Based on constructal theory and entransy theory,a generalized constructal optimization of a solidification heat transfer process of slab continuous casting for a specified total water flow rate in the secondary cooling zone was carried out.A complex function was taken as the optimization objective to perform the casting.The complex function was composed of the functions of the entransy dissipation and surface temperature gradient of the slab.The optimal water distribution at the sections of the secondary cooling zone were obtained.The effects of the total water flow rate in the secondary cooling zone,casting speed,superheat and water distribution on the generalized constructal optimizations of the secondary cooling process were analyzed.The results show that on comparing the optimization results obtained based on the optimal water distributions of the 8 sections in the secondary cooling zone with those based on the initial ones,the complex function and the functions of the entransy dissipation and surface temperature gradient after optimization decreased by 43.25%,5.90%and 80.60%,respectively.The quality and energy storage of the slab had obviously improved in this case.The complex function,composed of the functions of the entransy dissipation and surface temperature gradient of the slab,was a compromise between the internal and surface temperature gradients of the slab.Essentially,it is also the compromise between energy storage and quality of the slab.The"generalized constructal optimization"based on the minimum complex function can provide an optimal alternative scheme from the point of view of improving energy storage and quality for the parameter design and dynamic operation of the solidification heat transfer process of slab continuous casting.
Based on the entransy dissipation extremum principle for thermal insulation process,the constructal optimizations for a plane insulation layer of the steel rolling reheating furnace wall with convective and radiative boundary conditions are carried out by taking the minimization of entransy dissipation rate as optimization objective.The optimal construct of the plane insulation layer is obtained.The results show that for the convective heat transfer boundary condition,the optimal constructs of the insulation layer obtained based on the minimizations of the entransy dissipation rate and heat loss rate are obviously different.Comparing the optimal construct obtained based on the minimization of the entransy dissipation rate with that based on the minimization of the heat loss rate,the entransy dissipation rate is reduced by 5.98%,which makes the global thermal insulation performance of the insulation layer improve.For the combined convective and radiative heat transfer boundary condition,compared the insulation layer having an increasing thickness with that having constant thickness and a decreasing thickness,the entransy dissipation rates are reduced by 16.59%and39.72%,respectively,and the global thermal insulation performance of the insulation layer is greatly improved.There exits an optimal constant coefficient a2;optwhich leads to the minimum dimensionless entransy dissipation rate of the insulation layer.The difference between the optimal constant coefficients a2;optobtained based on the minimizations of the entransy dissipation rate and the maximum temperature gradient of the insulation layer is small.This makes the corresponding thermal stress obtained based on the minimum dimensionless entransy dissipation rate also be small,and the global thermal insulation performance and thermal safety of the insulation layer are improved simultaneously.The results obtained can provide some guidelines for the optimal designs of the insulation layers.
