Experimental Research And Numerical Analysis Of Heat Transfer Enhancement In Pulsating Plate Heat Exchanger

Plate heat exchangers are widely used in electric power,chemical,and other industries,and play an important position in industrial production.The plate heat exchanger has many advantages such as small volume,small footprint,large logarithmic average temperature difference,easy disassembly,and strong adaptability.In order to improve the heat transfer characteristics of the plate heat exchanger,A lot of research has been carried out on heat exchangers by a large number of domestic and foreign scholars and technicians.The early stage is mainly focused on passively enhanced heat exchange,such as optimizing the inclination,wave height,wave distance and flow channel germetry of corrugated plates.This article starts with the technology of active enhanced heat exchange,applying pulsation to the fluid medium entering the plate heat exchanger,the effects of pulsation frequency,pulsation amplitude,and mass flow on the heat transfer characteristics and flow characteristics of plate heat exchangers are discussed through experiments and numerical simulation.In order to study the effect of pulsating flow on the plate heat exchanger,the pulsation experiment bench of the plate heat exchanger was first set up,heat exchange medium uses the most common water.The experiment is divided into two parts.First,the experiment is performed under a steady state.In order to study the heat transfer characteristics of plate heat exchangers under different mass flow rates by controlling the mass flow of water.Second,the experiment is conduct heat exchange experiments of plate heat exchangers under pulsating conditions.A pulsation generating device is installed in the heat exchange system,study on the heat transfer characteristics and flow characteristics of plate heat exchangers by changing the pulsation frequency and mass flow.The experimental results show that in the steady state,the heat transfer coefficient and pressure drop of the inlet and outlet increase with the increase of mass flow,and the heat transfer factor and Fanning friction factor increase with the decreasing of mass flow.Under pulsating conditions,when the pulsating frequency remains constant,the average heat transfer coefficient and pressure drop of the plate heat exchanger increase with the increase of mass flow rate,and the heat transfer factor and Fanning friction factor all increase with the decrease of the mass;When the mass flow rate remains constant,the average heat transfer coefficient and heat transfer factor of the plate heat exchanger first increase and then decrease with the increase of the pulsation frequency,that is,there is an optimal pulsation frequency of 1.8 Hz.In a pulsation cycle,multiple pressure wave peaks appear in the internal flow channel of the plate heat exchanger.When the pulsation frequency is large and the mass flow rate is also large,the number of pressure wave peaks in the cycle will decrease.The internal pressure decays regularly.Numerical simulation of heat transfer of plate heat exchanger under pulsating flow state,and the model of plate heat exchanger used in the experiment is established in a one-to-one ratio.In order to fit the experiment,the boundary is set according to the inlet,outlet and heat exchange conditions during the experiment.In order to study the heat transfer characteristics and flow characteristics of the plate heat exchanger,by changer the pulsation frequency and mass flow rate In the simulation.The conclusions obtained are consistent with the experimental conclusions,that is,the optimal pulsation frequency of 1.8 Hz exists.the plate heat exchanger has the best heat transfer characteristics.The outlet temperature of the cold fluid of the plate heat exchanger changes periodically,and the pressure gradient of the internal flow channel also changes periodically.At the position of the contact,the fluid vortex street changes periodically with the pulsation cycle,Under the condition of pulsation frequency is 1.8Hz,the pulsation amplitude and mass flow rate were changed to study the effect of pulsation amplitude on the heat transfer and flow of the plate heat exchanger.The results show that with the increase of pulsation amplitude,the average heat transfer coefficient also increases.Finally,the field synergy principle is used to study the degree of synergy between the temperature field and the velocity field of the internal flow channels of the plate heat exchanger.The results show that the field synergy number of the plate heat exchanger under pulsating conditions first rises and then decreases with the increase of the pulsation frequency,that is,there is an optimal field synergy number.The field synergy number decrease with the mass flow increase,and increase with the amplitude increases.