The Numerical Simulation of Flow and Boiling Heat Transfer of Two Phases in Horizontal Tube

In order to reduce energy consumption of the evaporator, the energy-saving technology of mechanical vapor recompression (MVR) was purposed. The flow and heat-transfer characters was studied in horizontal boiling tube for the evaporator by using multiphase mixture model of Fluent and adding user-defined source term functions of mass transfer and energy transfer on phase boundary. The effect of velocity and temperature of wall to flow and boiling heat transfer were studied. The simulation results show that velocity has influence to boiling heat transfer in the same conditions, with the velocity increasing, the drag force of bubbles increases, the frequency of falling off tube wall rises also, the boiling heat transfer is enhanced, and heat transfer coefficient also increases. With the temperature of wall rises, the degree of superheat of the flow on the wall increases, it makes more steam nuclear to breed steam bubbles and enhance the liquid evaporate. But with intensity of evaporation increase, bubbles gathering on the upper of tube increase and heat transfer coefficient decreases. For evaporator with horizontal boiling tubes, increasing the velocity of the fluid or reducing temperature of wall is an effective way to enhance the boiling heat transfer.