International Journal of Computer Applications (0975 – 8887) Volume 145 – No.12, July 2016 1 Transient and Mixed Convection From a Variable Tilt Angle Duct With a Built in Electric Module Adnan A. Abdulrasool Professor of al.Mustansyria University Iraq, Baghdad Province, University of al.Mustansyria Hadi A. Basher Assist Prof. of Wasit University Iraq, Wasit Province, University of Wasit Nagham Q. Shari University of Wasit Iraq, Wasit Province, University of Wasit ABSTRACT The present work represents experimental and numerical work to study the natural, transient, mixed and forced convection heat transfer from a cube which represent an electric module fixed in a relatively long duct tilted at different angles of = 0° (horizontal), = 30°, = 45° and = 90°. Module side length (L=30mm) fixed at different locations of (X/L=5,10 and 15) with different input power of (0.147, 0.51, 0.96, 1.65, 2.34 and 3.075) watt, which represent a heat flux of (32.67, 113.33, 213.33, 366.67, 520 and 683.33) W/m 2 respectively. A fan fixed at duct end is operated to move the air within the duct with different air velocities of (0.2, 0.3, 0.5, 0.7 and 0.8) m/s giving Reynolds number values of (381.9, 763.7, 954.7, 1336.6 and 1527.5) respectively. The system is operating in a transient heat transfer is calculated till steady state is reached. The heat transfer coefficient is estimated in this case. Testing the Gr/Re 2 values shows that the operating mode is in the mixed convection reaching a forced convection when operating of the highest velocity within the duct.Operating the system in transient and steady state mixed convection mode show that higher air velocities enhances the heat transfer due to giving a chance for the air to transfer the heat during its flow around the cube. The study shows that a little effect is recognized for the module position and the tilt angle specially at mixed convection operation Nemclature : Surface area of cube ( 2 ), CP: Air specific heat capacity (J/Kg.°C), ℎ : Hydraulic diameter (), : Grashof number, : Gravitational acceleration (/ 2 ), ℎ: Convection heat transfer coefficient (/ 2 .K), : Electric current (), : Thermal conductivity of air (/.K), : Length of cube (), : Mass flow rate (/), : Nusselt number, : Prandtl number , q: Input power (W), : Rayleigh number ∆ 3 , : surface temperature (). ∞ : Air temperature (), : Time (), : Electric voltage (), : Thermal expansion coefficient (1/), : Kinematics viscosity of air ( 2 /). Keywords Mixed convection in a duct, cube mixed convection, Duct heat transfer with tilt angle. 1. INTRODUCTION Advanced very large-scale integration (VLSI) technology has" triggered significant improvements "in the performance of electronic systems in the past decades. With the trend" "toward higher circuit density and faster procedure speed, however, there is a steady grab hold of the dissipative heat flux at the components, themes, and system levels. That has been shown that most procedure parameters of the electronic components are highly damaged by its temp as well" as their "immediate thermal environment". This kind of causes an increasing demand for highly efficient digital "cooling technologies to meet this demand, various electronic digital cooling schemes have" recently been developed [1]. In cases of mixed convection (natural and forced occurring together) one would often like to know how much of the convection is due to external constraints, and how much is due to natural convection occurring in the system". ""The relative magnitudes of the Grashof and Reynolds number squared determine which form of convection dominates, [2]. If Gr/Re 2 ≫1 forced convection may be neglected, whereas if Gr/Re 2 <<1 natural convection may be neglected. If the ratio is approximately one, then both forced and natural convection need to be taken into account and called mixed convection"." In common put it to use "is metal object brought in to contact with an electronic component's hot" "surface- though in many instances, a thin thermal interface materials mediates between the two surfaces. Microprocessors and power handling semiconductors are good examples of electronics that desire a heat sink to reduce their temperature through" "increased thermal mass and heat dissipations (primarily by" louage and convection and also to a smaller extent by radiation)[3]. W. S. Kim and M. N. Ozisik [4], 1987, studied the thermal transients in forced convection inside ductwork "have numerous applications in the design of control systems for heat exchangers". "In this work inductive solutions are developed for unsteady laminar forced convection inside circular tubes and parallel plate channels ensuing from a step deviation in the wall high temperature flux. The generalized integral transform technique (1974) [5] and the classical Laplace" transformation are used to create "a simple lowest order solution as well as" increased alternatives. Kuan-Tzong Lee and Wei-MonYan [6], 1998, offered detailed numerical study to measure the "effects of wall transpiration on laminar mixed convection flow and heat transfer in the" access region of horizontal rectangular ducts. They found that, either wail injection or wall structure suction has some considerable impact on the flow framework "and heat transfer performance. In addition, the correlating equations for the average fRe and Nu are presented". Han-Chieh Chiu eta. [7], 2007, studied numerically the put together heat transfer of convection and radiation in square ducts rotating in a parallel mode. He fixed the coupled momentum and energy equations by the "DuFort- Frankel numerical scheme to measure the interactions of convection with radiation. This individual found that, The result of rotation in the square duct much more important than