Why temperature is decreased shaply when calculation is started??
 

Hello all, plate air cooling is the topic

I made 6points on the surface of plate to plot the temperature along the time.

After starting calcuation temperature of vertex is dropped sharply and increase slowly.

I think it is not physcal for cooling. usually temperature will be decreased very slowly for air cooling.

initial temp for plate is 780℃ , ambient air temp is 20℃

there is plot snap below please advise something. thanks

Hi Hackis,

I need some more information on the problem setup.

What did you do? Did you solve the flow field before patching the plate with a temperature? Did you mesh the boundary layer correctly?

This is a common case in textbooks, did you determine a Biot-number? If heat transfer coefficient is large, you might need an inflation layer within the plate as well.

here are what i did
 

first of all thank you for your respond

here are what i did befor solving this model

1. befor patching the plate with a temperature, i initialized thr flow field as 293K, -1.5m/s

2. there are two domains(solid=steel, fluid=air)
3. one interface with two domains, so i selected coupled thermal boundary
4. i didn't determine a Biot-number, heat transfer coefficient
because there is no option specify a Bi or HTC
(if it is possible please give me some advise)
5. instead of that i specified thermal properties of air and solid, because convection and conduction are influenced by material properties, flow characterics of fluid.
(specific heat, thermal conductivity, heat diffusivity, heat expansion coeff,
density)
6. i meshed hexagonal for solid and trigonal for fluid
the worst EquiSize Skew : 0.896
Orthogonal Quality : 0.103
does this mesh could be problem?
i attatch plane view of mesh for solid and fluid field
7. heat transfer coefficient is 35.5467 W/㎡*K avg. (computed value)
8. also i found the fact that plot using total temperature for wall shadow(solid) was started from inital temperature(1063K), not static temperature. is it right physically?? i attatch the plot.

thanks again think about the problem together, i wish solve this plz.

Hello,I think you don't have a good mesh quality (orthogonal quality: 0.103 is low), and will give errors in the results. In my opinion, you need to alter the mesh size.

thanks for respond
 

thank you for your opinion, and i try to mesh again for better quality.

i attach another plot that comparing total & static temp plot along for each wall(fluid interface) and shadow wall(solid interface).