Heat exchanger

Abstract

The heat exchanger has an axis and at least one heat-exchange body ( 5 ) encompassing said axis, annular in cross-section and comprising sheet metal elements ( 23, 27 ) which are present in succession around the axis and are involute in cross-section and between which edge strips ( 24, 25, 28, 29 ) welded to said sheet metal elements alternately at their involute side edges ( 23 c, 23 d, 27 c, 27 d ) and at their inner and outer edges ( 23 a, 23 b, 27 a, 27 b ) are arranged and which alternately bound passages ( 33, 34 ) for a first and a second fluid ( 15, 16 ). Each passage ( 33, 34 ) contains an intermediate layer ( 31, 32 ) which consists of a knitted wire fabric. The edge strips ( 24, 25, 28, 29 ) and the knitted wire fabrics hold the successive sheet metal elements ( 23, 27 ) in a stable and durable manner a distance apart and result in only little thermal conduction in the direction of flow.

1 . Heat exchanger comprising at least one heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) which is annular in cross-section, encompasses an axis ( 2 ) and has sheet metal elements ( 23 ,  27 ,  127 ) which are present in succession around said axis and together alternately bound first passages ( 33 ) for a first fluid ( 15 ) and second passages ( 34 ,  134 . 1 ,  134 . 2 ) for a second fluid ( 16 ), each sheet metal element ( 23 ,  27 ,  127 ) having an inner edge ( 23   a ,  27   a ), an outer edge ( 23   b ,  27   b ) and two side edges ( 23   c ,  23   d ,  27   c ,  27   d ) running from the inner edge ( 23   a ,  27   a ) to the outer edge ( 23   b ,  27   b ), adjacent sheet metal elements ( 23 ,  27 ,  127 ) having substantially constant distances from one another along their side edges ( 23   c ,  23   d ,  27   c ,  27   d ), characterized in that each sheet metal element ( 23 ,  27 ,  127 ) forms a quadrilateral, that metallic edge strips ( 24 ,  25 ) are arranged between the sheet metal elements ( 23 ,  27 ,  127 ) together bounding a first passage ( 33 ) and run along the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of said sheet metal elements and are firmly and tightly connected to the relevant sheet metal elements ( 23 ,  27 ,  127 ) and that metallic edge strips ( 28 ,  29 ) are arranged between the sheet metal elements ( 23 ,  27 ,  127 ) together bounding a second passage ( 34 ,  134 . 1 ,  134 . 2 ) and run along the inner edges ( 23   a ,  27   a ) and the outer edges ( 23   b ,  27   b ) of said sheet metal elements and are firmly and tightly connected to the relevant sheet metal elements ( 23 ,  27 ,  127 ).  
     
     
         2 . Heat exchanger according to  claim 1 , characterized in that the inner edge ( 23   a ,  27   a ) and the outer edge ( 23   b ,  27   b ) of each sheet metal element ( 23   a ,  27   a ) [sic] are straight and parallel to one another and that the two side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of each sheet metal element ( 23 ,  27 ,  127 ) are parallel to one another and at right angles to the inner edge ( 23   a ,  27   a ) and outer edge ( 23   b ,  27   b ).  
     
     
         3 . Heat exchanger according to  claim 1  or  2 , characterized in that the sheet metal elements ( 23 ,  27 ,  127 ) are connected by welding or hard soldering or adhesive bonding to the edge strips ( 24 ,  25 ,  28 ,  29 ) and thus to one another.  
     
     
         4 . Heat exchanger according to any of  claims 1  to  3 , characterized in that the sheet metal elements ( 23 ,  27 ,  127 ) together bounding a first passage ( 33 ) are free, at their inner edges ( 23   a ,  27   a ) and outer edges ( 23   b ,  27   b ), between the edge strips ( 24 ,  25 ) arranged at their side edges ( 23   c ,  23   d ,  27   c ,  27   d ), from rigid connections between said edge strips.  
     
     
         5 . Heat exchanger according to any of  claims 1  to  4 , characterized in that the two side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ) and the edge strips ( 24 ,  25 ) running along them form end surfaces ( 5   c ,  5   d ) facing away from one another, that the two passages ( 34 ,  134 . 1 ,  34 . 2 ) [sic] have inlet orifices ( 34   a ,  134 . 1   a ,  134 . 2   a ) lying in one of the end surfaces ( 5   c ,  5   d ) and outlet orifices ( 34   b ,  134 . 1   b ,  134 . 2   b ) lying in one of the end surfaces ( 5   c ,  5   d ), that the sheet metal elements ( 23 ,  27 ,  127 ) together bounding a second passage ( 34 ,  134 . 1 ,  134 . 2 ) are free, at the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of these sheet metal elements ( 23 ,  27 ,  127 ), in at least one of the following regions, or rigid connections between them; 
 a) between the edge strips ( 28 ,  29 ) arranged at their inner edges ( 23   a ,  27   a ) and outer edges ( 23   b ,  27   b ),  
 b) between the inlet orifices ( 34   a ,  134 . 1   a ,  134 . 2   a ) and the edge strips ( 28 ) arranged at the inner edges ( 23   a ,  27   a ) and between the outlet orifices ( 34   b ,  134 . 1 . b ,  134 . 2   b ) [sic] and the edge strips ( 29 ) arranged at the outer edges ( 23   b ,  27   b ),  
 c) between the inlet orifices ( 34   a ) and the outlet orifices ( 34   b ).  
 
     
     
         6 . Heat exchanger according to any of  claims 1  to  5 , characterized in that each first passage ( 33 ) has, at the inner edges ( 23   a ,  27   a ) of the two sheet metal elements ( 23 ,  27 ,  127 ) bounding it, at least one orifice ( 33   a ) which connects the first passage ( 33 ) between these inner edges ( 23   a ,  27   a ) through to a space adjacent to said edges and that each first passage ( 33 ) has, at the outer edges ( 23   b ,  27   b ) of the two sheet metal elements ( 23 ,  27 ,  127 ) bounding it, at least one orifice ( 33   b ) which connects the first passage ( 33 ) between these outer edges ( 23   b ,  27   b ) through to a space adjacent to said edges.  
     
     
         7 . Heat exchanger according to any of  claims 1  to  6 , characterized in that each second passage ( 34 ,  134 . 1 ,  134 . 2 ) has, in the proximity of the outer edges ( 23   b ,  27   b ) and in the proximity of the inner edges ( 23   a ,  27   a ) of the two sheet metal elements ( 23 ,  27 ,  127 ) bounding it, in each case at least one orifice ( 34   a ,  34   b ,  134 . 1   a ,  134 . 1   b ) which connects the second passage ( 34 ,  134 . 1 ,  134 . 2 ) between two opposite side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of these sheet metal elements ( 23 ,  27 ,  127 ) through to a space adjacent to said edges.  
     
     
         8 . Heat exchanger according to  claim 7 , characterized in that those orifices of the passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) which are present at or near the inner edges ( 23   a ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ) serve as inlet orifices ( 33   a ) of the first passages ( 3 ) or as outlet orifices ( 34   b ,  134 . 1   b ,  134 . 2   b ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ), that those orifices of the passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) which are present at or near the outer edges ( 23   b ,  27   b ) serve as outlet orifices ( 33   b ) of the first passages ( 33   a ) or as inlet surfaces ( 34   a ,  134 . 1   a ,  134 . 1   b ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ), that fluid conducting means ( 7 ,  107 ,  207 ) are present in order to convey the first fluid ( 15 ) to the inlet orifices ( 33   a ) of the first passages ( 33 ) and away from the outlet orifices ( 33   b ) of the first passages ( 33 ) and in order to convey the second fluid ( 16 ) to the inlet orifices ( 34   a ,  134 . 1   a ,  134 . 1   b ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ) and away from the outlet orifices ( 34   b ,  134 . 1   b ,  134 . 2   b ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ), and that the fluid conducting means ( 7 ,  107 ,  207 ) are formed in order to feed the first fluid to the inlet orifices ( 33   a ) of the first passages ( 33 ) at a temperature which is higher than the temperature at which the second fluid ( 16 ) is fed to the inlet orifices ( 34   a ,  134 . 1 ,  134 . 2 ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ) so that the first fluid  825 ) [sic] releases heat to the second fluid ( 16 ) and the or each heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) has a temperature generally decreasing outward away from the axis ( 2 ).  
     
     
         9 . Heat exchanger according to  claim 8 , characterized in that the inlet orifices ( 33   a ) of the first passages ( 33 ) are arranged in a first inlet region ( 5   e ), the outlet orifices ( 33   b ) of the first passages ( 33 ) are arranged in a first outlet region ( 5   f ), the inlet orifices ( 34   a ,  134 . 1   a ,  134 . 2   a ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ) are arranged in a second inlet region ( 5   g ) and the outlet orifices ( 34   b ,  134 . 1   b ,  134 . 2   b ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ) are arranged in a second outlet region ( 5   h ) of the or a heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) and that each inlet region ( 5   e ,  5   g ) and outlet region ( 5   f ,  5   h ) runs in an annular manner around the axis ( 2 ).  
     
     
         10 . Heat exchanger according to any of  claims 1  to  9 , characterized in that the inner edges ( 23   a ,  27   a ) of the sheet metal elements ( 23 ,  27 ,  127 ) and the edge strips ( 28 ) arranged at the inner edges ( 23   a ,  27   a ) define an inner lateral surface ( 5   a ), that the sheet metal elements ( 23 ,  27 ,  127 ) adjacent to one another are at least approximately a constant distance apart from their inner edges ( 23   a ,  27   a ) to their outer edges ( 23   b ,  27   b ) and that those sections of the sheet metal elements ( 23 ,  27 ,  127 ) which are adjacent to the inner edges ( 23   a ,  27   a ) have, in a cross-section at right angles to the axis ( 2 ), a tangent which makes with the inner lateral surface ( 5   a ) an angle which is 65° to 115° and, for example, 80° to 100°, the sheet metal elements ( 23 ,  27 ,  127 ) being preferably substantially involute in a section at right angles to the axis ( 2 ).  
     
     
         11 . Heat exchanger according to any of  claims 1  to  10 , characterized in that the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ) and the edge strips ( 24 ,  25 ) arranged at the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) define two end surfaces ( 5   c ,  5   d ) of the or each heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) and that the inlet orifices ( 34   a ,  134 . 1   a ,  134 . 2   a ) and the outlet orifices ( 34   b ,  134 . 1   b ,  134 . 2   b ) of the second passages ( 34 ,  134 . 1 ,  134 . 2 ) are arranged at end surfaces ( 5   c ,  5   d ) facing away from one another.  
     
     
         12 . Heat exchanger according to  claim 1 , characterized in that it has at least one pair of heat-exchange bodies, comprising a first heat-exchange body ( 105 . 1 ,  205 . 1 ) and a second heat-exchange body ( 105 . 2 ,  205 . 2 ), that each heat-exchange body ( 105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) has an inner and an outer lateral surface, that the second passages ( 134 . 1 ) having the inlet orifices ( 134 . 1   a ) arranged in an end surface ( 105 . 1   c ) of the first heat-exchange body ( 105 . 1 ,  205 . 1 ) have secondary outlet orifices ( 134 . 1   a ) arranged in the other end surface ( 105 . 1   d ) in the proximity of the outer lateral surfaces of the first heat-exchange body ( 105 . 1 ,  205 . 1 ), that the second passages ( 134 . 2 ) having the outlet orifices ( 134 . 2   b ) of the second heat-exchange body ( 105 . 2 ,  205 . 2 ) which are arranged in an end surface ( 105 . 2   c ) have secondary inlet orifices ( 134 . 2   c ) arranged in the other end surface ( 105 . 2   c ) in the proximity of the inner lateral surface of the second heat-exchange body ( 105 . 2 ,  205 . 2 ) and that the fluid conducting means ( 107 ,  207 ) are formed in order to convey the second fluid ( 16 ) into the first heat-exchange body ( 105 . 1 ) at those inlet orifices ( 134 . 1   a ) of the second passages ( 134 . 1 ) which are arranged in an end surface ( 105 . 1   c ) and then to convey part of this fluid ( 16 ) from the secondary outlet orifices ( 134 . 1   c ) of the first heat-exchange body ( 105 . 1 ) to those second inlet orifices ( 134 . 2   a ) of the second heat-exchange body ( 105 . 2 ,  205 . 1 ) which are arranged in an end surface ( 105 . 2   c ) and in order to convey second fluid ( 16 ) which flows out of the second outlet orifices ( 134 . 1   b ) arranged in an end surface ( 105 . 1   b ) of the first heat-exchange body ( 105 . 1 ,  205 . 1 ) to the secondary inlet orifices ( 134 . 2   c ) of the second heat-exchange body ( 105 . 2 ,  205 . 2 ).  
     
     
         13 . Heat exchanger, in particular according to any of  claims 1  to  12 , comprising at least one heat-exchange body ( 5 ,  105 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) having successive sheet metal elements ( 23 ,  27 ,  127 ) which alternately bound passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) for a first fluid ( 15 ) and a second fluid ( 16 ) and between which gas-permeable intermediate layers ( 31 ,  32 ,  132 . 2 ) are arranged, each sheet metal element ( 23 ,  27 ,  127 ) having two side edges ( 23   c ,  23   d ,  27   c ,  27   d ) facing away from one another, characterized in that the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ) belonging to the same heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) and/or edge strips ( 24 ,  25 ) arranged at these side edges ( 23   c ,  23   d ,  27   c ,  27   d ) together define two end surfaces ( 5   c ,  5   d ,  105 . 1   c ,  105 . 1   d ,  105 . 2   c ,  105 . 2   d ) of the heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ), that at least one metallic foil ( 45 ,  46 ,  75 ,  76 ,  146 ) rests against the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ) at each end surface ( 5   c ,  5   d ,  105 . 1   c ,  105 . 1   d ,  105 . 2   c ,  105 . 2   d ) and that a heat insulation ( 47 ,  48 ,  88 ,  157 ) is arranged on that side of each foil ( 45 ,  46 ,  75 ,  76 ,  146 ) which faces away from the sheet metal elements ( 23 ,  27 ,  127 ).  
     
     
         14 . Heat exchanger according to  claim 13 , characterized in that each foil ( 45 ,  46 ,  75 ,  76 ,  146 ) is at most 0.1 mm and, for example, 0.03 mm to 0.07 mm thick.  
     
     
         15 . Heat exchanger according to  claim 12  or  13 , characterized in that the insulation ( 47 ,  48 ,  88 ,  147 ) presses the foil ( 45 ,  46 ,  75 ,  76 ,  146 ) against the sheet metal elements ( 23 ,  27 ,  127 ), the insulation ( 47 ,  48 ,  88 ,  147 ) being, for example, elastically deformable.  
     
     
         16 . Heat exchanger according to any of  claims 13  to  15 , characterized in that at least two foils ( 75 ,  76 ) which have sections which are adjacent to the end surfaces ( 5   c ,  5   d ,  105 . 1   c ,  105 . 1   d ,  105 . 2   c ,  105 . 2   d ) and overlap one another are present at each end surface ( 5   c ,  5   d ,  105 . 1   c ,  105 . 1   d ,  105 . 2   c ,  105 . 2   d ) of the or each heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ).  
     
     
         17 . Heat exchanger, in particular according to any of  claims 1  to  16 , comprising at least one heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) which is annular in cross-section, encompasses an axis ( 2 ) and has sheet metal elements ( 23 ,  27 ,  127 ) which are present in succession around said axis and together alternately bound first passages ( 33 ) for a first fluid ( 15 ) and second passages ( 34 ,  134 . 1 ,  134 . 2 ) for a second fluid ( 16 ), each sheet metal element ( 23 ,  27 ,  127 ) having an inner edge ( 23   a ,  27   a ), an outer edge ( 23   b ,  27   b ) and two side edges ( 23   c ,  23   d ,  27   c ,  27   d ) running from the inner edge ( 23   a ,  27   a ) to the outer edge ( 23   b ,  27   b ), adjacent sheet metal elements ( 23 ,  27 ,  127 ) having substantially constant distances from one another along their side edges ( 23   c ,  23   d ,  27   c ,  27   d ), the passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) extending between orifices ( 33   a ,  134 . 1   b ,  134 . 2   b ,  134 . 2   c ) in the proximity of the inner edges ( 23   a ,  27   a ) and orifices ( 33   b ,  34   a ,  134 . 1   a ,  134 . 1   c ,  134 . 2   a ) in the proximity of the outer edges ( 23   b ,  27   b ), characterized in that the sheet metal elements ( 23 ,  27 ,  127 ) have a dimension, measured along their side edges ( 23   c ,  23   d ,  27   c ,  27   d ), which is at least two times a dimension of the sheet metal elements ( 23 ,  27 ,  127 ) which is measured along the axis ( 2 ).  
     
     
         18 . Heat exchanger according to  claim 17 , characterized in that it has at least two heat-exchange bodies ( 105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) a distance apart along the axis ( 2 ).  
     
     
         19 . Heat exchanger according to  claim 17  or  18 , characterized in that the distance between adjacent sheet metal elements ( 23 ,  27 ,  127 ) is at most 10 mm and preferably at most 2 mm.  
     
     
         20 . Heat exchanger according to any of  claims 17  to  19 , characterized in that the or each heat-exchange body ( 5 ,  105 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) has at least 500 passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) distributed around the axis ( 2 ).  
     
     
         21 . Heat exchanger, in particular according to any of  claims 1  to  20 , comprising at least one heat-exchange body ( 5 ,  105 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) having successive sheet metal elements ( 23 ,  27 ,  127 ) which alternately bound passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) for a first fluid ( 15 ) and a second fluid ( 16 ) and between which gas-permeable intermediate layers ( 31 ,  32 ,  132 . 2 ) are arranged, each sheet metal element ( 23 ,  27 ,  127 ) having two side edges ( 23   c ,  23   d ,  27   c ,  27   d ) facing away from one another and parallel to one another, and at least substantial parts of the passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) running along the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) characterized in that each intermediate layer ( 31 ,  32 ,  132 . 2 ) consists of a knitted wire fabric ( 37 ) which has rows ( 37   a ) of stitches comprising stitches ( 37   b ) which are adjacent to one another and are formed from cohesive wire sections, and that these rows ( 37   a ) of stitches are generally approximately at right angles to the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ).  
     
     
         22 . Heat exchanger according to  claim 21 , characterized in that each knitted wire fabric ( 37 ) is fastened at points to one, and only one, sheet metal element ( 23 ,  27 ) adjacent to it, for example each knitted wire fabric ( 37 ) being fastened by a few spot welds to said sheet metal element ( 23 ,  27 ) adjacent to it.  
     
     
         23 . Heat exchanger according to  claim 21  or  22 , characterized in that two rows ( 37   a ) of stitches present in succession along the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) have at most a single cohesive wire section, apart from the interlinked stitches ( 37   b ).  
     
     
         24 . Heat exchanger according to any of  claims 21  to  23 , characterized in that the or each heat-exchange body ( 5 ,  105 . 1 ,  105 . 2 ,  205 . 1 ,  205 . 2 ) encompasses an axis ( 2 ) and is annular in a cross-section at right angles to said axis, that each sheet metal element ( 23 ,  27 ,  127 ) has an inner edge ( 23   a ,  27   a ) and an outer edge ( 23   b ,  27   b ), that the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) run from the inner edge ( 23   a ,  27   a ) to the outer edge ( 23   b ,  27   b ) and make an angle with the axis ( 2 ), that sheet metal elements ( 23 ,  27 ,  127 ) adjacent to one another have substantially constant distances from one another along the whole lengths of their side edges ( 23   c ,  23   d ,  27   c ,  27   d ) and that the passages ( 33 ,  34 ,  134 . 1 ,  134 . 2 ) are closed along at least the largest parts of the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ).  
     
     
         25 . Heat exchanger according to  claim 24 , characterized in that a first passage ( 33 ) for the first fluid ( 15 ) and a second passage ( 34 ,  134 . 1 ,  134 . 2 ) for the second fluid ( 16 ) are present alternately in succession around the axis ( 2 ), that edge strips ( 24 ,  25 ) running at each first passage ( 33 ) along the side edges ( 23   c ,  23   d ,  27   c ,  27   d ) of the sheet metal elements ( 23 ,  27 ,  127 ) bounding this first passage ( 33 ) are arranged between the two sheet metal elements ( 23 ,  27 ,  127 ) and are connected firmly and tightly to the latter and that edge strips ( 28 ,  29 ) running at each second passage ( 34 ,  134 . 1 ,  134 . 2 ) along the inner edges ( 23   a ,  27   a ) and along the outer edges ( 23   b ,  27   b ) of the sheet metal elements ( 23 ,  27 ,  127 ) bounding this second passage ( 34 ,  134 . 1 ,  134 . 2 ) are arranged between the sheet metal elements ( 23 ,  27 ,  127 ) and are firmly and tightly connected to the latter.  
     
     
         26 . Heat exchanger according to  claim 24  or  25 , characterized in that the sheet metal elements ( 23 ,  27 ,  127 ) adjacent to one another are everywhere at least approximately a constant distance apart, apart from any edge strips ( 24 ,  25 ,  28 ,  29 ) connected at edges ( 23   a ,  23   b ,  23   c ,  23   d ,  27   a ,  27   b ,  27   c ,  27   d ) of said sheet metal elements to said sheet metal elements and arranged between adjacent sheet metal elements ( 23 ,  27 ,  127 ), are completely smooth, straight and parallel to one another in the axial direction and are curved completely parallel to one another and smooth and, for example, substantially involute in sections perpendicular to the axis ( 2 ), so that the sheet metal elements ( 23 ,  27 ,  127 ) are free of protuberances and indentations, such as, for example, waves and/or ribs and the like, and of angled and/or curved edge sections.  
     
     
         27 . Heat exchanger according to any of  claims 21  to  26 , characterized in that each sheet metal element ( 23 ,  27 ,  127 ) has a thickness which is at most 5 mm, expediently at most 1 mm, preferably at most 0.5 mm and, for example, at most 0.3 mm, and that the knitted wire fabrics ( 37 ) consist of wires whose thickness is at most 5 mm, expediently at most 1 mm, preferably at most 0.8 mm and, for example, 0.3 mm to 0.7 mm, the sheet metal elements ( 23 ,  27 ,  127 ) and knitted wire fabrics ( 37 ) preferably consisting of stainless steel.