Thermodynamic Evaluation of a Combined ORC-TFC Cycle for Low-Temperature Power Generation by using Microsoft Excel

This paper presents a thermodynamic evaluation of a combined power generation cycle for recovering the energy of low-temperature heat sources such as solar energy and industrial waste energy. The cycle connects the simple Organic Rankine Cycle (ORC) with the Trilateral Flash Cycle (TFC) via a cascade condenser. By applying the TFC in the high-temperature circuit and the ORC in the low-temperature circuit, the combined cycle enjoys the merits of the two subsidiary cycles. For evaluating the thermodynamic performance of the cycle, an Excel-based model is described that determines the fluid properties by using special functions developed by VBA. The accuracy of the functions is checked by comparing their estimations with relevant published data for the basic ORC and TFC using a number of relevant fluids. The performance of the combined cycle is first evaluated by comparison with those of the simple TFC and ORC with R152a as the working fluid in all three cycles. It is then evaluated with five fluids of low GWP which are R1234yf in the ORC circuit and R152a, R600, R600a, or R717 in the TFC circuit