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In order to boost the heat transfer rate in a conical coiled tube (CCT) using an active technique, a solenoid valve was placed ahead of the CCT and employed as a pulse generator in this research. Experimentally, the effect of pulsation on heat transfer and pressure drop in the CCT was investigated. Experiments were conducted for pulsating flow throughout a Womersley number (Wo) range of 30–48, which corresponds to a pulsating frequency of 4–10 Hz, a Dean number (De) of 1148–2983, and a coil torsion (λ) of 0.02–0.052. Results revealed that pulsating flow yields larger Nu values than steady flow. A rise in heat transfer characteristics is achieved by decreasing both the pulse frequency and the coil torsion. A pulsating flow at 4 Hz (Wo = 30) was shown to promote heat transfer by the most of all the examined frequencies. The average Nu increases as De increases, although the friction factor often decreases as De increases. When the coil torsion is reduced from 0.052 to 0.02 while maintaining the same De and Wo, the average Nu and ƒ increase by 23% and 30%, respectively. A correlation for the average Nusselt number and friction factor was presented, taking frequency and coil torsion into account. [ABSTRACT FROM AUTHOR]

The performance characteristics of a triple conically tube heat exchanger (TCTHE) are experimentally and numerically conducted. The new design developed by addition a new fluid path to a double conically tube heat exchanger (DCTHE). The research aims to evaluate the TSTHE thermal characteristics at various operating and designing key parameters involve water Reynolds number, water inlet temperatures variation, flow arrangements, inclination angles, and pitch ratios (coil torsions). A numerical model in 3D Cartesian was developed using Ansys 14.5 software package to give a clear insight on TCTHE thermal performance on a level of details not always available in experiments. A finite volume discretization method was applied to solve the governing equations. The experiments were carried out at Dean number from 450 to 6200 corresponding to Reynolds number from 2750 to 35,050. The results revealed that the effectiveness of TCTHE presents higher value compared to that of DCTHE by 50% and 57% for both experimental and numerical results. Decreasing the water inlet temperature from 80 °C to 50 °C enhances the Nusselt number, Nu by 23.2%. The counter flow pattern records a higher Nu compared to parallel flow pattern by 21.5%. Also, decreasing the coil torsion from 0.0111 to 0.035 enhances Nu by 34.4%, on expense of increasing the friction factor by 9.4%. Another outcome, the higher thermo-hydraulic performance index occurred at lower coil torsion of 0.035 and at 90o inclination angles (vertical orientations). Finally, new correlations involve Nusselt number, friction factor, as well as effectiveness were presented. [ABSTRACT FROM AUTHOR]