Design and Development of a Reciprocating Low-Temperature Freon Expander

摘要

The design and development of a 20-ton refrigeration system to be powered by 140 exp 0 F waste hot water is described. The system consists of a Rankine cycle driving a reverse-Rankine cycle, integrated in that they share a common working fluid (R-22), a common condenser, and a common crankcase housing the expander and compressor. A reciprocating single-acting counterflow expander provides a combination of high efficiency in the desired capacity range, modularity, and adaptability to existing compressors. Because the temperatures and pressures of the Rankine cycle fell within the design envelope of a standard refrigeration compressor, the compressor and expander could be housed within the same crankcase by converting some of the compressor cylinders to expander cylinders by replacing the cylinder heads. The expander heads incorporate rotary valves which offer high flow coefficients; they permit higher flow areas and more straightforward flow paths than poppet valves. Rotary valve design presents little risk considering the use of compatible oil, the low operating temperatures, and close clearances that are consistent with minimal differential thermal expansion. Valve timing was optimized by a computerized finite difference technique that performed mass and energy balances and calculated flow through the valves as the crankshaft progressed incrementally. This calculation predicted that breathing losses would amount to only 13%.Thermal losses are expected to be minimal, for temperature differences are low and thermal transport properties poor. Mechanical losses are expected to be less than those of an internal combustion engine; m.e.p. is comparable, and the expander cylinder environment is less hostile to the lubricating oil. (ERA citation 06:030863)