Heat exchanger

A heat exchanger comprising:

• a generally cylindrical metallic housing with a peripheral wall centered on a vertical axis, a substantially flat bottom and a substantially flat top;
• a source of combustion gases at said bottom, said housing being provided with an exit port for said combustion gases at a level substantially above said bottom;
• tubing in said housing traversed by an organic liquid to be heated by said combustion gases;
• and
• conduit means in contact with outer surfaces of said housing for the passage of a cooling fluid absorbing some of the heat generated in said housing, said conduit means comprising a multiplicity of channels open toward said outer surfaces, said channels passing in a multiplicity of helicoidal turns around at least part of said peripheral wall, said cylinder wall being divided into a lower part of smaller diameter and an upper part of larger diameter, said tubing forming an inner coil with closely adjoining turns extending within said housing over nearly the full height thereof and an outer coil closely adjoining turns surrounding said inner coil within said upper part, said exit port being located near the junction of said lower and upper parts whereby combustion gases rising inside said inner coil are deflected at said top and descend along said outer coil to said exit port, said helicoidal turns being of varying pitch with minimum spacing in the vicinity of said top.