I have 2oz. of a mist (similar to water) flowing through a tube. Heating coil around outside of tube. Temp.?

Question

I am trying to find the Watts necessary to heat 2oz. of a mist (similar to water) flowing through a tube at 2oz. per min. There is a heating coil on the outside of the tube. Without knowing much about the tube material, what is an estimate of how much power is required to heat the mist flow from 70 deg. F to 550 deg. F?

Thank you for any assistance.

Answer 1

Sans specifics, it's nearly impossible to give you any straight answer. There are so many variables (specific heat of the substance, material of the heating coil, conductivity and geometry of the tube, etc.) that I cannot even give you a hint as to a specific number. The temperature of the heating coil will have to be somewhat higher than 550F, but how much higher is up for grabs.

I think you're going to have to do this empirically. Try measuring the temperature change with the heating coil at different settings to see what kind of effect it has. This should give you a ballpark number for your wattage.

If you can lengthen the time that the "mist" is passing through the heated part of the tube, it will increase your heat transfer. Insulating the heating coil from the outside environment will also help.

Answer 2

If it's similar to water, it will vaporize well before the temperature gets to 550F, unless somehow you are maintaining a high pressure in the tube. Nevertheless, let's proceed with the calculation.

As a starting point:

Use the specific heat of water to calculate the energy needed to raise 2 oz. of water from 70F to 550F.

Then, divide that energy by 60 sec to get a ballpark figure for the power.

However, the actual power required will be higher than that. You need additional power to heat the air or gas in the tube. Also, you don't say how well insulated the tube+heater is; heat will be lost to the surroundings if the insulation is poor.

Answer 3

I it needs to get to 550°F it may take a fair bit of power. I'd say start off with about half of the maximum power that the heater can provide, see what the temperatures are at the expected flow rate, and then adjust it up or down as required.


Doug