NON-EQUILIBRIUM THERMODYNAMIC ANALYSIS ON THE PERFORMANCE OF AN IRREVERSIBLE THERMALLY DRIVEN BROWNIAN MOTOR

Based on the general model of thermally-driven Brownian motors, an equivalent cycle system is established and the Onsager coefficients and efficiency at the maximum power output of the system are analytically calculated from non-equilibrium thermodynamics. It is found that the Onsager reciprocity relation holds and the Onsager coefficients are affected by the main irreversibilities existing in practical systems. Only when the heat leak and the kinetic energy change of the particle in the system are negligible, can the determinant of the Onsager matrix vanish. It is also found that in the frame of non-equilibrium thermodynamics, the power output and efficiency of an irreversible Brownian motor can be expressed to be the same form as those of an irreversible Carnot heat engine, so the results obtained here are of general significance. Moreover, these results are used to analyze the performance characteristics of a class of thermally-driven Brownian motors so that some important conclusions in literature may be directly derived from the present paper.

Electrokinetic Generation Efficiency With Finite External Loads

Electrokinetic (EK) pumping efficiency has recently been a hot topic due largely to its applications in microfluidics for liquid transport. As the Onsager reciprocity relation suggests that the exact opposite of EK pumping is EK generation, experimental study on the efficiency of the latter is seldom reported. This paper examines electrokinetic generation efficiency in the presence of finite external loads through the use of different ceramic filters. The electrical output power was measured experimentally as a function of different external loadings. When the experiments were performed continuously on subsequent days, the EK generation efficiency for all the tested filters can be made to increase and approach a maximum limit. The experimental data also indicated that, when pore size of the filter decreases, the curve for potential versus current becomes more non-linear and the maximum efficiency does not occur when the current is half the zero-potential current.