Distribution Characteristics Of Medium Flow In Horizontal Parallel Pipes

Parallel piping is widely used in boilers,chemical production equipment,natural gas liquefaction devices,automotive air conditioning and other heat exchangers.In production,the uneven distribution of medium flow between branches of parallel piping is the main reason for the overall efficiency and safety decrease of heat exchanger.In this paper,the flow distribution characteristics of single phase medium(air)and gas-liquid two phase medium(air and water)in parallel four branches are studied by the method of experimental research and numerical simulation,and the pressure field,velocity field and other related data are analyzed.The relationship between uneven fluid distribution and working conditions and structural factors is discussed.Under the working condition of single phase medium,the following conclusions are obtained by numerical simulation and experimental study on the parallel branch system of the direct angle T three pass structure and the curved pipe transition T three pass structure with four inner diameters 15mm and long 300mm respectively on the head of long 1200mm and inner diameter.When the direct T structure is used in parallel,the flow distribution law between the branches is increased from first branches near the entrance to the fourth branch pipes,which is the same as the distribution trend of the static pressure distribution in order.When the T type structure is in parallel,the flow of the medium from the first branch to the fourth branch pipes is raised first and then decreased.The static pressure distribution in the head is also the same as that in the branch outlet.The influence of different working condition factors and structural factors on the flow distribution characteristics is analyzed by numerical simulation.It is found that under the case of direct T type structure,the inhomogeneous degree STD increases gradually with the increase of the entrance apparent velocity;when the curved T type structure is used,the influence of the inhomogeneous degree on the inhomogeneous degree between the parallel pipes is very small.The increase of the pipe diameter ratio will make the flow distribution more uniform and reduce the inhomogeneity of the flow distribution effectively.In the geometric scale of the research object,the effect of the change of the pipe spacing on the drag force is not obvious,and the effect on the overall inhomogeneity in the parallel pipe is very small;the branch pipe is connected with the head of the pipe.Compared with the right angle T connection,the T connection with the elbow transition can significantly improve the flow distribution uniformity between the branches,and the connection mode between the first branch pipe and the fourth branch pipe and the connection between the pipe and the pipe is the best.The characteristics of gas-liquid two phase distribution in the outlet of four branch pipes with horizontal parallel pipe are obtained by means of visual experimental research,and the transformation law of the internal flow pattern is determined.The effects of gas-liquid two phase working conditions on the flow distribution characteristics of the four branch pipes in parallel piping are analyzed.The results of the flow distribution are tested before and after the optimization of the structure.In the study area,the gas phase heterogeneity degree STD is about 5%,and the liquid phase heterogeneity STD is above 35%under the annular flow condition.The uneven distribution of liquid phase is the main cause of uneven distribution of annular flow in parallel piping.It is found that the gas flow discharge flow in the four branch pipe of the straight T parallel pipe is shown as the first branch pipes near the direction of flow and the fourth branch pipes far away from the flow direction,which are far lower than the middle two branch pipes.The liquid distribution law is contrary to the gas distribution law,which shows that the liquid flow rate of the middle two pipes is far higher than that of the two branch pipes.Quantity.Increasing the apparent velocity of the imported gas phase can effectively reduce the inhomogeneity of liquid phase,and increase the apparent velocity of the liquid phase to make the liquid phase inhomogeneity increase obviously,and the influence of the working condition factors on the distribution of the inhomogeneity of the gas phase between the branches is very small.Therefore,increasing the apparent velocity of imported gas in a reasonable range is an effective way to reduce the overall non-uniformity.After the connection between the bent T parallel structure and the branch pipe,the inhomogeneity of the liquid phase between the branches is reduced by more than 40%,and the inhomogeneity of the gas phase is increased,but the variation of the gas phase inhomogeneity is smaller,and the inhomogeneity of the STD remains below 5%.