Energy and Exergy Performance of Three Sensible Heat Storage Systems During Charging

Two packed bed storage systems of two different rock pebble samples are charged using Sunflower Oil as the heat transfer fluid (HTF) and are compared with an oil only thermal energy storage (TES) system. Energy and exergy rates are evaluated during charging at a heater set temperature of 260 0C with flow-rates of 4, 8 and 12 mls
^-1
respectively. The oil storage system charges up fastest, followed by the small pebbles TES and lastly by the large pebbles TES. The fast charging of the oil storage system is due to its lower thermal mass. The small pebbles TES has a lower void fraction as compared to the larger pebbles making its rate of temperature rise faster. Higher charging energy and exergy rates are obtained with the small pebbles TES system. Energy and exergy rates are found to be dependent on temperature differences between the top and the bottom of the storages. Exergy rates are lower than energy rates since they consider heat losses. The small pebbles show the highest energy rates, exergy rates and total exergy stored during charging. The big pebbles have the largest thermal mass and thus show the largest total energy stored.