Development of Low-Cost Components for Residential Heating Technology: DirectContact Condensing Heat Exchanger. Final Report, October 1989-December 1992

摘要

The objective of the project was to develop a novel, low-cost, durable condensingheat exchanger concept for use in high-efficiency residential gas furnaces. A patent application for the concept was filed in June 1991, and granted in March 1992. The concept involves taking hot (e.g. 500 F) flue gases from the primary heat exchanger and bubbling them directly through the liquid condensate, which is maintained and recirculated within a finned-tube condensing heat exchanger. The bubbling action created by a conventional induced-draft blower and a bubble distributor submerged only one inch produces rapid and complete heat transfer between the flue gas and the condensate. The surging two-phase flow of gases and liquid through the upper row of tubes in the inclined heat exchanger results in efficient heat transfer to the circulating air, and recirculation of the condensate within the heat exchanger. Experiments with a prototype furnace yielded steady-state efficiencies between 92 and 98 percent. Accelerated corrosion tests were performed on three different proof-of-concept secondary heat exchangers, and indicated that the novel heat exchanger passes the test even at higher than normal levels of chloride spiking in the natural gas. The Gas Research Institute is developing a licensing agreement.