Indirect evaporative cooling heat exchanger

Abstract

A heat exchanger including a header having a plurality of header openings with rigid tubes that may be made of plastic are inserted in the openings. The tubes are sealed to the header to prevent leakage between the header and the tubes to prevent water and air leakage between the wet, scavenger air stream flowing through the tubes and a dry air stream flowing around the tubes. A method of making the heat exchanger includes providing the openings with a flange and uses an interference fit between the rigid heat exchange tubes and the header openings. A self-leveling sealant may be used to seal the heat exchanger tubes to the header using, for example, a paint roller and/or a paint sprayer.

What is claimed is: 
     
       1. A method of sealing a plurality of rigid tubes to a metal header having a plurality of openings therethrough, comprising:
 forming a flange into each of the openings in the header;   inserting the rigid tubes into the openings in the header, the header having an exterior surface and an interior surface and the rigid tubes having a top portion and a bottom portion, the rigid tubes are inserted with the bottom portion first, and are placed into the openings of the header so that the top portion of the rigid tubes are substantially flush with the exterior surface of the header; and   applying a sealant to the exterior surface of the header and the inserted rigid tubes by an absorbent applicator and/or a spray applicator.   
     
     
       2. The method of  claim 1 , wherein applying the sealant includes rolling an adhesive over the header. 
     
     
       3. The method of  claim 1 , wherein at least one groove is provided in the tubes. 
     
     
       4. The method of  claim 1 , wherein an end surface of the rigid tubes is angled with respect to a bottom end portion of the rigid tubes. 
     
     
       5. The method of  claim 1 , wherein an end surface of the rigid tubes has a compound angle with respect to a bottom end portion of the rigid tubes. 
     
     
       6. The method of  claim 4 , wherein the end surface of the rigid tubes is angled at approximately 20 to 30 degrees from the horizontal. 
     
     
       7. The method of  claim 1 , wherein the sealant is a self-leveling adhesive. 
     
     
       8. The method of  claim 1 , wherein the flange extends in a direction perpendicular from the exterior surface of the header. 
     
     
       9. The method of  claim 1 , further comprising providing each of the openings with a flange before inserting the rigid tubes,
 wherein the flange extends in a direction perpendicular from the substantially uniform exterior surface of the header.   
     
     
       10. The method of  claim 1 , further comprising providing each of the openings with a flange before inserting the rigid tubes,
 wherein the flange extends in a direction perpendicular from the substantially planar exterior surface of the header.   
     
     
       11. A heat exchanger for an indirect evaporative cooling unit, comprising:
 a header having a plurality of openings penetrating the header; and   a plurality of rigid plastic tubes inserted in the openings in the header, ends of the plurality of rigid plastic tubes being sealed in a leak tight manner to the header,   wherein the plurality of rigid plastic tubes are each configured to expand and contract within a predetermined range to separate solid deposits accumulating on the plurality of rigid plastic tubes.   
     
     
       12. The heat exchanger of claim 11, wherein the solid deposits are the result of evaporation of water on the plurality of rigid plastic tubes. 
     
     
       13. The heat exchanger of claim 11, wherein the separated solid deposits are deposited in a sump that is routinely flushed to remove the separated solids from the heat exchanger. 
     
     
       14. The heat exchanger of claim 11, wherein the expansion and contraction of the plurality of rigid plastic tubes within the predetermined range is caused by changes in an interior pressure of the plurality of rigid plastic tubes. 
     
     
       15. The heat exchanger of claim 14, wherein the changes in the interior pressure of the plurality of rigid plastic tubes are caused by changes in a speed of the air flowing through an interior of the plurality of rigid plastic tubes. 
     
     
       16. The heat exchanger of claim 14, wherein the changes in the interior pressure of the plurality of rigid plastic tubes are in a range of up to 0.5 inches of water column pressure. 
     
     
       17. The heat exchanger of claim 11, wherein the predetermined range is up to 0.025 inches. 
     
     
       18. The heat exchanger of claim 11, wherein the plurality of rigid plastic tubes have a wall thickness of about 0.020 inches. 
     
     
       19. The heat exchanger of claim 11, wherein the plurality of rigid plastic tubes have an internal web structure to flexibly maintain tube dimensions, and to maintain the expansion and contraction of the plurality of rigid plastic tubes within the predetermined range. 
     
     
       20. The heat exchanger of claim 11, wherein the plurality of rigid plastic tubes are sealed to the header by an adhesive. 
     
     
       21. The heat exchanger of claim 11, wherein the plurality of rigid plastic tubes are sealed to the header by a self-leveling liquid. 
     
     
       22. The heat exchanger of claim 11, wherein the plurality of rigid plastic tubes include grooves formed on an internal surface to provide increased surface area and reduce thermal resistance. 
     
     
       23. The heat exchanger of claim 11, wherein the plurality of rigid plastic tubes comprise polyvinylchloride. 
     
     
       24. The heat exchanger of claim 11, wherein the plurality of rigid plastic tubes comprise corrosion resistant polymers having a fire and smoke retardant rating that meets or exceeds UL94 V-O or V-1 rating. 
     
     
       25. An indirect evaporative cooling unit including the heat exchanger of claim 11. 
     
     
       26. An indirect/direct evaporative cooling unit including the heat exchanger of claim 11. 
     
     
       27. A heat exchanger for an indirect evaporative cooling unit, comprising:
 a header having a plurality of openings penetrating the header; and   a plurality of rigid plastic tubes that individually have two opposing planar major walls connected to each other by two opposing rounded minor walls, the plurality of rigid plastic tubes being inserted in the openings in the header, and ends of the plurality of rigid plastic tubes being sealed in a leak tight manner to the header,   wherein the plurality of rigid plastic tubes are each configured to expand and contract within a predetermined range to separate solid deposits accumulating on the plurality of rigid plastic tubes.   
     
     
       28. An evaporative cooling unit comprising:
 a base;   a frame supported by the base;   a heat exchanger within the frame, the evaporative cooling unit being configured to provide water and air to the heat exchanger;   a fan configured to intake air into the evaporative cooling unit; and   an exhaust configured to exhaust air from the evaporative cooling unit,   wherein the heat exchanger comprises:   a header having a plurality of openings penetrating the header; and   a plurality of rigid tubes inserted in the openings in the header and ends of the plurality of rigid tubes being sealed in a leak tight manner to the header, the plurality of rigid tubes each being configured to expand and contract within a predetermined range to separate solid deposits accumulating on an internal or external surface of the plurality of rigid tubes.   
     
     
       29. The evaporative cooling unit of claim 28, wherein the evaporative cooling unit is an indirect evaporative cooling unit. 
     
     
       30. The evaporative cooling unit of claim 28, wherein the evaporative cooling unit is an indirect/direct evaporative cooling unit that further comprises a direct cooling stage. 
     
     
       31. The evaporative cooling unit of claim 28, wherein the plurality of rigid tubes are open to the environment within the evaporative cooling unit. 
     
     
       32. The evaporative cooling unit of claim 28, wherein the rigid tubes are rigid plastic tubes.