Three-heat-reservoir thermal Brownian heat transformer and its performance limits

Abstract

Waste heat recovery has great value in energy saving and decreasing environmental pollution. A three-heat-reservoir (THR) heat transformer can raise waste heat to a higher temperature for recovering and reusing easily. At present, the research on THR heat transformer is mainly focusing on macro field. This paper extends the THR heat transformer cycle to micro field, and models a THR thermal Brownian heat transformer. The model is a combined cycle of a thermal Brownian heat pump driven by a thermal Brownian engine. According to non-equilibrium thermodynamics, the analytical expressions for heating load and coefficient of performance (COP) are derived. The coupling relation of the combined cycle is obtained by solving the heat balance equation, and the operating mechanism of the new cycle is explained. The external load, barrier height, potential asymmetry and temperature ratio effects on system performances are studied, and the maximum heating load and corresponding COP are given. The optimal operating range and performance limits are obtained. Results show that the THR thermal Brownian heat transformer can raise the “heat” to a higher temperature. The heating load can reach peak value by modulating the design parameters carefully. The system operates in a quasi-static state and the heating load is zero when COP increases to its upper bound, and the system is reversible at this time. The new model proposed in this paper can guide the design of actual device, and the performance limit can guide the performance optimization of the actual device.