Tubular heat exchanger

A tubular heat exchanger, comprising:

• a top;
• a plurality of tubes stacked in multiple stages to have a front gap among the tubes narrower than a rear gap among the tubes, each tube having:
• a front cell formed inside;
• a plurality of middle cells formed inside;
• an end cell formed inside, wherein the front cell is thicker than the end cell;
• an upper surface formed of an inclined surface progressively and symmetrically reduced and inclined rearwardly from a front end of said each tube to a rear end of said each tube with respect to a tube center line;
• and
• a lower surface formed of an inclined surface progressively and symmetrically reduced and inclined rearwardly from a front end of said each tube to a rear end of said each tube with respect to the tube center line, wherein the tubes are stacked in a tilted position such that the tube center line is tilted in a slope of a predetermined angle to maintain the lower surface horizontally parallel to a wind direction;
• and
• a plurality of zigzag-bent heat-radiating fins placed among the tubes, each heat-radiating fin comprising:
• a horizontal upper surface, wherein the horizontal upper surface is brazed and welded to the lower surfaces of the tubes;
• and
• a lower surface formed of an inclined surface progressively enlarged and inclined rearwardly from a front end of said each heat-radiating fin to a rear end of said each heat-radiating fin with respect to a horizontal fin center line, wherein the lower surface is brazed and welded to the upper surfaces of the tubes.