The cooling problem has become a serious subject in order to keep away from malfunctioning for a high performance and miniaturized electronic component. For instance, the monitor backlight LED must be cooled adequately. In this thesis, a natural convection cooling problem for the vertical channel with equally spaced heating blocks on one wall is studied by a numerical modeling to simulate a monitor backlight LED cooling. A control volume method is employed for the numerical modeling. The results of heat transfer coefficients and hot spots for various channel gap, LED spacing and Rayleigh number are presented. This study can provide design reference for related cooling problems.

Current high power LEDs are used popularly, energy saving can be achieved if the heat transfer performance of a high power LED is increased. Numerical analysis is carried out herein to study the parameters effect on the cooling performance for the heat sinks of the LED projector. The parameters include fin spacing, fin depth, fin thickness, base thickness and flow speed. The numerical results reveal that the parameters of the heat sinks significantly affects the average Nusselt Number. The results of this study can provide design references for LED projector.

The power supply for electronic devises is demanded to be lighter and smaller in nowadays market. Therefore, the cooling problem becomes the major design challenge due to reduced heat transfer area. In this thesis, a numerical computation method is employed to numerically simulate the natural convection heat transfer field for a small power supply placed on the ground or table in atmospheric conditions. The effects of parameters are studied including internal heat sink structure, shell structure, heat rate of generation, body size and ground material. The results of the present study can provide design reference.

Heat transfer and fluid flow are studied numerically for a repeating microchannel array with water as the circulating fluid. Generalized transport equations are discretized and solved in three dimensions for velocities, pressure, and temperature. The SIMPLE algorithm is used to link pressure and velocity fields, and a thermally repeated boundary condition is applied along the repeating direction to model the repeating nature of the geometry. The computational domain includes solid silicon and fluid regions. The fluid region consists of a microchannel with a hydraulic diameter of 85.58μm. Independent parameters that were varied in this study are channel aspect ratio and Reynolds number. The aspect ratios range from 0.10 to 1.0 and Reynolds number ranges from 50 to 400. A constant heat flux of 90 W/cm2 is applied to the northern face of the computational domain, which simulates thermal energy generation from an integrated circuit. A simplified model is validated against analytical fully developed flow results and a grid independence study is performed for the complete model. The numerical results for apparent friction coefficient and convective thermal resistance at the channel inlet and exit for the 0.317 aspect ratio are compared with the experimental data. The numerical results closely match the experimental data. This close matching lends credibility to this method for predicting flows and temperatures of water and the silicon substrate in microchannels. Apparent friction coefficients linearly increase with Reynolds number, which is explained by increased entry length for higher Reynolds number flows. The mean temperature of water in the microchannels also linearly increases with channel length after a short thermal entry region. Inlet and outlet thermal resistance values monotonically decrease with increasing Reynolds number and increase with increasing aspect ratio. Thermal and friction coefficient results for large aspect ratios (1 and 0.75) do not differ significantly, but results for small aspect ratios (0.1 and 0.25) notably differ from results of other aspect ratios.

Gas turbine engines are the main propulsion source for world wide aviation and are also used for power generation. Even though they rely mainly on fossil fuel and emit climate active gasses, their importance is not likely to decrease in the future. But more efficient ways of using finite resources and hence reducing emissions have to be found. Thus, the interest to improve engine efficiency is growing. Considering the efficiency of the underlying thermodynamic cycle, an increase can be achieved by raising the turbine inlet temperature or compression ratio. Due to the complex nature of the underlying flow physics, however, the aero-thermal processes are still not fully understood. For this reason, one needs to perform research at high spatial and temporal resolution, in turn creating the need for effective means of postprocessing the large amounts of data. This dissertation addresses both sides of the problem - using high-scale, high resolution simulations as well as effective post processing techniques. As an example for the latter, a temporal highly resolved data set from wall pressure measurements of a transonic compressor stage is analyzed using proper orthogonal decomposition. The underlying experiments were performed by collaborators at Technical University Darmstadt. To decompose signals into optimal orthogonal basis functions based on temporal correlations including temperature, a formal mathematical framework is developed. A method to rank the reduced order representations with respect to heat transfer effectiveness is presented. To test both methods, a Reynolds-averaged Navier-Stokes (RANS) simulation and large eddy simulation (LES) are performed on turbulent heat transfer in a square duct with one single row of pin fins. While the LES results show closer agreement to experiments, both simulations unveil flow parts that do not contribute to heat transfer augmentation and can be considered wasteful. From the most effective mode, a wall contour for the same domain is derived and applied. In the wall contoured domain, energy in wasteful modes decreased, heat transfer increased and the temperature fluctuations at the wall decreased. Another stagnating boundary layer flow is examined in a direct numerical simulation of a first stage stator vane. Elevated levels of free stream turbulence and integral length scale are generated to simulate the features of combustor exit flow. The horseshoe vortex dynamics cause an increase in endwall heat transfer upstream of the vane. The link between energy optimal orthogonal basis functions and flow structures is examined using this data and the reduced order heat transfer analysis shows high energy modes with comparatively low impact on turbulent heat transfer. The analysis further shows that there are multiple horseshoe vortices that oscillate upstream of the blade, vanish, regenerate and can also merge. There is a punctual correlation of intense vortex dynamics and peaks in the orthogonal temperature basis function. For all data considered, the link between the energy optimal orthogonal basis functions and flow structures is neither guaranteed to exist nor straightforward to establish. The orthogonal expansion locks onto flow parts with high fluctuating kinetic energy - which might or might not be the ones that are looked for. The heat transfer ranking eliminates this problem and is valid independently of how certain basis functions are interpreted.

The effects on heat transfer in a two-dimensional parallel plate channel with sixteen porous baffles in a staggered arrangement with a uniform heat flux heating applied to the top and bottom walls has been numerically investigated. Developing Flow (DF) was considered for this study. The Brinkman-Forchheimer-extended Darcy model was used for modeling the heat transfer and fluid flow through the porous baffles. The flow was assumed to be laminar. A finite volume based method in conjunction with the SIMPLEC algorithm was used to solve the model equations. Calculations were made by varying several independent parameters such as Reynolds number (Re), Darcy number ⎞ (Da), thermal conductivity ratio ⎛⎜ k e kf ⎠⎟ , baffle thickness ( * ) , non-dimensional w ⎝ baffle spacing ( * ) , and non-dimensional baffle height ( * ) . w The results of the study established that porous baffles out perform solid baffles from a pressure drop point of view. However, porous baffles under perform solid baffles from a heat transfer point of view. The ratio representing increase in heat transfer per unit increase in pumping power (heat transfer performance ratio) was found to be less than unity for all cases. Increasing the Darcy number was found to produce less desirable heat transfer enhancement ratios. Increasing the non-dimensional baffle spacing (d/w) and the baffle aspect ratio (H/w) were found to enhance heat transfer.

<p>The air gap method is a modification of the common way of building indoor walls and floors. The aim of the method is to make a construction, less fragile to water damage, with air gaps where moisture can be removed with a thermally driven air flow, caused by a heating cable. The thesis includes a number of experimental studies of this method.</p><p>Temperature and convective air flow in a vertical air gap was studied and it was noted how air flow increased with raised power of the heating cable. The air flow for one meter of wall varied between 50 m3/day (13 air changes per hour) and 140 m3/day (36 air changes per hour). The lower value was caused by a temperature difference in the range 0.2-0.3 oC. Without heating no air flow was found.</p><p>In studies of moisture and RH in wet “slab on ground” constructions, it was noted how the slab in the room with the air gap method dried to a much higher extent than the slab in the room built in an ordinary way. It was also noted that moisture was transported from the air gap in the floor and up through the air gap in the wall. In the room with the air gap construction, the RH values beneath the floor was at a lower level (and below 75 % RH) than the RH values beneath the floor of conventional construction. Mould does not grow below 75 % RH.</p><p>In the study of a flooded intermediate floor it was noted how the thermally driven convective air flow evidently speeded up drying of the construction. Mould growth was only noted in the case where the heating cables were turned off.</p> / <p>Spaltmetoden är en modifiering av det reguljära sättet av att bygga innerväggar och bjälklag. Syftet med metoden är att skapa en byggnadskonstruktion som är mindre skör med avseende på fuktskador. Detta görs med spalter där fukt kan avlägsnas genom ett termiskt drivet luftflöde som orsakas av en värmekabel. Denna avhandling innehåller ett antal experimentella studier på metoden. Spaltmetoden har studerats med avseende på 1. Samband mellan temperatur och luftflöde, 2. Uttorkning och RF nivåer i golvkonstruktioner samt 3. Översvämning av ett mellanbjälklag</p><p><strong>1. Samband mellan temperatur och luftflöde</strong></p><p>Temperatur och konvektivt luftflöde har studerats i en vertikal spalt och resultatet visar att luftflödet ökar med ökad effekt hos värmekabeln. Luftflödet i en vägg med en meters bredd varierade mellan 50 kubikmeter/dag (13 luftväxlingar per timme) och 140 kubikmeter/dag (36 luftväxlingar per timme). Det lägre flödet orsakades av en temperaturskillnad på 0,2-0,3 oC mellan luftspalt och rum. När värmekabeln var avstängd så registrerades inget luftflöde.</p><p><strong>2. Uttorkning och RF nivåer i golvkonstruktioner ovan betongplatta</strong></p><p>Detta experiment visade att fukt har transporterats från spalten i golvet genom spalten i väggen ut i rumsluften. I spaltkonstruktion var RF inuti golvkonstruktionen lägre (och understeg 75 % RF), jämfört med den konventionella konstruktionen, (mögel växer inte under 75 % RF). Det har också registrerats att betongplattan som hörde till spaltmetoden torkade ut snabbare än betongplattan som var inbyggd i ett gängse rum.</p><p><strong>3. Översvämning av ett mellanbjälklag</strong></p><p>I studien där ett mellanbjälklag blev översvämmat noterades att spaltmetoden förkortade torktiden från 21 dagar till 13 vid den fuktigaste mätpunkten. Mögelväxt noterades endast då värmekabeln hade varit frånslagen.</p><p> </p><p> </p>

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 155-168). Available also in a digital version from Dissertation Abstracts.

High Efficiency Deep Grinding (HEDG) combines high depths of cut, high grinding wheel speeds with high work piece feed rates to deliver a very high stock removal process that can produce components free of surface damage. High contact temperatures are a characteristic of the process and this produces a mass of hot grinding sparks being ejected from the grinding zone. Neat oil cutting fluids are typically used in HEDG due to their excellent lubricity, but the high grinding wheel speeds employed leads to high levels of highly volatile cutting fluid mist in the machine canopy. This mist can mix with the hot grinding sparks being ejected from the grinding zone to create a potential fire hazard. The project aim was to produce a cutting fluid application strategy for the HEDG regime, focusing on establishing the thermal characteristics of cutting fluids in order to determine the optimum cutting fluid for the HEDG process. The cutting fluid application strategy also involved investigating the optimum means by which to apply the cutting fluid, based on minimising amount of cutting fluid used in the process and in reducing the potential fire hazard. The characteristics that have a thermal impact on the grinding process are the cooling, lubrication, ignition and misting properties of the fluid. A series of tests were established to investigate these properties and therefore allow different fluids to be compared and contrasted for their suitability for the HEDG regime based. Once an optimal cutting fluid had been established, the project then investigated the optimal method of applying this fluid, with particular reference to the type and design of the nozzle used to apply the fluid to the grinding zone. As part of these trials, a series of benchmark tests were also conducted using long established cutting fluid application techniques to enable the benefits of the new strategy to be evaluated. The project concluded that high viscosity neat oil ester based cutting fluids were the best fluids to be used in the HEDG regime due to they excellent lubricity and low misting properties coupled to their relatively high resistance to ignition when compared to neat mineral oils. The studies also found that using a high viscosity ester based fluid and then applying it using a coherent jet nozzle, significant reductions in the grinding powder and specific grinding energy could be achieved whilst significantly lowering the amount of mist in the machine, thus reducing the potential fire hazard and the volume of cutting fluid used by the process.

Geological carbon dioxide (CO₂) capture and storage in geological formations has the potential to reduce anthropogenic emissions. The viability of technology depends on the long-term security of the geological CO₂ storage. Dissolution of CO₂ into the brine, resulting in stable stratification, has been identified as the key to long-term storage security. The dissolution rate determined by convection in the brine is driven by the increase of brine density with CO₂ saturation. Here we present a new analog laboratory experiment system to characterize convective dissolution in homogeneous porous medium. By understanding the relationship between dissolution and the Rayleigh number in homogeneous porous media, we can evaluate if convective dissolution occurs in the field and, in turn, to estimate the security of geological CO₂ storage fields. The large experimental assembly will allow us to quantify the relationship between convective dynamics and the Rayleigh number of the system, which could be essential to trapping process at Bravo Dome. A series of pictures with high resolution are taken to show the existence and movement of fingers of analog fluid. Also, these pictures are processed, clearly showed the concentration of analog fluid, which is essential to analyze the convective dissolution in detail. We measured the reduction in the convective flux due to hydraulic dispersion effect compared to that in homogeneous media, to determine if convective dissolution is an important trapping process at Bravo Dome. / text