Novel automotive thermal management technologies based on composite phase change materials and nanofluids

Lin, Xuefeng (2024). Novel automotive thermal management technologies based on composite phase change materials and nanofluids. University of Birmingham. Ph.D.

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Abstract

In the context of promoting energy conservation and addressing energy crises globally, the automotive industry, especially the electric vehicle sector, faces significant technical challenges. High energy consumption and insufficient reliability are key factors hindering the development of automobiles, particularly electric vehicles. These issues are primarily concentrated in several subsystems of vehicles such as battery packs, air conditioning, and liquid cooling systems. Batteries are prone to overheating or reduced activity under extreme temperature conditions, air conditioning systems consume a lot of energy, and cooling systems lack efficiency, all of which severely impact vehicle performance and safety. To address these issues, the focus has been on enhancing the actual efficiency of battery thermal management systems (BTMS), improving the energy efficiency of electric vehicle air conditioning systems, and optimizing the performance of automotive cooling systems. The core technologies focused on include the use of Composite Phase Change Materials (CPCMs) to optimize BTMS, the development of Thermal Energy Storage (TES) devices based on CPCMs to enhance air conditioning systems' energy efficiency, and the application of nanofluid automotive coolants to improve the cooling efficiency of automotive cooling systems.

This study employs a combination of experimental and simulation methods. Initially, methods for preparing composite phase change materials and nanofluids were explored, and their material properties were analyzed. Subsequently, the thermal management performance of a flat lithium iron phosphate battery based on phase change cooling was designed and tested. Additionally, a TES device based on CPCM that could provide heating functionality for electric vehicle air conditioning was designed, tested, and its feasibility and actual energy-saving effects were assessed. Finally, the application effects of nanofluids in automotive cooling systems were verified through system-level testing.

The study achieved significant research outcomes:

• The developed CPCM consists of 70wt% capric acid/paraffin (phase change material) and 30wt% OBC (skeletal material), enhanced with 3wt% graphite to improve its thermal conductivity. This material boasts high phase change enthalpy and stable temperature cycling performance, along with excellent shear and compression resistance.
• Tests on BTMS using CPCM containing 3wt% graphite showed that the maximum temperature rise of the battery decreased from 18.3°C to 6.4°C, with an average increase in cooling efficiency of 161.8%. The battery's natural cooling rate more than tripled, extending the time the battery remains at an optimal working temperature, effectively mitigating localized overheating and uneven heat distribution, thus enhancing the battery's safety and operational efficiency.
• In tests on the electric vehicle air conditioning system, a device filled with 4.7 kg of paraffin-OBC-graphite CPCM raised the cabin temperature from 7°C to 14°C in two hours under no sunlight and static conditions, with an average heating output of 193W, saving 0.643 kWh of battery power and extending the driving distance by 4.95 kilometers. Under various outdoor temperatures and weather conditions, the thermal storage device provided over 80W and 160W of effective heating power in two hours, under unlit and lit conditions respectively, effectively reducing the frequency of use and energy consumption of the onboard air conditioning system and enhancing the electric vehicle's driving range.
• Thermal transfer performance tests of nanofluid automotive coolant showed that under the same test conditions, a 1 wt% rGO nanofluid achieved a thermal transfer performance of 4535.3 W, an increase of 1080.3 W over the base fluid, with a thermal transfer coefficient increase of 75.54%-88.55%. Combining the thermal conductivity, viscosity, and suspension stability studies of rGO-DI water nanofluids, the nanofluid demonstrated enhanced heat transfer capabilities and stable suspension properties, contributing to improved engine efficiency and reduced energy consumption.

The innovations of this study are in three technical breakthroughs: firstly, the optimized formulation of CPCMs which are low-cost, easy to manufacture, and also accommodate the characteristics of flexible materials, providing sufficient mechanical protection to the battery and enhancing safety and stability through improved heat dissipation and insulation; secondly, the development of TES devices effectively integrates the energy management of air conditioning systems, utilizing industrial waste heat effectively, reducing energy consumption, and its independent compact system design increases usability; finally, the application of nanofluid technology significantly enhances the performance of cooling systems without physically increasing the heat dissipation area, thereby significantly improving the vehicle's economy and environmental friendliness.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):