Visual Detection And Analysis Of Bubbles In Cold Flow Passage Of Plate Heat Exchanger

The plate heat exchanger is an efficient and compact heat exchange device with a wide range of applications.The plate heat exchanger usually use the compound of air and water as a cold flow medium.Its heat transfer efficiency is directly related to the behavior of air bubbles in cold flow.In order to find out the bubble behavior in complex flow,this study uses a mixture of air and water as the medium,and sets the fluid inlet and outlet at different positions.Experimental and theoretical studies on two-phase flow in the cold runner of plate heat exchanger by visualization technology and numerical simulation technology.(1)This paper analyzes the influence of dimple structure on gas/liquid phase of plate heat exchanger based on numerical simulation technology.Through the simulation calculation of the three-dimensional calculation domain of the dimple-type plate heat exchanger,the effects of the dimple structure on the gas/liquid phase flow in the cold runner during vertical installation and lateral installation are studied.The gas-liquid phase distribution and streamline type are discussed respectively.The trajectory and velocity vector distribution are introduced,and the unit Reynolds number is introduced to analyze the changes of these parameters in depth.Then the velocity distribution and pressure distribution in the calculation domain are analyzed to further understand the motion law of the liquid phase in the flow channel.The study found that the presence of dimples hinders and blocks the mainstream.The different inclination angles of the dimples have a direct relationship between the flow rate and the pressure difference.The closer the fluid is to the top of the dimple,the faster the flow rate and the smaller the pressure difference.(2)Flow visualization is a direct and effective way to study gas-liquid two-phase flow.This paper designs and builds a flow field visualization experiment system,including visual flow channel,visualized experimental bench and high-speed camera system,which can clarify the two-phase flow characteristics in the plate heat exchanger more clearly and intuitively.At the same time,a set of analysis schemes was designed for the visualization experiment.It includes the tracking of the trajectory of gas-liquid two-phase flow,the classification and statistics of bubble size,the distribution of free bubbles in the vertical direction of the flow channel,and the relationship between bubble behavior and liquid flow rate and inlet and outlet position.(3)The flow distribution characteristics of gas-liquid two-phase flow in the plate heat exchanger are affected by the installation position and the inlet and outlet position.In this paper,we use the visual experiment system to collect and study the behavior of flow in these working condition in which the plate heat exchanger was installed in a vertical way and horizon way,while set the inlet and outlet as up and down,up and up,down and up,down and down.The study found that under six conditions,when fluid flows out of the lower outlet,if the fluid enters from the upper inlet,an air zone will appear,and if the fluid enters from the lower inlet,a bubble zone will be formed.However,when fluid exits the outlet of the passage,no matter where the fluid enters,there is no air zone and no bubble zone,but the buoyancy of the bubble has a significant effect on the bubble distribution.