磁布雷顿制冷循环性能的优化分析

基于统计力学的性质推导出了顺磁系统的热力学关系,并构建了以满足居里定律的顺磁材料为工作物质的一般磁布雷顿制冷循环模型。研究了内不可逆性和传热不可逆性对循环优化性能的影响。根据该循环模型,推导出了循环的各种优化关系并深刻讨论了循环的性能特性,所得结果将有助于实际的磁制冷机的优化设计和应用。     

费米气体布雷顿制冷循环的性能分析

基于理想费米气体的状态方程，建立以理想费米气体^3He为工质的布雷顿制冷循环模型，导出循环的输入功、制冷系数和制冷量等重要参数的普遍表达式。对几种有趣的情况作了详细的讨论。确定了布雷顿制冷循环正常运行的压强比界限。     

回热损失对磁斯特林制冷循环制冷率的影响

从铁磁质的磁化强度一般表示式出发，探讨热阻和回热损失对磁斯特林制冷循环性能的影响，导出最大制冷率及其它性能参数。得到了结果适用于以顺磁质为工质的磁斯特林制冷循环。并指出在理想回热条件下的结论也适用于磁卡诺制冷循环。     

Performance characteristics of an irreversible regenerative magnetic Brayton refrigeration cycle using Gd0.74Tb0.26 as the working substance

The cycle model of an irreversible regenerative magnetic Brayton refrigerator using Gd_0.74Tb_0.26 as the working substance is established. Based on the experimental characteristics of iso-field heat capacities of the material Gd_0.74Tb_0.26 at 0 T and 2 T, the corresponding iso-field entropies are calculated and the thermodynamic performance of an irreversible regenerative magnetic Brayton refrigeration cycle is investigated. The effects of the irreversibilities in the two adiabatic processes and non-perfect regenerative process of the magnetic Brayton refrigeration cycle on the cooling quantity, the heat quantity released to the hot reservoir, the net cooling quantity and the coefficient of performance are discussed in detail. Some significant results are obtained.     

多种不可逆性对磁埃里克森制冷循环性能的影响

建立以顺磁盐为工质的不可逆埃里克森制冷循环新模型,探讨热阻、热漏、回热损失及工质内部不可逆性等对循环性能的影响,分析和讨论制冷循环的重要性能参数及优化工作区域,所得结论比现有文献的相关结论更普遍,可为磁制冷机的优化设计和性能评价提供新理论参考.     

变温热源不可逆布雷顿制冷循环制冷率和制冷系数优化

用有限时间热力学方法分析变温热源不可逆简单布雷顿制冷循环的特性,分别以制冷率和制冷系数为优化目标,优化了循环中换热器的热导分配以及工质和热源间的热容率匹配,并采用数值计算分析了压比、换热器总热导、压缩机和膨胀机效率、工质热容率等参数对最优制冷率和制冷系数的影响特点.所得结果对工程制冷系统设计有一定的指导意义.     

不可逆回热式玻色布雷顿制冷循环性能分析

基于玻色气体的热力学性质和回热式布雷顿制冷循环的不可逆模型,导出循环的一些重要性能参数,如循环的制冷量、回热量、输入功和性能系数的一般表达式。通过数值计算获得了循环的一些重要的性能特性曲线,分析了循环的不可逆性和回热特性对玻色布雷顿制冷机性能的影响。     

磁布雷顿制冷机优化循环性能及参数设计

基于统计力学和磁工质的热力学性质,建立磁布雷顿制冷机循环新模型,探索热漏、有限速率热传导,绝热过程不可逆性和绝热时间等对循环性能的影响,应用对数平均温差及热力学分析方法,导出制冷率、性能系数的数学表式,并应用数值方法分析、评估磁布雷顿制冷循环的优化性能特性,所得结果为磁制冷机的优化设计和性能改善提供参数设计参考。     

混合工质脉管制冷的热力学性能预测

提出了用于预测混合工质脉管制冷热力学性能的改进型Brayton制冷循环,建立了制冷系统制冷量和制冷系数COP的理论表达式。在对多种低温流体的预测计算的基础上,提出了具有应用潜力的混合工质对。计算结果表明,如果用10%氮与90%氦的混合工质对代替纯氦,脉管制冷机在80K温度下的制冷系数和制冷量分别可以提高9.5%和6.7%。此外还讨论了其它可能用于80K温区脉管制冷的混合工质对,如氢-氦、氩-氦、氖-氦混合物等。     

Thermodynamics of magnetic refrigeration

A comprehensive treatment of the thermodynamics of cyclic magnetic refrigeration processes is presented. It starts with a review of the work, heat and internal energy of a magnetized specimen in a magnetic field, and a list of the thermodynamic potentials is given. These are based on the very recent discovery of an alternative Kelvin force. It is shown that this force is compatible with the internal energy proposed by Landau and Lifshitz. New formulas for the specific enthalpies are presented. Cyclic processes are discussed in detail, e.g. the Brayton, Ericsson and Carnot cycles. Magnetic refrigeration and magnetic heat pump cycles are preferably designed by applying the cascade or/and regeneration principle. Cascade systems allow wider temperature ranges to be obtained. The main objective of this article is to yield a theoretical basis for an optimal design of new magnetic refrigeration and heat pump devices.     

不可逆布雷顿制冷循环的性能优化

基于不可逆布雷顿制冷循环模型,导出循环制冷率和性能系数之间优化关系所应满足的方程,利用数值解,研究内不可逆性和传热不可逆性对优化性能的影响.讨论了循环的各种优化性能,所得结果对实际制冷系统的优化设计有一定的指导意义.     

Assessment of condensation heat transfer correlations in the modelling of fin and tube heat exchangers

This is the second paper of a series that assesses the performance of a refrigeration system model by means of cycle parameters. In this case, the condensation temperature is the parameter to study and it is focused on fin and tube condensers. It also studies the influence of the heat transfer models on the estimation of this refrigeration cycle parameter and different correlations for the heat transfer coefficients have been implemented in order to characterise the heat transfer in the heat exchangers. The flow inside the heat exchangers is considered one-dimensional as in previous works. In the cycle definition, other submodels for all the cycle component have been taken into account to complete the system of equations that characterises the behaviour of the refrigeration cycle. This global system is solved by means of a Newton–Raphson algorithm and a known technique called SEWTLE is used to model the heat exchangers. Some experimental results are employed to compare the condensation temperatures provided by the numerical procedure and to evaluate the performance of each heat transfer coefficient. These experimental results correspond to an air-to-water heat pump and are obtained by using R-22 and R-290 as refrigerants.     

回热式布雷顿制冷循环的性能优化

基于回热式不可逆布雷顿制冷循环模型，导出循环的制冷率、性能系数和输入功率等一些重要性能参数的一般表达式及制冷率和性能系数之间优化关系所满足的方程，研究回热和各种不可逆性对其优化性能的影响，讨论了循环的优化运行区间及其性能界限，确定了最佳传热面积。通过数值计算分析了设计参数对循环的制冷率、性能系数和输入功率的影响。     

传热不可逆回热式布雷顿制冷机分析

用有限时间热力学方法分析实际隐态制冷装置性能，导出了恒温和变温热源条件下实际闭式回热式布雷顿制冷循环制冷率与压力比和制冷系数与压力比之间的解析关系。考虑了不可逆性包括高，低温侧换热器和回热器的不可逆传热损失，压缩机和膨胀机中的非等熵压缩和膨胀损失，以及管路系统中的压力损失，通过优化两个换热器和回热器之间的热导率分配或传热面积分配可得循环最优性能，由数值算例给出了各项损失对循环制冷率和制冷系数的影响。     

Impact of the initial field on the thermodynamic performance of room-temperature magnetic refrigeration cycle

The thermodynamic cycle performance of Gadolinium (Gd) and Gd_0.87Dy_0.13 used as the working substance in regeneration magnetic Brayton and Ericsson refrigeration cycles are investigated under different external magnetic field conditions. Based on the experimental iso-field heat capacities of Gd with different magnetic fields, the effects of magnetic field change on thermodynamic performances including the magnetic entropy change, cooling quantity, non-perfect regeneration, net cooling quantity, and coefficient of performance (COP) are analyzed and discussed. The present work shows the possibility of reducing the regenerative losses and thereby improving the net cooling quantity for a given field change by selecting optimal initial and final magnetic field values. The similar analysis and calculation of the related thermodynamic performances are further applied to the magnetic material Gd_0.87Dy_0.13 which exhibits better net cooling quantities when compared to Gd at low temperature.     

Developments in reverse Brayton cycle cryocooler in China

As one of the primary methods of cryogenic refrigeration, reverse Brayton cycle cryocooler, which includes high-speed turbine using gas bearing and compact heat exchanger, has many advantages such as long-life, high reliability and efficiency. In this paper general aspects of reverse Brayton cycle cryocooler in China are introduced, such as its application in the space simulation program, mechanical cryocooler for lower temperature space applications. The main design parameters and operating performance of cryocoolers are presented in this paper.     

Analysis of room temperature magnetic regenerative refrigeration

Results of a room temperature magnetic refrigeration test bed and an analysis using a computational model are presented. A detailed demonstration of the four sequential processes in the transient magnetocaloric regeneration process of a magnetic material is presented. The temperature profile during the transient approach to steady state operation was measured in detail. A 5 °C evolution of the difference of temperature between the hot end and the cold end of the magnetocaloric bed due to regeneration is reported. A model is developed for the heat transfer and fluid mechanics of the four sequential processes in each cycle of thermal wave propagation in the regenerative bed combined with the magnetocaloric effect. The basic equations that can be used in simulation of magnetic refrigeration systems are derived and the design parameters are discussed.     

Parametric optimization of a new combined refrigeration cycle – active thermal potentiostatting system

The active thermal potentiostatting system proposed by Martinovskii and Tsirlin is directly generalized to a more practical case, in which one intermediate chamber, besides a thermal potentiostatting chamber, and two irreversible refrigeration cycles are included and the influence of the thermal resistance between the working fluid and the reservoirs, the heat leakages from the environment to the intermediate chamber and from the intermediate chamber to the potentiostatting chamber are taken into account. Expressions for the main parameters of the system are derived. By using the optimal control theory, the minimum total power input of the system with non-zero cooling rates is calculated and the temperatures of the working fluid in the isothermal processes of the refrigeration cycles are optimized. The optimal allocation of the heat-transfer areas of the heat-exchangers in the refrigeration cycles is discussed in detail. The results obtained here are more general and useful than the relevant results in literature and can provide some valuable guidance for the optimal design and operation of real active thermal potentiostatting systems.     

Mass recovery adsorption refrigeration cycle—improving cooling capacity

The study investigates the performance of two-bed, silica gel-water adsorption refrigeration cycle with mass recovery process. The cycle with mass recovery can be driven by the relatively low temperature heat source. In an adsorption refrigeration cycle, the pressures in adsorber and desorber are different. The chiller with mass recovery process utilizes the pressure difference to enhance the refrigerant mass circulation. Cooling capacity and coefficient of performance (COP) were calculated by cycle simulation computer program to analyze the influences of operating conditions. The mass recovery cycle was compared with conventional cycle such as the single stage adsorption cycle in terms of cooling capacity and COP. The results show that the cooling capacity of mass recovery cycle is superior to that of conventional cycle and the mass recovery process is more effective for low regenerating temperature.     

Thermoeconomic optimization of a two stage combined refrigeration system: a finite-time approach

A finite-time thermoeconomic performance analysis based on a new kind of optimization criterion has been carried out for a two-stage endoreversible combined refrigeration cycle model. The optimal performances and design parameters that maximize the objective function (cooling load per total cost) are investigated. In this context, the optimal temperatures of the working fluids, the optimum performance coefficient, the optimum specific cooling load and the optimal distribution of the heat exchanger areas are determined in terms of technical and economical parameters. The effects of the economical parameter that characterizes the investment and energy consumption costs on the general and the optimal performances have been discussed.