Metallic porous body incorporated by casting into a heat exchanger

Abstract

The present invention relates to a co-cast heat exchanger element intended for a central heating boiler, which heat exchanger element is made from substantially aluminum, the heat exchanger element being provided with walls which enclose a water carrying channel, and with at least one wall which encloses at least one flue gas draft to which a burner can be connected, at least one wall which encloses the at least one flue gas draft being water-cooled in that it also forms a boundary of the water-carrying channel, while one of the water-cooled walls is provided with heat exchanging surface enlarging pins and/or fins which extend in the respective flue gas draft and is also provided with other heat exchanging surface enlarging metallic porous structures.

1 . A heat exchanger element ( 1 ) comprising walls ( 2 ) from substantially aluminium, said walls ( 2 ) enclosing at least one water carrying channel ( 3 ) and having at least one flue gas draft ( 7 ), at least one wall forming a boundary between said water carrying channel ( 3 ) and said flue gas draft ( 7 ), said at least one wall being provided with fins and/or pins ( 8 , 9 ) which enlarge the heat-exchanging surface and which extend in the flue gas draft ( 7 ), characterised in that said heat exchanger element further comprises a porous metallic body ( 10 ) from substantially aluminium, said porous metallic body being placed downstream said heat exchanging surface enlarging pins and/or fins ( 8 ,  9 ) in the direction of the flue gas flow, said walls being cast around said porous body to form a co-cast heat-exchanger element. 
     
     
         2 . A heat exchanger element ( 1 ) according to  claim 1 , wherein the porous metallic body ( 10 ) is an open cell metallic foam. 
     
     
         3 . A heat exchanger element ( 1 ) according to  claim 1 , wherein the porous metallic body ( 10 ) is a metallic spacer material. 
     
     
         4 . A heat exchanger element ( 1 ) according to  claim 1 , wherein at least one cross sectional surface of said pin and/or fin is smaller than 25 mm 2 . 
     
     
         5 . A heat exchanger element ( 1 ) according to  claim 1 , wherein said water carrying channel comprises a parallel path with respect to the flue gas draft. 
     
     
         6 . Process for the production of a heat exchanger element for a boiler containing a metallic porous body, said process comprising the steps of:
 a) providing a metallic porous body   b) putting said metallic porous body in a core box;   c) closing said core box;   d) blowing a mixture of sand and binder into the void space in the core box, thereby obtaining a hybrid structure of metallic porous body filled with said sand-binder mix,   e) hardening said sand-binder mix thereby obtaining a metallic porous body—sand core;   f) removing the core box;   g) integrating said metallic porous body—sand core in a flue gas draft sand core;   h) placing said flue gas draft sand core in a moulding box together with a water side core;   i) pouring molten metal into said moulding;   j) cooling of the cast workpiece;   k) removing the sand cores.   
     
     
         7 . Process for the production of a heat exchanger element for a boiler containing a metallic porous body, said process comprising the steps of:
 a) providing a metallic porous body   b) putting said metallic porous body in a flue gas draft-core box;   c) closing said flue gas draft core box;   d) blowing a mixture of sand and binder into the void space in the core box, thereby obtaining a hybrid structure of metallic porous body filled with said sand-binder mix,   e) hardening said sand-binder mix thereby obtaining a metallic porous body—sand core;   f) removing the core box;   g) placing said flue gas draft sand core in a moulding box together with a water side core;   h) pouring molten metal into said moulding;   i) cooling of the cast workpiece;   j) removing the sand core.   
     
     
         8 . Process for the production of a heat exchanger element for a boiler containing a metallic porous body via lost foam investment casting, said process comprising the steps of:
 a) providing a metallic porous body   b) putting said metallic porous body in a flue gas draft-core box;   c) closing said flue gas draft core box;   d) blowing a mixture of sand and binder into the void space in the core box, thereby obtaining a hybrid structure of metallic porous body filled with said sand-binder mix,   e) hardening said sand-binder mix thereby obtaining a metallic porous body—sand core;   f) removing the core box;   g) building in said metallic porous body sand core into the polystyrene pattern of the heat exchanger element;   h) coating of the polystyrene pattern—metallic porous body hybrid cluster with ceramic;   i) drying the ceramic coating;   j) placing said polystyrene pattern—metallic porous body hybrid cluster into a casting flask and backing up said cluster with un-bonded sand;   k) performing mold compaction;   l) pouring the polystyrene pattern with the molten metal;   m) cooling of the cast workpiece;   n) removing the sand cores.   
     
     
         9 . Process according to  claim 6 , wherein said metallic porous body is a metallic foam. 
     
     
         10 . Process according to  claim 6 , wherein said metallic porous body is a metallic spacer material. 
     
     
         11 . Process according to  claim 6 , wherein after step e) said sand core is removed from the periphery of said hybrid structure, thereby obtaining a small border of only metal porous body struts. 
     
     
         12 . Process according to  claim 6 , wherein the metal is aluminium or an aluminium-alloy. 
     
     
         13 . A heat exchanger element obtained by the methods as in  claim 6 . 
     
     
         14 . A heating boiler provided with a heat exchanger element according to  claim 1 .