Study on thermal efficiency of low- to medium-temperature organic Rankine cycles using HFO-1234yf

HFO-1234yf is a new refrigerant with a nearly zero global warming potential (GWP) and ozone depletion potential (ODP): it exhibits thermodynamic properties similar to HFC-134a. The potential of HFO-1234yf as a working fluid for organic Rankine cycles (ORC) is elucidated through a first-order simulation. A fundamental thermodynamic model of ORC with five types of cycles-trilateral, saturated, superheated, sub-critical, and supercritical-is used to compare the thermal efficiency of HFO-1234yf with that of other working fluids. HFO-1234yf was found to offer a thermal efficiency that was comparable to that of HFC-134a. This paper provides a useful map that clearly shows the best possible thermal efficiency among the five types of cycles for various expander inlet and condensation temperatures. The highest thermal efficiency range (8.8%-11.4%) was obtained when the supercritical ORC was used at an expander inlet temperature of 170 +/- 10 degrees C and a condensation temperature range of 20-40 degrees C for the given pump and expander efficiency. It is concluded that HFO-1234yf is a potential working fluid for ORC applications, especially for those with low- to medium-temperature heat sources. (C) 2011 Elsevier Ltd. All rights reserved.