The Numerical Simulation Of Falling Film Evaporator On Horizontal Tubes

The horizontal-tube falling film evaporator occurs in numerous energy conversion and transport applications, including seawater desalination, refrigeration and air conditioning systems, chemical reactors and process industry heat exchange equipment. This type of evaporator provides a very effective means of transporting energy due to its advantages over other evaporators as small temperature difference, external thin film thickness and phase change on both sides of a tube. Most of experiments and models put an important part in heat transfer at horizontal tube, there is only a few analysis about micro film thickness and film temperature.In order to get a deep and direct understanding of the microscopic mechanism of falling film at horizontal tubes and heat transfer characteristics, the method of numerical calculation is adopted. It needs to determine governing equation and initial velocity by the boundary theory and temperature. The model of falling film evaporation includes liquid viscosity and gravity of liquid film. By calculating the program of falling film evaporation out of tube, film thickness, film velocity, and film temperature and local heat transfer coefficient are got. The model of condensation includes shear force and gravity. By calculating the program of condensation inside of tube in the condition that the temperature of tube is constant, the film thickness, stratified angle, local heat transfer coefficient are got. By combining the model of falling film evaporation out of tube and condensation inside of tube on the base of heat flux equality, a numerical calculation can be developed to describe the process of heat transfer on a horizon tube. Under the condition of the temperature is constant at per unit length, the character of heat transfer can be got. The result of simulation shows:The simulation results show that the model of horizontal tube falling film evaporation is accurate, comparing with the experiment; The distribution of the thermal developing region and thermal developed region along the tube circumference for a single tube and tube bundle are got. Radical velocity is the major reason for the convection the thin film evaporation through the analysis on the profiles of the local film velocity and local heat transfer coefficient in the falling film. For the condensation liquid increase, the film thickness is increasing, the stratified angle is decreasing, the area of heat transfer is decreasing, the heat transfer coefficient is decreasing along axial distance. The flow field and heat transfer rate are improved by means of optimizing the flow density distribution of liquid film outside a tube on basis of the variation of the internal condensation process. The heat transfer coefficient is promoted by preheating of two processes. Micro heat transfer simulation of falling film evaporator on horizontal tubes promotes to understand the theory of falling film evaporator. The result of calculation of falling film evaporator for tube bundle is beneficial to the design of evaporator.