Clamshell Heat Exchangers

Abstract

A clamshell heat exchanger for use in a combustion furnace of an HVAC system is presented that includes in one instance two passageways coupled by a turnaround passageway. The first passageway that receives the combustion products diverges. A cross section of the first passageway resembles a tear drop or air foil with the widest portion closest to the second passageway. The second passageway also diverges from the turnaround portion towards the outlet. The second passageway may include a baffle that forms two flow streams. Other embodiments are presented.

What is claimed: 
     
         1 . A clamshell heat exchanger for use in a direct combustion furnace of an HVAC system, the clamshell heat exchanger comprising:
 a first clamshell half;   a second clamshell half;   wherein coupling the first clamshell half to the second clamshell half forms an assembled clamshell heat exchanger comprising:   an inlet and an outlet,   a first passageway, which is a combustion passageway, having a first end and a second end, wherein the inlet is proximate the first end,   a turnaround passageway having a first end and second end, wherein the second end of the first passageway is fluidly coupled to the first end of the turnaround passageway,   a second passageway, which is an exhaust passageway, having a first end and a second end, wherein the first end is fluidly coupled to the second end of the turnaround passageway and wherein the outlet is proximate the second end of the second passageway,   wherein the first passageway is fluidly coupled to the turnaround passageway and the second passageway is fluidly coupled to the turnaround passageway to form a flow pathway for combustion products, and   wherein a lateral cross section of the first passageway has more area above a lateral centerline than below the lateral centerline.   
     
     
         2 . The clamshell heat exchanger of  claim 1 , wherein the lateral cross section of the first passageway is shaped like an upside down tear drop. 
     
     
         3 . The clamshell heat exchanger of  claim 1 , wherein the lateral cross section of the first passageway is shaped like an airfoil with a leading edge facing upward. 
     
     
         4 . The clamshell heat exchanger of  claim 1 , wherein the first passageway diverges along a majority of the flow pathway from the inlet to the turnaround passageway. 
     
     
         5 . The clamshell heat exchanger of  claim 1 , wherein the first passageway diverges along a majority of the flow pathway from the first end to the second end of the first passageway and wherein the second passageway diverges along a portion of the flow pathway from the first end to the second end of the second passageway. 
     
     
         6 . The clamshell heat exchanger of  claim 1 ,
 wherein the first passageway diverges along a majority of a flow pathway from the first end to the second end with a slope of at least 0.08; and   wherein the second passageway diverges along a majority of a flow pathway from the first end to the second end with a slope of at least 0.08.   
     
     
         7 . The clamshell heat exchanger of  claim 1 , further comprising a baffle formed on an inboard portion of the second passageway forming two flow streams. 
     
     
         8 . The clamshell heat exchanger of  claim 1 , further comprising a first dimple and a second dimple on an inboard portion of the second passageway. 
     
     
         9 . The clamshell heat exchanger of  claim 1 , wherein the flow pathway increases in height along a majority of a length of the flow pathway. 
     
     
         10 . The clamshell heat exchanger of  claim 1 , wherein the second passageway has a outer wall and an inner wall that converge at least within a final ten percent of the flow pathway proximate the outlet with a slope of at least 1.25 towards the outlet. 
     
     
         11 . The clamshell heat exchanger of  claim 1 ,
 wherein the lateral cross section of the first passageway is shaped like an upside down teardrop;   wherein the first passageway diverges along a flow pathway from the first end to the second end with a slope of at least 0.08 for a majority of the flow pathway in the first passageway;   wherein the second passageway diverges along the flow pathway from the first end to the second end with a slope of at least 0.08 for a majority of the flow pathway in the second passageway;   further comprising a baffle formed on an inboard portion of the second passageway forming two flow streams; and   wherein the second passageway has a top wall and a bottom wall that converge within a final ten percent of the flow pathway proximate the outlet with a slope of at least 1.25.   
     
     
         12 . A clamshell heat exchanger for use in a combustion furnace, the clamshell heat exchanger comprising:
 a first clamshell half;   a second clamshell half;   wherein, when coupled, the first clamshell half and the second clamshell half form the clamshell heat exchanger;   a first passageway coupled to an inlet for receiving combustion products from a burner assembly, the first passageway having a longitudinal length in a first direction and comprising a first portion of a flow pathway;   a turnaround passageway coupled to the first passageway and comprising a second portion of a flow pathway that receives fluids going in a first direction and turns the fluids at least 120 degrees;   a second passageway coupled to the turnround passageway and having a longitudinal length in the first direction and comprising a third flow pathway that is opposite in direction to the first flow pathway and that comprises two flow streams; and   wherein the first passageway has a lateral cross section resembling an airfoil with its leading edge closest to the second passageway.   
     
     
         13 . The clamshell heat exchanger of  claim 12 , wherein the lateral cross section of the first passageway has a first area to one side of a lateral centerline, wherein the first area is closest to the second passageway with respect to the lateral centerline, and wherein the first area is greater than a second area that is on an opposite side of the lateral centerline. 
     
     
         14 . The clamshell heat exchanger of  claim 12 , further comprising a baffle formed on an inboard portion of the second passageway forming two flow streams. 
     
     
         15 . A clamshell heat exchanger for a combustion furnace, the clamshell heat exchanger comprising:
 a heat exchanger body formed with an inlet and an outlet;   a first passageway, turnaround passageway, and a second passageway formed in the heat exchanger body that together define a flow pathway from the inlet through the first passageway, then the turnaround passageway, then the second passageway, and finally to the outlet;   wherein an outer wall portion and an inner wall portion of the first passageway diverge from one another; and   wherein the first passageway is not symmetric about a lateral centerline.   
     
     
         16 . The clamshell heat exchanger of  claim 15 , wherein a lateral cross section of the first passageway is shaped like a teardrop having a widest portion closest to the second passageway. 
     
     
         17 . The clamshell heat exchanger of  claim 15 , with respect to the inner and outer wall of the first passageway, one wall is substantially straight in elevation view and the other is angled, and wherein a slope between the outer wall and the inner wall of the first passageway is greater than or equal to 0.08 for at least a majority of a longitudinal length of the first passageway. 
     
     
         18 . The clamshell heat exchanger of  claim 15 , wherein for at least a majority of a longitudinal length of the second passageway, an outer wall and an inner wall of the second passageway diverge from one another. 
     
     
         19 . The clamshell heat exchanger of  claim 15 , wherein the clamshell body comprises a first clamshell half and a second clamshell half coupled at least along a peripheral edge. 
     
     
         20 . The clamshell heat exchanger of  claim 15 , further comprising a baffle formed on the clamshell body in the second passageway to form two flow streams. 
     
     
         21 . The clamshell heat exchanger of  claim 15 , wherein the first passageway has a first end proximate the inlet and a second end opposite the first end, and the first passageway diverges from proximate the first end to the second end by at least 35%. 
     
     
         22 . The clamshell heat exchanger of  claim 15 , wherein the second passageway has a first end proximate the turnaround passageway and a second end proximate the outlet, and the second passageway diverges from proximate the first end of the second passageway to a widest portion of the second passageway by at least 14%.