system to produce hot air 4

[hesham kady]

hello,
I need your help with a problem.
I need to create a system to have a hot air with high temperatures up to 800C.
Do you have ideas to help me?
electrical heaters or combustors will be the best choice for me?
the required flow rate is so small at atmosphere pressure.
thanks.

 

[Latexman]

How small is the required flow rate?

Good Luck,
Latexman

 

[hesham kady]

about 1 ft3/min or less.
the important issue is the constant temperature with a +-3C.
this is the point for me, flow rate is not important for me .

 

[MintJulep]

https://farnam-custom.com/standard-products/process-air-heaters?locale=en

Or other manufacturers.

 

[LittleInch]

Wow. 797 to 803 C?? Unless everything else is equally accurate this looks to be impractical.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Stick.]

Is that temperature requirement a tolerance on the bulk temperature over time, or is it a tolerance on the temperature profile across the outlet of the device at any instant in time (or both I suppose)? Either way it will be tricky, but one will probably be worse than the other. My gut says to follow MintJulep's general suggestion and try to farm out the hard work to a specialist.

 

[hesham kady]

thanks for your replies.
to understand more, the hot air will pass through a small chamber ( about 10 cm*10cm) then to the ambient.
the temperature of the air is required to be fixed at a certain value.
electrical heaters are expensive and need an accurate controller which mean a high cost.
Are there no other solutions? like combustors
I look for effective and cheep solution

 

[LittleInch]

Cheap but effective and accurate to +/- 0.35% are mutually exclusive things.

Burning something will produce a lot more than 1cf/min and any sort of HX would be more expensive than the electric heater.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Stick.]

The problem with combustion as a heat source is that the flame temperature will far exceed your desired bulk fluid temperature, creating a large temperature gradient within the fluid, meaning you'll have to somehow mix it downstream of the flame to get your ±3°C temperature tolerance. I'm not saying that can't be done or even done cheaply, but it's probably not a trivial engineering task. Also, I'd be surprised if you didn't need a very accurate controller for the burner in this instance, which would drive up the cost of a combustion based option.

I'll caveat my above statements by saying I usually work on systems 4+ orders of magnitude larger than what you're describing that also tend not to exceed 300°C, so maybe there are tricks that work better at your scale that I'm just not aware of.

 

[Latexman]

Stick is right. Good temperature control in fired equipment is mostly a mixing and measurement problem.

Is there a process variable downstream that is utilizing this heat? Look more closely at the response of that variable; not the temperatures in the fired equipment. If you can fix the heat input into the fired equipment, and ignore temperature variation, I bet the downstream process variable will behave nicely.

Good Luck,
Latexman

 

[georgeverghese]

Small fluctuations in feed flow to the temp sensor which feeds back to the temp controller can also cause transient temp fluctuations, since both RTD and thermocouple sensors show some response lag ( RTD worse than thermocouple type).

 

[3DDave]

I would have a large oven ahead of the target section with a circulating fan to ensure uniform temperature followed by a laminar flow straightening section so the temperature remains uniform. This would supply the thermal inertia to stabilize the temperature.