الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 127 |  |  |
| | | from | 127 | | |
Abstract
The present work introduces a numerical simulation for the characteristics of convective heat transfer and the pressure DROP inside the shell-side of a horizontal shell and semi-circular tubes (SCTs) heat exchanger of a counter flow configuration using ANSYS fluent CFD. The numerical cases are carried out for two cases; cold pure water and Al2O3/water nanofluid with different nanoparticles volume concentrations (0%≤φ≤1%) in the shell-side.
Throughout the present study, 504 cases are performed for different spacing ratios of the SCTs bases (0≤≤0.5), flow rate of the shell-side fluid ranges from 6 to 18 L/min, which corresponds to Reynolds number range of 3290≤Resh≤17755, while the shell-side fluid inlet temperature varies from 15 to 25C, which corresponds to Prandtl number of 4.75≤Prsh≤7.27. In addition, a hot pure water flows through the internal tubes at a constant total flow rate of 42 L/min and its inlet temperature is held constant at 50C.
The results reveal that splitting the internal tubes of a shell and tube heat exchanger significantly increases the rate of heat transfer and the flow resistance in the shell-side when compared with that in the heat exchangers of circular tubes at the same operating conditions. In addition, the shell-side average Nusselt number and friction factor increase and the exchanger effectiveness with increasing the SCTs spacing ratio. Compared with the circular tubes case, using SCTs of = 0.5 achieves the maximum increases in the shell-side average Nusselt number and friction factor by 76.7% and 17.7%, respectively, for water cases and by 164.8% and 20.1%, respectively, for all Al2O3/water nanofluid cases.
Furthermore, the shell-side average Nusselt number, friction factor and the exchanger effectiveness increase with increasing the Al2O3 nanoparticles loading in the shell side. Compared with the pure water (φ = 0), the maximum increases in the shell-side average Nusselt number and friction factor are by 35.9% and 10.3%, respectively, at φ = 1%.
In addition, the results assured that increasing the shell side Reynolds number augments its average Nusselt number and reduces its friction factor and the exchanger effectiveness. While there is a slight increase in shell-side average Nusselt number with
iii
decreasing the shell-side inlet temperature, while its effect on the shell-side friction factor can be ignored.
In addition, the hydrothermal performance index (HTPI) is calculated to ensure the use of semi-circular tubes and the addition of Al2O3 nanoparticles to water in the heat exchanger shell is a successful tool to improve the heat transfer compared to the required pumping power. The results show that the HTPI is greater than unity for all ranges of the investigated parameters. In addition, the HTPI increases with increasing the SCTs spacing ratio and with increasing the Al2O3 nanoparticles loading in the shell side.
Moreover, using Al2O3/water nanofluid of φ = 1% with the shell and SCTs heat exchanger of = 0.5 provides the maximum values of the HTPI; 2.6 and 2.47 at lower and higher shell-side flow rates, respectively. Finally, numerical correlations are proposed to predict the shell-side average Nusselt number and Fanning friction factor as function of the investigated parameters.