Abstract:
Heat exchangers utilizing flat surfaced passages to contact, contain and utilize fluidized small solid particles is provided. Top and bottom woven wire mesh or perforated sheet corrugated with rounded or flat-sided ridges are attached to respective top and bottom sides of said passage to increase its surface and to prevent said small solid particles from exiting said heat exchanger. A variety of shapes of the small solid particles are provided to further enhance the heat transfer rate. More energy efficient systems of all kinds will result from the use of these smaller heat exchangers.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    This invention relates to heat exchangers generally, and, more particularly, to heat exchange processes and to heat exchangers that contain and utilize fluidized small solid particles to improve the transfer of heat on one side of the wall that separates two fluids.  
           [0003]    2. Background Art  
           [0004]    High heat transfer rates have been reported for surfaces immersed in small solid particles that are suspended and kept in motion by an upward flow of a fluid. The overall heat transmission coefficient of a heat exchanger is in the range from 35 to 50 BTU/hr° F.ft 2  (i.e. British thermal unit per hour-degree Fahrenheit-square foot). Details of the heat exchanger are described in my pending U.S. patent application Ser. No. 09/028,053 filed on Feb. 23, 1998. The heat exchanger includes a fluidized bed of small solid particles that are suspended in a flow of a fluid in which the downward tendency of the small solid particles to fall by gravity is equaled by the upward drag force of the fluid flow. The heat exchanger includes a plurality of flat surfaced pipes or tubes, a top woven wire mesh or perforated sheet disposed on top surfaces of the flat surfaced pipes, and a grid plate disposed on bottoms of the flat surfaced pipes. The small solid particles are disposed between the flat surfaced pipes and between the top woven wire mesh and the grid plate. This heat exchanger, however, needs additional new features for the top woven wire mesh or perforated sheet and the grid plate to make the heat exchanger more efficient.  
         SUMMARY OF THE INVENTION  
         [0005]    It is an object of the present invention to provide an improved heat exchanger exhibiting increased efficiency.  
           [0006]    It is another object to provide a heat exchanger that maintains the same capacity although constructed smaller in size.  
           [0007]    It is still another object to provide a heat exchanger having folded and shaped woven wire mesh or perforated sheets able to reduce the overall pressure drop within the heat exchanger during operational service.  
           [0008]    It is yet another object to provide an improved orifice plate equipped with a plurality of orifices allowing fluid passage.  
           [0009]    It is a further object to provide a heat exchanger having a more efficient fluidized bed.  
           [0010]    It is also an object to provide a heat exchanger able to improve heat exchange rates by using small solid particles having tetrahedron or pyramid shapes.  
           [0011]    These and other objects may be achieved with a heat exchanger that contains solid particles in a fluidized bed inside the heat exchanger, that has heat transfer surfaces that are not immersed in the solid particles, that has a loosely packed fluidized bed of small solid particles, that generally only allows a bubbling boiling movement of the solid particles direction rather than allowing a circulating motion, that does not need to use devices to restrain the fluidized bed, does not require any special coating on the heat exchanger surface, that has no vertical tubes, that maintains the two fluids exchanging beat separate from each other, does not require using heating elements in the fluidized bed, that uses flat walls to increase the heat transfer coefficient, that does not use slits or slots, that does not have a space between the distributor plate and the bottom of the tube inlets that creates circulating fluid patterns, that does not require embedding larger particles in the fluidized bed, and uses small solid particles with shapes that allow for an increased amount of heat exchange. This should allow heat exchangers of all types to be made smaller than priorly possible while still maintaining the same level of heat transfer between the two fluids.  
           [0012]    The heat exchanger includes flat surfaced pipes or tubes conveying one of the fluids involved horizontally. The flat surfaced pipes are spaced-apart from each other and firmly attached to a grid plate that is perforated with orifices that introduce the other fluid involved in the heat exchange process and flowing upward and between the flat surface pipes. A top woven wire mesh or perforated sheet is held tightly against the tops of the flattened pipe or tubes to keep the small solid particles from falling out from a top portion of the heat exchangers between the tops of the flattened pipe when the heat exchangers are handled. The bottom woven wire mesh or perforated sheet is held tightly against the bottom or inlet side of the grid plate to keep the small solid particles from draining out from a bottom portion of the heat exchanger between the bottoms of the flattened pipe whenever the heat exchanger has no upward flowing fluid through the orifices. The small solid particles are disposed to move within a heat exchanging space defined between the flat surfaced pipes and between the top woven wire mesh or perforated sheet and the bottom woven wire mesh or perforated sheet. Bubbles are formed above the orifices whenever more fluid is introduced through the orifices than will pass through the spaces between the small solid particles.  
           [0013]    The woven wire mesh or perforated sheets on the top and bottom can be folded or shaped to both increase their respective surface areas and decrease the volume of the heat exchanging space which will thereby reduce the overall pressure drop when in service. Some versions of the improved heat exchangers may be constructed without any orifice plate. The orifice plate may contain one or more orifices in a given enclosed area. The orifices may be round, square or of some other shape. Tetrahedron or pyramid shaped particles may be used for the small solid particles to be manufactured. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]    A more complete appreciation of this invention, and many of the attendant advantages thereof, will be readily apparent as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference symbols indicate the same or similar components, wherein:  
         [0015]    [0015]FIG. 1 is a cross-sectional view of the heat exchanger that is at a right angle to the flat surfaced pipe or tubing that conveys one of the fluids horizontally;  
         [0016]    [0016]FIG. 2 is a cross-sectional view taken along lines II-II′ of FIG. 1;  
         [0017]    [0017]FIGS. 3A, 3B,  3 C and  3 D are top views of the orifice plate showing various configurations and types of orifices that may be employed in the construction of a heat exchanger in accordance with the principles of the present invention;  
         [0018]    [0018]FIG. 4 is a cross-sectional view of another embodiment of the heat exchanger constructed according to the principles of the present invention;  
         [0019]    [0019]FIG. 5 is a cross-sectional view taken along lines V-V′ of FIG. 4; and  
         [0020]    [0020]FIGS. 6A, 6B,  6 C and  6 D are three-dimensional views of small particles that may be manufactured that are with shapes of tetrahedrons or pyramids for use in a heat exchanger constructed according to the principles of the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    Turning now to the drawings, FIG. 1 is a cross-sectional view of a heat exchanger when viewed at a right angle to a plurality of parallel and horizontally spaced-apart flat surfaced pipes or tubes  1  that convey one of the fluids involved in a heat exchange process horizontally. The direction of the second fluid that is conveyed through the heat exchanger is denoted by arrows A. Small solid particles  2  are drawn as triangles to represent tetrahedrons, which is one of the preferred shapes for particles. Preferably, particles  2  are solid. Flattened pipe or tube  1  is attached to a grid plate  3  that is perforated with the orifices  4  that introduce the other fluid involved.  
         [0022]    Top woven wire mesh or perforated sheet  5  is held tightly against the tops of the flattened pipe or tube  1  to keep the particles  2  from falling out when the heat exchanger is handled. The angle θ between the flattened top surface of pipe  1  and the neighboring downward fold of top woven wire mesh or perforated sheet  5  can be between approximately 30° and 90°. The folded or shaped top woven wire mesh or perforated sheet  5  increases its surface area and decreases the volume of a heat exchanging space which will thereby reduce the overall pressure drop when in service.  
         [0023]    Bottom woven wire mesh or perforated sheet  6  is held tightly against the bottom or inlet side of the grid plate  3  to keep the particles  2  from draining out from between neighboring pipes  1  whenever the heat exchanger has no upwardly flowing fluid through the orifices as indicated by the upwardly rising direction of arrows A. Bubbles  7  are formed above the orifices  4  whenever more fluid is introduced through the orifices  4  than will readily pass through the interstices between solid particles  2 .  
         [0024]    [0024]FIG. 2 is a cross-sectional view of the heat exchanger that is taken along cross-sectional line II-II′ in FIG. 1. The side of pipe  1  that conveys the horizontally flowing fluid is shown as well as its fluid flow that is indicated by arrows B that point from left to right. Particles  2 , grid plate  3  perforated by orifices  4 , upper wire mesh  5 , lower wire mesh  6 , and bubbles  7  are shown again. Pitch divider fins  8  are spaced-apart from each other and coupled to two spaced-apart and adjacent flat surfaces of pipes  2  facing each other and are provided in order to increase heat transfer surface even when the heat exchanger is not pitched for drainage. Particles  2  move within the heat exchanging space defined by the two spaced-apart pitch divider fins  8 , two spaced-apart flat surfaces of pipes  1 , upper wire mesh  5 , and lower wire mesh  6 .  
         [0025]    [0025]FIG. 3A shows a top view of grid plate  3  where shown in FIGS. 1 and 2. There is only one orifice  4  shown in the area bounded by the walls of the flattened pipe or tubing  1  and two adjacent pitch divider fins  8 .  
         [0026]    [0026]FIG. 3B shows a second embodiment of grid plate  3  constructed according to the principle of the present invention. One orifice is shown centered in the area bounded by the walls of the flattened pipe or tubing  1  and two adjacent pitch divider fins  8  with four other orifices  4  located each one in each corner.  
         [0027]    [0027]FIG. 3C shows a third embodiment of grid plate  3 . Four orifices  4  are shown in the area bounded by the walls of the flattened pipe or tubing  1  and two adjacent pitch divider fins  8 .  
         [0028]    [0028]FIG. 3D shows a fourth embodiment of grid plate  3 . Eight orifices  4  are shown in the area bounded by the walls of the flattened pipe or tubing  1  and two adjacent pitch divider fins  8 . Four of orifices  4  are shown as squares. The orifices  4  can be round, square, elliptical or polygonal.  
         [0029]    [0029]FIG. 4 is a cross-sectional view of the heat exchanger that is taken at a right angle to the flat surfaced pipe or tubing  1  that conveys one of the fluids involved horizontally. The small solid particles  2  are drawn as triangles to represent tetrahedrons (which is one of the preferred solid shapes). The flattened pipe or tubing  1  is firmly attached to bottom woven wire mesh or perforated sheet  6  which is shown as formed into flat-sided alternating ridges and groves. Note that there is no grid plate  3  required for this construction. The top woven wire mesh or perforated sheet  5  is held tightly against the tops of the flattened pipe or tubing  1  to keep the small solid particles  2  from falling out when the heat exchangers are handled. Note that the top woven wire mesh or perforated sheet  5  is now shown as being formed into rounded alternating ridges and groves which will result in less pressure drop through the heat exchangers when in service. The large dark arrows A that point up indicate the upward flowing fluid. Bubbles  7  are formed above the bottom woven wire mesh or perforated sheet  6  whenever more fluid is introduced than will pass through the spaces between the small solid particles  2 .  
         [0030]    [0030]FIG. 5 is a cross-sectional view of the heat exchanger that is taken at a right angle to FIG. 4 as shown in FIG. 4. The side of the flattened pipe or tubing  1  that conveys the horizontally flowing fluid is shown as well as its fluid flow that is indicated by the large dark arrows B that point from left to right. The small solid particles  2 , the top woven wire mesh or perforated sheet  5 , the bottom woven wire mesh or perforated sheet  6 , and the bubbles  7  are shown again as shown in FIG. 4. Pitch divider fins  8  are shown as being provided for increased heat transfer surface even when the heat exchanger is not pitched for drainage.  
         [0031]    [0031]FIG. 6A shows a shape of small solid particles having a tetrahedron that has all four equilateral triangles of the same size where the side lengths are all equal. FIG. 6B shows a tetrahedron that has four triangular faces that are not necessarily equal including the case where all four triangles could be of different dimensions. FIG. 6C shows a pyramid that has four triangles that are of equal dimensions and the base is a square. FIG. 6D shows a polyhedron that has a polygonal base with triangular sides that meet at a common vertex. The tetrahedron shown as FIG. 6A is expected to be the most used shape for the small solid particles to be manufactured.  
         [0032]    According to the present invention as described above, the heat exchanger is reduced in size and exhibits much higher heat transfer rates when using the grid plate perforated with a plurality of orifices, the folded or shaped woven wire mesh or perforated sheets on the top and bottom of the heat exchanger, and tetrahedron or pyramid shaped small solid particles. The use of folded or shaped woven wire mesh or perforated sheets reduce the overall pressure drop within the heat exchanger when in service  
         [0033]    Although the preferred embodiment of the present invention has been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.