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

Abstract

Three-heat-reservoir (THR) heat pump has the originality of using low-grade heat to achieve pumping heat, and it can recycle waste heat and reduce environmental pollution effectively. Based on the research ideas of macro THR heat pumps and micro three-terminal thermoelectric devices, this paper proposes a THR thermal Brownian heat pump cycle model. This cycle is driven by low-grade “heat” to work, and it may be seen as a combined cycle consisting of a two-reservoir thermal Brownian heat pump and a two-reservoir thermal Brownian engine. Using non-equilibrium thermodynamics, expressions for heating load and coefficient of performance (COP) are derived. The coupling relation between external forces of two motors is obtained by solving the heat balance equations, and cycle performance is further obtained. The maximal heating load is obtained by optimizing barrier height, and the lower limit of COP is also given. Results show that the THR thermal Brownian heat pump can achieve pumping heat by using low-grade “heat”. The internal parameters affect the coupling between two-heat-reservoir thermal Brownian engine and two-heat-reservoir thermal Brownian heat pump, which determines cycle performance directly. The curve of heating load about COP presents a parabolic-like shape, and an optimal COP exists to maximize heating load.