Heat exchanger

Abstract

The present invention provides a fluid-to-fluid through-the-wall heat exchanger for condensation of a vapour in a primary fluid stream, wherein a flow path ( 5 ) of the primary fluid stream is defined by an inner cylinder ( 1 ), an outer cylinder ( 2 ) arranged concentrically to and surrounding the inner cylinder, and a helical space holder ( 3 ) arranged between the inner and the outer cylinder. Additionally, the cylinder surfaces delimiting the primary flow path are made of or coated with corrosion resistant material in order to reduce a contamination of the primary fluid. Compared to other condensers with identical ratings, this heat exchanger shows a smaller flow resistance, resulting in a smaller power demand of the blower or pumps, It is therefore particularly suitable for fuel cell systems where the condensed water has to be recirculated in the system and where purity demands are high and parasitic blower power should be minimal. The manufacturing of such a double envelope cylindrical heat exchanger is particularly simple and cost effective.

1 . A heat exchanger of the fluid-to-fluid through-the-wall type for condensation of a vapour in a primary fluid stream, with an inlet ( 4 ), a helical primary flow path ( 5 ) and an outlet ( 6 ) for said primary fluid stream, wherein the helical primary flow path ( 5 ) is defined by an outer cylinder surface ( 11 ) of an inner cylinder ( 1 ), an inner cylinder surface ( 22 ) of an outer cylinder ( 2 ) arranged concentrically to the inner cylinder ( 1 ) and a helical space holder ( 3 ) arranged between the inner and the outer cylinder, 
 characterised in that at least one of an inner surface ( 12 ) of the inner cylinder ( 1 ) or an outer surface ( 21 ) of the outer cylinder ( 2 ) delimits a secondary flow path for a cooling fluid ( 8 ) flowing along said cylinder surface ( 12 , 21 ), in that said cylinder ( 1 , 2 ) separating the primary and the secondary flow paths is made of a first material and coated, on the cylinder surface ( 11 , 22 ) delimiting the helical primary flow path ( 5 ), with a layer comprising a chemically resistant material other than said first material, and in that the helical space holder ( 3 ) is not attached to the coated cylinder surface ( 11 , 22 ).    
     
     
         2 . The heat exchanger according to  claim 1 , characterised in that the inner cylinder ( 1 ) is at least partially open and delimits a secondary flow path for the cooling fluid ( 8 ).  
     
     
         3 . The heat exchanger according to  claim 1 , characterised in that the helical space holder ( 3 ) consists of or is coated with a chemically resistant and preferably non-metallic material.  
     
     
         4 . The heat exchanger according to  claim 1  or  2 , characterised in that a third cylinder ( 9 ) is provided concentrically to the cylinders ( 1 , 2 ) at a radial distance d2 from a cylinder surface ( 12 , 21 ) delimiting the secondary flow path and in that the third cylinder ( 9 ) further delimits the secondary flow path for the cooling fluid ( 8 ).  
     
     
         5 . The heat exchanger according to  claim 1  or  4 , characterised in that cooling fins ( 7 ) are provided on the cylinder surface ( 12 , 21 ) delimiting the secondary flow path.  
     
     
         6 . The heat exchanger according to  claim 4 , characterised in that a second helical space holder is provided between the cylinder surface ( 12 , 21 ) and the third cylinder ( 9 ) delimiting the secondary flow path.  
     
     
         7 . The heat exchanger according to  claim 2 , characterised in that the cylinder axis is oriented vertically with the inlet ( 4 ) for the primary fluid stream on top, and in that the inner cylinder ( 1 ) is dimensioned such as to sustain a natural convection of the cooling fluid ( 8 ).  
     
     
         8 . The heat exchanger according to one of the preceding claims, characterised in that the cylinder axis is oriented vertically and the space holder ( 3 ) conducts the condensing water towards the interface between the space holder ( 3 ) and the cylinder surfaces ( 11 , 22 ) delimiting the helical primary flow path ( 5 ).  
     
     
         9 . A use of a heat exchanger according to any of the preceding claims for condensation of water vapour in a fuel cell system with a closed water cycle.  
     
     
         10 . A method of producing a heat exchanger of the fluid-to-fluid through-the-wall type for condensation of a vapour in a primary fluid stream, with an inlet ( 4 ), a helical primary flow path ( 5 ) and an outlet ( 6 ) for said primary fluid stream, wherein the helical primary flow path ( 5 ) is defined by an outer cylinder surface ( 11 ) of an inner cylinder ( 1 ), an inner cylinder surface ( 22 ) of an outer cylinder ( 2 ) arranged concentrically to the inner cylinder ( 1 ) and a helical space holder ( 3 ) arranged between the inner and the outer cylinder, and wherein the inner cylinder ( 1 ) is made of a first material and delimits a secondary flow path for the cooling fluid ( 8 ), comprising 
 coating the outer cylinder surface ( 11 ) of the inner cylinder ( 1 ) with a layer comprising a chemically resistant material other than said first material,    winding the space holder ( 3 ) around the inner cylinder ( 1 ) or attaching the space holder ( 3 ) to the inner surface ( 22 ) of the outer cylinder ( 2 ).