Heat Transfer Coefficient Nusselt Number Research Articles

Numerical analysis of concentric jet impingement heat transfer to the concave surface of the cone

This work includes numerical investigation of concentric jet impingement heat transfer to the concave surface of 30° apex angle conical surface. Heat transfer results are represented in terms of nondimensional heat transfer coefficient Nusselt number along the slant edge of the cone. Turbulence intensity, static pressure distribution along slant edge of the cone, and velocity contours in the domain are also presented for a detail understanding of the flow behavior. Different geometrical parameters like diameter of pipe (10 mm, 14 mm, and 20 mm) and L/D (4.25, 6.25, and 10.25) are considered for heat transfer analysis. Jet Reynolds number is varied between 25000 and 82000 for each diameter and L/D case. It is observed that Nusselt number value is minimum close to the apex of the cone due to stagnation region, then increases with increase in the distance from the apex of the cone and becomes maximum due to maxima in the turbulence intensity and decreases with increases in the distance. Nusselt number value decreases with increase in the L/D. Nusselt number increases with increase in the jet Reynolds number. There is an insignificant influence of the diameter of pipe on Nusselt number for identical jet Reynolds number and L/D.

A Comparison of Circular Duct and Real Hexagonal Duct Results Using Hydraulic Diameter

To see whether the turbulent flow correlations derived for circular ducts can be used for hexagonal cross-sectional ducts using hydraulic diameter, turbulent flow in hexagonal ducts is numerically investigated under constant wall temperature boundary condition using ANSYS Fluent 17.0 software. Investigated parameters are the Reynolds number between 10×103Re50×103 and side angle of the duct varying between 30o and 90o. Standard k-ε model is used as turbulence model. General expressions are proposed for fully developed dimensionless heat transfer coefficient Nusselt number and fully developed Darcy friction factor in terms of Reynolds number and side angle for hexagonal-shaped cross-sectional duct. Results show that side angle of hexagonal duct affects the pressure drop along duct and heat transfer coefficient in duct. Results point out that regular hexagonal duct, =60o, gives minimum pressure drop and maximum Nusselt number. It is concluded that correlations given in the literature for circular ducts in turbulent flow can give 14% higher dimensionless heat transfer coefficient, Nusselt number, than that of actual hexagonal duct flow.