Thermal Energy Storage Aggregate using Low-Cost Organic Phase Change Materials
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The extent of energy economization of the structure depends on the thermal envelope performance. Thus, creating building materials capable of enhancing energy efficiency in the buildings is crucial. On the other hand, the icing of pavements during cold temperatures represents significant pedestrian and vehicle safety concerns. De-icing salts and other routine winter maintenance activities are intended to improve safety but have considerable cost and environmental runoff concerns and cause decreased infrastructure lifespan. As a remedy, the literature has recently investigated using different phase change material (PCM) types and their incorporation techniques into cement-based materials (CBMs). The outcome of such analysis has demonstrated similar negative and positive impacts on the overall performance of CBMs. So, it is challenging for the researchers to select one PCM type or incorporate a technique over the other. But, if appropriate PCMs and means of integration are employed, they can minimize these undesirable properties of PCMs on the CBMs. This study has developed thermal energy storage aggregates (TESA) to cope with the aforementioned problems. TESA is made through vacuum impregnation of expanded clay lightweight aggregate (LWA) with low-cost and widely available organic PCMs such as individual or blends of coconut oil (CO), soybean oil (SO), and paraffin wax (PW). TESA is coated with anti-bleeding materials to prevent leakage. TESA is made to produce concrete with good thermal, durability, and mechanical properties. This study's findings showed that the differential scanning calorimetry (DSC) analysis of the as-received PW or prepared PWSO and COSO or after multiple thermal cycles showed high latent heat of fusions necessary to store a large quantity of heat. A wide range of melting points could be suitable for different degrees of phase transitions. Vacuum impregnated TESA showed PCMs absorption capacity of 30.20% for PW, 28.00% for PWSO, and 27.42% for COSO. Moreover, to prevent leakage, the TESA was coated with latex. The application of low-cost/widely available PCMs/TESA, developed in this study, can be beneficial for improving the thermal infrastructure performance in different weather conditions such as summer and winter. In summer, TESA concrete developed better thermal performance due to the sensible and latent heat behaviour of PCMs impregnated in TESA. TESA enhanced the thermal conductivities but slightly decreased the compressive strength of concrete compared to the control. However, at the top surface layer of concrete, about 25 mm thick, TESA concrete stored a large quantity of heat due to sensible and latent heat mechanisms occurring during the absorption of sunlight; thus, TESA concrete provided higher thermal insulation than the control sample. Therefore, TESA may control and minimize the temperature fluctuation in concrete and could utilize it to enhance the thermal inertia of buildings during hot seasons or tropical climates. In winter, TESA concrete showed the relative contribution of both sensible and latent heat storage behaviours. A methodology considering system energy input and discharge using a battery storage analogy is presented, allowing heat movement quantification under actual winter conditions. TESA concrete demonstrated the most significant increase in heat storage and delayed freezing. While many studies have shown PW to provide good high-temperature behaviour, the relatively high melting point means that only PW can realize sensible heat improvement alone. Thus, blending SO with PW or CO enhanced the thermal performance of concrete in the winter season by leveraging the lower melting points and latent heat capacity. TESA concrete is one potential approach requiring little operational management to reduce the amount of de-icing salts or other winter maintenance while minimizing environmental impacts and safety concerns. Hence, TESA could provide a sustainable and feasible option for cold regions. This study demonstrated the positive impacts of low-cost PCMs in producing new building materials capable of providing excellent thermal insulation in summer, and great resisting freezing and thawing cycles in winter, thus improving the thermal infrastructure performance in developed/developing countries in different weather conditions.
Table of Contents
Introduction -- Literature Review -- Methodology -- Assessment of low cost organic phase change materials for improving infrastructure thermal performance -- Performance investigation of low-cost PCM-modified concrete in high operating temperature conditions -- Low-cost PCM-modified concrete for reducing deicing needs -- Conclusion and further studies
Ph.D (Doctor of Philosophy)