Study On The Influence Of Inner Ring Plug On The Flow Resistance Characteristics Of Tube With Sudden Expansion And Sudden Contraction

Circulating water pipe network is widely used in cooling,heating and industrial engineering fields,such as central air conditioning in large buildings and chemical engineering.Sudden-expansion and sudden-contraction are the most common pipe fittings in the pipe network.Therefore,the research on how to reduce the local energy loss of the sudden-expansion and sudden-contraction pipes is of great significance to the theory of drag reduction and the practical engineering application.In this paper,ring plugs of different inner diameters are built in different positions in the sudden expansion pipeline of D10-D20 and D10-D50 and the thick pipe near sudden expansion and sudden contraction pipeline of D20-D10 and D50-D10,and the water solution of 160 ppm and 320 ppm drag reducer is used as the fluid respectively.The variation of local energy loss with the geometric size and placement of the plug was experimented.Firstly,according to the basic principle of fluid dynamics,the pipeline flow system with sudden expansion and contraction with built-in plug is built.The static pressure measuring points were arranged after the positions of the upstream and downstream fully developed sections were determined by experiments to test and analyze the change characteristics of the local energy loss when the clean water and surfactant drag reduction aqueous solution flow flowed through the plugs placed at different locations and with different geometric sizes under different Reynolds numbers.The experimental results of sudden expansion pipe flow show that: In clear water,the local energy loss coefficient firstly decreases and then increases with the increase of the distance between the plunger and the sudden expansion interface and the inner diameter of the plunger.With the increase of the inner diameter of the plunger,the optimal drag reduction position of the plunger moves backward.The maximum reduction rates of the local energy loss of D10-D20 and D10-D50 sudden expansion pipes are 27% and 26%,and the corresponding inner diameters of the plunger are 12.5mm and 18 mm,respectively.In the 160 ppm aqueous solution of drag reducer,the local energy loss coefficient of D10-D20 sudden expansion pipe flow has the same trend with the change of the inner diameter of the ring plug and the distance between the ring plug and the sudden expansion interface.The local energy loss coefficient of D10-D50 sudden expansion pipe flow increases with the increase of the inner diameter of the ring plug,and the change trend with the change of the position of the ring plug is the same as that of clean water.The local energy loss of D10-D20 and D10-D50 sudden expansion pipe flow can be reduced by 23% and 28% at the maximum,and the corresponding inner diameters of the ring plug are 12.5mm and 18 mm,respectively.In 320 ppm water solution,the local energy loss coefficient of D10-D20 sudden expansion pipe is similar to that of clean water with the change of distance from sudden expansion interface and the inner diameter of ring plug.The local energy loss coefficients of D10-D50 sudden expansion pipe flow are the same as clean water with the change of the plug position,but monotonically increase with the increase of the inner diameter.The maximum local energy loss of D10-D20 and D10-D50 tube flow can be reduced by 26% and 32%,and the corresponding inner diameters of the ring plugs are 12.5mm and 18 mm respectively.The experimental results of the sudden shrinkage flow show that: in clear water,the sudden shrinkage flow changes with the inner diameter and location of the ring plug the same as the sudden expansion flow,but for D20-D10 and D50-D10 the local energy loss can be reduced by 54% and 35% at the maximum,and the corresponding inner diameters of the ring plug are 12.5mm and 18 mm respectively.When the fluid medium is 160 ppm of drag reducer,the local energy loss coefficient of D20-D10 sudden shrinkage pipe flow decreases first and then increases with the increase of the inner diameter of the ring plug.The local energy loss coefficient increases with the increase of the distance between the ring plug and the sudden shrinkage interface.The local energy loss coefficients of D50-D10 burst shrinkable pipes increase with the increase of the inner diameter and the distance between the plug and the burst shrinkable interface.For D20-D10 and D50-D10 burst shrinkable pipes,the local energy loss can be reduced by 70% and37%,and the corresponding inner diameter of the plug is 12.5mm and 18 mm,respectively.When the fluid medium is 320 ppm of drag reducer aqueous solution,the local energy loss coefficient of the sudden shrinkage pipe increases with the increase of the inner diameter of the ring plug and the distance between the ring plug and the sudden expansion interface.For D20-D10 and D50-D10 sudden shrinkage pipe,the local energy loss can be reduced by 26% and 32% at most,and the corresponding inner diameters of the ring plug are 12.5mm and 18 mm,respectively.This research was supported by the National Natural Science Foundation of China.The conclusions of this research will provide scientific reference for improving the overall drag reduction effect of circulating surfactant in water solution flow.