Sustainable cold economy via thermal energy storage

• Main Author: Koh, See Wee
• Other Authors: School of Mechanical and Aerospace Engineering
• Format: Final Year Project
• Language: English
• Published: 2016
• Subjects: DRNTU::Engineering
• Online Access: http://hdl.handle.net/10356/67738
• Institution: Nanyang Technological University

The increased demand for cold energy in areas for food distribution and storage, building cooling and domestic refrigeration is a challenging task to meet in the hot tropical climate of Singapore. Without sufficient renewable energy sources and space constraints in our city-state, higher electricity consumption to provide cold energy cannot be sustained. The concept of a sustainable cold economy encompasses recovery of waste cold energy, cold energy storage and higher efficiency in cold generation and better utilization of current resources. Recently, increase in innovative uses for cold energy recovered from cryogenic sources such as re-gasification of liquefied natural gas had seen increase in interest in cold thermal energy storage (CTES). This project’s key objective is in phase change material CTES (PCM CTES) systems and in their heat exchanger components and storage medium. The project covered an extensive review of the methodology for designing of PCM CTES - requirement and methods of assessing PCM for use in CTES and volume sizing methodologies. Following which experiments were conducted using the differential scanning calorimeter (DSC) with various concentrations of aqueous mono ethylene glycol (MEG) solutions to determine their thermal properties. The results from the DSC provided essential information- a range of melting and freezing temperatures and latent heat of fusions values of the various concentration of MEG- which are crucial in a design of CTES system. Graphite powder at micron size was then added to the material to investigate the effects on reduction of supercooling. It was found that 30% volume composition of MEG gave stable result at the desired operation range while 31% volume composition of MEG and 33% volume composition of MEG + 12% weight composition of graphite gave good thermal physical properties at the desired operation range. The enhancement was observed to reduce the supercooling level by around 60% which might be attributed to improvement in nucleation rates. Thermal cyclic tests were conducted on the 2 compositions and results showed that the material requires some initial charge and discharge cycles to reach its full potential and it is thermally stable for at least 50 cycles with no deterioration of the latent heat observed. A CTES system using the investigated material to recover waste cold was proposed with its functional requirement and material selection process.