Fabrication materials and techniques for plate heat and mass exchangers for indirect evaporative coolers

Abstract

Heat exchanger plates for indirect evaporative coolers, of the type having a dry side having low permeability to an evaporative liquid and formed to allow a product fluid to flow over a heat transfer area of its surface, a wet side designed to have its surface wet by an evaporative liquid, and formed to allow a working gas to flow over its surface to evaporate the evaporative liquid, are formed such that the wet side comprises a hydrophobic fiber sheet and the dry side comprises a non-permeable sealing layer on the sheet. Heat seal strips are formed at the inlet and outlet of the plates and air flow perforations are formed through the plates.

1 . A heat exchanger plate for use in an indirect evaporative cooling system, the plate comprising:
 a dry side having low permeability to an evaporative liquid and formed to allow a product fluid to flow over a heat transfer area of its surface; and   a wet side designed to have its surface wet by an evaporative liquid, and formed to allow a working gas to flow over its surface to evaporate the evaporative liquid;   wherein the wet side comprises a hydrophobic material formed to wick the evaporative fluid.   
   
   
       2 . The plate of  claim 1 , further comprising heat seal strips formed at an inlet edge and an outlet edge of the plate. 
   
   
       3 . The plate of  claim 1  wherein the wet side comprises a spun bond material and the non-permable material comprises an extruded layer. 
   
   
       4 . The plate of  claim 3  wherein the spun bond material is polypropylene and the non-permeable material is polypropylene/polyethylene. 
   
   
       5 . The plate of  claim 1 , further comprising channel guides to channel the working gas and the product fluid. 
   
   
       6 . The plate of  claim 1  wherein the dry side is hydrophilic. 
   
   
       7 . An indirect evaporative cooler comprising:
 a plurality of generally parallel, spaced apart plates wherein each plate has
 a dry side having low permeability to an evaporative liquid and formed to allow a product fluid to flow over a heat transfer area of its surface; 
 a wet side designed to have its surface wet by an evaporative liquid, and formed to allow a working gas to flow over its surface to evaporate the evaporative liquid; and; 
 wherein the wet side comprises a hydrophobic material configured to wick the evaporative liquid; 
   and wherein the plates alternate such that wet sides face wet sides and dry sides face dry sides.   
   
   
       8 . The indirect evaporative cooler of  claim 7  wherein the plates are oriented generally horizontally and further comprise heat seal strips formed at an inlet edge and an outlet edge of the plates. 
   
   
       9 . The indirect evaporative cooler of  claim 7 , wherein the plates further form a trough containing the evaporative fluid between wet sides. 
   
   
       10 . The method of fabricating heat exchanger plates for use in an indirect evaporative cooling system comprising the steps of:
 (a) forming a sheet of material having a dry side of the sheet which has low permeability to an evaporative liquid and is configured to allow a product fluid to flow over a heat transfer area of its surface; and a wet side of the sheet which is hydrophobic and is configured to wick the evaporative fluid and to allow a working gas to flow over its surface to evaporate the evaporative liquid; and   (b) cutting the sheets into plates wherein each plate has an inlet edge opposite an outlet edge;   
   
   
       11 . The method of  claim 10 , further comprising the steps of:
 (c) forming wet channels on wet sides of plates generally parallel to the inlet and outlet edges; and   (d) forming dry channels on dry sides of plates.   
   
   
       12 . The method of  claim 10  further comprising the step of forming heat seal strips at the inlet and outlet edges. 
   
   
       13 . The method of  claim 12  wherein the step of forming wet channels comprises forming wet channel guides, and wherein a wet channel guide overlaps the heat seal strip at the inlet edge and a wet channel guide overlaps the heat seal strip at the outlet edge. 
   
   
       14 . The method of  claim 10 , further comprising the step of forming perforations in the sheets. 
   
   
       15 . The method of  claim 14 , wherein the step of forming dry channels comprises forming channel guides generally perpendicular to the inlet edge and the outlet edge, and where the step of forming perforations forms perforations in a line perpendicular to the inlet edge and outlet edge. 
   
   
       16 . The method of  claim 10  wherein the step of forming further forms the dry side to be hydrophilic.