Why the solution is higher than the initial conditions in a model without heatsource?

I want to simulate heat conduction and convection without internal heat source and look at the temperature distribution.The initial temperature is 50.But the result of the temperature is higher than the initial condition, why is that?

Here is my code.

Any help would be greatly appreciated.

model = createpde('thermal','transient');   
gm = importGeometry(model,'1.STL');     
figure
pdegplot(model,'FaceLabels','off','CellLabels','off','FaceAlpha',0.5','EdgeLabels','on');
view([0 90])
[gm,ID] = addFace(gm,1);
generateMesh(model);
thermalProperties(model,'ThermalConductivity',368,'MassDensity',8960,'SpecificHeat',386);
internalHeatSource(model,0);
thermalBC(model,'Face',1:5,'ConvectionCoefficient',13.5,'AmbientTemperature',26);
thermalIC(model,50)
tlist = linspace(1,60,60);
R1 = solve(model,tlist);
figure('units','normalized','outerposition',[0 0 1 1])
pdeplot3D(model,"ColorMapData",R1.Temperature(:,end))
Tmax = max(max(R1.Temperature))
Tmin = min(min(R1.Temperature))

Answer 1

[Riccardo Scorretti]

Dear YL,

In my opinion which is observed in the figure is just a uniform temperature T = 50, plus a numerical noise, which may be due to the mesh used to discretize the problem. Basically, the obtained result is that the temperature is constant. By the way, if you look carefully at your picture you can see that "hot spots" are centered in nodes.

I suggest you to check the formulation of your problem. For instance, try with a much higher convection coefficient, or add a source, or simulate over longer time -- just to see what happens. Play with the parameters of your formulation, and I'm sure you will find quickly the source of the problem.

Best regards

[怡凡 刘]

Dear Riccardo

Thanks for your reply.

Following your prompt, I modified the meshgrid size. It was found that the temperature did drop.I think it might be a mesh quality issue.

In addition to this, I would like to ask another question.

In this simulation, there is natural convection heat dissipation of the air. During this process, the air characteristics will change.

I think the convection coefficient and ambient temperature set by the following line of code are unchanged, so how to simulate the heat dissipation between the surrounding air and the solid?

thermalBC(model,'Face',1:5,'ConvectionCoefficient',13.5,'AmbientTemperature',26);

Looking forward to your reply, any help would be greatly appreciated.