THE EFFECT OF NON-UNIFORM FLOW ON HEAT TRANSFER COEFFICIENT OF A CYLINDER WALL

The present study has been carried out to investigate the problem of heat transfer by force convection as unsteady state conduction ((i.e. lumped-capacitance system)) from the out side surface of horizontal cylinder in cross flow of air was studied. Experimental works were involved for this purpose. The cylinder is closed ended and heat insulated, circular in cross-section and its internal surface dissipates heat uniformly (constant heat flux). The cylinder is placed in rectangular wind tunnel that was used for the experimental tests having length equal to (244 cm) with inlet and outlet cross- section areas equal to (6.25*12.5 cm) and (6.25*25 cm) respectively and Reynold’s number is (Re = 6*105). The section area of the wind tunnel diverges downstream from the inlet position at a distance equals to (160 cm) from its entery. One cylinder of aluminum for different cylinder positions were used, diameter of cylinder is 4.96 cm, cylinder length is 6.7 cm and thickness of cylinder is 5 mm and it was placed at 6.5 cm from the discontinuous wall. Ten sets of reference temperature (To) were used for each cylinder position (Y =3.7, 7.75, 15.25, 19 cm). From Appendix (A), one of fife test section at (θ =90) is used and one node of twelve thermocouple nodes at (θ on the cylinder to measure surface temperature were used. )90= The experimental results were made in the form of temperature vs time interval (t). The computational results were made by a package program (MATLAP 6.1) from the experimental results in this study. This package is focused on calculating heat transfer coefficient, Nusselt number, Temperature ratio, time ratio. It was concluded that the rate of decreasing in surface temperature of cylinder (T) with time interval (t) will be increased as reference temperature (To =150, 140, 130, 120, 110, 100, 90, 80, 70, 60 Co) is increased and cylinder position (Y=3.7, 7.75, 15.25, 19 cm) is decreased. At some reference temperature (To =150, 140, 130, 120, 110, 100, 90, 80, 70, 60 Co) and cylinder position (Y=3.7, 7.75, 15.25, 19 cm), heat transfer coefficient and Nusselt number was found to increase with time interval (t). Finally, heat transfer coefficient and Nusselt number will be increased as cylinder position (Y=3.7, 7.75, 15.25, 19 cm) is decreased.