Patent Application
20120055660
The following disclosure relates generally to fluid conduits for use in heat exchangers and, more particularly, to dual wall tubing for use in heat exchangers.
Copper tubing has many uses in heating, ventilation, and air conditioning (HVAC) applications. Various arrangements of tubing have been used in heat exchangers to hold at least one of the fluids taking part in the heat transfer. These tubing arrangements may leak causing contamination between fluids: if the tubing carrying one of the fluids ruptures the fluids within and without the tube may be mixed.
Dual wall heat exchanger conduits are commonly used in heat pump water heaters to avoid leakages of refrigerant and oils into a potable water supply. Conventional dual wall heat exchanger conduits have utilized a first tube inserted into and pressed against a second tube. Either the first or the second tubes can have protrusions which create a leak path between the tubes. These protrusions can lead to high thermal contact resistance between the tubes, rendering the heat exchanger relatively inefficient.
Some heat exchanger conduits have fluids flowing through the space between the inner tube and the barrier tube. This arrangement poses a risk of fluid cross-contamination in the event of a tube rupture. These heat exchanger conduits further utilize a tapered structure, such that the exchangers are increasingly flattened from end to end in a stepwise or continuous manner to compensate for different fluid properties in warm versus cold regions. This tapering requires more manufacturing complexity than if the exchanger was of a continuous height along all or most of its length.
It would therefore be advantageous to provide a double-walled heat exchanger conduit, having high heat transfer properties, that is relatively easy to manufacture and not prone to detrimental leaks.
The present disclosure describes various embodiments of a tubing assembly, such as a heat exchanger conduit, having an outer barrier tube with a plurality of fluid-carrying inner tubes nested therein. In one embodiment, the nested tube heat exchanger conduit can be manufactured by inserting two or more inner tubes into a circular or at least partially circular barrier tube and at least partially flattening at least some length of the assembly. The heat exchanger conduit can include one or more void spaces within the barrier tube and adjacent to the inner tubes which serve to contain any leaks in the inner tubes and vent any leaks to the atmosphere. These and other aspects of the present disclosure are described in greater detail below.
Certain details are set forth in the following description and in
Many of the details, dimensions, angles and other features shown in the Figures are merely illustrative of particular embodiments of the disclosure. Accordingly, other embodiments can have other details, dimensions, angles and features without departing from the spirit or scope of the present invention. In addition, those of ordinary skill in the art will appreciate that further embodiments of the invention can be practiced without several of the details described below.
In the Figures, identical reference numbers identify identical, or at least generally similar, elements. To facilitate the discussion of any particular element, the most significant digit or digits of any reference number refers to the Figure in which that element is first introduced. For example, element 110 is first introduced and discussed with reference to
The inner tubes 112 and the barrier tube 110 can have various sizes in accordance with the present disclosure depending on the intended application. In one embodiment, for example, the barrier tube 110 can have an outer diameter D1 ranging from about 0.3 inch to about 1.4 inches, or from about 0.5 inch to about 0.9 inch, prior to flattening and the inner tubes 112 can have a diameter D2 ranging from about 0.06 inch to about 0.8 inch, or from about 0.1 inch to about 0.4 inch, prior to flattening. In other embodiments, the inner tubes 112 and/or barrier tube 110 can have diameters D1, D2 that fall outside of these ranges. In further embodiments, all or some of the inner tubes 112 may each have different diameters.
When the heat exchanger conduit 100 is flattened, both the barrier tube 110 and the inner tubes 112 take on an oval shape, as illustrated in
In one embodiment, the inner tubes 112 and the barrier tube 110 can have wall thicknesses T1, T2 respectively, ranging from about 0.008 inch to about 0.045 inch, or from about 0.016 inch to about 0.032 inch. In some embodiments, the barrier tube thickness T1 and the inner tube thickness T2 can be the same, while in further embodiments the tube thicknesses T1, T2 can be different. The length of the heat exchanger conduit 100 can vary in different embodiments of the invention. In some embodiments, for example, the length of the heat exchanger conduit 100 can range from about 1 foot to about 100 feet, or about 3 feet to about 40 feet, depending on the intended use of the heat exchanger conduit 100. For example, for pump-assisted water heater systems, the heat exchanger conduit 100 may be about 10 feet or may be multiple sections of about 3 feet. For systems where the heat exchanger conduit 100 is placed in a tank, the tube may be longer, up to about 40 feet. In yet other embodiments, the heat exchanger conduit 100 can be manufactured in other lengths, depending on the intended application of the conduit 100.
As those of ordinary skill in the art will appreciate, the foregoing dimensions of the nested tube heat exchanger conduit 100 are merely illustrative of various embodiments of heat exchanger conduits configured in accordance with the present disclosure. Accordingly, other embodiments of the present disclosure can include flattened tubes having different diameters, heights, thicknesses, shapes, lengths, etc. depending on the particular application of use and/or a number of different variables including, for example, the wall thickness of the tube, the outer diameter of the tube, the amount of flattening, etc. Therefore, those of ordinary skill in the art will appreciate that various embodiments of the invention described herein are not necessarily limited to any particular tube configuration, but extend to all such configurations falling within the scope of the present disclosure.
In the illustrated heat exchanger conduit 100, three inner tubes 112 are nested within the barrier tube 110. In other embodiments, the heat exchanger conduit 100 can include more or fewer inner tubes 112. The heat exchanger conduit 101 in
During manufacture of the heat exchanger conduit 100, the inner tubes 112 can be placed within the barrier tube 110 using various methods. In one embodiment, for example, the barrier tube 110 can be partially pre-flattened to a height that is between its original diameter D1 and its final flattened height H1. Once the barrier tube 110 is partially pre-flattened, the inner tubes 112 can be fed inside the barrier tube 110. Once the inner tubes 112 are nested within the barrier tube 110, the entire heat exchanger conduit 100 can be flattened. In other embodiments, the inner tubes 112 may be fed into the barrier tube 110 prior to flattening the barrier tube. In another embodiment, the barrier tube 110 flattened onto the inner tubes 112 through the use of a suitable “sinking” process. As is known, sinking involves pulling a tube through a die so that the resulting tube has a smaller diameter and the same or increased wall thickness. In further embodiments, the barrier tube 110 may be formed around the inner tubes 112 by stretch reducing or twisting the barrier tube 110 through the application of the Poisson effect. Stretch reducing and/or twisting the barrier tube 110 involves increasing the length of the barrier tube 110 by stretching the barrier tube 110 longitudinally, thereby reducing the diameter of barrier tube 110 until the barrier tube 110 is flattened onto the inner tubes 112.
A number of suitable methods known in the art can be used to flatten the heat exchanger conduit 100. For example, in one embodiment the heat exchanger conduit 100 is compressed to the desired height H1 using a vice or press. In some embodiments, the heat exchanger conduit 100 is flattened using opposing rollers. The pressure drop of the inner tubes 112 can be measured after flattening to ensure that the tubes 112 remain open along their entire length.
Flattening the heat exchanger conduit 100 increases the surface contact between adjacent inner tubes 112 and between the inner tubes 112 and the barrier tube 110. This increased surface contact lowers the heat transfer resistance between fluids inside the inner tubes 112 and outside the barrier tube 110. Additionally, the flattening operation reduces the hydraulic diameter of the inner tube, which leads to high convective heat transfer rates and reduced refrigerant inventory. In one embodiment, the heat exchanger conduit 100 can be twisted. The twisting aids in forcing the inner tubes 112 and barrier tube 110 together to increase conductive heat transfer among the tubes.
When the heat exchanger conduit 100 is flattened, one or more voids 122 are created adjacent to and between the inner tubes 112. In the illustrated embodiment, the inner tubes 112 contact each other so that the voids 122 are not in fluid communication with each other (i.e. the voids are isolated from each other). The voids 122 may take on various shapes. In one embodiment, for example, at least one of the voids 122 can extend the entire length of the heat exchanger conduit 100. In other embodiments, one or more of the voids 122 can extend only part of the length of the heat exchanger conduit 100. In still further embodiments, the voids 122 can have different shapes along the length of the conduit 100, and/or some portions of the voids 122 may be in fluid communication with each other.
The first fluid 330 and second fluid 332 can be any one of numerous fluids. In one embodiment, first fluid 330 can be a working fluid, such as a refrigerant, while second fluid 332 can be potable water. In various embodiments, the first fluid 330 may be any working fluid such as, ammonia, propane, carbon dioxide, steam, or water. In other embodiments, first fluid 330 is a working fluid and second fluid 332 is air. In further embodiments, the first fluid 330 is potable water and the second fluid 332 is a working fluid and/or a gas. In yet further embodiments, the first fluid 330 and the second fluid 332 are the same fluids.
The various embodiments of heat exchanger conduits 100 described herein have several applications for use as heat exchangers. In a heat pump water heater, for instance, water is heated using hot refrigerant gases from a refrigerant compressor discharge. High pressure refrigerant or a refrigerant and oil mixture flows inside the inner tubes 112. As high pressure refrigerant is condensed, it transfers heat to a potable water stream that flows in the fluid space 324. In this embodiment, the barrier tube 110 is made of a material that is compatible with potable water such as copper. The inner tubes 112 must be made of a material and material thickness combination that can withstand the pressure and temperatures of the refrigerant. Making both tubes from copper or a copper alloy is a highly-preferred embodiment, as copper has a high conductivity, is easily formed, and can easily be joined to the other fluid system connections. As pressure is applied from the refrigerant, the higher pressure can cause the inner tubes 112 to have a tendency to round and thus press out on the barrier tube 110. The illustrated configuration has the advantage that when the inner tubes 112 are pressurized, they can press into the barrier tube 110, increasing contact and reducing any resistance to heat transfer. The barrier tube 110 can provide some resistance to this rounding tendency, which can help keep the ovalized shape of the inner tubes 112.
There are numerous other embodiments for using the heat exchanger conduit 100 as a heat exchanger. In a charge air cooler for an engine, for example, the fluid 330 flowing in the inner tubes 112 can be an engine/cooling refrigerant or bottoming cycle working fluid. The fluid 332 in the fluid space 324 outside the barrier tube 110 can be air or an air/exhaust gas mixture. In this embodiment, aluminum or stainless steel may be a preferred material for the inner tubes 112 and/or barrier tube 110. In a heat exchanger using exhaust gas, the fluid 330 flowing inside the inner tubes 112 can be potable water, a bottoming cycle working fluid, or emission reduction fluid. The fluid 332 flowing in the fluid space 324 outside the barrier tube 110 can be exhaust gas. In this embodiment, stainless steel may be a preferred material for the barrier tube 110. In another embodiment, the heat exchanger conduit may be used as a solar water heater with potable water as the outer fluid 332 flowing in fluid space 324 and a heat transfer fluid as the inner fluid 330 flowing in the inner tubes 112. In a further embodiment, the heat exchanger may again be used as a solar water heater, but with potable water as the inner fluid 330 and a heat transfer fluid as the outer fluid 332.
If the inner tubes 112 rupture during operation, the void space 122 serves as a leak containment space and the two heat transfer fluids 330, 332 do not mix. This leak-capturing feature is important in any use of the heat exchanger conduit where it would be problematic or dangerous to have the first 330 and second 332 fluids mix. When heating potable water using refrigerant, for example, having an uncontained rupture in a refrigerant tube could be toxic to the water supply. The same threat arises when potable water is heated using exhaust gases where acids and particulate from the exhaust gas could be toxic to the water. Heat exchange systems on engines or fuel cells also must maintain fluids apart from each other. Otherwise, a contaminated fluid in the power-producing unit could result in toxins in the exhaust or cause the power-producing unit to malfunction.
As with the embodiments discussed above, one or more voids 822 are created adjacent to and between the inner tubes 812 when the heat exchanger conduit 800 is flattened. In some embodiments, the inner tubes 812 contact each other and the voids 822 are not in fluid communication with each other. The voids 822 may take on various shapes. In one embodiment, for example, at least one of the voids 822 can extend the entire length of the heat exchanger conduit 800. In other embodiments, one or more voids 822 can extend only part of the length of the heat exchanger conduit 800. In still further embodiments, the voids 822 can have different shapes along the length of the heat exchanger conduit 800.
End fittings 940 and 942 are attached to opposite ends of the outer sleeve 902, fluidly sealing the outer sleeve 902 to the barrier tube 910. The end fittings 940 and 942 each have a fluid inlet and/or outlet. In the illustrated embodiment, a first fluid (e.g. a working fluid such as a refrigerant) flows through the inner tubes 912. A second fluid (e.g. a fluid to be cooled or heated by the working fluid) can enter the heat exchanger 900 through the inlet of end fittings 940, flow through the fluid space between the barrier tube 910 and the outer sleeve 902, and exit at the outlet of the end fitting 942 having been cooled or heated by the first fluid.
Forming the heat exchanger 900 into a coil can induce secondary flows in the first fluid flowing through the inner tubes 912 and in the second fluid flowing through the fluid space between the barrier tube 910 and the outer sleeve 902. Secondary flows can occur when a fluid flows through a coiled tube and can be caused by a pressure gradient between the inner wall and outer wall of the coiled tube. Secondary flows can cause increased turbulence in the first and second fluid flows, thereby increasing heat transfer between the two fluids.
From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the various embodiments of the invention. Further, while various advantages associated with certain embodiments of the invention have been described above in the context of those embodiments, other embodiments may also exhibit such advantages, and not all embodiments need necessarily exhibit such advantages to fall within the scope of the invention. Accordingly, the invention is not limited, except as by the appended claims.
The present application claims priority under 35 U.S.C. 119(e) to U.S. Provisional Application Ser. No. 61/379,484, filed Sep. 2, 2010, the disclosure of which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61379484 | Sep 2010 | US |
