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。     

Detailed numerical modeling of a linear parallel-plate Active Magnetic Regenerator

A numerical model simulating Active Magnetic Regeneration (AMR) is presented and compared to a selection of experiments. The model is an extension and re-implementation of a previous two-dimensional model. The new model is extended to 2.5D, meaning that parasitic thermal losses are included in the spatially not-resolved direction.The implementation of the magnetocaloric effect (MCE) is made possible through a source term in the heat equation for the magnetocaloric material (MCM). This adds the possibility to model a continuously varying magnetic field.The adiabatic temperature change of the used gadolinium has been measured and is used as an alternative MCE than mean field modeling. The results show that using the 2.5D formulation brings the model significantly closer to the experiment. Good agreement between the experimental results and the modeling was obtained when using the 2.5D formulation in combination with the measured adiabatic temperature change.     

Two-dimensional mathematical model of a reciprocating room-temperature Active Magnetic Regenerator

A time-dependent, two-dimensional mathematical model of a reciprocating Active Magnetic Regenerator (AMR) operating at room-temperature has been developed. The model geometry comprises a regenerator made of parallel plates separated by channels of a heat transfer fluid and a hot as well as a cold heat exchanger. The model simulates the different steps of the AMR refrigeration cycle and evaluates the performance in terms of refrigeration capacity and temperature span between the two heat exchangers. The model was used to perform an analysis of an AMR with a regenerator made of gadolinium and water as the heat transfer fluid. The results show that the AMR is able to obtain a no-load temperature span of 10.9 K in a 1 T magnetic field with a corresponding work input of 93.0 kJ m⁻³ of gadolinium per cycle. The model shows significant temperature differences between the regenerator and the heat transfer fluid during the AMR cycle. This indicates that it is necessary to use two-dimensional models when a parallel-plate regenerator geometry is used.     

A 2D hybrid model of the fluid flow and heat transfer in a reciprocating active magnetic regenerator

This paper evaluates the thermal behavior of a magnetic-Brayton-based parallel plate reciprocating active magnetic regenerator (AMR). A time-dependent, 2D model of the fluid flow and the coupled heat transfer between the working fluid and the solid refrigerant (gadolinium) is proposed. A hybrid calculation method which consists of an analytical solution for the flow and a numerical solution for the thermal field has been adopted. Results for the cooling capacity as a function of the temperature span and mass flow rate agree well with trends observed in experimental data and other theoretical models available in the literature. The volume of fluid displaced through the channels during the isofield processes influences significantly the AMR performance. For a cycle frequency of 1 Hz, the cycle-averaged cooling capacity reaches a maximum when the utilization factor is 0.1 and the displaced fluid volume equals 62% of the fluid volume of the AMR.     

Validation of a mathematical and numerical model for dynamic 1-D moisture content evolution in layered building elements

The paper describes the experiment conducted to validate predictions, derived by the heat and mass transfer numerical analysis computer code MA1DW, for dynamic moisture-content evolution. The tests included two samples: an autoclaved aerated concrete (AAC) and a regular concrete rendered by thermal plaster (CTP). An excellent fit was derived for temperature evolutions in both samples. A good fit was derived for the trends and general evolutions of moisture contents, with much better absolute-value approximations for the AAC samples. This demonstrated the significance of establishing reliable Design Values for material coefficients. The validation actually supplied the confidence for undertaking the further steps of development and modification of the computer code into a 2-D analysis tool.

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Résumé Cet article décrit l'expérience qui a été effectuée afin de valider les prédictions dérivées par le code d'ordinateur d'analyse numérique de transfert de matière. MA1DW pour l'évolution dynamique de la teneur en humidité. Deux échantillons ont servi dans les essais: du béton aéré par autoclave (autoclaved aerated concrete—AAC) et un béton habituel, enduit de platre thermique (CTP). Une excellente concordance des évolutions de la température s'est ensuivie dans les deux échantillons. Une bonne concordance des tendances et des évolutions générales de la teneur en humidité a été observée, avec des approximations de valeur absolue bien meilleures dans les échantillons de béton aéré par autoclave. Ceci a démontré l'importance d'établir des valeurs de conception fiables pour les coefficients des matériaux. En fait, la validation a approté l'assurance que l'on peut continuer ultérieurement le développement et la modification du code d'ordinateur en un instrument d'analyse bidimensionnel.

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Editorial Note The Israeli National Building Research Institute (Technion) is a RILEM Titular Member.