Abstract:
A pulse tube refrigerator/cryocooler apparatus including: an inlet for receiving a cyclically moving volume of gas; a regenerator device fluidly connected to the inlet for storing and recovering thermal energy from the gas; a pulse tube fluidly connected to the regenerator; and a conduit fluidly connected at one end to the pulse tube and fluidly connected at its opposite end to a container, said container providing a storage volume for gas, wherein apparatus is configured such that the cyclically moving gas enters the regenerator in a direction parallel to its elongate axis.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates to a pulse tube refrigerator/cryocooler apparatus and to a gas flow distribution device for use therewith. 
         [0002]    The general function of a pulse tube cryocooler apparatus is well known to one skilled in the art, and generally includes the following features/components:
   a) a piston for effecting cyclical movement of gas (e.g. Helium);   b) a regenerator for storing and recovering thermal energy of the gas moving cyclically in that direction as a result of the piston;   c) a pulse tube fluidly connected to the regenerator, acting as an insulator between the regenerator and the remainder of the cryocooler;   d) an inertance tube offering restriction and inertial effect to the cyclically moving gas, fluidly connected to the pulse tube; and   e) a container (often referred to as a “reservoir”) fluidly connected to the inertance tube, for storing a volume of gas.   
 
         [0008]    The function of the cryocooler is to provide cooling to a device, particularly cryogenic temperatures. The present invention has been devised to achieve temperatures lower than 80K. 
         [0009]    According to a first aspect of the present invention, we provide a pulse tube refrigerator/cryocooler apparatus including:
   a) an inlet for receiving a cyclically moving volume of gas;   b) a regenerator device fluidly connected to the inlet for storing and recovering thermal energy from the gas;   c) a pulse tube fluidly connected to the regenerator; and   d) a conduit fluidly connected at one end to the pulse tube and fluidly connected at its opposite end to a container, said container providing a storage volume for gas,   e) wherein apparatus is configured such that the cyclically moving gas enters the regenerator in a direction parallel to its elongate axis.   
 
         [0015]    According to a second aspect of the present invention, we provide a pulse tube refrigerator/cryocooler apparatus including:
   a) an inlet for receiving a cyclically moving volume of gas;   b) a regenerator device fluidly connected to the inlet for storing and recovering thermal energy from the gas;   c) a pulse tube fluidly connected to the regenerator; and   d) a conduit fluidly connected at one end to the pulse tube and fluidly connected at its opposite end to a container, said container providing a storage volume for gas,   e) wherein the inlet is connected to the regenerator by a gas flow distribution device which distributes gas substantially evenly across and/or around the cross-sectional area of the regenerator.   
 
         [0021]    According to a third aspect of the present invention, we provide a gas flow distribution device for use in a pulse tube refrigerator/cryocooler apparatus, including:
   a) an inlet;   b) a plurality of outlets; and   c) a plurality of gas flow paths connecting the inlet to each of the outlets, wherein the length of the gas flow paths from the inlet to each respective outlet are substantially identical to each other.   
 
         [0025]    Further features of the various aspects of the invention are set out in the claims attached hereto. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    Embodiments of the invention will now be described by way of example only with reference to the accompanying drawings, of which: 
           [0027]      FIG. 1  is a perspective cross-sectional view through an apparatus in accordance with the present invention; 
           [0028]      FIG. 2  is a close up cross-sectional view of a region of apparatus of  FIG. 1 ; 
           [0029]      FIG. 3  is a close up cross-sectional view of a region of apparatus of  FIG. 1 ; 
           [0030]      FIG. 4  is a close up cross-sectional view of a region of apparatus of  FIG. 1 ; 
           [0031]      FIG. 5  is a perspective view of a gas distribution device in accordance with the present invention; 
           [0032]      FIG. 6  is a further perspective view of the gas distribution device of  FIG. 5 ; 
           [0033]      FIG. 7  is a plan view of the gas distribution device of  FIG. 5 ; 
           [0034]      FIG. 8  is a perspective view of the gas flow path within the gas distribution device of  FIG. 5 ; 
           [0035]      FIG. 9  is a perspective view of an alternative configuration of the gas flow paths; and 
           [0036]      FIGS. 10 to 15  are illustrative views of alternative configurations of gas flow paths for a gas distribution device in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0037]    Referring to  FIG. 1  this shows a pulse tube refrigerator/cryocooler apparatus  10  in accordance with the present invention. The apparatus  10  includes an inlet  12  for receiving a cyclically moving volume of gas, e.g. Helium. The inlet  12  is therefore connected, in use, to a device (not shown) which can provide such a cyclically moving volume of gas. This aspect of the apparatus will not be discussed in any further detail as there are many devices in the prior art which can provide such functionality. 
         [0038]    The apparatus  10  also includes a regenerator device  14 , a pulse tube  16  and a conduit (or inertance tube as it is often known in the art)  18 . The regenerator device  14  in this example has a central opening which receives the pulse tube  16 . Thus the two are co-axial with each other, with the pulse tube being fluidly connected to the regenerator  14  at their ends remote from the inertance tube  18 . This end also supports a “cold end” part  25 . The part  25  is the part of the apparatus  10  which is to be lowered to a temperature in the order of 80K during use, and is thus connectable to any further apparatus to be so cooled. 
         [0039]    The inertance tube  18  is fluidly connected at one end to the pulse tube by the intermediary of an opening  40  in a gas flow distribution device  30  (discussed in more detail later) and at its opposite end to the internal volume of a container  20 . The container  20  (which is often referred to in the art as a “reservoir”) provides a storage volume for the Helium gas and in hand with the inertance tube  18  provides the necessary phase shift between the mass flow rate and pressure of the cyclically moving gas in order to give rise to the cooling effect at the part  25 , which effect is well known in the art. 
         [0040]    Advantageously, the present invention is configured such that the cyclically moving gas enters/exits the regenerator  14  in a direction parallel to its elongate axis. In other words, the gas entering the inlet  12  passes through the gas flow distribution device  30  (discussed later) and into the regenerator  14 , substantially evenly across its annular cross-section such that the gas moves in the axial direction of the regenerator  14 . Such a configured flow of the cyclically moving gas ensures that minimal mixing of gas occurs which leads to improved efficiency of the apparatus  10 . 
         [0041]    As mentioned above, the apparatus  10  includes a gas flow distribution device  30  which distributes gas substantially evenly across and/or around the cross-sectional area of the regenerator  14 . The gas flow distribution device (which can be seen better in  FIGS. 2 through 9 ) includes an inlet  32  which is fluidly connected to the inlet  12  and a plurality of outlets  34  ( a  through  q ) which are connected to the inlet  32  by respective gas flow paths. 
         [0042]    The gas flow distribution device  30  is preferably manufactured by a rapid prototyping technique, e.g. selective metal laser sintering, which enables complex gas flow paths to be provided between the inlet  32  and each of the respective outlets  34   a  to  q . Other rapid prototyping techniques could be used. 
         [0043]      FIG. 8  illustrates the gas flow paths constructed within the gas flow distribution device  30  from which it can be seen that each gas flow path (i.e. the path between the inlet  32  and each respective outlet  34   a - q ) includes a first gas flow path portion  36  which divides into two second gas flow path portions  37   a,    37   b.  Each gas flow path portion  37   a, b  divides into three respective third gas flow path/portions:  38   a, b  and  c  from gas flow path portion  37   a  and  38   d, e  and  f  from the gas flow path portion  37   b.  Finally each of the gas flow path portion  38  divides into three fourth gas flow path portions  39  (with respective letter numbering) each of which leads to a respective gas flow path outlet  34  (with respective letter numbering). 
         [0044]    The length of each of the gas flow paths between the inlet  32  and the respective outlet  34  are substantially identical to each other, which means that the gas flow distribution device  30  is configured such that the flow rate of gas exiting/entering one outlet  34  is substantially identical to all of the other outlets  34  during use. This substantially even distribution of the gas flow through the device  30  ensures substantially even distribution of the gas across the annular cross-sectional area of the regenerator  14 . In hand with that, the smooth transition between each adjacent gas flow path portion, and the configured cross-sectional area thereof, ensures minimal pressure drop between the inlet  32  and each respective outlet  34 . Thus, the pressure of the cyclically moving gas at each of the outlets  34  is substantially the same. Thus, the resistance to flow along the gas flow paths are substantially identical to each other. 
         [0045]    As shown in the figures, the gas flow distribution device  30  includes a generally axially extending opening  40  which fluidly connects the pulse tube  16  to the inertance tube  18 . The outlets  34  of the gas flow paths are positioned around the generally axially extending opening  40 . In the present example there are  18  outlets  34 , and thus they are each positioned at an angle of  20  degrees around the axis of the opening  40 . 
         [0046]    As can be seen from the figures, the end portion of each of the fourth gas flow path portions  39  is aligned substantially parallel with the axis of the regenerator, which means that the flow of the gas into the regenerator  14  is linearized with the axis of the regenerator  14 . 
         [0047]    In order to assist with this linearization of the gas into the regenerator  14 , the apparatus  10  is also provided with a gas flow linearization device  50  which is positioned in between the gas flow distribution device  30  and the pulse tube/regenerator. The gas flow linearization device  50  fluidly connects to the outlets  34  of the gas flow distribution device  30 . In more detail the gas flow linearization device  52  includes a plurality of first gas flow path channels  52  which are positioned substantially evenly around the periphery of the device  50  and which are aligned substantially parallel with each other. The first gas flow path channels  52  communicate with the outlets  34  from the device  30 , at one end, and at an opposite end with the regenerator  14 . 
         [0048]    The device  50  also includes a plurality of second gas flow path channels  54  which are positioned inwardly towards the axis of the device  50 . These channels  54  provide fluid communication between the opening  40  of the device  30  and the pulse tube  16 . 
         [0049]    The channels  52 ,  54  can take many forms, but it should be noted that in  FIGS. 3 and 4  there are shown two different configurations. In  FIG. 3  the channels  52  are substantially rectangular in cross-section, whilst the channels  54  are circular in cross-section. In  FIG. 4  both the channels  52  and  54  are generally circular in cross-section. These elongate gas flow path channels  52 ,  54  further linearize the flow of gas between the pulse tube and the conduit (in the case of the channels  54 ) and between the outlets  34  and regenerator  14  (in the case of the channels  52 ). 
         [0050]    Whilst in the present embodiment pulse tube  16  extends through an axially extending opening in the regenerator  14 , it should be noted that the pulse tube and regenerator could, in alternative embodiments, be connected in end-to-end relationship, as is well known in the art of cryocoolers. 
         [0051]    Referring to  FIGS. 9 to 15 , these show alternative configurations of the gas flow paths between the inlet to the device  30  and its outlets  34 . In  FIG. 9  the inlet  32 ′ divides into four outlets  34 ′ a  to  d . In the embodiments shown in  FIGS. 10 ,  11 ,  12 ,  13 , the inlet  32 ″ is circular in cross-section, as are the outlets  34 ″  a  through  x , and each has a opening  40 ″ positioned within the outlets  34 ″. The only difference is the configuration of the outlets  34 ″. In  FIG. 10  they form a generally circular array, similar to the embodiment shown in  FIG. 8 . In  FIG. 11  they form a rectangular (square) array. In  FIG. 12  they form a generally triangular array. In  FIG. 13  the outlets form a generally hexagonal array with two rows of outlets around the periphery of the opening  40 ″. 
         [0052]    In  FIG. 14  the inlet  32 ″ is rectangular (square) in cross-section, as are the outlets  34 ″, with the outlets  34 ″ being provided in a rectangular (square) array. Finally, in  FIG. 15  the inlet  32 ″ is circular in cross-section, but the outlets  34 ″ are hexagonal and are provided in a nested array (e.g. honeycomb configuration). 
         [0053]    It should be appreciated, however, that the cross-sectional shape of the inlet(s) and outlet(s) may be any desired shape, provided that the length of and/or resistance to flow along each of the plurality of gas flow paths are substantially identical to each other. 
         [0054]    When used in this specification and claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps or integers are included. The terms are not to be interpreted to exclude the presence of other features, steps or components. 
         [0055]    The features disclosed in the foregoing description, or the following claims, or the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for attaining the disclosed result, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.