Ali Akbar Merrikh

Analytical Solution of Forced Convection in a Duct of Rectangular Cross Section Saturated by a Porous Medium

A theoretical analysis is presented to investigate fully developed (both thermally and hydrodynamically) forced convection in a duct of rectangular cross-section filled with a hyper-porous medium. The Darcy-Brinkman model for flow through porous media was adopted in the present analysis. A Fourier series type solution is applied to obtain the exact velocity and temperature distribution within the duct. The case of uniform heat flux on the walls, i.e. the H boundary condition in the terminology of Kays and Crawford [1], is treated. Values of the Nusselt number and the friction factor as a function of the aspect ratio, the Darcy number, and the viscosity ratio are reported.

Parametric evaluation of foster RC-network for predicting transient evolution of natural convection and radiation around a flat plate

Compact thermal modeling of hand-held and ultra-low power microelectronic systems has recently attracted a great deal of attention. In this study time-dependent evolution of heat transfer around a flat plate was numerically investigated. The flat plate is subjected to internal heat generation from the inner boundary via a discrete heat source. It is cooled on the outer boundary via buoyancy and radiation. The main objective of this work was to understand the limitation of a Foster RC-network in predicting transient behavior of a non-linear system as such. Non-linearity of the system stems from the physics of flow and heat transfer evolution around the flat plate, resulting time- and power-dependent boundary conditions. Special attention was paid to the characteristics and number of the network ladders for resolving the time-history of the temperature as a function of the input power. The studied system resembles a hand-held, fanless, device operating at room ambient.

Thermal performance of dual piezoelectric cool jet for ultra-thin mobile applications

In order to dissipate heat from future low form factor microelectronic systems the use of piezoelectric blowers has recently attracted a great deal of attention. These zero-mass flow devices comprised of two piezoelectric membranes, whose oscillation frequency and amplitude can be electrically tuned, provide a net positive momentum which can be used to actively cool various device components. In order to evaluate the potential use of these cooling devices an open-air bench system has been developed. Experimental performance of a piezoelectric cooling device is compared to natural convection over a heated surface with an attached heat sink. Furthermore the convective heat transfer rate displays a maximum value at a certain threshold which corresponds with previously reported computational results.

Investigation of Two-Phase, Vapor Chamber Based Thermal Management of Multiple Microserver Chips

Thermal management of microserver chips is of much interest to the semiconductor industry due to the significant performance benefits associated with heat spreading, resulting in very effective hot spot cooling in active cooling environments. This paper investigates thermal management of a multi-chip microserver module using two-phase heat transfer in a vapor chamber. A simulation model capturing two-phase flow of H2O in a vapor chamber was developed for understanding the effect of various parameters on thermal performance of the vapor chamber. The performance of a single high power chip is compared with a system of multiple lower power chips. Emphasis is on the impact of using multiple lower power chips instead of a single high power chip on the heat spreading capability of a flat, thin, vapor chamber. Also, it is shown that using a system of multiple low power chips, provides designers with the opportunity for designing vapor chamber with same functionality as single chip but reduced mass. Results highlight the challenges and opportunities involved in such an approach. The results shown in this paper will be useful for the design of two-phase cooling for microserver chips.Copyright

Robust Thermal Management for Embedded CPU and GPUs in Displays

Digital signage systems are large format displays that are typically installed in public areas for advertisement and informative publications. This emerging technology is considered as a major category in the large format display market. In general, a digital signage system consists of a flat panel display consisting of high brightness screen and operation circuits. Also, special features of high performance embedded computing system exist in very small form factors. Such products, however, are accompanied with high heat dissipation of the internal components and are usually exposed to very harsh environments for more frequent exposure to customers. Also the installation schemes of the products vary for different objectives, and a robust thermal design is required to guarantee the system reliability considering corner scenarios within the design space. The objective of the present study is to investigate the effect of installation environment on the thermal performance of a display assembly resembling a digital signage system. Design criteria for a proper thermal management scheme are proposed. The thermal characteristics of a digital signage system are presented in various operation conditions and each thermal design parameter is discussed thoroughly to ensure the reliability requirements of the digital signage system are met.Copyright

Low-Profile Chipset Microprocessor Heatsink Optimization for Server Form Factor

We present a methodology for optimizing footprint, metal mass and thermal performance of an aluminum extruded heatsink for cooling chipset microprocessors in server form-factor. The analysis is based on predefined volume flow rate of air at a constant temperature assumed to be available upstream of the package. The front-to-back cooling assumption covers the worst case ambient conditions, typical of chipset boundary condition in servers. We present studies covering a range of heatsink footprints in order to compare and minimize the heatsink footprint, at the same time satisfying thermal specification of the chipset microprocessor. The study also focuses on the system-level assessment of the optimum 60×40 mm2 footprint and corner cases by studying the effect of motherboard thermal conductivity as well as blockages on the heatsink case-to-ambient thermal resistance.Copyright

Heatsink Mass Optimization Methodology for Desktop Microprocessor Cooling

We present a novel modeling methodology for optimizing the mass of aluminum-extruded heatsinks for cooling desk-top microprocessors. The two-stage study aims at reducing mass of an aluminum-extrusion heatsink by taking advantage of the existing thermal resistance margin. In Stage 1, we investigated several possible combinations of base shapes to minimize the mass of the base region. Base shape is optimized by dividing the base volume into several blocks of equal width, with the objective of progressively minimizing the mass of the peripheral region while shaping the middle region to minimize spreading resistance. Three base shape profiles—namely, wedge, semielliptical, and flat top—were selected for further study. In Stage 2, a thorough base, fin thickness, and fin count study was carried out by mathematical optimization. The result of this optimization exercise was a 30% reduction in the heatsink mass. The degradation in thermal resistance of the mass-reduced design is within the acceptable margin and me...