The main objective of this Master Thesis project is the development of a new methodology to perform Computational Fluid Dynamics (CFD) conjugate heat transfer simulations for internal combustion engines, at the Fluid and Combustion Simulations Department (NMGD) at Scania CV AB, Södertalje, Sweden. This new method allows to overcome the drawbacks identified in the former methodology, providing the ability to use the more advanced polyhedral mesh type to generate good quality grids in complex geometries like water cooling jackets, and integrating all the different components of the engine cylinder in one unique multi-material mesh. In the method developed, these advantages can be used while optimizing the process to perform the simulations, and obtaining improved accuracy in the temperature field of engine components surrounding the water cooling jacket when compared to the experimental data from Scania CV AB tests rigs. The present work exposes the limitations encountered within the former methodology and presents a theoretical background to explain the physics involved, describing the computational tools and procedures to solve these complex fluid and thermal problems in a practical and cost-effective way, by the use of CFD.A mesh sensitivity analysis performed during this study reveals that a mesh with low y+ values, close to 1 in the water cooling jacket, is needed to obtain an accurate temperature distribution along the cylinder head, as well as to accurately identify boiling regions in the coolant domain. Another advantage of the proposed methodology is that it provides new capabilities like the implementation of thermal contact resistance in periodical contact regions of the engine components, improving the accuracy of the results in terms of temperature profiles of parts like valves, seats and guides. The results from this project are satisfactory, providing a reliable new methodology for multi-material thermal simulations, improving the efficiency of the work to be performed in the NMGD department, with a better use of the available engineering and computational resources, simplifying all the stages of multi-material projects, from the geometry preparation and meshing, to the post-processing tasks.

Buoyant flows are present in nature and also in many engineering applications,from domestic heating to the cooling of nuclear power plants. This experimental study focuses on the effects of angle of inclination on buoyancy-driven flows inside tall, rectangular, differentially-heated cavities. The objective is to produce detailed local flow and thermal data, which will advance our understanding of the flow physics and also provide CFD validation data. It considers a 2.18m × 0.52m × 0.0762m cavity, resulting in an aspect ratio of 28.6, with its two opposing long walls maintained at constant but different temperatures, while all the remaining walls are thermally insulated. The Rayleigh number, based on the temperature difference and spacing of the long sides, is 0.86 x 106 for most cases and the working fluid is air (Prandtl number0.71). Experimental data for the flow and the thermal fields, using laser Doppler anemometry and Chromel-Alumel thermocouple traverses respectively, are presented for the cavity inclined at 60° and 15° to the horizontal, for both stable (the hot surface being the upper surface) and unstable (the hot surface the lower one) orientations. The 15° stable case is investigated at a higher Rayleigh number of 1.54 x106 and some additional data for the 15° unstable case are also presented at this high value of Rayleigh number. Comparisons with the measurements of Betts and Bokhari [1], for the same cavity at the vertical position, are also included. For moderate angles of inclination, the flow is two-dimensional and the effects of inclination are primarily confined to the fluctuating fields. For large angles of inclination, the flow becomes three-dimensional. In the unstable 15° angle of inclination case, a set of four longitudinal vortices are formed over the entire length of the cavity, with four counter-rotating re-circulation cells within the cross-section parallel to the thermally active walls. The enhanced mixing at 15° unstable inclination leads to uniform temperature in the cavity core and thus only minor deviations from two dimensionality in the thermal field. A modest rise in Rayleigh number, in the 15° unstable case, does not affect the mean motion, but causes an increase in the normalised turbulence intensities, which in turn leads to a more uniform temperature within the cavity core and a practically two-dimensional thermal field. The stable 15° angle of inclination case, surprisingly, leads to the formation of two longitudinal vortices and two re-circulation cells. The lack of mixing, in the 15° stable case, leads to more noticeable three-dimensional thermal field. The thesis includes a full set of flow and thermal predictions and also spectral analysis of thermal fluctuations, which show a significant effect of the angle of inclination on both the power density level and the ranges of frequencies involved.

The introduction of phase change material fluid and nanofluid in micro-channel heat sink design can significantly increase the cooling capacity of the heat sink because of the unique features of these two kinds of fluids. To better assist the design of a high performance micro-channel heat sink using phase change fluid and nanofluid, the heat transfer enhancement mechanism behind the flow with such fluids must be completely understood. A detailed parametric study is conducted to further investigate the heat transfer enhancement of the phase change material particle suspension flow, by using the two-phase non-thermal-equilibrium model developed by Hao and Tao (2004). The parametric study is conducted under normal conditions with Reynolds numbers of Re=600-900 and phase change material particle concentrations ¡Ü0.25 , as well as extreme conditions of very low Reynolds numbers (Re < 50) and high phase change material particle concentration (0.5-0.7) slurry flow. By using the two newly-defined parameters, named effectiveness factor and performance index, respectively, it is found that there exists an optimal relation between the channel design parameters, particle volume fraction, Reynolds number, and the wall heat flux. The influence of the particle volume fraction, particle size, and the particle viscosity, to the phase change material suspension flow, are investigated and discussed. The model was validated by available experimental data. The conclusions will assist designers in making their decisions that relate to the design or selection of a micro-pump suitable for micro or mini scale heat transfer devices. To understand the heat transfer enhancement mechanism of the nanofluid flow from the particle level, the lattice Boltzmann method is used because of its mesoscopic feature and its many numerical advantages. By using a two-component lattice Boltzmann model, the heat transfer enhancement of the nanofluid is analyzed, through incorporating the different forces acting on the nanoparticles to the two-component lattice Boltzmann model. It is found that the nanofluid has better heat transfer enhancement at low Reynolds numbers, and the Brownian motion effect of the nanoparticles will be weakened by the increase of flow speed.

In the presented thesis work, meshfree method with distance fields was extended to obtain solution of nonlinear transient heat transfer problems. The thesis work involved development and implementation of numerical algorithms, data structure, and software. Numerical and computational properties of the meshfree method with distance fields were investigated. Convergence and accuracy of the methodology was validated by analytical solutions, and solutions produced by commercial FEM software (ANSYS 12.1). The research was focused on nonlinearities caused by temperature-dependent thermal conductivity. The behavior of the developed numerical algorithms was observed for both weak and strong temperature-dependency of thermal conductivity. Oseen and Newton-Kantorovich linearization techniques were applied to linearized the governing equation and boundary conditions. Results of the numerical experiments showed that the meshfree method with distance fields has the potential to produced fast accurate solutions. The method enables all prescribed boundary conditions to be satisfied exactly.

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Aluminum and aluminum-alumina powder mixtures were used to produce pyramidal fin arrays on aluminum substrates using cold spray as an additive manufacturing process. Using aluminum-alumina mixtures instead of pure aluminum powder could be seen as a cost-effective measure, preventing nozzle clogging. The fin geometries that were produced were observed using a 3D digital microscope to determine the flow passages width and fins geometric details. Heat transfer and pressure tests were carried out using different ranges of appropriate Reynolds numbers for the sought commercial application to compare each fin array and determine the effect of alumina content. It was found that the presence of alumina reduces the fins’ performance when compared to pure aluminum but that they still outperform traditional fins. Numerical simulations were performed and were used to explain the obtained experimental results. The numerical model opens up new avenues in predicting different parameters such as pressure and substrate temperature.

The present thesis has been carried out during the spring of 2017 on behalf of Gavlegårdarna AB. This is a public housing company in Gävle (Sweden) which is a large energy consumer, over 200 million SEK per year, and has the ambitious goal of reduce its energy consumption by 20 % between 2009 and 2020. Many multi-family apartment blocks were built during the "million programme" in the 60’s and 70’s when thermal comfort was the priority and not the energy saving. Nevertheless, this perspective has changed and old buildings from that time have been retrofitted lately, but there are many left still. In fact, one of these buildings will be retrofitted in the near future so a valid model is needed to study the energy saving measures to be taken. The aim of this thesis is to get through a calibration process to obtain a reliable and valid model in the building simulation program IDA ICE 4.7.1. Once this has been achieved it will be possible to carry out the building’s energy performance assessment. IDA ICE has shown some limitations in terms of thermal bridges which has accounted for almost 15 % of total transmission heat losses. For this reason, it is important to make a detailed evaluation of certain joints between elements for which heat losses are abundant. COMSOL Multiphysics® finite element software has been used to calculate these transmittances and then use them as input to IDA ICE to carry out the simulation. Through an evidence-based methodology, although with some sources of uncertainty, such as, occupants’ behaviour and air infiltration, a valid model has been obtained getting almost the same energy use for space heating than actual consumption with an error of 4% (Once the standard value of 4 kWh/m2 for the estimation of energy use in apartments' airing has been added). The following two values have been introduced to IDA ICE: household electricity and the energy required for heating the measured volume of tap water from 5 °C to 55 °C. Assuming a 16 % of heat losses in the domestic hot water circuit, which means that part of the heat coming from hot water heats up the building. This results in a lower energy supply for heating than the demanded value from IDA ICE. Main heat losses have been through transmission and infiltration or openings. Windows account 11.4 % of the building's envelope, thus the losses through the windows has supposed more than 50 % of the total transmission losses. Regarding thermal comfort, the simulation shows an average Predicted Percentage of Dissatisfied (PPD) of 12 % in the worst apartment. However, the actual value could be considerably lower since the act of airing the apartments has not been taken into account in the simulation as well as the strong sun's irradiation in summer which can be avoided by windows shading. So, it could be considered an acceptable level of discomfort. To meet the National Board of Housing Building and Planning, (Boverket) requirements for new or rehabilitated buildings, several measures should be taken to improve the average thermal transmittance and reduce the specific energy use. Among the energy saving measures it might be interesting replace the windows to 3 pane glazing, improve the ventilation system to heat recovery unit, seal the joints and intersections where thermal bridges might be or add more insulation in the building’s envelope.

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.