In a fluidised bed, hot sand at 850 ◦C serves as the heating medium for atmospheric air at a pressure of 0.1 MPa, from its initial temperature 20 ◦C to practically 850 ◦C. The hot air is then fed to a...

In a fluidised bed, hot sand at 850 ◦C serves as the heating medium for atmospheric air at a pressure of 0.1 MPa, from its initial temperature 20 ◦C to practically 850 ◦C. The hot air is then fed to a furnace. Calculate the blower power and the heat fed to the air. Given: inner diameter of the fluidising chamber 3 m, kinematic viscosity of air ν(850 ◦C) = 1.513 · 10⁻⁴
m²/s, gas constant for air 0.2872 kJ/kgK, mean specific heat capacity between 30 ◦C and 850 ◦C: cp = 1.163 kJ/kgK, specific heat capacity cp(20 ◦C) = 1.007 kJ/kgK, density of sand S = 2500 kg/m³
, particle diameter d_P
= 0.5 mm, sphericity ϕ_S
= 0.86, height H₀
of the quiescent sand layer H₀
= 0.5 m, void fraction of the quiescent sand layer ε_S
= 0.36, void fraction at the minimum fluidising point ε_nf
= 0.44, void fraction at 10 times the minimum fluidisation velocity ε = 0.55, blower efficiency η_v
= 0.7.