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。     

逆布雷顿(Reverse-Brayton)循环空气制冷机系统试验台的建立

采用逆布雷顿循环的空气制冷机在普冷和深冷领域得越来越广泛地应用。而且随着国际上对ＣＦＳｓ工质的限制,对环境无污染的空气制冷机具有更加广泛的应用前景。同时,对逆布雷顿循环低温制冷机的研究有利于空间和宇航制冷技术的发展。为了更好地对逆布雷顿循环制冷系统的性能进行研究,西安交通大学低温工程研究所搭字逆布雷顿循环的空气制冷机多功能试验台,可对透平膨胀机、换热器和制冷系统的性能进行试验研究,并可采用不同的工     

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。     

螺旋压缩膨胀制冷机制冷循环热力性能分析

螺旋压缩膨胀制冷机是一种近似布雷顿循环的新型制冷机,与布雷顿制冷循环相比,其压缩过程更接近于等温压缩过程.首先提出了螺旋压缩膨胀制冷机制冷循环,其次采用数学理论计算方法就特定工况下螺旋压缩膨胀制冷机制冷循环过程的热力性能和制冷系数与布雷顿循环进行比较研究.研究发现:一定条件下,得到相同制冷量时,螺旋压缩膨胀制冷机制冷循...     

磁布雷顿制冷循环

讨论并介绍了磁布雷顿制冷循环,指出磁布雷顿制冷循环具有某些独特优点,因而也是磁制冷新技术发展中不可忽视的一种重要循环方式。     

广义三热源制冷循环的等效联合系统

首先将工作在有限高温热源和两个恒温热源之间的一类广义三热源制冷循环抽象为一个广义卡诺热机驱动一个卡诺制冷机的等效联合系统,然后应用广义卡诺热机和卡诺制冷机的有限时间热力学理论,导出广义三热源制冷循环在不可逆传热情况下的最佳制冷系数与制冷率间的关系。由此讨论这类制冷循环的各种优化性能,并给出这类制冷循环在几种特殊情况下的等效联合系统。所得的结果可为吸收式制冷机、喷射式制冷机和化学热泵等制冷设备的进一步开发和利用提供参考依据。     

顺磁质Ericsson制冷循环的优化分析

应用有限时间热力学理论研究了顺磁质Ｅｒｉｃｓｓｏｎ制冷循环的优化，得出了最佳制冷率和制冷系数之间的基本优化关系，取得了一些有意义的结果。对这类实际制冷机优化设计具有指导意义。     

一种极具发展潜力的制冷技术--磁制冷

介绍了一种历史悠久但又极具发展潜力的制冷方式-磁制冷技术.从磁制冷的基本原理-磁热效应(MCE)出发,分别从熵和热力学的角度分析了MCE,给出了MCE的表征参数及常用测试方法,列举了常见的磁制冷循环及几种典型的磁制冷机,总结了磁制冷技术的研究历史,并对其进行了展望.     

磁制冷核心问题及高效利用新方式

旋转式磁制冷机是目前室温磁制冷机的主流技术方案,本文针对制约现有磁制冷机的关键因素,综述了磁回热器的高效传热、多组磁回热器的流路控制、多层磁工质复叠制冷及磁体、系统集成等核心问题的最新研究进展并提出了发展方向,深入总结了通过复合制冷的方式拓展磁制冷应用范围及制冷性能的途径及潜力,以助于明确未来磁制冷的研究方向,为研发高性能磁制冷机提供思路。     

变温热源不可逆布雷顿制冷循环制冷率密度优化

用有限时间热力学分析方法,制冷率密度为热力学优化目标,分析了变温热源条件下不可逆布雷顿制冷循环的性能,得到了普适的解析关系式,并由数值计算分析了压比、热导率分配以及工质和热源间热容率匹配等参数对制冷率密率的影响特点.     

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.     

Thermodynamic design of hydrogen liquefaction systems with helium or neon Brayton refrigerator

A thermodynamic study is carried out for the design of hydrogen liquefaction systems with helium (He) or neon (Ne) Brayton refrigerator. This effort is motivated by our immediate goal to develop a small-capacity (100 L/h) liquefier for domestic use in Korea. Eight different cycles are proposed and their thermodynamic performance is investigated in comparison with the existing liquefaction systems. The proposed cycles include the standard and modified versions of He Brayton refrigerators whose lowest temperature is below 20 K. The Brayton refrigerator is in direct thermal contact with the hydrogen flow at atmospheric pressure from ambient-temperature gas to cryogenic liquid. The Linde-Hampson system pre-cooled by a Ne Brayton refrigerator is also considered. Full cycle analysis is performed with the real properties of fluids to estimate the figure of merit (FOM) under an optimized operation condition. It is concluded that He Brayton refrigerators are feasible for this small-scale liquefaction, because a reasonably high efficiency can be achieved with simple and safe (low-pressure) operation. The complete cycles with He Brayton refrigerator are presented for the development of a prototype, including the ortho-to-para conversion.     

使用箔片径向气体轴承的透平-逆布雷顿循环空气制冷机

设计了一台小型透平－逆布畦顿循环空气制冷机,并将一种新型的箔片径向气体轴承应用在该制冷机系统的透平膨胀机上,通过试验,对空气制冷机的机械性能及热力性能进行了考核。     

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.     

Performance characteristics of an irreversible magnetic Brayton refrigeration cycle

Based on the thermodynamic properties of a paramagnetic salt, an irreversible model of the magnetic Brayton refrigeration cycle is established, in which the working substance is a special paramagnetic material. The expressions of the important performance parameters, such as the coefficient of performance, refrigeration load and work input, are derived. Moreover, the optimal performance parameters are obtained at the maximum coefficient of performance. The results obtained here may include the ones of the magnetic Brayton refrigeration cycle using the magnetic material obeyed the Curie law as the working substance, the magnetic Brayton refrigeration cycle without regeneration and the eversible magnetic Brayton refrigeration cycle. Therefore, the results obtained here have general significance and will be helpful to deeply understand the performance of a magnetic Brayton refrigeration cycle.     

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.     

An Electronic Demagnetization Stage for the 0.5K to 1.8K Temperature Range

We have designed and built a demagnetization stage to operate between 1.8K and 0.5K, a somewhat unusual temperature range for adiabatic demagnetization refrigeration. The lower bound in temperature is dictated by the thermal performance of our ³ He gas heat switch, the upper by NASA specifications. We intend this demagnetization stage to be the fast stage of a proposed two-stage continuously operating adiabatic demagnetization refrigerator (ADR) which will operate between 1.8K and 50 mK. Here we discuss thermal, mechanical, magnetic and chemical considerations which led to novel features in our salt pill design.     

Performance modeling of AMR refrigerators

A system modeling approach for predicting the performance of active magnetic regenerators using a one-phase approximation is presented. The approach is described for an arbitrary AMR device independent of the magnetic refrigerant, thermal losses or magnetic waveform. A general expression for magnetic work is derived which can be used for cycles where the low-field intensity is not zero. Additionally, a means of treating the varying magnetic field waveform as a single high and low field is described. The model is applied to a permanent magnet magnetic refrigerator using water–glycol as the heat transfer fluid. Simulated results are compared to experimental data which vary by heat load, frequency and utilization. A sensitivity analysis is performed using utilization, adiabatic temperature change, effective conductivity and particle size as independent variables. Comparisons to experimental data show that reducing the calculated magnetocaloric effect by 25% provides good agreement between simulations and experimental results.