The Investigation On The Performance Of Microscopic Brownian Heat Engines

In recent years, the research on directed transport has become a new hotspot in biological, physical experiments etc.. Inspired by Feynman ratchet and detent, the directed transport was named as the ratchet effect. When the environment of a system is decided by the thermal fluctuations, the transport of Brownian motor will be controlled and influenced by the noise. Related molecular machines, such as the concept of Brownian motors, molecule pumps and molecule channel occurs. The traditional reversible thermodynamics can't adequately describe the case at which fluctuation is dominant. As a result, the thermodynamic heat engine model must be integrated thermal fluctuations effect and, in meanwhile, be allowed reversible in the directional transport process. Compared with the real heat engines, the Brownian heat engines are mainly driven by the barrier associated with time, temperature difference or chemical potential difference. The heat engine model can be constructed by a spatial temperature and a ratchet potential barrier. In this thesis, the thermodynamic properties, the effect of irreversible factors on the properties of a Brown heat engine driven by thermal, and how to improve the efficiency of Brownian heat engine are studied.In chapterⅠ, we mainly introduce the study background of the thesis and the dynamical theory of the Brownian motion.In chapterⅡ, the thermodynamic properties of a thermal Brownian heat engine driven by thermal are studied. A Brownian microscopic heat engine driven by temperature differences, which consists of a Brownian particle moving in a sawtooth potential with an external load where the viscous medium is periodically in contact with hot and cold reservoir along space coordinate. In order to clarify the underlying physical pictures of the heat engine, the heat flow via the potential energy and the kinetic energy of the particles are considered simultaneously. Based on the master equation describing the particles jump among barriers, the expressions of current, the efficiency and power output of the heat engine are derived analytically. The general performance characteristic curves are plotted by numerical calculation. In chapter III, an approach to enhance the efficiency of a Brownian heat engine is studied, the expressions for the efficiency and the power output are derived analytically. The effect of the external load, the height of two potentials ratio and ratio of the temperature of the hot and cold reservoirs on the thermodynamic performance of heat engine is discussed in detail. It is shown that the efficiency of the engine can enhance but the power output reduces.In chapter IV, a Brownian microscopic heat engine with a particle hopping on a one-dimensional lattice driven by a discrete and periodic temperature field in a periodic sawtooth potential is investigate. Based on describing the jumps among the three states, the heat flow via the potential energy and the kinetic energy of the particles are considered simultaneously, the expressions of current, the efficiency and power output of the heat engine are derived analytically. The general performance characteristic curves are plotted by numerical calculation.