Effect of Mixed Working Fluid Composition on Binary Cycle Condenser Heat Transfer Coefficients

Abstract

The use of mixed working fluids in binary power plants can increase plant performance provided the heat exchangers are designed to take advantage of these fluids’ non-isothermal phase changes. In the 1980’s testing was conducted at DOE’s Heat Cycle Research Facility (HCRF) where mixtures of different compositions were vaporized at supercritical pressures and then condensed. The focus of these efforts was on using the data collected to verify that Heat Transfer Research Incorporated (HTRI) codes were adequate for designing heat exchangers that could be used with mixtures. The HCRF investigations included a test series with mixtures of propane and 0% to 40% (molar) isopentane at condenser tube orientations of 10°, 60°, and 90° off the horizontal. Testing was performed over a range of working fluid and cooling fluid conditions. Though the condenser used in this testing was water cooled, the working fluid condensation occurred on the tube-side of the heat exchanger. This tube-side condensation is analogous to that in an air-cooled condenser. The sensitivity of the condensing coefficients to these composition, tube orientation and process conditions is being evaluated as the initial step in an assessment of the suitability of air-cooled condenser designs to take advantage of the performance gains possible with these fluids.