In common bubble cap distillation column design practice, riser area is approximately equal to (where, A_{a} = Annular passage area, and S_{a} = Slot area)

Heat transfer co-efficient, h_{G}(K_{cal}/hr.m^{2} .°C) and mass velocity of air, G (kg/hr.m^{2} ) for air flow parallel to the surface in case of constant drying rate in batch drying is related as h_{G} = 0.0176G^{0.8}. But when the flow of air perpendicular to the surface is encountered, this equation changes to

Pressure drop due to pipe fittings can be estimated by the equation, , where, L_{e} = equivalent length of straight pipeline which will incur the same frictional loss as the fitting and D = diameter of the fitting. The value of (dimensionless) for 45° elbow and 180° close return bends would be respectively around