Experimental Study On Pulsating Flow Intensifying Heat Transfer Performance Of Plate Heat Exchanger

Pulsating flow can effectively enhance convective heat and mass transfer.It is widely used in engineering and biological systems.In the interval of laminar flow and transitional flow,it can enhance the mixing degree of fluids,thin the boundary layer,and solve the uneven distribution of fluids.It has good application prospects for further improving the heat exchange performance of heat exchangers and reducing heat loss.An experimental bench for the pulsating flow enhanced heat exchange experiment of the plate heat exchanger was built to test the performance of the herringbone plate heat exchanger,and the heat exchange working medium was water.Experiments are carried out under steady-state conditions,the Reynolds number is controlled by controlling the mass flow of water,and the heat transfer performance of the plate heat exchanger under different Reynolds numbers is studied;the experiment is carried out under pulsation,by changing the different pulsations of the pulsating flow of the main flow path Parameter variables(Reynolds number,pulsating frequency,duty cycle,pulsating pressure waveform)are used to study the heat transfer performance of the plate heat exchanger.Experiments on heat transfer characteristics show that pulsating flow will always enhance heat transfer,but the effect of enhancing heat transfer is more obvious in the transition flow interval;experiments on fluid flow characteristics show that as the Reynolds number increases,the flow resistance of pulsating flow increases.Slowly,and as the pulsating frequency increases,the flow resistance of the pulsating flow increases greatly.The study found that under the same Reynolds number,adding a pulsating flow to the steady-state flow will enhance heat transfer,and as the Reynolds number increases,the total heat transfer coefficient of the plate heat exchanger increases,indicating that with the Reynolds number As the number increases,the heat exchange effect gets better and better.The field synergy theory is introduced.The field synergy number decreases with the increase of the Reynolds number.The increase of the Reynolds number will make the synergy between the temperature field and the velocity field worse,and the increase of the Reynolds number will increase the heat transfer and energy consumption.Therefore,the method of increasing the field synergy number is much better than the method of increasing the Reynolds number.In the case of equal Reynolds numbers,in the laminar flow section,the total heat transfer coefficient and heat transfer enhancement factor of the plate heat exchanger both decrease with the increase of the pulsation frequency,and the heat transfer enhancement factor is up to 7.68;in the transition flow section,The total heat transfer coefficient and heat transfer enhancement factor of the plate heat exchanger first decrease and then increase with the increase of the pulsation frequency.The heat transfer enhancement effect in the transition flow section is significantly higher than that in the laminar flow section,and the heat transfer enhancement factor can reach the highest 15.11;In the turbulent flow section,the total heat transfer coefficient and heat transfer enhancement factor of the plate heat exchanger first decrease and then increase with the pulsation frequency,reach the extreme value at the frequency of 45 Hz,and then decrease again.It can be seen that the frequency is 45 Hz The enhanced heat transfer effect is more obvious in the turbulent flow zone.At a frequency of 10-30 Hz,the higher the duty cycle,the higher the total heat transfer coefficient of the plate heat exchanger.As the pulsating frequency increases,the percentage of the optimal duty cycle gradually decreases,and the optimal duty cycle changes from low frequency D=100% becomes d=60% at 50 Hz.The experiment produces a variety of pressure waveforms,which are attributed to two types: sinusoidal and sawtooth.The pulsating waveform has a better heat transfer effect in the sawtooth shape.Within the scope of this experiment,there is the best heat transfer point.In the transition flow interval,when Re=336 and f=33Hz,the total heat transfer coefficient and heat transfer enhancement factor of the plate heat exchanger both reach the highest value of15.51,the heat transfer effect Best;in the turbulent interval,when Re=373 and f=45Hz,the heat transfer enhancement factor is the largest,which is 13.1,that is,the heat transfer efficiency is the highest and the heat transfer effect is the best.