Friction Stir Welding(FSW) experiments are conducted using 6061-T6 aluminum as specimens. The temperatures at different distances from the center of the joint are measured. Curve fitting analyses are used to predict the temperature distribution and calculate the central temperature of the joint, proceeding by measuring temperature. A second order curve is found to better fit the experiment values by the least square method.

The need to simultaneously estimate thermal properties stems from the desire to analyze complex structures which do not have the flexibility to be experimentally tested in multiple configurations. In order to produce reliable and accurate thermal property estimates, the experiments must be carefully developed. A carefully designed experiment maximizes the sensitivity of the temperature distribution with respect to the unknown thermal properties, as well as providing minimum correlation between the estimated properties. Two objectives were set forth in this research. First to apply existing predicted optimal experimental designs developed by Moncman (1994) to simultaneously estimate the two-dimensional thermal properties of the carbon-fiber/epoxy-matrix composite, AS4/3502. Due to the anisotropic nature of the composite, the effective thermal conductivities through the thickness and in the plane of the composite needed to be estimated along with the volumetric heat capacity. After simultaneously estimating the properties, the second objective was to verify that the predicted optimal designs provided the most accurate estimates. In accomplishing both objectives, the research plan developed in three distinct stages. As a starting point, the one-dimensional analysis was performed to gain confidence in the experimental setup and procedure. Due to the successful estimation of the one-dimensional properties, the experiments were expanded into a two-dimensional analysis. This analysis attempted to simultaneously estimate all three thermal properties from one optimal, transient, temperature measurement. But due to correlation problems invoked by experimental errors, it was unsuccessful. Therefore, the research focused on the estimation of the in-plane thermal conductivity and the volumetric heat capacity. After successfully estimating the properties, the optimal designs were verified through additional testing with perturbations applied to the optimal settings. Complete success was not accomplished in this study due to partially satisfying the first objective. All three thermal properties were estimated for the anisotropic composite but due to near correlation between the thermal conductivities, they could not be determined from a single, optimal experiment. Therefore in an attempt to uncorrelate the thermal properties it is recommended that the experiments be performed with multiple sensors. In addition, alternative boundary conditions should be considered on their ability to provide more sensitive information on the thermal properties and practicality to experimentally maintain. The second objective, verifying the optimal designs, was completely successful in demonstrating that the optimal parameter settings did produce the most accurate thermal property estimates. Therefore, an optimally designed experiment using multiple sensors should allow for the accurate and simultaneous estimation of the thermal properties for complex structures. / Master of Science

Thesis (MEng)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Rubber is the main component of the pneumatic tire. When rubber is put under cyclic loading, like when a tire is rolled, heat is generated and stored in the rubber, due to hysteresis. Heat stored in the tire is increased by factors like under-inflation, overloading, speeding and defects in the tire. The heat causes high temperatures in the tire due to the poor thermal conductivity of rubber. When the temperature in the rubber increases to 185 °C, pyrolysis and thermo-oxidation starts and can cause the tire to eventually explode. A numerical model of a rolling passenger vehicle tire was developed to calculate the temperature distribution inside the tire and analyse the effect of different operating conditions on the temperature. Operating conditions include loading, inflation pressure, rolling velocity and ambient temperature. The tire was modelled by a single rubber type, using the Mooney-Rivlin material model. The bead wire was modelled using an isotropic material model, while the body and steel cord plies were modelled as rebars. The cavity, used to inflate the tire, included the pressure increase due to the volume change, when the tire is loaded. The numerical model was validated using experimental data from tests done on an actual tire. These tests included deformation and contact stress analysis, as well as surface temperature measurements. Numerical results showed an increase in temperature when the load, rolling velocity and the ambient temperature were increased, as well as when the inflation pressure was decreased. The trends of the numerical data matched the trends of the experimental data. However, the values of the numerical model were not consistent with the experimental data due to material properties from literature being used to model the tire. / AFRIKAANSE OPSOMMING: Rubber is die hoofkomponent in die pneumatiese band. As rubber onder ’n sikliese las geplaas word, soos wanneer ’n band rol, word hitte gegenereer en in die rubber gestoor as gevolg van histerese. Die hitte wat in die band gestoor word, word verhoog deur faktore soos lae inflasiedruk, hoë las, hoë rol snelhede en gebreke in die band. Die hitte veroorsaak hoë temperature in die band weens die swak termiese geleiding van rubber. As die temperatuur in die band hoër as 185 °C raak, vind piroliese en termo-oksidasie plaas en die band kan uiteindelik ontplof. ’n Numeriese model van ’n passasiersmotorband is ontwikkel om die temperatuurverspreiding te bepaal, asook om die effek van verskillende werkstoestande op die temperatuur te analiseer. Die band is gemodelleer met een tipe rubber en die Mooney-Rivlin materiaal-model is gebruik om die rubber te beskryf. Die spanrand van die band is deur ’n isotropiese materiaalmodel gemodelleer, terwyl die hoof- en staalkoordlae as bewapening gemodelleer is. Die holte wat gebruik word om die band op te blaas, neem die druk toename as gevolg van die verandering in volume in ag wanneer die band belas word. Die numeriese model was bekragtig met eksperimentele data wat deur toetse op ’n werklike band onttrek is. Die toetse sluit die volgende in: vervormingen kontakspanninganalises, asook temperature wat op die oppervlak van die band gemeet is. Die numeriese resultate toon ’n toename in temperatuur wanneer die las, rolsnelheid en omgewingstemperatuur verhoog word, asook waneer die inflasiedruk verlaag word. Die numeriese model se tendense stem ooreen met die eksperimentele data, maar die waardes van die numeriese model is nie in ooreenstemmig met die eksperimentele data nie. Die verskil is as gevolg van die materiaaleienskappe wat uit die literatuur geneem is.

A feedwater heater is a typical component in power plants which increases the cycle efficiency. Over the last decade, renewable energies have significantly developed and been employed in the power grid. However, weather conditions are inconsistent and therefore produce variable power. Fossil fuel power stations are often required to supplement the variable renewable energies, which increased the rate of power cycling to an unforeseeable extent over the past decade. Power cycling results in changes in the flow rate, pressure, and temperature of a feedwater heater’s inlet flows. In a tubesheet-type feedwater heater, these transients induce cycling stress in the tubesheet and failures due to thermal fatigue occur. The header-type feedwater is currently employed in high pressure applications as it is more resistant to thermal fatigue compared to the tubesheet-type. However, the tubesheet-type is more cost effective to construct and maintain. It would be advantageous if the cyclic thermal stresses in the tubesheet can be better analysed and alleviated to support the use of the tubesheet-type. A detailed transient temperature distribution of the tubesheet is required to understand the thermal fatigue. Normally, engineers opt towards a full CFD to obtain such results. However, the size and complexity of a feedwater heater is immense and cannot be simulated practically solely using CFD spatial elements. This study developed a multiscale approach that thermally couples 1D network elements, CFD spatial elements, and macroscopic heat transfer correlations to reduce the computational expense substantially. The combination of the various selected techniques and the specific application of this methodology is unique. This approach is capable of obtaining the detailed transient temperature distribution of the tubesheet in a reasonable time, as well as include the effects of the upstream and downstream components within the network model. The methodology was implemented using Flownex and Ansys Fluent for the 1D network and CFD solvers, respectively. The internal tube flow was modelled using 1D network elements, while the steam was modelled with CFD. Thermal discretisation, mapping, and convergence were considered to create a robust methodology not limited to feedwater heaters only. Additionally, a method was developed to analyse flow maldistribution in tube-bundles using the coupled 1D-3D approach. The implementation of the methodology consists of two parts, of which one is for development purposes, and the other serves as a demonstration. The development was done on a simple TEMA-FU heat exchanger which is representative of a feedwater heater. The methodology was tested by varying the primary fluid’s flow rates, changing the fluid media, and conducting transient simulations. The temperature distributions obtained were compared against a full CFD model and corresponded very well with errors less than 4%. A reduction in computational time of more than 40% was achieved but is highly dependent on the specific problem. Improvements to be made in future studies include the accuracy of the laminar case method and the stability of the flow maldistribution algorithm. The methodology was demonstrated by applying it to an existing industrial feedwater heater. No plant data was available to use for input conditions and therefore were assumed. The steam in the DSH was modelled using 3D CFD elements and the tube flow with 1D network elements. The condensing zone’s heat transfer was approximated using an empirical correlation. A steady state case was simulated and the outlet temperatures corresponded well with the manufacturer’s data. The temperature distribution of the tubesheet and surrounding solids were obtained. Finally, assumed sinusoidal transient perturbations to the inlet conditions were imposed. It was evident that the thermal gradients of both sides of the tubesheet were misaligned which highlights the thermal lag and inertia that cause differential temperatures. The 1D-CFD methodology was developed successfully with results that proved to correspond well, for a wide range of conditions, to full CFD. The methodology was applied and can be, in future work, validated with experimental results or extended by modelling upstream and downstream components in the network solver. / Dissertation (MEng (Mechanical Engineering))--University of Pretoria, 2019. / Mechanical and Aeronautical Engineering / MEng (Mechanical Engineering) / Unrestricted

Machine components made of steel are subjected to heat treatment processes for improving mechanical properties in order to enhance product life and is usually done by quenching. During quenching, heat is transferred rapidly from the hot metal component to the quenchant and that rapid temperature drop induces phase transformation in the metal component. As a result, quenching generates some residual stresses and deformations in the material. Therefore, to estimate the temperature distribution, residual stress, and deformation computationally; three-dimensional finite element models are developed for two different steel components – a spur gear and a circular tube by a static and a dynamic quenching analyses, respectively. The time-varying nodal temperature distributions in both models are observed and the critical regions are identified. The variations of stress and deformation after quenching along different pathways for both models are studied. The convergence for both models is checked and validations of the models are done.

Proton exchange membrane fuel cell (PEMFC) is a potential alternative energy conversion device for stationary and automotive applications. Wide commercialization of PEMFC depends on progress that can be achieved to enhance its reliability and durability along with cost reduction. It is desirable to operate the PEMFC at uniform local current density and temperature distributions over the surface of the membrane electrode assembly (MEA). Non-uniform distributions of both current and temperature over the MEA could result in poor reactant and catalyst utilization as well as overall cell performance degradation. Local current distribution in the PEMFC electrodes are closely related to operating conditions, but it is also affected by the organization of the reactant flow arrangements in PEMFCs. Reactant depletion and water formation along the flow channel leads to current variation from the channel inlet to the exit, which leads to non-uniformity of local electrochemical reaction activity, and degradation of the cell performance. Flow arrangements between the anode and cathode streams, such as co-, counter- and cross- flow can exacerbate the effect of the non-uniformity considerably, producing complex current distribution patterns over the electrode surfaces. Thus, understanding of the local current density and its spatial characteristics, as well as the temperature distributions under different physical and operating conditions, is crucially important in order to develop optimum design and operational strategies. Despite the importance of the influence of the flow arrangement on the local current and temperature distributions under various operating conditions, few systematic studies have been conducted experimentally to investigate this effect. In this research, an experimental setup with special PEMFC test cells are designed and fabricated in-house, in order to conduct in-situ mapping of the local current and temperature distributions over the electrode surfaces. A segmented flow field plate and the printed circuit board (PCB) technique is used to measure the current distribution in a single PEMFC. In situ, nondestructive temperature measurements are conducted using thermocouples to determine the actual temperature distribution. Experimental studies have been conducted to investigate the effect of different flow arrangements between the anode and cathode (co-, counter-, and cross- flow) on the local current density distribution over the MEA surface. Furthermore, local current distribution has been characterized for PEMFCs under various operating conditions such as reactant stoichiometry ratios, reactant backpressure, cell temperature, cell potentials, and relative humidity for each one of the reactant flow arrangements. The dynamic characteristics of the local current in PEMFC under different operating conditions also have been studied. Temperature distributions along the parallel and serpentine flow channels in PEMFs under various operating conditions are also investigated. All independent tests are conducted to identify and optimize the key design and operational parameters for both local current and temperature distributions. It has been found that the local current density distribution is strongly affected by the flow arrangement between the anode and cathode streams and the key operating conditions. It has also been observed that the counter-flow arrangement generates the most uniform distribution for the current density, whereas the co-flow arrangement results in a considerable variation in the current density from the reactant gas stream inlet to the exit. Low stoichiometry ratio of hydrogen at the anode side has a predominant effect on the current distribution and cell performance. Further, it has been found that the dynamic characteristics and the degree of fluctuation of local current density inside PEMFC are strongly influenced by the crucial operating conditions. In-situ, nondestructive temperature measurements indicate that the temperature distribution inside the PEMFC is strongly sensitive to the cell’s current density. The temperature distribution inside the PEMFC seems to be virtually uniform at low current density, while the temperature variation increases up to 2 oC at the high current density. Finally, the present work contribution related to the local current and temperature distributions is required to understand the effect of each individual or even several operating parameters combined together on the local current and temperature distributions. This will help to develop an optimum design, which leads to enhancing the reliability and durability in operational PEMFCs.

Analysis of the drilling fluid temperature in a circulating well is the main objective of this study. Initially, an analytical temperature distribution model, which utilizes basic energy conservation principle, is presented for this purpose. A computer program is written in order to easily implement this model to different cases. Variables that have significant effect on temperature profile are observed. Since the verification of the analytical model is not probable for many cases, a computer program (ANSYS) that uses finite element method is employed to simulate different well conditions. Three different wells were modeled by using rectangular FLOTRAN CFD element that has four nodes. Maximum drilling fluid temperature data corresponding to significant variables is collectedfrom these models. This data is then used to develop an empirical correlation in order to determine maximum drilling fluid temperature. The proposed empirical correlation can estimate the temperature distribution within the wellbore with an average error of less than 16%, and maximum drilling fluid temperature with an average error of less than 7 %.

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.

Solid oxide fuel cell (SOFC) is a device that converts the chemical energy of the fuel into the electricity by the chemical reactions at high temperatures (600-1000oC). Heat is also produced besides the electricity as a result of the electrochemical reactions. Heat produced in the electrochemical reactions causes the thermal stresses, which is one of the most important problems of the SOFC systems. Another important problem of SOFCs is the low fuel utilization ratio. In this study, the effect of the flow arrangement on the temperature distribution, which causes the thermal stresses, and the method to increase the fuel utilization, is investigated. An SOFC single cell experimental setup is developed for Cross-Flow arrangement design. This setup and experimental conditions are modeled with Fluent&reg / . The experimental results are used in order to validate and verify the model. The model results are found to capture with the experimental results closely. The validated model is used as a reference to develop the models for different flow arrangements and to investigate the effect of the flow arrangement on the temperature distribution. A method to increase the SOFC fuel utilization ratio is suggested. Models for different flow arrangements are developed and the simulation results are compared to determine the most advantageous arrangement.

Proton exchange membrane fuel cell (PEMFC) is a potential alternative energy conversion device for stationary and automotive applications. Wide commercialization of PEMFC depends on progress that can be achieved to enhance its reliability and durability along with cost reduction. It is desirable to operate the PEMFC at uniform local current density and temperature distributions over the surface of the membrane electrode assembly (MEA). Non-uniform distributions of both current and temperature over the MEA could result in poor reactant and catalyst utilization as well as overall cell performance degradation. Local current distribution in the PEMFC electrodes are closely related to operating conditions, but it is also affected by the organization of the reactant flow arrangements in PEMFCs. Reactant depletion and water formation along the flow channel leads to current variation from the channel inlet to the exit, which leads to non-uniformity of local electrochemical reaction activity, and degradation of the cell performance. Flow arrangements between the anode and cathode streams, such as co-, counter- and cross- flow can exacerbate the effect of the non-uniformity considerably, producing complex current distribution patterns over the electrode surfaces. Thus, understanding of the local current density and its spatial characteristics, as well as the temperature distributions under different physical and operating conditions, is crucially important in order to develop optimum design and operational strategies. Despite the importance of the influence of the flow arrangement on the local current and temperature distributions under various operating conditions, few systematic studies have been conducted experimentally to investigate this effect. In this research, an experimental setup with special PEMFC test cells are designed and fabricated in-house, in order to conduct in-situ mapping of the local current and temperature distributions over the electrode surfaces. A segmented flow field plate and the printed circuit board (PCB) technique is used to measure the current distribution in a single PEMFC. In situ, nondestructive temperature measurements are conducted using thermocouples to determine the actual temperature distribution. Experimental studies have been conducted to investigate the effect of different flow arrangements between the anode and cathode (co-, counter-, and cross- flow) on the local current density distribution over the MEA surface. Furthermore, local current distribution has been characterized for PEMFCs under various operating conditions such as reactant stoichiometry ratios, reactant backpressure, cell temperature, cell potentials, and relative humidity for each one of the reactant flow arrangements. The dynamic characteristics of the local current in PEMFC under different operating conditions also have been studied. Temperature distributions along the parallel and serpentine flow channels in PEMFs under various operating conditions are also investigated. All independent tests are conducted to identify and optimize the key design and operational parameters for both local current and temperature distributions. It has been found that the local current density distribution is strongly affected by the flow arrangement between the anode and cathode streams and the key operating conditions. It has also been observed that the counter-flow arrangement generates the most uniform distribution for the current density, whereas the co-flow arrangement results in a considerable variation in the current density from the reactant gas stream inlet to the exit. Low stoichiometry ratio of hydrogen at the anode side has a predominant effect on the current distribution and cell performance. Further, it has been found that the dynamic characteristics and the degree of fluctuation of local current density inside PEMFC are strongly influenced by the crucial operating conditions. In-situ, nondestructive temperature measurements indicate that the temperature distribution inside the PEMFC is strongly sensitive to the cell’s current density. The temperature distribution inside the PEMFC seems to be virtually uniform at low current density, while the temperature variation increases up to 2 oC at the high current density. Finally, the present work contribution related to the local current and temperature distributions is required to understand the effect of each individual or even several operating parameters combined together on the local current and temperature distributions. This will help to develop an optimum design, which leads to enhancing the reliability and durability in operational PEMFCs.