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1-Newbie

## Understanding Thermal Analysis

Hello,

I am a new Creo convert from Solidworks. I am trying to better understand Creo's thermal analysis. I am looking for a new more informative definition of "prescribed temperature" in Creo. I am running a analysis on a cattle brander to see the heat transfer from the logo heated end up through the shaft to the handle. To see how long I need to make the shaft. Can someone please verify I am setting it up correctly. Right now I am applying a heat load to the logo end of around 650 F. I am then applying a convective boundary condition on the rest of the part with a convective coefficient of 25 w/m^2K, and a bulk temperature 75 F. Then I am applying a prescribed temperature at the end where your hand holds it of 75 F simulating the end where there is no temperature change. What do you guys think? Is there something you would do differently? Thanks in advance for the help.

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1 ACCEPTED SOLUTION

Accepted Solutions
4-Participant
(To:fphelps)

Hi Frank

I would do this slightly different.

First let's assume you do a steady state analysis. At the hot end (glowing red) is the logo. You would typically not apply a heat load there, and a heat load is not 650F, A heat load would be in Watt.

I would typically put the prescribed temperature there (Ok 650F). Asuming the logo has a fair heat capacity (it will stay at the same temperature for a while).

You heat transfer coefficient along the shaft is not bad (see the picture from the engineering toolbox). Now you already have sufficient input. The steady state analysis will calculate the temperature of the handle, you can redo this for different shaft lengths until your handle stays below 100F (or 40C or something, low enough to be comfortable). The steady state will give you a fairly pessimistic (=high) temperature for the handle. It could take hours for it to heat until it reaches that temperature.

For that we would use a transient thermal, but that's the next class.

Regards

Erik

7 REPLIES 7
4-Participant
(To:fphelps)

Hi Frank

I would do this slightly different.

First let's assume you do a steady state analysis. At the hot end (glowing red) is the logo. You would typically not apply a heat load there, and a heat load is not 650F, A heat load would be in Watt.

I would typically put the prescribed temperature there (Ok 650F). Asuming the logo has a fair heat capacity (it will stay at the same temperature for a while).

You heat transfer coefficient along the shaft is not bad (see the picture from the engineering toolbox). Now you already have sufficient input. The steady state analysis will calculate the temperature of the handle, you can redo this for different shaft lengths until your handle stays below 100F (or 40C or something, low enough to be comfortable). The steady state will give you a fairly pessimistic (=high) temperature for the handle. It could take hours for it to heat until it reaches that temperature.

For that we would use a transient thermal, but that's the next class.

Regards

Erik

1-Newbie
(To:ehaenen)

Eric, am I right in the understanding that a coefficient of 20 would be a cooling effect, while it would be vice versa on the other end? Thanks again.

4-Participant
(To:fphelps)

Frank

You give a coefficient and a bulk temperature.

The coeffciient is like how hard the cooling fan is blowing, the bulk temperature is the temperature of the air blowing by.

A coefficient of 20 w/mK means the air is (almost) standing still (not cooling). A higher number gives better cooling.

Hope this helps

Erik

1-Newbie
(To:ehaenen)

Ok, great thanks. What would be something I could compare a coefficient of 5 to? Something like a fan on high as mentioned in your last post, or maybe something more powerful. Thanks in advance.

1-Newbie
(To:fphelps)

The heat transfer coefficient is a measure for amount of energy transferred per time, per surface area, per degree temperature difference. So for forced convection one would expect a higher value than for free convection. I.e. the harder your PC fans blow on the CPU, the more energy it can get rid of.

According to this link, 5 W/m2,K is a typical free convection value (vertical plate), whereas forced convection ranges from 10 to 200 W/m2,K in air.

11-Garnet
(To:fphelps)

Hi Frank,

I'm not a thermal expert (I've used it a couple of times), but looking at the documentation it sounds like a heat load is a power (rate of heat energy input), not a temperature - so check the units on that:

If I was doing this, I think I'd set a prescribed temperature at the fire end (not a heat load):

https://help.ptc.com/creo_hc/creo30_sim_hc/usascii/index.html#page/sim/simulate/modstr/prestemps/ref...

but then I'd leave the handle end with just the convection condition (or even with nothing, simulating the insulation of the hand holding it). As I understand it, a prescribed temperature is like joining that surface to an infinite heat reservoir at that fixed temperature - it will make that surface equal to that temperature, with whatever heat flow in or out that requires. You're after zero heat flow into the hand.

If you leave the handle end 'free', it will end up with a temperature which depends on the length of the handle and the values of your convection condition - then you can run a sensitivity analysis to see the relationship between length and handle temperature. (It will always be slightly higher than your bulk temperature, btw, unless you have an infinitely long handle or an infinitely large convection coefficient.)

HTH!

1-Newbie
(To:fphelps)

Eric, Jonathan- Thanks for the input you guys are both right. I was typing this information up from memory this morning and I had it backwards. Thanks for the help with everything.

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