Enhanced effectiveness evaporator for a micro combined heat and power system

Abstract

An evaporator for a micro combined heat and power system. The evaporator includes a heat source, an enclosure made up of at least a heating chamber and a primary fluid flowpath, and tubing that intersects the primary fluid flowpath. In one embodiment, the heat source is a burner such that the primary fluid is an exhaust gas formed by a combustion process at the burner, and the primary fluid flowpath is for the transport of the exhaust gas. The tubing defines a secondary fluid flowpath with a proximal portion adjacent the heat source and a distal portion downstream in the flowpath from the proximal portion. Working fluid first flows through the distal portion in counterflow relationship with the exhaust gas, then flows through the proximal portion in co-flow relationship with the exhaust gas. This circuiting avoids the excessive working fluid temperature of traditional counterflow heat exchangers, while providing better heat transfer efficiency than traditional co-flow heat exchangers.

We claim:  
     
         1 . An evaporator comprising: 
 a heat source configured to produce an elevated temperature primary fluid;    an enclosure including a heating chamber and a primary fluid flowpath, said heating chamber configured to transport at least a portion of the heat generated from said heat source to said flowpath; and    tubing disposed within said flowpath and adjacently spaced relative to said heat source such that during heat source operation heat transferred therefrom is sufficient to superheat an organic working fluid passing through said tubing, said tubing including: 
 a distal portion configured to be the point of entry of said organic working fluid into said evaporator such that said distal portion defines a downstream position in said flowpath, such that during said evaporator operation, said organic working fluid flowing through said distal portion is in counterflow relationship with said elevated temperature primary fluid; and  
 a proximal portion in fluid communication with and disposed upstream of said distal portion in said flowpath, such that during said evaporator operation, said organic working fluid flowing through said proximal portion is in co-flow relationship with said elevated temperature primary fluid so that upon exiting said evaporator, the temperature of said organic working fluid does not exceed a predetermined maximum.  
   
     
     
         2 . An evaporator according to  claim 1 , wherein said heat source is a burner.  
     
     
         3 . An evaporator according to  claim 2 , wherein said elevated temperature primary fluid is an exhaust gas produced by said burner.  
     
     
         4 . An evaporator according to  claim 1 , wherein said predetermined maximum is the maximum allowable temperature of said working fluid.  
     
     
         5 . An evaporator according to  claim 1 , wherein said counterflow relationship in said distal portion is a cross-counterflow relationship.  
     
     
         6 . An evaporator according to  claim 1 , wherein said co-flow relationship in said proximal portion is a cross-co-flow relationship.  
     
     
         7 . A micro combined heat and power system comprising: 
 a working fluid circuit configured to transport an organic working fluid, said working fluid circuit comprising: 
 a pump configured to circulate said organic working fluid through said working fluid circuit;  
 an evaporator configured to convert said organic working fluid from a subcooled liquid into a superheated vapor, said evaporator comprising: 
 a heat source configured to produce an elevated temperature primary fluid;  
 an enclosure including a heating chamber and a primary fluid flowpath, said heating chamber configured to transport at least a portion of the heat generated from said heat source to said flowpath; and  
 tubing disposed within said flowpath and adjacently spaced relative to said heat source such that during heat source operation heat transferred therefrom is sufficient to superheat said organic working fluid passing through said tubing, said tubing including a distal portion and a proximal portion, said distal portion configured to be the point of entry of said organic working fluid into said evaporator from said pump such that said organic working fluid flowing through said distal portion is in counterflow relationship with said elevated temperature primary fluid, said proximal portion in fluid communication with and disposed upstream of said distal portion in said flowpath such that said organic working fluid flowing through said proximal portion is in co-flow relationship with said elevated temperature primary fluid and upon exiting said evaporator, the temperature of said organic working fluid does not exceed a predetermined maximum;  
 
 an expander in fluid communication with said tubing such that said organic working fluid received therefrom remains superheated after expansion in said expander; and  
 a condenser in fluid communication with said expander; and  
   at least one energy conversion circuit operatively responsive to said working fluid circuit such that upon operation of said cogeneration system, said at least one energy conversion circuit is configured to provide useable energy.    
     
     
         8 . A micro combined heat and power system according to  claim 7 , wherein said heat source is a burner.  
     
     
         9 . A micro combined heat and power system according to  claim 8 , wherein said elevated temperature primary fluid is an exhaust gas produced by said burner.  
     
     
         10 . A micro combined heat and power system according to  claim 7 , wherein said expander is a scroll expander.  
     
     
         11 . A micro combined heat and power system according to  claim 7 , wherein said counterflow relationship in said distal portion is a cross-counterflow relationship.  
     
     
         12 . A micro combined heat and power system according to  claim 7 , wherein said co-flow relationship in said proximal portion is a cross-co-flow relationship.  
     
     
         13 . A Rankine cycle cogeneration system comprising: 
 a working fluid circuit comprising: 
 an evaporator comprising: 
 a heat source configured to produce an elevated temperature primary fluid;  
 an enclosure including a heating chamber and a primary fluid flowpath, said heating chamber configured to transport at least a portion of the heat generated from said heat source to said flowpath; and  
 tubing disposed within said flowpath and adjacently spaced relative to said heat source such that during heat source operation heat transferred therefrom is sufficient to superheat said organic working fluid passing through said tubing, said tubing including a distal portion and a proximal portion, said distal portion configured to be the point of entry of said organic working fluid into said evaporator such that during said system operation said organic working fluid flowing through said distal portion is in counterflow relationship with said elevated temperature primary fluid to define a predominantly subcooled liquid flow regime, said proximal portion in fluid communication with and disposed upstream of said distal portion in said flowpath such that during said system operation said organic working fluid flowing through said proximal portion is in co-flow relationship with said elevated temperature primary fluid to define sequentially a predominantly bulk boiling liquid flow regime and superheated vapor flow regime, respectively;  
 
 conduit configured to transport an organic working fluid through said working fluid circuit, at least a portion of said conduit fluidly coupled to said tubing;  
 an expander in fluid communication with said conduit such that said organic working fluid received therefrom remains superheated after said expansion in said expander;  
 a condenser in fluid communication with said expander; and  
 a pump configured to circulate said organic working fluid through at least said conduit, expander and condenser; and  
   at least one energy conversion circuit operatively responsive to said working fluid circuit such that upon operation of said cogeneration system, said at least one energy conversion circuit is configured to provide useable energy.    
     
     
         14 . A Rankine cycle cogeneration system according to  claim 13 , wherein said counterflow relationship in said distal portion is a cross-counterflow relationship.  
     
     
         15 . A Rankine cycle cogeneration system according to  claim 13 , wherein said co-flow relationship in said proximal portion is a cross-co-flow relationship.  
     
     
         16 . A cogeneration system comprising: 
 a working fluid circuit comprising: 
 an evaporator comprising: 
 a heat source configured to produce an elevated temperature primary fluid;  
 an enclosure including a heating chamber and a primary fluid flowpath, said heating chamber configured to transport at least a portion of the heat generated from said heat source to said flowpath; and  
 tubing disposed within said flowpath and adjacently spaced relative to said heat source such that during heat source operation heat transferred therefrom is sufficient to superheat said organic working fluid passing through said tubing, said tubing including: 
 a distal portion configured to be the point of entry of said organic working fluid into said evaporator such that during heat source operation said organic working fluid flowing through said distal portion is in counterflow relationship with said elevated temperature primary fluid; and  
 a proximal portion in fluid communication with said distal portion such that during heat source operation said organic working fluid flowing through said proximal portion is in co-flow relationship with said elevated temperature primary fluid, said proximal portion including a first tube section disposed adjacent said heat source and a second tube section disposed intermediate said first tube section and said distal portion;  
 
 
 conduit configured to transport an organic working fluid through said working fluid circuit, at least a portion of said conduit fluidly coupled to said tubing;  
 an expander in fluid communication with said conduit such that said organic working fluid received therefrom remains superheated after said expansion in said expander;  
 a condenser in fluid communication with said expander; and  
 a pump configured to circulate said organic working fluid through at least said conduit, expander and condenser; and  
   at least one energy conversion circuit operatively responsive to said working fluid circuit such that upon operation of said micro combined heat and power system, said at least one energy conversion circuit is configured to provide useable energy.    
     
     
         17 . A cogeneration system according to  claim 16 , wherein at least a portion of said tubing includes fins in thermal communication therewith.  
     
     
         18 . A cogeneration system according to  claim 16 , wherein said counterflow relationship in said distal portion is a cross-counterflow relationship.  
     
     
         19 . A cogeneration system according to  claim 16 , wherein said co-flow relationship in said proximal portion is a cross-co-flow relationship.  
     
     
         20 . A micro combined heat and power system comprising: 
 a working fluid circuit comprising: 
 an organic working fluid;  
 an evaporator comprising: 
 a burner configured to produce an exhaust gas;  
 an enclosure defining an exhaust gas flowpath in fluid communication with said burner; and  
 tubing in thermal communication with said flowpath such that heat transferred to said tubing from said exhaust gas is sufficient to superheat said organic working fluid passing through said tubing, said tubing including: 
 a distal portion remote from said burner such that during said burner operation said organic working fluid flowing through said distal portion is in cross-counterflow relationship with said exhaust gas;  
 a proximal portion in fluid communication with said distal portion such that during said burner operation said organic working fluid flowing through said proximal portion is in cross-co-flow relationship with said exhaust gas, said proximal portion including a first tube section disposed adjacent said burner and a second tube section disposed intermediate said first tube section and said distal portion; and  
 a plurality of fins connected to a portion of at least one of said proximal or distal portions;  
 
 
 conduit configured to transport said organic working fluid through said working fluid circuit, at least a portion of said conduit fluidly coupled to said tubing;  
 an expander in fluid communication with said conduit such that said organic working fluid received therefrom remains superheated after said expansion in said expander;  
 a condenser in fluid communication with said expander; and  
 a pump configured to circulate said organic working fluid through at least said conduit, expander and condenser; and  
   at least one energy conversion circuit operatively responsive to said working fluid circuit such that upon operation of said micro combined heat and power system, said at least one energy conversion circuit is configured to provide useable energy.