Performance evaluation of serpentine tube coupled with modified twisted tapes utilized as heat extraction coil in solar ponds

Abstract

The thermal energy collected and stored by solar ponds is usually extracted by using some heat exchangers, where curved tubes form their core. The present study aims to appraise the performance of a serpentine tube under varied mass flow rates and inlet temperatures of the working fluid. Three different types of twisted tapes nominated as uniform twist pitches (U), low to high twist pitches (LH), and high to low twist pitches (HL) are employed to enhance the heat extraction rate. This article is the first report addressing the application of non-uniform twisted tapes as turbulators in a serpentine tube. In this regard, a solar pond simulator containing salt water is designed and fabricated. Numerical simulations are also carried out to display the transport phenomena inside the models. The numerical results are compared with the experimental data, and a close agreement is found. From the thermal point of view, the sequence of twisted tapes is LH > HL > U, while it follows the order of U > LH > HL according to the frictional loss. The findings demonstrate that depending on operating conditions, the heat extracted by the modified cases is 4 to 70% more than the base model. It is also found that employing non-uniform twisted tapes results in lower flow resistance compared to the uniform case. The pressure drop augmentations produced by U, LH, and HL TTs are 26.5%, 17.5%, and 10.4%. Further, the overall performance index is higher than unity for all the enhanced cases. The best case is the twisted tape having low to high twist pitches (LH) which has an average performance index from 2.03 to 2.71.