A direct ethanol fuel cell is the device to directly convert the chemical energy of the ethanol and oxygen into the electricity and heat. To improve the electrical power density and increase the energy conversion efficiency as much as possible, a three-heat-reservoir refrigeration cycle is coupled to the direct ethanol fuel cell, so that the waste heat of the fuel cell can be effectively utilized. The performances of the direct ethanol fuel cell and hybrid system are systemically assessed and compared.The whole performance of the hybrid system is optimized. The maximum power densities of the hybrid system can attain, respectively, 0.20, 0.21, and 0.22 (Js-1cm-2), which are 1.41, 1.71, and 2.10 times those of the fuel cell, when the temperatures of the fuel cell are 328.15, 338.15, and 348.15 (K). The partial current densities, voltage output, and flow density of waste heat of the fuel cell, and coefficient of performance and cooling rate of the three-heat-reservoir cycle are determined at a given molar concentration of the inlet ethanol at the optimum power density, and consequently, the optimum selection criterion of the molar concentration of the inlet ethanol is obtained.

As a novel configuration of electrochemical cycles, electrochemical energy converters (EECs) show great potential in efficient and versatile low-grade heat harvesting. Nevertheless, the complex construction and operation of the existing multi-cell EEC models pose a great challenge to their practical implementation. In this study, a novel electrolyte-flow Stirling EEC model is proposed by employing three stationary electrochemical cells with all-liquid redox couples, in which the complex entire cell motion in multi-cell EEC models is replaced by the circulating electrolytes among three cells. Accordingly, continuous operation is readily achieved with this significantly simplified design and operation. Notably, the cooling power and net power output properties of the electrolyte-flow EEC explicitly demonstrate three energy conversion and transport modes with flexible control to meet dynamic power and cooling loads. Due to the involvement of multiple energy forms, a more comprehensive performance assessment framework accounting for the energy grade difference is innovatively developed by introducing exergy analysis. Moreover, special attention is devoted to exploring the heat-refrigeration conversion performance of the electrolyte-flow EEC, from which optimal operation strategies and parameter impacts are determined. Additionally, the comparisons between the electrolyte-flow EEC and various existing heat-driven refrigerators are presented to emphasize its competitive performance.

The full oxidation of ethanol in a direct alcohol fuel cell remains a significant technical obstacle. A thermodynamic model of the cell has been developed, incorporating a mixed solution of methanol and ethanol, which considers the oxidation of methanol as well as the complete and incomplete oxidations of ethanol. If the activities of the catalysts at electrodes are stable, the effects of C-C bond cleavage in alcohol and further oxidation of intermediates on the performance of the cell can be quantitatively described. The physical driving force of the electrochemical reactions is displayed by using thermodynamics, then the irreversible losses from the ionization activity, ohm resistance, and finite-rate diffusion of fuels are considered, and finally, the optimization criterion is determined. The optimum power density and optimum efficiency are monotonically decreasing functions of the molar concentration of ethanol in the solution. However, the molar concentration of ethanol in the cell is suggested smaller than 0.0107 mol/cm(3) to balance the two performance indicators. In such a range, the optimum power density and optimum efficiency are greater than 0.7626 J/s/cm(2) and 19.6%, respectively, and the required molar composition of alcoholic solution at the inlet of the channel, the molar concentration of methanol, and three partial current densities in the cell are proposed. The research supplies a novel way to improve the performance of direct alcohol fuel cells.

The thermodynamic analysis of the methanol steam reforming hydrogen production process by electromagnetic induction heating was carried out,and the energy consumption was compared with that of the conventional heating method.The results show that the temperature has a relatively large influence on the reaction process,and when the temperature is low(150～200℃),the methanol conversion rate changes drastically with the rise of pressure,and at temperatures higher than 200℃,the pressure has almost no effect on the methanol conversion rate,and the higher the temperature is,the lower the effect of pressure on the hydrogen production rate is.The proportion of CO in carbon compounds in the product decreased with the increase of S/C at high temperature.The induction-heated reactor with a grid-connected system for renewable power generation reduces CO2 emissions and saves conventional fossil energy,while the energy efficiency of the reforming-to-hydrogen process by induction heating is comparable to that of conventional heating.

In view of the current global energy crisis and urgent need to protect the environment, there is a need to research the direct methanol fuel cells (DMFCs) which have energy development potential. The electromotive force of the fuel cell is calculated by using the thermodynamics and considering the consumption of the reactants from the electrochemical reaction and crossover through the membrane. The actual DMFCs exist the voltage drop from the overpotentials and current leakage from the permeation of the methanol. By citing some relevant empirical formulas and experimental data, the relationship between the performance indexes and the diffusion coefficient of the methanol, molar concentration of the methanol in solution, operating temperature and so on is derived. The effect of the key operating parameters on the performance of the system is explored. The running conditions for the optimum efficiency of the DMFC are determined.

Proton exchange membrane fuel cells (PEMFCs) based on syngas are a promising technology for electric vehicle applications. To increase the fuel conversion efficiency, the low-temperature waste heat from the PEMFC is absorbed by a refrigerator. The absorption refrigerator provides cool air for the interior space of the vehicle. Between finishing the steam reforming reaction and flowing into the fuel cell, the gases release heat continuously. A Brayton engine is introduced to absorb heat and provide a useful power output. A novel thermodynamic model of the integrated system of the PEMFC, refrigerator, and Brayton engine is established. Expressions for the power output and efficiency of the integrated system are derived. The effects of some key parameters are discussed in detail to attain the optimum performance of the integrated system. The simulation results show that when the syngas consumption rate is 4.0 x 10(-5) mol s(-1) cm(-2), the integrated system operates in an optimum state and the product of the efficiency and power density reaches a maximum. In this case, the efficiency and power density of the integrated system are 0.28 and 0.96 J s(-1) cm(-2), respectively, which are 46% higher than those of a PEMFC.

A new theoretical model of the thermally self-sustained proton exchange membrane fuel cell (PEMFC) is proposed, where syngas is preheated by the heat from the reaction in the fuel cell and water gas shift reactions, and the endothermic steam reforming process of methane is maintained by absorbing a part of the combustion heat of residuary hydrogen from the fuel cell. Based on some thermal equilibrium equations, the temperatures of syngas and combustion product in different stages are calculated, respectively. The power density and conversion efficiency of the PEMFC are derived. The influences of the molar flow rate of syngas, hydrogen utilization ratio, and working temperature of the fuel cell on the property of the PEMFC are discussed detailedly. In the rational range of the operating temperature, the maximum power densities and corresponding efficiencies are calculated, the optimum values of several key parameters at the maximum power densities are determined, and the optimal selection criteria of molar flow rate of syngas and other parameters are provided.

External chemical reactors for steam reforming and water gas shift reactions are needed for a proton exchange membrane (PEM) fuel cell system using syngas fuel. For the preheating of syngas and stable steam reforming reaction at 600 °C, residual hydrogen from a fuel cell and a certain amount of additional syngas are burned. The combustion temperature is calculated and the molar ratio of the syngas into burner and steam reformer is determined. Based on thermodynamics and electrochemistry, the electric power density and energy conversion efficiency of a PEM fuel cell based syngas are expressed. The effects of the temperature, the hydrogen utilization factor at the anode, and the molar ratio of the syngas into burner and steam reformer on the performance of a PEM fuel cell are discussed. To achieve the maximum power density or efficiency, the key parameters are determined. This manuscript presents the detailed operating process of a PEM fuel cell, the allocation of the syngas for combustion and electric generation, and the feasibility of a PEM fuel cell using syngas.

A hybrid system including the solid oxide fuel cell (SOFC), Carnot cycle, and Brayton cycle is proposed, where the high-grade waste heat and residual fuel from the SOFC is utilized and transformed into power. Based on electrochemistry and thermodynamics, the electric power, flow rate of waste heat, and composition of residual fuel from the SOFC are calculated, respectively, under a given flow rate of natural gas into the anode of SOFC. The working substance of Carnot cycle absorbs heat in the cooling-tube of SOFC stack and the efficiency of the cycle is derived by considering the finite-rate heat transfer and internal irreversible losses. The working substance of Brayton cycle absorbs high-temperature heat from the combustion products of the residual hydrogen and the efficiency of Brayton cycle is obtained by considering the finite-rate heat transfer and irreversible compression and expansion processes. To achieve optimal power of SOFC or the maximum power of the hybrid system, the favorable working temperature, mole flow rate of natural gas, and hydrogen utilization factor in SOFC are calculated by using MATLAB software. (C) 2017 Elsevier Ltd. All rights reserved.

A hybrid system consisting of solid oxide fuel cell (SOFC) and absorption refrigerator is established, where hydrogen and carbon monoxide are the reactant in electrochemical reactions of SOFC, and air conditioning is derived for the residence due to the utilization of waste heat from the SOFC. The molar ratio of carbon monoxide to hydrogen consumed in the electrochemical reactions is suggested 0.053 to attain the optimal equivalent energy conversion efficiency of the hybrid system. The maximum equivalent energy conversion efficiency of the SOFC and refrigerator hybrid system will reach 87%. The curves of energy conversion efficiency of the hybrid system eta(H) and SOFC eta varying with current density of the SOFC, respectively.[GRAPHICS]A hybrid system consisting of solid oxide fuel cell (SOFC) and absorption refrigerator is established, where hydrogen and carbon monoxide are the reactant in electrochemical reactions of SOFC, and air conditioning is derived for the residence due to the utilization of waste heat from the SOFC. On the basis of electrochemistry and thermodynamics, the electric voltage and power of the SOFC, the cooling rate of refrigerator under given flow rate of high-temperature heat, and the equivalent energy conversion efficiency and power of the hybrid system are obtained. The effect of some of the key parameters including molar ratio of carbon monoxide to hydrogen consumed in the electrochemical reactions, the working temperature of the SOFC on the performance of the hybrid system is investigated. The optimal operation strategy is explored to achieve the high equivalent energy conversion efficiency of the hybrid system, for example, the molar ratio of carbon monoxide to hydrogen consumed in the electrochemical reactions is suggested 0.053 to attain the optimal equivalent energy conversion efficiency of the hybrid system. The maximum equivalent energy conversion efficiency of the SOFC and refrigerator hybrid system will reach 87%. (C) 2016 Elsevier Ltd. All rights reserved.

The hybrid system comprised by a proton exchange membrane (PEM) fuel cell and internal combustion engine shows many advantages for vehicle applications. The hybrid system can recover the un-reacted hydrogen from fuel cell, utilize heat in the combustion product from cylinder, or combine the advantages of both. Based on thermodynamics and electrochemistry, an indirect integration system of the PEM fuel cell and Otto cycle is established for vehicle applications. The irreversibilities such as the entropy production and overpotentials in the fuel cell, the finite-rate heat transfer between the air in the Otto cycle and combustion chamber wall, the irreversible compression, expansion, and regeneration processes in the Otto cycle are considered. The excellence of the PEM fuel cell compared with internal combustion engine is shown in terms of energy conversion efficiency. When the vehicle is speeding or launching suddenly, not only the flow rate of natural gas into the hybrid system should be increased but also a specific coupling mode between two powertrain systems should be found. Copyright (c) 2015 John Wiley & Sons, Ltd.

A novel model of the molten carbonate fuel cell (MCFC) and gas turbine (GT) hybrid system with direct internal reforming is established, where the fuel cell and the auxiliary burner are taken as the heat reservoirs of the GT. Expressions for the power output and efficiency of the hybrid system are derived by considering various irreversible losses resulting from the overpotentials in the MCFC, the heat leakage in the auxiliary burner, and the finite-rate heat transfer and compression, expansion, and regeneration processes in the GT. The effects of some key parameters including the molar fraction of the oxygen in the oxidant, the utilization factor of the hydrogen in the MCFC on the performance of the hybrid system are revealed. It is found that the efficiency of the hybrid system will be increased by adding the utilization factor of the hydrogen, and the maximum power output of the hybrid system will be achieved when the utilization factor of the hydrogen is equal to 0.78. Moreover, the flowing rates of the syngas and oxidant and the molar fraction of the oxygen in the oxidant are determined under the optimal efficiency or maximum power output of the hybrid system.

On the basis of the models of various developed high-temperature fuel-cell heat-engine hybrid systems, a unified model of hybrid systems is proposed. General expressions for the power output and efficiency of hybrid systems, high-temperature fuel cells such as solid oxide fuel cells (SOFCs) and molten carbonate fuel cells (MCFCs), and heat engines including the Brayton, Otto, Diesel, Atkinson, Braysson, and Carnot engines are, respectively, derived by using the theories of electrochemistry and non-equilibrium thermodynamics. The effects of main irreversible losses existing in real fuel cells and heat engines on the performance of hybrid systems are investigated. The general performance characteristics and optimal operating regions of some of the key parameters of hybrid systems are discussed in detail. A variety of special typical cases are discussed. The important results in the literature can be readily reproduced, and the interesting findings of our study are presented.

A novel model of the solid oxide fuel cell-gas turbine hybrid system with fuel reforming is established, where the residual fuel from the fuel cell is further burned in a combustor and the solid oxide fuel cell (SOFC) and combustor act as the high-temperature reservoirs of the gas turbine (GT). The irreversibilities existing in real systems including the overpotentials and heat leakage in the SOFC, the finite-rate heat transfer between the working substance of the gas turbine and the reservoirs, and the irreversible compression, expansion, and regeneration processes in the gas turbine are considered. By using the theories of electrochemistry and non-equilibrium thermodynamics, expressions for the power output and efficiency of the hybrid system are derived and the advantages of the hybrid system compared with the pure SOFC are represented. The optimally operating regions of some of the important parameters including the power output and efficiency of the hybrid system and the rate of the fuel flowing into the SOFC are determined. The rate of the air flowing into the cell at the optimal efficiency of the hybrid system is also derived. The results obtained here may provide some theoretical bases and optimization criterion for the design and operation of practical syngas SOFC-based hybrid systems. (C) 2014 Elsevier Ltd. All rights reserved.

A new model of micro-/nanoscaled heat engines consisting of two thin long tubes with the same length but different sizes of cross section, which are filled up with ideal quantum gases and operated between two heat reservoirs, is put forward. The working fluid of the heat engine cycle goes through four processes, which include two isothermal processes and two isobaric processes with constant longitudinal pressure. General expressions for the power output and efficiency of the cycle are derived, based on the thermodynamic properties of confined ideal quantum gases. The influence of the size effect on the power output and efficiency is discussed. The differences between the heat engines working with the ideal Bose gas and Fermi gas are revealed. The performance of the heat engines operating at weak gas degeneracy and high temperatures is further analyzed. The results obtained are more general and significant than those in the current literature.

With the help of the current models of proton exchange membrane (PEM) fuel cells and three-heat-source heat pumps, a generic model of a PEM fuel cell/heat-driven heat pump hybrid system is established, so that the waste heat produced in the PEM fuel cell may be availably utilized. Based on the theory of electrochemistry and non-equilibrium thermodynamics, expressions for the efficiency and power output of the PEM fuel cell, the coefficient of performance and rate of pumping heat of the heat-driven heat pump, and the equivalent efficiency and power output of the hybrid system are derived. The curves of the equivalent efficiency and power output of the hybrid system varying with the electric current density and the equivalent power output versus efficiency curves are represented through numerical calculation. The general performance characteristics of the hybrid system are analyzed. The optimally operating regions of some important parameters of the hybrid system are determined. The influence of some main irreversible losses on the performance of the hybrid system is discussed in detail. The advantages of the hybrid system are revealed.

In this study, a new molten carbonate fuel cell-gas turbine hybrid system, which consists of a fuel cell, three heat exchangers, a compressor, and a turbine, is established. The multiple irreversible losses existing in real hybrid systems are taken into account by the models of a molten carbonate fuel cell and an open Brayton cycle with a regenerative process. Expressions for the power outputs and efficiencies of the subsystems and hybrid system are derived. The maximum power output and efficiency of the hybrid system are numerically calculated. It is found that compared with a single molten carbonate fuel cell, both the power output and efficiency of the hybrid system are greatly enhanced. The general performance characteristics of the hybrid system are evaluated and the optimal criteria of the main performance parameters are determined. The effects of key irreversibilities on the performance of the hybrid system are investigated in detail. It is found that the use of a regenerator in the gas turbine can availably improve the power output and efficiency of the system. The results obtained here are significant and may be directly used to discuss the optimal performance of the hybrid system in special cases.