3.1.2. Effect of the sound pressure level
From the discussion in the previous section, the sound frequency
was fixed at 1.5 KHz in the following experiments. Fig. 4 showed the
curves of pressure drop versus gas velocity at different sound pressure
levels from 90 dB to 150 dB. It was observed that beyond the sound
pressure level of 100 dB, the fluidized quality of lignitewas independent
of sound pressure level. Based on the data from Fig. 4, the minimum
fluidization velocity versus the sound pressure level was displayed in
Fig. 5. The minimum fluidization velocity values were obtained from
Fig. 5. The rate of decrease in minimum fluidization velocity was not
significant in the beginning up to a sound pressure level of 90 dB. The
minimum fluidization velocity decreased appreciably beyond 120 dB.
The minimum fluidization velocity attained a minimum value, the
lowest being attributed to the highest sound pressure level (SPL =