With the increasing cost of fuel, methods for increasing the efficiency of heat exchanger assemblies for extracting heat from the products of combustion of fuel burners has become increasingly more cost effective. One means of increasing the efficiency of heat recovery has been to burn the fuel in small-volume, water-walled combustion chambers. Forced draft or pulsed combustion techniques are utilized to achieve high rates of heat transfer and to vent the products of combustion.
Recently, systems have been proposed to cool the products of combustion below the dew point temperature of those products, typically below 130.degree. F., in order to condense some of the vapor and thereby extract the latent heat of vaporization of that vapor. To cool the products of combustion to that extent and to minimize the size, and thus the cost, of the heat exchanger assemblies, efficient heat exchangers must be designed.
An object of this invention is to provide an efficient water heating system in which heat is extracted from the products of combustion by condensing vapor in the products, the system having an acceptable size and cost.
The condensate from natural gas combustion products is mildly acidic, and the acidic nature of the condensate is expected to be a potential cause of corrosion. The acidic nature of the condensate may result from sulfuric acid, nitric acid, and carbonic acid.
A further object of this invention is to provide a water heating system designed to withstand the corrosive effects of the condensate at a minimal cost.