Thermodynamic characteristics of a Brownian heat pump in a spatially periodic temperature field

Abstract

This paper has studied the thermodynamic performance of a thermal Brownian heat pump, which consists of Brownian particles moving at a periodic sawtooth potential with external forces and contacting with the alternating hot and cold reservoirs along the space coordinate. The heat flows driven by both potential and kinetic energies are taken into account. The analytical expressions for the heating load, coefficient of performance (COP) and power input of the Brownian heat pump are derived and the performance characteristics are obtained by numerical calculations. It is shown that due to the heat flow via the change of kinetic energy of the particles, the Brownian heat pump is always irreversible and the COP can never attain the Carnot COP. The study has also investigated the influences of the operating parameters, i.e. the external force, barrier height of the potential, asymmetry of the sawtooth potential and temperature ratio of the heat reservoirs, on the performance of the Brownian heat pump. The effective regions of external force and barrier height of the potential in which the Brownian motor can operates as a heat pump are determined. The results show that the performance of the Brownian heat pump greatly depends on the parameters; if the parameters are properly chosen, the Brownian heat pump may be controlled to operate in the optimal regimes. Brownian heat pump, COP, heating load, heat flow, performance characteristics, finite time thermodynamics PACS: 05.40.JcIn the past few decades, the study of Brownian motors has attracted considerable attention due to their importance in developing miniaturized engines which help to utilize energy resources at the microscopic scale [1-4] and in understanding and application of the molecular motors [5,6].Brownian motors are of spatially asymmetric but periodic structure in which the transport of Brownian particles is driven by some nonequilibrium processes [7][8][9][10][11][12][13][14]. According to the nonequilibrium driving force of the Brownian motors, Parrondo and de Cisneros [15] distinguished the Brownian motors mainly into three classes: the forced ratchet (motor), chemical motors-driven out of equilibrium by chemical potential differences, and thermal motorsdriven out of equilibrium by temperature differences. The Brownian heat pump to be studied in this paper belongs to the last kind-thermally driven Brownian motors.The model of thermal Brownian motor driven by nonuniform temperature was first studied by Büttiker [16], van Kampen [17], and Landauer [18]. Since then, many authors [19][20][21][22][23][24][25][26] have studied the performance of thermally driven Brownian heat engines and obtained many important results. Recent studies have shown that under certain conditions, the thermal Brownian motor can work as a refrigerator or a heat pump [27][28][29][30].One important aspect of the studies on Brownian heat engines and refrigerators, is their thermodynamic properties [13,15,19,30]. The efficiency analysis of Brownian heat engines has fascinated many resear...

A generalized model of an irreversible thermal Brownian refrigerator and its performance

“…However, this is the case in which the irreversible heat flow via the kinetic energy of the particles is neglected [44,76]. If the heat flow via the kinetic energy is taken into account, the efficiency of the Brownian heat engines and the coefficient of performance (COP) of the Brownian refrigerator can not attain Carnot efficiency and Carnot COP [30,72,75,[78][79][80], even at quasistatic limit. Without considering the heat flow via the kinetic energy, Asfaw and Bekele [28,35,46] studied the efficiency and COP performances of a Brownian motor driven by a contact with heat reservoirs at different temperatures which can act as a heat engine or refrigerator.…”

“…Furthermore, considering the heat flow via the kinetic energy, Asfaw [79] discussed the effect of subdividing the ratchet potential on the performance of the thermally driven Brownian heat engine and refrigerator with and without external force. Ding et al [80] studied the heating load and COP performances of a thermal Brownian heat pump and explored extensively the influences of operating parameters on the performance of the heat pump.…”

Entransy dissipation minimization for a class of one-way isothermal mass transfer processes

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Constructal optimization of a vertical insulating wall based on a complex objective combining heat flow and strength

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