分段蒸发与冷凝对分子蒸馏过程的影响

Effects of Segmented Condensation and Evaporation on a Molecular Distillation Process

在对分子蒸馏液膜表面流体流动和传质传热分析的基础上,建立了二维分子蒸馏模型。通过二组分物系模拟仿真,研究了分段蒸发与冷凝对蒸馏量、目标组分质量分数和液膜表面温度的影响。研究结果表明:通过分子蒸馏分段冷凝可以减少实际蒸馏过程中由于脱气不完全造成的“喷溅”现象、冷凝面分子返蒸发效应和得到质量分数梯度较大的目标组分,并可以增大蒸馏量。分子蒸馏的分段梯度升温蒸发,导致蒸发液膜表面温度的阶跃式上升,可以在一次分子蒸馏过程中分离蒸汽压相差较大的多组分物料并得到所需质量分数要求的目标组分。

In this study, balance equations of a binary mixture for molecular distillation were derived on the basis of the relation of heat and mass transfer in liquid films on both the evaporation and condensation surfaces. The effects of segmented condenser and evaporators on degree of evaporation, composition of condensate, surface temperature of evaporating and condensing film were studied. Results showed that influence of splashing on desired substance caused by insufficient removal of gases and re-evaporation were minimized by the segmented condenser. The component with larger mass concentration gradient of desired substance and increasement of evaporation degree were obtained. The temperature of evaporating film surface was increased through the rising temperature evaporation in segmented evaporator. The separation of mixtures with obvious different vapor pressures could be fulfilled and desired mass concentration of component could be obtained by the segmentwd evaporator.