A closed two-phase thermofluidic oscillator with zeotropic mixtures for low-grade heat recovery

Abstract A thermodynamic model is developed for calculating the net specific work, thermal efficiency and relative Carnot efficiency of a closed two-phase thermofluidic oscillator using zeotropic mixtures as working fluids. Nine zeotropic mixtures including R401A, R401B, R401C, R407A, R407B, R407C, R404A, R408A and R410A are screened as candidate working fluids for experiments, which are preselected on the basis of the proposed thermodynamic model. The influences of zeotropic mixture on the onset temperature difference and oscillation frequency are then experimentally investigated. The lowest onset temperature difference of 18.6 °C is achieved with R401C as working fluid, showing good applicability to low-grade heat recovery. R410A produces the highest oscillation frequency of 4.9 Hz. Besides, experiments are also performed to examine how pressure ratio is affected by zeotropic mixture. The highest pressure ratio of 1.067 is obtained with R401C as working fluid, when the hot temperature is 187 °C. The system with R410A has the potential for higher energy density thanks to its higher operating pressure. For the first time, this work verifies the applicability of zeotropic mixture for a two-phase thermofluidic oscillator.