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Hello,
I am trying to run a transient thermal analysis and am having trouble setting up the boundary conditions. Here is the set up:
I am running the transient analysis on block 2. I have a prescribed temperature of 20degC on the bottom surface of the block, and then a heat load (in Watts) applied to the top surface. My error may be in trying to calculate the heat load on top possibly?
I want to determine the time it takes for the bottom surface to reach 170degC.
What is your question exactly? Is your model not running, or are the results not as expected?
One thing I can already say: If the bottom surface is constrained to 20degC, it will never reach 170degC. You need to remove that constraint if you want the bottom surface to change temperature.
The model runs, but the time it takes to heat is 0.0002 sec which is not right at all and I get a extremely large dynamic temp. I am unsure what to set the boundary conditions to. All that is happening is the upper block comes into contact with the lower one. I am trying to see how long it takes for the bottom surface of block 2 to reach 170 degC.
So are you saying to only apply a heat load?
To calculate the load I am using the equation:
Q = A_block2*k_aluminum*delta_T/thickness_block2
Tim,
it seems you want to use Prescribed Temperature (20 degree) for the initial temperature.
However, it is a constraint and will stay constant all through the analysis, so the surface can never reach any temperature other than 20 degree.
The strange result may be somehow caused by analysis finding a steady state very soon, because the temperature doesn't change.
I don't know a strategy to define different temperatures for the initial moment and otherwise keep it unconstraint.
You can only set one global temperature.
Maybe it is somehow possible to heat up block 1 within the analysis and then stop heating and look at what happens, when it reached 170 degree?
Thanks,
Gunter
It seems as if you have some modeling and/or unit issue. I can set up a similar problem and get realistic results. What does the actual problem look like? Is there an electric heater that gives a well defined power input? Or do you by some means maintain 170 degrees in block 1? What is the initial condition? From your description, it sounds like block 1 has a uniform temp of 170 degrees, and block 2 of 20, correct? I don't quite understand your formula there, what is "A_block2" and "k_aluminium"?
Only applying a heat load should work. Not sure if it simulates exactly what you want (you haven't told us yet what you are actually simulating).
You may also need a heat transfer coefficient that indicates how well the different parts transfer heat to each other.
I agree with Mats it sounds like a unit issue, if the solution is so far off.
@Mats: That formula is for calculating heat transfer, see for instance here:
I'm not sure if that is the right way to calculate the heat load in this case. I would sooner expect the heat load to be known from another source, for instance energy dissipation of a CPU on to a heat sink.
One problem is this: Block 2 will NEVER get to 170 degrees. It will only get to a temperature between 170 and 20, and that temperature will depend on the ratio of mass*specific-heat of the two blocks. So if you are trying to find a solution to the problem of T2 where T2 is defined as when block 2 becomes 170 degrees, you will be waiting a very long time.....