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Snow melt thru a panel 1

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m2e

m2e

Mechanical
Jun 28, 2006
92
This is for an industrial application. How do you calculate the amount of heat required *inside* an enclosure, so that the exterior wall would not accumulate snow or ice? I supposed the goal is to maintain the external wall surface temperature to be above freezing point.

Some of the variables that we will need:
- External ambient temperature
- Wind speed
- R-value of the wall
- Wall thickness and area

Some of the answers that I need:
- wall inside temperature
- heating power required

Any ideas on how to approach this?
 
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SAE AIR 1168-4 Ice, Rain, Fog, and Frost Protection is the ticket for you. While it's intended to address aircraft deicing and anti-icing, the requirements are relatively similar. Table 3F-3 was specifically for anti-icing for windshields.

AIR_1168-4_ooup7u.png

AIR_1168-4-2_pe7pzg.png


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Just curious how large this enclosure is. Even at the low air speed of 100 knots, the requirement is 1,200 BTUH per square foot. Wow, that is a lot of heat. Wind speeds for your enclosure will certainly be less, but the required amount of heat may be more than you think. Again, curious on the size of your enclosure.
If it is small, would something like heat trace or a gutter ice melting coil do the trick?
 
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That was for running clear, so no ice accumulation whatsoever; the idea is that the windshield will never be obscured. Note also, the windspeed is assumed to be consistent with actual flight, unlike a winter storm, where there would be gusts and lulls.

For an enclosure, that requirement is unnecessary, and any buildup is apparently acceptable so long as there's no ice in direct contact. That could allow for power densities down in the 0.25 W/in^2 or lower.

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I agree with BronYrAur the heating requirements could be...obscene if this enclosure is bigger than a shoe box.

An assessment as to why this box needs to remain snow free should be made and perhaps the need for only a single surface needing to be ice-free could be maintained. Perhaps just a window? Or just the handle or latch areas?

Keith Cress
kcress -
 
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Thanks for providing this. Using the table and chart, assuming the lowest number, 2.5 W/in^2, for a 10ft x 10ft panel, the power required is 36 kW. This seems to be excessive. Perhaps the tables are for high altitude, high speed, and cold ambient temperature?

Is there any way to calculate the requirements of 4000 ft, -15F, and 12 mph wind speed?
 
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Somehow I wasn't getting the notification emails so I've missed a few messages. It's a telecom type building and the ice buildup is blocking the RF signal. Heat tracing doesn't work because it'll block the signal too.
 
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"For an enclosure, that requirement is unnecessary, and any buildup is apparently acceptable so long as there's no ice in direct contact. That could allow for power densities down in the 0.25 W/in^2 or lower."

Could you elaborate a bit on this? How would buildup affect the power densities? How about cyclic deicing? Would that lower the power requirement?
 
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There are lots of possibilities, but you need to clearly state what the requirement is.
> What is the intent of not accumulating ice?
> Is there a requirement to maintain a certain ice free zone around the box?

Certainly, one obvious option is to allow for the ice to build up and then deice, leaving an ice dam around the box that would minimize the air speed against the box wall itself. However, most of the more efficient approaches also requires additional intelligence, i.e, how does the system know that there has been ice build-up? How will it know what the wind speed is?

Below is the equation that supposedly generated the table, but I would suggest that you find a copy of the document and go through the equation and the section on "Running Wet Anti-icing". Mß is the "local water catch" value that's a messy function of air speed, blah, blah, and is what is responsible for the shape of the curve.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1582762302/tips/equation_3F-21_aduelu.tiff[/url]

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What type of an enclosure are you interested in figuring out heat loss.
 
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It's a telecom enclosure. Some antennas are housed inside and the ice on the walls blocks the signal.
 
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Ah, so then no ice buildup would be acceptable within the field of view of those antennas? That would suggest requiring no visible ice within 5 to 10 ft of the panel?

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Yes, at lease as little ice as possible
 
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I'd use mylar or Katon heaters up to directly below the antennas. Consider some form of insulation on the outside where the heaters are to encourage the heat to move up the wall material the antenna region.

Alternatively a blower forced heating system with insulation everywhere the antennas aren't to get the heat to the antenna regions. Run the heaters whenever outside temperatures drop to 34F.

Keith Cress
kcress -
 
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Yes, blower heater is a possibility, but first I'll need to size the heater.
 
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Is there a drawing of the installation? I'm having trouble visualizing how you're going to keep the ground clear of snow. Wind blown snow tends to pile up around obstacles, so while you might clear the physical surface of snow, there may be a big pile of it, just inches away.

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I am not at the liberty to disclose any drawings, but ground snow is not a problem because the antennas are well above the snow level. The ice that are causing problems is rime ice.
 
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Seems to me... after some thought.. You should do the relatively simple calcs to find the power needed to heat the walls to 34F in still air at the lowest temperature known to exist at the location.

The logic is if there is precipitation at that coldest temp the walls will still be too warm for it to accumulate. If there's also wind driven icing conditions the ice will actually insulate the box walls from the moving air again allowing the walls to get back to 34F. Of course that will melt any ice that's touching the enclosure walls resulting in ALL the ice sliding off since the ice against the enclosure surface is the only ice supporting the rest.

Keith Cress
kcress -
 
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