Comparative analysis on thermal–hydraulic performance of curved tubes: Different geometrical parameters and working fluids

•A comparative study is carried out on performance of curved tubes.•Effects of different geometrical parameters and working fluids are examined.•Helical, spiral, and serpentine tubes have better thermal performance, respectively.•Working fluids with the higher Prandtl number show better thermal performance.•Universal correlations are developed for curved tubes at studied ranges.

A comparative 3–D analysis is carried out on the thermal–hydraulic performance of the curved tubes namely helical, spiral, and serpentine with different geometrical parameters. Likewise, the effects of three conventional liquid working fluids namely water, engine–oil, and ethylene–glycol inside the tubes are investigated and compared. The results show that at the same geometrical and operating conditions, the helical tube has the best performance compared to the other ones. For all the curved tubes, the geometrical parameters at the lower values display a better performance in comparison with the higher ones. It is also detected that the working fluids with the higher Prandtl numbers have greater values of Nusselt number. However the effect of Prandtl number on the friction factor is not considerable. Finally, generalized correlations are developed for each curved tube as function of Reynolds number, Prandtl number, and geometrical parameters. It seems that the results of the current work can provide helpful guidelines for designers and manufactures in order to select the optimum curved tube, geometrical parameter, and working fluid for use in the heat exchange devises based on their specific applications in the industries such as refrigeration, automobile, chemical, food, and aerospace.