Experimental investigation of the solid filler influence in thermocline storage systems through the comparison of two different setups

Two liquid/solid thermocline heat storage systems are compared. Both setups have similar size and operate with thermal oil as heat transfer fluid but one consists of a packed bed of alumina spheres with a void fraction of 0.485, while the other consists of a packed bed of rock and sand with a void fraction of 0.270. A dimensionless approach based on the thermal front velocity (i.e. the velocity of the thermocline) and the discharge efficiency is used to compare the thermal behavior of the two setups. The comparison shows that the dimensionless behavior of both systems is very similar and seems insensitive to the operating conditions in the range tested (temperature level and fluid flow). This dimensionless approach is therefore promising to analyze and size thermocline heat storage systems.