Numerical Simulation Of Natural Circulation And Bubble Characteristics Of Subcooled Boiling In Narrow Rectangular Channel Under Rolling Condition

Flow boiling under rolling force field has different phenomenon with it under static condition,in order to dive deeper into the effects of rolling motion on the natural circulation characteristics of the whole system,this article adopted Mixture model and User Defined Function witch import phase transition model and the additional inertial forces to 3D simulate natural circulation system with water;natural circulation's result and Volume of Fluid model were used to simulate the narrow rectangular channel in natural circulation and forced subcooled flow boiling.The natural loop simulation of the whole loop can provide variation of mass flow rate of different rolling condition,through compiled UDF to obtain driving force of natural circulation and pressure drop of heating section,the effects of different rolling periods and amplitudes on the mass flow rate,total driving force,pressure drop and Nu number of the narrow rectangular were analyzed.The results indicated that the import of the rolling motion would make the parameters change periodicity,the change period was equal to the rolling period,the larger rolling amplitude and frequency,the greater fluctuation range of parameter.This paper used Tecplot soft to processes the result of simulation that of forced flow in narrow channel under rolling condition,this article gain the bubble sliding velocity.To obtain bubble's diameter,Matlab soft was used to processes the picture of simulation's result.The influent of different maximum rolling angle and period on the bubble characteristics were analyzed.The result show that bubbles' sliding velocity and diameter changed periodicity,the change period was equal to the rolling period.Because the tangential inertial force,centripetal inertia force and inertia force and Coriolis force were relatively small that compared with gravity force,The change of the component of gravity in the direction of flow and vertical flow was the main reason for the change of bubble sliding velocity.Through the qualitative analysis of the bubble force,it is concluded that bubble's diameter was proportional to its sliding velocity.We obtained the characteristic of bubble nucleation and sliding velocity from the result of simulation that of natural circulation flow narrow channel under rolling condition.The result showed that the boiling phenomenon changed periodicity.The bubble nucleation characteristic of natural circulation flow was different from forced flow.when backflow occurred,The fluid flows back into the narrow rectangular channel and was secondary heated,and channel generated bubble.The smaller rolling period and lager amplitude,the longer time of generated bubble.In terms of bubble force,the drag force of the bubble was greatly changed,and the drag force became the main reason for the bubble sliding velocity.