Heating 1meter copper tubes for textile finishing 3

[Sunflame]

Dear Engineers!
I would like to heat two copper tubes 1 meter long each to about 200 celsius degrees for a textile finishing application.
The tube's diameter is 35mm, thickness is 1,5mm and an electric heater 300mm long is placed inside the tube on one side or both.
As copper is a good heat conductor, do you think I will be able to maintain around 180 degrees celsius in the middle of the tubes?

 

[Compositepro]

Are these rollers supposed to do the compacting of the fibers as well? That would never be done with such small diameter rollers. Copper tubing is not strong/stiff enough, nor will it take the wear unless this is for an experiment only. Compaction requires large diameter rollers to squeeze the fiber web without distorting or wrinkling it.

 

[Sunflame]

Yes these would do the compacting also.

 

[MortenA]

This web calculator may help you:

https://www.thermal-wizard.com/tmwiz/default.htm

 

[MortenA]

Just did a quick check for a 1 m long tube with Ø35 mm and found that the natural convection heat loss (including radiation) is 400W at 200ºC with an ambient temperature of 20ºC - so your heaters should be able to deliver enough power, but if they switch off when the heater reaches 200ºC then the tube will of course be colder at a distance from the heater - exactly how much this wont tell you. A small IR scanner can be bougth at your local hardware shop - doubt it will cost more than €50 - it should be accurately enough. Try it out if you already have all the gear

 

[Compositepro]

Copper is highly reflective in the IR band, so IR thermometers do not work. Particularly cheap ones with no emissivity adjustment.

 

[moltenmetal]

Not sure I understand still- the problem is poorly formulated and I think the use of English is hampering communication as well.

You have a tube, 100 cm long. Two of them, but no matter.

You insert what sounds like a cartridge heater into each "side"- by this, I think you mean "end". No indication of the tolerance between the ID of the tube and OD of the cartridge heater, but let's say it's a reasonably tight fit.

Each cartridge heater is 30 cm long

Then you ask if it will be hot enough in the middle, i.e. in the 40 cm of the tube which is unheated.

Are you expecting copper- a tube which is 1.5 mm thick- to be sufficiently thermally conductive to conduct heat down its LENGTH to do any useful heating?

Sorry, but you need a 1 metre long cartridge heater, or two 50 cm long ones. You can't leave a gap in the middle and expect it to not be substantially colder if the intention is to heat something flowing past the tube.

I'm not going to bother doing heat transfer calcs for you because you haven't given a clear indication of what exactly is going on. But your options/alternatives could include circulating hot oil through the tubes, or if that won't give sufficient temperature uniformity, using a vapour which condenses at the temperature you're interested in. 200 C is a little too high pressure for steam in a copper tube of that size and wall thickness, but there are other options- assuming you have enough slope to drain the condensate that forms.

 

[Sunflame]

Hey moltenmetal,
Indeed english is one of my languages and not the primary. Anyway you understood the problem well.
I may be rethinkink the diameter of the rollers, but in the end it comes down to what temperature is to be expected in the non-heated 40cm middle section just by the conductivity of the copper tube, while the two heaters on the ends are indeed in tight fit with the tube and can heat up to 200 celsius degrees.

 

[moltenmetal]

You have a tube, only 1.5 mm thick, and you expect a significant quantity of heat to be conducted along its long axis.

Give up on that approach.

Even if you covered that 40 cm long middle section with insulation, and heated each of the 30 cm ends to 200 C, the temperature in the middle of the 40 cm section would be lower than 200 C. That copper tube has a large area for both conduction and radiation to the external environment, and the only thing carrying heat down the tube is the tube itself, which is made of a good conductor but is very thin (only 1.5 mm). You need something more conductive than NOTHING in the middle of that tube. Even a solid copper rod would be better than nothing- and it likely will not do the job.

Fill the space with a heater. Or pump hot oil through the tube. Which do you need? Dunno- depends on the tube exterior heat transfer conditions which a) you have not posted enough information to calculate, and b) the people on this forum have better things to do than to calculate for you for free.

Best of luck.

 

[IRstuff]

Conductivity of copper is NOT infinite, therefore, you will wind up with a cool region in the middle. Moreover, with a 1m wide material, your tube needs to be a minimum of around 1.1 meters to account for the thermal loss at the ends. Your heaters are supplying power, not temperature, and power will flow as it wants to flow. I think you need a minimum of 3 heaters, two short ones for the ends and a long one in the middle.

1.5-mm thickness is definitely not enough for uniformity control.

30-mm diameter sounds way too small to perform compression of the material. How much pressure is required and how are you going to apply it? It's likely your 30-mm tube will bend in the middle. Anything that transfers force uniformly across the width will cause additional heat loss.

How are you going to transfer electrical power to the heaters while they're rotating?



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