微通道内纳米制冷剂流动沸腾传热预测模型

Prediction Model for Flow Boiling Heat Transfer of Nanorefrigerant in Microchannels

以R141b制冷剂为基液,Al_2O_3为纳米颗粒,采用两步法制备了质量分数分别为0.2%、0.5%和0.8%的Al_2O_3-R141b纳米制冷剂,并进行了纳米制冷剂及R141b纯制冷剂在水力直径为1.33 mm的矩形微通道内流动沸腾传热实验。实验工况范围:饱和压力为176 k Pa,入口过冷度为6~12℃,体积流量为20~50 L/h,热流密度为11.1~26.6 k W/m^2。实验结果与7个纯工质传热模型、2个纳米制冷剂传热模型进行比较评价。结果发现,在本实验研究范围内,纯工质传热模型不适用于纳米制冷剂传热系数的预测;Peng-Ding纳米制冷剂传热模型与KimMudawar纯工质传热模型组合对纳米制冷剂传热系数的预测值最接近实验值,平均绝对误差为17.22%,且能较好地反映纳米颗粒对流动沸腾传热影响的规律;结合实验数据对Peng-Ding模型的纳米影响因子(纳米制冷剂与纯制冷剂的传热系数之比)关联式进行修正,新关联式具有较好的预测效果,平均绝对误差为15.2%,且与Bertsch模型的组合能较好地预测微通道内纳米制冷剂传热系数,平均绝对误差降为16.4%。

R141b and Al2O3 were selected as base fluid and nanoparticle,respectively,and the two-step method was used to prepare Al2O3-R141 b nanorefrigerant. The mass fractions were 0. 2%,0. 5% and0. 8%,respectively. The flow boiling heat transfer of Al2O3-R141 b nanorefrigerant and R141 b refrigerant in rectangular microchannels with hydraulic diameter of 1. 33 mm was experimentally investigated.Experimental conditions included saturation pressure of 176 k Pa,inlet subcooling from 6℃ to 12℃,volume flow rate from 20 L / h to 50 L / h,and heat flux from 11. 1 k W / m2 to 26. 6 k W / m2. The experimental results were used to evaluate seven heat transfer models for pure working fluid and two heat transfer models for nanorefrigerant. Results showed that the pure working fluid heat transfer models were not suitable for nanorefrigerant. The Peng-Ding heat transfer model for nanorefrigerant combined with the Kim-Mudawar model for pure working fluid gave relatively good agreement with experimental data,the mean absolute error（ MAE） was 17. 22%,which reflected the effect of nanoparticles on flow boiling heat transfer. A new nanoparticle impact factor（ the ratio of heat transfer coefficient of nanorefrigerant to refrigarant） correlation was proposed based on Peng-Ding model and experimental data, the new correlation had good predictability with MAE of 15. 2%,and the new correlation combined with the Bertsch model provided good prediction of heat transfer coefficient for nanorefrigerant in microchannels,and the MAE was decreased to 16. 4%.