Patent Application
20140048238
This patent disclosure relates generally to a heat exchanger and, more particularly, to a heat exchanger in which thermal energy from fluid in a plurality of tubes is transferred to the surrounding environment.
Heat exchangers are used in a variety of applications to transfer heat from one medium to another. A common application may be to cool a fluid for reuse in a process or application that initially heated the fluid. For example, an internal combustion engine may be associated with a heat exchanger to cool a fluid coolant that has been circulated through the engine to remove heat generated by the internal combustion process. Heat exchangers are also available in a wide variety of configuration. One common configuration includes a plurality of hollow tubes bundled together in which the process fluid can circulate before being returned to the process. In the example of the internal combustion engine, the medium to which heat is transferred to may be the surrounding environment.
A problem associated with heat exchangers arises from the thermal expansion and contraction of materials and the fact that heat exchangers by design transfer thermal energy between circuits or regions at different temperatures. The thermal difference may cause non-uniform dimensional changes in the interconnected parts of the heat exchanger that could heighten thermal stresses between co joined parts and which could lead to rupture or failure. One approach to mitigating the problem of thermal stress buildup in heat exchangers is described in U.S. Application Publication 2008/0011456 titled “Heat Exchanger Having Integral Elastic Regions.” The '456 publication describes using elastic sleeves or regions to interconnect different components of a heat exchanger that might be at different temperatures. The elastic regions can distort or displace to accommodate dimensional differences caused by non-uniform thermal dynamic expansion or contraction of the parts. The '456 publication, however, can require complex joining techniques to attach the different materials and requires additional elastic parts at an added cost. Accordingly, there is a need for an improved heat exchanger.
The disclosure describes, in one aspect, a frameless heat exchanger including a plurality of tubes each extending between a first end and a second end. The plurality of tubes are arranged parallel to and aligned with each other to form a tube core. Each tube can be attached to an adjacent tube at the respective first and second ends. At least some of the plurality of tubes are in fluid communication with adjacent tubes in the tube core at the first ends to form a first manifold and at least some of the plurality of tubes are in fluid communication with adjacent tubes at the second ends to form a second manifold. The plurality of tubes and the first and second manifolds are interconnected for relative movement of the plurality of tubes to accommodate thermal expansion and contraction of the plurality of tubes.
In another aspect, the disclosure describes a method of assembling a frameless heat exchanger. The method includes forming a plurality of elongated, hollow tubes with each tube extending between a first end and a second end. The method further involves arranging the plurality of tubes into a tube core where each tube is substantially parallel to and longitudinally aligned with each other tube. The tubes are further arranged so that the first ends are aligned along a first side edge of the tube core and the second ends are aligned along a second side edge of the tube core. The method secures the plurality of tubes together by joining the first ends with each other and joining the second ends with each other such the primary structural connection between the plurality of tubes is at the first ends and the second ends.
In further aspect, the disclosure describes a frameless heat exchanger for transferring heat from a fluid circulating therein to a surrounding environment. The heat exchanger includes a plurality of elongated, straight hollow tubes extending between a first end and a second end to define a longitudinal axis. The plurality of tubes are arranged substantially, parallel to and aligned with each other along their longitudinal axes to form a tube core. Each tube may have a generally flat cross-section normal to the longitudinal axis with the flat-cross section defining opposing upper and lower surfaces of the tube. A cup-shaped upper boss may be disposed at each of the first and second ends protruding upwards from the upper surface. Additionally, a cup-shaped lower boss is disposed at each of the first and second ends protruding downwards from the lower surface. The upper bosses and the lower bosses are aligned at the first ends to form a first bellows manifold, and the upper bosses and the lower bosses are aligned at the second ends to form a second bellows manifold. The tube core is structurally supported by the plurality of tubes and the first and second bellows manifolds
This disclosure relates to heat exchangers for exchanging heat between two or more mediums, typically fluids. Although the specific examples of heat exchangers described herein are typically intended for use with internal combustion engines, heat exchangers in accordance with the disclosure can more broadly be used in any appropriate application or process such as heating and cooling applications, energy production, chemical and material processing, etc. The specific heat exchangers described herein typically function by transferring heat from a first fluid circulating inside the heat exchanger to a second fluid such as atmospheric air surrounding and flowing over the surfaces of the heat exchanger. The transfer mechanism is commonly referred to as convection although the specific details of the thermodynamic transfer mechanism should not be considered a limitation on the claims. In some embodiments, the process may be reversed so that heat from the surrounding environment is transferred to the fluid circulating in the heat exchanger to raise its temperature.
Referring to
To structurally support and protect the tubes 12, the first and second manifolds 16, 18, and the thin-walled fins 20, the prior art heat exchanger 10 includes a top plate 22, an opposing bottom plate 24 and first and second side plates 26, 28 that are arranged about and rigidly secured to the tube core 14. The plates 22, 24, 26, 28 can be made from rigid, structural steel and can be welded together to form a support frame 30 disposed about the rectangular perimeter of the tube core 14. Welding, rivets and/or threaded fasteners can be used to rigidly attach the support frame 30 to the tube core 14 and first and second manifolds 16, 18. The plates 22, 24, 26 and 28 can be made from the same or different materials as the tubes 12 and can have different thickness dimensions.
A problem arising with the prior art heat exchanger 10 is that the tubes 12 and the manifolds 16, 18 may undergo thermal expansion and contraction due to the heated fluids circulating therein in a non-uniform manner with respect to the support frame 30. For example, the parallel tubes 12 may increase in length by a larger dimension than the top or bottom plates 22, 24, which are not in direct contact with the heated process fluids, causing thermal and mechanical stresses to build in the heat exchanger as the support frame 30 constrains the enlarged tubes. Additionally, the support frame 30 may be made of a different material having a different coefficient of thermal expansion than the tube 12 or may have different dimensions so as to respond differently than the tubes. These stresses can concentrate in stress regions 40 located proximate to the joints and attachment points between the tube core 14 and the support frame 30 which may occur at the four corners of the rectangular support frame. If severe enough, the thermal stresses can cause the joints and/or attachment points to fracture or rupture leading to failure of the heat exchanger. Similar problems arise if the process is reversed and the fluid circulating in the tubes is cooled with respect to the environment. As described above, prior art methods to mitigate this problem often involve the use of elastic joints and the like, with resulting drawbacks.
Referring to
To establish fluid communication between the heat exchanger 100 and its associated process or application, the heat exchanger can include a first manifold 120 disposed along the first side edge 116 of the tube core 110 and a second manifold 122 disposed along the second side edge 118. The first and second manifolds 120, 122 can be generally vertical and define a respective first manifold axis 124 and a second manifold axis 126. Further, the first and second manifolds 120, 122 can extend along the height of the tube core 110 so that they are perpendicular to the plurality of tubes 102 and the first and second manifold axis 124, 126 are perpendicular to the longitudinal direction 108 of the tubes. The first manifold 120 can function as an intake manifold receiving heated fluid from the process and directing it to the tubes 102 and the second manifold 122 can function as an outlet manifold receiving the cooled fluid from the tubes and returning it to the process. To physically connect with hose lines or such from the associated process, the first manifold 120 and the second manifold 122 can include a respective first and second threaded hose fittings 130, 132 disposed proximate the top edge 112 of the tube core 110.
Fluid can circulate through the heat exchanger 100 by entering the first manifold 120, passing longitudinally through the tubes 102, and exiting the second manifold. Air or another medium moving or flowing perpendicularly to the tube core 110 can pass through the spaced-apart tubes 102, adsorbing heat by convection and transferring the absorbed heat away from the heat exchanger 100. To facilitate heat transfer by increasing the surface area available for cooling, a plurality of fins 134 may be disposed between the spaced-apart tubes 102 and may extend between the first and second manifolds 120, 122. The fins 134 can be formed from thin-walled corrugated metal undulating between adjacent tubes 102 conveying the heated fluid.
To accommodate or militate against thermal cycling, the resulting dimensional changes, and thermal stress buildup, the heat exchanger 100 can be designed so that the tubes 102 can freely expand and contract along their longitudinal axes 108 with respect to each other and the first and second manifolds 120, 122. In one embodiment, this can be accomplished by eliminating the support frame including the top and bottom plates and the side plates. The support frame therefore no longer constrains expansion of the bundle of tubes. The individual tubes 102 are free to expand and contract along their longitudinal direction 108 to reestablish the lengthwise dimension of the tube core 110 given by the distance between the first and second side edges 116, 118. Additionally, elimination of the support frame also eliminates the attachment points and joints where thermal and mechanical stress could concentrate.
In this embodiment, the plurality of tubes 102 in the tube core 110 is generally self-supporting and provides structural rigidity for the heat exchanger 100. To increase structural rigidity in the absence of the support frame, one or more tubes among the plurality of tubes can be reinforced and can accommodate increased structural loads. In particular, referring to
In one embodiment, the reinforced first tube 140 can be disposed along the top edge 112 of the tube core 110 while the standard second tubes 150 can make up the remainder of the tubes in the tube core. In a further embodiment, another reinforced first tube 140 can be disposed along the bottom edge 114 of the tube core 110. In yet a further embodiment, at least three reinforced tubes 140 can be disposed throughout the tube core 110, e.g., along the top edge 112, the bottom edge 114 and therebetween. The reinforced first tubes 140 provide structural rigidity to maintain the rectangular shape of the heat exchanger while allowing for relative expansion and contraction of the standard second tubes 150 in the lengthwise direction. The reinforced first tubes 140 can act as the primary structural support in the longitudinal direction 108 between the spaced-apart first and second manifolds 120, 122. The reinforced first tubes 140 may also function to absorb or redirect the thermal stresses along the longitudinal direction 108. Additionally, the fins 134 can be removed from an uppermost surface of the first tubes 140 along the top edge 112 and from a lowermost surface of a first tube at the bottom edge 114 to simplify handling and prevent their damage.
To further accommodate expansion and contraction of the tubes 102, in the embodiment illustrated in
To enable flexible bending of the first and second manifolds while providing support for the heat exchanger, in an embodiment, the manifolds can be constructed as bellows-style manifolds. Referring to
Disposed at the first ends 104 of each tube 102 can be an upper boss 170 protruding upwards from the upper surface 162 and a lower boss 172 protruding downwards from the lower surface 164 such that the upper and lower bosses are generally aligned along the first manifold axis 124. The upper and lower bosses 170, 172 are hollow, made from thin-walled material and can have a domed or rounded cup-like shape with a decreasing diameter as they protrude away from the respective upper and lower surfaces 162, 164. The upper boss 170 of one tube 102 can merge or join with the lower boss 172 of an adjacent tube so that together the two form an hourglass contour that maybe referred to as a bellows 174. The hourglass shape and the thin-walled construction of the bellows 174 permits a degree of distortion to accommodate relative movement between adjacent tubes 102 and flexibility of the first and second manifolds 120, 122. For example, the contoured hourglass shape of the bellows 174 may allow the upper boss 170 to tilt with respect to the lower boss 172, enabling the entire manifold 120 to bend with respect to the first manifold axis 124. Additionally, the shape of the bellows 174 may allow a degree of expansion and contraction vertically in the direction indicated by the first manifold axis 124. To allow fluid to flow between adjacent tubes 102, referring to
In the embodiment in which all the bellows both align along the manifold axes are in continuous fluid communication, the flow pattern or circuit through the heat exchanger may be referred to as a single pass pattern. As illustrated in
Referring to
To facilitate installation of the heat exchanger 200 in the absence of a support frame, a first side bracket 250 and a corresponding second side bracket 252 can be disposed along the respective first side edge 216 and second side edge 218 of the heat exchanger. The side brackets 250, 252 can be stamped or pressed from sheet metal or plate metal into a C-shaped or U-shape with three integral walls 254 bent at 90° angles to each other and that define an internal channel 256. When the first side bracket 250 is attached to the heat exchanger 200, the first side edge 216 can be received in the internal channel 256 so that the three integral walls 254 generally encompass the first manifold 220. The first side bracket 250 thereby protects the first manifold 220 from puncture or the like. The second side bracket 252 can be similarly disposed about the second side edge 218 and encompasses the second manifold 222. To physically attach the heat exchanger 200 to an attachment surface or the like, the first and second side brackets 250, 252 each can include a respective first and second ear-like, protruding mounting flange 260, 262 aligned with the longitudinal direction 208 and directed away from the tube core 210. The first and second mounting flanges 260, 262 can be flush with a face of the tube core 210 so as to install the bracket flush against a surface.
The first and second mounting flanges 260, 262 can include apertures 264 disposed therein that can receive mounting bolts, rivets, etc., to physically secure the heat exchanger to an installation feature on an associated machine or process. The dimensions and the locations of the apertures 264 can correspond with the installation patterns on prior art heat exchangers to facilitate retrofitting of existing machines or processes with the new heat exchangers. For example, a prior art heat exchanger having a support frame rigidly supporting a plurality of tubes and manifolds as described with respect to
To ensure the first and second side brackets 250, 252 do not interfere with thermal-induced dimensional changes of the plurality of tubes 202 or the flexibility of the first and second manifolds 220, 222, the attachment between the side brackets and the heat exchanger 200 can be flexible and/or provide for play to allow relative motion between the brackets and the tube core. One of the three integral walls 254 can have one or more elongated slots 266 disposed through it to provide access to the respective first or second side edge 216, 218 of the tube core 210. The slots 266 can receive an appropriately located rod-like extension member such as a bolt or a dowel pin securely joined to and protruding from the tube core 210. Further, the slots 266 can be larger than the bolt or pin to allow relative motion of the bolt or pin within the static slots. In some embodiments, rubber or an elastomer can be disposed between the bolt or pin and the slots to dampen the relative motion as part of a feature sometimes referred to as an isolation mount. The slots 266 can allow for longitudinal and vertical motion of the tube core 210 with respect to the brackets 250, 252 that may be rigidly secured to an installation.
The present disclosure is applicable to heat exchangers in general and particularly to heat exchangers that cool a process fluid heated by an associated application such as an internal combustion engine and that returns the fluid to the application. Referring to
To accommodate thermal expansion and contraction of the tubes, in an embodiment, the plurality of the tubes 102 can be grouped into reinforced first tubes 140 and standard second tubes 150. The reinforced first tubes 140 can be disposed at a top edge 112 of the heat exchanger 100 and can provide structural rigidity in the longitudinal direction 108 while allowing the standard second tubes 150 to expand and contract. In another embodiment, the first and second manifolds 120, 122 can be flexible so that they can bend in concave and convex directions as the plurality of tubes expand and contract. To improve the flexibility of the manifolds, the manifolds can be formed to function as bellows.
It will be appreciated that the foregoing description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. All references to the disclosure or examples thereof are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to certain features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context.
