Patent Publication Number: US-2010116466-A1

Title: Axial Heat Exchanger for Regulating the Temperature and Air Comfort in an Indoor Space

Description:
FIELD OF THE INVENTIONS 
     The present invention relates to an axial heat exchanger for exchanging heat between two mediums, preferably a gas medium and a liquid medium and most preferably air and water. More particularly, the invention relates to a heat exchanger for regulating the air temperature and the air comfort in a defined space, preferably in an indoor space and more particularly to a heat exchanger that is suitable for exchanging heat between a slowly flowing gas medium and a flow of a fluid or liquid medium having a low temperature difference. 
     BACKGROUND OF THE INVENTIONS 
     1. Introduction 
     Transfer of heat is a very common operation in connection with natural and human induced activities. Heat transfer mainly depends on three different mechanisms, namely conduction, convection and radiation. 
     Heat transfer by conduction is essentially characterized by no observable motion of matter. In metallic solids there is motion of unbound electrons and in liquids there is transport of momentum between molecules and in gases there is molecular diffusion (the random motion of molecules). Heat transfer by convection is essentially a macroscopic phenomenon that arises from the mixing of fluid elements, wherein natural convection may be caused by differences in density and forced convection may be caused by mechanical means. Heat transfer by radiation is essentially characterized by the presence of electromagnetic waves. All materials radiate thermal energy. When radiation falls on a second body it will be transmitted reflected or absorbed. Absorbed energy appears as heat in the body. 
     Transfer of heat in most heat exchangers takes place mainly by conduction and possibly convection as heat passes through one or several layers of material to reach a flow of heat absorbing fluid or gas. However, other transferring mechanisms may be involved to some extent. The layer or layers of material are normally of different thicknesses and with different thermal conductivities. Consequently, knowledge of the overall heat transfer coefficient is essential in the design of a heat exchanger. With known overall heat transfer coefficient the required heat transfer area is calculated by an integrated energy balance across the heat exchanger. 
     Heat exchangers are available in a number of various designs. The most common types are the tubular heat exchanger, the plate heat exchanger and the scraped surface heat exchanger. The choice of construction material differ depending on application. In the food industry the predominant materials are stainless or acid proof steel or even more exotic materials like titanium, the latter typically for fluids containing chlorides. In other industries heat exchangers made out of mild steel may be sufficient. 
     Plate heat exchangers are often used on low-viscous applications with moderate demands on operating temperatures and pressures, typically below 150° C. and 25 bars. Gasket material is chosen to withstand the operating temperature at hand and the constituents of the processing fluid. In the food industry plate heat exchangers are typically used for milk and juice pasteurisers operating at temperatures below 100° C. and pressures below 15 bars. 
     Tubular heat exchangers are typically used in applications where the demands on high temperatures and pressures are significant. Also, tubular heat exchangers are employed when the fluid contains particles that would block the channels of a plate heat exchanger. In the food industry tubular heat exchangers are typically used for milk and juice sterilisers operating at temperatures up to 150° C. Tubular heat exchangers are also used for moderate to high-viscous and particulate products, e.g. tomato salsa sauce, tomato paste and rice puddings. In some of these cases the operating pressure can exceed 100 bars. Particles up to 10-15 mm in size can be treated in tubular heat exchangers without problems. 
     Scraped surface heat exchangers are used in applications where the viscosity is very high, where big lumps are part of the fluid or where fouling problems are severe. In the food industry scraped surface heat exchangers are used e.g. on products like strawberry jam with whole strawberries present. 
     The treatment in the heat exchanger is so gentle and the pressure drop so low that the berries will pass the system with only very little damage. The scraped surface heat exchanger is, however, the most expensive solution and is therefore used only when plate heat exchangers and tubular heat exchangers would not perform adequately. 
     2. Related Art 
     US2006231242 disclosed an axial heat exchanger that is suitable for exchanging heat between a slowly flowing gas medium and a flow of a fluid or liquid medium having a low temperature difference, and they are particularly unsuitable as heat exchangers for regulating the temperature of air slowly flowing through the exchanger for the purpose of regulating the temperature and air comfort in a defined space, preferably in an in door space. This heat exchanger is provided with an elongated and substantially axially extending outer channel that is adapted to enclose a flow of a first gas medium. The heat exchanger also comprises a plurality of substantially parallel inner channels that are adapted to enclose a flow of a second liquid medium. The inner channels are arranged inside the outer channel so as to extend substantially axially along the inside of said outer channel for enabling a transfer of heat between said first gas medium and said second liquid medium. The heat transfer is improved to some extent as the number of inner channels increases and it is further improved in that at least one of the inner channels is joined with at least one elongated sheet. The sheet is arranged to extend substantially axially along the inner channel so as to substantially coincide with the direction of f low of the first gas medium through the outer channel. 
     SUMMARY 
     The heat exchanger disclosed below provides for an increased heat exchanging surface. The sheet members or fins that are connected to the inner channels are shaped to exploit the available space in a better way and fit better into a tubular outer channel. Due to the shape and positioning of the fins the amount of dead space—in particularly near the wall of the tubular outer channel—is reduced. The proposed fin structure can easily be applied to existing heat exchangers. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an inner heat exchanging structure  100  according to a first embodiment of the present invention. 
         FIG. 2  is a perspective view of the cross-section of the inner heat exchanging structure  100  in  FIG. 1B  substantially cut along the line X-X. 
         FIG. 3  shows a plurality of axial heat exchangers A 1  according to the first embodiment of the invention shown in  FIGS. 1B and 2 . 
         FIG. 4  is a perspective view of an inner heat exchanging structure  100  according to a second embodiment of the present invention. 
         FIG. 5  shows a schematic cross-section of the heat exchanger A 1  shown in  FIGS. 1 and 2 . 
         FIG. 6  shows a schematic cross-section of the heat exchanger according to a third embodiment of the present invention. 
         FIG. 7  shows a schematic cross-section of an axial heat exchanger according to a fourth embodiment of the present invention. 
         FIG. 8  shows a schematic cross-section of an axial heat exchanger according to a fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTIONS 
       FIG. 1  is a perspective view showing an inner heat exchanging structure  100  according to a first embodiment of the present invention. The inner heat exchanging structure  100  in  FIG. 1  is also shown in  FIG. 2 , substantially cut along the line X-X in  FIG. 1  to uncover a perspective view of the cross-section of the inner heat exchanging structure  100 . The inner heat exchanging structure  100  is shown in  FIG. 2  arranged inside an outer channel structure  200 . The outer channel structure  200  and the enclosed inner heat exchanging structure  100  in  FIG. 2  forms an axial heat exchanger A 1  according to a first embodiment of the present invention. The outer channel may be received in an insulation body (not shown). 
     The exemplifying outer channel structure  200  shown in  FIG. 2  has a cylindrical or tubular shape. The inner diameter of the exemplifying outer channel  200  may be approximately 100-500 millimeters, more preferably approximately 100-300 millimeters and most preferably approximately 100-200 millimeters. The wall of the outer channel  200  may have a thickness of a few millimeters, preferably less than two millimeters. Other wall thicknesses and other diameters are clearly conceivable. The length of the exemplifying outer channel  200  may be approximately 400-3000 millimeters, more preferably approximately 500-2000 millimeters and most preferably 600-1500 millimeters, though other lengths are clearly conceivable. The shape and cross-section of the outer channel structure  200  may evidently differ, as long as it encloses the inner heat exchanging structure  100  in a way that enables a first medium to flow along the axial heat exchanger A 1  between the sheets (fins)  110  of the inner heat exchanging structure  100  and the wall of the outer channel structure  200 . The outer channel structure  200  is adapted to contain a flow of a gas medium, preferably air or a similar gas. The medium channels  210  are also indicated in the schematic cross-section of the axial heat exchanger A 1  shown in  FIG. 5 . It can be observed that the medium (e.g. air) may flow in one or the other of the two possible directions inside the outer channel  200 . 
     The wall of the outer channel structure  200  in  FIG. 2  is preferably made of a light weight material, e.g. a light metal as aluminum or a plastic material, a carbon fiber material or similar. It is also preferred that the wall of the outer channel structure  200  is comparably thin. A canvas, a cloth, a foil, a film or any similar suitable thin sheet material may therefore form the outer channel structure  200 . The sheet material may e.g. be made of metal, rubber, plastic or a fabric or similar. Consequently, a preferred embodiment of the outer channel structure  200  may e.g. have a wall that is made of a plastic cloth, a plastic foil or some similar substantially medium-tight (e.g. air-tight) cloth material or similar having a small weight. The sheet material is preferably wrapped or otherwise arranged around the outside edges of the inner heat exchanging structure  100  so as to form an outer channel structure  200  that encloses the inner heat exchanging structure  100 . The sheet material may e.g. be a shrink wrap or even a shrinking tubing that is heated to shrink and fit on the outside of the inner heat exchanging structure  100 . 
     The enclosing outer channel  200  has now been discussed in some detail and the attention is again directed to the inner heat exchanging structure  100  of the heat exchanger A 1  shown in  FIG. 2 . It is clear from  FIG. 2  that the heat exchanging structure  100  comprises five fins  110  shaped as thin sheets. At least four of these fins  110  are clearly shown in  FIG. 1 . The sheet or fin  110  may have a thickness of some tenths of a millimeter to a few millimeters, preferably less than two millimeters. 
     The sheets or fins  110  in  FIG. 1-2  extend in a first axial direction that is substantially parallel to the axial extension and/or the centre axis X 1  of the inner heat exchanging structure  100  in  FIG. 1  and the outer channel  200  in  FIG. 2 . The fins  110  extend substantially along the whole length of the inner heat exchanging structure  100 . As can be seen in  FIG. 2 , the fins  110  of the heat exchanging structure  100  arranged in the axial heat exchanger A 1  are extending in the axial extension of the outer channel structure  200 , so as to substantially coincide with the direction of flow of a medium that flows within the enclosing outer channel structure  200 . 
     The sheets or fins  100  have first component  112  and a second component  114 . The first component  112  of the sheets or fins  110  in  FIGS. 1 and 2  extends in a radial direction, in addition to extending in an axial direction as previously explained. The radial direction extends substantially outwards from the centre or centre axis of the heat exchanging structure  100  towards the outer channel structure  200 . This extends ends at a distance from the outer channel wall. The second component  114  of the sheets or fins  110  extends along the wall of the outer channel  200 , i.e. substantially tangentially from the end of the first component  112  near the outer channel structure. The second component is in the shown embodiment curved, with a curvature identical or similar to the curvature of the outer channel. However, the second component could also be a not curved panel, as disclosed with the second embodiment below, or could be formed by two or more panels that are connected to one another at an angle (not shown) to approximate the curve of the outer wall. 
     Preferably, the first component  112  and the second component  114  of the sheet or fin  110  are formed from a singe piece of sheet material by bending or other shaping process. Alternatively, the first  112  and second component are made from two parts that are connected to one another by suitable know techniques. 
     The second component  114  leaves a small gap to the channel structure  200 . 
     Even though the exemplifying fin  110  in the heat exchanging structure  100  in  FIG. 2  is a straight rectangular sheet arranged in parallel with the extension of the outer channel  200 , certain embodiments of the present invention may have sheets or similar that are curved or twisted. For example, sheets that extend in a spiral pattern or similar along the inside of the outer channel structure  200  or similar, or sheets that form one or several medium channels—comparable to the medium channels  210  in  FIGS. 2 and 6   a —which channels e.g. extend in a spiral shaped structure along the inside of an axial outer channel  200  or similar. 
     The fins  110  in  FIGS. 1-2  are made of a heat conductive material, preferably a metal and more preferably a lightweight metal as aluminum or similar. The material can be provided with indentations or the like (not shown) to improve the stability and rigidity of the sheet and to enhance turbulence in the flow along the surface of the sheets or fins  110 . 
     Each fin  110  is joined with an inner small, straight and preferably tubular channel  120  that is positioned in the middle or near the middle of the fin  110 . The wall of the exemplifying inner channel  120  may have a thickness of a few tenths of a millimeter to a few millimeters, preferably less than one millimeter, whereas the inner diameter of the inner channel  120  may be approximately 4-20 millimeters, preferably approximately 5-15 millimeters and most preferably approximately 6-10 millimeters. Other wall thicknesses and other diameters are clearly conceivable. The inner channel  120  is preferably made of the same heat conductive material as the fin  110  or a similar material that enables a good transport of heat between the inner channel  120  and the fin  110 . The straight inner channel  120  extends along the entire rectangular fin  110  from one short end to the other. The inner channel  120  is preferably adapted to contain a flow of a fluid or liquid medium, preferably water. 
     It should be added that the present invention is not limited to the channels  120  in  FIGS. 1-2 . On the contrary, a channel may have a cross-section that is circular or oval as well as partly circular and/or partly oval, or that is triangular, quadratic, rectangular or otherwise polygonal, or a cross-section that is a combination of these examples. Moreover, a fin  110  may be joined with a channel in other positions and/or according to other patterns. For example a channel may be joined with a fin  110  so as to extend along the fin  110  in an s-shaped pattern from one short end to the other. A sheet or a fin  110  or similar may also be provided with two or more channels without departing from the scope of the invention. 
     The perspective view in  FIG. 1  shows that the heat exchanging structure  100  is provided with a lower distribution manifold  130  extending radially out of the heat exchanging structure  100 . The lower distribution manifold  130  is connected to a lower distribution channel  140  that in turn is connected to the lower end of each channel  120  in the fins  110  by means of curved lower tubular connecting channels  122  arranged at the lower end of the heat exchanging structure  100 . The upper end of each channel  120  in the fins  110  is in turn connected to an upper distribution hub  150  by means of a curved upper tubular connecting channel  121  arranged at the upper end of the heat exchanging structure  100 . The upper collecting hub  150  is in turn connected to a center channel  160  that extends axially downwards from the collecting hub  150  substantially coinciding with the centre axis of the heat exchanging structure  100 . The wall of the exemplifying center channel  160  may have a thickness of a few tenths of a millimeter to a few millimeters, preferably less than two millimeters, whereas the inner diameter of the center channel  160  may be approximately 20-100 millimeters, preferably approximately 25-75 millimeters and most preferably approximately 25-50 millimeters. Other wall thicknesses and other diameters are clearly conceivable. The lower end of the center channel  160  has a curved section  161  that terminates the center channel  160  in a center-channel manifold  170 , which extends radially out of the heat exchanging structure  100  at the lower end, preferably below the fins  110  and preferably below the lower distribution manifold  130 . 
     Such properties as the diameter and wall thickness of the outer channel  200 , the diameter and wall thickness of the inner channels  120 , the shape and thickness of the fins  110 , the choice of material for the outer channel  200 , the inner channels  110  and the fins  110  can easily be adapted in a well known manner by a person skilled in the art, so as to fit the application in question, e.g. depending on the temperature, the density, the viscosity, the pressure, the flow rate etc. of the medium that is supposed to flow through the outer channel  200  and the medium that is supposed to flow through inner channels  110 . 
     Exemplifying Cross-Sections 
     As indicated above, the fins  110  or sheets or similar in an axial heat exchanger A 1  according to an embodiment of the present invention may be arranged according to different patterns having different cross-sections, wherein the fins  110  or sheets or similar are extending in the axial extension of an outer enclosing channel  200 , so as to substantially coincide with the direction of flow of a medium that flows within the outer channel  200 . 
     A small number of schematic cross-sections are given below to illustrate the variety of possible cross-sections. 
       FIG. 5  shows a schematic cross-section of the previously discussed heat exchanger A 1  in  FIGS. 1-2 , wherein the same numerals denote the same objects in all the  FIGS. 1-2  and  6   a.    
       FIG. 6  shows a schematic cross-section of another possible pattern for arranging the fins or sheets within an outer channel of an axial heat exchanger according to an embodiment of the present invention. This third embodiment has no central inner channel  60 . 
       FIG. 7  shows a schematic cross-section of an axial heat exchanger according to fourth that is essentially the same as the previously discussed axial heat exchanger A 1  shown in  FIGS. 1-2 . However, the outer channel  200  of the heat exchanger A 1  with a circular cross section has been replaced in  FIG. 6   d  by an outer channel structure  600  with a hexagonal cross section. The shape of the second components of the sheets  110  has been adapted correspondingly. 
       FIG. 8  shows the same axial heat exchanger as the one shown in  FIG. 7 , with the exception that the axial heat exchanger in  FIG. 8  has four fins  110  instead of six fins  110  as in the heat exchanger shown in  FIG. 7 . It is especially advantageous to provide the rectangular axial heat exchanger in  FIG. 6   f  with an outer rather thick protective cover consisting of a foamed plastic or a cellular plastic. This offers superior properties for transportation and storing. The protective cover may remain on the heat exchanger after installation of the exchanger. 
     A few schematic cross-sections have been briefly been discussed to illustrate the variety of possible embodiments of the present invention. However, other embodiments of the axial heat exchanger of the present invention may have fins or sheets that are arranged according to other suitable patterns that may or may not extend around the centre axis of an inner heat exchanging structure (e.g. the centre axis of the inner heat exchanging structures  100 ,  300 ), e.g. according a triangular, quadratic, rectangular, circular or semicircular pattern. 
     Operation and Use of Axial Heat Exchangers According to Embodiments of the Invention 
     A first medium is supplied to the axial heat exchanger A 1  trough the lower distribution manifold  130  and the lower distribution channel  140 , from which the media flows into the channels  120  in the fins  110  and on to the upper distribution hub  150  and from there back through the center channel  160  that terminates in the center-channel manifold  170  from which the medium will be discharged from the heat exchanger A 1 . A second medium is supplied so as to flow through the heat exchanger A 1  along the axial channel or channels  210  arranged in the space between the outer channel structure  200  and the inner heat exchanging structure  100 . Heat will consequently be exchanged between the first and second media via the fins  110  arranged on the heat exchanging structure  100 , provided that there is a temperature difference between the two media. 
     The first medium may flow in a direction that is opposite to the direction indicated above. The second media may flow by means of natural convection through the channel or channels  210 , especially in embodiment wherein the inner diameter of the outer channel structure  200 , is comparably large, e.g. 100-200 millimeters or more. In other words, some embodiments of the present invention may not need a fan or similar to propel the second media, whereas a fan or similar may be preferred or needed in other embodiments. 
     Axial heat exchangers according to the present invention can be used in a variety of different applications and in a variety of structures. In particular, a plurality of axial heat exchangers according to the invention may particularly be used connected in series or connected in parallel. 
       FIG. 4  shows a plurality of axial heat exchangers A 1  according to the first embodiment of the invention as discussed above in connection with  FIGS. 1-2 . The heat exchangers A 1  have been arranged in parallel to enable a substantially simultaneous flow of a first medium (preferably air) through each the heat exchanger A 1  along the medium channel or channels  210  as discussed above in connection with  FIG. 2 . The heat exchangers A 1  must not be arranged side by side along a straight line as in  FIG. 5   b.  On the contrary, the heat exchangers A 1  may be arranged side by side in a circle or in a semi-circle, or in a square or according to some other polygonal pattern. 
     Each parallel heat exchanger A 1  in  FIG. 5   b  have been coupled to a supply channel arrangement extending along the parallel heat exchangers A 1  for providing each exchanger with a second medium (preferably water). Accordingly, the lower distribution manifold  130  of each heat exchanger A 1  has been coupled to a first supply channel  710 , whereas the center-channel manifold  170  of each heat exchanger A 1  has been coupled to a second supply channel  720 . The supply channel arrangement  710 ,  720  and the medium tempering source  700  shown in  FIG. 5   b  can be the same as those previously described in connection with  FIG. 5   a.    
     Dashed lines in  FIG. 3  illustrate a box-like distribution channel  730 . Such a shared distribution channel  730  or similar may be arranged to cover one end of every parallel heat exchanger A 1  for enabling a substantially parallel and possibly forced flow of a first medium through each parallel heat exchanger A 1 . The distribution channel  730  in  FIG. 5   b  is arranged at the upper end of the parallel heat exchangers A 1 . It should be emphasized that the lower ends may be covered instead or as well. The upper ends in  FIG. 5   b  may protrude a suitable distance into apertures (not shown) that have been arranged in the long-side of the box-like distribution channel  730  facing towards the parallel heat exchangers A 1 . The parallel heat exchangers A 1  can be substantially sealed towards the outer side of the distribution channel  730  and the heat exchangers A 1  are preferably fully open towards the inside of the distribution channel  730 . The first medium can be provided to the distribution channel  730  from a supply channel (not shown) connected to the distribution channel  730 . The arrow  740  in  FIG. 5   b  indicates a possible direction of flow of the first medium into the distribution channel  730 . 
       FIG. 4  illustrates a second embodiment of the invention, which is a variation of the first embodiment with the main difference being in the second component  114  of the sheets  10  being not curved, i.e. plainer plates. 
     According to an embodiment, the heat exchanger is provided with only a single, preferably central inner channel. 
     The sheet member  110  has been shown as an L-shaped components but a T-shape is also within the scope of the invention. 
     The large heat exchanging surfaces that can be obtained in an axial heat exchanger according to the present invention makes it possible to operate with low temperature differences between the first medium and the second medium. For example, embodiments of the present invention can operate with a comparable low difference in temperature between heating water and heated air flowing through and out from the exchanger or exchangers for creating a comfortable temperature in a defined space, e.g. in a room or a similar indoor space. A heat exchanger according to an embodiment of the present invention can certainly be adapted to use air having an input temperature as low as −18° C. to produce air having an output temperature as high as +18° C. by utilizing heated water or similar having an temperature as low as +35° C. In a heat exchanger according to the present invention can generally be adapted to enable heating of indoor spaces and similar by utilizing heated water having a temperature below +40° C. This should be compared to the water temperature supplied to radiators in ordinary hot-water heating systems, which in general is approximately +55° C. and which may be as high as +75° C. in a cold winter day when the outdoor temperatures is as low as e.g. −18° C. 
     The various aspects of what is described above can be used alone or in various combinations. The teaching of this application is preferably implemented by a combination of hardware and software, but can also be implemented in hardware or software. The teaching of this application can also be embodied as computer readable code on a computer readable medium. It should be noted that the teaching of this application is not limited to the use . . . . 
     The teaching described above has numerous advantages. Different embodiments or implementations may yield one or more of the following advantages. It should be noted that this is not an exhaustive list and there may be other advantages, which are not described herein. One advantage of the teaching of this application is that it provides for a heat exchanger that suitable for exchanging heat between a slowly flowing gas medium and a flow of a fluid or liquid medium having a low temperature difference that has an increased heat exchange surface. Another advantage of the teaching of this application is that it provides for a heat exchanger that is suitable for exchanging heat between a slowly flowing gas medium and a flow of a fluid or liquid medium having a low temperature difference with a flange system that fits better into a tubular outer channel. Yet another advantage of the teaching of this application is that that it provides for a heat exchanger that is suitable for exchanging heat between a slowly flowing gas medium and a flow of a fluid or liquid medium having a low temperature difference that allows for heat exchange with fluid that is not flowing near a radial fin, i.e. shorter average distance between the metal and the gas medium without causing too much friction. A further advantage of the teaching of this application is that that it provides for a heat exchanger that is suitable for exchanging heat between a slowly flowing gas medium and a flow of a fluid or liquid medium having a low temperature difference that is easy to retrofit to existing heat exchangers. Another advantage of the teaching of this application is that that it provides for a heat exchanger that is suitable for exchanging heat between a slowly flowing gas medium and a flow of a fluid or liquid medium having a low temperature difference that is constructed with few joints or creases. 
     Although the teaching above has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the teaching. 
     The term “comprising” as used in the claims does not exclude other elements or steps. The term “a” or “an” as used in the claims does not exclude a plurality. The single processor or other unit may fulfill the functions of several means recited in the claims.