heat transfer 2

[billbattle]

I am looking for, how to calculate how much time it takes for incoming material to come up to room temperature. Specifically we machine allot of acetal. We seem to have an issue this time a year with larger diameter stocks ~3". We are in Michigan so the material is coming in on a cold truck. How long before it becomes up to room temperature?

 

[EdStainless]

Get out your heat transfer text book and look up Heisler charts.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

 

[racookpe1978]

Come on!

Look at your basic thermodynamics. Then tell me if you have provided ANYBODY with enough information to begin addressing your question.

Be honest:
Do we know what "room temperature" is for your factory floor or your warehouse or your storage area? Even if indoors, and assumed in Michigan in "winter"?
What temperature is "adequate" to begin working? 32? 40? 48? 58? 68? 78?
How cold is it outside? What is the starting temperature of the rods?
How many rods?
How long?
What metal?
What diameter are the rods? The 3 inches you mentioned, or all of the other diameters you implied were being shipped, but didn't mention?
How are the rods stored? Stacked tight next to each other? Spread out on wood pallets?
What air flow is in the storage area? Natural convection only? Have you tried fans?
Radiant heaters nearby? Or overhead? Only room air, heated elsewhere?

You have stated you have a problem. Now, give us enough information to begin discussing it. Otherwise, you've only said, " I have a heat transfer problem. Please solve it."

Think.

 

[billbattle]

I need the thermal properties information. I have yet to find it on acetal. I have found formulas for determining rate/time from mass I don't have the material properties to use them.

I'm not dealing with heat transfer though a wall or heat transfer from a liquid or gas inside a pipe to the outside etc.

 

[Latexman]

Why don't you stock the acetal needed for tomorrow's production today? That'll give it 24 hours to reach room temperature. Do an experiment with the largest piece that is worked to see if that will be alright.

Good luck,
Latexman

Technically, the glass is always full - 1/2 air and 1/2 water.

 

[marty007]

There is more to heat transfer than just transferring heat from inside to outside of a pipe.

You have a time dependent heat transfer problem:
[ol 1]
[li]The heat first has to transfer from the room temperature air to the surface of the bar. This could either be natural or forced convection. Any good heat transfer book can help.[/li]
[li]Once the heat has reached the surface of the material, it now has to conduct into the material. This is a conduction heat transfer problem.[/li]
[li]Both of these aspects will be time-dependent. This is a very typical problem, so I'm sure a good heat transfer book will have an example.[/li]
[/ol]

The details you'll need to solve the question are:
[ul]
[li]Starting material temperature (cold Michigan night)[/li]
[li]Room temperature (coldest expected machine shop temp to be conservative)[/li]
[li]Details for determining external convection (to be conservative you could assume natural convection)[/li]
[li]Phyical properties (specific heat/thermal conductivity)[/li]
[/ul]

With all that said. Because of all the theory involved, unknowns relating to the convection and physical properties, I'd recommend just doing some sampling/testing. Measure the temperature on a couple of bars, take them inside, then measure them every 10/20/30 minutes (whatever you feel is reasonable) to get a feel. This would probably be a lot easier and you'd be a lot more confident with the answer you get.

 

[chicopee]

If you have a single cod rod, laying horizontally and supported on a rack exposed to forced worm air, we could theoretically provide a time element. The problem is somewhat difficult because, seldom will you have a single rod stored on a rack, air temperature within the room fluctuates, the physical properties of plastic change as its internal temperature change and other unaccounted factors. Whatever we can calculate for you, the answer will not be exact. As suggested do an experiment and measure the surface temperature of the stock intermittently but keeping in mind that there will be a transient period in which the core temperature will be different than that of the surface temperature and the ends of the rod will warm up quicker than the middle of the rod. I suppose that you can use an infrared thermometer for the readings. For properties of Acetals, see the JPG attachment which is dated 1991 but I don't think that such plastic as changed much.

 

[dvd]

Get a data logger and a thermocouple. Drill a hole to the middle of a piece of acetal, where the hole just fits the thermocouple and embed it. You could put a dab of superglue on the thermocouple junction to assure good contact with the material. Put the acetal outside or otherwise get it to the lowest temperature you anticipate and them measure temperature and time to come up to temperature. There are too many assumptions to get very accurate results from calculation.

 

[billbattle]

Thanks. Testing is where I am headed.
After a little research it looks like my material may be a little green. We could be rushing it into production.