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Old   March 18, 2008, 19:24
Default heat conducting in a solid domain
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Rogerio Fernandes Brito
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Subject: CAE program for heat conducting

Which is the better CAE program to simulate the heat conducting in a block? I tried using FEMLAB 3.0a (3.0.0.228) from COMSOL, but the results had a big deviation! It happened with the CFX-v5.6 and ANSYS CFX-v11.0 programs too. The softwares are listed below:

FLUENT, ABAQUS v6.7, Flow3D or some another one. Thanks!

Details: I wanna simulate a sample (=cemented carbide tool) like that:

Total dimension of the sample (x, y, z): 0.0127 x 0.0127 x 0.0047 (m) = 1.27 x 1.27 x 0.47 (cm) = 12.7 x 12.7 x 4.7 (mm)

Dimension of the cavity with air (Pr = 0.70) (x, y, z) (for example, 10 times the dimension of the sample): 127.0 x 127.0 x 47.0 (mm)

Interval of acquisition of data = 0.22 seconds

Initial temperature of the sample and the air too= 29.2 (C) = 302.35 K

Number of thermocouples = 4

Co-ordinated (s) of the (s) thermocouple (you are):

x= 0.0095 (m) y= 0.0035 (m) z= 0.0047 (m) x = 9.5 (mm) y= 3.5 (mm) z= 4.7 (mm)

x= 0.0043 (m) y= 0.0035 (m) z= 0.0047 (m) x = 4.3 (mm) y= 3.5 (mm) z= 4.7 (mm)

x= 0.0035 (m) y= 0.0089 (m) z= 0.0047 (m) x = 3.5 (mm) y= 8.9 (mm) z= 4.7 (mm)

x= 0.0065 (m) y= 0.0059 (m) z= 0.0047 (m) x = 6.5 (mm) y= 5.9 (mm) z= 4.7 (mm)

Area (s) (s) for the (s) heat flow (s) (the heat flux [W m^-2] is in the center of the square for the coordinate z=0.0 ):

xo= 0 x=0.0104

yo= 0 y=0.0104

zo= 0.0 z=0.0

About the sample: The values of thermal properties used to calculate these temperatures are 43.1 W/m.K and 14.8 x 10^-06

m/s.

As boundary conditions, it was considered that all the faces were submitted to a constant convection heat transfer

coefficient (h = 20 W/mK and Tinfinite = 302.35 K).

About the results, using CFX-v5.6: Im making a comparison with experimental data and it had a big deviation, around 30%.

More details about the results obtained with CFX-v5.6: Im using CFX-v5.6 and making a comparison with experimental data and also with a numerical data (method elemnt method) from Solidonio* reseacher (*from Federal University of Uberlandia, in Brazil - www.ufu.br). Solidonio has been used this kind of boundary condition (h=20 and T=302.35 [K]). In my study, i had to put the sample (metal) within a bigger cavity with air (laminar flow) with isothermal wall at T = 302.35 [K]. Solidonio did a simulation using only the sample, only a heat conducting simulation. On the sample, im using MC1 = 0.8 and this sample has 12.7 x 12.7 x 4.7 [mm]. Maybe, i would improve the mesh, but i dont have a good PC, onlye a AMD Athon with 512 MB of memory RAM. Its good to remember that my Biot number on this sample is much lower than 0.1, so my results show that, in all the sample, i have the same temperatura, around 338 [K] for t = 48 [s] and the experimental data gives around T = 49 + 273.15 [K]. A big deviation.

I said: "...Its good to remember that my Biot number on this sample is much lower than 0.1, so my results show that, in all the sample, i have the same temperature...". I mean that i dont know if the results will get better, if i make another mesh wit more elements on the sample. On the fluid (air), im using a coarse mesh! I dont want to study the flow around the sample. On CFX-v5.6, i cant make only a heat conducting simulation in a unique solid. I must make two solids, one is the fluid (air at 25 C) e another is the solid.

The method used by Solidonio* is the Finite Element Method (FEM), its not a commercial software. He* had developed this 3D software. The sample has the following thermal parameters. Density "ro": 14,900.0 [kg/m]; Specific Heat Capacity Cp: 195.85 [J/(kg K)]; Thermal Conductivity K: 43.1 [W/(m K)]; Thermal Diffusivity Coefficient "alfa": 14.8E-06 [m/s].

The deviation is around 30% when im comparing with experimental data! I dont know whats happening! The sample {12.7 x 12.7 x 4.7 [mm]} is too smal with a small Biot number (much lower than 0.1). So, the gradient of the temperature is the same through the sample in a z direction. When I improve the mesh (with small volumes), there is no advance on the results! I put 0.38 as MC1 on sample mesh and 20.0 (MC2) on the cavity walls (mesh). Next week, Ill change the g (9.81 [m s^-2] direction. Today, Im simulating with K = 100 and not with K = 43.1 (thermal conductivity). Im making a simulation on CFX-v5.6.

Thanks for your contribution!
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