Heat Exchanger

Abstract

In a heat exchanger, a respective meander passage 3 1 , 3 2 in each of two stages connecting heat absorbing tubes 31 divided into the two stages and arranged in a flow direction of a combustion gas in an inside of a casing 1 from one side to the other side in a Y-axis direction is constituted, and both a heat absorbing tube 31 of # 11 at an upstream end of the meander passage 3 1 in one of the stages and a heat absorbing tube 31 of # 21 at a downstream end of the meander passage 3 2 in the other of the stages are made to be positioned at the one side in the Y-axis direction, a distance La between the heat absorbing tubes 31, 31 of # 11 and # 21, is made longer than a respective distance Lb between each heat absorbing tube 31 other than the heat absorbing tube 31 of # 11 at the upstream end of the meander passage 3 1 in the one of the stages and such each heat absorbing tube 31 other than the heat absorbing tube 31 of # 21 at the downstream end of the meander passage 3 2 in the other of the stages as is the closest to each heat absorbing tube 31 other than the heat absorbing tube 31 of # 11 at the upstream end in the one of the stages.

What is claimed is: 
     
         1 . A heat exchanger heated by a combustion gas, comprising,
 a rectangular cylindrical casing an inside of which the combustion gas flows in; on a premise that two orthogonal directions crossing a flow direction of the combustion gas in the casing are defined as an X-axis direction and a Y-axis direction, respectively; a plurality of heat absorbing fins stacked and arranged in the X-axis direction in the casing;   a plurality of heat absorbing tubes piercing through the heat absorbing fins and side plates of both sides in the X-axis direction of the casing, and an inside of which a fluid to be heated flows in, and a connecting portion connecting the heat absorbing tubes in series at outsides of the side plates of both sides in the X-axis direction of the casing, wherein the heat absorbing tubes are divided into two stages and arranged in the flow direction of the combustion gas, a meander passage connecting a plurality of the heat absorbing tubes in each stage from an outermost side of one side in the Y-axis direction to an outermost side of the other side in the Y-axis direction is constituted by a plurality of the heat absorbing tubes in each stage and the connecting portion for each stage, the meander passage is provided in each of the two stages consisting of a first stage at the upstream side in the flow direction of the combustion gas and a second stage at the downstream side in the flow direction of the combustion gas, the heat absorbing tubes at the upstream and downstream ends of the meander passage in one of the first and second stages are positioned at the outermost sides of the one and the other sides in the Y-axis direction, respectively, and the heat absorbing tube at the downstream end in the one of the first and second stages and the heat absorbing tube at the upstream end, which is positioned at the outermost side of the other side in the Y-axis direction, of the meander passage in the other of the first and second stages are connected to each other, allowing the fluid to be heated to flow from the meander passage in the one of the first and second stages to the meander passage in the other of the first and second stages,   wherein:   a distance between the heat absorbing tube at the upstream end positioned at the outermost side of the one side in the Y-axis direction of the meander passage in the one of the stages and the heat absorbing tube at the downstream end positioned at the outermost side of the one side in the Y-axis direction of the meander passage in the other of the stages is longer than a respective distance between each heat absorbing tube other than the heat absorbing tube at the upstream end of the meander passage in the one of the stages and such each heat absorbing tube other than the heat absorbing tube at the downstream end of the meander passage in the other of the stages as is the closest to each heat absorbing tube other than the heat absorbing tube at the upstream end of the meander passage in the one of the stages.   
     
     
         2 . The heat exchanger as claimed in  claim 1 , wherein a direction for lengthening the distance between the heat absorbing tube at the upstream end of the meander passage in the one of the stages and the heat absorbing tube at the downstream end of the meander passage in the other of the stages is set to the flow direction of the combustion gas. 
     
     
         3 . The heat exchanger as claimed in  claim 1 , wherein in a case where the one of the stages is the first stage and the other of the stages is the second stage,
 wherein:   notches are provided with each heat absorbing fin at portions positioned at a more upstream side in the flow direction of the combustion gas than each heat absorbing tube of the meander passage in the second stage, the notches corresponding to the heat absorbing tube at the downstream end of the meander passage in the second stage are defined as first notches and the notches corresponding to each heat absorbing tube other than the heat absorbing tube at the downstream end of the meander passage in the second stage are defined as second notches, and the first notches are formed larger than the second notches.   
     
     
         4 . The heat exchanger as claimed in  claim 1 , wherein in a case where the one of the stages is the first stage and the other of the stages is the second stage,
 wherein:   a ventilation resistant portion which suppresses the combustion gas from being directed to the heat absorbing tube at the downstream end of the meander passage in the second stage is provided.   
     
     
         5 . The heat exchanger as claimed in  claim 1 , wherein in a case where the one of the stages is the first stage and the other of the stages is the second stage, an exhaust gas gathering portion covering an opening at the downstream end in the flow direction of the combustion gas of the casing is provided, and an exhaust port for discharging the combustion gas is opened at the exhaust gas gathering portion,
 wherein:   the exhaust port is provided at a deviated portion of the other side in the Y-axis direction of the exhaust gas gathering portion.