Abstract:
A annular recuperator to recover waste heat from a gas turbine exhaust in order to preheat the compressed air delivered to the gas turbine combustor, formed with gas flow passages for the relatively hot turbine exhaust gases and air flow passages for the relatively cool compressed air separated by thin, thermally conductive metal foil barriers. The flow passages have contoured gaps between the foil surfaces in order to establish the desired air/gas aerodynamic friction induced pressure drop and mass flow profiles within the recuperator core. The gaps are set by an array of dimples in the metal foil barriers with each dimple having a precisely controlled height. The metal foil barriers are formed by first dimpling and then bending a single sheet metal strip to form a convoluted foil structure that is wrapped around an inner cylinder and the ends joined. An outer cylinder is then installed around the wrapped, convoluted foil barrier structure. The ends of the foil strips are welded closed and the turbine exhaust gas flow passages are left open at the ends. The inlet and outlet ports for the compressed air are formed in the opposite ends of the inner cylinder to face radially and the turbine exhaust gases enter and exit axially at the opposite ends of the core.

Description:
RELATED APPLICATIONS  
       [0001]    This patent application claims the priority of provisional patent applications serial No. 60/246,682, filed Nov. 7, 2000 and serial No. 60/250,860, filed Dec. 1, 2000. 
     
    
     STATEMENT REGARDING FEDERALLY SPONSORED DEVELOPMENT  
       [0002] The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of the Advanced MicroTurbine System Contract NO. DE-FC02-01CH11058 awarded by the Department of Energy. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0003]    A turbogenerator electric power generation system is generally comprised of a compressor, a combustor including fuel injectors and an ignition source, a turbine, and an electrical generator. Often, the system includes a recuperator to preheat combustion air with waste heat from the turbine exhaust. The ability of the recuperator to transfer waste heat from the exhaust to the combustion air can significantly impact the efficiency of the turbogenerator system, and an efficient recuperator can substantially lower system fuel consumption. Therefore, what is needed is a recuperator for a turbogenerator system to efficiently transfer heat from turbine exhaust gas to combustion air.  
         BRIEF SUMMARY OF THE INVENTION  
         [0004]    The present invention meets the above need by providing, in one aspect, an annular recuperator for transferring heat from a hot fluid stream to a cool fluid stream, comprising a generally cylindrical annular housing having an inner wall, an outer wall, and axially opposed first and second ends defined between the inner wall and the outer wall, and a single elongated sheet of material formed in a continuous serpentine pattern of surfaces extending between the inner wall and the outer wall to define a plurality of fluid flow channels therebetween extending from the first end to the second end, the surfaces formed with protrusions extending therefrom to abut an adjacent surface.  
           [0005]    In a further aspect, the present invention provides a method to construct an annular recuperator for transferring heat from a hot fluid stream to a cool fluid stream, comprising disposing a generally cylindrical inner wall within a generally cylindrical outer wall to define axially opposed first and second ends therebetween, providing an elongated sheet of material, forming protrusions extending from both sides of the sheet, folding the sheet into a serpentine pattern of facing surfaces, and disposing the folded sheet between the walls with the surfaces extending between the inner wall and the outer wall to define a plurality of fluid flow channels therebetween extending from the first end to the second end, each protrusion abutting an adjacent surface.  
           [0006]    In another aspect of the invention, the fluid flow channels form alternating cold channels for the cool fluid stream and hot channels for the hot fluid stream, and the recuperator also comprises a plurality of inlets formed in the inner wall at the first end and in fluid communication with the cold channels to admit the cool fluid stream therein, and a plurality of outlets formed in the inner wall at the second end and in fluid communication with the cold channels to allow the cool fluid stream to exit therefrom. Every pair of surfaces defining a cold channel therebetween may be joined together along their edges extending from the inner wall to the outer wall to form a fluid seal along each edge. One or more of the protrusions may abut a like protrusion extending from an adjacent surface, or may abut the adjacent surface. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]    [0007]FIG. 1 is perspective view, partially in section, of a turbogenerator system with an annular recuperator according to the present invention;  
         [0008]    [0008]FIG. 2 is a diagram showing in cross section the spacing and placement of cold and hot channels in the annular recuperator of FIG. 1;  
         [0009]    [0009]FIG. 3 is a enlarged detailed view of cold and hot channels in the annular recuperator of FIG. 2;  
         [0010]    [0010]FIG. 4( a ) is a perspective view of a sheet of material for forming the annular recuperator of FIG. 2;  
         [0011]    [0011]FIG. 4( b ) is a front view of the sheet of material of FIG. 4( a );  
         [0012]    [0012]FIG. 5 is a side view of the sheet of material of FIG. 4( a ) formed into a serpentine convolute pattern, with some of the dimensions exaggerated to show detail;  
         [0013]    [0013]FIG. 6 is a side view of a cold channel formed by the convoluted sheet of FIG. 5;  
         [0014]    [0014]FIG. 7 is a perspective view of an inner wall used with the recuperator of FIG. 2;  
         [0015]    [0015]FIG. 8 is an enlarged front view of a recuperator core formed with the convolute sheet of FIG. 5;  
         [0016]    [0016]FIG. 9 is an enlarged view showing a radially outer section of the recuperator core of FIG. 8;  
         [0017]    [0017]FIG. 10 is an enlarged view showing a radially inner section of the recuperator core of FIG. 8;  
         [0018]    [0018]FIG. 11 is an enlarged view of the radially outer section shown in FIG. 9;  
         [0019]    [0019]FIG. 12 is an enlarged front view showing the radially inner section of the recuperator core of FIG. 10 disposed over the inner wall of FIG. 7;  
         [0020]    [0020]FIG. 13 is a front view of the sheet of material of FIG. 4 showing the dimples formed therein;  
         [0021]    [0021]FIG. 14 is a side view, in section, taken along line  14 - 14  of FIG. 13;  
         [0022]    [0022]FIG. 15 is a side view, in section, taken along line  15 - 15  of FIG. 13;  
         [0023]    [0023]FIG. 16 is an enlarged perspective view of a section of the sheet of material of FIG. 13;  
         [0024]    [0024]FIG. 17 is an enlarged perspective view of a section of the sheet of material of FIG. 13 showing a single dimple;  
         [0025]    [0025]FIG. 18 is a front view of the sheet of material of FIG. 13 showing the dimple pattern near a cold channel outlet;  
         [0026]    [0026]FIG. 19 is a sectional view of the recuperator core taken along line L-L of FIG. 8;  
         [0027]    [0027]FIG. 20 is a sectional view of the recuperator core taken along line M-M of FIG. 8;  
         [0028]    [0028]FIG. 21 is a sectional view of the recuperator core taken along line N-N of FIG. 8;  
         [0029]    [0029]FIG. 22 is a sectional view of the recuperator core taken along line O-O of FIG. 8;  
         [0030]    [0030]FIG. 23 is a sectional view of the end of a cold and a hot channel, near the axial end area of the recuperator core of FIG. 8, shown without dimples; and  
         [0031]    [0031]FIG. 24 is a sectional view of the end of a cold and a hot channel, near the axial center area of the recuperator core of FIG. 8, shown without dimples. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    Referring to FIG. 1, integrated turbogenerator system  12  generally includes generator  20 , power head  21 , combustor  22 , and recuperator (or heat exchanger)  23 . Power head  21  of turbogenerator  12  includes compressor  30 , turbine  31 , and bearing rotor  32 . Tie rod  33  to magnetic rotor  26  (which may be a permanent magnet) of generator  20  passes through bearing rotor  32 . Compressor  30  includes compressor impeller or wheel  34  that draws air flowing from an annular air flow passage in outer cylindrical sleeve  29  around stator  27  of the generator  20 . Turbine  31  includes turbine wheel  35  that receives hot exhaust gas flowing from combustor  22 . Combustor  22  receives preheated air from recuperator  23  and fuel through a plurality of fuel injector guides  49 . Compressor wheel  34  and turbine wheel  35  are supported on bearing shaft or rotor  32  having radially extending air-flow bearing rotor thrust disk  36 . Bearing rotor  32  is rotatably supported by a single air-flow journal bearing within center bearing housing  37  while bearing rotor thrust disk  36  at the compressor end of bearing rotor  32  is rotatably supported by a bilateral air-flow thrust bearing.  
         [0033]    Generator  20  includes magnetic rotor or sleeve  26  rotatably supported within generator stator  27  by a pair of spaced journal bearings. Both rotor  26  and stator  27  may include permanent magnets. Air is drawn by the rotation of rotor  26  and travels between rotor  26  and stator  27  and further through an annular space formed radially outward of the stator to cool generator  20 . Inner sleeve  25  serves to separate the air expelled by rotor  26  from the air being drawn in by compressor  30 , thereby preventing preheated air from being drawn in by the compressor and adversely affecting the performance of the compressor (due to the lower density of preheated air as opposed to ambient-temperature air).  
         [0034]    In operation, air is drawn through sleeve  29  by compressor  30 , compressed, and directed to flow into recuperator  23 . Recuperator  23  includes annular housing  40  with heat transfer section or core  41 , exhaust gas dome  42 , and combustor dome  43 . Heat from exhaust gas  110  exiting turbine  31  is used to preheat compressed air  100  flowing through recuperator  23  before it enters combustor  22 , where the preheated air is mixed with fuel and ignited such as by electrical spark, hot surface ignition, or catalyst. The fuel may also be premixed with all or a portion of the preheated air prior to injection into the combustor. The resulting combustion gas expands in turbine  31  to drive turbine impeller  35  and, through common shaft  32 , drive compressor  30  and rotor  26  of generator  20 . The expanded turbine exhaust gas then exits turbine  31  and flows through recuperator  23  before being discharged from turbogenerator  12 .  
         [0035]    Recuperator  23  receives, channels, and transfers heat from hot fluid stream  100  (comprised of the turbine exhaust gas) to cool fluid stream  110  (comprised of the compressed air from compressor  30 ). To increase its efficiency, recuperator  23  maximizes the thermal intermixing of the two streams while keeping the streams physically separate and also minimizing the flow resistance encountered by the two streams. Recuperator  23  thus includes a plurality of low temperature, high pressure “cold” passages or channels disposed adjacent to high temperature, low pressure “hot” passages or channels in an alternating pattern repeated over the entire diameter of the recuperator core.  
         [0036]    As discussed below in detail, the present invention recognizes that a problem to be solved for providing an efficient recuperator is matching the cold, high-pressure fluid flow to the hot, low-pressure fluid flow throughout the recuperator maximize the amount of heat energy transferred to the cool fluid stream (e.g. combustion air) from the hot fluid stream (e.g. the turbine exhaust). This entails promoting evenly distributed fluid mass flows throughout the recuperator in both the cold channels and the hot channels. As detailed below, conventional designs typically promote evenly distributed mass flow through the hot channels but not in the cold channels.  
         [0037]    Referring to FIG. 2 and FIG. 3, recuperator core  41  is shown in greater detail as formed of alternating cold channels  80  and hot channels  82  disposed in an annular pattern defined by outer annulus  84  and inner annulus  86 . Outer annulus  84  corresponds to annular housing  40  of recuperator  23 . Referring to FIG. 4, in a preferred method of construction of annular recuperator  23 , metal sheet  200  has elongated generally rectangular surface  201  defined by parallel, longer edges  205  and  206  and parallel, shorter edges  207  and  208 , and formed with longitudinally extending lips  202  and  204  along each of longer sides  205  and  206 , respectively. Lips  202  and  204  may be formed by folding or bending sheet  200 , or welding material, or any other practicable method, and both extend toward the same direction from surface  201 .  
         [0038]    Referring to FIG. 5, sheet  200  is folded into a convolute or serpentine pattern  210  with facing surfaces  212  connected to each of the two adjacent surfaces  212  along outer edges  214  and inner  216  respectively, and formed into the annular shape of recuperator core  41  with inner edges  216  abutting inner annulus  86  (as shown in FIG. 2) and shorter edges  207  and  208  connected to one another (such as by welding). Surfaces  212  define therebetween hot channels  82  alternating with cold channels  80  and, because they extend toward the same direction from surface  201 , lips  202  and  204  abut themselves along radially extending edges  218  to seal off the longitudinal ends of the cold channels. In a preferred method of fabrication lips  202  and  204  are pinched and/or welded to form an air-tight seal. Hot channels  82  are defined between facing surfaces  212  with open longitudinal ends to accept exhaust gas  100  (as shown in FIG. 1) to flow therethrough.  
         [0039]    Referring again to FIGS. 2 and 3, channels  80  and  82  may be formed with a generally rectangular cross section and thereafter may be molded into a generally arcuate configuration. This arcuate configuration allows both cold and hot channels to maintain a relatively constant cross section along their radial length. As discussed elsewhere, protrusions extending from cold channels  80  through hot channels  82  (shown in FIGS. X-Y) space surfaces  212  apart as well as direct fluid flow through the channels. Outer edges  214  of cold channels  80  abut annular housing  40  but are typically not connected to the housing to be able to move with respect to the housing as may be necessitated by thermal expansion and contraction. Inner edges  216  are preferably welded to inner annulus  86 .  
         [0040]    Referring to FIG. 6, core  41  of recuperator  23  is bounded by outer annular housing  40  and inner cylinder  122  defining inner annulus  86 . As also shown in FIG. 7, inner cylinder  122  is formed with high pressure inlets  127  and high pressure outlets  128 . Recuperator core is disposed such that each cold channel  80  is in fluid communication with one high pressure inlet  127  and one high pressure outlet  128  to allow high pressure cool fluid stream  100  to flow therethrough. Referring to FIG. 7, both high pressure inlets  127  and high pressure outlets  128  may be formed, in one embodiment, by axially slitting or slicing inner cylinder  122  and then bending the sliced material to form louvers  131  and  132 , respectively. In operation, high-pressure cool fluid stream  100  exits compressor  30  and enters cold channels  80  through inlet  127 , travels along the axial length of the cold channels, and eventually exits through outlets  128 . In a preferred embodiment, hot fluid stream  110  flows through hot channels  82  in the opposite to cool fluid stream  100 . Hot channels  82  are formed with completely open axial ends, and thus hot fluid stream  100  is substantially evenly distributed throughout each hot channel.  
         [0041]    Referring to FIG. 8, cold channels  80  and hot channels  82  at the outer diameter (near outer annulus  84 ) of recuperator core  41  are designated as  80   o  and  82   o  respectively while at the inner diameter (near inner annulus  86 ) are designated  80   i  and  82   i,  respectively. One cold channel  80  together with an adjacent hot channel  82  is considered to comprise a recuperator core cell  137 . The recuperator core  41  may include as many as five hundred cells  137 .  
         [0042]    Referring to FIG. 9, the outer diameter of recuperator core  41  is shown in enlarged detail. FIG. 10 shows the inner of recuperator core  41  in enlarged detail. Referring to FIG. 11, and as previously mentioned, opposite shorter edges  207  and  208  of sheet  200  are joined together to close serpentine pattern  210  of sheet  200  into a continuous pattern and to form air-tight seal  140  between hot fluid flow  100  and cold fluid flow  110 . Similarly, lips  202  and  204  extending along longer edges  205  and  206 , respectively, are also joined together (to themselves) at each axial end, respectively, of each cold channel  80  to form air-tight seal  139  between hot fluid flow  100  and cold fluid flow  110 . Forming seal  139  also has a pinching effect on the cross section of the cold channels, thereby in effect widening the hot channel inlets and outlets to reduce turbulence and promote even mass flow throughout the hot channels.  
         [0043]    With continued reference to FIGS.  8 - 11 , the spacing in cold channels  80  is maintained by plurality of cold channel dimples  142  on one side of each surface  212 . Dimples  142  extend from one surface  212  to contact the adjacent surface  212  to maintain cold channel spacing. The spacing in hot channels  82  is established by plurality of opposed hot channel dimples  144  extending from each surface  212  away from cold channel dimples  142 , with each dimple  144  from one surface  212  contacting a corresponding dimple  144  from the adjacent surface  212 . Hot channel dimples  144  serve to stabilize surfaces  212  against the crushing force caused by the pressure difference between the cold, high-pressure channels and the hot, low-pressure channels. Using pairs of abutting hot channel dimples  144  provides superior strength to using a single, larger dimple. Additionally, because hot channel dimples  144  are smaller and thus have a smaller footprint, cold channel dimples  142  can be disposed between hot channel dimples  144  to provide superior structural strength and fluid flow distribution.  
         [0044]    Referring to FIG. 12, an enlarged view of the high pressure inlet end of recuperator core  41  shows the positioning of louvers  131  formed in inner cylinder  122  at high pressure inlet  127 . Louvers  132  forming high pressure outlet  128  (as shown in FIG. 7) are similarly formed and disposed.  
         [0045]    Referring to FIGS.  13 - 15 , sheet  200  is bent to form cold channels  80  and hot channels  82  and is further formed with cold channel dimples  142  and hot channel dimples  144  to define alternating double dimpled sections  147  and single dimpled sections  148 . FIGS.  13 - 15  depict the axial central section of recuperator core  41 . The positioning and spacing of hot channel dimples  144  in the axial central section of core  41  are generally the same along the axial length of this section since the central section is removed from high pressure inlet  127  and high pressure outlet  127 . Double dimpled section  147  includes hot channel dimples  144  extending from surface  212  in one direction and cold channel dimples  142  extending from surface  212  in the other direction. Single sided dimpled section  148  includes hot channel dimples  144  extending from surface  212  in only one direction.  
         [0046]    Referring to FIGS.  16 - 18 , a portion of the central area of a double dimpled section  147  is illustrated. FIG. 16 depicts an area of nine hot channel dimples  144  with at least portions of sixteen cold channel dimples  142  also shown. In FIG. 17, an enlarged single hot channel dimple  144  is shown amongst four cold channel dimples  142 .  
         [0047]    The outlet section end of a single dimpled section  148  is shown in FIG. 18 and generally illustrates the relative positions of hot channel dimples  144  and cold channel dimples  142  on opposite sides of sheet  200  in this area. The outlet section end of a single dimpled section  148  includes both upwardly projecting hot channel dimples  144  and downwardly projecting cold channel dimples  142 . The cold channel dimples  142  at both the outlet end and the inlet end of single dimpled section  148  serve to form a weir to slow the flow of high pressure fluid  110  from simply moving down recuperator core  41  adjacent to inner cylinder  122  and to encourage the high pressure fluid to travel radially to and from the outer diameter area of the recuperator core near outer annular housing  40 . Selecting the sizing and distribution of the dimples appropriately thus promotes more evenly distributed fluid mass flows through the cold and hot channels and can be used to direct mass flow from areas of high flow concentration (e.g. near inner cylinder  122 ) towards areas of lower flow concentration (e.g. near annular housing  40 ).  
         [0048]    Through the axial center area of recuperator core  41 , the height of hot channel dimples  144  is axially constant but increases radially outwardly to account for the increasing cross-sectional area of the channels in the radially outward direction. At the axial end of the core, the height of the hot channel dimples is also axially constant but at a lower height that in the axial center area of the recuperator core. Downwardly projecting cold channel dimples  142  are introduced in the axial end area and vary in height radial but are axially constant in height except for the axially innermost column which has less height.  
         [0049]    FIGS.  19 - 22  depict cold channels  80  and hot channels  82  (with the dimples not shown) at different diameters in the recuperator core  41 . FIG. 19 is a sectional view of the core generally illustrating the hot and cold channels near the outer diameter of the recuperator along line L-L of FIG. 8. The channels near the center diameter of the recuperator along line M-M of FIG. 8 are illustrated in FIG. 20. FIG. 21 is generally illustrating the channels between the center diameter and the inner diameter of the recuperator along line N-N of FIG. 8 while the channels near the inner diameter of the recuperator along line O-O of FIG. 8 are shown in FIG. 22.  
         [0050]    At both the outer diameter positions of FIG. 19 and the central diameter positions of FIG. 20, gap H of cold channels  80  are generally the same as are gaps L in hot channels  82 . While high pressure passage gap H reaches this gap at line A, high pressure gap H in the central diameter position reaches this gap at line F. The central diameter position high pressure gap reaches its greatest gap Y at line B and its narrowest gap X at line E. Line B is displaced farther inward from the end of the core than line A.  
         [0051]    The greatest high pressure passage gap Y′ in the diameter between the central diameter position and the inner diameter position is at line C while the narrowest gap X′ is at line F. Line C is further displaced inward from line B while line F is also displaced inward from line E. The greatest gap Y″ at the inner diameter position high pressure gap is at line D, while the narrowest gap X″ is at line G, with line D displaced inward from line C and line G displaced inward from line F.  
         [0052]    The axial distance between lines A, B, C, and D may be generally the same. The axial distance between lines E, F, and G may likewise be the same but normally would be about twice the distance between lines A, B, C, and D. While gaps H and L of cold channels  80  and hot channels  82  respectively may generally be the same for the outer and central diameter positions, gaps H′ of the diameter position between the central diameter position and the inner diameter position would normally be less than gap H with gap H″ of the inner diameter position being less than H′. L′ is also less than L, and L″ is less than L′. H′+L′ can be about eighty-five percent of H+L, while H″+L″ can be about seventy percent of H+L.  
         [0053]    Referring to FIGS. 23 and 24, cold channels  80  and hot channels  82  are shown without the dimples and are both formed with tapered end sections at both inner cylinder  122  and outer annular housing  40 . This taper is greater at the axial end area of the core as best illustrated in FIG. 24. Hot channels  82  are more restricted at the axial end area of the core than in the axial center area of the core.  
         [0054]    Although the invention has been described with reference to particular embodiments, these embodiments are offered merely for illustration and ease of discussion of the general inventive concept. Numerous modifications and additions may be made to the embodiments described herein without departing from the scope and spirit of the invention. Thus, the invention may used with any other fluid capable of carrying heat, and is not limited solely to air or solely to gases. Practice of the invention is also not limited solely to counterflow recuperator designs.  
         [0055]    Having now described the invention in accordance with the requirements of the patent statutes, those skilled in the art will understand how to make changes and modifications to the disclosed embodiments to meet their specific requirements or conditions. Such changes and modifications may be made without departing from the scope and spirit of the invention, as defined and limited solely by the following claims.