Flow and heat transfer performances of the corrugated spiral channel with longitudinal fins

Heat exchangers serve as pivotal components in heat exchange systems. Compared with the straight channels, spiral channels have better performance due to the curvature of the centrifugal force generated by the secondary flow. Consequently, heat exchangers employing spiral channels find widespread application in agricultural engineering, including greenhouse air conditioning, water circulation systems, and agricultural product processing and storage for effective heat management. In this paper, we propose enhancing the heat transfer efficiency of spiral channels by introducing corrugations with longitudinal fins on the outer channel wall. To elucidate the impact of corrugation, we establish three-dimensional models of smooth spiral channels, corrugated spiral channels, and corrugated spiral channels with longitudinal fins. Initially, we investigate the influence of corrugated number on flow and heat transfer performance numerically. Through comparative analysis involving the development and variation of velocity and vorticity fields, average Nusselt number Nu, fanning friction factor f, average Dean number Dn_m, secondary flow intensity Se under different corrugated numbers, and the performance evaluation factor of heat exchanger based on comprehensive (PEC₀), insights are drawn. Subsequently, longitudinal fins are integrated into the corrugated spiral channel, and a numerical study is conducted to assess the effect of varying geometric parameters of the longitudinal fin on the fluid flow and heat transfer performance inside the channel. Analysis of different longitudinal fin widths and heights on velocity and temperature fields, Nu, f, and performance evaluation factor of heat exchanger based on comprehensive (PEC_w) of the channel is performed. The findings indicate that corrugated spiral channels outperform smooth spiral channels in heat transfer and flow performance. With increasing corrugated number n, secondary flow intensity within the corrugated spiral channel intensifies. Notably, at a Reynolds number of 550, a multi-vortex structure emerges in the corrugated spiral channel with a corrugated number of 21. At Reynolds number 750 and corrugated number 21, the Nusselt number of corrugated spiral channel increases by 47.08% compared to the smooth spiral channel. At the same time, the resistance loss in the channel also increases, and the Fanning friction factor of the corrugated spiral channel increases by 59.20%. When the Reynolds number is 750, the PEC₀ of the corrugated spiral channel with 18 corrugations is the highest, which increases by 27.66% compared to the smooth spiral channel. On this basis, longitudinal fins are added to the corrugated spiral channel, and it is observed by numerical simulation that symmetrical longitudinal vortices are induced by the fins. Further, the longitudinal fins induce symmetrical longitudinal vortices, enhancing flow and heat transfer in the channel's middle section. Under the condition of constant fin width and increasing fin height, the comprehensive heat transfer performance of the channel has a maximum value, that is, when fin width w=W/3, fin height h=H/6 and Reynolds number Re=250, the highest PEC_w is 1.157. When the fin height is fixed, increasing the fin width w will also make the PEC_w of the channel first increase and then decrease. The correlation formulas for Nusselt number Nu, Fanning friction factor f and secondary flow intensity Se in corrugated spiral channel are fitted, with deviations within ±14.0%, ±10.2% and ±4.4%, respectively. This provides a certain reference for the application of corrugated spiral channels with longitudinal fins in the thermal design and usage of heat exchangers.