Numerical Study On Flow Heat Transfer And Thermal Stress Of Printed Circuit Heat Exchanger

Printed Circuit Heat Exchanger(PCHE)has broad development potential in the nuclear industry,chemical technology,fuel processing,power energy,refrigeration and other industrial fields due to its compact structure,high-efficiency heat transfer and high temperature and high pressure resistance.Because of the manufacturability and durability of the straight channel PCHE and zigzag-channel PCHE,this paper takes the straight channel PCHE and zigzag-channel PCHE as the research object,and carries out the numerical simulation research under high temperature and high pressure conditions.Firstly,the research focuses on the effects of fluid thermal properties on the flow and heat transfer in the straight channel PCHE.It is concluded that the fluid thermal properties should be treated with variable properties under high temperature and high pressure conditions.And the numerical simulation of single-phase flow and heat transfer for zigzag-channel PCHE,the research mainly includes studying the flow and heat transfer characteristics of the zigzag-channel PCHE in different angles(0°,10°,15°,20°,25°,30°)and different Reynolds numbers(200?1000).The numerical simulation finds that the existence of the periodic corner of the zigzag-channel makes the fluid create boundary layer separation and forms a vortex much more easily as it flows through the corner.The larger the angle is,the easier it is to create a vortex within the channel.And the local fanning friction factor,local convective heat transfer coefficient,local wall heat flux in the zigzag-channel present fluctuations.According to the comprehensive evaluation factor(Nu/Nu₀)/(f/f₀)^1/3,it is found that when the angle of the zigzag-channel is 15°,the best heat transfer performance is obtained.Then the numerical simulation analyzes the thermal stress of the Zigzag-channel with an angle of 15°.On the basis of it,the numerical simulation optimizes the structure of the traditional zigzag PCHE channel by adding round corners at the turning point.Then,compared the characteristics of flow and heat transfer and thermal stress between the optimized zigzag-channel and the traditional zigzag-channel.The results show that there is a larger thermal stress at the corner of the zigzag-channel.Added the rounded structure can effectively reduce the thermal stress at the corner.When the rounded radius is 5 mm,the flow heat transfer and thermal stress performance are optimal.Finally,the numerical simulation of flow boiling is carried out by using the zigzag-channel with an angle is 15°to study the effects of system pressure,heat flux and inlet velocity on bubble generation,heat transfer characteristics and pressure drop characteristics in the zigzag-channel.Bubbles are first formed in the contact area between the plane and the semi-circular surface in the zigzag-channel.With the increase of system pressure and the acceleration of inlet flow rate,the bubble formation rate in zigzag-channel decreases.Therefore,at the same time,the single-phase liquid region in the channel becomes larger,the proportion of single-phase heat transfer increases,and the surface heat transfer coefficient decreases.With the increase of heat flux,the convective heat transfer coefficient and pressure increases.