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Thermal Engineering

Thermal engineering of electric battery/charging systems

The electric vehicle (EV) technology has made tremendous progress in the past few years and shows promise to reduce our heavy dependence on fossil fuels for transportation and the associated adverse greenhouse gas emissions. However, the performance of these systems is significantly affected by temperature. Therefore, they require homogeneous cooling in an appropriate range for efficient performance and to maintain their state of health, and minimize safety risks. Also, maintaining uniform temperatures in a battery in a prescribed range during charging and discharging is especially challenging because, under extreme conditions such as high power discharging and overcharging, the battery temperature can rise dramatically and may result in thermal runaway or even explosion. My research examines the impact of the thermal characteristics of batteries on their performance and life and develops novel and effective thermal management strategies.

Cold climate heat pumps

Space heating is the largest component of energy consumed by Canada’s building sector and accounts for up to two-thirds. Heat pumps (HPs) have the capacity to increase energy efficiency (also known as the coefficient of performance or COP) by a factor of 2 to 4 relative to typical electric resistance heaters. However, the COP of air-source HPs, which have several competitive advantages, depends on the ambient temperature, and for cold climates like Canada, achieving high COPs at a temperature below -20C is a challenge. My research group is working on solutions to this problem. We have developed a few prototypes that can provide significant benefit, and we are working with an industry partner who is interested in our technology for potential commercialization. 

Research Highlights

Development of flow control methods for drag and soiling mitigation over a generic vehicle

picture1.pngElectric vehicles are currently accepted as a solution to reduce our carbon print in the road transportation industry. Electric vehicles are powered by electric battery packs and their performance directly depends on the battery pack’s operational efficiency. Lithium-ion batteries are widely used due to their high energy and power density, low self-discharge rate, fast charging capability, and extended lifecycle. However, the ideal operating range for the batteries is 25°C to 40°C. Below 25°C the energy output of the battery reduces due to increased internal resistance. Whereas above 40°C the degradation rate of the battery increases, which decreases its lifespan. Moreover, temperature non-uniformity in the battery pack reduces its power capacity and causes an imbalance in the discharging and charging rates of the batteries. Additionally, very high temperatures result in the thermal instability of the battery due to irreversible chemical reactions.

The research team for this project includes PhD student Seham Shahid, MASc student Yuyang Wei, and MASc student Branson Chea. The team has developed novel concepts that incorporate jet inlets, multiple vortex generators, and liquid jackets in the Lithium-ion battery pack to maintain the temperature of the batteries within the optimum operating range. Additionally, the team has also developed a strategy that utilizes latent heat of water to extract heat from the batteries. In this strategy the flow of water in hydrophilic channels is obtained through capillary action which eliminates the requirement of liquid pumping power. To further achieve an improved thermal performance of the batteries, hybrid cooling strategies are being developed that combine air cooling, liquid cooling, and phase change materials.

The highlights of upcoming research include novel thermal management strategies with the capacity for disrupting thermal runaway events in lithium battery packs; new modular battery pack designs with easy scalability in power and energy; new high-fidelity numerical models to accurately predict the thermal performance of the hybrid strategies; and application of advanced multi-objective optimization techniques to optimize the performance of the battery pack designs.