Study On Thermodynamic Analysis And Multi-Objective Optimization Of Printed Circuit Heat Exchangers

As for supercritical CO₂ Brayton Cycle（SCO₂-BC）,which has good application prospect in high energy nuclear power plant,regenerator makes an important influence on its system performance,in additional,supercritical CO₂（SCO₂）properties are dramatically affected by temperature and pressure.Due to Printed Circuit Heat Exchangers（PCHE）have some advantages such as resists high temperature and high pressure,compact structure,it is a good choice for regenerator in the SCO₂-BC.It is of great significance to explore the flow and heat transfer performance of PCHE with different structures under the condition of variable physical properties,and to carry out multi-objective optimization on the structure,so as to reduce the irreversible loss,increase the comprehensive performance of PCHE and improve the overall performance of SCO₂-BC.Based on theoretical derivation and numerical simulations,this paper compared and analyzed comprehensive heat transfer performance and entransy dissipation number of PCHE with various cross section shapes,and optimized the Zigzag channel structure with semicircular cross section.The main work and conclusions are as follows:（1）As for the universal countercurrent flow heat exchanger model,on the basis of entransy theory and calculus of variations,the relationship between the temperature distribution of hot and cold fluid at the lowest entransy dissipation,minimum entransy dissipation number,entransy transfer efficiency and the total number of heat transfer units,as wall as the relationship between the minimum entransy dissipation,minimum thermal resistance and effectiveness are derived.The results show that when entransy dissipation is minimum,the temperature difference of cold flow fluid is constant,and the temperature difference decreases gradually with the increase of total heat transfer units;heat transfer performance and irreversible loss should be considered in the selection of total heat transfer units;entransy theory is more suitable for the optimization of heat transfer process than entropy theory.（2）At the same equivalent diameter of 0.92 mm,the flow and heat transfer performance of PCHE with three cross section shapes（semicircular,circular and square）are compared,and the comprehensive performance factor and entransy dissipation number are used as comprehensive evaluation indexes to make comprehensive comparison.It can be found that under the same operating parameters,the circular section channel has better flow performance and heat transfer performance,the square section channel has the worst flow performance,and the semicircular section channel has the worst heat transfer performance,but the semicircular section channel temperature field is relatively uniform;the heat transfer quantity of the semicircular cross section channel is the largest,which is 29.12%and 3.12%larger than that of the circular cross section and square cross section respectively;the entransy dissipation number of semicircular section is the smallest,which is 9.33%、13.92%smaller than that with circular cross section and square cross section respectively;the comprehensive performance factor of circular cross section channel is the largest,the comprehensive performance factor of hot fluid is 12.35%and 30.82%larger than that of semicircular cross section and square cross section respectively;the comprehensive performance factor of cold fluid is 7.88%and 21.67%larger than that of semicircular cross section and square cross section respectively.（3）Aiming at Zigzag channel PCHE with semicircular cross section,multi-objective optimization was carried out with hot fluid radius,cold fluid radius and Zigzag channel angle as design variables and comprehensive performance factor and entransy dissipation number as optimization objectives.On the premise of ensuring the comprehensive performance and the irreversible loss are optimal,the structure with hot channel radius of 0.75mm,cold channel radius of 0.84mm and Zigzag channel angle of 24.24° is optimal when the heat transfer is large.Under this structure,the comprehensive performance factor of cold fluid and hot fluid increases by 10.34%and 12.35%respectively,the entransy dissipation number increases by 17.79%,the overall performance of PCHE is improved.