Mechanical Operations GATE-2015
Q 1. A cylindrical packed bed of height 1 m is filled with equal-sized spherical particles. The particles are nonporous and have a density of 1500 Kg/m3. The void fraction of the bed is 0.45. The bed is fluidized using air (density 1 kg/m3). If the acceleration due to gravity is 9.8 m/s2, the pressure drop (in Pa) across the bed at incipient fluidization (up to one decimal place) is __________________.
Q 2. A typical batch filtration cycle consists of filtration followed by washing. One such filtration unit operating at constant pressure difference first filters a slurry during which 5 liters of filtrate is collected in 100 s. This is followed by washing, which is done for tw seconds and uses 1 liter of wash water. Assume the following relation to be applicable between the applied pressure drop ΔP, cake thickness L at a time t, and volume of liquid V collected in time t:
\frac{\mathrm{ΔP}}L=k_1\frac{dV}{dt};\;\;\;L=k_2V,\;if\;L\;is\;changingk1 and k2 can be taken to be constant during filtration and washing. The wash time tw, in seconds (up to one decimal place), is _______________.