Abstract
Laminar mixed convection in the entrance region of horizontal and inclined semicircular ducts has been investigated. The governing momentum and energy equations were solved numerically using a marching technique with finite control volume approach following the SIMPLER algorithm. Results were obtained for thermal boundary condition of uniform heat input axially and uniform wall temperature circumferentially, incorporating Pr = 7, Re = 500, inclination angles (α = 0° and 20°), and a wide range of Grashof numbers. These results include velocity and temperature distributions at different axial locations as well as axial distribution of local Nusselt number and local wall friction factor. It was found that Nusselt number is close to the forced convection values near the entrance region, then decreases to minimum value as the distance from the entrance increases, and then rises due to the effect of free convection before reaching a constant value (fully developed). As Grashof number increases Nusselt number and wall friction factor increase in both developing and fully developed regions for horizontal and inclined ducts. A comparison with the experimental data in the thermal entrance region was also conducted and the comparison was satisfactory.
Highlights
Laminar combined forced and free convection flows in ducts received much attention in the recent years because of their wide range of applications, such as compact heat exchangers
They oriented the flat wall of the duct in vertical position using two thermal boundary conditions H1 and H2; H2 thermal boundary condition is defined as a constant heat flux axially and circumferentially
These equations were solved for each radial line using the tridiagonal matrix algorithm (TDMA), and the domain was covered by sweeping line by line in the angular direction
Summary
Laminar combined forced and free convection flows in ducts received much attention in the recent years because of their wide range of applications, such as compact heat exchangers. Nandakumar et al [1] studied numerically the problem of fully developed laminar mixed convection flow in horizontal semicircular ducts for the H1 thermal boundary condition with the flat wall at the bottom. Busedra and Soliman [4] investigated the effect of duct inclination on laminar mixed convection in inclined semicircular ducts under buoyancy-assisted and opposed conditions. They oriented the flat wall of the duct in vertical position using two thermal boundary conditions H1 and H2; H2 thermal boundary condition is defined as a constant heat flux axially and circumferentially
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