Cool Storage is a well-known technique that been used to increase the energy efficiency of cooling systems. This
paper represents a novel experimental work for the effect of internal capsules surface roughness on the performance
of encapsulated cool storage systems. In this study, distilled water was used as a phase change material
inside capsules. Internal surface roughness of 0, 3, 7 and 12 μm were tested using the same heat transfer fluid
Characteristics. Heat transfer fluid (HTF) composed of 50–50 wt. of (water–ethylene glycol) was used with a
fixed volume flow rate of 12 L/min LPM and four different inlet temperatures of −6, −8, −10 and −12 C. The
solidified mass fraction, charging rate and energy storage were calculated and plotted versus the charging time
to determine the surface roughness effect on the cooling performance of the system. Results showed that the
internal surface roughness of capsules had adverse effect on the system performance through increasing the total
freezing (charging) time. Results also indicated that the charging time increased by 14–17% at inlet flow
temperature of −12 and −6 ̊C, respectively at the higher roughness values compared with the smooth surface capsule e.g. zero roughness parameter.