How to rewrite devolatilization by UDF
 

I am going to rewrite devolatilization by DEFINE_DPM_LAW in coal burn model.I will use coal thermogravimetry curve to replace devolatilization model.I know the switch condition of pulverized coal combustion process to be achieved in Switch Law.I don't know how Fluent programs about the weight loss rate of pulverized coal particles in Devolatilization.And I don't know how the loss of quality converts into volatile.Who can help me?