Electric and hybrid electric vehicles are gaining momentum as a sustainable alternative to conventional combustion based transportation. The operating temperature of the vehicle will vary significantly over the vehicle lifetime and this variance in operating temperature will strongly impact the performance, driving range, and durability of batteries used in the vehicles. In the first part of this thesis, an experimental facility is developed to accurately quantify the effects of battery operating temperature on discharge characteristics through precise control of the battery operating temperatures, utilizing a water-ethylene glycol solution in a constant temperature thermal bath. A prismatic 20Ah LiFEPO4 battery from A123 is tested using the developed method, and temperature measurements on the battery throughout discharge show a maximum variation of 0.3°C temporally and 0.4°C spatially at a 3C discharge rate, in contrast to 13.1°C temperature change temporally and 4.3°C spatially when using the conventional air convection temperature control method under the same test conditions. A comparison of battery discharge curves using the two methods show that the reduction in spatial and temporal temperature change in the battery has a large effect on the battery discharge characteristics. The developed method of battery temperature control yields more accurate battery discharge characterization due to both the elimination of state-of-charge drift caused by spatial variations in battery temperature, and inaccurate discharge characteristics due to battery heat up at various discharge and ambient conditions. Battery discharge characterization performed using the developed method of temperature control exhibits a reduction in battery capacity of 95% when the operating temperature is decreased from 20°C to -10°C at 3C discharge rate. A reduction of 35% in battery capacity is observed when for the same temperature decrease at a 0.2C discharge rate. The observed effect of operating temperature on the capacity of the tested battery highlights the importance of an effective thermal management system, the design of which requires accurate knowledge of the heat generation characteristics of the battery under various discharge rates and operating temperatures. In the second part of this thesis, a calorimeter capable of measuring the heat generation rates of a prismatic battery is developed and verified by using a controllable electric heater. The heat generation rate of a prismatic A123 LiFePO4 battery is measured for discharge rates ranging from 0.25C to 3C and operating temperature ranging from -10°C to 40°C. Results show that the heat generation rates of Lithium ion batteries are greatly affected by both battery operating temperature and discharge rate. At low rates of discharge the heat generation is not significant, even becoming endothermic at the battery operating temperatures of 30°C and 40°C. Heat of mixing is observed to be a non-negligible component of total heat generation at discharge rates as low as 0.25C for all tested battery operating temperatures. A double plateau in battery discharge curve is observed for operating temperatures of 30°C and 40°C. The developed experimental facility can be used for the measurement of heat generation for any prismatic battery, regardless of chemistries. The characterization of heat generated by the battery under various discharge rates and operating temperatures can be used to verify the accuracy of battery heat generation models currently used, and for the design of an effective thermal management system for electric and hybrid electric vehicles in the automotive industry.

Electric and hybrid electric vehicles are gaining momentum as a sustainable alternative to conventional combustion based transportation. The operating temperature of the vehicle will vary significantly over the vehicle lifetime and this variance in operating temperature will strongly impact the performance, driving range, and durability of batteries used in the vehicles. In the first part of this thesis, an experimental facility is developed to accurately quantify the effects of battery operating temperature on discharge characteristics through precise control of the battery operating temperatures, utilizing a water-ethylene glycol solution in a constant temperature thermal bath. A prismatic 20Ah LiFEPO4 battery from A123 is tested using the developed method, and temperature measurements on the battery throughout discharge show a maximum variation of 0.3°C temporally and 0.4°C spatially at a 3C discharge rate, in contrast to 13.1°C temperature change temporally and 4.3°C spatially when using the conventional air convection temperature control method under the same test conditions. A comparison of battery discharge curves using the two methods show that the reduction in spatial and temporal temperature change in the battery has a large effect on the battery discharge characteristics. The developed method of battery temperature control yields more accurate battery discharge characterization due to both the elimination of state-of-charge drift caused by spatial variations in battery temperature, and inaccurate discharge characteristics due to battery heat up at various discharge and ambient conditions. Battery discharge characterization performed using the developed method of temperature control exhibits a reduction in battery capacity of 95% when the operating temperature is decreased from 20°C to -10°C at 3C discharge rate. A reduction of 35% in battery capacity is observed when for the same temperature decrease at a 0.2C discharge rate. The observed effect of operating temperature on the capacity of the tested battery highlights the importance of an effective thermal management system, the design of which requires accurate knowledge of the heat generation characteristics of the battery under various discharge rates and operating temperatures. In the second part of this thesis, a calorimeter capable of measuring the heat generation rates of a prismatic battery is developed and verified by using a controllable electric heater. The heat generation rate of a prismatic A123 LiFePO4 battery is measured for discharge rates ranging from 0.25C to 3C and operating temperature ranging from -10°C to 40°C. Results show that the heat generation rates of Lithium ion batteries are greatly affected by both battery operating temperature and discharge rate. At low rates of discharge the heat generation is not significant, even becoming endothermic at the battery operating temperatures of 30°C and 40°C. Heat of mixing is observed to be a non-negligible component of total heat generation at discharge rates as low as 0.25C for all tested battery operating temperatures. A double plateau in battery discharge curve is observed for operating temperatures of 30°C and 40°C. The developed experimental facility can be used for the measurement of heat generation for any prismatic battery, regardless of chemistries. The characterization of heat generated by the battery under various discharge rates and operating temperatures can be used to verify the accuracy of battery heat generation models currently used, and for the design of an effective thermal management system for electric and hybrid electric vehicles in the automotive industry.

A major challenge in the development of next generation electric and hybrid vehicle technology is the control and management of heat generation and operating temperatures. Vehicle performance, reliability and ultimately consumer market adoption are integrally dependent on successful battery thermal management designs. It will be shown that in the absence of active cooling, surface temperatures of operating lithium-ion batteries can reach as high as 50 °C, within 5 °C of the maximum safe operating temperature. Even in the presence of active cooling, surface temperatures greater than 45 °C are attainable. It is thus of paramount importance to electric vehicle and battery thermal management designers to quantify the effect of temperature and discharge rate on heat generation, energy output, and temperature response of operating lithium-ion batteries. This work presents a purely experimental thermal characterization of thermo-physical properties and operating behavior of a lithium-ion battery utilizing a promising electrode material, LiFePO4, in a prismatic pouch configuration. Crucial to thermal modeling is accurate thermo-physical property input. Thermal resistance measurements were made using specially constructed battery samples. The thru-plane thermal conductivity of LiFePO4 positive electrode and negative electrode materials was found to be 1.79 ± 0.18 W/m°C and 1.17 ± 0.12 W/m°C respectively. The emissivity of the outer pouch was evaluated to enable accurate IR temperature detection and found to be 0.86. Charge-discharge testing was performed to enable thermal management design solutions. Heat generated by the battery along with surface temperature and heat flux at distributed locations was measured using a purpose built apparatus containing cold plates supplied by a controlled cooling system. Heat flux measurements were consistently recorded at values approximately 400% higher at locations near the external tabs compared to measurements taken a relatively short distance down the battery surface. The highest heat flux recorded was 3112 W/m2 near the negative electrode during a 4C discharge at 5 °C operating temperature. Total heat generated during a 4C discharge nearly doubled when operating temperature was decreased from 35 °C to 5 °C, illustrating a strong dependence of heat generation mechanisms on temperature. Peak heat generation rates followed the same trend and the maximum rate of 90.7 W occurred near the end of 5 °C, 4C discharge rate operation. As a result, the maximum value of total heat generated was 41.34 kJ during the same discharge conditions. The effect of increasing discharge rate from 1C to 4C caused heat generation to double for all operating temperatures due to the increased ohmic heating. Heat generation was highest where the thermal gradient was largest. The largest gradient, near negative electrode current collector to external tab connection and was evaluated using IR thermography to be 0.632 °C/mm during 4C discharge with passive room temperature natural convection air cooling. Battery designs should utilize a greater connection thickness to minimize both electrical resistance and current density which both drive the dominant mode of heat generation, ohmic heating. Otherwise cooling solutions should be concentrated on this region to minimize the temperature gradient on the battery.

The main purpose of this study was to examine the difference in intrapulpal temperature (IPT) comparing a “grinding” and a “cutting” technique during single crown preparation. The difference in preparation time between the two techniques was also examined. A thermocouple was placed in the pulp chamber of 20 extracted human permanent molar teeth. The teeth were placed in a silicone model. The model was immersed in a thermostatically controlled water bath with a temperature of 37 degrees centigrade (°C), and with a water level reaching the cementoenamel junction at the teeth. For both preparation techniques an electric handpiece (NSK Ti-Max Ti85L 1:5) was used. A diamond bur was used for the “grinding” and a carbide bur for the “cutting” technique. The IPT during preparation was measured with a K-thermocouple connected to Testo 176 T4 temperature data logger. There was a significant difference in IPT rise between the two techniques for preparing the teeth. The “cutting” technique showed a higher mean temperature, 31.9 °C, compared to the “grinding”, 29.5 °C (p<0.05). Neither reached the critical value of 5.5 °C IPT increase. The “grinding” technique averaged a longer preparation time of 106 seconds per tooth than the “cutting” technique (p<0.05). Our study shows that the “cutting” technique results in a higher mean temperature but that both preparation techniques can be considered as safe in regard to IPT during single crown preparation as long as sufficient water cooling is applied.

Commercially available polycrystalline Ni (Ni200; grain size: 32 μm) and electrodeposited nanocrystalline Ni (grain size: 57 nm), Ni-2.6%Fe (grain size: 25 nm) and Ni-8.5%Fe (grain size: 20 nm) were analyzed for the phenomena of stress-induced heat generation and strain localization during plastic deformation at room temperature (i.e. 250C). Tensile specimens according to ASTM E8 standard dimensions were tested at strain rates of 10-2/s and 10-1/s, respectively, to record the amount of heat dissipated and the change of localized strain using a high resolution infrared (IR) detector and digital image correlation (DIC) camera, respectively. Results have shown that the maximum temperatures that were recorded in nanocrystalline Ni and Ni-Fe alloys were at least 300C lower than the onset temperatures for subgrain coalescence previously measured through differential scanning calorimetry. It can be concluded that thermally activated grain growth during tensile testing of nanocrystalline Ni and Ni-Fe alloys is not likely to occur.

Commercially available polycrystalline Ni (Ni200; grain size: 32 μm) and electrodeposited nanocrystalline Ni (grain size: 57 nm), Ni-2.6%Fe (grain size: 25 nm) and Ni-8.5%Fe (grain size: 20 nm) were analyzed for the phenomena of stress-induced heat generation and strain localization during plastic deformation at room temperature (i.e. 250C). Tensile specimens according to ASTM E8 standard dimensions were tested at strain rates of 10-2/s and 10-1/s, respectively, to record the amount of heat dissipated and the change of localized strain using a high resolution infrared (IR) detector and digital image correlation (DIC) camera, respectively. Results have shown that the maximum temperatures that were recorded in nanocrystalline Ni and Ni-Fe alloys were at least 300C lower than the onset temperatures for subgrain coalescence previously measured through differential scanning calorimetry. It can be concluded that thermally activated grain growth during tensile testing of nanocrystalline Ni and Ni-Fe alloys is not likely to occur.

In order to simulate the histories of temperature distributions and plastic flow of the dwell phase during a friction stir welding process, the Newton-Raphson method is used to solve the simultaneous equations of energy and momentum in the cylindrical-coordinate system. Comparing the simulation with the results of experiment, results show that the contact condition between the tool and the workpiece is at pure sliding without plastic flow at the beginning of the dwell phase until the temperature rises to about 300¢XC at the depth of 1.5 mm. In this period, the heat generation comes from the sliding friction between two surfaces. After the plastic flow occurs, the heat generation rises rapidly, and then decreases to a saturated value so that the temperature rise also achieves a constant value. Thermal expansion of the workpiece will increase the plunge force, so that the heat generation and the temperature raise increase. At the steady state condition, with increasing sticking proportion, the heat generation and the temperature quickly achieve a saturated value. For the steady-state condition, results show that the speed of plastic flow and shear strain rate increase with increasing rotational speed. The control of the contact state variable can effectively describe the heat generation and the distribution of plastic flow in different contact conditions. Comparing the simulation with the results of experiment, the contact condition can be identified.

Dental implants are an effective alternative for the replacement of missing teeth. The success of the implant depends on how well a bone heals around the implant, a process known as osseointegration. However, excessive heat generated during the bone drilling will cause cell death and may prevent osseointegration of the implant, resulting in early failure. There are many factors which contribute to the heat generation during drilling. Experiments were carried out to investigate the affect of variable drilling factors on heat generation during drilling operation. Natural bone is not an ideal material for such research, as it varies widely in density and other parameters of interest.. It would be desirable to have a more uniform and consistent material to use in such studies. However, such a material must be similar to bone to allow the results to be extrapolated to the clinical situation. The current study describes and validates a model for use in such studies. Polymethylmethacrylate (PMMA) is the material chosen for our studies. A theoretical model was developed to study the effect of different drilling parameters on temperature rise during drilling operations. Comparison of observed results obtained from experiments was made with the results from theoretical study. Comparison of results for PMMA and human bone are also shown explaining how PMMA material can be substituted for human bone. The results suggest that the PMMA model is an acceptable surrogate for bone in such studies.

O presente trabalho trata da modelagem da condução de calor transiente com geração de calor em meios heterogêneos, e tem o objetivo de desenvolver um modelo multiescala adequado a esse fenômeno. Já existem modelos multiescala na literatura relacionados ao problema proposto, e que são válidos para os seguintes casos: (a) o elemento de volume representativo tem tamanho desprezível quando comparado ao comprimento característico macroscópico (e como consequência, a microescala tem inércia térmica desprezível); ou (b) a geração de calor é homogênea na microescala. Por outro lado, o modelo proposto nesta tese, o qual é desenvolvido utilizando uma descrição variacional do problema, pode ser aplicado a elementos de volume representativos finitos e em condições em que a geração de calor é heterogênea na microescala. A discretização temporal (diferenças finitas) e as discretizações espaciais na microescala e na macroescala (método dos elementos finitos) são apresentadas em detalhes, juntamente com os algoritmos necessários para implementar a solução do problema. Nesta tese são apresentados casos numéricos simples, procurando verificar não só o modelo teórico multiescala desenvolvido, mas também a implementação feita. Para tanto, são analisados, por exemplo, (a) casos em que considera-se a microescala um material homogêneo, tornando possível a comparação da solução multiescala com a solução convencional (uma única escala) pelo método dos elementos finitos, e (b) um caso em um material heterogêneo para o qual a solução completa, isto é, modelando diretamente os constituintes no corpo macroscópico, é obtida, tornando possível a comparação com a solução multiescala. A solução na microescala para vários casos analisados nesta tese sofre grande influência da inércia térmica da microescala. Para demonstrar o potencial de aplicação do modelo multiescala, simula-se a cura de um elastômero carregado com negro de fumo. Embora a simulação demonstre que a inércia térmica não precise ser considerada para esse caso em particular, a aplicação da presente metodologia torna possível modelar a cura do elastômero diretamente sobre a microescala, uma abordagem até então não utilizada no contexto de métodos multiescala. Essa metodologia abre a possibilidade para futuros aperfeiçoamentos da modelagem do estado de cura. / This work deals with the modeling of transient heat conduction with heat generation in heterogeneous media, and its objective is to develop a proper multiscale model for this phenomenon. There already exist multiscale models in the literature related to this proposed problem, and which are valid for the following cases: (a) the representative volume element has a negligible size when compared to the characteristic macroscopic size (and, as a consequence, the microscale has a negligible thermal inertia); or (b) the heat generation is homogeneous at the microscale. On the other hand, the model proposed in this thesis, which is developed using a variational description of the problem, can be applied to finite representative volume elements and in conditions in which the heat generation is heterogeneous at the microscale. The time discretization (finite difference) and the space discretizations at both the microscale and the macroscale (finite element method) are presented in details, together with the algorithms needed for implementing the solution of the problem. In this thesis, simple numerical cases are presented, aiming to verify not only the theoretical multiscale model developed, but also its implementation. For this, it is analyzed, for instance, (a) cases in which the microscale is taken as a homogeneous material, making it possible the comparison of the multiscale solution with the conventional solution (one single scale) by the finite element method, and (b) a case in a heterogeneous material for which the full solution, that is, modeling all constituents directly on the macroscale, is obtained, making it possible the comparison with the multiscale solution. The solution at the microscale for several cases analyzed in this thesis suffers a large influence of the microscale thermal inertia. To demonstrate the application potential of the multiscale model, the cure of a carbon black loaded elastomer is simulated. Although the simulation shows that the thermal inertia does not have to be considered for this case in particular, the application of the present methodology makes it possible to model the cure of the elastomer directly at the microscale, an approach not used in multiscale methods context until now. This methodology opens the possibility for future improvements of the state of cure modeling.

O presente trabalho trata da modelagem da condução de calor transiente com geração de calor em meios heterogêneos, e tem o objetivo de desenvolver um modelo multiescala adequado a esse fenômeno. Já existem modelos multiescala na literatura relacionados ao problema proposto, e que são válidos para os seguintes casos: (a) o elemento de volume representativo tem tamanho desprezível quando comparado ao comprimento característico macroscópico (e como consequência, a microescala tem inércia térmica desprezível); ou (b) a geração de calor é homogênea na microescala. Por outro lado, o modelo proposto nesta tese, o qual é desenvolvido utilizando uma descrição variacional do problema, pode ser aplicado a elementos de volume representativos finitos e em condições em que a geração de calor é heterogênea na microescala. A discretização temporal (diferenças finitas) e as discretizações espaciais na microescala e na macroescala (método dos elementos finitos) são apresentadas em detalhes, juntamente com os algoritmos necessários para implementar a solução do problema. Nesta tese são apresentados casos numéricos simples, procurando verificar não só o modelo teórico multiescala desenvolvido, mas também a implementação feita. Para tanto, são analisados, por exemplo, (a) casos em que considera-se a microescala um material homogêneo, tornando possível a comparação da solução multiescala com a solução convencional (uma única escala) pelo método dos elementos finitos, e (b) um caso em um material heterogêneo para o qual a solução completa, isto é, modelando diretamente os constituintes no corpo macroscópico, é obtida, tornando possível a comparação com a solução multiescala. A solução na microescala para vários casos analisados nesta tese sofre grande influência da inércia térmica da microescala. Para demonstrar o potencial de aplicação do modelo multiescala, simula-se a cura de um elastômero carregado com negro de fumo. Embora a simulação demonstre que a inércia térmica não precise ser considerada para esse caso em particular, a aplicação da presente metodologia torna possível modelar a cura do elastômero diretamente sobre a microescala, uma abordagem até então não utilizada no contexto de métodos multiescala. Essa metodologia abre a possibilidade para futuros aperfeiçoamentos da modelagem do estado de cura. / This work deals with the modeling of transient heat conduction with heat generation in heterogeneous media, and its objective is to develop a proper multiscale model for this phenomenon. There already exist multiscale models in the literature related to this proposed problem, and which are valid for the following cases: (a) the representative volume element has a negligible size when compared to the characteristic macroscopic size (and, as a consequence, the microscale has a negligible thermal inertia); or (b) the heat generation is homogeneous at the microscale. On the other hand, the model proposed in this thesis, which is developed using a variational description of the problem, can be applied to finite representative volume elements and in conditions in which the heat generation is heterogeneous at the microscale. The time discretization (finite difference) and the space discretizations at both the microscale and the macroscale (finite element method) are presented in details, together with the algorithms needed for implementing the solution of the problem. In this thesis, simple numerical cases are presented, aiming to verify not only the theoretical multiscale model developed, but also its implementation. For this, it is analyzed, for instance, (a) cases in which the microscale is taken as a homogeneous material, making it possible the comparison of the multiscale solution with the conventional solution (one single scale) by the finite element method, and (b) a case in a heterogeneous material for which the full solution, that is, modeling all constituents directly on the macroscale, is obtained, making it possible the comparison with the multiscale solution. The solution at the microscale for several cases analyzed in this thesis suffers a large influence of the microscale thermal inertia. To demonstrate the application potential of the multiscale model, the cure of a carbon black loaded elastomer is simulated. Although the simulation shows that the thermal inertia does not have to be considered for this case in particular, the application of the present methodology makes it possible to model the cure of the elastomer directly at the microscale, an approach not used in multiscale methods context until now. This methodology opens the possibility for future improvements of the state of cure modeling.