Zemin Ding

Performance analysis of irreversible energy selective electron (ESE) heat pump with heat leakage

A model of an irreversible energy selective electron (ESE) heat pump with heat leakage is established in this paper. The general expressions for heating load and coefficient of performance (COP) of the ESE heat pump in the maximum heating load operation regime and the intermediate operation regime are derived respectively. The optimum performances of the ESE heat pump in these two different operation regimes are analysed by detailed numerical examples. The characteristic curves of COP versus heating load considering heat leakage in maximum heating load operation regime are parabolic-like ones, and the COP will approach a fixed value as the heating load increases. This is due to the fact that electrons that contribute positively to heat pumping are all transmitted through the energy filter in this regime. The characteristic curves of COP versus heating load with and without considering heat leakage in intermediated operation regime are all parabolic-like ones, and the COP will be below unity as the heating...

Performance analysis of a vacuum thermionic refrigerator with external heat transfer

A model of a vacuum thermionic refrigerator with external heat transfer is proposed. The general expressions for cooling load and coefficient of performance (COP) are derived using the combination of finite time thermodynamics and nonequilibrium thermodynamics. The optimum regions of cooling load and COP are obtained and the effect of the heat reservoir temperature on the optimal performance of the device is analyzed by detailed numerical examples. The effects of work function on the cooling load and COP performances of the thermionic device are also investigated. By comparing the results obtained herein with those using the traditional analysis without considering external heat transfer, it is shown that the present analysis is more practical for real vacuum thermionic devices. The results may provide guidelines for the design and application of practical thermionic refrigerators

Performance optimization of a total momentum filtered energy selective electron (ESE) heat engine with double resonances

Abstract A model of an energy selective electron (ESE) heat engine with double resonances which filter electrons according to their total momentum is established in this paper. The optimal performance of the double resonance ESE heat engine is analyzed by using the theory of finite time thermodynamics (FTT). The performance of the double resonance ESE heat engine is compared with that of the single resonance device. It is shown that the double resonance device can generate more power but at the same time becomes less efficient. Performance comparisons are also performed between the total momentum filtered ESE heat engine in which the electrons are transmitted according to the total electron momentum in all the three dimensions and the conventional ESE heat engine where the electrons are filtered according to the momentum in the direction of transport only. It is found that the total momentum filtered ESE heat engine outperforms the conventionally filtered ESE heat engine on both power output and efficiency performance. Moreover, the effects of resonance width, energy spacing of two resonances and cold reservoir temperature on the performance of the total momentum filtered double resonance heat engine are analyzed in detail by numerical calculations. In practical operation of the double resonance ESE heat engine, the values of resonance width, energy spacing and cold reservoir temperature should be small in order for the device to obtain higher efficiency.

Optimum performance analysis of Feynman's engine as cold and hot ratchets

Abstract It was shown by Velasco et al. [J. Phys. D: Appl. Phys., 34(2001), 1000–1006] that the Feynmans ratchet can operate as a cold or hot ratchet and pawl engine. This paper takes a further step toward analyzing the optimum performances of the cold and hot ratchets and exploring the similarities and differences between them. The power and efficiency performances of both the cold and hot ratchets are analyzed with respect to the internal parameter. The influences of heat leakage and heat reservoir temperature ratio on the performances of the devices are investigated, and performance comparisons between the two kinds of ratchets are performed. Moreover, the analytical expression of the efficiency at maximum power for the hot ratchet is derived by optimizing both the internal and the external parameters. The fundamental optimal relation between power and efficiency for the cold and hot ratchets is explored through detailed numerical examples. The results obtained in this paper for the hot ratchet are further compared with those obtained by Tu [J. Phys. A: Math. Theor., 41(2008), 312003] for the cold ratchet. It is finally concluded that it is better for the Feynmans ratchet to operate as a cold ratchet and pawl engine.

Generalized model and optimum performance of an irreversible thermal Brownian microscopic heat pump

A generalized model of an irreversible thermal Brownian microscopic heat pump is established in this paper. It is composed of Brownian particles which are moving in a periodic sawtooth potential with external forces and contacting with alternating hot and cold reservoirs along the space coordinate. The generalized irreversible Brownian heat pump model incorporates heat flows driven by both the potential and kinetic energies of the particles as well as the heat leakage between the hot and cold reservoirs. This paper derives the expressions for heating load, power input and coefficient of performance (COP) of the Brownian heat pump. The optimum performance of the generalized heat pump model is analyzed by using the theory of finite time thermodynamics (FTT). Effects of the design parameters, i.e., the external force, the heat leakage coefficient, barrier height of the potential, asymmetry of the sawtooth potential and heat reservoir temperature ratio on the performance of the Brownian heat pump are discussed in detail. The performance of the Brownian heat pump depends strictly on the design parameters. Through the proper choice of these parameters, the Brownian heat pump can operate in the optimal regimes. The optimum COP performance and the fundamental optimal relations between COP and heating load are studied by detailed numerical examples. It is shown that due to the heat leakage between the heat reservoirs and heat flow via the change of kinetic energy of the particles, both the heating load and COP performances of the Brownian heat pump will decrease. The effective ranges of the external force and barrier height of the potential in which the Brownian motor system can operate as a heat pump are further determined.

Power and efficiency performances of a micro thermal Brownian heat engine with and without external forces

Power and efficiency performances of a thermal Brownian heat engine, which consists of Brownian particles moving in a periodic sawtooth potential with and without external forces and contacting with alternating hot and cold reservoirs along the space coordinate, are studied in this paper. 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 engine is always irreversible and the efficiency can never approach the Carnot efficiency. The influences of the operation parameters, i.e. barrier height of the potential, asymmetry of the potential and temperature ratio of the heat reservoirs on the power output, the efficiency and the current performances of the Brownian heat engine are investigated in detail by numerical analysis. When there is no external force, the power output versus efficiency characteristic curves are closed loop-shaped ones, which are similar to those of real conventional irreversible heat engines; whereas when the external force is considered, the power output versus efficiency characteristic curves of the heat engine changed into open loop-shaped ones. Furthermore, the limited regions of the external force and barrier height of the potential are explored by analyzing the current property of the model. It is shown that by reasonable choice of the parameters, the Brownian heat engine can be controlled to operate in the optimal regimes.

Performance Analysis and Optimization of a Single-Barrier Solid-State Thermionic Refrigerator With External Heat Transfer

A model of a single-barrier solid-state thermionic refrigerator with external heat transfer is established in this paper. The performance of the refrigerator is analyzed and optimized by using the combination of finite-time thermodynamics and nonequilibrium thermodynamics. The general expressions for cooling load and coefficient of performance (COP) of the refrigerator are derived. The optimum regions of cooling load and COP are obtained and the effects of the heat reservoir temperature and thermal conductance of the barrier material on the performance of the refrigerator are analyzed by detailed numerical examples. The results obtained are compared with those obtained by using traditional analysis without considering external heat transfer. For the fixed total heat transfer surface area of two heat exchangers, the ratios of the heat transfer surface area of the hot-side heat exchanger to the total heat transfer surface area of the heat exchangers are optimized for maximizing the cooling load and COP of the refrigerator, respectively. The effects of the total heat transfer surface area and the applied voltage on the optimum performance of the refrigerator are analyzed. The results obtained herein may provide some theoretical guidelines for the design and application of practical solid-state thermionic refrigerators.

A unified description of finite time exergoeconomic performance for seven typical irreversible heat-engine cycles

Finite time exergoeconomic performance optimization of a universal irreversible heat-engine cycle model, which consists of two constant thermal-capacity heating branches, two constant thermal-capacity cooling branches and two adiabatic branches, is investigated by taking the profit rate criterion as the optimization objective. The analytical formulae for power, efficiency and profit rate function of the universal irreversible heat-engine cycle model with the losses of heat transfer, heat leakage and internal irreversibility are derived. The focus of this article is to search the compromised optimization between economics (profit rate) and the energy utilization factor (efficiency) for irreversible cycles. Moreover, analysis and optimization of the model are carried out in order to investigate the effects of these losses and cycle process on the performance of the universal irreversible heat-engine cycle model using numerical examples. The results obtained herein include the performance characteristics of seven typical irreversible heat engines, including Carnot, Diesel, Otto, Atkinson, Brayton, Dual and Miller cycles.