Patent Application
20160370119
The present disclosure relates to a heat exchanger; more particularly, to a heat exchanger having a refrigerant distribution control device.
Residential and commercial heat pump systems are known to employ modified automotive heat exchangers, which are desirable for its proven high heat transfer efficiency, durability, and relatively ease of manufacturability, as heat pump heat exchangers. A conventional automotive heat exchanger typically includes an inlet manifold, an outlet manifold, and a plurality of refrigerant tubes hydraulically connecting the manifolds for refrigerant flow therebetween. The refrigerant tubes utilized are typically flat tubes having a plurality of micro-channels, or ports, for refrigerant flow and are manufactured from extruded aluminum alloy or folded from a sheet of aluminum alloy. Corrugated fins interconnect adjacent refrigerant tubes to increase the available heat transfer area, as well as to increase the structural integrity of the heat exchanger. The core of the heat exchanger is defined by the refrigerant tubes and interconnecting corrugated fins.
Heat pump heat exchangers, also known as heat pump coils, are capable of operating as an evaporator and as a condenser. A heat pump system typically includes two heat pump heat exchangers, one located outdoor and the other indoor. When the heat pump system is in cooling mode, the indoor heat pump heat exchanger operates in evaporator mode and the outdoor heat pump heat exchanger operates in condenser mode. When the heat pump system is in heating mode, the indoor heat pump heat exchanger operates in condenser mode and the outdoor heat pump coil operates in evaporator mode.
To meet the demands of residential and commercial applications, the size of the core of the heat pump heat exchanger needed to be increased accordingly, which in turn dramatically increased the lengths of the inlet and outlet manifolds. For a heat pump heat exchanger operating in evaporator mode, the increased length of the manifolds tends to result in refrigerant mal-distribution through the row of refrigerant tubes. The effects of momentum and gravity, due to the large mass differences between the liquid and gas phases, can result in separation of the phases in the inlet manifold and cause poor refrigerant distribution through the row of refrigerant tubes. Poor refrigerant distribution degrades evaporator performance and can result in uneven temperature distribution over the core.
To assist in providing uniform refrigerant distribution through the refrigerant tubes, it is known to dispose an inlet distributor tube within the inlet manifold for distributing the two-phase refrigerant throughout the length of the inlet manifold. The distributor tube extends along substantially the length of the inlet manifold and includes a plurality of substantially evenly spaced orifices for evening distributing a liquid refrigerant to the inlets of the refrigerant tubes. Similarly, an outlet collector tube is disposed within the outlet manifold for evenly collecting the vapor refrigerant exiting the outlet ends of the refrigerant tubes.
The outlet collector and distributor tubes are costly in terms of materials, manufacturing, and shipping of the tubes, as well as the time and labor required for the assembling of the tubes in the outlet and inlet manifolds, respectively. Accordingly, there remains a need for a heat pump heat exchanger having a refrigerant distribution control that eliminates the need for at least one of the outlet collector and distributor tubes.
The invention relates to a heat exchanger assembly having a first manifold, a second manifold spaced from the first manifold, and a plurality of refrigerant tubes in hydraulic communication with the first manifold and the second manifold. The second manifold includes a first end, a second end opposite from the first end, and a refrigerant inlet adjacent the first end. The plurality of refrigerant tubes includes micro-channels and tube ports configured for accepting refrigerant flow into and out of the micro-channels. A portion of the tube ports are selectively obstructed or closed such that a refrigerant entering into the second manifold, inlet manifold, through the refrigerant inlet would flow substantially uniformly across the bank of refrigerant tubes from the second manifold to the first manifold; thereby providing uniform heat transfer across the core of the heat exchanger assembly. At least one of the obstructed tube ports may include an inserted sliver of braze amendable material. As an alternative, the at least one of the obstructed tube ports may be pinched closed. As another alternative, at least one of the obstructed tube ports may be formed by inserting a pin of reduced diameter into the selected port and then squeezing the port from the outside to size it and then removing the pin.
An advantage of selectively closing tube ports to achieve uniform distribution of refrigerant through the core is the potential elimination for the need of one or more refrigerant distribution tubes. This would reduce the cost of the heat exchanger due to the reduction in costs of materials required, reduction in labor for assembly, and shipping cost due to overall weight reduction. Another advantage of selectively closing the tube ports would allow for greater flexibility in the design of the heat exchanger assembly since a different sized collector is not required for different heat exchanger configurations.
In the drawings as hereinafter described, a preferred embodiment is depicted; however, various other modifications and alternative designs and construction can be made thereto without departing from the spirit and scope of the invention.
This invention will be further described with reference to the accompanying drawings in which:
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The first manifold 102 is shown above the second manifold 104 with respect to the direction of gravity; therefore, the first manifold 102 is known as the upper manifold 102 and the second manifold 104 is known as the lower manifold 104. Either manifolds 102, 104 may function as an inlet or outlet manifold 102, depending on the mode of the heat exchanger. In evaporator mode, a two-phase gas/liquid refrigerant flows from the lower manifold 104 through the row of refrigerant tubes 116 to the upper manifold 102. As the two-phase refrigerant absorbs heat from the stream of ambient air, the refrigerant expands into a low pressure vapor refrigerant. In condenser mode, a high pressure vapor refrigerant flows from the upper manifold 102 to the lower manifold 104 and condenses to a high pressure liquid refrigerant as heat is dissipated to the stream of ambient air. In other words, the upper manifold 102 functions as an outlet manifold 102 when the heat exchanger assembly 100 is in evaporator mode and as an inlet manifold 102 when the heat exchanger assembly 100 is in condenser mode.
Due to higher heating and cooling load demands, residential and commercial heat exchangers require manifolds 102, 104 to be typically 3 to 8 times the length of a conventional automotive manifold. This dramatically increases the lengths of the upper and lower manifolds 102, 104 along manifold axis A and A′, respectively. Distribution tubes (not shown) are known to be used in either or both of the manifolds 102, 104 in order to provide even refrigerant distribution across the row of refrigerant tubes 106 to provide uniform heat transfer across the core 112. A conventional distribution tube typically includes a cylindrical hollow tube having a plurality of orifices spaced along its length and extends substantially the full length of the manifolds 102, 104. Distribution tubes used in the inlet manifold 102 are known as inlet distributors and distribution tubes used in the outlet manifolds 102 are known as outlet collectors.
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The precise locations and number of tube port 211a closures can be determined based on the desired restriction of refrigerant flow in that portion of the core 212 of the heat exchanger assembly 200 to achieve uniform flow of refrigerant through the core 112 of the heat exchanger assembly 200. For example, if a greater portion of refrigerant flow is desired through the row of tubes 206 nearest the refrigerant inlet 214, then a great number of refrigerant tubes 206 farthest from the refrigerant inlet 214 will be required to have its tube ports 211a closed or obstructed. In other words, if the momentum effect of refrigerant flowing to the end of the inlet header 204 is to be mitigated in order to achieve uniform refrigerant flow through the core 212 of the heat exchanger 200, then the tube ports 211a in the refrigerant tubes 206 within that portion of the core 212 farthest form the refrigerant inlet 214 are closed. The closure of the tube ports 211a raises the refrigerant pressure drop in the selected sections of the core 112, thus forcing the refrigerant to other sections of the core 212 that would normally be starved of refrigerant due to fluid momentum and distribution geometry.
The advantages of selectively closing tube ports 211a includes the reduction in the cost of manufacturing by eliminating at least the collector and the labor for the installation of the collector This would allow for greater flexibility in the heat exchanger assembly 200 design because a different size or shape collector is not required for each collection configuration required. Also, by closing off certain tube ports 211a, the refrigerant velocity in the remaining open ports will increase, and depending upon the flow velocity, will increase heat transfer in the open ports 211; thereby, maintaining the same overall heat transfer for a given heat exchanger.
The manifolds 202, 204, refrigerant tubes 206, and fins 208 may be formed of a heat conductive material amendable to brazing, preferably an aluminum alloy. The refrigerant tubes 206 may be extruded from an aluminum alloy or formed by the folding of a sheet of aluminum alloy. The refrigerant tubes 206 and fins 208, forming the core 212, are assembled onto a stacker and the manifolds 202 are then assembled onto the core 212 forming the heat exchanger assembly 200. The assembly is then brazed into an integral heat exchanger assembly 200. While an upper manifold 202 and a lower manifold 204 is shown, it is not intended to be so limiting as to one being higher or lower than the other with respect to the direction of gravity. Those of ordinary skill in the art would recognize that the manifolds 202 may be positioned on the same horizontal plane utilizing a return tank or bending the refrigerant tubes 206 into U-flow tubes.
Prior to assembly of the core 212, the closure of the tube ports 211a may be accomplished by pinching the tube ports shut so long as the pinching does not extend into or below the tube to the header joint. The tube ports 211a may also be closed by inserting a sliver of aluminum alloy or other materials amendable to brazing into the designated tube ports 211a and brazing the tube ports 211a closed during the braze process. The tube ports 211a may be partially plugged rather than completely plugged, which can be accomplished by inserting a pin of reduced diameter into the selected ports and then squeezing the port from the outside to size it and then removing the pin. This plugging operation can take place in the stacker after the core 112 is assembled but before the manifolds 102 are installed, to reduce the process complexity.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description.
