Abstract:
A heat exchanger is disclosed for cooling a gas from a first temperature to a second temperature. The exchanger comprises a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber. The first heat exchanging chamber comprises an inlet for receiving a coolant into the chamber and an outlet through which the coolant can exit the first chamber, the coolant being arranged to pass over the portion of the heat pipes which extend within the first chamber. The second heat exchanging chamber comprises an inlet for receiving the gas at a first temperature into the chamber and an outlet through which the gas can exit the second chamber at a second temperature. The gas is arranged to pass along the second chamber between the inlet and the outlet, along a path comprising a substantially constant cross-sectional area to minimize the pressure drop between the inlet and the outlet.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional application claims the benefit of provisional application No. 61/612,251 filed on Mar. 17, 2012, entitled “Gas-to-Water Heat Exchanger”, including Appendix A, which application and appendix are incorporated herein in their entirety by this reference. 
     
    
     BACKGROUND 
       [0002]    The present invention relates to a heat exchanger and particularly, but not exclusively to a heat exchanger comprising heat pipes. 
         [0003]    A heat pipe is a hermetically sealed evacuated tube typically comprising a mesh or sintered powder wick and a working fluid in both the liquid and vapour phase. When one end of the tube is heated the liquid turns to vapour upon absorbing the latent heat of vaporization. The hot vapour subsequently passes to the cooler end of the tube where it condenses and gives out the latent heat to the tube. The condensed liquid then flows back to the hot end of the tube and the vaporization-condensation cycle repeats. Since the latent heat of vaporization is usually very large, considerable quantities of heat can be transported along the tube and a substantially uniform temperature distribution can be achieved along the heat pipe. 
         [0004]    It is known to utilize a heat exchanger comprising separated chambers and a plurality of heat pipes which extend between the chambers, such that heat can become transferred from one chamber to the other. In this respect, by passing a heated fluid through one chamber, the heat pipes can transfer the heat absorbed from the heated fluid to the other chamber wherein a cooled fluid may pass to subsequently absorb the heat from the heat pipes. 
         [0005]    However, when passing a fluid through a chamber of the heat exchanger it is found that the pressure drop between an inlet and an outlet of the respective chamber can be significant. This is found to reduce the heat transfer efficiency between the fluid and the heat pipes within the chamber with the result that the heat can rapidly increase to dangerous levels within the chamber. 
       SUMMARY 
       [0006]    We have now devised an improved heat exchanger which alleviates the above-mentioned problem. 
         [0007]    In accordance with the present invention, there is provided a heat exchanger for cooling a gas from a first temperature to a second temperature, the exchanger comprising a first heat exchanging chamber, a second heat exchanging chamber and an array of heat pipes which are arranged to extend from within the first heat exchanging chamber to within the second heat exchanging chamber; 
         [0008]    the first heat exchanging chamber comprising an inlet for receiving a coolant into the chamber and an outlet through which the coolant can exit the first chamber, the coolant being arranged to pass over the portion of the heat pipes which extend within the first chamber; 
         [0009]    the second heat exchanging chamber comprising an inlet for receiving the gas at a first temperature into the chamber and an outlet through which the gas can exit the second chamber at a second temperature; wherein, 
         [0010]    the gas is arranged to pass along the second chamber between the inlet and the outlet along a path comprising a substantially constant cross-sectional area to minimize the pressure drop between the inlet and the outlet. 
         [0011]    The provision of a substantially uniform cross-sectional area for the gas flow reduces regions of significant pressure gradients within the chamber. The heat exchanger of the present invention thus ensures a minimal pressure drop and thus a substantially uniform transfer of heat between the gas and the heat pipes at all positions within the chamber. 
         [0012]    Preferably, the second heat exchanging chamber further comprises a deflection plate which is arranged to deflect the passage of gas across the heat pipes in passing between the inlet and the outlet of the second chamber. The deflection plate is arranged to cause the gas to pass predominantly across the heat pipes as opposed to along the heat pipes to increase the thermal transfer between the heat pipes and the gas and thus the thermal transfer between the first and second chambers. 
         [0013]    The deflection plate preferably extends substantially radially of the second chamber and comprises an outer periphery which is spaced from a side wall of the second chamber. The gas is thus arranged to pass through an annular aperture defined between the outer periphery of the deflection plate and the side wall of the chamber, in passing between the inlet and the outlet of the second chamber. 
         [0014]    The inlet and outlet of the second chamber are preferably disposed on a longitudinal axis of the heat exchanger. 
         [0015]    Preferably, the deflection plate comprises a gate disposed therein which is arranged to open and close a central region of the deflection plate. The gate serves as a valve to control the passage of gas direct from the inlet to the outlet of the second chamber, through the plate. The gate preferably comprises a butterfly valve. 
         [0016]    The outlet of the first chamber preferably comprises a sensor for sensing the temperature of the liquid exiting the first chamber. The gate is preferably arranged to open and close in dependence on the sensed temperature of the liquid exiting the first chamber. 
         [0017]    Preferably, the array of heat pipes comprises heat pipes arranged in substantially concentric circular rows. The heat pipes are preferably orientated substantially parallel to each other. 
         [0018]    The rows of heat pipes preferably comprise a plurality of flow disturbers disposed at separated positions along the rows and which serve to create a turbulent flow of liquid within the row. The flow disturbers preferably comprise a plurality of rods which extend along the length of the first chamber substantially parallel to the heat pipes. Successive rods along each row are preferably disposed at opposite sides of the row to redirect the flow of liquid along the row. 
         [0019]    The first and second heat exchanging chambers are preferably separated by a separation plate, through which the heat pipes extend. Preferably, the heat pipes extend in sealing relation with the separation plate via sealing means. Preferably, the sealing means comprises a collar separately disposed around each heat pipe which is arranged to compress a sealing ring against the separation plate. 
         [0020]    The first chamber preferably further comprises a compression plate disposed above the heat pipes, which is arranged to abut the upper region of the heat pipes at one side thereof and comprises a plurality of compression springs disposed on the other side thereof. 
         [0021]    The compression springs are preferably arranged to extend against a lid of the first chamber and act to urge the compression plate against the heat pipes and thus the heat pipes within the separation plate. During operation of the heat exchanger the temperature of the heat pipes will increase and it is found that this temperature increase causes a small expansion of the heat pipes. The compression plate and springs enable the heat pipes to freely expand while maintaining a bias of the heat pipes toward the separation plate. 
         [0022]    Note that the various features of the present invention described above may be practiced alone or in combination. These and other features of the present invention will be described in more detail below in the detailed description of the invention and in conjunction with the following figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    In order that the present invention may be more clearly ascertained, some embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0024]      FIG. 1  is a longitudinal sectional view of a heat exchanger according to an embodiment of the present invention; 
           [0025]      FIG. 2  is a transverse sectional view of the heat exchanger of  FIG. 1  taken across line A-A; 
           [0026]      FIG. 3  is a transverse sectional view of the heat exchanger of  FIG. 1  taken along line B-B; 
           [0027]      FIG. 4  is a plan view of the baffle disposed within the second chamber; 
           [0028]      FIG. 5  is a magnified longitudinal sectional view of a heat pipe disposed within a separation plate, illustrating the sealing means; 
           [0029]      FIG. 6  is a magnified view of a spring disposed upon the compression plate; and 
           [0030]      FIG. 7  is a transverse sectional view of the heat exchanger of  FIG. 1  taken across line B-B, with side walls of the heat exchanger opened. 
       
    
    
     DETAILED DESCRIPTION 
       [0031]    The present invention will now be described in detail with reference to several embodiments thereof as illustrated in the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of embodiments of the present invention. It will be apparent, however, to one skilled in the art, that embodiments may be practiced without some or all of these specific details. In other instances, well known process steps and/or structures have not been described in detail in order to not unnecessarily obscure the present invention. The features and advantages of embodiments may be better understood with reference to the drawings and discussions that follow. 
         [0032]    Referring to  FIGS. 1 to 3  of the drawings, there is illustrated a heat exchanger according to an embodiment of the present invention. The heat exchanger  10  comprises a first heat exchanging chamber  11  and a second heat exchanging chamber  12 . Each chamber  11 ,  12  comprises a substantially cylindrical housing  13 ,  14 , which are mounted one on top of the other such that a longitudinal axis of the first chamber  11  extends in a substantially collinear relationship with a longitudinal axis of the second chamber  12  and thus the heat exchanger  10 . 
         [0033]    The first chamber  11  of the heat exchanger  10  is disposed above the second chamber  12  and comprises an inlet  15  and an outlet  16  which are disposed within an arcuate side wall of the housing  13 . The inlet and outlet  15 ,  16  of the first chamber  11  are arranged to enable a liquid coolant such as water, to pass into and out from the chamber  11 , respectively. The first chamber  11  further comprises a passage  17  which extends along the first chamber  11  substantially along the longitudinal axis thereof. The passage  17  is defined by a substantially cylindrical wall  18  which seals the interior of the first chamber  11  from the passage  17 , and extends between an opening  19  disposed in an upper end wall  20  of the first chamber  11  to an upper region of a separation plate  21 . 
         [0034]    Referring to  FIG. 4  of the drawings, the separation plate  21  comprises a first aperture  22  disposed substantially at the centre thereof which is arranged to align with the cylindrical wall  18  defining the passage  17 , such that the wall  18  extends substantially around a periphery of the first aperture  22 . The second chamber  12  is secured to the underside of the separation plate  21  and thus the first chamber  11 , and comprises an inlet  23  disposed substantially upon the longitudinal axis of the chamber  12 , within a lower end wall  24  thereof. The first aperture  22  disposed within the separation plate  21  and the passage  17  serve as an outlet of the second chamber  12 , such that the gas to be cooled for example, is arranged to pass into the second chamber  12  through the inlet  23  disposed in the lower end wall  24  of the second chamber  11  and out of the second chamber through the first aperture  22  and along the passage  17 . 
         [0035]    The heat exchanger  10  further comprises a plurality of substantially linear heat pipes  25  which extend from within the first chamber  11 , through an array of second apertures  26  disposed within the separation plate  21  around the first aperture  22 , and terminate in the second chamber  12  so as to enable heat to be transferred between the chambers  11 ,  12 . The heat pipes  25  extend substantially parallel to the longitudinal axis of the first and second chambers  11 ,  12  and are configured in a substantially concentric arrangement of rows of heat pipes  25 , as illustrated in  FIGS. 2 and 3  of the drawings, centered substantially on the longitudinal axis. In this manner each chamber  11 ,  12  comprises a plurality of arcuate rows of heat pipes  25 , having different radii of curvature. 
         [0036]    Adjacent circular rows of heat pipes  25  within the first chamber  11  are separated by a wall  26  which extends along the length of the first chamber  11  and defines a channel  27  along which the liquid can flow. Adjacent walls  26  comprise an aperture  28  disposed at opposite ends thereof such that the liquid is cause to flow in a clockwise direction, for example, within the channel  27  in passing across one row of heat pipes  25  substantially around the chamber  11 , before passing radially of the chamber  11  to the adjacent row of heat pipes  25 , and subsequently in a counter-clockwise direction in passing across the heat pipes  25  in the adjacent row. 
         [0037]    The channel  27  disposed in the first chamber  11  further comprises a plurality of rods  29  which extend substantially parallel to each other and the longitudinal axis of the heat exchanger  10 . The rods  29  are disposed along the channel  27  between the heat pipes  25 , and successive rods  29  along the channel  27  are disposed at opposite sides of the channel  27  to prevent the liquid from simply passing around a side of the channel  27  without significantly extracting the heat from the heat pipes  25 . The rods  27  act to create a turbulent flow within the channel  27  and thus encourage the interaction of the liquid with the heat pipes  25  to maximize the transfer of heat between the heat pipes  25  and the liquid. 
         [0038]    The second chamber  12  comprises a deflection plate or baffle  30  which extends across the chamber  12 , substantially transverse the longitudinal axis of the chamber  12 , between the inlet  23  and the outlet region defined by the first aperture  17  in the separation plate  21 . The baffle  30  extends substantially radially of the second chamber  12  from a central region thereof, and comprises an outer periphery which is spaced from the housing  14  of the second chamber  12  to define an annular passage  31 . The heat pipes  25  are arranged to extend through apertures  30   a  in the baffle  30  in sealing relation therewith, such that the gas is arranged to pass across the heat pipes  25 , through the annular passage  31 , and back across the heat pipes  25 , in moving from the inlet  23  to the outlet region of the second chamber  12 . 
         [0039]    The baffle  30  comprises a gate or valve  32 , such as a butterfly valve, which can be configured between a fully open state in which the gas is arranged to pass direct from the inlet  23  to the outlet region without substantially passing through the annular passage  31 , a closed state in which the majority of the gas is arranged to pass through the annular passage  31  in passing from the inlet  23  to the outlet region of the second chamber  12 , and various intermediate states in which a portion of the gas is arranged to pass through the valve  32  and a portion of the gas is arranged to pass through the annular passage  31 . The cross-sectional area of the annular passage  31  is substantially matched to the cross-sectional area of the inlet  23  and outlet region of the second chamber  12  to minimize the pressure drop of the gas between the inlet  23  and outlet region of the second chamber  12 . 
         [0040]    Referring to  FIG. 5  of the drawings, the heat pipes  25  are supported within the heat exchanger  10  by the separation plate  21  via a series of collars  33  disposed upon the heat pipes  25 . The collars  33  are arranged to extend within each of the second apertures  26  and serve to seal the heat pipes  25  to the separation plate  21 , such that the interior of the first and second chambers  11 ,  12  remain isolated from each other. 
         [0041]    The second apertures  26  comprise an internal flange  34  which extends into the respective second aperture  26  to reduce the diameter of the second aperture  26  at the side of the plate  21  adjacent the second chamber  12 . The flanges  34  separately act as a seat for a sealing ring  35 , such as an O-ring, such that the collars  33  separately disposed upon the heat pipes  25  are arranged to extend into the respective aperture  26  from within the first chamber  11  and compress the sealing ring  35  against the flange  34  and the heat pipe  25 , to seal the heat pipe  25  within the separation plate  21 . 
         [0042]    The longitudinal ends of the heat pipes  25  disposed within the second chamber  12  are uncoupled and separated from the lower end wall  24  of the second chamber  12 , whereas the longitudinal end of the heat pipes  25  disposed within the first chamber are arranged to abut the underside of a compression plate  36 . The compression plate  36  is substantially annular in shape, and is sized to extend between the cylindrical wall  18  defining the passage  17  and the arcuate side walls  13  of the first chamber  11 . 
         [0043]    The upper side of the compression plate  36  comprises a plurality of compression springs  37  which are arranged to abut the upper wall  20  of the first chamber  11 , as illustrated in  FIG. 6  of the drawings. When the upper wall  20  is secured upon the first chamber  11  to seal the first chamber  11 , the springs  37  are arranged to partially compress to urge the compression plate  36  upon the upper ends of the heat pipes  25  and thus bias the heat pipes  25  into the second apertures  26  to maintain the seal between the heat pipes  25  and the separation plate  21 . During use it is found the increase in temperature of the heat pipes  25  causes the heat pipes  25  to expand which can cause thermal stresses to develop within the heat exchanger  10 . The compression plate  36  and springs  37  enable the heat pipes to expand to relieve any stresses which develop, while maintaining an intimate seal of the heat pipes within the second apertures of the separation plate  21 . 
         [0044]    In use, the gas to be cooled is arranged to pass into the second chamber  12  via the inlet  23  and subsequently pass radially outwardly across the heat pipes  25  due to the baffle  30 , through the annular passage  31 . The gas is then caused to pass radially inwardly of the second chamber  12 , back across the heat pipes  25  toward the outlet region. As the gas passes across the heat pipes  25 , the heat associated with the gas becomes transferred to the heat pipes  25 , causing the gas to become cooled. The heat transferred to the heat pipes  25  is then communicated along the heat pipes  25  to the first chamber and becomes extracted therefrom by the flow of liquid, for example water, within the channel  27 . The outlet  16  of the first chamber comprises a sensor (not shown), for example a thermocouple sensor, for sensing the temperature of the liquid exiting the chamber  11 . If the monitored temperature of the liquid rises above a threshold value, then in order to control the amount of heat recovered from the gas, the valve  32  on the baffle  30  is opened accordingly to vent a portion of the gas direct to the outlet region and thus reduce the amount of heat transferred between the gas and the heat pipes  25 . 
         [0045]    Referring to  FIG. 7  of the drawings, the arcuate walls  14  of the second chamber  12  may be hinged or otherwise removable from the heat exchanger to provide for access into the chamber  12  for cleaning and maintenance. The skilled reader will recognize however, that the arcuate side walls  13  of the first chamber  11  may also be hinged or removable for cleaning and maintenance. 
         [0046]    For further details of the present invention, please see attached Appendix A. 
         [0047]    While this invention has been described in terms of several embodiments, there are alterations, modifications, permutations, and substitute equivalents, which fall within the scope of this invention. It should also be noted that there are many alternative ways of implementing the methods and apparatuses of the present invention. It is therefore intended that the following appended claims be interpreted as including all such alterations, modifications, permutations, and substitute equivalents as fall within the true spirit and scope of the present invention.