Experimental investigation of laminar flow and heat transfer characteristics in square minichannels with twisted tapes

摘要

The flow and heat transfer characteristics of distilled water in a minichannel heat sink (MCHS) fitted with twisted tapes under laminar flow are investigated experimentally in present study. Nine twisted tapes with lengths of L_t = 50 mm, 100 mm and 150 mm, and twist ratios of Y = 3, 4, and 5 are employed as inserts. The results show that average heat transfer coefficient (h_(ave)), pressure drop per unit length (△P_(pul)) and thermal enhancement factor (η) increase with the decrease in twist ratio or/and the increase in twisted tape length. The heat transfer enhancement factor (h_(ave)/h_(ave,0), where subscript 0 denotes plain MCHS) and the pressure drop increasing factor (△P_(pul)/△P_(pul,0)) are in the ranges of 1.29-2.49 and 1.68-4.72, respectively. The average values of η for each MCHS with twisted tape are in a range of 1.09-1.46. The full-length (L_t = 150 mm) twisted tape with Y = 3 yields the best heat transfer rate, the highest flow resistance and the best overall thermal performance compared to other eight twisted tapes. In addition, the empirical correlations for h_(ave) and △P_(pul) are developed based on the experimental results. The predicted h_(ave) and △P_(pul) are within ±5% and ±6% deviation, respectively, compared to the experimental data.