Analysis On Flow And Descaling Performance Of Laminar Pulsating Flow In Heat Exchanger

The flow channels of plate and circular pipes are widely applied in compact heat exchangers,such as plate heat exchangers and shell-and-tube heat exchangers because of their large heat exchange area,compact structure and easy design.However,there are different degrees of fouling in the flow channel of the heat exchanger.When the laminar flow in the plate and round pipe is pulsating,it can effectively change the flow characteristics of the flow field,which is beneficial to the descaling.Therefore,it is theoretical and practical significance to analysis the flow characteristics of pulsating flow in plate and circular pipes in heat exchangers,and to explore the effect of different pulsating parameters on the flow characteristics and descaling performance of pulsating flow.Numerical simulation and experimental research are used to study the flow characteristics and descaling performance of the pulsating flow in a plat and circular tube in this paper.The CFD is used to simulate the flow characteristics of pulsating flow in the channel.The velocity and velocity gradient of the flow field under different pulsating frequency and amplitude are compared,and the wall friction coefficient is calculated.The results show that the "speed loop" effect appears in the near wall surface of the plate and the circular tube under the high pulsation frequency.The peak value of wall friction coefficient decreases with the increase of pulsation frequency.Under the same pulsating amplitude,the wall friction coefficient of the plate decreased to 60%,and the wall friction coefficient of the circular pipes decreased to 56.5%.The wall friction coefficient increases with the increase of the pulsation amplitude.Under the same pulsating frequency,the wall friction coefficient of the plate improved up to 100%,and the wall friction coefficient of the circular pipes improved up to 71.4%.The descaling properties of pulsating flow was illustrated with the wall shear stress,the greater the wall shear stress,the greater the fouling denudation rate,and was more beneficial to the descaling.It is found that,the wall shear stress decreased as the pulsationfrequency increased,and increased with the increase of the pulsation amplitude.The best perforated descaling of pulsation parameters had been obtained during the same output power at a constant flow rate in plate and circular pipes.Finally,a large number of experimental studies had been researched with the particle image velocimetry.The periodic evolution of the vortex can be divided into formation,growth,expansion and disappearance under the condition of pulsating flow in the channel of a plate and circular tube is obtained.The velocity distribution under different fluctuating frequency and amplitude is analyzed and compared in plate and circular pipes,which is consistent with the numerical simulation results.It is found that the velocity distribution of the cross section appears to "speed loop" effect,which is consistent with the numerical simulation,the correctness of the conclusion is verified.