Heat exchanger having a compact design

Abstract

Disclosed is a heat exchanger having an economizer configured as a ring of tubes in a periphery of the heat exchanger. The heat exchanger includes a cylindrical flue collector and a manifold at either end of the cylindrical flue collector. The manifold has a plurality of chambers. The manifold can be made of steel or plastic and governs fluid flow rate and direction within a ring of tubes. At least two rings of heat exchanging tubes, an outer ring and an inner ring, are within the cylindrical flue collector. The rings of tubes are concentric with respect to each other.

What is claimed is: 
     
         1 . A heat exchanger comprising:
 a cylindrical flue collector;   a manifold at either end of the cylindrical flue collector, the manifold having a plurality of chambers; and   an inner ring of heat exchanging tubes and an outer ring of heat exchanging tubes within the cylindrical flue collector, wherein the rings of tubes are concentric with each other, sets of heat exchanging tubes being in fluid communication a respective chamber, the sets of heat exchanging tubes having alternating fluid flow direction and configured within the rings of tubes so that fluid flows through all of the sets of tubes and flows around the entire circumfry of each set before outletting from the ring of tubes;   wherein the outer ring is an upstream ring of tubes configured to preheat water flowing therethrough; and   wherein the inner ring is downstream of the outer ring and configured to transfer additional heat to water flowing therethrough.   
     
     
         2 . The heat exchanger as recited in  claim 1  wherein the rings of tubes comprise tubes having a main section with a circular cross-section and an end section with a flattened cross-section. 
     
     
         3 . The heat exchanger as recited in  claim 2  further comprising a tube sheet for securing each of the tubes within the heat exchanger. 
     
     
         4 . The heat exchanger as recited in  claim 3  wherein the tube sheet is a barrier between the manifold and a tube chamber within the cylindrical flue collector. 
     
     
         5 . The heat exchanger as recited in  claim 4  wherein the tubes are welded directly into the manifold. 
     
     
         6 . The heat exchanger as recited in  claim 1  wherein the outer ring of tubes is an economizer. 
     
     
         7 . The heat exchanger as recited in  claim 1  wherein tubes comprise fins. 
     
     
         8 . The heat exchanger as recited in  claim 7  wherein the fins are formed from stainless steel. 
     
     
         9 . The heat exchanger as recited in  claim 8  wherein the fins are formed from a hybrid of stainless steel and titanium. 
     
     
         10 . The heat exchanger as recited in  claim 1  wherein the manifold is formed from plastic and governs fluid flow rate and direction within a ring of tubes. 
     
     
         11 . The heat exchanger as recited in  claim 1  further comprising baffles for enhancing heat transfer between gas within the cylindrical flue collector and fluid within the tubes. 
     
     
         12 . The heat exchanger as recited in  claim 1  further comprising fins integrated with the tubes, wherein the baffles are coupled with respect to an outer ring of tubes to increase flue gas flow along the tubes and fins. 
     
     
         13 . The heat exchanger as recited in  claim 12  wherein the baffles are positioned in gaps between tubes of the outer ring of tubes. 
     
     
         14 . A heat exchanger configured to heat water, the heat exchanger comprising:
 a plurality of heat exchange tubes, each heat exchange tube having
 a main section with a circular cross-section, 
 an end section with a non-circular cross-section, and 
   a tube sheet having a plurality of through holes;   wherein end sections of the heat exchange tubes are received respective through holes of the tube sheet and are proximal to one another in an arc; and   wherein a dimension of the end sections extending along the arc is smaller than a dimension of the end sections extending transverse to the arc, thereby providing a first gap between the end sections of the heat exchange tubes that is larger than a second gap between the main sections of the heat exchange tubes.   
     
     
         15 . The heat exchanger as recited in  claim 14  wherein the flattened cross-section is oval. 
     
     
         16 . The heat exchanger as recited in  claim 14  wherein the flattened cross-section is rectangular. 
     
     
         17 . The heat exchanger as recited in  claim 14  further comprising a transition zone between the main section and the end section. 
     
     
         18 . The heat exchanger as recited in  claim 17  wherein the tube is welded to the tube sheet at an end of the end section that is in contact with the transition zone. 
     
     
         19 . The heat exchanger as recited in  claim 14  wherein a distance between centerlines of adjacent tubes is one and a half times a diameter of the main section. 
     
     
         20 . A heat exchanger configured to heat water, the heat exchanger comprising:
 a plurality of heat exchange tubes, each heat exchange tube having
 a main section with a circular cross-section, and 
 an end section with a non-circular cross-section, 
   wherein end sections of the heat exchange tubes are positioned proximal to one another along an arc; and   wherein a distance of a center of each tube from an adjoining tube center is approximately one and a half times or less than the tube diameter.   
     
     
         21 . The heat exchanger as recited in  claim 20  wherein the tube has a flattened cross-section. 
     
     
         22 . The heat exchanger as recited in  claim 20  wherein the flattened cross-section is rectangular. 
     
     
         23 . The heat exchanger as recited in  claim 20  wherein the flattened cross-section is oval. 
     
     
         24 . The heat exchanger as recited in  claim 20  further comprising tube fins. 
     
     
         25 . The heat exchanger as recited in  claim 24  wherein the tube fins are microfins.