'Regular' wire for low-watt heating ?

[JesperMP]

Am I crazy for considering this ?

I need to protect a steel tube ø200mm 500 mm long from condensation of moisture on its inside. I need something like 20W. I just need to raise the temperature of the tube slightly above ambient.

I have looked for heating cable, and I can find plenty that are typically used for frost protection of water pipes etc. But I dont like these.
They are typically 230V AC, and I prefer to not have high voltage at all at the location of the tube.
Also these heating cables are relatively clunky.

So I was thinking why not use 'regular' wire to make a DIY of sorts of heating.
I would use a small DIN rail transformer to get 24V AC, and then drive 2A directly into a single wire wound around the tube.
I am thinking about using high temperature wire (even though it is probably not necessary), something like HELUKABEL 25511 which is a thin 0.14mm².
I would possibly make it more efficient by wrapping isolation around the tube and heating wire.

Tell me, am I on a completely wrong path ?
Are there standards or regulations that prohibits the above idea ?

 

[BryanG]

Your maths works out OK in terms of Voltage, Current and Resistance, I calculate you would need about 60 metres of cable wrapped about every 10mm. You will need to consider that you will be creating an Inductor and an electromagnet.

 

[tarik1978]

I propose using heat cable like this one:
https://www.oemheaters.com/product/6152/24v-dc-heat-cable-35-wattsfoot

 

[JesperMP]

Woops, it is ø100mm 300 mm long, not ø200mm 500 mm long.

My bad ..

I would need to make ~120 turns of the wire around the tube to get 20W.
Since the tube is quite smaller than I thought, maybe 10 W is enough to get it warm enough to avoid the condensation.
The 0.14mm² is the thinnest I can find when it has to be isolated. That is what decides the lenght. To reduce the wattage, I have to increase the wire length i.e. increase the number of turns.
Or use a 12V power supply instead of 24V.

@BryanG.
Good point about the inductor. I will take care to wind half of the wire one way, then the other half the other way.
I think I can wind the wire quite closely since it is high temperature type, and the wattage is quite low.

@tarik1978.
That heater cable for 24VDC could be fine.
I would like to find a similar cable in EU.

 

[JesperMP]

I think I have found a couple of local vendors. It seems to be common to use 24V heat cable in farming to frost protect feed trays.

 

[mendonsy]

Have you considered an IR heat lamp like they use for raising young chickens?

 

[JesperMP]

@mendonsy.
I need to heat the circumference of the tube. So heating on one side with one lamp would not be enough.
And not only the tube would be heated up but everything that gets illuminated by the lamp and that would be undesirable.
And there really is no place to fit such a heat lamp. The tube is inside a relatively small chamber.

Points for thinking out of the box though.

 

[drbitboy]

Going back to basics: you want to keep the surface temperature of the tube above the dewpoint of the vapor or gas (air?) in the tube, and the tube is inside a relatively small chamber.

Can a bulb go inside the tube, and heat the surface from inside?

Can you control the dewpoint inside the chamber instead?

How about a more comprehensive description of the entire process, constraints (e.g. can't heat other parts of the process)?

- drbitboy, D.M.D.

 

[TWS]

This vendor can make anything you want.
https://customheatersandresearch.com/.

 

[JesperMP]

@drbitboy, description:
Warm (~45˚C) and moist (~4%) sand is to be filled into a cup that is ø100 mm.
The filling goes on for ~5 seconds every ~50 seconds.
The tube in question is aiding in guiding the sand into the cup.
The sand is very sticky if it hits the wall of the tube.
The sand stream will be adjusted as much as possible to not hit the walls, but it cannot be 100% assured that no sand will hit the wall.
A further concern is that the ambient temperature may be quite cold (~0˚C) and there may be moisture in the air that could condensate on the surface of the tube.
Due to that the process will not heat the tube, the tube will remain at a temperature close to the air temperature - if not heated by the heating cable.
This will make the tendency to sticking even worse.
There is no and it is not foreseen that there shall be a mechanical cleaning device or similar.
The tube must be 'self cleaning'.
It is not possible to have anything in way of the sand stream.
edit: The whole thing is in a machine. The area where the outside of the tube is available for the eventual heating is in a part of the machine that makes an enclosed chamber.

So my plan is to manufacture the tube of stainless steel, have its inside polished to mirror finish, and then heat the tube slightly.
That is the gist of it.

@TWS. Thanks but I will try to solve it by standard (and inexpensive .. ) i.e. not custom parts.

here are a couple of heating cables I have found:

Heat cable for tubing or trays (cut to length):
https://www.esska-dk.com/shop/FLV-varmekabel-24-volt-17W-m-selvbegraensende--503100017024-7230

Heat cable for vehicle lamps (fixed length):
https://www.beskoonline.dk/elektris...lbehoer/modstande-for-led-baglygter/093865124