Evaporator with phase change material

An evaporator configured to transfer heat between air flowing through the evaporator and refrigerant within the evaporator, and transfer heat between the refrigerant within the evaporator and phase change material (PCM) within the evaporator. The evaporator includes a first plate, a second plate, and a first tube. The second plate is coupled to the first plate to form an assembly that defines a cavity to contain PCM. The assembly also defines a first opening that cooperates with corresponding first openings in other assemblies to define a first manifold to convey refrigerant. The first manifold is defined when the assembly is arranged with the other assemblies to form a stack. The first tube is in fluidic communication with the first manifold. The assembly cooperates with an adjacent assembly of the other assemblies when the stack is formed to define a first slot configured to receive the first tube.

TECHNICAL FIELD OF INVENTION

The disclosure relates to an air conditioning system for cooling the passenger compartment of an automobile; more particularly, to an evaporator of the air conditioning system; and still more particularly, to an evaporator equipped with phase change material.

BACKGROUND OF THE INVENTION

Fuel efficiency in an automobile may be enhanced by shutting off the gasoline engine during brief periods of time when power from the engine is not required for propulsion, such as when the automobile is coasting or temporarily stopped at an intersection. However, the compressor of a traditional air conditioning system runs off the crankshaft of the gasoline engine, and therefore, the engine continues to operate during those inefficient periods to provide cooling comfort for the passengers of the automobile.

U.S. Pat. No. 7,156,156, issued to Haller et al. on Jan. 2, 2007 (hereinafter referred to as Haller '156), provides one solution to the problem of the air conditioning system not functioning when the engine is not running. The Haller '156 patent shows an evaporator having a refrigerant flowing there-through for transferring heat from a flow of air to the refrigerant in a first operating mode with the engine of the automobile running. The evaporator includes a manifold extending in a horizontal direction. At least one tube is in fluid communication with manifold and extends downward in a vertical direction away from the manifold.

The evaporator defines at least one cavity, or tank, for storing a phase change material (PCM) to transfer heat from the PCM to the refrigerant to cool and freeze the PCM in the first operating mode with the engine of the automobile running. The cavities of the Haller '156 patent are disposed adjacent to and engaging the plurality of tubes. In a second operating mode with the engine of the automobile dormant, heat is transferred directly from the flow of air to the PCM in the cavities to cool the flow of air and to melt or warm the PCM.

There remains a continuing need for improved evaporators having a PCM to increase the efficiency of air conditioning systems that continue to operate during brief periods of time when the engine of the automobile is shut off to increase the fuel efficiency of the automobile.

SUMMARY OF THE INVENTION

In accordance with one embodiment, an evaporator for an air conditioning system is provided. The evaporator is configured to transfer heat between air flowing through the evaporator and refrigerant within the evaporator, and transfer heat between the refrigerant within the evaporator and phase change material (PCM) within the evaporator. The evaporator includes a first plate, a second plate, and a first tube. The second plate is coupled to the first plate to form an assembly that defines a cavity to contain PCM. The assembly also defines a first opening that cooperates with corresponding first openings in other assemblies to define a first manifold to convey refrigerant. The first manifold is defined when the assembly is arranged with the other assemblies to form a stack. The first tube is in fluidic communication with the first manifold. The assembly cooperates with an adjacent assembly of the other assemblies when the stack is formed to define a first slot configured to receive the first tube.

In another embodiment, the evaporator includes a second tube. The assembly is further configured to define a second opening that cooperates with corresponding second openings in the other assemblies to define an second manifold to convey refrigerant. The second manifold is defined when the stack is formed. The second tube is in fluidic communication with the second manifold. The assembly and the adjacent assembly further cooperate to define a second slot configured to receive the second tube.

Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

Shown in theFIGS. 1-4, wherein like numerals indicate corresponding parts throughout the views, is a plate type heat exchanger, hereafter the evaporator100, having louvered clam shell housings200containing a phase change material (PCM)250. The louvered clam shell housings200enables a more efficient evaporator that contains less mass and parts resulting in ease of manufacturability. The added advantages of the louvered clam shell housings200will be readily appreciated, as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings.

A typical air conditioning system for an automobile includes a compressor driven by the automobile's engine. The compressor cycles a two-phase refrigerant through an evaporator, in which the refrigerant expands into a vapor phase while extracting heat energy from a stream of ambient air flowing through the evaporator core, which is defined by the evaporator's refrigerant tubes and interconnecting fins, thereby cooling the air stream. The stream of cooled air may be routed to the automobile cabin to provide comfort cooling for the passengers.

For conservation of fuel, the engine of the automobile may be turned off at predetermined conditions, such as when the automobile is coasting down gradient or temporarily stopped at an intersection. During the period of time when the engine is turned off, the engine is not driving the compressor that cycles the refrigerant through the evaporator. The air conditioning system of such an automobile may be provided with an evaporator having a phase change material to extend the period of cooling to the passenger compartment when the engine is turned off and not driving the compressor.

Shown inFIGS. 1 and 2is an exemplary embodiment of the evaporator100having a plurality of louvered clam shell housings200. The louvered clam shell housings200contain a material (PCM)250that is in thermal communication with the top region116of the evaporator100. The evaporator100may be manufactured from a plurality of stamped metallic plates105. Each of the stamped metallic plates105define features known to those of ordinary skill in the art, such as manifold openings106, bosses107about the manifold openings106, internal ribs108, and flanges109. The plurality of stamped metallic plates105are assembled into the evaporator100by stacking the stamped metallic plates105and then brazing the various parts together. The manifold openings106, bosses107, internal ribs108, and flanges109of each metallic plate cooperates with the corresponding manifold openings106, bosses107, internal ribs108, and flanges109of the adjacent instances of the stamped metallic plates105to define a pair of upper manifolds112, a pair of lower manifolds114, and a plurality of refrigerant tubes110hydraulically connecting the upper manifolds112and the lower manifolds114. The terms upper and lower are used with respect to the direction of gravity.

A plurality of louvered clam shell housings200are disposed between the refrigerant tubes110near the top region116of the evaporator100adjacent the pair of upper manifolds112. The louvered clam shell housings200may surround a portion of the pair of upper manifolds112or, as an alternative, may be positioned in the upper portion118of the refrigerant tubes110immediately below the upper manifolds112. A PCM250, such as a liquid saturated hydrocarbon having a molecular formula of CnH2n+2, a paraffin wax, or any other material that may remain in a liquid phase at room temperature, is disposed in each of the louvered clam shell housings200. A heat conductive material such metallic particles or fibers may be added into the PCM250contained in the louvered clam shell housings200to increase the heat transfer efficiency.

Best shown inFIG. 2, when the air conditioning system is in the second operating mode, engine is turned off and the compressor is not cycling refrigerant through the evaporator100, heat energy is transferred from the higher temperature vapor refrigerant within the refrigerant tubes110to the lower temperature PCM250contained in the louvered clam shell housings200, thereby cooling and condensing the refrigerant into a liquid phase. As the higher density condensed liquid phase refrigerant drops downward toward the lower portion120of the refrigerant tubes110due to gravity, the refrigerant absorbs heat from the flow of ambient air stream and expands back into a vapor phase. The lower density vapor refrigerant floats upwardly toward the lower temperature PCM250where the vapor refrigerant is subsequently re-cooled and re-condensed to repeat the cycle. This cycling of the refrigerant within the refrigerant tube is referred to as a thermal siphon cycle as shown inFIG. 2and referenced as TSC. By positioning the PCM250to be in thermal contact with only the upper portion118of the refrigerant tubes110, the lower temperature PCM250induces a steady thermal siphon within the refrigerant tubes110that allows the refrigerant to continue to cool the on-coming air stream while the compressor is not operating for brief periods of time. The thermal siphon cycle continues until either the engine is powered on driving the compressor or the cooling capacity of the PCM250is depleted.

Referring toFIG. 3, each of the clam shell plates210includes complementary features that allow one of the clam shell plates210to be rotated180degrees about a central axis A and assembled onto another one of the clam shell plates210to form the louvered clam shell housings200. The clam shell plates210may be stamped or otherwise formed from a sheet of heat conductive material, such as aluminum, to define louvers230, a port226, and manifold openings224.

The upper portion118of the refrigerant tubes110may include through-holes124that extend from one surface of the refrigerant tube to the opposite surface of the refrigerant tube. The louvered clam shell housings200may include a port226that cooperate with the through-holes124in the refrigerant tubes110to define a passageway126through the evaporator100for hydraulic communication of the PCM250between the louvered clam shell housings200. The passageway126allows for the ease of filling the louvered clam shell housings200with the PCM250during manufacturing and also allows for the PCM250to migrate from one of louvered clam shell housings200to another to account for unequal expansion and/or contraction of the PCM250in the louvered clam shell housings200due to thermal gradient across the evaporator100.

Maintaining the PCM250immediately below the pair of upper manifolds112allows greater thermal conductivity between the PCM250and the refrigerant in the refrigerant tube. The length of the louvered clam shell housings200extending along the refrigerant tube may be adjusted to provide the desired volume of PCM250required to achieve the desire cooling performance while the air conditioning system is operating in the second mode, during which the compressor is not cycling refrigerant through the evaporator100.

It is preferable to fill less than the full capacity of the louvered clam shell housings200with the PCM250to account for the volumetric expansion of the material at elevated temperatures up to 200° F. The position of the port226is positioned with respect to the louvered clam shell housings200to allow the PCM250to migrate between the louvered clam shell housings200. If the port226is too high, the PCM250cannot redistribute and equalization of the louvered clam shell housings200volume between spaces will not occur. A uniform distribution of PCM250will minimize cost and ensure optimum operation. If a louvered clam shell housings200has an excess of the PCM250, it will result in additional cost. With too little of the PCM250, it will result in poor performance in that portion of the evaporator100.

Referring toFIGS. 3 and 4, each of louvered clam shell housings200is assembled from two substantially identically formed instances of the clam shell plates210. Each of the clam shell plates210includes an exterior surface212, an interior surface214opposite that of the exterior surface212, a rim216extending perpendicular from the perimeter of the interior surface214, a plurality of tabs218extending from the rim216, and a central rib228extending through a center axis (A). Each of the clam shell plates210further defines a pair of manifold openings224and a port226.

A plurality of louvers230is formed in a first portion220and second portion222located on either side of the central axis (A) below the manifold openings224of the clam shell plate210. The louvers230may be formed by folding a plurality of slats231defined between pairs of slits at approximately a right angle relative to the interior surface214. To increase the number of louvers230, long narrow bumps may be formed and subsequently slit to define the slats231to have a rectangular shape with a length (L). A set of louvers230may extend in a first direction on one side of the central axis A and another set of louvers230may extend in a second direction on the other side of the central axis A. The first direction may be at a right angle to the central axis A and the second direction may be parallel to the central axis A.

Two of the clam shell plates210are assembled in a louvered clam shell housings200by first rotating one of the clam shell plates210one-hundred eighty degrees (180°) about the central axis (A) such that the interior surface214of one of the clam shell plates210is oriented toward the other. Two of the clam shell plates210are then brought together such that the rim216of each clam shell plates210are engaged to one another. The tabs218of one of the clam shell plates210cooperates with the tabs218of another of the clam shell plates210to lock two of the clam shell plates210together to provide the louvered clam shell housings200defining an interior chamber232to contain the PCM250.

Shown inFIG. 4, the slats231are bumped, slit, and folded such that the distal edges234of the louvers230of one of the clam shell plates210may engage the distal edges234of the louvers230of another of the clam shell plates210at a90degree angle once two of the clam shell plates210are joined. The crossing engagement of the distal edges234of the louvers230provides structural integrity to the louvered clam shell housings200and in turn, increases the overall structural integrity of the evaporator100once the louvered clam shell housings200are assembled and brazed into position between the refrigerant tubes110. The louver openings236are defined in the clam shell plates210by the slitting and folding of the louvers230enables the PCM250to directly physically contact the exterior surfaces of the refrigerant tubes110, thereby increasing thermal conductivity between the PCM250and refrigerant within the refrigerant tubes110.

FIGS. 5-7illustrate a non-limiting example of an alternative embodiment of an evaporator300for an air conditioning system (not shown). The evaporator300is configured to transfer heat between air flowing through the evaporator and refrigerant within the evaporator, and transfer heat between the refrigerant within the evaporator and phase change material (PCM) within the evaporator. As explained above, the PCM is present to help maintain the temperature of the evaporator300when the system is not circulating the refrigerant and thereby enable conditioned air to be provided from the evaporator when the compressor is not operating.

FIG. 6illustrates some non-limiting details of the evaporator300. The evaporator300includes a first plate302and a second plate304. When the first plate302and the second plate304are coupled together by brazing, for example, an assembly306is formed that may include other optional parts described below. The assembly306defines a cavity312to contain the PCM, seeFIG. 3reference number250for an example. The first plate302and the second plate304cooperate so the assembly306can also define a first opening314that cooperates with corresponding first openings in other assemblies310, and other plumbing known to those in the art to define a first manifold316to convey refrigerant to or from refrigerant tubes that make up the core of the evaporator300. That is, the first manifold316is defined when the assembly306is arranged with an adjacent assembly308which is one of the other assemblies310, and the other assemblies310to form a stack320. It should be appreciated that the assembly306is shown as parts spaced apart for the purpose of explanation, and that when the first plate302and the second plate304are coupled, the assembly306will appear similar to the adjacent assembly308.

The evaporator300also includes a first tube322in fluidic communication with the first manifold316. The assembly306, in particular the second plate304of the assembly306, cooperates with the adjacent assembly308of the other assemblies310when the stack320is formed to define a first slot324configured to receive the first tube322. That is, the assembly306and the adjacent assembly308include or define relief areas that define the first slot324when the assembly306and the adjacent assembly308are joined together as part of the process of forming the stack320by, for example, brazing. As will be recognized by those in the art, the assembly306and the other assemblies310cooperate to form a header portion326of the evaporator300, and the first tube322and a plurality of other tubes330cooperate to form a body portion328of the evaporator300.

As will be explained in more detail below, the evaporator300illustrated is sometimes referred to as a two-row evaporator. As such, the evaporator300may include a second tube332, however this is not required. It is contemplated that the teachings presented herein can be applied to a single-row type evaporator that has only a single layer of tubes as opposed to the two rows of tubes illustrated herein where the first tube322was one of a first layer of tubes, and the second tube332was one of a second layer of tubes. It is also contemplated that the teachings presented herein can be applied to multiple-row (e.g. four-row) type evaporators with more than two rows. However, since multiple-row evaporators are presently popular, the non-limiting example presented in the drawings is other than a single-row evaporator.

Accordingly, the assembly306may be further configured to define a second opening334that cooperates with corresponding second openings in the other assemblies310to define a second manifold336to convey refrigerant to or from the second tube332. Like the first manifold316, the second manifold336is defined when the stack320is formed by arranging or stacking an alternating arrangement of parts corresponding to the first plate302and the second plate304. It follows that the second tube332is in fluidic communication with the second manifold336, so the assembly306and the adjacent assembly308further cooperate to define a second slot338configured to receive the second tube332. In order to keep refrigerant of the first tube322segregated from refrigerant of the second tube332, the plates (e.g. the first plate302and the second plate304) may include a partition feature340on either or both of the plates.

If the evaporator300is a two-row type evaporator, the evaporator300may be configured so the first tube322conveys refrigerant away from the first manifold316, and the second tube332conveys refrigerant toward the second manifold336. Accordingly, the evaporator300may include a return manifold342(FIG. 5) that receives refrigerant from the first tube322and routes that refrigerant back into the second tube332. Alternatively, the return manifold342may be configured to receive refrigerant from both the first tube322and the second tube332for routing to other parts of the air conditioning system.

FIG. 7further illustrates some non-limiting details of the evaporator300. In order to maximize heat transfer between refrigerant and PCM in the header portion326, the first plate302and the second plate304may be advantageously configured to space apart the end of the first tube322and the first manifold316. That is, the assembly306and the adjacent assembly308may further cooperate to define a first passage344to fluidicly couple the first tube322to the first manifold316, and thermally couple the refrigerant in the first passage344to PCM in the cavity312. Because first passage344allows for the end of the first tube322to be spaced apart from the first manifold316, the thermal coupling between the refrigerant in the first passage344and the PCM in the cavity312is via a single layer of that in this instance part of the second plate304. This arrangement stands in contrast to evaporator configurations where the ends of the tubes are close to the manifolds such that the thermal coupling between refrigerant and PCM is through the wall of the tube and a wall section of whatever is containing the PCM, i.e. two layers of metal. That is, in this example, the first plate302and the second plate304each define a wall section346that is in direct contact with PCM350on one side of the wall section346and in direct contact with refrigerant348on the other side of the wall section346.

As noted previously, the teachings presented herein are applicable to single-row and multiple-row evaporators. As such, it follows that for the non-limiting example presented in the drawings, the assembly306and the adjacent assembly308may further cooperate to define both the first passage344to fluidicly couple the first tube322to the first manifold316and thermally couple refrigerant in the first passage344to PCM in the cavity312, and a second passage352(FIG. 6) to fluidicly couple the second tube332to the second manifold336and thermally couple refrigerant in the second passage352to PCM350in the cavity312.

In order to further improve thermal coupling of the PCM350to the refrigerant348in either the first passage344or the second passage352, the cavity312may be equipped with a fin354or other suitable thermal conducting device to better couple heat into and out of the PCM350.

The first plate302and the second plate304may also be configured so each defines a fill opening356that cooperates with corresponding fill openings in the other assemblies310to define a fill manifold358for hydraulic or fluidic communication of PCM between the cavities (e.g. the cavity312and corresponding cavities of the other assemblies310) of each of the assemblies (e.g. the assembly306and the other assemblies310) when the stack320is formed. Providing the fill manifold358is advantageous for the ease of filling the cavities with the PCM350during manufacturing and allowing for the PCM350to migrate from one cavity to another to account for unequal expansion and/or contraction of the PCM350due to thermal gradient across the evaporator300.

Accordingly, an evaporator300for an air conditioning system is provided. The evaporator300is configured to transfer heat between air flowing through the body portion328of the evaporator and refrigerant348within the evaporator, and also transfer heat between the refrigerant348within the evaporator and phase change material (the PCM350) within the evaporator. As shown inFIG. 2, the presence of the PCM350can induce or establish a thermal siphon within the tubes if the refrigerant348is not being otherwise circulated by the air conditioning system. The cavities for the PCM necessary manifolds are created by an alternating series of parts similar to the first plate302and the second plate304.

Prior attempts at evaporators with PCM provide PCM cartridges that are substituted for tubes within the body portion or core matrix of the evaporator. However these PCM cartridges undesirably restrict the flow of air through the body portion of the evaporator. The replacement of tubes by PCM cartridges also reduces the number of air fins in contact with the refrigerant tubes resulting in reduced airside heat transfer. The evaporator300described herein overcomes or solves this problem placing the PCM chambers (i.e. the cavity312) at the top of the core as part of the header portion326, and thereby out of the airflow region.

It has also been observed with prior attempts at evaporators with PCM that airside misdistribution will result in poorly utilized PCM. Regions of low airflow will not fully utilize the PCM whereas high airflow areas will utilize it quicker. This problem is solved by locating the PCM at the top of the evaporator so the PCM can always be utilized to condense the refrigerant regardless of the differences in airflow along the length of the tubes.

It has also been observed with prior attempts at evaporators that tube insertion in the upper manifold creates a volume between the end of the tube and the lower wall on manifold which prevents refrigerant from returning to the tubes and being available to create or maintain the thermal syphon. This problem is solved by eliminating tube insertion into the manifold. Any liquid in the manifold area can easily return to the lower portion of the core.

Additional benefits realized by the configuration of the evaporator300described herein include that thermal siphon condensing is improved. When condensation occurs within the small ports of the refrigerant tube, the liquid returning to the lower portion competes with the vapor moving upward towards the upper manifold. Elimination of the restrictive ports in condensing portion of the thermal siphon improves function.

Thermal conduction is improved due to the reduction in number of layers of material. Previous art has two thicknesses of material between the PCM and he refrigerant that is condensing. The evaporator300described herein has just one layer resulting less thermal resistance to heat transfer.

The tubes slots, formed from the two plates (e.g. the first plate302and the second plate304) are more forgiving of variations in tube geometry than lanced slots. Forming the tube slots from two halves and then a manifold allows manufacturing to adjust parameters to accommodate varying tube geometry. For example, a bow in the profile of the tube can be accommodated with by less initial compression on the clam shell assembly (the manifold). After the tubes are inserted, additional force can be applied to achieve the desired dimensions. The plates can be assembled together, and then assembled into a sub-assembly to improve and facilitate manufacturing and reducing cost associated with dedicated operations to clinch the parts together. The individual plates and subsequent sub-assemblies may be held together by nesting as shown, or by a clinched tab or a snap feature. Holding the parts together can also be achieved within the equipment design without utilizing a future on the part.

It is also noted that the configuration of alternating plates could be used in the non-PCM end of the evaporator to form the return manifold342. In such a configuration, the plates would not need the wall section346present in the header portion326.