Abnormally high temperature while modelling radiant cooling panel
 

Hello, I am trying to model a radiant cooling panel but the temperature of the aluminum panel is abnormally high (the heat flux is only 92 W/m2 but the temperature reaches 5000+ K). When I modelled it without the panel (only the pipe, split in half; bottom and top, the heat flux applied to the bottom part) there seem to be no mistake, and this only happens when I use the panel. Any mistake I might have overlooked? The boundary conditions and supporting images are attached in the link below. Many thanks in advance!
https://imgur.com/a/OBbrS7Y