We are going to look at the analogy of heat and mass transfer in case of flow around a sphere. So, we have a sphere with diameter , where air is flowing around with a velocity .

When the sphere is hot, we have a heat flux. When the sphere is evaporating slowly, we have mass flow. Prove that if the Reynolds Number is much bigger than 1 the ratio of the heat flow over the mass flow is independent from the velocity and the viscosity of the air flowing around it.