Thermo-hydraulic analyses of the absorber tube with molten salt-based nanofluid and porous medium inserts

Abstract

In this work, a new combination technique of molten salt-based nanofluid and porous medium inserts is presented for the thermo-hydraulic performance improvement of the absorber tube. The effects of porous medium configurations, porosities, nanoparticle concentrations, materials, and Reynolds numbers are discussed in terms of the flow and heat transfer characteristics as well as the performance evaluation criterion (PEC). According to the results, the enhanced tube inserted with wall attached type porous medium can achieve much better heat transfer performance. Molten salt-based nanofluid shows considerable heat transfer performance inside the tube with a porous medium, compared with pure molten salt flow inside a smooth tube. Among the four kinds of materials, the best one for the porous medium is copper. The combination for the best thermo-hydraulic performance is proposed with the 0.125% (mass fraction) molten salt-based nanofluid and the absorber tube with copper metal foam (porosity of 0.9005), after systematically comparing the simulation results. This combination accomplishes the best heat transfer enhancement with 12.44 times of Nusselt number higher than pure molten salt inside the smooth tube at the Reynolds number of 1×104. The peak PEC value of 5.98 is reached at the Reynolds number of 6×104. Finally, the improvement of the thermo-hydraulic performance of this combination technique was proved through physical discussions based on the temperature and velocity profiles.