The advantages of cold-formed thin-walled steel studs are many and their applications in building constructions continue to grow. They are used as load-bearing members. An example is lightweight wall panel assemblies which consist of channel steel studs with gypsum plasterboard layers attached to the two flanges, often with interior insulation. At present, expensive fire tests or advanced numerical modelling methods are necessary in order to discover the fire resistance of such wall assemblies. For common practice this is not effective and a simplified method, suitable for use in daily design, is necessary. The aim of this research is to develop such simplified methods. The first main objective of this study is to develop a simple approach to calculate the temperature distributions in the steel section, in particular the temperatures on both the exposed and unexposed sides when the panel is exposed to fire exposure from one side. These two temperatures are the most influential factors in the fire resistance of this type of wall assembly. The proposed method calculates the average temperatures in the flanges of the steel section and assumes that the temperature in the web is linear. The proposed method is based on a simple heat balance analysis for a few nodes representing the key components of the wall panel. The thermal resistance of these nodes are obtained by the weighted average of thermal resistances in an effective width of the panel within which heat transfer in the panel width direction is assumed to occur. The proposed method has been extensively validated by comparison with numerical parametric studies. In order to calculate the ultimate capacity of steel studs, the traditional method is by using effective width. However, this method is now being questioned as it considers elements of section in isolation and does not consider interaction between the elements. In addition, this method is not appropriate to be extended to steel studs under fire conditions. The cross-section under fire conditions has non-uniform temperature distribution which results in the non-uniform distribution of mechanical properties. Using an effective width method to deal with this problem will require many assumptions whose accuracy is uncertain. Recently, the direct strength method (DSM) has been developed and its accuracy for ambient applications has been comprehensively validated. This method calculates cross-sectional plastic resistance and elastic critical loads for local, distortional and global buckling modes with the aid of simple computer programs. The elastic and plastic resistances are then combined to give the ultimate resistance of the structure using interaction equations. This method is suited to steel studs with non-uniform temperature distribution in the cross-section. The second main objective of this study is to extend the direct strength method for application to thin-walled steel studs having non-uniform elevated temperature distributions in the cross-section. It has been found that the DSM concept is applicable, but the interaction equations should be modified to allow for the effects of elevated temperature (non-uniform temperature distribution and changes in stress-strain relationships). Also the effects of thermal bowing should be included when calculating the plastic resistance and the elastic buckling loads of the cross-section. This research has proposed new interaction equations and has developed design tools. By comparing the results of the proposed method with validated Finite Element simulations over a very large range of parametric studies, the proposed method has been demonstrated to be valid. The validation studies include both standard and parametric fire exposures and are generally applicable.

An investigation into the thermo-mechanical closure effect when a fluid leaks through a crack is presented here. The extended finite element method is the modelling scheme adopted for this, and the application of heat flux and pressure jump conditions along the crack is one of the novel contributions of this work. By modelling the fluid as one dimensional steady state and obtaining a heat transfer coefficient, it has been shown here that coupling the fluid with the structure is possible all within a single element. Convergence studies done with analytical models as a benchmark demonstrate the accuracy of the new method. Simulations are performed with the new element for conditions seen in both gas cooled and water cooled reactors. Significant crack closure is observed when the bulk fluid temperature is 20oC hotter than the structure. It was also found that the amount of closure due to crack wall heating varies depending on the external boundary conditions, this is quantified in the thesis.

With the current development of the computer industry, CFD simulations have become the widespread standard in the industry, forming a baseline tool for numerous designs and safety procedures. This extensive dependence on the CFD codes rather than experiments raises the issue of the reliability of the results obtained from these codes. This thesis is intended to study the dependence of the CFD results on the grid types, numerical schemes and turbulence models. Additionally, comparisons between a general purpose commercial code STAR-CCM+ and a specialized code FDS are presented towards the end of this thesis. To study the numerical errors introduced by the grids and schemes, a laminar flow induced by natural convection inside a square cavity was considered first. Using Richardson’s extrapolation, a grid independent solution was calculated and compared with the results obtained from different grid types and schemes for Rayleigh (Ra) numbers , and . Comparison plots showed a higher dependence of the accuracy of the results on the cell shapes along with the order of the scheme and the cell size. Additionally, with the same cavity a grid dependence study for the and model has been done at .To test the reliability of the Quasi-DNS performed by an Unstructured Finite Volume (FV) CFD code, Turbulent Kinetic Energy (TKE) budgets should be calculated. User subroutines were developed to calculate the budgets of the TKE and to verify the user subroutines, prior to coaxial cylinder test case, a Q-DNS of the channel flow at has been performed using different grid configurations and numerical schemes. Results obtained from the Q-DNS of the channel flow on the polyhedral cells with the bounded central differencing scheme were found to be in good agreement with the reference DNS data. After the validation test case, a Q-DNS of the buoyancy driven turbulent flow inside a horizontal annular cavity at a high Rayleigh number, Ra = 1.18x109 with outer to inner cylinder ratio of 4.85 was carried out using a commercial code. Comparisons of Q-DNS results with low-Re URANS models, and model, showed that the latter models are able to capture the general flow features but fail to predict the large unsteadiness and high turbulence levels in the plume. However, local heat transfer rates along the inner and outer cylinder walls are on average of acceptable accuracy for engineering purposes. Finally, a full scale industrial test case of a fire in a compartment has been simulated. Both URANS ( model) and LES (Smagorinsky model) approaches are applied to model the turbulence with and without incorporating the combustion modelling. A comparison of the CFD results with the experimental data showed that for building fire simulations, accuracy of the results is more sensitive to the correlations used in the combustion modelling rather than the type of the turbulence model.

In a typical modern gas turbine engine, the nozzle guide vanes (NGVs) endure the highest operating temperatures. There exists a great drive in the turbine industry to increase the turbine inlet temperatures leading to higher thermal efficiency. This has led to a drive to increase turbine vane- and blade-cooling. Numerical modelling has to a large degree replaced empirical codes and models as the main research tool regarding simulation of blade-cooling. Outdated empirical solvers have made way for commercial CFD solvers such as FLUENT, a Reynolds-averaged Navier-Stokes (RANS) solver. One such empirical solver, TACT1, has until recently still proved to yield acceptable results. A comparative study has been done using the T56 NGV blade to establish the differences, advantages and disadvantages of these 2 codes. The engine and subsequent NGV blade were analysed using NREC, STAN5, LOSS3D and TACT1. RANS simulations were found to be computationally expensive. TACT1 yielded acceptable results compared with computational cost. For modern-day designers, RANS would be the preferred tool. / Dissertation (MEng)--University of Pretoria, 2009. / Mechanical and Aeronautical Engineering / unrestricted

Extensive work is reported in literature on the reduction of iron oxides with carbonaceous reductants. Most of this work considered isothermal reaction of the material mixture, although as shown in some studies, isothermal reaction conditions are not often the norm because of sample size and heating arrangement in the experiment. In industrial processes, such as the rotary hearth type processes and the IFCON® process for iron ore reduction, the norm is non-isothermal reaction. Simulation of industrial processes should take non-isothermal reaction into account if the heat transfer effects within the process are to be investigated. To avoid the complications of coal volatiles in the experimental set-up, few studies were done with coal as reductant. The primary aim of the work presented here is to quantify radiation heat transfer to the surface of an iron ore and coal mixture heated uni-directionally from the sample surface to show the importance of heat transfer in the IFCON® process. Secondary aim of this work are to show the effects of layer thickness, coal volatiles, phase chemistry and particle size in this reaction system. The experimental set-up consists of a tube furnace modified to transport the sample into and out of the experimental tube furnace heating zone under a protected atmosphere, whilst the product gas is analysed throughout the experiment by quadropole mass spectrometer. The sample surface temperature, heating zone temperatures and material bed temperatures were measured throughout the experiment. A sample cutter-splitter was developed to divide the reacted sample into three horizontal segments for chemical analyses. The sample surface temperature and the heating zone temperatures were used as inputs to a radiation network calculation to quantify radiation heat transferred to the sample surface. The radiation network calculation was calibrated against heat-mass balance calculations for pre-reduced ore and graphite samples reacted at furnace temperatures of 1300, 1400 and 1500°C. The results show that radiative and conduction heat transfer control prevails for 16 mm to 40 mm material layers heated uni-directionally from the material layer surface. It is shown that coal volatiles contribute to reduction in the stagnant material layer. Also, smaller particle sizes result in increased reaction rates because of a decrease in the diffusion limited effects which were seen in reaction of the base size of coal and ore particles. / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2009. / Materials Science and Metallurgical Engineering / unrestricted

The demand for smaller but more powerful electronic components is ever increasing. This demand puts a strain on engineers to produce optimal cooling designs for these electronic components. One method for cooling these electronic components is with heat sinks which effectively increase the surface area available for extracting the heat from the electronic components. Computational Fluid Dynamics (CFD) software is sometimes used to aid in the design process, but CFD simulations are computationally expensive and take long to complete. This causes the design engineer to test only a few proposed designs based on his/her experience and select the design that performs the best out of the tested designs, which might not be the optimum. The temperature distribution inside the heat sink can be solved relatively quickly with the diffusion equation, but the flow around the heat sink complicates the CFD simulation and increases the solving time significantly. Therefore, applications have been developed where the interaction between the heat sink and the flow around the heat sink is replaced by heat transfer coefficients. These coefficients are calculated from correlated equations which contain the flow properties. The flow properties are extracted from a flow network solver, which solves the flow around the heat sink. This procedure results in less expensive simulations, which can be used together with an optimisation procedure to develop an optimum cooling design. In this dissertation, a correlation for the contraction heat transfer coefficients of rectangular pin fin heat sinks was developed. A methodology was developed where consecutive regression lines were fitted to a large set of data extracted from numerous CFD simulations. The combination of these regression lines formed the basis of the correlation, which was divided into two correlations; one for laminar flow and another for turbulent flow. The correlations were tested against CFD simulations as well as experimental data. The results indicate that these correlations can be effectively used to calculate the contraction heat transfer coefficients on pin fin heat sinks. / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

Heat exchangers have a wide range of applications and engineers need accurate correlations to optimise the design of these heat exchangers. During the design process, the best compromise between high heat transfer coefficients and relatively low pressure drops is usually in the transitional flow regime. Limited research has been done on tube flow in the transitional flow regime. These studies considered either fully developed flow, or average measurements of developing flow across a tube length. No research has been done with the focus on developing flow in smooth tubes in the transitional flow regime. Therefore, the purpose of this study was to experimentally investigate the heat transfer and pressure drop characteristics of developing flow in the transitional flow regime. An experimental set-up was designed, built and validated against literature. Heat transfer and pressure drop measurements were taken at Reynolds numbers between 500 and 10 000 at three different heat fluxes (6.5, 8.0 and 9.5 kW/m2). A total of 398 mass flow rate measurements, 19 158 temperature measurements and 370 pressure drop measurements were taken. Water was used as the test fluid and the Prandtl number ranged between 3 and 7. The test section was a smooth circular tube and had an inner diameter and length of 11.52 mm and 2.03 m, respectively. An uncertainty analysis showed that the uncertainties of the Nusselt numbers and Colburn j-factors varied between 4% and 5% while the friction factor uncertainties varied between 1% and 17%. Five different flow regimes (laminar, developing laminar, transitional, low-Reynolds-number-end and turbulent) were identified in the first part of the tube during the experiments and nomenclature was developed to more clearly identify the boundaries of the different flow regimes. The developing laminar regime was unique to developing flow and decreased along the tube length. Both the start and end of transition were delayed along the tube length and the width of the transition region decreased slightly. This is in contrast with the results obtained in literature where the effect of the non-dimensional distance from the inlet on fully developed flow in the transition region was investigated. Transition was also slightly delayed with increasing heat flux, but secondary flow effects had no significant influence on the width of the transition region. The relationship between heat transfer and pressure drop was investigated and correlations were developed to predict the Nusselt number as a function of friction factor, Reynolds number and Prandtl number in the laminar, transitional, low-Reynolds-number-end and turbulent flow regimes. Overall, it can be concluded that the heat transfer characteristics of developing and fully developed flow differ significantly and more work needs to be done to fully understand the fundamentals before the heat transfer and pressure drop characteristics are fully understood. / Dissertation (MEng)--University of Pretoria, 2015. / Mechanical and Aeronautical Engineering / Unrestricted

Orientadores: Antonio Carlos Bannwart, Marcelo Moreira Ganzarolli / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica e Instituto de Geociências / Made available in DSpace on 2018-08-22T03:35:14Z (GMT). No. of bitstreams: 1 Betonico_GustavodeCarvalho_M.pdf: 2382106 bytes, checksum: a84e8f76b2a2dcf28078dd9283ecef59 (MD5) Previous issue date: 2013 / Resumo: Neste trabalho foi desenvolvido um modelo para determinação da temperatura do motor de uma bomba centrífuga submersa (BCS) sob condições variáveis de vazão e carga. Este leva em consideração o comportamento acoplado entre o motor, a bomba e o sistema de produção. Assim, dada uma frequência ajustada no variador de frequência, a temperatura do motor é determinada como resultado do equilíbrio entre a produção de calor, calculada a partir da potência que a bomba demanda do motor, e a extração do calor, calculada a partir da vazão. Neste modelo, considera-se a BCS instalada num módulo de bombeamento submarino localizado perto do poço produtor. Foi estudada a transferência de calor por convecção no módulo de bombeio, onde um escoamento descendente ocorre no anular externo entre o revestimento e a camisa de refrigeração e um fluxo ascendente ocorre no anular interno entre a camisa de refrigeração e o motor. Um estudo de transferência de calor por convecção foi elaborado comparando modelos baseados no perfil de temperatura plenamente desenvolvido com modelos que consideram o desenvolvimento da camada limite térmica. Uma vez que o único ponto de medição da temperatura se localiza na extremidade inferior do enrolamento de estator, o modelo desenvolvido neste trabalho também determina a distribuição de temperatura do motor. Um estudo de caso foi realizado com diversas viscosidades de óleo e frações de água. Os resultados mostram a elevação da temperatura do motor, quando sua velocidade é continuamente aumentada. Também se mostrou que, negligenciar os efeitos do desenvolvimento da camada limite térmica, quando ocorre escoamento laminar, pode resultar num motor superaquecido, onde na verdade, a temperatura máxima do motor é muito menor do que o seu limite superior. Modelos baseados no perfil temperatura plenamente desenvolvidos sofrem de imprecisão, quando utilizados em aplicações de fluidos viscosos, devido ao grande comprimento entrada térmica / Abstract: A model to predict the motor temperature of an electrical submersible pump, under variable conditions of flow rate and loading, has been developed. This model takes into account the coupled behavior between motor, pump and production system. Thus, given a frequency set in the variable speed drive, the motor temperature is determined as a result of the equilibrium between the heat generation, calculated from the power that the pump demands from the motor, and the heat extraction, calculated from the flow rate. In this model, the electrical submersible pump is supposed to be installed in a subsea pumping module located near the producer well. It has been studied the convective heat transfer in the pumping module, where a downward flow occurs in the external annulus between the casing and the shroud, and an upward flow happens in the internal annulus between the shroud and the motor. A convective heat transfer study has been run comparing models based on fully developed temperature profile and models that consider the development of the thermal boundary layer. Since the only point of temperature measurement is located at the lower end of the stator winding, the model developed in this work also determines the temperature distribution of the motor. A case study has been run with several oil viscosities and water cut. The results show a motor temperature rise when motor speed is continuously increased. It is also showed that, when laminar flow occurs, neglecting the effect of the thermal boundary layer development may result in an overheated motor prediction where actually, motor maximum temperature is much smaller than its upper limit. Fully developed temperature profile models suffer of inaccuracy when used in viscous fluid applications, due to its big thermal entry length / Mestrado / Explotação / Mestre em Ciências e Engenharia de Petróleo

Orientador: Carlos Alberto Carrasco Altemani / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecânica / Made available in DSpace on 2018-08-24T09:07:23Z (GMT). No. of bitstreams: 1 Loiola_BrunaRafaella_M.pdf: 2801156 bytes, checksum: 0bbef2296c5a3a938f63b6246554ab2d (MD5) Previous issue date: 2013 / Resumo: A transferência de calor conjugada por convecção forçada-condução de dois aquecedores protuberantes montados na parede inferior (substrato) de um duto retangular foi investigada através de medidas experimentais em laboratório. Potência elétrica era dissipada em resistências embutidas nos aquecedores feitos de alumínio, que eram resfriados em regime permanente por um escoamento forçado de ar no duto. Cada aquecedor transferia calor por convecção diretamente das suas superfícies em contato com o escoamento e por condução para a placa do substrato através da interface comum. Esta condução de calor espalhava na placa do substrato e era transferida por convecção da placa para o escoamento de ar no duto. O resfriamento conjugado dos aquecedores na placa de substrato foi descrito por uma matriz de coeficientes conjugados obtidos por meio de testes experimentais realizados com um aquecedor ativo por vez, em uma faixa do número de Reynolds do escoamento entre 1600 e 6400. Foram utilizadas duas montagens experimentais praticamente idênticas, uma com a placa do substrato de acrílico e a outra, de alumínio. O número de Nusselt adiabático, que é um descritor invariante do processo convectivo de troca de calor, também foi avaliado nos testes com o substrato de acrílico. Os coeficientes conjugados obtidos nestes testes foram então utilizados para prever as temperaturas dos aquecedores em testes adicionais com os dois simultaneamente ativos, sob condições variadas de escoamento e aquecimento. A concordância dessas temperaturas indicou que esses coeficientes são descritores invariantes do resfriamento conjugado dos aquecedores discretos no duto. Simulações numéricas do escoamento e da transferência de calor no duto considerado foram efetuadas com o pacote computacional PHOENICS em um domínio tridimensional semelhante ao duto experimental. Os resultados numéricos obtidos foram comparados com as medidas experimentais / Abstract: Conjugate heat transfer by forced convection-conduction of two protruding heaters mounted on the lower wall (substrate) of a rectangular duct was investigated through experiments in laboratory. Electric power dissipation in the Aluminum heaters¿ embedded resistances was transferred under steady state conditions to forced airflow in the duct. Heat losses from each heater included direct convection from its surfaces in contact with the airflow and conduction to the substrate plate through their common interface. This heat conduction was spread in the substrate plate and eventually transferred by convection from the plate to the airflow in the duct. The heaters¿ conjugate cooling was described by a conjugate matrix with coefficients obtained from experimental tests with a single active heater at a time, in the range of the airflow Reynolds number from 1,600 to 6,400. Two almost identical assemblies were used, one with a Plexiglas plate and the other with Aluminum. The adiabatic Nusselt number, an invariant descriptor of the convective heat transfer, was also evaluated in the tests with the Plexiglas plate. The conjugate coefficients were used to predict the heaters¿ temperatures from additional tests with both active heaters, for arbitrary airflow rates and heaters¿ power dissipation. An agreement of these temperatures indicated that the conjugate coefficients are invariant descriptors of their conjugate cooling. Numerical CFD simulations were performed using the PHOENICS software in a three dimensional domain similar to the experimental assembly. The numerical results were compared to those of the experiments / Mestrado / Termica e Fluidos / Mestra em Engenharia Mecânica

Recent technological developments have made it possible to design various microdevices where fluid flow and heat transfer are involved. For the proper design of such systems, the governing physics needs to be investigated. Due to the difficulty to study complex geometries in micro scales using experimental techniques, computational tools are developed to analyze and simulate flow and heat transfer in microgeometries. However, conventional numerical methods using the Navier-Stokes equations fail to predict some aspects of microflows such as nonlinear pressure distribution, increase mass flow rate, slip flow and temperature jump at the solid boundaries. This necessitates the development of new computational methods which depend on the kinetic theory that are both accurate and computationally efficient. In this study, lattice Boltzmann method (LBM) was used to investigate the flow and heat transfer in micro sized geometries. The LBM depends on the Boltzmann equation which is valid in the whole rarefaction regime that can be observed in micro flows. Results were obtained for isothermal channel flows at Knudsen numbers higher than 0.01 at different pressure ratios. LBM solutions for micro-Couette and micro-Poiseuille flow were found to be in good agreement with the analytical solutions valid in the slip flow regime (0.01 < Kn < 0.1) and direct simulation Monte Carlo solutions that are valid in the transition regime (0.1 < Kn < 10) for pressure distribution and velocity field. The isothermal LBM was further extended to simulate flows including heat transfer. The method was first validated for continuum channel flows with and without constrictions by comparing the thermal LBM results against accurate solutions obtained from analytical equations and finite element method. Finally, the capability of thermal LBM was improved by adding the effect of rarefaction and the method was used to analyze the behavior of gas flow in microchannels. The major finding of this research is that, the newly developed particle-based method described here can be used as an alternative numerical tool in order to study non-continuum effects observed in micro-electro-mechanical-systems (MEMS).