Problem in rising outlet water temperature in PCM based System
 

Hello, I hope you are doing well, I have a question and I would be grateful if you could guide me I am simulating the below system,

System

Double tube heat exchanger
************************************************** ************
Inlet domain is water:::::::
Boundary condition:::::
Tinlet=30 C
Inlet= mass flow inlet=0.02 kg/s
Outlet= Outflow
************************************************** ********
Outer domain is PCM:::::
Boundary condition::::
Outer Wall under the influence of Irradiation 900 W/m^2
melting temperature=54 C
************************************************** ****************
The initial temperature of system=30 C
*************************************************
But I have a problem, The outlet water temperature does not change.

I changed the length, PCM volume, and shape of the water domain( U shape and ...), It still hasn't changed.

Please help me, thanks
Thank you in advance for your time