Thermal stability of working fluids for organic Rankine cycles: An improved survey method and experimental results for cyclopentane, isopentane and n-butane

In this work we present an improved survey method for the evaluation of the thermal stability of working fluids for organic Rankine cycles. The method presented here represents an improvement of a test methodology already used in literature, based on the analysis of temperature and pressure measurements of a fluid subjected to increasing thermal stress temperatures. Compared to the already known methodology, the survey technique presented in this work offers a different evaluation of the measured vapor pressure deviations and a different estimation method of the decomposition rates. After the description of the experimental apparatus and of the test methodology, we present and discuss some experimental results of the thermal stability of three fluids of interest for organic Rankine cycle applications, namely Cyclopentane, Isopentane and n-Butane, in the temperature range between 220 °C and 350 °C.