Exploring the Potential of Phase Change Material for Thermal Energy Storage in Building Envelopes

Buildings, with their significant energy consumption, pose a pressing concern for the future. Inadequate heating, ventilation, and air-conditioning (HVAC) systems further exacerbate thermal management difficulties and energy requirements. To address these challenges, Phase Change Materials (PCMs) offer valuable potential for sustainable energy reduction within the building sector, leveraging passive cooling and heating techniques. Numerical study has been conducted to explore the impact of embedding PCM within the building envelope on energy efficiency and thermal performance. The results reveal that PCM integration significantly reduces temperatures across all sections compared to scenarios without PCM. By passively absorbing and storing heat energy during phase change, PCM mitigates heat transfer through convection and conduction, leading to improved energy efficiency and reduced power consumption for cooling and heating purposes. Within the first 2 hours, the PCM achieves 50% of its average melting process, followed by a gradual decrease in the melting rate. It takes approximately 6 hours for the PCM to completely melt. As the PCM undergoes the melting process, the system's entropy values increase, reflecting an increase in disorder. At the tip of the building, the entropy value reaches 130 K/kg·K, which is more than three times the initial value. The integration of PCM in building envelopes shows promising potential for enhancing energy efficiency, thermal comfort, and durability. Future research should focus on optimizing PCM placement and configuration to maximize its benefits in diverse building designs and climatic conditions

A Computational Study of Particulate Colloidal Systems

Particulate colloids exist in a broad range of natural, biological and industrial systems. To examine the particle aggregationbehaviour in these systems, and to propose feasible aggregation control strategies, a novel computational model is developed based on the Eulerian-Lagrangian framework.Computational fluid dynamics techniques are utilised to simulate the flow field of the base fluid, and discrete phase modellingapproach is used to compute the particle trajectories, with both long-range and contact particle-particle interactions considered. Two-way coupling is adopted to model particle-fluid interactions.Three studies of different colloidal systems are conducted using the developed model. In the first study, the morphology of gold nanoparticles is analysed at various particle volume fractions and base fluid pH levels. It is observed that small isolated particle clusters are formed at low particle volume fractions, whilst a more complex and interconnect particle network is formed at higher particle volume fractions. It is also found that larger but more compact particle aggregates are formed under acidic conditions (pH = 3.5), compared with neutral and basic conditions (pH = 6.7 and 9.4).The second study investigates the particle structures in magnetic nanofluids under static external magnetic fields with constant direction and magnitude. In the absence of the magnetic field, a randomly-oriented particle network is formed. With the application of external magnetic fields, distinct chain-like particle structures are observed parallel to the direction of the applied magnetic fields. The formation of the chain-like structures is more rapid, and the chain-like structures formed are thicker at higher magnitudes of the magnetic field. This observation is consistent between the two-dimensional and three-dimensional simulations.A novel particle aggregation control strategy is proposed in the third study via the application of alternating and rotating magnetic fields. It is demonstrated that the aggregation of magnetic-responsive particles is promoted under rotating magnetic fields, especially at higher rotating frequencies. It is also demonstrated that complete particle disaggregation can be achieved under alternating magnetic fields.Lastly, it is concluded that the computational model developed is a breakthrough in numerically predicting the particle aggregation behaviour in colloidal systems, and can be extended to many other studies

Thermal Performance of Nanofluids in Microchannel Equipped with a Synthetic Jet Actuator

Numerical investigations of heat transfer enhancement in three-dimensional micro-channels with singlesynthetic jet using Al2O3-water, CuO-water and TiO2-water combinations were conducted. The effects of different types of nanoparticles at particle volume concentrations of 1%, 2% and 5% on the thermal erformance in the micro-channel were examined. The numerical tool was validated against existing xperimental data on the heat transfer characteristic of nanofluids in micro-channel. Heat transfer enhancement using nanofluids based on the eulerian model was assessed for the cases without synthetic jet operator and with synthetic jet operator. In general, the thermal performance was greatly influenced by the thermal conductivity and dynamic viscosity of the type of nanofluids used. As the particle volume concentration increased, the heat transfer performance also improved. The result showed that the heat transfer performance of nanofluids with Al2O3 and CuO used in this study was better than that of pure water with the operation of th e synthetic jet actuator. Overall, nanofluids with Al2O3-water at 5% particle volume concentration showed the best cooling performance whereas nanofluids with TiO2 fails to improve the thermal performance.15 page(s