Investigation of the Effect of Pulse Frequency in Solid-Gas Fluidized Bed as an Energy Storage Tank

In this research, temperature measurements were performed experimentally in a solid-gas bubble bed with 184 μm silica sand particles and an inlet air of 60 °C to determine the effect of flow pulse on the energy transfer and storage efficiency. A solenoid valve was installed to supply pulsed air to the substrate and the effect of the alternating frequency cycle on the incoming air was investigated by applying the on-off condition. Results for frequency ranges from 1 Hz to 10 Hz indicated the surface of the bed fluctuates with the pulse frequency, and the amplitude of the oscillation decreases with an increase in frequency. Higher frequency improves heat transfer coefficient compared to continuous state. This, along with increasing the apparent velocity of the carrier gas, increases the energy storage efficiency.  At three speed ratios with respect to the minimum fluidization velocity (Umf) of 1.5, 2 and 2.5, a maximum efficiency of 28% was observed at 7 Hz frequency and speed ratio of 2.5.