Heat transfer from 400 deg(f) with -140 deg(f) nitrogen

[usfence]

New process exploration, I imagine I will need a little more detail as well to solve. Where do I start?

CONDITION: With a continuously moving extrusion 30 ft/min going through a die block at 400 deg(f) and using high velocity (100 mi/hr)nitrogen gas -140 deg(f) released inside extrusion for rapid cooling.

QUESTION: What will the resultant temperature balance be in the die, will the nitrogen pull down the die temp or will it be negated as the extrusion is constantly being drawn away.

 

[pmover]

some thoughts:

heat transfer (hot to cold) is dependent upon mass of extruded material, heat capacity of mass, heat transfer coefficient of nitrogen, and temperature difference.

amount of heat removed from extruded material (assume conduction methods) approximately equals heat absorbed by the n2 coolant (convection methods), less heat losses to atmosphere, etc. assuming no radiation effects.

without knowing dimensional and property details of extruded material, the results can not be determined.
-pmover

 

[kenvlach]

pmover is right, need more data.
Is material Al 6063 ?
What is extrusion wall thickness?
What is geometry of the die/extrusion?
How close is the N2 nozzle to the part? [I imagine
the high velocity is to overcome a bubble layer at the surface.]
What about using water?

Is this cooling a good idea to begin with?
Sometimes, the heat produced by extrusion can be utilized as part of the Al heat treatment process.

 

[usfence]

Extrusion is PVC, wall thickness is .050, shape is rectangular 6" x 3/4" with two internal ribs evenly spaced spanning 3/4" gap. N2 is being introduced at 3 locations centered in the relative cavities within the extrusion mandrel. Water is not an option as that was where we are and this is to be a new process which will allow rapid cooling and permit higher throughput.

I appreciate the input to this point, let's keep it going.

Thank all

 

[JKEngineer]

usfence -
I don't fully picture the situation that you have, so some of this may reflect errors in my understanding.

If I understand correctly:
3 hollow cross section of PVC, hot
3 streams of very cold (-140F) nitrogen gas put inside at 100 mi/h
metal die both internal and external

To analyze the system I would look at the heat transfer between:
outer die and air, both convective and radiative
outer die and any heat source, including the hot PVC (contact, I assume)
inner die/mandrels and PVC and/or N2
hot PVC and N2 (I assume the N2 is flowing with the PVC not across or against the flow)

The heat transfer analysis would require information about the heat transfer coefficients for each of the stages listed, mass and thermal property information, flowrate information. The flowrate information is vital to establishing the heat balance limits, i.e., temperature rise of matl A vs corresponding T drop of matl B - such as N2 and PVC.

The geometry will come into play. The heat transfer by conduction through each material will come into play.

For first level answers, a lot can be simplified and ignored. You could for example, compare the heat "supplied" by the flow of PVC to the possible heat removed by the N2. This would be straight heat balance, not heat transfer. It will establish the possible limits, that would be approached to some degree as limited by the heat transfer and contact time or distance.

If the geometry cannot be ignored, then you need to develop a model of the system. My approach, which is one of the services I offer, would be to build an FEA model of the system and develop the combination of heat balance and heat transfer information for all the parts of interest.

HTH, let me know if I can be of assistance. You can find me through my website.
Jack M. Kleinfeld, P.E. Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering

http://www.KleinfeldTechnical.com