Patent Description:
Power electronics devices such as motor drives generate waste heat during operation of the device. Additionally, when the power electronics devices heat up the operational efficiency of the devices can degrade adding to the amount of heat generated. When utilized in a refrigeration system to drive, for example, a compressor of the refrigeration system, effective thermal integration of these devices can be an important aspect to the system's overall efficiency and reliability. Consequently, a goal of the system integrator is to maintain these components within a range of operating temperatures which will maximize the system efficiency. Accordingly, there remains a need in the art for heat exchangers configured to closely integrate with power electronic devices which can maintain optimal temperatures for these components under a variety of load conditions. Further, it is desired to increase capacity of such heat exchangers while reducing a pressure drop impact.

<CIT> discloses a silicon-based microchannel phase change heat exchanger comprising an upper layer of glass and a bottom layer of silicon. The silicon layer is provided with open microchannels and an array of nucleation cavities to nucleate bubbles. Various heat exchangers for cooling electronics components are also described in <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. <CIT> and <CIT> disclose heat pipes used with electronics components <CIT> can be considered as the closest prior art and discloses a heat exchanger comprising an array of longitudinal (along the flow direction) microchannels.

According to a first aspect of the invention, a power electronics assembly is provided. The power electronics assembly includes one or more power electronics devices, and a heat exchanger to which the one or more power electronics devices are mounted. The heat exchanger includes an inlet manifold and an outlet manifold, and one or more fluid pathways extending between and connecting the inlet manifold and the outlet manifold, the heat exchanger configured to transfer thermal energy from the one or more power electronics devices into a flow of fluid passing through the one or more fluid pathways. The one or more fluid pathways include one or more internal enhancements and channel configurations to enhance thermal energy transfer by promoting boiling of the flow of fluid and to reduce the pressure drop in the pathways under a two-phase flow condition. The flow of fluid is a flow of liquid refrigerant diverted from a condenser of a heating, ventilation, and air conditioning (HVAC) system. The one or more internal enhancements include one or more inclined notches formed in the one or more fluid pathways, the one or more inclined notches extending unbroken around an entire internal perimeter of the fluid pathway, the one or more inclined notches having a rectangular cross-sectional shape and being oriented to extend across the fluid pathway relative to the direction of the flow of fluid along the fluid pathway.

The one or more fluid pathways may have a wavy shape along a length of the one or more fluid pathways.

The (each) notch may be oriented at a notch angle of between <NUM> and <NUM> degrees relative to the flow of fluid through the one or more fluid pathways.

A cross-sectional area of the one or more fluid pathways may increase along the flow direction of the flow of fluid from a pathway inlet to a pathway outlet.

A heat exchanger outlet may have a larger cross-sectional area than a heat exchanger inlet.

A wavy plate may be located in the (each) fluid pathway extending at least partially across the fluid pathway(s).

The wavy plate may include a plurality of perforations along at least a partial length of the fluid pathway(s). One or more of a perforation number or a perforation size may increase from a fluid pathway inlet to a fluid pathway outlet by reducing the flow restrictions along the flow direction of the flow of fluid under the two-phase flow condition.

The heat exchanger may be formed from a first plate including a first pathway portion of the one or more fluid pathways and a second plate including a second pathway portion of the one or more fluid pathways.

The first pathway portion may be vertically offset from the second pathway portion.

According to a second aspect of the invention, a method of cooling one or more power electronics devices is provided. The method includes securing the one or more power electronics devices to a heat exchanger, the heat exchanger including one or more fluid pathways. A flow of fluid is circulated through one or more fluid pathways to transfer thermal energy from the one or more power electronics to the flow of fluid passing through the one or more fluid pathways. The one or more fluid pathways include one or more internal enhancements and channel design to enhance thermal energy transfer by promoting boiling of the flow of fluid and to reduce the pressure drop in the pathways under two-phase flow condition. The flow of fluid is a flow of liquid refrigerant diverted from a condenser of a heating, ventilation, and air conditioning (HVAC) system. The one or more internal enhancements include one or more inclined notches formed in the one or more fluid pathways, the one or more inclined notches extending unbroken around an entire internal perimeter of the fluid pathway. The one or more inclined notches have a rectangular cross-sectional shape and are oriented to extend across the fluid pathway relative to the direction of the flow of fluid along the fluid pathway.

The one or more notches may be oriented at a notch angle of between <NUM> and <NUM> degrees relative to the flow of fluid through the one or more fluid pathways.

A cross-sectional area of the one or more fluid pathways may increase from a pathway inlet to a pathway outlet.

A heat exchanger outlet may have a greater cross-sectional area than a heat exchanger inlet.

A wavy plate may be located in the (each) fluid pathway.

The wavy plate may include a plurality of perforations.

One or more of a perforation number or a perforation size may increase from a fluid pathway inlet to a fluid pathway outlet.

The heat exchanger may be formed from a first plate including a first pathway portion of the one or more fluid pathways and a second plate including a second pathway portion of the one or more fluid pathways. The first pathway portion may be vertically offset from the second pathway portion.

The following descriptions should not be considered limiting. Certain embodiments of the invention will now be described, with reference to the accompanying drawings, in which like elements are numbered alike.

Illustrated in <FIG> is an embodiment of a power electronics assembly <NUM>. The power electronics assembly <NUM> includes one or more power electronics devices <NUM> mounted to a heat exchanger <NUM> utilized to reject and dissipate thermal energy generated by the power electronics devices <NUM> during operation. In some embodiments, the power electronics devices <NUM> include a variable frequency drive (VFD) operably connected to a compressor <NUM> of a heating, ventilation, and air conditioning (HVAC) system <NUM>.

Referring to <FIG>, the HVAC system <NUM> includes, for example, a vapor compression circuit <NUM> including the compressor <NUM>, a condenser <NUM>, an expansion device <NUM> and an evaporator <NUM> arranged in series and having a volume of refrigerant flowing therethrough. The power electronics assembly <NUM> is connected to the vapor compression circuit <NUM> such that a portion of the flow of liquid refrigerant exiting the condenser <NUM> is diverted through the heat exchanger <NUM>, bypassing the expansion device <NUM> and is directed from the heat exchanger <NUM> to the evaporator <NUM>. The liquid refrigerant from the condenser <NUM> absorbs thermal energy generated by the power electronics devices <NUM>. This thermal energy generated by the power electronics devices <NUM> may cause the refrigerant passing through the heat exchanger <NUM> to boil, changing phase of the refrigerant from liquid to vapor inside the heat exchanger <NUM>.

Referring now to <FIG>, an exemplary heat exchanger <NUM> is illustrated in more detail. As shown, the heat exchanger <NUM> includes a plurality of enclosed fluid pathways <NUM> extending therethrough, enabling a flow of fluid <NUM> such as, for example, refrigerant, glycol, or water to flow therein. The fluid pathways <NUM> extend between a heat exchanger inlet <NUM> through which the flow of fluid <NUM> enters the heat exchanger <NUM>, and a heat exchanger outlet <NUM> through which the flow of fluid <NUM> exits the heat exchanger <NUM>. In some embodiments, the heat exchanger outlet <NUM> is oriented vertically upwardly as shown to prevent vapor lock in the heat exchanger <NUM> flowpath under boiling condition. The heat exchanger inlet <NUM> is connected to the fluid pathways <NUM> via an inlet manifold <NUM> to distribute the flow of fluid <NUM> to the fluid pathways <NUM>, and similarly the heat exchanger outlet <NUM> is connected to the fluid pathways <NUM> via an outlet manifold <NUM>. Immediately downstream of the inlet manifold <NUM>, orifices <NUM> of different diameters, increasing with increasing distance from the heat exchanger inlet <NUM> are provided to distribute the flow of fluid <NUM> from the inlet manifold <NUM> equally among all of the fluid pathways <NUM>. The enhancement features described in the following text will be in the fluid pathways <NUM> downstream of the respective orifices <NUM>.

In some embodiments, the heat exchanger <NUM> is formed from a metal material, such as aluminum, aluminum alloy, steel, steel alloy, copper, copper alloy, or the like, and referring again to <FIG>, may be formed from two or more plates <NUM>, <NUM> abutting one another along a side and joined using any suitable means such as brazing, welding, clamping, compressing, bolting, and the like. The plates <NUM>, <NUM> may each include a portion of the fluid pathways <NUM>, the inlet manifold <NUM>, the outlet manifold <NUM>, the heat exchanger inlet <NUM> and/or the heat exchanger outlet <NUM> formed therein. The mating surfaces of the plates <NUM>, <NUM> can be configured to correspond to one another, e.g., to fit together and seal the fluid circuit therebetween. The mating surfaces of the plates <NUM>, <NUM> can include precision surfaces formed from a process having highly accurate and precise dimensional control, such as through computer numerical control (CNC) machining process and/or net shape, or near net shape manufacturing process. Optionally or additionally, a sealing material can be disposed between the plates <NUM>, <NUM> to aide in preventing leakage from the fluid circuit.

In operation, the flow of fluid <NUM>, liquid refrigerant from the condenser <NUM>, enters the heat exchanger <NUM> at the heat exchanger inlet <NUM> and is distributed to the fluid pathways <NUM> via the inlet manifold <NUM>. The heat exchanger <NUM> conducts thermal energy from the power electronics devices <NUM> and thermal energy is exchanged with the flow of fluid <NUM> flowing through the fluid pathways <NUM>, resulting in cooling of the power electronics devices <NUM>. The vapor flow of fluid <NUM> is then collected at the outlet manifold <NUM> and exits the heat exchanger <NUM> at the heat exchanger outlet <NUM>.

The heat exchanger <NUM> described herein includes notches as will be described below and may include one or more additional features, as will be described below, to improve heat transfer capacity of the heat exchanger <NUM> while reducing a pressure drop penalty of operation of the heat exchanger <NUM>. While the features are described independently below, one skilled in the art will readily appreciate that the features may be incorporated into the heat exchanger <NUM> either independently or in combinations of two or more of the features to promote nucleate boiling heat transfer and to reduce pressure drop under two-phase flow condition while quality increases along the flow direction. The flow of fluid <NUM> provided to the heat exchanger <NUM> is diverted from the condenser <NUM> and in some embodiments enters the heat exchanger <NUM> in a liquid phase with <NUM>% vapor quality or up to <NUM>% vapor quality. The presently disclosed heat exchanger <NUM> may be operated to ensure the vapor quality of the flow of fluid <NUM> exiting the heat exchanger <NUM> has a vapor quality of from about <NUM>% to about <NUM>%, or in another embodiment from about <NUM>% to about <NUM>%, or in yet another embodiment from about <NUM>% to about <NUM>%, or about <NUM>%. The vapor quality change happens as the heat from power electronics devices <NUM> is absorbed by the flow and used for phase change of the liquid refrigerant to vapor while travelling from the heat exchanger inlet <NUM> to the heat exchanger outlet <NUM>.

Referring now to <FIG> the fluid pathways <NUM> of the heat exchanger <NUM> may be formed to increase heat transfer area along a heat exchanger length <NUM>. The fluid pathways <NUM> may have a wavy shape along the heat exchanger length. In some embodiments, the wavy shape is a sinusoidal shape, but it is to be appreciated that other shapes may be utilized. In some embodiments, a peak-to-peak wavelength <NUM> of the fluid pathway <NUM> is in the range of <NUM> millimeters to <NUM> millimeters, while an amplitude <NUM> of the wave shape is in the range of <NUM> to <NUM> times a pathway diameter <NUM> of the fluid pathway <NUM>. The wave shape may extend along an entire length of the fluid pathway <NUM>, while in some embodiments the wave shape may extend along only a portion of the length of the fluid pathway <NUM>. While in the configuration of <FIG>, the wavy shapes of adjacent fluid pathways <NUM> are in phase such that the fluid pathways <NUM> extend parallelly, in other embodiments such as shown in <FIG> the wavy shapes of the fluid pathways are out of phase, or opposed such that the flow area changes periodically along the length of the heat exchanger <NUM>.

The fluid pathways <NUM> have heat transfer enhancement features formed therein. As shown in <FIG>, the fluid pathways <NUM> have notches <NUM> or grooves formed in a pathway wall <NUM> at a notch angle <NUM> relative to the direction of fluid flow through the fluid pathway <NUM>. The notches <NUM> aid in spreading the flow of fluid <NUM> along the Notches will help spreading the liquid along the pathway wall <NUM> thereby keeping the pathway wall <NUM> wet, and promoting nucleate boiling at the pathway wall <NUM>. Further, the notches <NUM> promote turbulence in the flow of fluid <NUM> to increase mixing of the flow of fluid <NUM>. The notches <NUM> extend unbroken around an entire perimeter of the fluid pathway <NUM>. In some embodiments, a notch depth <NUM> is in the range of <NUM>-<NUM> micron. A notch width <NUM> may be in the range of <NUM>-<NUM> micron, while a notch pitch <NUM> between adjacent notches <NUM> may be in the range of <NUM>-<NUM> microns. In some embodiments, the notch angle <NUM> is between <NUM> degrees and <NUM> degrees. Notches <NUM> have a rectangular shape.

Referring now to <FIG>, the fluid pathways <NUM> may have an increasing cross-sectional area, such that an outlet cross-sectional area <NUM> at the outlet manifold <NUM> is greater than an inlet cross-sectional area <NUM> at the inlet manifold <NUM>. The change in cross-sectional area may be achieved by one or more steps <NUM> formed in the fluid pathway as in <FIG>, or alternatively may be a gradual, continuous increase in area as illustrated in <FIG>. The area change will help in reducing the pressure drop in the fluid pathways <NUM> as volume of vapor flow under two-phase condition increases from inlet to outlet.

Referring now to <FIG>, the outlet manifold <NUM> may be sized relative to the inlet manifold <NUM> to account for the increased vapor volume at the outlet manifold <NUM>. For example, the outlet manifold <NUM> may have a larger hydraulic diameter <NUM> than the inlet manifold hydraulic diameter <NUM>. Similarly, the heat exchanger outlet <NUM> may be sized to have a larger flow area than the heat exchanger inlet <NUM> to similarly account for the increased vapor volume under two-phase condition at the heat exchanger outlet <NUM> to reduce the pressure drop along the heat exchanger <NUM>.

Referring now to <FIG>, in some embodiments a wavy plate <NUM> is disposed in the fluid pathway <NUM> extending partially across a pathway height <NUM>. In some embodiments, the wavy plate <NUM> extends between <NUM> and <NUM> percent across the pathway height <NUM>. In some embodiments the wavy plate <NUM> has a plate thickness <NUM> between <NUM>-<NUM> millimeters. The wavy plate <NUM> may have a plate wavelength <NUM> between <NUM>-<NUM> millimeters, and/or a plate amplitude <NUM> between about <NUM> percent and <NUM> percent of the pathway height <NUM> i. e covering <NUM> to <NUM>% of the pathway height. The wavy plate <NUM> increases turbulence and mixing of the flow of fluid <NUM> in the fluid pathway <NUM>. The wavy plate <NUM> can either cover the partial length of the pathway <NUM> or the entire length of the pathway <NUM>. In addition, the wavy plate <NUM> can be installed perpendicular to face <NUM> (vertical face) or it can be inclined at an angle <NUM>-<NUM> deg. This would help draining of the liquid towards the heated wall, so it will keep the wall wet and enhance nucleate boiling. Also, the meniscus formed at the junction of the waveplate and trough of the wave would assist in thin film evaporation.

Referring now to <FIG>, in some embodiments the wavy plate <NUM> extends entirely across the pathway height <NUM> and includes a plurality of perforations <NUM> formed therein. In some embodiments, the perforations <NUM> are between <NUM> millimeters and <NUM> millimeters in diameter. The wavy plate <NUM> may be configured such that an open area for the flow of fluid <NUM> through wavy plate <NUM> increases along the flow direction of the flow of fluid <NUM> along the fluid pathway <NUM>. This may be accomplished by increasing the number of perforations <NUM> and/or increasing the size of the perforations <NUM>. The area change will help in reducing the pressure drop in the fluid pathway <NUM> as volume of vapor flow increases from inlet to outlet under two-phase boiling condition. More (i.e. an increased number of) perforations <NUM> also results in higher heat transfer area and improves the heat transfer performance. In addition, to manage the pressure drop, the number of perforations <NUM> near the entrance of the fluid pathway <NUM> can be increased and relative to that flow area must increase along the length. The wavy plate <NUM> can either cover the partial length of the fluid pathway <NUM> or the entire length of the fluid pathway <NUM>. This would help reduce the pressure drop resistance.

As shown in <FIG>, in a heat exchanger <NUM> having a two plate <NUM>, <NUM> construction, each plate <NUM>, <NUM> has a portion of the fluid pathway <NUM> formed therein. A first pathway portion <NUM> formed in the first plate <NUM> may be offset in a vertical direction relative to a second pathway portion <NUM> formed in the second plate <NUM>. The offset of the first pathway portion <NUM> and the second pathway portion <NUM> may be between <NUM> percent and <NUM> percent of the pathway height <NUM>, and may be biased such that the first plate <NUM> has the power electronics devices <NUM> mounted thereto, and the first pathway portions <NUM> are vertically lower than the second pathway portions <NUM>. This arrangement aids in directing the flow of liquid into the first pathway portions <NUM> closer to the power electronics devices <NUM> as shown in <FIG>, so the vapor is pushed away from the portion <NUM> to portion <NUM>, thereby improving heat transfer effectiveness by increasing nucleate boiling in the first pathway <NUM> and also preventing the first pathway portions <NUM> from drying out. Further, the fluid pathways <NUM> may be provided with additional two or more corners as shown in <FIG> to promote thin film evaporation when the flow will be transitioned to annular flow. The corners of the fluid pathways <NUM> will have a liquid meniscus that will promote thin film evaporation.

The enhanced features of the heat exchanger <NUM> as disclosed herein promote convective flow boiling for high heat transfer rate, reduced pressure drop and improved compactness of the heat exchanger <NUM>.

Claim 1:
A power electronics assembly (<NUM>), comprising:
one or more power electronics devices (<NUM>); and
a heat exchanger (<NUM>) to which the one or more power electronics devices (<NUM>) are mounted, the heat exchanger comprising (<NUM>):
an inlet manifold (<NUM>) and an outlet manifold (<NUM>); and
one or more fluid pathways (<NUM>) extending connecting the inlet manifold (<NUM>) and the outlet manifold (<NUM>), the heat exchanger (<NUM>) configured to transfer thermal energy from the one or more power electronics devices (<NUM>) into a flow of fluid (<NUM>) passing through the one or more fluid pathways (<NUM>);
wherein the one or more fluid pathways (<NUM>) include one or more internal enhancements (<NUM>) and channel configurations to enhance thermal energy transfer by promoting boiling of the flow of fluid (<NUM>) and to reduce the pressure drop in the pathways (<NUM>) under a two-phase flow condition;
wherein the flow of fluid (<NUM>) is a flow of liquid refrigerant diverted from a condenser (<NUM>) of a heating, ventilation, and air conditioning (HVAC) system (<NUM>);
wherein the one or more internal enhancements (<NUM>) include one or more inclined notches (<NUM>) formed in the one or more fluid pathways (<NUM>), the one or more inclined notches extending unbroken around an entire internal perimeter of the fluid pathway;
the one or more inclined notches (<NUM>) having a rectangular cross-sectional shape and being oriented to extend across the fluid pathway (<NUM>) relative to the direction of the flow of fluid along the fluid pathway.