The research conducted at the department of Electrical Engineering of the University of South Florida campus in Tampa only covers the electrical aspect of electric drives. However, the performance of electric machinery is significantly impacted by temperature variation. The literature review shows three main control techniques in use today in electric drives namely, Scalar control, Direct Torque control and Field Oriented control. This thesis presents a temperature rise of rotor bars, stator winding, stator core and stator frame in a running three phase field-oriented controlled induction machine. A literature search shows that none of research has been carried out to investigate a thermal response of a field-oriented controlled induction motor. With this motivation, we were able to implement a lumped parameters thermal model of a three-phase field-oriented IM in MATLAB Simulink, which allows us to determine that rotor bars have the highest temperatures rising to 84 degrees Celsius. This confirms that rotors bars are the hottest part of a running IM as stipulated in literature.

Friction stir welding (FSW) has been studied extensively for the past two decades. Thermal modeling has been of particular interest, as the quality of the weld is dependent upon the temperature history of the work piece during the process. Since direct temperature measurements of the welded zone are not possible, an analytical model was developed to predict the temperature in this area. This model requires parameters that cannot be easily experimentally determined, so a best fit for these parameters was acquired via regression analysis by comparing the model to experimental data acquired outside of the weld zone. The model was then validated by comparing it to additional temperature data, not including the data used for regression analysis.

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Electric motors for vehicle applications are required to have high efficiency and small size and weight. Accurately modeling the thermal properties of an electric motor is critical to properly sizing the motor. Improving the cooling of the motor windings allows for a more efficient and power-dense motor. There are a variety of methods for predicting motor temperatures, however this paper discusses the advantages and accuracy of using a nodal lumped thermal model. Both commercially available and proprietary motor thermal modeling software are evaluated and compared. Thermal improvements based on the model in both contact interfaces and winding encapsulant are evaluated, showing motor improvements in the ability to handle heat losses of approximately forty percent greater than the baseline, resulting in either higher power or lower motor temperatures for the same package size. / Master of Science

We have created a three-dimensional, implicit finite difference model that can accurately calculate temperatures within the bulk of a sample during a friction stir fabrication process. The model was written in Wolfram Mathematica® 7 for Students, and allows for time-efficient calculation of thermal profiles. The non-dimensionality of the model allows for accurate refinement of the temporospatial mesh, and provides portability across material types. The model provides insight as to the mechanism of heat generation by qualifying the fraction of mechanical energy converted to thermal energy for different material types and sample geometries. Finally, our model gives an understanding of the effects of the heat transfer at the boundaries of the workpiece and suggests a backside heat loss localized at the center of the tool due to a decrease in thermal contact resistance. We have explored the effects of processing parameters on the performance of the friction stir fabrication process. The process has four stages; tool insertion, warm-up, bead formation, and steady-state translation. The tool insertion phase is characterized by a rapid increase in system horsepower requirements. During the warm-up phase, the mechanical energy of the rotating tip is converted to thermal energy. Once enough thermal energy has been transferred to the workpiece, the volume between the tip and the workpiece is filled by feedstock material. Finally, the tool is translated under relatively steady-state conditions. The success or failure of the process is dependent on adequate material delivery to the system. The horsepower requirements of the process depend on the material type and the rate of material delivery. We have explored the effect of processing parameters on the microstructure of the processed samples. Optical microscopy shows that the stratification of layers within the weld and the depth of the weld are both dependent on the processing parameters. EBSD analysis coupled with Vicker's microhardness measurements of the processed pieces show that the grain size within the weld nugget is constant over the range of processing parameters available to the system. Data also show that pressure and heat inherent in friction stir processing of strain-hardened Al5083 counteract strengthening of the temper of the alloy. / Ph. D.

Improving the climate system of cars is important since it is the largest auxiliary load in a standard vehicle with an increase of fuel consumption by up to 20%. In Electric Vehicles (EV) the range of the car is more limited than in a fossil fueled car; furthermore there is a limited waste heat available from the EV, approximately 2-3kW at 40oC for heating and defogging in winter. The goals of this report have been part of an existing European project (ICE) where the climate system of an electric minibus is being investigated. The specific objectives of this project were to develop a radiation model and integrate it in the existing thermal model of the cabin, validating the new model with existing experimental data, including the thermal model in the overall model of the complete vehicle and to use the existing AC-model to optimize the control with the aim of decreasing the energy consumption maintaining thermal comfort inside the cabin. The radiation model uses total radiation on a horizontal surface in order to calculate the radiation hitting the different parts of the car body and windows, finally the total radiative power entering the minibus is calculated. After including these calculations into the thermal model it could be seen that the results from the model in terms of cabin temperatures fit the experimental values surprisingly well. The control of the AC-system was optimized for a hot and sunny summer day in Italy which resulted in the AC-system working very hard following that the best control strategy was to reduce only the speed of the compressor in order to save energy. Calculations show that in the Normal European Driving Cycle (NEDC) the potential energy savings of following this control strategy can result in an energy saving of the AC-system by up to 27% compared to an unregulated case, with a maintained thermal comfort resulting in 4,2% increase in autonomy.

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The thermal regime of a gearbox is of considerable importance to its performance. Several significant gearbox parameters, such as the efficiency and fatigue life of its components, are temperature dependent. It is thus important to be able to determine the temperatures of the gearbox components during operation, but they are difficult to measure experimentally. A simulation model capable of predicting these temperatures would therefore be a valuable tool. The objective of this master’s thesis was to create a model capable of simulating the thermal regime of a truck gearbox during operation. To do this, mechanical losses in the gearbox, heat exchange with the surroundings, as well as heat transfer between components had to be accounted for. The model was created using the 1D simulation software LMS Imagine.Lab Amesim 14.0, and is based on a combination of mechanical and thermal networks. Details of the mechanical and thermal interactions between components are calculated using empirical and analytical formulas for mechanical losses and heat transfer. The result of the thesis is a model which can be used to simulate either real or idealised load cases, from which temperatures of gear wheels, shafts, bearings, housing and gearbox oil may be studied, as well as gearbox losses and heat transfer. Comparisons between simulated and measured gearbox efficiencies show good correlation. It is also shown that the model can predict oil temperatures which agree with in-vehicle measurements. Due to a lack of measurement data, most simulated component temperatures cannot be compared to measured values. However, temperature measurements performed for one of the gear wheels indicate that the model can be used to predict their temperature. In order to demonstrate the capabilities of the model, example results from both real and idealised load cases are presented.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Steve Eckels / A new human thermal model was developed to predict the thermal responses of human body in various environments. The new model was based on Smith's model, which employed finite element method to discretize the human body. The body parts in our new model were not limited to the cylindrical shape as in Smith's model, but subjected to arbitrary shapes. Therefore, the new model is capable of dealing with more complicated shapes of the human body. Steady-state and transient temperatures of fifteen body parts were calculated for three environments: cold, neutral, and warm. Our results were compared with the data from Zhang's experimental research on the human subjects. For all three conditions, our results showed better agreement with experimental data than Smith's results did. The maximal deviation is 1ºC for neutral and warm condition; for cold condition, a maximal deviation of 3.5ºC is reported at hand. The comparison indicated that our new model could provide a more accurate prediction on the body temperatures. Follow-up experiments were conducted to investigate the local and overall heat transfer from a moving cylinder in air flow. This study was expected to provide the local convective heat transfer coefficients of the human body to our new human thermal model to simulate moving humans. An experiment of a stationary cylinder in cross flow was performed to verify the accuracy and consistency of our system. Then, the experiment of a transverse oscillating cylinder in cross flow was conducted, with a oscillation frequency of 0.15 and Strouhal number of 0.3 to 1.5, depending on wind velocity. The overall Nusselt number (Nu) of the oscillating cylinder remained unaffected, compared to the stationary cylinder. This observation showed agreement with previous studies. The pivot experiment was performed to investigate swinging movement of human arms. The cylinder was positioned axially in cross flow, and reciprocated on a fixed point between horizontal and vertical positions under three wind speeds and two oscillating frequencies. The results showed that the overall Nu was between the Nu at horizontal and vertical positions in stationary state. A correlation was presented to predict the Nu of pivotal moving cylinder by using stationary Nu at horizontal and vertical positions. The correlation was proved to be valid ( error less than 5%) within the range of conditions in our experiment.

Fuel cells are predicted to be the power delivery devices of the future. They have many advantages such as the wide fuel selection, high energy density, high efficiency and an inherent safety which explains the immense interest in this power source. The need for advanced designs has been limited by the lack of understanding of the transport processes inside the fuel cell stack. The reactant gases undergo many processes in a fuel cell that cannot be observed. Some of these processes include convective and diffusional mass transport through various types of materials, phase change and chemical reaction. In order to optimize these variables, an accurate mathematical model can provide a valuable tool to gain insight into the processes that are occurring. The goal of this dissertation is to develop a mathematical model for polymer electrolyte-based fuel cells to help contribute to a better understanding of fuel cell mass, heat and charge transport phenomena, to ultimately design more efficient fuel cells. The model is a two-phase, transient mathematical model created with MATLAB. The model was created by using each fuel cell layer as a control volume. In addition, each fuel cell layer was further divided into the number of nodes that the user inputs into the model. Transient heat and mass transfer equations were created for each node. The catalyst layers were modeled using porous electrode equations and the Butler-Volmer equation. The membrane model used Fick's law of diffusion and a set of empirical relations for water uptake and conductivity. Additional work performed for this dissertation includes a mathematical model for predicting bolt torque, and the design and fabrication of four fuel cell stacks ranging in size from macro to micro scale for model validation. The work performed in this dissertation will help improve the designs of polymer electrolyte fuel cells, and other polymer membrane-based fuel cells (such as direct methanol fuel cells) in the future.