Enhancing HCFC−141b Hydrate Cold Thermal Energy Storage Density by EL Series Surfactants in Quiescent Conditions

To solve the problems of the slow growth rate and low cold thermal energy storage density of refrigerant hydrates, the addition of surfactants is an effective way to promote hydrate formation. Three polyoxyethylene castor oil (EL) surfactants with different hydrophilic-lipophilic balance (HLB) values (EL-20, EL-30, and EL-60) were selected as promoters to study their effects on HCFC-141b hydrate formation. The experimental results showed that the EL series of surfactants significantly reduce the hydrate nucleation induction time. The system with a mass fraction of 1.5% EL-20 exhibited the shortest hydrate induction time of 73 min, and the stability of hydrate formation was good. The micelles formed by the EL surfactants provide more nucleation sites, which accelerate hydrate formation. The hydrate cold thermal energy storage density is related to the HLB value of the surfactants. The system with a mass fraction of 1.5% EL-20 had the maximum cold thermal energy storage density of 246.48 kJ/kg and the fastest hydrate growth rate of 5.06 kJ/(kg·min), as EL-20 had a suitable HLB value. There is a "memory" effect during hydrate formation and dissociation cycle. The system with a mass fraction of 1.5% EL-20 surfactant exhibited the most favorable performance during the hydrate formation and dissociation cycles. After seven hydrate formation and dissociation cycles, the increase in temperature remained stable during hydrate formation.