Research
Conjugate Cooling of a Protruding Heater in a Channel with Distinct Flow Constraints
The conjugate cooling of a single block heater mounted on a conductive wall of a parallel plates channel was investigated under distinct laminar airflow constraints: fixed flow rate, fixed channel flow pressure drop and fixed pumping power. The heater was cooled by direct forced convection to the airflow and by conduction through its contact with the channel wall. The investigation was performed for a two-dimensional configuration with fixed channel geometry and variable heater height. At the channel entrance the flow velocity and temperature were uniform. The channel wall thickness was constant and its thermal conductivity ranged from 0 to 80 that of the air, while the heater thermal conductivity was equal to 500 that of the air. The conservation equations were solved numerically by the control volumes method with the SIMPLE algorithm. The results were expressed in dimensionless form, considering the three distinct flow constraints. For a fixed flow rate, the heater temperature always decreased as the heater height increased. For the other two flow constraints, there is a critical relative heater height which minimizes its thermal resistance to the airflow. The results also indicated that for a conductive substrate, the conduction from the heater to the substrate plate cannot be neglected in comparison to the direct convective cooling to the airflow.
Laminar Flow around an Array of 3D Protruding Heaters Mounted in Cross-Stream Direction
Numerical analysis was performed to investigate the characteristics of the laminar fluid flow around an array of 3D protruding heaters mounted on the bottom substrate of a parallel plane channel using the ANSYS/Fluent® 14.0 commercial software. The fluid flow was considered to have constant properties under steady state conditions. In the channel inlet, the velocity profile was uniform. This problem is associated with forced flow over the electronic components mounted on printed circuit boards. The conservation equations and their boundary conditions were numerically solved in a single domain through a coupled procedure. The discretization of the equations was based on the Control Volumes Method. The algorithm SIMPLE was used to solve the pressure-velocity couple. Due to the non-linearity of the momentum equation, the correction of the velocity components and the pressure were under-relaxed to prevent instability and divergence. After a study of the computational mesh independence, the numerical results were obtained, displayed as a 3D non-uniform mesh with 212,670 control volumes. This computational mesh was more concentrated near the solid-fluid interface regions due to the larger primitive variable gradients in these regions. An investigation was done on the effects of the Reynolds numbers where the Reynolds numbers ranged from 100 to 300 and was dependent on the heights of the protruding heaters. The main characteristics of the fluid flow consisted of a small recirculation upstream of the heaters, the formation of horseshoe vortices around the protruding heaters’ side walls and a large recirculation region downstream of the heaters. The fluid dynamics parameters of interest, the velocity profiles, local and average skin friction coefficient, pressure distribution and the Darcy-Weisbach friction factor, were found and compared to the results available in the literature.
