Heat Exchanger

This application is a continuation of U.S. patent application Ser. No. 18/084,775, filed Dec. 20, 2022, which claims priority to and the benefit of U.S. Provisional Patent Application No. 63/291,509, filed Dec. 20, 2021, which is incorporated herein by reference in its entirety for all purposes.

The present disclosure provides systems, materials, devices, and methods related to passive cooling systems. In particular, the present disclosure provides a passive heat exchanger system with enhanced cooling capacity for environments ranging from outdoor electronic enclosures to commercial and residential buildings.

To address and alleviate the challenges and inefficiencies that arise because of heat generated naturally from the sun or from using electronic and industrial equipment, two main categories of cooling systems are generally recognized: active and passive cooling systems. The advantages of passive cooling technologies include energy efficiency and lower financial cost, making these systems particularly useful for the thermal management of both buildings and electronic products. Passive cooling achieves high levels of natural convection and heat dissipation by utilizing a heat sink to maximize the radiation and convection heat transfer modes. Such heat transfer modes cool electronic products and environments to keep them under the maximum allowed operating temperature.

Active cooling, on the other hand, refers to cooling technologies that rely on an external device to enhance heat transfer. Through active cooling technologies, the rate of fluid flow increases during convection, which dramatically increases the rate of heat removal. Active cooling solutions include forced air through a fan or blower, forced liquid, and thermoelectric coolers (TECs), which can be used to optimize thermal management on all levels. Fans are used when natural convection is insufficient to remove heat. They are commonly integrated into electronics, such as computer cases, or are attached to CPUs, hard drives or chipsets to maintain thermal conditions and reduce failure risk. The main disadvantage of active thermal management is that it requires the use of electricity (e.g., a passive solution can use some electricity, such as fans, whereas active thermal management generally uses a pump or compressor in addition to the fans) and therefore results in higher costs, compared to passive cooling.

For electronic enclosures, which generally include systems designed to house and protect sensitive and valuable computer and electronic equipment (e.g., equipment used by the Telecom, Industrial, Natural Resources Refining, Federal and Municipal Government or other industries), it is necessary for the internal area of the enclosure to be climate controlled (e.g., regulated temperature and humidity) and to be protected from the intrusion of dust and debris from the outside environment. Often times, to control the environment of the electronic enclosure, a climate control unit (CCU) is used. A CCU is designed to reduce intrusion of outdoor contaminates like dust, water, salt etc. while also controlling the temperature of the equipment being protected. Examples of active cooling CCUs include air conditioners, heat pumps, and water source geothermal HVAC systems. Examples of passive cooling CCUs include air to air heat exchangers, heat pipes, and thermosiphons. Passive cooling typically offers lower electrical consumption, with less heat removal capacity in comparison to an active cooling unit.

With increasing heat load requirements in electronic enclosures, as well as commercial and residential buildings, currently available passive cooling technology has not been widely implemented despite its advantages. Although active cooling technologies provide increased capacities, higher costs coupled with increased energy consumption creates operational burdens. Thus, there is a demand for a CCU that operates with low energy consumption while still offering higher heat removal that will effectively bridge the gap between passive and active cooling technologies.

The Summary is provided to introduce a selection of concepts that are further described below in the Detailed Description. This Summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

One aspect of the present disclosure provides a heat exchanger including a first coil panel having a first lower header and a first upper header and a second coil panel having a second lower header and a second upper header. The heat exchanger further includes a first tube and a second tube extending between the first upper header and the second upper header, and a third tube and a fourth tube extending between the first lower header and the second lower header. A working fluid is positioned within the first coil panel, the second coil panel, the first tube, the second tube, the third tube, and the fourth tube.

In some embodiments, the first coil panel is positioned below the second coil panel.

In some embodiments, the first upper header is positioned between the first lower header and the second lower header.

In some embodiments, the first coil panel is angled with respect to a vertical plane.

In some embodiments, the first coil panel forms an angle with respect to the vertical plane within a range of 0 degrees to 80 degrees. In some embodiments, the angle is 20 degrees.

In some embodiments, the second coil panel is angled with respect to the vertical plane.

In some embodiments, the second coil panel forms an angle with respect to the vertical plane within a range of 0 degrees to 80 degrees. In some embodiments, the angle is 20 degrees.

In some embodiments, the heat exchanger further includes a fifth tube extending between the first upper header and the second upper header, and a sixth tube extending between the first lower header and the second lower header; wherein the working fluid is positioned within the fifth tube and the sixth tube.

In some embodiments, a flowrate of the working fluid between the first coil panel and the second coil panel is within a range of 0.3 in/s to 1.0 in/s.

In some embodiments, the first tube includes a diameter within a range of 12 mm to 22 mm.

In some embodiments, the first coil panel includes a plurality of channels, and wherein each of the plurality of channels includes a plurality of microchannels, and wherein each of the plurality of microchannels comprise a plurality of fins extending from the plurality of microchannels that increase the surface area for heat transfer.

In some embodiments, the first lower header and first upper header are sealed to create sealed compartments, wherein the working fluid can move freely within both the sealed compartments, wherein the first upper header comprises working fluid in a substantially gaseous state, and wherein the first lower header comprises working fluid in a substantially liquid state.

In some embodiments, the heat exchanger further includes a dividing wall positioned between the first coil panel and the second coil panel.

In some embodiments, the first tube, the second tube, the third tube, and the fourth tube extend through the dividing wall.

One aspect of the present disclosure provides a heat exchanger assembly including a housing with an external air inlet, an external air outlet, an internal air inlet, and an internal air outlet. The heat exchanger assembly further includes a heat exchanger including an angled condenser panel, an angled evaporator panel, and a working fluid. The heat exchanger assembly further includes a first fan positioned at the internal air inlet configured to create an internal airflow through the housing from the internal air inlet to the internal air outlet, and a second fan positioned at the external air inlet configured to create an external airflow through the housing from the external air inlet to the external air outlet. The external airflow is isolated from the internal airflow.

In some embodiments, the angled condenser panel is positioned above the angled evaporator panel.

In some embodiments, the heat exchanger further includes a first plurality of tubes extending between an upper evaporator header and an upper condenser header, and a second plurality of tubes extending between a lower evaporator header and a lower condenser header.

In some embodiments, the external airflow is isolated from the internal airflow by a dividing wall positioned within the housing.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present document, including definitions, will control. Preferred methods and materials are described below, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure. All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety. The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting.

The terms “comprise(s),” “include(s),” “having,” “has,” “can,” “contain(s),” and variants thereof, as used herein, are intended to be open-ended transitional phrases, terms, or words that do not preclude the possibility of additional acts or structures. The singular forms “a,” “and” and “the” include plural references unless the context clearly dictates otherwise. The present disclosure also contemplates other embodiments “comprising,” “consisting of” and “consisting essentially of,” the embodiments or elements presented herein, whether explicitly set forth or not.

For the recitation of numeric ranges herein, each intervening number there between with the same degree of precision is explicitly contemplated. For example, for the range of 6-9, the numbers 7 and 8 are contemplated in addition to 6 and 9, and for the range 6.0-7.0, the number 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7, 6.8, 6.9, and 7.0 are explicitly contemplated.

“About” and “approximately” are used to provide flexibility to a numerical range endpoint by providing that a given value may be “slightly above” or “slightly below” the endpoint without affecting the desired result.

In the foregoing description of preferred embodiments, specific terminology has been resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar technical purpose. Terms such as “top” and “bottom”, “front” and “rear”, “inner” and “outer”, “above”, “below”, “upper”, “lower”, “vertical”, “horizontal”, “upright” and the like are used as words of convenience to provide reference points.

Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear; in the event, however of any latent ambiguity, definitions provided herein take precedent over any dictionary or extrinsic definition. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

With reference to, a heat exchanger assemblyincludes a housingand a heat exchanger(i.e., a passive heat exchanger). The housingincludes an internal air inletand an internal air outleton a first side, and an external air inletand an external air outleton a second side, opposite the first side(). In the illustrated embodiment, the internal air inletand the internal air outletare covered with a grate and/or mesh material. The heat exchanger assemblyis generally mounted to an enclosure-of-interest, such as but not limited to, an enclosure (e.g., cabinet) that houses electrical or computer equipment, or a commercial or residential building.

As described herein, embodiments of the heat exchanger assemblyand systems of the present disclosure can be mounted to the enclosure-of-interestto reduce heat load generated within the enclosure-of-interest(e.g., heat load generated by computer or electrical equipment). In accordance with these embodiments, the devices and systems of the present disclosure can provide enhanced or improved cooling capacity and/or performance for a given enclosure without contaminating internal and external airflow paths.

With continued reference to, the heat exchanger assemblyfurther includes a first fanand a second fan. The first fanis positioned at the internal air inletand is configured to create an internal airflowthrough the housingfrom the internal air inletto the internal air outlet. The second fanis positioned at the external air inletand is configured to create an external airflowthrough the housingfrom the external air inletto the external air outlet. In the illustrated embodiment, the first fanis positioned vertically above the second fan. In some embodiments, the fans&are controlled to operate at a variable speed. In other embodiments, the fans operate at a constant speed.

With reference to, the internal airflowis isolated from the external airflow. In the illustrated embodiment, the internal airflowis isolated and separated from the external airflowby a dividing wall(a.k.a. divider plate) positioned within the housing. In other words, the dividing wallfacilitates the separation of an external airflow path from an internal airflow path to prevent contamination of the internal environment of the enclosure-of-interestwith dust, debris, dirt, salt, precipitation, and the like, from the environment outside of the enclosure-of-interest. In some embodiments, the dividing wallcreates a substantially air-tight seal that divides the housinginto a first chamberA and a second chamberB. In the illustrated embodiment, the dividing wallis oriented approximately vertically in the housing. In other embodiments, the dividing wall is angled with respect to a vertical axis. In some embodiments, the dividing wallis welded, brazed, or fitted mechanically with a sealant compound into position during assembly of the heat exchanger assemblysuch that it is generally in a fixed position. Welding can include, for example, TIG welding or laser welding, though other suitable types of welding could also be used.

With reference to, the heat exchangerincludes a first coil paneland a second coil panel. In the illustrated embodiment, the dividing wallis positioned between the first coil paneland the second coil panel. The first coil panelis separated from the second coil panelin the illustrated embodiment. In other words, the first coil panelis in the first chamberA and the second coil panelis in the second chamberB. In some embodiments, the coil panels,are microchannel coil panels. In other embodiments, the coil panels,are fin and tube type panels. In the illustrated embodiment, the first coil panelis an evaporator and the second coil panelis a condenser.

In some embodiments, the coil panels,includes channels or microchannels and a plurality of fins extending from the channels or microchannels. The fins provide increased surface area for heat transfer between the microchannels and the airflow. In some embodiments, the fins extend from one or both lateral sides of a microchannel such that the fins occupy the space between adjacent microchannels. Examples of such microchannels and fins are described in U.S. patent application Ser. No. 17/434,120, filed Aug. 26, 2021, which is incorporated herein in its entirety.

In some embodiments, the heat exchanger assemblyinclude two or more microchannels, including, but not limited to, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 30, 40, 50, 60, 70, 80, 90, 100 or more separate microchannels within a single channel within a coil panel. The number of channels and microchannels is determined based on various factors, such as system parameters, the working fluid, the size and spatial limitations of the enclosure-of-interest, the heat load of the enclosure-of-interest, the external environment, and the like. The configurations of the channels and microchannels (e.g., size, shape, depth) also varies on these and other factors. Generally, the channels and microchannels are configured to maximize heat transfer within a given area; therefore, any configuration that contributes to greater heat transfer can be used. In some embodiments, the channels and microchannels are symmetrically configured and/or are of uniform shape and size with respect to the other channels and microchannels in the heat exchanger. In other embodiments, the channels and microchannels are asymmetrically configured and/or are of variable shape and size with respect to the other channels and microchannels in the heat exchanger.

With continued reference to, the first coil panelincludes a first lower headerpositioned at a bottom endof the first coil paneland a first upper headerpositioned at a top endof the first coil panel. Likewise, the second coil panelincludes a second lower headerpositioned at a bottom endof the second coil paneland a second upper headerpositioned at a top endof the second coil panel. In the illustrated embodiment, the first coil panelis positioned below the second coil panel, as viewed from the frame of reference of. In other words, with respect to a gravity vector the first coil panelis positioned lower than the second coil panel. As such, the angled condenser panelis positioned above the angled evaporator panel. In the illustrated embodiment, the first upper headeris positioned vertically between the first lower headerand the second lower header, as viewed from the frame of reference of. In other words, the first coil paneland the second coil paneldo not overlap vertically. In other embodiments, the first coil panel and the second coil panel overlap vertically such that the first upper headeris positioned vertically between the second lower headerand the second upper header.

The upper headers,and the lower headers,are positioned at the terminal ends of the coil panels,and create sealed compartments in which the working fluid can pass from one channel to another to equalize pressure among the channels in the system. For example, the headerencloses the terminal ends of the channels in the upper coil panelto create a sealed compartment. The upper headers,generally contain the working fluid in a substantially gaseous state, which forms condensate when exposed to cooler external air (). The lower headers,generally contain the working fluid in a substantially liquid state, which evaporates when exposed to warmer air from the internal environment of an enclosure-of-interest (). The exact depth by which the terminal ends of the channels extend into the upper and lower headers can vary depending on factors such as the number of channels, the type of working fluid, the size of the sealed compartment, and the like.

Additionally, in some embodiments, the upper headers,and the lower headers,are symmetrically configured and/or are of uniform shape and size with respect to each other. In some embodiments, the upper headers,and the lower headers,are asymmetrically configured and/or are of variable shape and size with respect to each other. The shape of the upper headers,and the lower headers,can be rounded, oval, square, octagonal, and the like. In some embodiments, the upper headers,and the lower headers,are welded, brazed, or fitted mechanically with a sealant compound into position during assembly of the heat exchanger device such that they are generally in a fixed position. Welding can include, for example, TIG welding or laser welding, though other suitable types of welding could also be used. In some embodiments, a header includes a charge port that provides an inlet for injecting the working fluid into the coil. Generally, once the working fluid is injected into the coil and properly pressurized, the charge port is permanently sealed off.

With continued reference to, the first coil panelis angled with respect to a vertical planeby a first angle. Likewise, the second coil panelis angled with respect to the vertical planeby a second angle. In some embodiments, the first angleis within a range of approximately 0 degree to approximately 80 degrees. In the illustrated embodiment, the first angleis approximately 20 degrees. In some embodiments, the second angleis within a range of approximately 0 degree to approximately 80 degrees. In the illustrated embodiment, the second angleis approximately 20 degrees.

In the illustrated embodiments, both of the panels,are angled (i.e., the first coil panelis an angled evaporator panel and the second coil panelis an angled condenser panel). In other embodiments, one of the coil panels is angled and the other coil panel is vertical. In the illustrated embodiments, the first angleis equal to the second angle. In other embodiments, the first angleis different than the second angle.

With continued reference to, a plurality of tubes interconnects the first coil paneland the second coil panel. In the illustrated embodiment, a first tubeA and a second tubeB extend between the first upper headerand the second upper header, and a third tubeA and a fourth tubeB extend between the first lower headerand the second lower header. As explained in greater detail herein, a working fluid is positioned within the first coil panel, the second coil panel, the first tubeA, the second tubeB, the third tubeA, and the fourth tubeB. In other words, a single common working fluid flows through the panels,and the tubesA,B,A,B. In some embodiments, a first plurality of tubes (e.g., tubesA,B) extend between an upper evaporator header and an upper condenser header and a second plurality of tubes (e.g., tubesA,B) extend between a lower evaporator header and a lower condenser header.

As used herein, the term “working fluid” generally refers to the fluid inside the channels/microchannels, and header, and can be any fluid or gas capable of absorbing and/or transmitting energy. The working fluid is generally in a saturated state (i.e., liquid phase and vapor phase are in simultaneous equilibrium), and it undergoes a phase change due to gain or loss of heat. As the working fluid absorbs heat generated from inside the enclosure-of-interest, the working fluid is vaporized in the lower coilof the heat exchangerand rises upward in a gaseous state to the upper coilof the heat exchanger. Then the working fluid is exposed to cooler ambient or external air, which causes the working fluid to condense and fall back to the lower coil portion in a liquid state. This process results in the passive removal of heat from the enclosure-of-interest.

In some embodiments, the working fluid is an environmentally compatible refrigerant. In some embodiments, the working fluid is a dielectric, non-flammable fluid with low toxicity. In some embodiments, the working fluid is a type of hydrocarbon, such as, but not limited to, acetone, ethylene, isobutane, methanol, ethanol, tetrofluoroethane, hydrofluoroether, and/or combinations thereof. In some embodiments, the composition of the working fluid and internal pressure are selected to provide a boiling point of the working fluid in the lower coil portion at about the desired operating temperature of the electronic devices in an enclosure-of-interest (e.g., approximately 30-100° C.). Examples of working fluid include, but are not limited to, Vextral XF (2,3-dihydrodeca-fluoropentane; DuPont), Flourinert Electronic Liquid FC-72 (3M), R134a (1,1,1,2-tetrofluoroethane; Honeywell), R1234yf (2,3,3,3-Tetrafluoroprop-1-ene; Honeywell), Novec 7100 (methoxy-nonafluorobutane; 3M), HFC245fa (1,1,1,3,3-Pentafluoropropane; Honeywell), R410a (mixture of difluoromethane (R-32) and pentafluoroethane (R-125); Honeywell), and various water/glycol mixtures.

In conventional thermosiphons, all the working fluid travels through a single tube, and this tube is often smaller than the needed thermosiphon flow rate, which causes a restriction in the system. In some embodiments, a tube size (e.g., tube diameter) is increased to increase the flow rate through the tube. In some embodiments, the tube diameter is within a range of approximately 12 mm to approximately 22 mm. Although increasing the tube size (e.g., tube diameter) can increase the flow rate, there is a practical limit due to the size of the headers on the coils panels.

In the illustrated embodiment, there are two tubes interconnecting a pair of headers, for a total of four tubes. In the illustrated embodiment, the first tubeA, the second tubeB, the third tubeA, and the fourth tubeB extend through the dividing wall. For example, the first tubeA and the second tubeB interconnect the first upper headerand the second upper header. In other embodiments, there are at least two (i.e., 2, 3, 4, etc.) tubes interconnecting a pair of headers. For example, in some embodiments, the heat exchanger assembly further includes a fifth tube extending between the first upper header and the second upper header, and a sixth tube extending between the first lower header and the second lower header, with the working fluid also positioned within the fifth and sixth tubes.

Advantageously, the flow restriction of conventional designs is resolved by the disclosure provided herein by increasing the number of tubes fluidly interconnected between the two coil panels,. The more than one tube reduces the flow restriction between the evaporator coiland the condenser coil. The additional flow capacity is beneficial in part because the working fluid flow is driven by gravity. In other words, with only gravity as the mechanism to cause the working fluid to flow, decreasing the flow restriction helps transfer heat from the evaporator to the condenser. In the illustrated embodiment, the flow of the working fluid is balanced between the first tubeA and the second tubeB and is also balanced between the third tubeA and the fourth tubeB.

Providing more than one tube interconnecting a pair of headers between a condenser and an evaporator, as illustrated herein, has the following distinct advantages. First, the increase in cross-sectional area allows for increased flow of the working fluid. In some embodiments, the flowrate of the working fluid between the first coil paneland the second coil panelis within a range of approximately 0.3 in/s (cubic inches per second) to approximately 1.0 in/s. Second, the thermal performance of the overall system is increased; even when all other factors remain the same (e.g., coil size, airflow, and fan tube diameter). In some embodiments, the thermal performance of the overall heat exchanger assemblyis increased at least approximately 30%. In some embodiments, the thermal performance of the heat exchanger assemblyis increased within a range of approximately 30% to approximately 50%. As such, the heat exchanger assemblydisclosed herein includes more than one tube fluidly coupling a pair of headers between a condenser and an evaporator, increased flowrate of the working fluid, and an increased tube diameter.