Numerical Simulation Research On Enhanced Boiling Heat Transfer Of Rough Surface Tube

Shell-side boiling tube and shell heat exchanger is widely used in petroleum,chemical,nuclear power,aviation and other industries.It is important to improve the heat transfer efficiency of heat exchange tube to improve the heat transfer performance of heat exchanger.At present,the sintered and sprayed porous surface heat exchange tubes have a high boiling heat transfer coefficient,,but its processing technology is complicated and the manufacturing cost is relatively high,and the mechanism of boiling heat transfer is not well understood.Therefore,in this paper,two kinds of rough surfacesurface porous heat exchange tubes are proposed.By using numerical simulation method,the pool boiling heat transfer performance of smooth tube,thin threaded tube and foam metal tube is compared,and analyzes the pools of fine threaded tubes and foam metal tubes with different structural parameters.The effect of different structural parameters on the pool boiling heat transfer effect of threaded tube and foam metal tube is further analyzed.Based on the gas-liquid counter current model,the heat transfer mechanisms of two rough surfacesurface porous heat exchange tubes are discussed.The main research and content are as follows:(1)The numerical simulation method is used to analyze the pool boiling heat transfer process of smooth tube,screw tube and foam metal tube under different heat flux conditions.The results show that the gas nucleation rate on the surface of foam metal and screw tube are higher than the surface of the smooth tube,and the gas nucleation rate on the surface of the foam metal is the fastest.And under the same working conditions,the boiling heat transfer coefficients of the foam metal tube and the threaded tube are larger than that of the smooth tube.The maximum boiling heat transfer coefficient of the foam metal tube is 3.4 times that of the smooth tube,and the maximum boiling heat transfer coefficient of the thin threaded tube is 3.19 times that of the smooth tube.(2)Under the condition of heat flux of 20 k W/m~2～140 k W/m~2,the effects of different thread pitch and thread groove depth on the boiling heat transfer performance of the thin threaded tube pool are analyzed.The results show that the pool boiling heat transfer performance increases with the increase of heat flux,under the same heat flux conditions,as the thread pitch of the thin threaded pipe decreases and the thread groove depth increases,the boiling heat transfer coefficient increases.(3)Under the conditions of heat flux of 20 k W/m~2～140 k W/m~2,the effects of different thicknesses and pore densities on the boiling heat transfer performance of the foam metal tube pool are analyzed.The results show that:under low heat flux conditions,with the thickness increases,the boiling heat transfer coefficient of the foam metal tube becomes larger.However,under high heat flux conditions,the enhancement effect of thickness on pool boiling heat transfer performance is weakened;under the same heat flux conditions,the increase in foam metal pore density can enhance heat transfer performance,and the foam metal structure can increase critical heat flux limit.(4)Based on the theoretical model of the gas-liquid counter flow mechanism in the porous layer,the viscous resistance limit and hydrodynamic limit of the two rough surfaceporous surface heat exchange tubes are discussed.It is concluded that the critical heat flux limit of the two types of rough surfaceenhanced heat exchange tubes is mainly determined by the viscous resistance limit,the critical heat flux density limit of the foam metal tube is greater than that of the thin threaded tube,and the heat transfer performance of the heat exchange tubes can be improved by reducing the particle size inside the rough surfaceporous layer or increasing the nucleation site.