The influence of structural parameters on heat transfer and pressure drop for hydrocarbon mixture refrigerant during condensation in enhanced spiral pipes

In this paper, the condensation heat transfer and pressure drop characteristics for hydrocarbon mixture upward flow in smooth and enhanced spiral pipes were numerically investigated. The numerical model was established and verified by experimental results in literatures. It discussed the influence of geometrical parameters on condensation heat transfer and pressure drop in three kinds of enhanced spiral pipes, which contained square corrugated pipe, sinusoidal corrugated pipe and spiral grooved pipe. The results indicate that in enhanced spiral pipes, both frictional pressure drop and heat transfer coefficient increase with the rise in corrugation (groove) height and the decrease of corrugation (groove) pitch. Meanwhile, compared to the smooth pipe, the augmentation on heat transfer for square corrugated, sinusoidal corrugated and spiral grooved pipes are 0.934-2.052, 1.103-2.216 and 1.206-1.804 times, respectively, while the increase of frictional pressure drop are 1.805-10.930, 1.272-7.176 and 0.851-3.587 times, respectively. Besides, the comprehensive heat transfer enhancement factor (CHF) was introduced to evaluate the overall heat transfer performance of enhanced pipes. It is found that as the corrugation (groove) height increases, the CHF increases in square and sinusoidal corrugated pipes but decreases in spiral grooved pipe; at the meantime, with the increase of corrugation (groove) pitch, the CHF first decreases and then increases in square and sinusoidal corrugated pipes while first increases and then decreases in spiral grooved pipe. The average CHFs for all square corrugated pipes, sinusoidal corrugated pipes and spiral grooved pipes are 0.872, 1.083 and 1.275, respectively. Moreover, the spiral grooved pipe with the relative groove height and pitch of 0.03535 and 5.0 shows the best overall heat transfer performance among others, whose average CHF can reach to 1.413. These results provide some instructions for the application of enhanced spiral tube in the design of spiral wound heat exchange (SWHE).