Abstract
This work presents experimental investigation of flow and heat transfer characteristics for entry length of turbulent flow in a rectangular duct fitted with porous media and air as the working fluid. Rectangular duct (300×30 mm) with a hydraulic diameter (54.54 mm) was subjected to constant heat flux from lower surface (1.5 ×102 –1.8 ×102 w/m2) and Reynolds number ranged (3.3x104 up to 4.8x104). Copper mesh inserts (as porous media) with screen diameter (54.5 mm) for vary distance between two adjacent screens of (10 mm), (15 mm) and (20 mm) in the porosity range of (0.98 - 0.99) are considered for experimentation. The effect of porous height ratio (full and partial) are also considered. It is observed that the enhancement of heat transfer by using mesh inserts when compared to a plain surface is more by a factor of (2.2) times where the skin fraction coefficient is about (5) times. An Empirical correlation for Nusselt number and friction factor are developed for the mesh inserts from the obtained results.
Highlights
Description Cross-sectional area (H.W)Aspect ratio Half duct height (H/2) Specific heat at constant pressure skin friction coefficientHydraulic diameter Friction factorAcceleration due to Gravity= 9.81 Duct height local heat transfer coefficient CurrentThermal conductivity LengthMass flow rate PressureUnits m 2 m kJ/kg.K m m/s2 m W/ m2.K A W/m.K m kg/s N/ m2 W W/m2 K K K m/s Volt m kg/m3 N/ m2The introduction of porous media inform of mesh wire for heat transfer enhancement is found in numerous applications, e.g, electronic cooling, drying processes, a solid matrix, heat exchangers and enhanced recovery of petroleum reservoirs
The flow in a duct can be divided in two parts: boundary flow and core flow
This figure illustrates that skin friction coefficient increases with decreasing porosity, which can be attributed to the same above reasons. These figures show that the increase of skin friction coefficient for clear flow in the entrance region is very slowly, while for porous flow is very sharp especially behind the porous media
Summary
Description Cross-sectional area (H.W)Aspect ratio Half duct height (H/2) Specific heat at constant pressure skin friction coefficientHydraulic diameter Friction factorAcceleration due to Gravity= 9.81 Duct height local heat transfer coefficient CurrentThermal conductivity LengthMass flow rate PressureUnits m 2 m kJ/kg.K m m/s2 m W/ m2.K A W/m.K m kg/s N/ m2 W W/m2 K K K m/s Volt m kg/m3 N/ m2The introduction of porous media inform of mesh wire for heat transfer enhancement is found in numerous applications, e.g, electronic cooling, drying processes, a solid matrix, heat exchangers and enhanced recovery of petroleum reservoirs. The commonly used methods in the boundary layer flow are :(a) disrupting the fluid boundary layer near the wall, (b) extending the solid surface to enhance heat transfer, (c) charging the chemical and physical nature of the surface. This method causes enhancement in the boundary flow. The more direct way is to make temperature as uniform as possible in the core flow in order to form a thin thermal boundary layer near the wall with great temperature gradient, not increase velocity gradient in the flow filled ,not to disrupt fluid near the boundary layer and not to extend continuous surface on the wall [2]
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