| Based on the reciprocating room-temperature magnetic refrigeration system,using Brayton magnetic refrigeration cycle,the convection heat transfer process between the magnetic materials and the flow in the active regenerator was simulated and experimentally analyzed.In the simulation study,the two-dimensional cross-section model of the regenerator was mainly established to study the influence of the velocity field of the fluid flow in the gap of regenerator and the effect of convection heat transfer of different inlet flow velocity in the active regenerator;For the experimental study,it was mainly aimed at the different filling in the active regenerator.The temperature of the cold end and the hot end of the regenerator was measured in real time under the conditions of the magnetic materials Gd of different sizes and different kinds of magnetic materials Gd and LaFeCoSi,and the change of the refrigeration coefficient of the active regenerator was compared under different porosity conditions.Combining the adiabatic temperature change and experimental results of Gd and La FeCoSi directly measured by the magnetocaloric effect,the advantages and disadvantages of the cooling effects of materials Gd and La FeCoSi were analyzed and compared.The main conclusions of the study were as follows:1.By selecting different inlet velocity of 0.06m/s,0.08m/s,0.1m/s,and 0.12m/s,the flow process of the two-dimensional cross-section model with parallel and staggered distributions of particles with a radius of 1.5mm in a regenerator was simulated.In order to achieve a full convection heat transfer process between the flow and the heat source of solid particles,the staggered distribution can achieve full contact of the particle surface with water,which is better for heat exchange,and its optimum inlet flow velocity is around 0.1 m/s.When the fluid traverses around the fork row particles,the temperature distribution of the fluid at the inlet is uniform,the temperature of the fluid is closing to the particles rises,and the temperature of the flow at the back surface of the particles is relatively higher,which is due to the occurrence of particle backflow,so that the disturbance enhances the heat transfer between the fluid and the solid.For this structure,the Nu of the heat transfer coefficient increases firstly,and then decreases.2.Through the experiments with different hot and cold flow time of 0.8mm and 0.3mm Gd,the temperature changes over time of the cold end was measured at different magnetization(or demagnetization)velocity of 0.1m/s,0.13m/s,and 0.16m/s.The results show that when the ratio of flow water quality to resident water quality V* is different,the change trends of the cold end temperature of the active regenerator corresponding to different magnetization(or demagnetization)velocity rates remain the same.For Gd with radius of 0.8 mm,when V* is taken to be 0.8 or 0.9,which approaches 1,the magnetization(or demagnetization)velocity is 0.16 m/s,the heat transfer efficiency between the materials Gd and the heat exchange fluid water is the best,and the corresponding cold end of the regenerator has the lowest temperature,and the lowest is 9.5°C;while for the radius of 0.3 mm,when V* is 9.7,which approaches 10 and the magnetization(or demagnetization)velocity is 0.16m/s,the temperature of the cold end of the active regenerator is the lowest,and the lowest temperature is 5.2°C.The optimum refrigerating efficiency COP of the materials with different radius is similar,but there is a significant difference in the cooling velocity between them.The cooling velocity of 0.3mm Gd is larger than 0.8mm Gd.3.Through the experimental study of the magnetic materials LaFeCoSi,the cooling temperature span corresponding to each magnetization(or demagnetization)rate with the convection time changes between 3.0~4.0 ℃,with the increasment of the magnetization(or demagnetization)velocity,the span is increasing.Therefore,in order to achieve a larger cooling temperature span for the room temperature magnetic refrigeration system,it is not suitable to select LaFeCoSi compounds as magnetic materials.Comparing the experiments of LaFeCoSi compounds and Gd,it is found that there are obvious differences in the curves of the two magnetic regenerators.Combined with the adiabatic temperature curves of the cooling temperature span,the cooling velocity of Gd is much larger than that of LaFeCoSi compounds and the cooling effect is better,under different room temperature conditions of 15°C,16°C,17°C and 18°C,the change trend of the temperature distribution of the cold end of the active regenerator remained the same,and the cooling temperature span was not much different. |
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