibility of the proposed technique or the prohibitively high cost of the solution. In years gone by, parallel flow heat exchangers and brazed aluminum heat exchangers in particular have received a lot of attention and interest, not only in the automotive field but also in the heating, ventilation, air conditioning and refrigeration industry (HVAC &; R). The main reasons for the use of parallel flow technology relate to its superior performance, high degree of compaction and improved resistance to corrosion. Parallel flow heat exchangers are now used in count applications. sizers and evaporators for multiple products and system designs and configurations. The applications of eváporadores, although they promise greater benefits and remunerations, are more challenging and problematic The poor distribution of the refrigerant is one of the main concerns and obstacles to the implementation of this technology in the evaporator applications. As it is known, the bad distribution of refrigerant in parallel flow heat exchangers occurs due to an uneven pressure drop inside the channels and in the inlet and outlet hoses, as well as a deficient design of the manifold distribution system. In the sleeves, the difference in length of the refrigerant trajectories, the phase separation and the severity are the main factors responsible for maldistribution. Within the heat exchanger channels, variations in the heat transfer rate, air flow distribution, manufacturing tolerances, and gravity are the dominant factors In addition, the recent trend of improving the performance of the heat exchanger promoted the miniaturization of its channels (so-called mini channels and microchannels), which in turn negatively impacted the refrigerant distribution. Since it is extremely difficult to control all of these factors, many of the previous attempts to handle a refrigerant distribution, especially in parallel flow evaporators, have failed. In refrigerant systems that use Parallel flow heat exchangers, inlet and outlet manifolds or manifolds (these terms will be used interchangeably through the text) usually have a conventional cylindrical shape. When the double-phased flow enters the collector, the vapor phase normally separates from the liquid phase. Since both phases flow independently, poor refrigerant distribution tends to occur. If the double phase flow enters the inlet sleeve at a relatively high speed, the liquid phase (liquid droplets) is carried by the flow moment beyond the inlet of the sleeve to the remote portion of the manifold. Therefore, the channels closest to the entrance of the hose: o receive predominantly the vapor phase and the channels away from the entrance of the hose receive the liquid phase for the most part. If, on the other hand, the speed of the double-phase flow entering the sleeve is low, there is not enough time to bring the liquid phase along the manifold. As a result, the liquid phase enters the channels closest to the entrance and the vapor phase proceeds to the furthest. Also, the liquid and vapor phases in the inlet sleeve can be separated by gravity forces, causing similar maldistribution consequences. In any case, the phenomenon of 1 to bad distribution quickly goes to Glistening and manifests itself in evaporator and degradation ent rendi general system, addition, enómeno maldistribution may cause the condicicjnes dual phase (superheat zero) at the exit of some channels, - promoting flooding potential in compressor suction that can quickly result in damage to the compressor. It is therefore an object of the present invention to provide a system and method that solves the problems of the prior art described previously. J The object of the present invention to provide a control pressure drop for the evaporator (microchannel or minichannel) parallel flow essentially equal pressure drop through the circuits of the heat exchanger and therefore eliminate refrigerant maldistribution and the problems associated with it. Furthermore, it is the object of the present invention to provide a coolant expansion at the inlet of each channel, thereby eliminating a double-phase flow predominantly in the inlet hose, which is one of the main causes of the bad refrigerant distribution It has been found that the introduction of a porous medium inserted into each parallel flow evaporator channel, or at the inlet of each parallel flow evaporator channel, establishes these objectives.

Porous media inserts can be welded to bronze in each channel during the welding in the entire heat exchanger, chemically bonded or mechanically fixed in the 1 igar. In addition, these inserts can be used as a primary expansion device (and only) for low-cost applications or as secondary expansion devices, in case an accurate superheat control and a thermostatic expansion valve (TXV) or a valve are required. Electronic expansion (EXV) is used as a primary expansion device. Any suitable porous insertion that achieves the above objectives can be used. Suitable and economical porous inserts can be formed of sintered metal, compressed metal, such as steel wool, specially designed porous ceramics 5, etc. When an economical porous media insert is placed in each channel of the parallel flow evaporator, or in the inlet of each parallel flow evaporator channel, it represents a greater resistance for the flow of refrigerant 5 inside the evaporator. In such circumstances, the main pressure drop region will be through these inserts and the variations in pressure drop in the channels or in the sleeves of the parallel flow evaporators that will play a negligible minor role). In addition, since the expansion ofThe coolant is located at the inlet of each channel, a predominantly simple phase liquid liquidb is transported through the inlet sleeve, especially in the case when the porous inlets are used as the primary and sole expansion devices. Therefore, a uniform refrigerant distribution is achieved, the performance of the evaporator and the system is improved and, at the same time, the following is not lost: 1 precise superheat control (whenever required). Also, low extra cost for the proposed method makes < ie this invention very attractive. BRIEF DESCRIPTION OF THE DRAWINGS For a further understanding of the objects of the invention, reference will be made to the following detailed description of the inverjción which will be read together with the attached drawings, wherein: Figure 1 is a schematic illustration of a heat exchanger parallel flow according to the prior art. Figure 2 is a partial side sectional view of one embodiment of the present invention. Figure 3 is an end view of a porous insert placed in the inlet in a channel of the present invention. Figure 4 is a perspective view of the porous insert illustrated in Figure 3 Figure 5 _. is a side sectional view illustrating a further embodiment of the present invention. Figure 5 3 is a side sectional view illustrating yet another modality of the present invention. Figure 6 is an end view of a plurality of channels in one embodiment of the invention. Figure 7a is a perspective view which illustrates a < eg porous lid of the invention. Figure b is a perspective view illustrating a second embodiment of porous cover. The Figure is a perspective view illustrating a third embodiment of porous cover. Now with reference to Figure 1, a parallel flow heat exchanger 1 (mini-channel or micro-channel) is shown which includes a manifold or sleeve. 12, an outlet manifold or sleeve 14 and a plurality of channels 16 arranged parallel that fluidically interconnect the inlet sleeve 12 in the outlet sleeve 14. Typically, the inlet and outlet manifolds 12 and 14 are cylindrical in shape, and the channels 16 are tubes (or extrusior.es) of flat or round cross section. Channels 1 6 usually have a plurality of internal and external heat transfer enhancement elements, such as fins. For example, external fins 18, uniformly disposed therebetween for the improvement of heat exchange process and structural rigidity, typically bronze-soldered with furnace. Channels 16 can teper improvement of internal heat transfer and structural elements as well. In operation, the refrigerant flows into the inlet opening 20 and into the internal cavity 22 of the inlet manifold 12. From the internal cavity 22, the refrigerant in the form of a liquid, a vapor or a mixture of liquid and vapor (the most typical scenario in the case of an evaporator with an expansion device located upstream) enters the channel openings 24 passing through the channels 16 to the internal cavity 26 of the outlet manifold 14. From there, the refrigerant, which normally now has the form of a vapor, in case of evaporator applications, flows out of the outlet opening 28 and then into the compressor (not shown). Externally from the caissons 16, the air is preferably circulated uniformly over the channels 16 and the associated vanes 18 by an air moving device, such as a fan (not shown), such that the transfer interaction Heat occurs between the air flowing out of the channels and the coolant inside the channels. According to one embodiment of the present invention, a porous insert is inserted into the entrance of each channel 16. When the channels 16 have internal structural elements such as support members 16a (Figure 3), normally included for structural rigidity and / or heat transfer improvement purposes, the porous inserts 5 incorporate slots 32 to accommodate the support members 16a when in position at the channel entrance (see Figure 4). ). Furthermore, in case it is desired to provide a varied degree of expansion and / or hydraulic impedance for the inserts 30 or 32, for example, to counteract other aforementioned factors affecting the distribution. - Cooling fluid between the channels 16, characteristics such as porosity values or geometric dimensions (depth of insertion, depth of introduction, etc.) of the inserts can be altered to achieve the desired result for each channel 16. Figure 5 > p illustrates another embodiment in which all entries in the channels 16 are covered by a single member 34 positioned within a sleeve 40. In addition, a support member 36 can be used to assist in establishing a relative position of the porous member 34 and the channels 16 within the sleeve 40. It should be noted that an assembly of the porous member 34 and the support member 36 can be fabricated from and combined into a single member made of porous material.

Figure i b is a further embodiment of the structure of Figure 5a in which the porous member is a composite of two different porous materials 34 and 34a, Obviously, a number of composite materials within the porous member may be more than two. Figure 6 illustrates a side view of Figure 5a. Figure 7a illustrates a unified elongate porous member 34b that seals multiple channels 16 at a predetermined distance from the channel inlet. Figure 7b illustrates an elongate porous member 34c that covers the ends of the multiple channels 16, Figure 7c is a modification of the structure of Figure 7b in which the porous member 34d is of a precise shape and covers the ends of the channels 16. The shape of the member 34d pore) can be any suitable configuration, instead of a rectangle in cross section. In addition, the porous member 34d is preferably positioned within the sleeve 40 such that there is a space between the interior wall of the mat 40 and the porous member 34a allowing a more uniform distribution of refrigerant before it enters the porous member 34d. in the channels 16. It should be understood that any type of porous member and / or material that achieves the objectives of the present invention can be used. Similarly, as illustrated in Figures 2-7, which any design or configuration that achieves the objectives of the invention can be employed in the use of the present invention. Also, it has been observed that porous inserts can be used in condenser and evaporator applications within intermediate sleeves as well. For example, if a heat exchanger has more than one coolant passage, an intermediate sleeve (between the inlet and drain hoses) is incorporated into the heat exchanger design. In the intermediate sleeve, the coolant typically is in a double phase state, and such heat exchanger configurations can similarly benefit from the present invention by incorporating the porous inserts in such intermediate sleeves. In addition, the porous inserts can be placed in a condenser inlet sleeve and in an evaporator outlet sleeve to provide only hydraulic resistance uniformity and pressure drop control and with less effect on the overall performance of the heat exchanger. Since, for particular applications, the various factors that cause maldistribution of the coolant to the channels are generally known in the design phase, invjención has found it feasible to introduce the design features that counteract them for to be able to eliminate the harmful effects on the evaporator and the general performance of the system as well as a potential flood of the compressor and damage. For example, in many cases, it is generally known that the coolant flows into the inlet hose at a high or low speed and how the phenomenon of maldistribution is affected by the velocity values. A person of ordinary skill in the art will recognize how to apply the teachings of this invention to other theoretical facets of the system. The present invention has been shown and described particularly with reference to the preferred embodiments as illustrated in the drawings, it will be understood by one skilled in the art that various changes in detail may be made therein without departing from the spirit and scope of the invention. ) the invention as defined by the claims.

Claims

CLAIMS 1. A mini-channel or microchannel thermochannel thermostatic side-stream exchanger because it comprises: a longitudinally extending inlet sleeve and having an inlet opening for conducting the fluid flow to the inlet sleeve and a plurality of bees outlet to drive the transverse fluid flow from the inlet sleeve; a plurality of channels, each having a channel inlet, aligned in a substantially parallel relationship and fluidically connected to the plurality of outlet openings pa was to conduct the fluid flow from the inlet sleeve; and an outlet sleeve fluidically connected to the plurality of channels to receive the fluid flow therefrom; where the heat exchanger contains at least one porous member positioned within the flow path of the heat exchanger of r, whereby the heat exchanger shows a significant reduction in the maldistribution of flow among the plurality of channels. 2. The parallel flow heat exchanger according to claim 1, characterized in that the heat exchanger is an evaporator. 3. The parallel flow thermistor exchanger according to claim 1, characterized in that the heat exchanger is a condenser. 4. The parallel flow heat exchanger according to claim 1, characterized in that the porous member has the shape of an insert placed in at least one channel. 5. The term parallel flow exchanger according to claim 4, characterized in that the porous insert is co-located in the channel inlet. 6. The parallel flow heat exchanger according to claim 5, characterized in that the porous insert is co-located adjacent to the channel inlet. 7. The parallel flow heat exchanger according to claim 5, characterized in that the porous insert is co-located within the channel. 8. The parallel flow heat exchanger according to claim 1, characterized in that the porous insert is plugged into the inlet sleeve or in direct fluid communication with an inlet sleeve, 9. The parallel flow heat exchanger in accordance with claim 1, characterized in that the porous insert is positioned in the outlet sleeve or in direct fluid communication with the outlet sleeve. 10. The parallel flow thermointerchanger according to claim 1, characterized in that the Porous insertion is placed in at least one of the sleeves or in direct fluid communication with at least one of the sleeves 11. The porous insert according to claim 1, characterized in that the insert is formed * of a material selected from the group consisting of a metal and a ceramic, 12. The porous insert according to claim 1, face • etherized because the insert is formed of a material selected from the group consisting of sintered metal, cushioned metal, wool Metal or metal wire. 13. The porous insert according to claim 1, characterized in that the insert is positioned longitudinally along a sleeve. 14. The porous insert according to claim 1, characterized in that there is a space between the insert and the interior wall surface of the sleeve. 15. The porous insert according to claim 1, characterized in that the insert is a composite of at least two different inserts, 16. The porous inserts according to claim 1, characterized in that the cross section of the insert is not Rectangular. same; wherein the heat exchanger contains at least one porous member positioned within the heat exchanger flow path, where the porous member is designed to provide at least one of an expansion control and a pressure drop control in the system, and where the thermointercharger shows a significant reduction of the maldistribution of flow between the plurality of channels, 21. The parallel flow heat exchanger according to claim 20, characterized in that the heat exchanger is an evaporator. 22. The terp or parallel flow exchanger according to claim 20, characterized in that the heat exchanger is a condenser. 23. The exchanger thermistor according to claim 20, characterized in that the porous member functions as a primary expansion device. 24. The exchanger exchanger according to claim 20, characterized in that the porous member functions as a secondary expansion device. 25. The parallel flow heat exchanger according to claim 20, characterized in that the porous member has the shape of an insert placed in at least one channel. 26. The parallel flow heat exchanger according to claim 25, characterized in that the porous member is placed in the channel inlet. 27. The parallel flow heat exchanger according to claim 26, characterized in that the porous member is positioned adjacent to the channel inlet. 28. The parallel flow heat exchanger according to claim 26, characterized in that the porous member is positioned within the channel. 29. The parallel flow exchanger according to claim 20, characterized in that the porous member is co-located in the inlet sleeve or in direct fluid communication with the inlet sleeve, 30. The parallel flow exchanger in accordance with claim 20, characterized in that the porous member is placed in the outlet sleeve or in direct fluid communication with the outlet sleeve. 31. The parallel flow heat exchanger according to claim 20, characterized in that the porous member is placed in the inlet sleeve or in direct fluid communication with the inlet sleeve. 32. The porous honeycomb according to claim 20, characterized in that the member is formed of a material selected from the group consisting of a metal and a ceramic. 33. The porous member according to claim 20, wherein the member is formed of a material selected from the group consisting of sintered metal, compressed metal, metal wool or metal wire. 34. The porous honeycomb according to claim 20, characterized in that the member is positioned longitudinally along the sleeve. 35. The porous member according to claim 20, characterized in that there is a space between the member and the inner wall surface of the sleeve. 36. The porous honeycomb according to claim 20, characterized in that the insert is a composite of at least two different members. 37. The porous member according to claim 20, characterized in that the cross section of the member is not rectangular, 38. The porous member according to claim 37, characterized in that the cross section of the member is a portion of a circle, The porous member according to claim 20, characterized in that the members show variable retrieval characteristics between at least two channels. 40. The insert according to claim 39, characterized in that the variable performance characteristics depend on at least one of porosity, depth, depth of insertion and material.