电场对微细通道内R141b制冷剂流动沸腾压降的影响

    Effect of electric field on flow boiling pressure drop characteristics of R141b in microchannel

    • 摘要: 在农业工程领域,微细通道散热技术在农产品培育系统、农业机械、农产品干燥系统中有着广泛的应用。通过施加电场可强化微细通道换热系统的传热效率,为探究电场对微细通道内制冷剂流动沸腾阻力的影响,该文采用了2种电极布置方式(针状和线状),以制冷剂R141b为试验工质,在系统压力为140 kPa,工质入口温度32.5 ℃、质量流率277.35~531.75 kg/(m2·s)、热流密度7.50~21.49 kW/m2、电压0~850 V工况下,在截面尺寸为2 mm×2 mm的矩形微细通道内进行流动沸腾试验,探究直流电场对微细通道内R141b流动沸腾压降特性影响。研究结果表明:在本文试验工况下,电场会增大微细通道内的摩擦压降,针状与线状电极电场作用下的微细通道内摩擦压降分量在总压降中所占比例均比无电极作用下的更大;电场作用下单位长度两相摩擦压降随电压、热流密度的增大而增大,针状电极与线状电极电场作用下平均单位长度两相摩擦压降分别比无电极作用下增加0.7%~15.4%和1.3%~18.7%;电压为0~250 V时,针状电极对压降的影响效果大于线状电极,电压大于400 V后,线状电极对压降的影响效果更为显著。通过COMSOL软件对6 mm长微细通道内2种电场的分布进行了模拟,模拟结果表明相同电压作用下,针状电极产生的电场强度最大值超过线性电极,但线状电极的电场有效作用范围超过针状电极。该文研究结果可为通过施加电场提高微细通道换热器的性能实现微细通道高效节能提供新思路。

       

      Abstract: Microchannel heat exchanger is highly efficient in heat exchange due to its microscopic structure and large heat exchange surface area ratio. Compared with conventional heat exchanger, it not only improves heat exchange efficiency but also saves space and reduces the weight of heat dissipation equipment. In agriculture, microchannel heat dissipation technology has been widely used in cultivation, machinery, and product drying. Microchannel increases resistance to fluid flow and could thus result in an increase in energy consumption. It could also give rise to a pressure-drop oscillation affecting operation of the system. Previous work showed that electric field has a beneficial impact on heat transfer efficiency in the microchannel heat exchanger. The purpose of this paper is to investigate how different electrodes (needle type and linear types) affect pressure drop of the boiling R141b coolant when it flows in the microchannel. The pressure in the system was kept at 140 kPa, the working inlet temperature was 32.5 ℃, the mass flow rate ranged from 277.35 to 531.75 kg/(m2·s), the heat flux density ranged from 7.50 to 21.49 kW/m2, the voltage ranged from 0 to 850 V, and the microchannel was rectangular with a cross section of 2 mm×2 mm. The results showed that the electric field under both electrodes increased the frictional pressure drop in the microchannel, compared with that without electric field. The frictional pressure drop of the two-phase along per unit length increased with both voltage and heat flux. The average two-phase frictional pressure drop along per unit length under the needle and the linear electrode was increased 0.7% to 15.4% and 1.3% to 18.7%, respectively, that without electric field. When the voltage changed from 0 to 250 V, the effect of the needle electrode on the pressure drop was greater than that of the linear electrode, while when the voltage was higher than 400 V, the effect of the linear electrode on the pressure drop was more significant. We simulated the electric field distribution in a microchannel 6 mm long using COMSOL for both electrodes. The results showed that under the same voltage, the maximum of the electric field intensity in the needle electrode was higher than that in the linear electrode, but the effective range of the electric field in the linear electrode was higher than that in the needle electrode. The results presented in this paper provide an alternative to improve performance of microchannel heat exchanger and reduce its energy consumption.

       

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