共查询到20条相似文献,搜索用时 546 毫秒
1.
A model of the behaviour of a two-stage semiconductor thermoelectric heat-pump with external heat transfer is devised. Performance of the heat-pump, assuming Newton’s heat-transfer law, is analyzed using the combination of finite-time thermodynamics and non-equilibrium thermodynamics. The analytical formula describing the heating load versus working electric-current, and the coefficient of performance (COP) versus working electric-current are derived. For the fixed total number of thermoelectric elements, the ratio of number of thermoelectric elements of the top stage to the total number of thermoelectric elements is also optimized for maximizing the heating load and the COP of the thermoelectric heat-pump. The effects of design factors on the performance are analyzed. 相似文献
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The performance of an air standard Atkinson cycle with heat-transfer loss, friction-like term loss and variable specific-heats of the working fluid is analyzed using finite-time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of variable specific-heats of the working fluid and the friction-like term loss on the irreversible cycle performance are analyzed. The results show that the effects of variable specific-heats of working fluid and friction-like term loss on the irreversible cycle performance should be considered in cycle analysis. The results obtained in this paper provide guidance for the design of Atkinson engines. 相似文献
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The performance of an air standard Otto-cycle is analyzed using finite-time thermodynamics. In the irreversible cycle model, the non-linear relation between the specific heat of the working fluid and its temperature, the friction loss computed according to the mean velocity of the piston, the internal irreversibility described by using the compression and expansion efficiencies, and the heat-transfer loss are considered. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the efficiency of the cycle are indicated by numerical examples. Moreover, the effects of internal irreversibility, heat-transfer loss and friction loss on the cycle performance are analyzed. The results obtained in this paper may provide guidance for the design of practical internal-combustion engines. 相似文献
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Reciprocating heat-engine cycles 总被引:4,自引:0,他引:4
The performance of a generalized irreversible reciprocating heat-engine cycle model consisting of two heating branches, two cooling branches and two adiabatic branches with heat-transfer loss and friction-like term loss was analyzed using finite-time thermodynamics. The relations between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relation between the power output and the efficiency of the cycle are derived. Moreover, analysis and optimization of the model were carried out in order to investigate the effect of the cycle process on the performances of the cycles using numerical examples. The results obtained herein include the performance characteristics of irreversible reciprocating Diesel, Otto, Atkinson, Brayton, Dual and Miller cycles. 相似文献
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Selahatt?n Gök Tun 《Solar Energy》1996,56(6):617-620
Maximum power and efficiency at the maximum power point of an internally and externally irreversible finite-size solar thermal power plant heat engine are treated. It was found that the thermal efficiency depends on the internal irreversibility resulting from the working fluid for a given value of reservoir temperatures ratio. It was also concluded that the heat-exchangers optimum size ratio must be less than one for maximum power output. 相似文献
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Optimum allocation of heat transfer surface area for cooling load and COP optimization of a thermoelectric refrigerator 总被引:4,自引:0,他引:4
The theory of finite time thermodynamics is applied to analyze and optimize the performance of a thermoelectric refrigerator, which is composed of multi-elements. For the fixed total heat transfer surface area of two heat exchangers, the ratio of the heat transfer surface area of the high temperature side heat exchanger to the total heat transfer surface area of the heat exchangers is optimized for maximizing the cooling load and the coefficient of performance of the thermoelectric refrigerator. The effects of various parameters on the optimum performance are analyzed. The results may provide guides for the analysis and optimization of practical thermoelectric refrigerators. 相似文献
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Closed intercooled regenerator Brayton-cycle with constant-temperature heat-reservoirs 总被引:2,自引:0,他引:2
The performance of an irreversible closed intercooled regenerator Brayton-cycle coupled to constant-temperature heat reservoirs is analyzed by using the theory of finite-time thermodynamics (FTT). Analytical formulae for dimensionless power and efficiency are derived. Especially, the intercooling pressure-ratio is optimized for the optimal power and the optimal efficiency, respectively. The effects of component (the intercooler, the regenerator, and the hot- and cold-side heat-exchangers) effectivenesses, the compressor and turbine efficiencies, the heat-reservoir temperature-ratio, and the temperature ratio of the cooling fluid in the intercooler and the cold-side heat reservoir on the optimal power and the corresponding efficiency and corresponding intercooling pressure ratio, as well as the optimal efficiency and the corresponding power and corresponding intercooling pressure-ratio are analyzed by detailed numerical examples. 相似文献
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《Applied Energy》2005,82(2):181-195
In this paper, in the viewpoint of finite-time thermodynamics and entropy-generation minimization are employed. The analytical formulae relating the power and pressure-ratio are derived assuming heat-resistance losses in the four heat-exchangers (hot- and cold-side heat exchangers, the intercooler and the regenerator), and the effect of the finite thermal-capacity rate of the heat reservoirs. The power optimization is performed by searching the optimum heat-conductance distributions among the four heat-exchangers for a fixed total heat-exchanger inventory, and by searching for the optimum intercooling pressure-ratio. When the optimization is performed with respect to the total pressure-ratio of the cycle, the maximum power is maximized twice and a ‘double-maximum’ power is obtained. When the optimization is performed with respect to the thermal capacitance rate ratio between the working fluid and the heat reservoir, the double-maximum power is maximized again and a thrice-maximum power is obtained. The effects of the heat reservoir’s inlet-temperature ratio and the total heat-exchanger inventory on the optimal performance of the cycle are analyzed by numerical examples. 相似文献
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《Applied Energy》2005,81(1):55-71
On the basis of an endoreversible absorption heat-pump cycle, a generalized irreversible four-heat-reservoir absorption heat-pump cycle model is established by taking account of the heat resistances, heat leak and irreversibilities due to the internal dissipation of the working substance. The heat transfer between the heat reservoir and the working substance is assumed to obey the linear (Newtonian) heat-transfer law, and the overall heat-transfer surface area of the four heat-exchangers is assumed to be constant. The fundamental optimal relations between the coefficient of performance (COP) and the heating-load, the maximum COP and the corresponding heating-load, the maximum heating load and the corresponding COP, as well as the optimal temperatures of the working substance and the optimal heat-transfer surface areas of the four heat-exchangers are derived by using finite-time thermodynamics. Moreover, the effects of the cycle parameters on the characteristics of the cycle are studied by numerical examples. 相似文献
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An endoreversible closed modified simple Brayton cycle model with isothermal heat addition coupled to variable-temperature heat reservoirs is established using finite-time thermodynamics. Analytical expressions of dimensionless power output, thermal efficiency, dimensionless entropy generation rate and dimensionless ecological function are derived. Influences of cycle thermodynamic parameters on ecological performance and optimal compressor pressure ratio, optimal power output, optimal cycle thermal efficiency and optimal entropy generation rate corresponding to maximum ecological function are obtained and compared with those corresponding to maximum power output. The results show that cycle thermal efficiency improvement and entropy generation rate reduction are obtained at the expense of higher compressor pressure ratio and a little sacrifice of power output at maximum ecological function. The compromises between power output and entropy generation rate and between power output and cycle thermal efficiency, respectively, are achieved. 相似文献
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The performance of multi-element thermoelectric-generators, assuming heat-transfer irreversibilities which obey the linear phenomenological heat-transfer law Q ∝ (ΔT−1), is studied in this paper by combining finite-time thermodynamics with non-equilibrium thermodynamics. The performance characteristics of the output power, efficiency and working electrical-current are described by numerical examples. 相似文献
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最大功率密度输出时Atkinson热机的效率 总被引:3,自引:0,他引:3
有限时间热力学主要研究循环的最大功率及相应效率。本文则以功率密度——循环输出功率与最大比容之比——作为优化目标分析Atkinson循环的性能,以兼顾发动机尺寸性能。计算表明最大功率密度输出时循环的效率总是大于最大功率输出时的效率,且前者相应的尺寸参数比后者要小。 相似文献
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应用有限时间热力学理论和方法建立了闭式内可逆回热布雷顿热电冷联产装置模型,导出了装置无量纲(火用)输出率和效率的解析式。通过数值计算分析了回热器热导率对(火用)输出率和(火用)效率的影响,发现存在临界压比,同时优化了压比,研究了热电比、制冷和供热温度等设计参数对最优(火用)输出率和(火用)效率以及相应最佳压比的影响,发现最优(火用)输出率时的设计压比要大于最优(火用)效率时的设计压比,最优(火用)输出率和(火用)效率均随冷用户温度的升高而减小,分别存在最佳的热用户温度使(火用)输出率和(火用)效率取得最大值,热用户温度对装置最优(火用)性能的影响比冷用户温度更为明显。 相似文献
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The optimal exergy-based ecological performance of a generalized irreversible Carnot-engine with losses due to heat-resistance, heat leakage and internal irreversibility, in which the heat-transfer between the working fluid and the heat reservoirs obeys a linear phenomenological heat-transfer law, is derived by taking an exergy-based ecological optimization criterion as the objective. This consists of maximizing a function representing the best compromise between the power output and entropy-production rate of the heat engine. A numerical example is given to show the effects of heat leakage and internal irreversibility on the optimal performance of the generalized irreversible heat-engine. The results provide theoretical guidance for the design of practical engines. 相似文献
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An irreversible cycle model of Meletis–Georgiou (MG) engine consisting of an isochoric heating branch, isochoric and isobaric cooling branches, two non-isentropic compression and two non-isentropic expansion branches and with heat transfer loss, internal irreversibility and the linear relation between specific heat of the working fluid and its temperature is established by using the theory of finite time thermodynamics. The analytical relations of the work output versus compression ratio, the efficiency versus compression ratio, as well as the work output versus efficiency are obtained by using numerical examples. The results show that the work output versus the efficiency characteristic of the irreversible MG cycle is a loop-shaped curve which is consistent with the general heat engine performance, and the cycle model considering the internal irreversibility and linear relation between specific heats of the working fluid and its temperature is closer to practice than the endo-reversible model with constant specific heats of the working fluid. 相似文献