水平管降膜蒸发器温度损失的计算与分析

Evaporation Temperature Loss Evaluation in Horizontal Tube Falling Film Evaporator

为了研究降膜蒸发管束阻力造成的压降及其对传热的影响,以降膜蒸发器内广泛应用的正三角排列管束为物理模型,采用由实验数据拟合出来的压降系数,计算了压降对应的温度损失,分析了蒸汽产率、饱和温度、管列数和喷淋密度对蒸发温度损失的影响。结果表明:温度损失随喷淋密度、管列数和蒸汽产率的增加而升高,随饱和温度的升高而减小;在相同的蒸汽质量流量下,45℃蒸汽的温度损失是70℃时的6倍,而喷淋密度为0.08kg/(m·s)时的温度损失约是0.02kg/(m·s)时的2倍;大型降膜蒸发器内管束区内的温度损失随管列数的增加呈现抛物线型升高。为保证各效蒸发器的传热效率,提出每一效蒸发器温度损失都相等的等温度损失设计思想,其对低温多效蒸发器的设计具有指导意义。

To investigate the vapor pressure drop due to the resistance force of tube bundle and the effect on heart transfer, triangular arrangement tube bundle widely applied to falling film evaporator is chosen as the physical model to evaluate the vapor temperature loss, and the fitting coefficient of pressure drop from the experimental data is provided. The effects of steam mass flux, saturated temperature, tube column number and water flow rate on vapor temperature loss are analyzed respectively. The results indicate that the temperature loss increases with the increase of water flow rate, steam mass flux and tube column number, while decreases with the increasing saturated temperature. With the equal steam mass flux, the temperature loss at 45 ℃ is six times of that at 70 ℃ and the temperature loss as water flow rate in 0.08 kg/（m ·s） is almost double of that as water flow rate in 0.02 kg/（m·s）; the temperature loss rises parabolically with the increasing tube column number in large falling film evaporator. A new design idea of equal temperature loss in each effect evaporator is proposed which facilitates ensuring the heat transfer efficiency.