Performance of a Modified Two-Phase Thermofluidic Oscillator With Low GWP Working Fluids for Lowgrade Waste Heat Recovery

Abstract

Two-phase thermofluidic oscillator has attracted considerable attention for low-grade heat recovery, thanks to its ability to operate across a small temperature difference between heat source and sink. The performance of a modified two-phase thermofluidic oscillator with the working fluids of low global warming potential (e.g., R152a, R1234yf and R1234ze(E)) for harvesting low-grade waste heat is investigated. An acoustic-electric analogy model is proposed for predicting the onset temperature difference and oscillation frequency, which is then verified by experiments. The model can well predict the oscillation frequency, with the differences of 4.4-6.8% from experimental data. The predicted and measured onset temperature differences are also in reasonable agreement, for the model underestimates by 5.4-13.4% compared with the experimental results. The influences of the lengths and diameters of feedback connection tube and vapor connection tube on the performance are also numerically studied. A lowest onset temperature difference of 14.4℃ can be obtained with the vapor connection tube diameter of 0.015 m and the working fluid of R1234yf. In addition, a highest oscillation frequency achieved is 3.04 Hz with R152a as working fluid, when the feedback connection tube diameter is increased to 0.019 m. This work verifies the feasibility of recovering low-grade waste heat to drive a two-phase thermofluidic oscillator with the low global warming potential working fluids.