When taking flow equation into consideration
 

Hi all. I am working on a Phase Change Material melting progress, it occurs in a cylinder capsule (D=7.5mm H=15mm); the bottom and side walls of the capture are keeping heated by 310K.
The PCM I choose RT-27, melting temperature is 302K. I am simulating the close-contact melting, So I do not use the VOF model. When not taking flow equation into consideration, the total melting time is 450s, but when flow equation is applied, the totally melting time reduced significantly to 80s.
Can anybody tell me what is wrong with it?