Hi, I hope somebody help me to figure a problem I have out or has same situtaion before.

Let me explain first the geometry I'm trying to model. It's very simple. I have a 20mm(W) by 5mm(H) by 30mm(L) square steel block and water flows through 1mm(W) by 1mm(H) by 30mm(L) square channel inside steel block. Very thin foil heater (1mm(W) by 500nm(H) by 1mm(L)) is heating the water flow at the bottom of the smaller square duct. The location of the heater is 10mm downstream from the inlet. Note that the thickness of the heater is very thin (500 nanometer)

I used structural mesh since all blocks are rectangular. When I run, I have a reversed flow error. This error didn't go away in time. The residuals becomes contant, but values are as high as 100. To figure this out, I tried to mesh same geometry WIHTOUT thin film heater (so I have the big steel block and the small water flow duct). In this case, I didn't have the reversed flow error. It means the problem occurs due to the thin film heater.

Does anybody know how to mesh thin film heater in this case? Please help me and appreciate your advice.

By the way, I used Velocity inlet and pressure outlet BCs.