The present work introduces a numerical simulation for the characteristics of convective heat transfer and the pressure drop inside the internal tube of a horizontal shell and conically coiled tube heat exchanger of counter flow configuration. Cold water flows in the internal tube while hot air flows in the shell of the heat exchanger.
Throughout the present study, 300 cases are performed for different coil taper angles (0≤≤90) and torsions (0.0641≤≤0.1206). The water flow velocity in the coiled tube ranges from 0.1 to 0.5 m/s, which corresponds to Reynolds number range of 857≤Re_t≤6327, while the tube-side fluid inlet temperature varies from 10 to 25C, which corresponds to Prandtl number of 5.86≤Pr_t≤9.25. In addition, a hot air flows in the shell of the heat exchanger at fixed flow velocity and inlet temperature of 0.5 m/s and 50C, respectively. The results reveal that the tube-side average Nusselt number and friction factor are reduced with increasing both the coil taper angle and torsion. Increasing the coil taper angle from 0 to 90 reduces the Nusselt number and friction factor by 21.4% and 26%, respectively, while increasing the coil torsion from 0.0641 to 0.1206 reduces them by 31.8% and 6.8%, respectively. Furthermore, increasing the tube-side Reynolds number augments its average Nusselt number and reduces its friction factor. While, there is a slight increase in the tube-side average Nusselt number with decreasing the tube-side inlet temperature, while its effect on the tube-side friction factor can be ignored. Additionally, the thermal performance index (TPI) is determined to compare the performance of the heat exchanger of conical coil with that of helical coil. The results demonstrate that the TPI decreases with increasing the coil taper angle, while the effect of the coil torsion can be ignored. Finally, numerical correlations are proposed to predict the tube-side average Nusselt number and Fanning friction factor as functions of the investigated parameters. |
