Brazil, January, 25th, 2008.

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 program too. The softwares are listed below:

FLUENT, ABAQUS v6.7, ANSYS CFX-v11.0, 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 (ºC) = 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

m²/s.

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

coefficient (h = 20 W/m²K and Tinf=302.35 K)

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

More details about the results obtained with CFX-v5.6: I´m 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, i´m 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 don´t have a good PC, onlye a AMD Athon with 512 MB of memory RAM. It´s 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: "...It´s 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 don´t know if the results will get better, if i make another mesh wit more elements on the sample. On the fluid (air), i´m using a coarse mesh! I don´t want to study the flow around the sample. On CFX-v5.6, i can´t make only a heat conducting simulation in a unique solid. I must make two solids, one is the fluid (air at 25 ºC) e another is the solid.

The method used by Solidonio* is the Finite Element Method (FEM), it´s not a commercial software. He* had developed this 3D software. The sample has the following thermal parameters. Density "ro": 14,900.0 [kg/m³]; Specific Heat Capacity Cp: 195.85 [J/(kg K)]; Thermal Conductivity K: 43.1 [W/(m K)]; Thermal Diffusivity Coefficient "alfa": 14.8E-06 [m²/s].

The deviation is around 30% when i´m comparing with experimental data! I don´t know what´s 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, I´ll change the g (9.81 [m s^-2] direction. Today, I´m simulating with K = 100 and not with K = 43.1 (thermal conductivity). I´m making a simulation on CFX-v5.6. I´ll use ANSYS CFX-11.0 to see if I will have a different results.

Thanks for your contribution!

For meshes using MC1=0.6 / MEL = 2.0 and MC1=0.5 / MEL = 4.0, the results had a small deviation, less than 10% for time t = 70s (from time t=0s up to 110s). With other MC1, the deviations are big with 30% of error, when i´m comparing with experimental data. In this case, i used MC1, on the solid, equal 0.2; 0,4; and 0.8. What´s the problem on my simulation? I´m using tetra mesh and CFX-v5.6. Does the hexa mesh has a better result?

MC1= mesh control on sample with 12.7 x 12.7 x 4.7 mm. MEL= maximum edge length on the cavity (with air) with 32.7 x 32.7 x 24.7 mm.