عمار مسلم هادي حميّد

ABSTRACT Heat dissipation from electronic devices is a crucial demand to keep their rated performance. Finned heat sinks are one of the efficient routes to dissipate the generated heat. This paper studies the performance of forced convective heat transfer from different shapes and arrangements of micro heat sinks. Ten designs of the micro heat sinks, included novel designs of micro fins, have been experimentally and numerically investigated in a rectangular air flow channel with Reynolds number ranging from 2000 to 11000. Laser etching technique has had been used in manufacturing the micro heat sinks while the CFD analysis have been conducted finite element method implemented in COMSOL Multiphysics. Results show that the proposed designs can significantly improve the fluid dynamic through the micro heat sink surface and thus the heat transfer performance. The enhancement in thermal transmittance because fluid-wall interaction has been proven to be effective in many designs in this study without relying on the contribution of the increase in the surface area. Therefore, this study provides significant rules to the design of micro-structured heat sinks for enhancing the heat transfer performance.

This experimental research depicts the role of coating hot surfaces by graphite and graphene on the process of heat dissipation from these hot surfaces. Three aluminum specimens have been prepared for test, one of theme is coated by graphite, another one by graphene a while the third is left free of coating for comparison purpose. Each specimen is tested separately in a home-made wind tunnel. A plate electrical heater is adhered on the bottom of the specimen to simulate the generated energy by a heat sink. A heat sink composed of high thermal conductivity was applied between the heater plate and the base plate of heatsink to reduce the contact resistance to heat flow. The experiments are conducted with four turbulent Reynolds number. The results reveal that the sample coated by graphene exhibits the best thermal dissipation while the uncoated specimen shows the worst thermal performance

To get rid of the heat better by improving the thermal performance of a heat sink, Al substrate was coated by a graphene layer with a different thickness by using a chemical spray method. The thickness of layers was changed by changing the spry time from 1000 to 5000 ms. Surface morphology was tested by using SPM to investigate the change that was occurred on the surface. In order to understand the performance of graphene-coated Al heat sink, a wind tunnel has been designed to investigate heat transfer coefficient, Nusselt number and thermal transmittance for each sample under turbulent flow condition with four values of Reynolds number. The results showed that graphene improves the thermal performance, and this performance is getting better with the thickness of graphene, up to critical thickness.

In this research, we focus on the performance of heat sink, new configurations of the micro heat sink with comprises of pinned copper pieces of appropriate dimensions have been proposed. Dozens of different shapes micro heat sinks have been manufactured from brass using Laser technique. These heat sinks have been coupled individually with a simulated electronic circuit including a power transistor to freely dissipate the generated heat. Bulk temperatures of heat sink and the power transistor have been measured using a thermal camera. The results showed that, in general, the finned heat sink of either configuration augments heat transfer compared with smooth one. It is found that the maximum percentage reductions in temperature of the transistor are demonstrated with two uncommon configurations, namely the leaves-shaped fin (LSF) 9.352% and the drop-shaped fin (DSF) 9.353%. on the other hand, a staggered wavy fin (SWF) shows minimum percentage reduction in transistor temperature, 0.952%. It has been shown that through this research and by using several models of heat sink, the increase in surface area is not only the factor (major) to increase the heat transfer to the surrounding environment. This makes it possible to design fins with a smaller surface area but more heat dispersion.

The three-dimensional numerical study of turbulent recirculating for air distribution in space. The study solved the partial differential equations by using finite-volume method. By using Ansys-FLUENT 6.3.26 to simulate the complex flow inside the physical model. Carried out the process of verifying the accuracy of the results obtained from the program and compare them together. The results of numerical model were compared with experimental predications of previous researchers. These comparisons show a good agreement. Therefore, the simulation of non-isothermal turbulent flow within the room, was made using three principle geometrical arrangement of the room with different locations of supply opening, which built by gambit(2.2.30) program. The predicted flow were plotted and discussed for buoyant flow. The study demonstrates that the flow behavior depends on location of the opening supply (up and down) and on the location of the obstruction. These parameters was modeled separately to understand how each of this parameters affects the flow pattern. The “Air Diffusion Performance Index” effected by these parameters greatly, and, found that the location of the opening supply is related directly to load centered. Also, the present work results show that the Coanda effect has large effect on the general form of air distribution, and then, on thermal comfort