Heat Transfer Enhancement in Solar Air Heaters
using Artificial Roughened Elements
Abubaker Elbaloshi and Junling Hu
Abstract—This project presents an intensive study of heat transfer and fluid flow processes in a smooth and
roughened rectangular ducts of solar air heater by using computational fluid dynamics (CFD). The effects of twodifferent shapes of transverse wire ribs roughness, Half-circular shape and V-down shape, on heat transfer and fluid
flow have been investigated. Four-different Reynolds numbers, six-different pitches (P) and five-different heights (e)
are chosen as design variables. A two-dimensional computational domain CFD simulation is performed using the
ANSYS FLUENT 15.0 code. The (Standard) k-ε model is selected as the most appropriate one. Results are validated
by comparing with available analytical results. It is apparent that the turbulence created by small artificial roughness
elements result in greater enhance in heat transfer over the rectangular duct. However, the use of artificial roughness
elements results in higher friction factors. Normally, this CFD simulation has predicted that the average Nusselt
number and average friction factor increase with increase in the roughness heights and increase with a certain value
of the distance between two bumps (a pitch). To investigate the optimized values of the height and pitch for each case,
the thermal factor (TF) has been determined. A maximum value of thermal enhancement factor has been found to be
1.03 for the Half-circular shape (at height, e = 1.3mm and pitch, P = 20mm) and 1.167 for the V-down shape (at
height, e = 1.3mm and pitch, P = 5mm). The maximum enhancement of Nusselt number and friction factor as a result
of effecting artificial roughness elements was found to be 1.4 (at height, e = 1.3mm and pitch, P = 10mm) and 2.5 (at
height, e = 1.3mm and pitch, P = 8mm) times than that of smooth duct for half-circular. For V-down, it has found to
be 1.4 (at height, e = 1.3mm and pitch, P = 10mm) and 2.5 (at height, e = 1.3mm and pitch, P = 8mm) times than that
of smooth duct.
Figure: A schematic of the 3-D computational domain and boundary conditions of a solar air heater (not to scale)
Keywords: Artificial Roughness Elements; Computational Fluid Dynamics, CFD; Analytical Fluid Dynamics,
AFD; Solar Air Heater.
2015 Faculty Day & Research
Student Poster Abstract
University of Bridgeport
April 27, 2015