Spray cooling has proven to be efficient in managing thermal load in high power applications. Reliability of electronic products relies on the thermal management and understanding of heat transfer mechanisms including those related to spray cooling. However, to date, several of the key heat transfer mechanisms are still not well understood. An alternative approach for improving the heat transfer performance is to change the film dynamics through surface modification. The main goal of this study is to understand the effects of nano-scale features on flat heater surfaces subjected to spray cooling and to determine the major factors in droplet impingement cooling to estimate their effects in the spray cooling system. Single droplet stream and simultaneous triple droplet stream with two different stream spacings (500 μm and 2000 μm), experiments have been performed to understand the droplet-surface interactions relevant to spray cooling systems. Experiments have been conducted on nano-structured surfaces as well as on flat (smooth) surfaces. It is observed that nano-structured surfaces result in lower minimum wall temperatures, better heat transfer performance, and more uniform temperature distribution. A new variable, effective thermal diameter (de), was defined based on the radial temperature profiles inside the impact zone to quantify the effects of the nano-structured surface in droplet cooling. Results indicate that larger effective cooling area can be achieved using nano-structured surface in the single droplet stream experiments. In triple stream experiments, nano-structured surface also showed an enhanced heat transfer. In single stream experiments, larger outer ring structures (i.e. larger outer diameters) in the impact crater were observed on the nano-structured surfaces which can be used to explain enhanced heat transfer performance. Smaller stream spacing in triple stream experiments reveal that the outer ring structure is disrupted resulting in lower heat transfer. Lower static contact angle on the nano-structured surface has been observed, which implies that changes in surface properties result in enhanced film dynamics and better heat transfer behavior. The results and conclusions of this study should be useful for understanding the physics of spray cooling and in the design of better spray cooling systems.

In recent years, the electronic chip is continuously developing in turning high performance. This trend urges the heat sink of electronic chip to become gradually important, and then that will develop many type of heat sink, which is water-cooling system. Therefore, the purpose of this paper is designing a high efficiency water-cooling element (WCE). The present study mainly aims at three points to bring up: (1) The different type chamber make use of the CFD package software FLUENT to study the pressure drop, velocity field and turbulent intensity deposition. (2) The different plank thickness, thermal conductivity and convection heat transfer coefficient use finite difference method to solve heat diffusion equation, and to confer thermal resistance value. (3) Then, machined this designed WCE and then measured its thermal resistance value. The results show: (1) The pressure drop main effect parameter is inlet velocity. (2) The thermal resistance value main effect parameter is convection heat transfer coefficient. (3) The plank thickness is inverse proportion relation with thermal resistance value. (4) The surface temperature range and mean surface temperature should become reference index in heat sink developmental process. (5) The cooling performance of Type D WCE is optimum in this paper. (6) The design is cross groove on convection surface, which should reduce thermal resistance value.

This thesis presents the experiment study results on the local heat transfer coefficients for air jet impinging on a flat rectangle board. A transient thermochromatic liquid crystal technique is used to visualize and record isotherms on an impingement surface. The parameter studied include Reynolds number¡]Re=108,142,170¡^,jet height from the rectangular board¡]H/D=0.086,0.172,0.259,0.345,0.431,0.52¡^, and size of outlet¡]B/D=1.45,1.86,2.41¡^. The correlation of average Nusselt number is curve-fitted with Re,H/D and B/D . According to the present study,heat transfer is best when the Reynolds number is large,the jet height is small,and the outlet area is large .

IC test socket and socket pogo pin are the major cost of consumption parts in IC testing house. Test yield is the key point to determine the profit for IC testing house. When the processing speed of CPU (Central Processing Unit) and GPU (Graphic Processing Unit) are boosting, heat generation and power dissipation became a serious problem for IC testing house. Most package type of CPU and GPU are packed by Flip-Chip BGA type. High temperature will melt the solder ball and cause test socket pogo pin to damage. The excellent cooling capability of impinging jet had been proofed by many literatures in past. In this article, impinging jet applied to IC test handler contact chuck is investigated. The contact chuck had been redesigned with thermal solution and uses a rectangle hot plate to simulate the thermal status of IC testing. A circular air jet impinged on the rectangle hot plate from the topside of contact chuck. Out flow open area, open area on the wall location and the distance between jet nozzle and hot plate are major parameters of this heat transfer problem. Parameter ¡§Z¡¨ is the distance between jet nozzle and hot plate; ¡§D¡¨ is the diameter of circular air jet. As shown in the result, ratio of Z/D and the location of out flow open area on the wall is obvious on heat transfer capability for redesigned contact chuck. Taguchi method and analysis of variance (ANOVA) method help to clarify the weighting of influence. The optimum Z/D is 0.5 and the optimum location of out flow open area is at dual side corner. Heat transfer capability can be improved approach to 70% after optimization. Width and height of out flow open area only made about 5% impact on heat transfer capability.

In this study, cooling of small form factor computer is numerically investigated. The numerical model is analyzed using a commercial computational fluid dynamics software Icepak&trade / . The effects of grid selection, discretization schemes and turbulence models are discussed and presented. In addition, physical phenomena like recirculation and relaminarization are addressed briefly. For a comparison with the computational fluid dynamics results, an experiment is conducted and some temperature measurements are obtained from critical locations inside the chassis.The computational results were found to be in good agreement with the experimental ones.

This thesis investigates temperature distribution and hence heat dissipation of buried power cables. Heat dissipation analysis of a simple practical application and the parameters that affect the heat dissipation are discussed. In analyzing temperature distribution in the surrounding medium , a computer program is developed which is based on gauss-seidel iteration technique. This method is applied to a sample test system and heat dissipation curves for several parameters are obtained. Also, current carrying capacities of various types of cables are determined using dissipated heat values.

Heat pipe is a passive two phase device capable of transferring large rates of heat with a minimal temperature drop. It is a sealed tube with a wick structure lined in it and with a working fluid inside the tube. It consists of three parts: an evaporator, a condenser and an adiabatic section. The heat pipes are widely used in electronics cooling and spacecraft applications. Although they can transfer large rate of heat in a short range, they have operating limits, namely: the capillary limit, the viscous limit, the entrainment limit, the sonic limit and the boiling limit. These limits determine the heat transfer capacity of the heat pipe. The properties of the working fluid, the structure of the wick, the orientation of the pipe, the length and the diameter of the tube etc. are the parameters that affect the limits. In this study, an analytical 1-D heat pipe model is formed and a computer code is prepared in order to analyze the effects of the parameters on the heat transfer capacity of a heat pipe. Water, Ammonia and Mercury are investigated as working fluids for different operating temperature ranges. The software is tested for a typical application for each working fluid.

Heat transfer of two-dimensional, hydrodynamically developed, thermally developing, single phase, laminar flow inside a microtube is studied analytically with constant wall temperature thermal boundary condition. The flow is assumed to be incompressible and thermo-physical properties of the fluid are assumed to be constant. Viscous dissipation and the axial conduction are included in the analysis. Rarefaction effect is imposed to the problem via velocity slip and temperature jump boundary conditions for the slip flow regime. The temperature distribution is determined by solving the energy equation together with the fully developed velocity profile. Analytical solutions are obtained for the temperature distribution and local and fully developed Nusselt number in terms of dimensionless parameters / Peclet number, Knudsen number, Brinkman number, and the parameter &amp / #954 / . The results are verified with the well-known ones from literature.

In this study, effect of surface roughness on convective heat transfer and fluid flow in two dimensional parallel plate microchannels is analyzed by numerically. For this purpose, single-phase, developing, laminar fluid flow at steady state and in the slip flow regime is considered. The continuity, momentum, and energy equations for Newtonian fluids are solved numerically for constant wall temperature boundary condition. Slip velocity and temperature jump at wall boundaries are imposed to observe the rarefaction effect. Effect of axial conduction inside the fluid and viscous dissipation also considered separately. Roughness elements on the surfaces are simulated by triangular geometrical obstructions. Then, the effect of these roughness elements on the velocity field and Nusselt number are compared to the results obtained from the analyses of flows in microchannels with smooth surfaces. It is found that increasing surface roughness reduces the heat transfer at continuum conditions. However in slip flow regime, increase in Nusselt number with increasing roughness height is observed. Moreover, this increase is found to be more obvious at low rarefied flows. It is also found that presence of axial conduction and viscous dissipation has increasing effect on heat transfer in smooth and rough channels.

Performance of a refrigerator can be characterized with its ability to maintain a preset low temperature by spending the least amount of electricity. It is important to understand natural convection inside a refrigerator for optimizing its design for performance. Computational Fluid Dynamics (CFD) together with experiments is a very powerful tool for visualizing flow and temperature fields that are essential for understanding a phenomenon that involves both fluid and heat flow. In this aspect, simulations are performed for compartment and total refrigerator models using the package program Fluent which is based on finite volume method. An experimental study is performed to determine the constant wall temperature boundary conditions for the numerical models. Effect of radiation is also investigated by comparing the numerical study of a different full refrigerator model with a similar one in literature. While evaluating the radiation effect, convection boundary condition is selected by defining overall heat transfer coefficient between the ambient room air at a constant temperature and the inner surfaces of the walls. Based on assumptions, related heat transfer analyses are done using compartment and total refrigerator model analyses. Performing CFD simulations of a refrigerator cabinet for visualizing the flow and temperature fields which is the aim of the study is achieved and some observations that can be useful in design optimization are made.