Thermal property, charging and discharging characteristics study on tetra-n-butyl ammonium bromide semi-clathrate hydrates for air-conditioning cold storage and secondary refrigerant applications

Highlights: • Thermal properties of Tetra-butyl ammonium bromide semi-clathrate hydrates (SCH) was studied. • Conductive heat transfer ability affected more as compared to heat storing ability. • Thermal properties significantly affected by initial addition of 0.05 $w_{\mathrm{TBAB}}$. • Supercooling property of SCH had a significant effect on charging performance. • In a spherical enclosure melting of SCH occurs in an eccentric manner. In this study, the heat of dissociation of tetra-n-butyl ammonium bromide (TBAB) semi-clathrate hydrates (SCH) together with thermal conductivity and specific heat of both TBAB aqueous solution (AQS) and solidified AQS (SAQS) was measured for various weight fractions of AQS ($w_{\mathrm{TBAB}}$) ranging from (0.050 to 0.400). AQS and SAQS properties were measured by varying temperature from (283.2 to 308.2) K and (243.2 to 283.2) K, respectively. Thermal properties of AQS, SAQS, SCH, and clathrate hydrates slurry (CHS) have been reported. Subsequently charging and discharging characteristics of 0.400 $w_{\mathrm{TBAB}}$ was studied in (42, 51, and 64) mm diameter spherical enclosures. Effect of diameter and wall temperature on charging characteristics were investigated, and the effect of diameter on discharging characteristics was explored. All the properties of AQS along with thermal conductivity of SAQS are influenced more by a change in $w_{\mathrm{TBAB}}$ than by a change in temperature whereas, the reverse trend is observed for specific heat of SAQS. Thermal conductivity of SAQS and specific heat of AQS showed minimal variation while changing temperature, whereas specific heat of SAQS showed minimal variation while altering the $w_{\mathrm{TBAB}}$. Supercooling property of SCH had a significant effect on charging performance, and supercooling degree of SCH depend on wall temperature. Change in diameter does not affect the supercooling degree of SCH. In a spherical enclosure, SCH melts eccentrically. Charging and discharging rate of SCH increases with an increase in diameter. Based on this, it is found that a higher diameter capsule provides better charging and discharging performance.