空气阻力系数对水滴运动及蒸发的影响

Effect of air drag coefficient on motion and evaporation of water droplet

应用喷灌条件下水滴的运动、蒸发及分布模型对水滴的飞行时间、飞行距离以及蒸发率进行了预测,并对5种空气阻力系数计算公式(Bird、Park、Fukui、伊沙叶夫、Wallis)求得的预测值和实测值进行了比较。结果表明:应用Bird、Wallis、Fukui公式预测的水滴飞行时间与实测值随水滴直径的变化趋势一致,应用Park和伊沙叶夫公式求得的水滴飞行时间预测值与实测值的相对误差最小;5种阻力系数公式均能较准确地预测水滴飞行距离,其中Park公式的预测精度最高;5种阻力系数公式对于单个水滴蒸发率的预测结果与实测值之间的平均相对误差在26.1%～30.2%之间;5种阻力系数公式对总蒸发率的预测影响不明显,预测值与实测值之间的平均相对误差在15.2%～17.5%之间。建议在水滴运动和蒸发计算中采用Park阻力系数公式。

Five different air drag coefficients presented by Bird, Park, Fukui, Yevgeny Isa and Wallis respectively were used to predict the flight time, travel distance, and evaporation rate of single droplet and total evaporation rate of spray droplets by applying the models of motion, evaporation and distribution of sprinkler droplet. The results show that in the prediction of the travel time for single droplet, the predicted values using the coefficients of Bird, Wallis, and Fukui with the change in droplet diameter have the same trend with the measured values. The predicted travel time for single droplet by using coefficients of both Park and Yevgeny Isa was closer to the measured values than the other three coefficients. In the prediction of evaporation rate for single droplet by using five different coefficients, the average relative errors between the predicted and measured values were in the range from 26.1% to 30.2%. No obvious differences could be found by using these five coefficients in the prediction of the overall droplet evaporation. The average relative errors between the predicted and measured values varied from 15.2% to 17.5%. Drag coefficient of Park is regarded as the best one to predict motion and evaporation of water droplet.