Help reqd. for heater coils

[abicash]

Hi
This is somewhat unrelated to electronics in general,but for a new project i require a 6kw heater which has to be placed in a confined metal tube of ID 83mm and height 150mm.
I am thinking of a ceramic insulator with multiple holes of height 150mm each.
Is there any such insulator readily available?

Moderators ,if this thread is inappropriate,please remove it
If someone has worked with these before i could use help here
Thanks and regards

 

[Reloadron]

You don't mention what medium will be heated? Will the tube be open or closed ended? If for example the medium was water in a closed system I would be thinking about an immersion heater along these lines. With an ID of 83mm and a height of 150mm that is tight for 6KW. You may want to think about giving a call to Chromalox or Watlow and talking to one of their application engineers. I have found both to be very helpful for heater applications.

Ron

 

[abicash]

Hello Ron

Thanks for the reply.

I was browsing the net and i found this

I will use 3 nichrome wires wound through this over a length of 150mm.Air will be blown through them.this whole assembly is enclosed in an SS pipe of ID 83mm.
I found a 89mm insulator of height 20mm (so i would use 7 discs)
but am unable to find an 83mm or lesser diameter.
I want an application temperature of 350C.
Please provide an insight

 

[alec_t]

You do realise the minimum order quantity for the former you linked to is 100?
Could you get a local glass-worker to make you some custom glass formers?

 

[Reloadron]

Could you get a local glass-worker to make you some custom glass formers?

That or begin getting friendly with learning ceramics and access to a small kiln. I don't see an easy off the shelf solution. I have, as mentioned, had very good luck working with applications engineers from element manufacturers.

Ron

 

[abicash]

Hello

Thanks for your interest guys.
It seems the local guys here too want a mould to be made and require a qty order.
I tried earlier with fiber ceramic and got it made but this particular ceramic does not sustain the body temperature of the coils (around 1100C) for air temperature of 350C at the other end (with air blown at 6cu.m/min)
Is a Triac control necessary for the coils?

 

[Reloadron]

You could control using a triac or SCR controller. Just remember you have a 6 KW load out there so I would be looking for or trying to design a 10 KW controller. What's the voltage supply?

Ron

 

[abicash]

Hi Ron

The voltage is 415V/50Hz,3 phase

The current through each coil is close to 12 amps.
In such a case i would opt for a ready-to-use TRIAC controller (as used in fan regulators)
Have seen such controllers in knocked down forms or DIY ,around.

My question was : Is there a need for a triac controller? since i require only 350C temperature and the coil would be capable of heating itself to say 1200C.
How is this normally or popularly done?
On the other hand ,will it be okay to reduce the wattage by increasing the coil resistance? by matching the form factor of the coil of course

 

[Reloadron]

As to heat control I would guess you have a few options. For example today's basic hair driers run 1 KW or more. The heat is a function of how much air from the fan passes through the elements. Some use a small bi metal thermal switch in the airflow. In your case depending on how you want it to run I would think about a thermocouple in the airflow connected to a proportional controller with a 4 to 20 mA out driving a three phase SCR controller. The trick with things like this is doing the calculations which I am very poor at doing. You do not want more heater than you need. Airflow rate and everything get figured into the equation. If the watt density is for example too high and the air flow too low the elements self destruct burning up. Again, working with air is not my forte.

Ron