Study On Flow Characteristics And Resistance Correlation In Internally Threaded Pipes

Under the background of carbon neutrality and peak carbon dioxide emissions goal,more and more countries and regions begin to pay attention to environmental protection and sustainable development,and energy conservation has become one of the important directions for the development of various industries.In the field of heat transfer,internally threaded tube has become an important heat transfer device because of its wide application and good heat transfer effect.Studying the flow characteristics and resistance characteristics of internally threaded pipes is helpful to optimize the design of internally threaded pipes and improve their comprehensive performance,thus promoting the development of energy conservation and emission reduction.In this paper,theoretical analysis and numerical simulation are used to study the characteristics of flow and pressure drop in internally threaded tubes at high Reynolds number in turbulence,and the calculation correlation of resistance coefficient is developed according to the simulation data.The main conclusions are as follows:(1)With the increase of Reynolds number,the pressure drop per meter shows a certain exponential growth trend,and the Reynolds number has a greater influence on the pressure drop at higher spiral angle.Reynolds number ranges from 20000 to 60000,and pressure drop multiple ranges from 7.22 to 7.79.The increase of rib number has little effect on the pressure drop per meter,and the pressure drop increases slightly with the increase of rib number at high Reynolds number.With the change of rib height,the pressure drop per meter increases linearly,and the greater Reynolds number,the higher the linear growth degree;At low helix angle,the increase of helix angle has little effect on the pressure drop per meter.However,at higher helix angle,the pressure drop per meter tends to increase,and the increase increases with the increase of Reynolds number.(2)With the increase of Reynolds number,the drag coefficient shows a downward trend,and the decline rate decreases with the increase of Reynolds number.With the increase of the number of ribs,the resistance coefficient further increases.When the number of ribs is between16 and 20,the growth rate of the resistance coefficient is the highest,and when the number of ribs reaches more than 20,the growth rate of the resistance coefficient gradually tends to be flat.The drag coefficient increases linearly with the increase of rib height,and under the same conditions,changing the spiral angle has little effect on the drag coefficient changing with rib height.With the increase of helix angle,the drag coefficient shows a significant increase trend,and the higher the helix angle,the greater the growth rate of drag coefficient.(3)Based on Webb model and Ravigururajan model,three resistance correlations for turbulent flow in internally threaded pipes are established,and the resistance coefficients under different flow and structural parameters are accurately predicted.Firstly,two resistance correlations are proposed based on the framework of Webb model,and then a new resistance correlation model is proposed by combining two theoretical models.The average relative prediction errors of the three models are reduced to about 11.23%,4.66% and 4.42%.The model is coupled with Nusselt number correlation,and the accurate prediction of heat transfer properties in the tube is realized.Compared with the prediction errors of Webb model and Ravigururajan model of about 8%,the prediction errors of Nusselt number based on the proposed resistance correlation are 2.78%,1.16% and 1.08% respectively,which improves the prediction accuracy of heat transfer performance.