www.ccsenet.org/mas Modern Applied Science Vol. 5, No. 2; April 2011 ISSN 1913-1844 E-ISSN 1913-1852 128 An Experimental Study for Mixed Convection through a Circular Tube Filled with Porous Media and Fixed Horizontally and Inclined Tahseen Ahmad Tahseen Mechanical Engineering, College of Engineering, Tikrit University, Iraq Received: December 2, 2010 Accepted: December 17, 2010 doi:10.5539/mas.v5n2p128 Abstract The porous media have a great influence on the heat transfer and storaging it characteristics. In this study an experimental work has been conducted to measure the mixed convection though the filled circular tubes. First, the test apparatus has been manufactured; filled circular tubes with a porous media and fixed horizontally first then tilted with different angles. Secondly, the circular tube is heated with a constant heat flux and, thermocouples have been stickled in proper positions. Then many readings, for temperatures, have been registered for each thermocouple with different speeds of the outlet air (from the circular tube) and the inclination angle of the tube has been changed many times to be 0 o , 30 o ,45 o & 60 o . These experiments have been conducted for the range (108.54Ra907.73) of Rayleigh number and for the range (29.31Pe516.94) of Peclet number. Three tests for the heat flux have been conducted, for each five Peclet number has been used. Finally, the experimental result shows that the surface temperature of pipe has a proportional relation with the tube length for all values of the heat flux and Peclet number. In addition, the heat transfer is achieved by free convection for small Peclet number, by forced convection for large Peclet number and by mixed convection for medium value of Peclet number. Keywords: Mixed convection, Constant heat flux, Porous media, Inclined Horizontal circular tubes Nomenclature A tube surface area (m 2 ) C specific heat (J.kg -1 . K -1 ) D tube diameter (m) d grain diameter (m) g acceleration due to gravity (m/s 2 ) Gr Grashof number h heat transfer coefficient (W.m -2 . o C -1 ) I electrical current (ampere) K permeability (m 2 ) k thermal conductivity (W.m -1 . o C -1 ) L tube length (m) m mass flow rate (kg.s -1 ) Nu Nusselt number Pe Peclet number Ra Rayleigh number Re Reynolds number Ri Richardson number Q heat input (W) q heat flux (W. m -2 ) T temperature ( o C) u velocity of air (m. s -1 )