Waqar Ali Khan

Analytical Modeling of Fluid Flow and Heat Transfer in Micro/Nano-Channel Heat Sinks

Laminar forced convection in two-dimensional rectangular microchannels and nanochannels under hydrodynamically and thermally fully developed conditions is investigated analytically in the slip-flow regime. Closed-form solutions for fluid friction and Nusselt numbers are obtained bysolving the continuum momentum and energy equations with the first-order velocity slip and temperature jump boundary conditions at the channel walls. An isoflux thermal boundary condition is applied on the heat sink base. The results of the present analysis are presented in terms of the channel aspect ratio, hydraulic diameter, momentum and thermal accommodation coefficients, Knudsen number, slip velocity, Reynolds number, and Prandtl number. It is found that fluid friction decreases and heat transfer increases compared with no-slip flow conditions, depending on the aspect ratios and Knudsen numbers that include the effects of the channel size or rarefaction and the fluid/wall interaction.

Optimization of Pin-Fin Heat Sinks in Bypass Flow Using Entropy Generation Minimization Method

An entropy generation minimization, EGM, method is applied to study the thermodynamic losses caused by heat transfer and pressure drop for the fluid in a cylindrical pin-fin heat sink and bypass flow regions. A general expression for the entropy generation rate is obtained by considering control volumes around heat sink and bypass regions. The conservation equations for mass and energy with the entropy balance are applied in both regions. Inside the heat sink, analytical/empirical correlations are used for heat transfer coefficients and friction factors, where the reference velocity used in Reynolds number and pressure drop is based on the minimum free area available for the fluid flow. In bypass regions theoretical models, based on laws of conservation of mass, momentum and energy, are used to predict flow velocity and pressure drop. Both in-line and staggered arrangements are studied and their relative performance is compared for the same thermal and hydraulic conditions. A parametric study is also performed to show the effects of bypass on the overall performance of heat sinks.Copyright

FLUID FLOW AND HEAT TRANSFER FROM A CYLINDER BETWEEN PARALLEL PLANES: ANALYTICAL APPROACH

In this study, an integral approach of the boundary layer analysis is employed to investigate the eects of blockage on fluid flow and heat transfer from a circular cylinder confined between parallel planes. The momentum equation is solved using the modified Von Karman-Pohlhausen method, which uses a fourth order velocity profile inside the hydrodynamic boundary layer. The potential flow velocity, outside the boundary layer, is obtained by the method of images. A third order temperature profile is used in the thermal boundary layer to solve the energy integral equation for isothermal and isoflux boundary conditions. Closed form solutions are obtained for the fluid flow and heat transfer from the cylinder with blockage ratio, Reynolds and Prandtl numbers as parameters. It is shown that the blockage ratio controls the fluid flow and the transfer of heat from the cylinder and delays the separation. The results for both thermal boundary conditions are found to be in a good agreement with experimental/numerical data for a single circular cylinder in a channel.