Ilker Tari

CFD Analyses of a Notebook Computer Thermal Management System and a Proposed Passive Cooling Alternative

A notebook computer thermal management system is analyzed using a commercial computational fluid dynamics software package (ANSYS Fluent). The active and passive paths that are used for heat dissipation are examined for different steady state operating conditions. For each case, average and hot-spot temperatures of the components are compared with the maximum allowable operating temperatures. It is observed that when low heat dissipation components are put on the same passive path, the increased heat load of the path may cause unexpected hot spot temperatures. A hard disk drive is especially susceptible to overheating and the keyboard surface may reach ergonomically undesirable temperatures. Based on the analysis results and observations, a new component arrangement considering passive paths and using the back side of the liquid crystal display screen is proposed and a simple correlation based thermal analysis of the proposed system is presented. It is demonstrated for the considered 16.1 in notebook and for a standard A4 paper sized notebook that placing the computer processing unit, the motherboard, and the memory on the lid creates enough surface area for passive cooling.

Forced Air Cooling of CPUs With Heat Sinks: A Numerical Study

A common ATX form factor personal computer system is modeled in detail. The flow and temperature fields inside the chassis are numerically investigated as a conjugate heat transfer problem. The computational effort is concentrated on the forced air cooling of the CPU using a heat sink. Three different commercial heat sink designs are analyzed by using commercial computational fluid dynamics software packages Icepak and Fluent. The grid independent, well converged, and well posed simulations are performed, and the results are compared with the experimental data. It is observed that flow obstructions in the chassis and the resulting air recirculation affect the heat sink temperature distribution. The specific thermal resistance values for the heat sinks are compared. It is observed that although they have different geometries, all of the three heat sinks have similar specific thermal resistances. The best heat sink is selected and modified in order to have a lower maximum temperature distribution in the heat sink by changing the geometry and the material. Especially, replacing aluminum with copper as the heat sink material improved the performance. The importance of modeling the entire chassis is demonstrated by comparing the simulation results with the results from a model of only the CPU-heat-sink-fan assembly.

CFD MODELING OF FORCED COOLING OF COMPUTER CHASSIS

Abstract In this study, Computational Fluid Dynamics, which has taken its position in the thermal design of electronic packages, was used in order to draw a CFD road map for forced cooling conjugate heat transfer analyses in heat generating electronic systems. The main sources of error in CFD analyses arise from inappropriate numerical models including turbulence models, radiation modeling and discretization schemes, insufficient grid resolution, and lack of convergence. A complete computer chassis model with heat sinks and fans inside was created and parametric analyses were performed to compare the effects of different turbulence models, discretization schemes, mesh resolutions, convergence criteria, and radiative heat transfer. Two commercially available CFD software packages were used, ANSYS Icepak for preprocessing and FLUENT for solution and postprocessing. The road map was applied to three different heat sinks modeled into the full chassis. Numerical results were compared with the available experimental data and they were in good agreement.

Passive cooling assembly for flat panel displays with integrated high power components

Passive cooling of flat panel display designs with integrated high power components is investigated with the help of recently available semi-empirical and CFD based heat transfer correlations. A heat-spreader-heat-sink assembly is proposed for effective external natural convection cooling of the display panel. A flat vertical surface and plate finned heat sinks with various fin heights are considered as heat sinks in the assembly. Heat dissipation limits for both types of heat sinks are determined for various panel dimensions. It is shown that for large panels, it is feasible to use passive cooling even when integrated computer components are used in panels for demanding applications such as video games, high definition video processing and 2- D to 3-D conversion.

Numerical Analysis of Phase Change Material Characteristics Used in a Thermal Energy Storage Device

ABSTRACT In this study, a numerical analysis is performed to investigate the freezing process of phase change materials (PCM) in a predesigned thermal energy storage (TES) device. This TES device is integrated with a milk storage cooling cycle operating under predefined practical conditions. Using this cooling unit, 100 litres of milk is kept cool at 4°C for 48 hours before it is collected. A 2-D model of the TES device is developed in COMSOL Multiphysics to analyze the phase change performance of water-based PCMs. The variations of thermal properties with temperature during the phase change are considered in the analysis. The model is used for exploring the solidification process of PCMs inside the TES device. Temperature variations with time, ice formation, and the impacts of boundary conditions are investigated in detail. Water PCM shows better characteristics in the solidification process in comparison to eutectic PCMs, which is mainly due to the differences between phase change temperatures of the PCMs.

A PSEUDOSPECTRAL ANALYSIS OF LAMINAR NATURAL CONVECTION FLOW AND HEAT TRANSFER BETWEEN TWO INCLINED PARALLEL PLATES

Three dimensional laminar natural convection flow of and heat transfer in incompressible air between two inclined parallel plates are analyzed with the Boussinesq approximation by using spectral methods. The plates are assumed to be infinitely long in streamwise (x) and spanwise (z) directions. For these directions, periodic boundary conditions are used and for the normal direction (y), constant wall temperature and no slip boundary conditions are used. Unsteady Navier-Stokes and energy equations are solved using a pseudospectral approach in order to obtain velocity and temperature fields inside the channel. Fourier series are used to expand the variables in × and z directions, while Chebyshev polynomials are used to expand the variables in y direction. By using the temperature distribution between the plates, local and average Nusselt numbers (Nu) are calculated. Nu values are correlated with φ, which is the inclination angle, and with Ra·cosφ to compare the results with the literature.Copyright

Energy and Exergy Analyses of a Solar-Hydrogen Based Energy System for the Emergency Room of a Hospital in Ankara, Turkey

A hybrid (solar-hydrogen) renewable energy system consisting of photovoltaic (PV) panels, proton exchange membrane (PEM) fuel cells, PEM-based electrolyzers, and hydrogen storage has been investigated for a stand-alone application, which was established for the emergency room of Kecioren Training and Research Hospital in Ankara, Turkey. A complete model of the hybrid renewable energy system has been developed using TRNSYS. The main goal of the study is to meet the electrical power demand of the emergency room without any shortage for a complete year in an emergency blackout condition. The emergency room has a peak electrical load of 5 kW and a yearly load of 37.23 MWh. The PV panels are mounted on a tiltable platform to improve the performance of the system. The total area of the PV panels is 300 m2, and the PEM fuel cell capacity is 5 kW. The hydrogen storage pressure is 55 bars with the capacity of 45 m3. Energy and exergy analysis is performed for the hydrogen cycle of the system for a complete year. Overall energy and exergy efficiencies of the hydrogen cycle of the system are calculated as 4.06% and 4.25%, respectively.

Proposal of a novel gravity-fed, particle-filled solar receiver

Solar Thermal Electricity power plants utilizing solid particles as heat transfer and storage media have been proposed by several research groups, with studies citing benefits of increased thermal efficiency and lower cost. Several types of solid particle receivers have been proposed, with leading designs consisting of particles falling or suspended in air. A new solid particle receiver is proposed here, consisting of a receiver fully packed with particles flowing downward with gravity. Particle flow rate is regulated with an outlet valve. This Particle-Filled receiver concept is compared to other receiver designs, and initial cold and hot experiments are conducted. Mass flux values of up to 379 kg m−2 s−1 are demonstrated, and heat transfer coefficients between 136 and 251 W m−2 K−1 are found.Solar Thermal Electricity power plants utilizing solid particles as heat transfer and storage media have been proposed by several research groups, with studies citing benefits of increased thermal efficiency and lower cost. Several types of solid particle receivers have been proposed, with leading designs consisting of particles falling or suspended in air. A new solid particle receiver is proposed here, consisting of a receiver fully packed with particles flowing downward with gravity. Particle flow rate is regulated with an outlet valve. This Particle-Filled receiver concept is compared to other receiver designs, and initial cold and hot experiments are conducted. Mass flux values of up to 379 kg m−2 s−1 are demonstrated, and heat transfer coefficients between 136 and 251 W m−2 K−1 are found.

Numerical Comparison and Sizing of Sensible and Latent Thermal Energy Storage for Compressed Air Energy Storage Systems

Compressed Air Energy Storage is a promising large-scale storage system in part because of its high power rating during discharge. But it is not the cleanest way of storing energy due to the necessity of an external heat source (typically the combustion of natural gas) to heat the air at the turbine inlet. This problem can be overcome with Thermal Energy Storage by storing the thermal energy of air at the compressor exhaust in order to be used for heating air before turbine. In this study, a numerical transient heat transfer model of Thermal Energy Storage is developed and the performance of Thermal Energy Storage is investigated based on heat storage capacity, required time to store unit amount of energy and air temperature profiles at the outlet of Thermal Energy Storage during discharge for the system. High heat storage per volume is necessary for more compact systems. Required time to store unit amount of energy is desired to be short for a fixed volume Thermal Energy Storage in order to maintain continuous operation; on the other hand, air at the outlet (turbine inlet) should be at a high temperature for the longest time possible to supply hot air to turbine. In order to investigate the effects of operating parameters, different volumes of Thermal Energy Storage tank filled with different storage mediums of various sizes are explored. Latent Heat and Sensible Heat Thermal Energy Storage systems are compared using magnesium chloride hexahydrate, paraffin, myristic acid and naphthalene as phase change materials and rock as sensible storage medium. Results show that Latent Heat Thermal Energy Storage gives a better performance than Sensible Heat Thermal Energy Storage. Among phase change materials, magnesium chloride hexahydrate provides the highest heat storage per volume. Required time to store unit amount of energy are comparable among the phase change materials. Magnesium chloride hexahydrate seems promising considering the discharge temperature profile at the Thermal Energy Storage outlet. Capsule size should be kept as small as possible which can be challenging in terms of manufacturing.Copyright

A passive cooling system proposal for multifunction and high-power displays

Flat panel displays are conventionally cooled by internal natural convection, which constrains the possible rate of heat transfer from the panel. On one hand, during the last few years, the power consumption and the related cooling requirement for 1080p displays have decreased mostly due to energy savings by the switch to LED backlighting and more efficient electronics. However, on the other hand, the required cooling rate recently started to increase with new directions in the industry such as 3D displays, and ultra-high-resolution displays (recent 4K announcements and planned introduction of 8K). In addition to these trends in display technology itself, there is also a trend to integrate consumer entertainment products into displays with the ultimate goal of designing a multifunction device replacing the TV, the media player, the PC, the game console and the sound system. Considering the increasing power requirement for higher fidelity in video processing, these multifunction devices tend to generate very high heat fluxes, which are impossible to dissipate with internal natural convection. In order to overcome this obstacle, instead of active cooling with forced convection that comes with drawbacks of noise, additional power consumption, and reduced reliability, a passive cooling system relying on external natural convection and radiation is proposed here. The proposed cooling system consists of a heat spreader flat heat pipe and aluminum plate-finned heat sink with anodized surfaces. For this system, the possible maximum heat dissipation rates from the standard size panels (in 26-70 inch range) are estimated by using our recently obtained heat transfer correlations for the natural convection from aluminum plate-finned heat sinks together with the surface-to-surface radiation. With the use of the proposed passive cooling system, the possibility of dissipating very high heat rates is demonstrated, hinting a promising green alternative to active cooling.