Variation of thermo-physical properties of thermal energy storage system with the use of aluminium/distilled water based nanofluid through a circular pipe

Abstract

The global conventional fuels in reserves are running out while the world energy consumption is increasing very fast. The scientific community agreed that thermal energy is one of the best solutions for energy supply in many parts of the world. The experimental setup consists of water heater, thermal storage system, storage water tank and pump. The thermal storage system is loaded with steel spheres, water and aluminum/water nanofluid is used as the heat transfer fluid. During charging process the heat transfer fluid is being heated inside the heater and passes through the storage tank in order to transfer its thermal energy to the steel spheres and the water inside storage tank. In order to evaluate the system performance characteristics during charging, the effects of varying the mass flow rate, heat transfer fluid temperature, initial temperature of the storage tank during charging and processes on the rate and amount of thermal energy storage. Moreover, several experiments are performed with water and aluminum/water nanofluid only as storage medium in order to compare the effect of steel spheres packed bed on the performance of the thermal storage system and its capacity. On the basis of experiment, it has been observed that increasing the mass flow rate results in decrease in time required to complete the charging process and increasing the heat transfer fluid temperature which results in an increase in rate and amount of thermal energy storage and hence time required to complete the charging process also increases. The steel spheres comes into thermal equilibrium in shortest time near inlet but time increases as we move further with the length of packed bed. During the study of pressure drop characteristics, conclusion has come to know that increase in mass velocity of fluid results in pressure drop across packed bed increases. Therefore the selection of flow rate is important which shows that pressure drop is directly driving away with mass flow rate of the fluid and at the same time Reynold number is also directly driving away with mass flow rate of the fluid.HTF mass flow rate has a considerable effect during charging. Increasing of mass velocity of fluid accelerates charging process for storage unit and cause early achieve of steady state. Nanofluids are more valuable in the energy storage and having less pressure drop through the bed during charging as compared to water. The choice of the ratio between diameter and height of packed bed is important because the increase in this ratio (D/L) results in increase of the cross sectional area and mass flow rate. This also causes the increase in the stored energy and reduction of the pressure drop.