How to calculate steel stripe warming when subject to electric current ?

[mpitkanen]

Hello all,

I'm in need to design a solution to prevent existing concrete surface to collect ice, when there is sparkling

water flying around. This is actually dam and the surfaces are the sides of it and dam is slightly leaking or

opened to let water run, so that there is lot of water drops everywhere.

Now I got idea to clean these concrete surfaces by high pressure water jets, glue RST-plate stripes side by side

using epoxy, and finally connect these plate to electric system to warm them max up to 30 deg. Celsius and

surrounding climate is below Zero.

The total area in question is ca. 30m2 per one dam and I have three dams.

My question is how to calculate the thickness of the plate, if they are f.ex. width=200 and length 5000

and what kind of current it might need??

Better off, if someone can give formula where these values could be calculated by myself?  ;>)

Best Regards Matti Pitkanen

www.pcskouvola.fi

[ValeryOchkov]

May be this (pics 18.8-18.12) will be a start pictures for you

Study 18. Differential Equations in Thermal Engineering

[Fred_Kohlhepp]

You've got quite a problem.  Actually, several of them.

• You need to figure out (guess, actually) how much heat you need to keep the plates warm.  This is where what Valery pointed you at may come in handy, although there are so many variables in your problem (how much "sparkling water" do you have to melt?  how much water is leaking over the plates? Is there wind or still air?) that determining heating requirements may be the largest issue.
• Electric heating isn't challenging.  If you know what the heat flux per unit area you need then you can figure current density for a given resistivity.  (Resistivity is a material property, I didn't say resistance.)  From current density and plate width you can get thickness.  From area, length and resistivity you get resistance, from resistance and current you get voltage.

It's going to be expensive!

[-MFra-]

Hi Matti,

I would use a so-called electric water heater, commonly used in homes where the gas network does not reach them, and with an electric pump, distribute hot water into a network of pipes or serpentine arranged on the walls where ice forms, a bit like you do to heat the floor. Heating with current could be dangerous.

[mpitkanen]

Hi F.M.

Spraying hot water is no solution, due to large area and eccessive heat loss, I think.

Direct surface warming is much more effective, because it prevents the iceing on surface.

We have just now an other rebuild project where new vertically moving steel-made dam plate

ca. 5 x 4 m2 slides between U-shaped RST-made guides on both sides. These guides are

electrically heated. Me being a structural engineer, have no idea ( yet ) what is the

voltage, AC/DC-mode or current, but I have been told, that it is working well and can be made

for my idea too.  ;>)

I have been asked to do preliminary design for cost estimate and budget, so I should know

with some accuracy the plate thickness.

BR Matti

[Fred_Kohlhepp]

You can calculate the resistance of a mild steel plate if you know the dimensions.  So for voltage you can get current, etc.

[mpitkanen]

Thanks Fred, now I can see some direction for my exams ;>)

How do you see my task: one big plate or several stripes ?

I'll come back next week, tomorrow in court as expert and week-end in Netherlands and back on Monday.

BR Matti

[Fred_Kohlhepp]

Trying to pass electricity directly thru structural steel seems to me to be difficult and risky.  There would be many opportunities for unintentional current paths.

I suggest that you consult with a good electrical power engineer--sooner rather than later.  If there's already a system in place that works, who designed and installed that?

[-MFra-]

Hi Matti,

I said to heat the surface with a conventional heating system. The heat conductive fluid , flowing in the appropriate pipes  and radiator, could be high temperatur oil instead of water.