Fankai Meng

Performance analysis for two-stage TEC system driven by two-stage TEG obeying Newton's heat transfer law

A combined device model of two-stage thermoelectric cooler (TEC) driven by two-stage thermoelectric generator (TEG) with external heat transfer, Joulean heat inside the thermoelectric device, and the heat leakage through the thermoelectric couple leg is proposed in this paper. The heat transfer between the reservoirs and hot or cold junctions of the combined device is assumed to obey Newtons heat transfer law. Several design variables are defined, based on which the performances of the combined device model are analyzed using the combination of finite time thermodynamics and non-equilibrium thermodynamics. For a fixed total thermal conductance of four heat exchangers, the allocations of the thermal conductance among the four heat exchangers are optimized for maximizing the cooling capacity and the coefficient of performance (COP) of the combined thermoelectric device. For the fixed total number of thermoelectric thermocouples of the combined device, the allocations of the number of thermoelectric thermocouples among the two thermoelectric generators and the two thermoelectric coolers are also optimized for maximizing cooling capacity and COP, respectively. The numerical calculations show that the external heat transfers affect the performance of combined thermoelectric device strongly. There are optimum allocations of the number of thermocouples and optimum allocations of thermal conductance of heat exchangers corresponding to the maximum cooling capacity and the maximum COP, respectively. When the total thermal conductance of heat exchangers extends to infinity, the results of this paper approach the non-equilibrium thermodynamic results obtained.

Thermodynamic analysis and optimisation of a new-type thermoelectric heat pump driven by a thermoelectric generator

SYNOPSIS A model of a new-type thermoelectric heat pump driven by a thermoelectric generator is built and the performance of the device is analysed and optimised based on non-equilibrium thermodynamics. The analytical formulae concerning heating load, non-dimensional heating load and coefficient of performance (COP) of the device versus the working electric current (or the distribution ratio of thermoelectric element numbers between the thermoelectric generator and the thermoelectric heat pump) are derived. The optimum non-dimensional working electric current and the optimum distribution ratio of thermoelectric element numbers are obtained. Moreover, the effects of temperature of the two heat reservoirs on the performance of the device are analysed and the COP versus non-dimensional heating load characteristic is obtained.

Performance characteristics of a multi-element thermoelectric generator with radiative heat transfer law

A finite-time thermodynamic model of multi-element thermoelectric generator with radiative heat transfer law Q∝ Δ (T 4) is built by combining finite-time thermodynamics with non-equilibrium thermodynamics. The characteristics of the power output and efficiency versus working electrical current are analysed. The effects of total number of thermoelectric elements and generator heat source temperature on the power output and efficiency are investigated. The results show that for the fixed total number of thermoelectric elements, there are two optimal working electrical currents corresponding to the maximum power output and the maximum efficiency, respectively. The optimal electrical currents decrease with the increase in the number of thermoelectric elements while increase with the increase in the generator heat source temperature. Higher generator heat source temperature can improve the power output more effectively than the efficiency.

Thermodynamic Analysis of TEG-TEC Device Including Influence of Thomson Effect

Abstract A thermodynamic model of a thermoelectric cooler driven by thermoelectric generator (TEG-TEC) device is established considering Thomson effect. The performance is analyzed and optimized using numerical calculation based on non-equilibrium thermodynamic theory. The influence characteristics of Thomson effect on the optimal performance and variable selection are investigated by comparing the condition with and without Thomson effect. The results show that Thomson effect degrades the performance of TEG-TEC device, it decreases the cooling capacity by 27 %, decreases the coefficient of performance (COP) by 19 %, decreases the maximum cooling temperature difference by 11 % when the ratio of thermoelectric elements number is 0.6, the cold junction temperature of thermoelectric cooler (TEC) is 285 K and the hot junction temperature of thermoelectric generator (TEG) is 450 K. Thomson effect degrades the optimal performance of TEG-TEC device, it decreases the maximum cooling capacity by 28 % and decreases the maximum COP by 28 % under the same junction temperatures. Thomson effect narrows the optimal variable range and optimal working range. In the design of the devices, limited-number thermoelectric elements should be more allocated appropriately to TEG when consider Thomson effect. The results may provide some guidelines for the design of TEG-TEC devices.

Influences of the Thomson Effect on the Performance of a Thermoelectric Generator-Driven Thermoelectric Heat Pump Combined Device

A thermodynamic model of a thermoelectric generator-driven thermoelectric heat pump (TEG-TEH) combined device is established considering the Thomson effect and the temperature dependence of the thermoelectric properties based on non-equilibrium thermodynamics. Energy analysis and exergy analysis are performed. New expressions for heating load, maximum working temperature difference, coefficient of performance (COP), and exergy efficiency are obtained. The performance is analyzed and optimized using numerical calculations. The general performance, optimal performance, optimum variables, optimal performance ranges, and optimum variable ranges are obtained. The results show that the Thomson effect decreases the general performance and optimal performance, and narrows the optimal operating ranges and optimum variable ranges. Considering the Thomson effect, more thermoelectric elements should be allocated to the thermoelectric generator when designing the devices. The optimum design variables for the maximum exergy efficiency are different from those for the maximum COP. The results can provide more scientific guidelines for designing TEG-TEH devices.

Optimum variables selection of thermoelectric generator-driven thermoelectric refrigerator at different source temperature

Based on the finite time thermodynamic model of thermoelectric generator-driven thermoelectric refrigerator with losses of external heat transfer, Joulean heat inside the thermoelectric device and the heat leakage through the thermoelectric couple leg, this paper analysed the effects of generator heat source temperature and refrigerator cooling temperature on the performance of the combined system using the combination of finite time thermodynamics and non-equilibrium thermodynamics. For a fixed total heat transfer surface area of four heat exchangers, the allocations of the heat transfer surface area among the four heat exchangers are optimised for maximising cooling load and the coefficient of performance (COP) at different source temperature of the combined thermoelectric refrigerator device, respectively. For a fixed total number of thermoelectric elements, the ratio of number of thermoelectric elements, i.e. the number of thermoelectric elements of the generator to that of the whole device is also optimised for maximising cooling load and the COP at different source temperature of the combined device, respectively. The change features of four design variables, i.e. the ratio of number of thermoelectric elements, the total heat transfer surface area ratio, the generator heat transfer surface area ratio and the refrigerator heat transfer surface area ratio are obtained, respectively. Moreover, optimum working electrical currents for maximum cooling load and COP at different total number of thermoelectric elements and different total heat transfer area are obtained, respectively.

Exergoeconomic performance analysis and optimisation of an irreversible-closed intercooled regenerated gas turbine cycle

ABSTRACT Based on finite time thermodynamic (FTT) model for a closed irreversible intercooled regenerated (ICR) gas turbine cycle, the analytical expressions of profit rate, power and efficiency are deduced. The dimensionless profit rate can reach its extreme value while the intercooling pressure ratio gradually increases, and the value has an additional maximum, i.e. the double-maximum, while the total pressure ratio gradually increases. The finite time exergoeconomic performance is maximised by optimising four heat conductance allocations with a given total heat exchanger conductance as well as the intercooling pressure ratio. Further optimising the total pressure ratio can make the double-maximum. Some characteristic parameters’ effects on the cycle exergoeconomic performance are analysed.