Fluorochemicals as working fluids for small rankine cycle power units

Abstract

A theoretical assessment has been made of the performances of the following fluorochemicals as working fluids for small Rankine cycle power units: 1. (a) Hexafluorobenzene (HFB) 2. (b) Dichlorotetrafluorobenzene (DCTFB) 3. (c) Perfluorodecalin (PFD) 4. (d) FC-75 . Entropy-temperature and enthalpy-temperature diagrams for these compounds were constructed on the basis of their physical properties. From these diagrams and from the application of the similarity concept to the performances of single-stage radial turbines as developed by Baljé [8], thermal efficiencies of a 10 kW unit generating 400 c/s a.c. were computed. It is found that efficiencies in the region of 20–25 per cent can be achieved for Perfluorodecalin, Dichlorotetrafluorobenzene and FC-75 by expanding the fluids from the supercritical state and using a feedback heat exchanger to recover the waste heat in the turbine exhaust. The size and cost of the feedback heat exchanger will constitute an important factor in the practical assessment of the fluorochemicals as working fluids.