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

Thermodynamic Evaluation of a Combined ORC-TFC Cycle by using Microsoft Excel

Abstract

This paper presents a new cycle for utilising the energy of low-temperature heat sources that combines the Organic Rankine Cycle (ORC) with the Trilateral Flash Cycle (TFC) via a cascade condenser. The performance of the combined cycle that allows different working fluids to be used in the two circuits is compared with those of the simple ORC and TFC cycles for a heat-source of 120oC by using R152a as the working fluid in the three cycles. Compared to the simple ORC, the results show that the combined cycle gives more power and a higher thermal efficiency. Compared to the simple TFC, the results show that the cycle gives less power, but a higher thermal efficiency. The cycle’s performance with R1234yf in the ORC circuit and R152a in the TFC circuit is also compared with that with R152a in both circuits at the same condenser temperature. The results show that the R1234yf/R152a pair gives more power than R152a alone, but less efficiency. The model developed for the cycle uses Microsoft Excel as the modelling platform and determines the fluid properties with VBA functions. The functions are validated with published data for the TFC model with three suitable organic working fluids which are R134a, R245fa, and R1233zd.