Numerical study of circumferential temperature difference reduction at the absorber tube of parabolic trough direct steam generation collector by inserting a twisted tape in superheated region

摘要

The present numerical simulation investigates the influence of a twisted tape inserts on circumferential temperature difference reduction and heat transfer enhancement in the absorber tube of parabolic trough collector. The effect of twisted tape geometrical parameters and the Reynolds number on the circumferential temperature difference, Nusselt number, friction factor and thermal performance factor is analyzed. Superheated steam is used as the heat transfer fluid. In present investigation, the Reynolds number is considered in the range of 104≤ Re?≤?9.79×105; clearance ratio and twist ratio are varied in the range of 0–0.5 and 2.5–10, respectively. For the considered range of these parameters, Nusselt number increases 1.0–1.7 times and friction factor increases in the range of 1.8–4.1 times. Therefore, the maximum thermal performance factor under identical pumping power is in the range of 0.85–1.1.Twisted tape with minimum twist ratio and zero clearance provides higher Nusselt number and friction factor due to strong generated swirl flow and increased fluid hydraulic path length. According to the numerical results, the maximum circumferential temperature difference decreases about 10–45% which will significantly reduce thermal stresses in the absorber tube.