The minimum fluidisation velocity (Um) can be calculated using the Ergun equation for fluidised beds, which is given by: Um = dp^2 * (p - f) * g / 150 * * (1 - m) Where: dp = particle diameter = 4x10^-4 m p = particle density = 3500 kg/m^3 f = fluid density g = gravity = 9.81 m/s^2 = fluid viscosity = 4.6x10^-5 N s/m^2 m = voidage at minimum fluidisation = 0.5 First, we need to calculate the fluid density (f). Since the air follows an ideal gas behaviour, we can use the ideal gas law: f = P / (R * T) Where: P = pressure = 200 kPa = 200,000 Pa R = ideal gas constant = 8.314 J/(mol*K) T = temperature = 1200 K Substituting the values, we get: f = 200,000 / (8.314 * 1200) = 20.07 kg/m^3 Now, we can substitute all the values into the Ergun equation: Um = (4x10^-4)^2 * (3500 - 20.07) * 9.81 / (150 * 4.6x10^-5 * 0.5) = 0.036 m/s So, the minimum fluidisation velocity is 0.036 m/s