This invention relates generally to coaxial heat exchangers, and in particular, to manufacturing processes and equipment for producing coaxial heat exchangers, such as for HVAC systems and water source heat pumps.
This section is intended to introduce the reader to various aspects of the art that may be related to various aspects of the presently described embodiments—to help facilitate a better understanding of various aspects of the present embodiments. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Modern residential and industrial customers expect indoor spaces to be climate controlled. In general, heating, ventilation, and air-conditioning (“HVAC”) systems circulate an indoor space's air over low-temperature (for cooling) or high-temperature (for heating) sources, thereby adjusting the indoor space's ambient air temperature. HVAC systems generate these low- and high-temperature sources by, among other techniques, taking advantage of a well-known physical principle: a fluid transitioning from gas to liquid releases heat, while a fluid transitioning from liquid to gas absorbs heat.
In a typical system, a fluid refrigerant circulates through a closed loop of tubing that uses compressors and other flow-control devices to manipulate the refrigerant's flow and pressure, causing the refrigerant to cycle between the liquid and gas phases. These phase transitions generally occur within the HVAC's heat exchangers, which are part of the closed loop and designed to transfer heat between the circulating refrigerant and outside environment. This is the foundation of the refrigeration cycle. The heat exchanger where the refrigerant transitions from a gas to a liquid is called the “condenser,” and the condensing refrigerant releases heat to the surrounding environment. The heat exchanger where the refrigerant transitions from liquid to gas is called the “evaporator,” and the evaporating refrigerant absorbs heat from the surrounding environment.
A heat pump is a compression refrigeration system that is designed to reverse the flow of refrigerant to transition between heating and cooling modes. A reversing valve controls the direction of refrigerant flow through the refrigerant loop, thereby determining whether the heat pump is in heating mode or cooling mode. When the refrigerant flow is reversed, the potion of the refrigerant loop that previously functioned as an evaporator functions as a condenser and vice versa.
Water source heat pumps (WSHP) generally rely on two loops and one or more heat exchangers that transfer heat between the loops. Water source heat pumps utilize a water loop and a refrigerant loop. Depending on the mode of operation, heat is absorbed by one loop and transferred to the other. Heat is often transferred between the refrigeration loop and water loop using coaxial heat exchangers.
Coaxial heat exchanges, also called tube-in-tube heat exchangers, are used in numerous applications including various heating, ventilation, air conditioning, and refrigeration (HVACR) applications. Like other forms of heat exchangers, coaxial heat exchangers are used to transfer heat from one fluid to another. While coaxial heat exchangers are also referred to as tube-in-tube heat exchangers, neither the inner nor outer tube is required to be round. Either the inner or outer tube may be substantially any shape that allows a fluid to flow through the tube. The inner tube and outer tube are each designed to resist the working pressures associated with the fluids within the inner and outer tube respectively. In some coaxial heat exchangers, a tube may contain grooves, lobes, fins, projections, or other elements that increase the surface area of a tube or promote a higher heat transfer coefficient, thereby allowing a greater exchange of heat between a fluid on the interior of the tube and a fluid on the exterior of the tube.
In WSHPs, coaxial heat exchangers are used to transfer heat between the refrigerant within the refrigerant loop and the water, water/anti-freeze solution, or other fluid within the water loop. Water/anti-freeze solutions include, but are not limited to, water/methanol and water/glycol solutions. The water or other fluid in the water loop then transfers heat to the outside environment, such as the air or ground.
Certain aspects of some embodiments disclosed herein are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention. Indeed, the invention may encompass a variety of aspects that may not be set forth below.
Embodiments of the present disclosure generally relate to a heating, ventilation, air conditioning or refrigeration (HVACR) system adapted utilizing a coaxial heat exchanger that has been formed according to the disclosed methods. In some embodiments, engineered tubing may be hydrostatically expanded to achieve a higher degree of contact and/or a press fit with an intermediate member. It will be appreciated that expanding the engineered tubing may create a friction fit and/or interference fit with the intermediate sleeve. The engineered tubing and sleeve may be positioned within an outer jacket, thereby creating an inner fluid pathway and outer fluid pathway which may be used for fluid to fluid heat exchange.
Some embodiments of the present disclosure generally relate to a coaxial heat exchanger for water source heat pumps comprising an extruded aluminum fin member comprising an interior and an exterior. In some embodiments, the interior of the extruded aluminum fin member has a substantially circular interior diameter and the exterior of the extruded aluminum fin member comprises a plurality of projecting structures. Some embodiments further comprise an engineered copper tube with a rifled interior. In some embodiments, the engineered copper tube is positioned within the extruded aluminum fin member and expanded using hydrostatic pressure to increase contact between the exterior of the engineered copper tube and the interior of the aluminum fin member. Embodiments further comprise an outer jacket positioned outboard of the extruded aluminum fin member.
Some embodiments of the present disclosure generally relate to a method for manufacturing a coaxial heat exchanger, the method comprising the steps of obtaining an engineered inner tube comprising an interior and an exterior, wherein the interior of the inner tube includes a rifled texture; annealing the engineered inner tube; positioning the engineered inner tube within the interior volume of an intermediate member comprising an interior and an exterior wherein the exterior of the intermediate member comprises projecting structures; deforming the engineered inner tube using a pressure to increase contact between the exterior of the engineered inner tube and the interior of the intermediate member; and positioning the intermediate member and engineered inner tube within an outer jacketing member.
Various refinements of the features noted above may exist in relation to various aspects of the present embodiments. Further features may also be incorporated in these various aspects as well. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to one or more of the illustrated embodiments may be incorporated into any of the above-described aspects of the present disclosure alone or in any combination. Again, the brief summary presented above is intended only to familiarize the reader with certain aspects and contexts of some embodiments without limitation to the claimed subject matter.
These and other features, aspects, and advantages of certain embodiments will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
One or more specific embodiments of the present disclosure will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project, numerous implementation-specific decisions must be made to achieve the developers' specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.
When introducing elements of various embodiments, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements.
Turning to the figures,
In water source heat pumps (WSHPs) the refrigerant transfers heat to and/or from a flowing stream of water or water-antifreeze mixture. This transfer of heat is typically performed using a coaxial heat exchanger. The water to refrigerant heat exchanger is generally referred to as the outdoor heat exchanger although it will be appreciated that the outdoor heat exchanger may be positioned indoors.
Coaxial heat exchanger 200 also includes an intermediate member 220 positioned outboard of the inner tube 210. The intermediate member 220 may be a configured as a sleeve with projecting members, folded fins, or a combination of the two. In some embodiments, a folded fin intermediate member may be arranged as a ruffled folded fin, plain folded fin, and/or a lanced and offset folded fin. In some embodiments, the projecting structures and/or fins of the intermediate tubing member may be textured, twisted, and/or axially rifled. In some embodiments, these surface features increase the mixing and/or turbulence of a flowing fluid, thereby enhancing the degree of heat transferred between the intermediate tubing member and the fluid.
As shown in
In some embodiments, intermediate member 220 is initially in a generally planar configuration and is wrapped around the inner tube 210 to form a tubular intermediate member. In some embodiments, the intermediate member is brazed to itself to maintain a tubular configuration rather than a planar form. Depending on the respective length of the inner tube and the intermediate member, in some embodiments, multiple intermediate members sections may be wrapped around the inner tube or positioned axially around the inner tube. In some embodiments, an intermediate member section is between 4 to 6 inches long. In some embodiments, an intermediate member 220 may comprise one or more than one intermediate member sections. In some embodiments, the intermediate member sections may be in contact with each other. In some embodiments, the intermediate member sections are separated by a gap. In some embodiments, the gap between intermediate member sections is smaller at the first or last portion of the heat exchanger as compared to the middle portion of the heat exchanger. In some embodiments, an intermediate member comprises a plurality of rings axially aligned around the inner tube. In such embodiments, one or more than one of the rings includes axially projecting structures.
The intermediate member 220 is positioned within an outer jacket 230. The outer jacket 230 is outboard of the intermediate member 220 and the inner tube 210. In some embodiments, the outer jacket 230 is rigid. In some embodiments, the outer jacket 230 contains metal, such as, for example, steel, stainless steel, copper, or aluminum. The outer jacket 230 is sufficiently strong to resist deformation at the appropriate working pressures such as, for example, refrigerant pressures.
The volume contained within the interior of the inner tube 210 is referred to as the inner volume 240. The volume between the interior of the outer jacket 230 and the exterior of the inner tube 210 is referred to as the outer volume 250.
In some embodiments, the coaxial heat exchanger 200 allows a first fluid to flow through the inner volume 240 while a second fluid flows through the outer volume 250. Heat is exchanged between the first and second fluids through the inner tube 210 and the intermediate member 220. In some embodiments, the first fluid is water and the second fluid is a refrigerant which undergoes a phase change as heat is exchanged between the water and refrigerant.
In some embodiments, in order to create and/or increase contact between the inner tube 210 and the intermediate member 220, the inner tube is expanded or otherwise deformed. The inner tube 210 may be expanded using pressure, such as, for example, hydrostatic pressure, or using mechanical expansion processing. In some embodiments, it is advantageous to expand the inner tube 210 using hydrostatic pressure in order to avoid crushing or significantly deforming the texture and/or rifling on the interior surface of the inner tube 210.
In some embodiments, before the inner tube 210 is expanded, the inner tube 210 is annealed. The inner tube 210 is annealed by heating it to a predetermined temperature and allowing the inner tube 210 to cool at a controlled rate. Once the inner tube 210 is annealed, the inner tube material is generally softer and may be more easily expanded.
In some embodiments, the inner tube 210 is optimized to transfer heat between a water solution in the inner volume 240 and a refrigerant in the outer volume 250 when the refrigerant is in a two-phase mixture or is in the process of changing phases (either evaporation or condensation). In some embodiments, the exterior of the inner tube contains ridges that are optimized to promote the evaporation of refrigerant by facilitating the formation of bubbles when the refrigerant evaporates. In some embodiments, the exterior of the inner tube contains ridges that are optimized to promote the condensation of refrigerant by facilitating the formation of droplets when the refrigerant condenses. It will be appreciated that embodiments that are optimized to facilitate evaporation of the refrigerant will also promote condensation of the refrigerant when compared to an inner tube with a generally smooth exterior surface.
In some embodiments, the first and/or last portions of a condenser or evaporator generally contain more single-phase refrigerant while the middle portion contains more liquid-vapor mixture. Accordingly, in some embodiments, engineered tubing with an enhanced textured exterior surface may be used for the middle portion of the inner tube and tubing with a smooth or otherwise unenhanced exterior surface may be used for the first and/or last portion of the inner tube. In some embodiments, regardless of the state of the exterior surface of the inner tube, the interior surface of the inner tube will contain an engineered textured surface to take advantage of the increased turbulence and heat transfer with the liquid water solution flowing through the interior of the inner tube.
In some embodiments, the intermediate member increases the surface area in contact with a refrigerant, whether the refrigerant is in a single-phase (liquid or vapor) or in a two-phase mixture. In some embodiments, the intermediate member facilitates greater heat transfer when the refrigerant is in a single phrase as compared to when the refrigerant is in a two-phase mixture. In some embodiments, the intermediate member is only present at the first and last portions of the coaxial heat exchanger. In some embodiments, the intermediate member is not included in the portions of the heat exchanger that are expected to contain significantly two-phase mixtures of refrigerant. In some embodiments, the intermediate member is made of multiple intermediate member sections. In some embodiments, there is a gap between each intermediate member section. In some embodiments, the gap between intermediate member sections is larger in the middle portion of the coaxial heat exchanger as compared to the end portions of the heat exchanger. In some embodiments, the gap between intermediate member sections is larger in the four feet middle section of a ten feet long heat exchanger than in the three feet sections at either end of the ten feet long heat exchanger.
In some embodiments, the linear length of a coaxial heat exchanger is about ten feet. In some embodiments, about three-foot long sections closest to the ends of the heat exchanger contain inner tube members with a generally smooth or otherwise unenhanced exterior surface while the middle about four-foot section contains enhanced engineered inner tube with an exterior surface designed to promote evaporation or condensation of the refrigerant.
In some embodiments, contact between the inner tube 410 and the intermediate tubing member 420 is increased by annealing the inner tube, then axially inserting the annealed inner tube into the intermediate tubing member and hydrostatically expanding the annealed inner tube within the intermediate tubing member. This process creates an increased degree of contact and facilitates heat transfer between the inner tube 410 and the intermediate tubing member 420. This arrangement allows the intermediate tubing member 420 to transfer heat between the first fluid, flowing within the inner volume within the inner tube 410 to or from a second fluid flowing in the outer volume between the intermediate tubing member 420 and the outer jacket (not shown) without the intermediate tubing member 420 being in contact with the first fluid. In some embodiments, the first fluid contains water and the second fluid contains a refrigerant such as, for example, R410A, R32, R454B, DR-55, R134a, R513A, R515A, R515B, HFO refrigerants such as HFO-1234ze, HFO-1233zd, or HFO-1234yf, or any number of combinations thereof. Expanding the annealed inner tube within the intermediate tubing member increases contact between the inner tube and intermediate member thereby facilitating thermal transfer. In some embodiments, expanding the inner tube within the intermediate member creates a press fit. This arrangement prevents the material of the intermediate tubing member from contacting the first fluid within the inner tube. This arrangement allows the intermediate member to contain materials that may not be suitable for sustained contact with the first fluid. Expanding the annealed inner tube using hydrostatic pressure allows the use of pre-existing engineered tubing or tech tube that has a rifled interior surface to be used with an extruded aluminum intermediate tubing member.
In some embodiments, the coupling 550 is also in contact with the exterior surface of the inner tube 510. In some embodiments, the coupling is sealed, adhered, and/or brazed to the exterior surface of the inner tube 510 and exterior surface of the tube member 520 to prevent leakage of the second fluid. In such embodiments, no outer jacket is required.
In some embodiments, the intermediate member serves as a double wall construction around the inner tube 610. This double wall construction prevents any mixing of the first and second fluids in the event that either the inner tube 610 or the intermediate member 620 corrodes or otherwise becomes damaged, resulting in a leak. In some embodiments, the outer jacket 630 is sealed around the non-fin portion 625 of the intermediate member 620. In some embodiments, the outer jacket 630 is arranged so that no separate coupling is required. As shown in
In some embodiments, the outer jacket 630 is brazed to the intermediate member 620 and any space between the intermediate member and inner tube is left open to the atmosphere. In such embodiments, if the intermediate member becomes damaged, any refrigerant flowing through the outer zone is released into the atmosphere rather than contaminating the circulating water solution within the inner tube. It will be appreciated that any space between the inner tube and intermediate member is very small and does not significantly reduce the thermal transfer between the first and second fluids.
In some embodiments, the intermediate member is configured to create an axial gap portion 840. The exterior surface of the inner tube is generally not covered by the intermediate member in the axial gap portion. In some embodiments, the heat exchanger is coiled after it is assembled. In some embodiments, the axial gap portion allows the heat exchanger to be coiled while reducing the amount of crimping or crushing of the intermediate member. If the intermediate member were significantly crimped or crushed, the damaged portion of the intermediate member could restrict the flow of fluid through the volume between the inner tube and outer jacket. In some embodiments, the axial gap portion is positioned at the interior radius of the coiled coaxial heat exchanger.
In some embodiments, a spacer (not shown) may be positioned axially to the inner tube. In some embodiments, the spacer may be positioned in the axial gap portion. In some embodiments, the spacer comprises a flexible material that allows fluid to pass through the spacer such as, for example, copper wool.
As shown in
While the aspects of the present disclosure may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. But it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.
This application claims the benefit of U.S. Provisional Application No. 62/984,525, filed Mar. 3, 2020. The entire disclosure of U.S. Provisional Application No. 62/984,525 is hereby incorporated herein by reference.
Number | Date | Country | |
---|---|---|---|
62984525 | Mar 2020 | US |