Abstract:
A solar receiver for conversion of solar radiation to thermal energy includes an enclosure defining a cavity and having an aperture for receiving an influx of concentrated solar radiation. A heat exchanger is received within the cavity for transferring heat out of the solar receiver. The heat exchanger comprises a plurality of heat exchange cells arranged in polygonal array within the cavity. Each heat exchange cell comprises an inlet, an outlet, and a heat exchange matrix interposed within a first volume defined between a first plate and a second plate spaced apart from the first plate. The inlet and outlet are in fluid communication with the first volume and the first plate, second plate, and heat exchange matrix are monolithically bonded as a unit. The first plate receives concentrated solar radiation and the heat exchange media defines a pathway for a fluid flowing from the inlet to the outlet between the first and second plates. The solar receiver further includes an inlet manifold in fluid communication with the inlet of each of the heat exchange cells and an outlet manifold in fluid communication with the outlet of the each of heat exchange cells. In a further aspect, a heat exchanger is provided.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims the benefit of priority under 35 U.S.C. §119(e) based on U.S. provisional application No. 61/319,042 filed Mar. 30, 2011. The aforementioned provisional application is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    The present disclosure relates generally to the field solar energy conversion, and more specifically to the use of solar receivers for heating gases. 
       DESCRIPTION OF PRIOR ART 
       [0003]      FIG. 1  schematically illustrates a prior art parabolic dish collector system, where incident solar rays  50  reflect off a mirrored parabolic dish concentrator  51 , concentrating reflected rays  52  through the aperture  53  of a cavity solar receiver. The receiver is composed of an entrance cone  54  that connects the cavity absorber panel to the aperture plane  53 . The absorber  55  is a heat exchanger with fluid inlet  56  and outlet  57 . The purpose of the solar absorber is to heat the fluid to elevated temperatures. 
         [0004]      FIG. 2  schematically illustrates a generalized representation of prior art for a cavity solar receiver. The receiver is composed of a cavity  56 , an aperture  53 , and the interconnecting cavity walls  54 . The aperture is usually sized to accept solar flux at the highest concentration ratio available from the solar reflecting surface. The concentrated solar energy  5  enters through the aperture  53  and irradiates the cavity interior surface  56 . This surface is referred to as the solar absorber. The conical cavity walls  54  connecting the absorber and the front plate containing the aperture is typically not irradiated by the focused solar rays. The solar heat-absorbing element  66  forms the interior surface of the cavity and contains the fluid which flows from the inlet  34  to the outlet  35 . Typically, the heat-absorbing elements  56  is an array of tubes. Other past designs incorporate two concentric cylinders, the inner first cylinder serves as the solar absorber cavity and the outer second cylinder forms an annular passage to contain the heat-absorbing fluid. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  illustrates the principle of using a parabolic dish concentrator to focus solar power through the aperture of a cavity solar receiver. 
           [0006]      FIG. 2  schematically provides a general definition of prior art for a cavity solar receiver. 
           [0007]      FIG. 3  illustrates the cross section of a heat exchanger element utilizing secondary surface fins between parallel plates. A heated fluid is contained within the plate-fin matrix and first surface of the heat exchanger is exposed to concentrated solar radiation. 
           [0008]      FIG. 4  illustrates the principle referred to as series heating for a first and a second fluid at unequal pressures. 
           [0009]      FIG. 5  illustrates an example of series heating, using a plate-fin composite cellular structure with inlet and outlet manifolds for first and second fluids. 
           [0010]      FIG. 6  illustrates two composite absorber elements, one rectangular and one trapezoidal, either of which may be formed into a polygonal shaped cavity. 
           [0011]      FIG. 7  illustrates a polygonal shaped cavity receiver formed of trapezoidal-shaped heat exchange cells. 
           [0012]      FIG. 8  illustrates one method for integrating the cell with a distribution manifold for the purpose of providing fluid to and from the cell. 
           [0013]      FIG. 9  illustrates a cross-sectional view of a solar cavity receiver composed of trapezoidal heat exchange elements with torroidal ring manifolds to provide inlet and outlet fluid transport. 
           [0014]      FIG. 10  provides an illustrative description of one method of manufacturing for the single layer cell structure for heating a single fluid. 
           [0015]      FIG. 11  provides an illustrative description of one method of manufacturing for a two layer cell structure employing the series heating principle for first and second fluids. 
           [0016]      FIG. 12  illustrates yet another method for connecting the heat exchanger cell to a manifold. 
           [0017]      FIGS. 13 and 14  illustrate exemplary gas turbine cycles with which the solar receiver in accordance with this disclosure may be employed. 
         SUMMARY 
         [0018]    In one aspect, a solar receiver for conversion of solar radiation to thermal energy is provided, which includes an enclosure defining a cavity and having an aperture for receiving an influx of concentrated solar radiation. A heat exchanger is received within the cavity for transferring heat out of the solar receiver. The heat exchanger comprises a plurality of heat exchange cells arranged in polygonal array within the cavity. Each heat exchange cell comprises an inlet, an outlet, and a heat exchange matrix interposed within a first volume defined between a first plate and a second plate spaced apart from the first plate. The inlet and outlet are in fluid communication with the first volume and the first plate, second plate, and heat exchange matrix are monolithically bonded as a unit. The first plate receives concentrated solar radiation and the heat exchange media defines a pathway for a fluid flowing from the inlet to the outlet between the first and second plates. The solar receiver further includes an inlet manifold in fluid communication with the inlet of each of the heat exchange cells and an outlet manifold in fluid communication with the outlet of the each of heat exchange cells. In a further aspect, a heat exchanger is provided. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0019]    The present disclosure is directed to a compact heat exchanger intended to function as a cavity solar receiver. While typical solar receivers utilize tubes formed in bundles and involutes, the present design employs a plurality of cellular panels forming a polygonal shell. The densely fined panels are compact heat exchangers designed to absorb highly concentrated solar flux from a parabolic solar concentrator. Its purpose is to enable efficient heating of either one or two separated fluids within the solar cavity. 
         [0020]      FIG. 3  illustrates a cross-sectional view of a heat exchange element  66  containing a first plate or sheet  1 , a fin or other heat exchange medium or matrix  2 , and a second plate or sheet  3 . The heat exchange element  66  is a monolithic cellular structure created when the fin  2  is bonded to the first sheet  1  and the second sheet  3 . The volume defined between the plates  1  and  3  serves as a passage for flowing fluid  4 . When the first plate  1  is exposed to concentrated solar radiation  5 , the flowing fluid  4  interior absorbs heat. In this arrangement, the fin  2  provides structural support for plates  1 ,  3 , given the load exerted by the pressurized fluid  4 . The space behind the second plate  3  is preferably insulated with refractory insulation material  13 . 
         [0021]    The fin  2  also conducts heat from the first plate  1  to the second plate  3 , thereby providing increased surface area for heat transfer between the fluid  4  and the radiated surface  1 .  FIG. 3  illustrates one of many types of enhanced surface fins. Others include pins, foam metals, porous metal structures, screen packs, wavy folded sheet, lanced folded sheet and other secondary surfaces commonly used in the heat exchanger industry. The heat exchanger industry refers to this a plate-fin construction. 
         [0022]      FIG. 4  illustrates an example of series heating, using a plate-fin composite cellular structure  67 . The plate-fin heat exchanger elements  67  include a first surface or plate  6 , which is irradiated by concentrated solar power  5 . A second surface or plate  8  serves to separate a first fluid  7  flowing between the plates  6  and  8  and a second fluid  9 . A third surface  10  serves to contain the second fluid  9  flowing between the second plate  8  and the third plate  10 . A first fin  11  or extended heat exchange matrix is interposed between the first  6  and second surface  8 , and a second fin  12  or extended heat exchange matrix is interposed between the second and third surfaces  8  and  10 . 
         [0023]    The three sheets or surfaces  6 ,  8 , and  10 , and the two fin matrix elements  11 ,  12  are bonded to form a composite heat exchanger element  67  with adequate structural integrity to support the structural loads, which are largely pressure-induced. The space behind the third surface  10  is preferably insulated with refractory insulation material  13 . The fluids  7  and  9 , passing through the first and second fin matrix elements  11  and  12 , respectively, are typically at differing pressures. Thus, the individual fin matrix geometries  11 ,  12  may be optimized to maximize the heat transfer coefficient for the allowable fluid pressure drops. 
         [0024]      FIG. 5  illustrates a cross sectional view of a two-cell solar absorbing heat exchanger with manifolds for series heated cavity solar receivers. Plates  6 ,  8 ,  10  are bonded to fin or matrix elements  11 ,  12  to form the heat exchanger, as described in  FIG. 4 . The first fluid  7  enters a manifold  14 , passes through the fin matrix  11  and exits at a higher temperature from manifold  16 . Likewise, the second fluid  9  enters a manifold  15 , passes through the fin matrix  12 , absorbs heat through the parting sheet  8 , and exits from a manifold  17 . In this so-called series heating arrangement, the highly conductive fin members are designed to cause the first  7  and second fluids  9  to remain approximately equal to one another in temperature as they flow between the two manifolds. 
         [0025]    If the two fluids enter at the same temperature, then the temperature of the second fluid  9  must necessarily lag below the temperature of the first fluid  7 , but through careful design practice, this difference may be minimized. In the preferred embodiment, the first fluid  7  would be the higher of the two fluid pressures. The higher-pressure fluid enables a proportionally denser fin or heat exchange matrix  11 . A denser fin or matrix is created by closer packed and/or shorter fins, which have the effect of achieving higher heat exchange coefficient between the fluid and the solar irradiated wall  6 . An increase in heat transfer coefficient and a denser fin matrix both serve to increase the maximum tolerable solar flux levels. The ability to tolerate highly concentrated solar flux levels allows for a minimization of the solar cavity size and cost. 
         [0026]    In a cavity solar absorber, formed into a cylindrical or conical shell comprising multiple heat exchange elements, with is base closest to the aperture, the concentrated solar flux levels are naturally highest near the base. A further characteristic of the preferred solar absorber embodiment is to locate the inlet manifolds  14  and  15  so that the fluid enters the base of the absorber matrix in the vicinity of the highest fluxes; thus forcing the coolest fluid into the region of highest concentrated solar flux. 
         [0027]      FIG. 6  illustrates two variations  76 ,  77  of a composite absorber cell which may be formed into a polygonal cylindrical or conical absorber shell. If the cell is rectangular ( 77 ), the polygonal cavity formed would be generally cylindrical. That is, with a large number of rectangular heat exchange cells, the heat exchanger would form a polyhedron shape approximating that of a cylinder. A rectangular cell would be the typical form created from the use of a folded fin heat exchange matrix that forms generally parallel channels. 
         [0028]    Composite screen fin, foam metal, or similar matrix allows fluid to flow in three mutually orthogonal directions, x, y, and z. Such a heat exchange matrix allows for converging composite panels with non-parallel sides, forming a trapezoidal cell  76 . 
         [0029]    The trapezoidal cell or panel  76  may be configured in an array that forms a solar absorbing cavity with a pyramidal interior. With a large number of the trapezoidal heat exchange cells  76 , the cavity shape approximates that of a cone, as shown in  FIG. 7 . In yet another practical variation using an omni-directional flow matrix, the cells thickness and fin matrix height may vary in the y-direction along the flow length in the z-direction. This special geometry would lead to a reduction in pressure drop, relative to the cell formed with parallel sheets.  FIG. 7  illustrates a solar-absorbing cavity receiver formed of trapezoidal heat exchange cells  76 . The cells may be either single layer, as described in  FIG. 3 , or two-layer, as described in  FIG. 4 . In the embodiment shown, a fluid enters inlet  79 , flows around torroidal ring manifold  78 , which serves the purpose to provide nearly uniform flow to the inlet of each heat-absorbing cell  76 . The heated fluid exits the cells  76  into a second toroid ring manifold  75 , and exits into conduit  80 . 
         [0030]      FIG. 8  illustrates a method of integrating the plate and fin cell into a tube or conduit. As previously described, the fin segments  11 ,  12  provide both structural and thermal enhancements to the cell. One method for delivering the flow into the cell or taking the heated flow out of the cell is shown in  FIG. 8 . For the purpose for this explanation,  FIG. 8  is described as an inlet manifold, however similar principles and construction methods may be applied to the fluid outlet end of the cell as well. 
         [0031]      FIG. 8  shows a cell in which the parting plates  6 ,  8 , and  10  extend beyond the length of the internal fin segments  11 ,  12 . A first array of pin fins  71  is shown in the volume between the first parting plate  6  and the second parting plate  8 , in communication with the first fluid, as it enters from fin matrix  11 . Likewise, a second array of pin fins  70  is located in the volume between second parting plate  8  and third parting plate  10 , arranged to communicate with the second fluid as it enters the first fin segment  11 . A tube or conduit  72  is aligned with a hole in parting plate  8 , with an opening sized to allow the tube  72  to penetrate through the fluid boundary to contact parting plate  6 . At the point of contact with the plate  6 , the tube  72  is slotted or castellated to enable the first fluid to enter the tube  72  from the space between parting plates  6  and  8 . An internal structural rib  74  is shown inside the tube  72  to provide structural enhancements. 
         [0032]    A tube or conduit  73  is aligned with a hole in the parting plate  10 , with an opening sized to allow the tube  73  to penetrate through the fluid boundary to contact parting plate  8 . At the point of contact, the tube  73  is slotted or castellated to enable the first fluid to enter the tube from the space between parting plates  8  and  10 . An internal structural rib  64  is shown inside the tube  73  to provide structural enhancements. 
         [0033]    As would be understood by persons skilled in the art upon a reading and understanding of this disclosure, several alternatives to the fins  70  and  71  may be employed to perform substantially similar purpose. For example, alternatives such as porous metal media, screen matrices, or machined square pins provide the necessary function of enabling the channeled flow from the fins  11 ,  12 , to travel in direction allowing the fluid to congregate at the transport tube  72 . It should also be clear that the aforementioned method of connecting a cell with internal fin structure to a pipe or conduit may be applied to a single cell or a double cell arrangement as shown in  FIG. 8 . 
         [0034]      FIG. 9  shows a method for manifolding plate-fin solar-absorbing cells to a toroid or ring manifold. In one embodiment, a plurality of the solar absorbing cells  76  are arranged within a cavity solar receiver. As illustrated in the close-up view, the ring manifold  75  for the hot exit fluid is arranged to be of smaller hoop diameter than the cavity diameter. The tubular conduit  72  of  FIG. 8  is extended radially inward to transport the fluids from the individual cells  76  using a toroidal ring manifold arrangement. Likewise, a ring manifold for the cell inlet fluid  78  is located at a larger radius than that formed by the solar absorbing cavity formed by a polygon. In should be clear to one skilled in the field that the fluid transport tubes  72  may be connected to manifolds of any number of geometries. For a solar cavity employing the series heating of two fluids, a similar method for connecting each solar absorber panel to a common hoop manifold may be employed. For the case illustrated in  FIG. 5 , four toroidal hoop manifolds would be required; two at the base of the cavity for the first and second fluids, and two at the top of the cavity receiver to collect the heated fluids. 
         [0035]      FIG. 10  illustrates one of many possible methods of construction, where first sheet  20  is formed into a substantially channel-shaped section with formed edges  21 . A fin or matrix heat exchange element  22  is sized to fit within the channel. A second sheet or plate  24  is also formed with a substantially channel-shaped section with edges  23 . The second channel  24  is formed with a width approximately equal to the width of the fin element  22  and sized to mate with the inside edge  21  of the first channel  20 . 
         [0036]    Final assembly is also shown in  FIG. 10 , where formed channel  22 , fin element  22 , and second channel  24  are fit together. The construction materials may be any number of metals or ceramic materials, as are commonly used in the heat exchanger industry. The three elements  20 ,  22 ,  24  are brazed, diffusion bonded, sintered, or bonded into a monolithic structure  26  by methods commonly employed in the metal-working and ceramics industry. If a metallic material is used, rather than a ceramic material, a weld  37  may be applied either before metallurgical bonding, to self-fixture the three elements, or after metallurgical bonding, to insure proper sealing and mechanical integrity. In using ceramic materials, the three elements may be sintered or sintered and hot-isostatic pressed (HIP) to form a monolithic element capable of supporting the pressure loads exerted by the interior fluid. 
         [0037]      FIG. 11  illustrates a method of construction for a two-layer heat exchanger cell  38 . A first channel section  30  is formed with edges  31 . A first fin segment  32  is sized to fit within the first channel. A second sheet or plate  33  is also sized with a width to fit within the first channel. A second fin or matrix segment  34  is also sized with a width to fit within the first channel. The second fin or matrix heat exchange element  34  is sized with a passage height and fin density appropriate to meet the heat transfer and pressure drop specifications of the second fluid. A third channel section  36  is formed with edges  35  and is also sized to fit within the first channel  30 . 
         [0038]    The final assembly  38  of elements  30 ,  32 ,  33 , and  36  is also illustrated in  FIG. 11 . All four elements may be formed of ceramic or metallic materials and bonded into a monolithic structure by means established with in the industry. In the case of a metal structure, a weld joint  37  is shown to provide sealing of the cell, joining parting sheets  30 ,  33 , and  36 . 
         [0039]      FIG. 12  illustrates one of several methods of joining the single layer  66  and two layer heat exchanger  67  elements into a manifold. A plurality of the heat exchange elements may be joined to a common inlet manifold  40  and exit manifold  44 . In the case of a single layer heat exchanger, the heat exchange element  66  has a fluid inlet  41  and outlet  43 . Cast or formed inlet manifold  40 , containing pressurized fluid is formed with a slot width substantially equal to that of heat exchange element  66 . A weld  42  is employed to secure the heat exchange element into the manifold  40 . Similarly, the outlet manifold  44  is sized with a slot to accept heat exchange element  66  and a weld  42  is employed to seal the cell into the manifold. 
         [0040]    A family of solar absorbers is illustrated, suitable for cavity-type solar receivers. When the present solar receiver is deployed with a conventional gas turbine cycle (see  FIG. 13 ), only a single pass through the solar receiver is required. A novel single-pass design for a cellular receiver construction is disclosed herein. The present solar receiver may also be deployed with a so-called intercooled recuperated reheat cycle (see  FIG. 14 ), which requires two passes through the solar receiver. 
         [0041]    A cavity solar receiver containing passages for both first and second stage heating has also been disclosed herein. The underlying principles of series heating arrangements for heating two or more isolated fluid streams are defined and illustrated. The invention has been described with reference to the preferred embodiments. Modifications and alterations may occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.