COMPARING THERMAL CONDUCTIVITIES

[richardforever]

Hello everyone,
I'm resolving a model in which i want to compare the conductivities of two bars of different materiales ( wood and metal). Both bars are insulated at the top and bottom sides.
I have a heat source on the left side of both bars fixed at a temp of 50ºC and at the right side i have a heat sink (or reservoir heat) where all the heat flux that passes through the bars is transfered to that place. The problem is how i model this boundary conditions in ansys?
To fix a temp of 50 ºC at the left side is easy but I'm lost in how to model the heat sink.
Besides that i want to do a transient thermal analysis to obtain a video in which i can see the differences.
¿Could anyone give me a clue to do that?. Thanks!

 

[rickfischer51]

By heat source do you mean internal heat generation?

You have to have a temperature associated with your heat sink, either a bulk temp in the body if the sink, or a temp and film coefficient of the cooling air. Generally you do not specify a temp at the heat source. Specify an hgen on one side and a sink temp on the other.

Rick Fischer
Principal Engineer
Argonne National Laboratory

 

[richardforever]

No, it's not a internal heat generation. I just want to fix a temp of 50ºc at the left edge of the bar. Furthermore the bar is all insulated, so it doesn't exist film coefficient with the air. The right side is a reservoir of heat ( a big area with a very high conductivity compared with the bar).
My doubt is how to model a transient example cause i don't understand very well how to do it.
I put an example of how I think it could be (I'm comparing the heat flux that pass through a metal bar and a wood bar):
/PREP7
RECTNG,,1,,0.05
RECTNG,1,2,-0.475,0.525
RECTNG,,1,-1.35,-1.4
RECTNG,1,2,-1.825,-0.825
AGLUE,ALL
ET,1,PLANE55
MP,KXX,1,57
MP,KXX,2,10000
MP,KXX,3,0.13
MP,KXX,4,10000
TYPE,1
MAT,1
/PNUM,AREA,1
APLOT
ASEL,,,,1
SMRT,1
AMESH,ALL
ASEL,ALL
APLOT
ASEL,,,,5
SMRT,1
AMESH,ALL
ASEL,ALL
ASEL,,,,3
SMRT,1
AMESH,ALL
ASEL,ALL
ASEL,,,,6
SMRT,1
AMESH,ALL
/SOLU
ANTYPE,4
TRNOPT,FULL
KBC,0
TIME,1000
AUTOTS,ON
DELTIM,10,2,50
NSEL,S,LOC,X,0
D,ALL,TEMP,50
ALLSEL,ALL
OUTRES,ALL,ALL
EQSLV,SPARSE
TUNIF,10
/STATUS,SOLU
SOLVE
FINISH
/POST1
PLNSOL,TEMP,
ANTIME,10,0.5,,1,2,0,3000
FINISH

The problem is that the change of temperature seems to be homogeneous (I mean that either the bar as the reservoir heat at the same speed (wood and steel case) but really they have different conductivities so i don't understand why that happens besides that how i can put a smaller step of time to do a larger video and see the transition of the heat of both bars since 10ºC which is the temp of the bar to the equilibrium state of 50ºC. I know that i'm doing something wrong. Thank you for the help.

 

[rickfischer51]

First, you can't run this as a transient because you have not specified density and specific heat. Second, all your elements are MAT=1, so you have uniform thermal conductivity throughout your model.

Rick Fischer
Principal Engineer
Argonne National Laboratory