An experimental study on heat transfer enhancement and flow characteristics of a tube with plain, perforated and dimpled twisted tape inserts

In order to increase the performance of a heat exchanger flowing ethylene glycol (EG) and water (W) mixtures, the effects of different twisted tapes on heat transfer and flow characteristics in a heat exchanger tube is experimentally investigated. Material of the twisted tapes and the tube is selected as stainless steel. Three different volumetric ratios of EG and W mixtures are used with the volumetric ratio of (0:100), (20:80) and (40:60). The twisted tapes having twist ratio of 5.88 are perforated and dimpled with pitch ratio of (P-p/y and P-d/y) of 0.25, 0.5 and 1.0. The experiments are conducted under constant heat flux and Reynold number ranging from 5217 to 22,754. The experiments for both the smooth tube and the typical twisted tape inserted tube are validated with the literature. The results indicated that the use of twisted tape inserts enhances the heat transfer performance. Experimental results revealed that novelty dimpled twisted tape insert provides higher heat transfer performance than the others. Adding the ethylene glycol on pure water has not major role on increase in the friction factor. As the amount of ethylene glycol in the mixture increases, thermo hydraulic performance decreases. The best thermo-hydraulic performance results are obtained as 1.42, 1.17 and 1.05 for dimpled twisted tape (P-d/y = 0.25) inserted tube at the lowest Reynolds numbers for the fluids which are (0:100), (20:80) and (40:60), respectively.