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Heat exchanger assembly

Heat exchanger assembly description/claims

This invention relates generally to cooling systems, and more particularly to heat exchangers usable in such cooling systems.

Typical refrigeration systems often utilize conventional fin-and-tube heat exchanger coils to dissipate heat from refrigerant passing through the heat exchanger coils. Usually, in large-scale cooling systems, a single, oftentimes large, conventional fin-and-tube heat exchanger coil 100, as depicted in prior art FIG. 3, is sized to dissipate or reject an amount of heat equal to the heat load of the refrigeration system. Multiple conventional fin-and-tube heat exchanger coils 100 might also be used. The fin-and-tube heat exchanger coil(s) is/are sized to dissipate the amount of heat in the refrigerant that was absorbed in other portions of the refrigeration system.

Usually, in large-scale cooling systems, the fin-and-tube heat exchanger coil(s) is/are positioned outside a commercial building, such as on a rooftop, to allow heat transfer between the fin-and-tube heat exchanger coil and the outside environment (i.e., to allow the heat in the refrigerant to dissipate into the outside environment). Further, natural or ram airflow may be augmented by a mechanical airflow that may be provided by a fan, for example, to assist in air-cooling the fin-and-tube heat exchanger coil.

Fin-and-tube heat exchanger coils, depicted generally at 100, in prior art FIG. 3, often display less than ideal efficiencies and relatively high cost in dissipating heat from the refrigerant passing through the coils as compared to newer technologies. Typically, fin-and-tube heat exchanger coils can be rather large for the amount of heat they can dissipate from the refrigerant as compared to newer technologies. Additionally, fin-and-tube heat exchanger coils use a great deal of copper in their construction. Presently, copper is a very expensive commodity. Further, the larger the heat exchanger coil becomes, the more refrigerant used in the refrigeration system, thus effectively increasing the risk of potential damage to the environment by an accidental atmospheric release. The efficiency of fin-and-tube heat exchanger coils is however not very dependent on the direction of the air flow relative to the coils the coils. This can be seen in prior art FIG. 3, the arrows indicating air flow over the various tubes 102.

A more recent form of heat exchanger is the microchannel coil (MCC) heat exchanger. Microchannel coil (MCC) heat exchangers are typically made of aluminum, replacing the costlier copper of the fin-and-tube heat exchanger coils. Further, in similar heat exchange applications, MCC heat exchangers can be made significantly smaller than fin-and-tube heat exchanger coils that effect similar heat exchanges. To date, however, microchannel coil (MCC) heat exchangers are known to be quite sensitive to the direction of airflow relative to the plane of the MCC heat exchanger. Efficiency drops off dramatically as the direction of airflow varies from the normal relative to the plane of the MCC heat exchanger.

Currently, the major application of microchannel coils is in the automotive industry. Microchannel coils 110 may be used as a condenser and/or an evaporator in the air conditioning system of an automobile. See prior art FIGS. 1 and 2. A microchannel heat exchanger coil, for example, in an automotive air conditioning system, is typically located toward the front of the engine compartment, where space to mount the heat exchanger coil is limited and where the direction of airflow is normal. Therefore, the microchannel heat exchanger coil, which is much smaller, lighter, and less costly than a conventional fin-and-tube heat exchanger coil that would otherwise be used in the automotive air conditioning system, is a suitable fit for use in an automobile.

Referring to FIGS. 2 and 7, the prior art MCC tube heat exchanger 110 includes an inlet header 116 and a spaced apart outlet header 118. Each of the headers 116, 118 has a fluid passageway 121 defied therein. The respective fluid passageways 121 are in fluid communication by means of the microchannel tubes 112 that extend between the headers 116,118. The headers 116,118 each have a known depth dimension 119. A heat exchanger plane 125 includes the longitudinal axes 126 of the headers 116, 118 and can be thought of as the windward face of the MCC tube heat exchanger 110. The plane 125 is usually presented normal to the incoming air flow.

The MCC tube heat exchanger 110 includes a plurality of microchannel tubes 112. Each microchannel tube 112 has a length dimension 114 extending from header 116 to header 118, as depicted in prior art FIG. 7. The two edges 120, 122 are joined by two spaced apart, parallel relatively long sides 124 defining a chord 123 of the microchannel tube 112. In cross section, the edges 120, 122 and sides 124 of the microchannel tube 112 define a very thin rectangle with an interior fluid passage 113. The fluid coupling of the headers 116, 118 is by means of the plurality of microchannel tubes 112. In the prior art MCC tube heat exchanger 110, the chord 123 of each of the microchannel tubes 112 is disposed orthogonally with respect to the plane 125 of the MCC tube heat exchanger and the length of the chord 123 is therefore limited to a maximum equal to the depth 119 of the respective headers 116, 118.

The prior art MCC tube heat exchanger 110 further includes fins 130, as depicted in prior art FIGS. 8 and 9. The fins 130 are typically formed of a single metallic ribbon that is compressed at series of bends 131, the bends 131 being formed in alternating directions. The ribbon of the fins 130 is affixed at the alternating bends 131 to respective adjacent microchannel tubes 112 in a heat conducting joint. The fins 130 include heat exchange surfaces 132. The plane of each of the heat exchange surfaces 132 is, in the prior art, usually disposed generally orthogonal with respect to a respective side 124 of an adjacent microchannel tube 112, adjacent heat exchange surfaces 132 being disposed in a parallel array. The height dimension 134 of the heat exchange surfaces 132 is absolutely limited by the distance 134 between adjacent microchannel tubes 112.

The plane of adjacent fins 130 of some prior art MCC heat exchangers 110 is angled with respect to one another. The ribbon forming the fins 130 has very sharp bends. See U.S. Pat. No. 6,988,538. Such alternate angling reduces the number of heat transferring heat exchange surfaces 132 that can be included in a given length 114 of the microchannel tube 112 and the sharp bends 131 provide for only a minimal heat conducting joint with the respective microchannel tube 112. For these reasons the alternating angling disposition is not favored as being less efficient than the parallel array disposition of prior art FIGS. 8 and 9.

For most efficient heat exchange in the prior art, the flow of air through the MCC tube heat exchanger 110 is normal to the plane 125 of the heat exchanger 110, as depicted in prior art FIGS. 1 and 2. Efficiency of the known MCC tube heat exchanger 110 depends on the flow of air being substantially parallel with the chord 123 and across the two sides 124, as depicted in prior art FIG. 2, and past the orthogonally disposed fins 130. For this reason, the most efficient of all known uses of the MCC technology has been with normal air flow relative to the plane of the MCC heat exchanger, where the leading edge 120 of each microchannel tube 112 is presented to the air flow and the air flow proceeds down both sides 124 to the trailing edge 122.

Angling the known MCC tube heat exchanger 110 to the direction of airflow results in known and calculable reductions of efficiency, as compared to normal airflow with the same MCC tube heat exchanger 110. Such angling is noted in Prior art FIGS. 4-6. Angling of the MCC tube heat exchanger 110 reduces the footprint of the heat exchanger unit, which in turn reduces cost. However, such angling disadvantageously sacrifices efficiency of the heat exchanger unit because the MCC tube heat exchanger 110 is angled with respect to the fan 140 and airflow through the MCC tube heat exchanger 110 is then not normal, but is turned. A resulting issue with heat exchanger units that are mounted on a rooftop is that the airflow is typically turned 90 degrees as it flows through the heat exchanger. This results from a horizontally mounted fan 140 drawing in a generally horizontal flow of air 142 and expelling the airflow 142 in a generally vertical direction. Such flow path change results in reduced efficiency of the MCC tube heat exchanger 110. For example a representative reference local loss coefficient of the orientation depicted in prior art FIG. 4 is 0.83. The coefficient is directly applied to a local mass flow, resulting in a significantly diminished mass flow.

The above reduction of mass flow has led engineers to angle known MCC heat exchangers 110 to the relative airflow, such as the 60 degree angle of prior art FIGS. 5 and 6 in which the direction of air flow 130 is not normal to the plane 125 of the MCC tube heat exchanger 110. Such angling advantageously results in a greater height dimension of the MCC heat exchangers 110 relative to the overall height of the heat exchanger unit. Further, angling the MCC heat exchangers 110 results in a reduced footprint of the heat exchanger unit, thereby reducing cost. While cost is reduced, efficiency is reduced as a result of the MCC heat exchangers 110 being angled with respect to the fan 140. In this case, the exemplary reference local loss coefficient of the angled orientation is 0.38, a considerable reduction as compared to the orientation of FIG. 4, but still a significant source of energy loss. Even this reduced loss generates a significant loss in airflow velocity and loss in efficiency of the MCC tube heat exchanger 110.

There is a need in the industry for more efficient MCC tube heat exchangers in applications in which the flow of air is not normal to the plane of the heat exchanger. In this situation, the direction of airflow is altered from the intake side of the MCC tube heat exchanger to the exhaust side by as much as ninety degrees. As noted above, with known MCC tube heat exchangers, such non-normal air flow significantly diminishes the efficiency of the MCC tube heat exchanger as compared to normal air flow on both the intake and exhaust sides of the MCC tube heat exchanger.

The present invention substantially meets the aforementioned needs of the industry by providing a high efficiency MCC tube heat exchanger for use with air flows that are not normal to the MCC heat exchanger. The present invention provides, in one aspect, a heat exchanger assembly adapted to efficiently condense a refrigerant in a refrigeration system where the flow of air to the MCC tube heat exchanger is not normal. The MCC tube heat exchanger assembly includes at least one microchannel heat exchanger coil including an inlet header and an outlet header, each microchannel of the coil being angled with respect to the plane of the MCC heat exchanger.

The present invention provides, in a further aspect, a method of assembling a MCC tube heat exchanger assembly. The MCC tube heat exchanger assembly may be adapted to condense a refrigerant for use in a refrigeration system. The method includes forming a MCC tube heat exchanger assembly with angled microchannel tubes and/or fins that provide for increased efficiency of the MCC tube heat exchanger assembly when the MCC tube heat exchanger assembly is angled with respect to the direction of airflow, i.e. the air flow is not normal to the plane of the MCC tube heat exchanger assembly.

The present invention provides, in addition to microchannel tubes and fins oriented to non-normal air flow, a greater heat transfer area of the respective microchannels and fins for a given depth of the headers of the MCC heat exchanger. Efficiency of the device of the present invention is therefore improved by two means. The first is angling the microchannel tubes and fins into the airflow and the second is the greater heat changer area of the microchannel tubes and fins presented to the air flow that is made possible by the angling of the microchannels and/or fins.

The present invention is a heat exchanger that includes a plurality of MCC microchannel tubes, each microchannel tube of the plurality of microchannel tubes having at least one microchannel fluid passage defined therein and having a chord, the chord being the orthogonal distance from a leading edge to a trailing edge, each microchannel tube of the plurality of microchannel tubes being disposed such that the chord is less than orthogonally disposed relative to a heat exchanger plane. The present invention is further a method of forming such a heat.

• Provisional Patent
• Utility Patent

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