Premixing device and hot-water supply apparatus

Abstract

A premixing device includes: a main pipe of a cylindrical shape, which is disposed so as to surround an air passage and has a fuel chamber of an annular shape, which is formed inside a pipe wall; a butterfly valve having an air inlet hole and rotatably disposed so as to be located within the air passage; at least one support part which internally has a fuel passage communicating with the fuel chamber and extends radially inward from an inner wall surface of the main pipe so as to be located within the air passage downstream of the butterfly valve; and a venturi ring supported by the at least one support part so as to be located within the air passage downstream of the butterfly valve. The fuel passage has an outlet opening into a space of the air passage on an inner circumferential side of the venturi ring.

1 . A premixing device, comprising:
 a main pipe of a cylindrical shape, which is disposed so as to surround an air passage and has a fuel chamber of an annular shape, which is formed inside a pipe wall;   a butterfly valve having an air inlet hole and rotatably disposed so as to be located within the air passage;   at least one support part which internally has a fuel passage communicating with the fuel chamber and extends radially inward from an inner wall surface of the main pipe so as to be located within the air passage downstream of the butterfly valve; and   a venturi ring supported by the at least one support part so as to be located within the air passage downstream of the butterfly valve,   the fuel passage having an outlet opening into a space of the air passage on an inner circumferential side of the venturi ring.   
     
     
         2 . The premixing device according to  claim 1 , wherein
 the venturi ring is arranged within the air passage so as to be concentric with the air inlet hole of the butterfly valve in a fully closed state.   
     
     
         3 . The premixing device according to  claim 1 , wherein
 the venturi ring is supported by a pair of support parts as the at least one support part, and   the pair of support parts are disposed on opposite sides of the venturi ring within the air passage so as to extend along a rotational axis of the butterfly valve.   
     
     
         4 . The premixing device according to  claim 3 , wherein
 each of the support parts has a first width along a pipe axial direction of the main pipe, which is greater than a second width along a direction perpendicular to the pipe axial direction.   
     
     
         5 . The premixing device according to  claim 4 , wherein
 a ratio of the second width of each of the support parts to a maximum thickness of the butterfly valve is at least 0.8 and at most 1.2.   
     
     
         6 . The premixing device according to  claim 1 , wherein
 the venturi ring has an inner circumferential surface into which the outlet of the fuel passage opens.   
     
     
         7 . The premixing device according to  claim 6 , wherein
 the inner circumferential surface of the venturi ring includes:
 a first tapered portion in which an inner diameter of the venturi ring decreases toward downstream; 
 a first throat portion located downstream of the first tapered portion and disposed in a region into which the outlet of the fuel passage opens; and 
 a first enlarging diameter portion in which the inner diameter of the venturi ring expands toward downstream, the first enlarging diameter portion being located downstream of the first throat portion. 
   
     
     
         8 . The premixing device according to  claim 7 , wherein
 the inner wall surface of the main pipe includes:
 a second tapered portion in which an inner diameter of the main pipe decreases toward downstream, the second tapered portion being located downstream of an upstream end of the venturi ring; 
 a second throat portion located downstream of the second tapered portion and disposed at a position corresponding to a downstream end of the venturi ring in a pipe axial direction of the main pipe; and 
 a second enlarging diameter portion in which the inner diameter of the main pipe expands toward downstream, the second enlarging diameter portion being located downstream of the second throat portion. 
   
     
     
         9 . A hot-water supply apparatus, comprising:
 the premixing device according to  claim 1  for generating an air-fuel mixture of fuel and combustion air;   a burner for burning the fuel contained in the air-fuel mixture from the premixing device; and   a heater for generating hot water by utilizing potential heat of combustion gas generated by burning the fuel in the burner.