Natural Convection
 

My problem was a natural convection.Consider an U-tube insulated on one half of the limb heated on the other half such that the fluid inside the tube will raise on by purely natural convection. In an unsteady case, (while solving )is it possible to get the mass flow rate (through one of it surface - heated side surface)through a UDF function and considering that mass flow rate as an input to the another surface.Anybody knows please answer my question.