An Experimental Investigation of R134a Clathrates with Liquid Additives

Abstract

Thermal energy storage (TES) using phase change materials is one of the most effective solutions for energy conservation. The selection of a phase changing material (PCM) with different liquid additives could improve the crystal growth rate and heat transfer characteristics. Direct contact heat transfer of PCM is one of the most influencing factors in improving the TES system performance. Numerous experimental runs were conducted to investigate the crystal growth formation time and its structural characteristics using different liquid additives under different operating conditions. The investigation was mainly based on the crystal growth formation time of the inclusion compound of R134a and the distilled water in the cold storage applications. Four different additives with different percentages were used to investigate their effectiveness on the clathrates characteristics. The additives used for this investigative work were ethanol, butanol, ethylene glycol, and glycerin. The onset time of crystal growth formation and the final endset time were recorded at different operating temperatures. Percentage of additives (for ethylene glycol, butanol and glycerin) used in this investigation varies between 1-4% while for the ethanol as additive, the percentage varies between 1.5%-4.5%. For the case of butanol, the refrigerant percentage was also varied in addition to the liquid additive percentage. The experimental results showed that additives impact on the clathrates formation time as well as clathrates characteristics. Minimum clathrates formation time was found to be 17 minutes for the ethylene glycol (as an additive) with the highest percentage of 4%. At the same time, the crystal structure remains fluffy. Although, the clathrates formation time was higher for the butanol initially but there was a sharp decrease in the clathrate crystal growth formation time throughout. Minimum clathrates formation time for the butanol (as an additive) was found to be 17.67 minutes for highest percentage of 4%. The clathrates formation for the butanol results into rock solid crystals. Same nature of crystals formation was demonstrated by the ethanol. The experimental results also concluded that there has to be a specific ratio between water and refrigerant on a mass basis in order for the clathrates to form with optimum operating conditions, which is close to 35%.