Message Board Thread - "Compensating for wind factor"

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Compensating for wind factor ati 8/23/2010
How does one apply the correction factor for wind speed when performing exterior thermography? For example: If you have a 10 (mph)correction factor for wind is 1.96. How do you apply the correction factor to come up with a more accurate temperature? Is there a seperate correction factor list for MPH and Celsius?

Tony
 
Re:Compensating for wind factor JKEngineer 8/23/2010
Where did you get the 1.96? Look at your source again and see if it is a correction for T or for heat flow, which is very much NOT the same.

The temperature of a surface will depend on the heat transfer at the surface, including flow from (an assumed) hot interior, convection to the air, radiation to the surroundings, and the material properties implied in the flow from the interior. This cannot be assessed with a single "factor". It could be assessed with a heat transfer analysis specific to the situation being examined. That analysis would not be freely translatable to other situations, or even to other configurations of the same components.

If you are in a situation that would justify a heat transfer analysis of this type, let me know. It is one of the services I offer.

Jack
Jack M. Kleinfeld, P.E.
Kleinfeld Technical Services, Inc.
Infrared Thermography, Finite Element Analysis, Process Engineering
Bronx, NY 10463

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Re:Compensating for wind factor Gary Orlove 8/23/2010
The following is an approximate rule of thumb for outdoor electrical inspections, but the data and technique may be helpful.

During outdoor inspection, the cooling effect of the wind should be taken into account. An overheating measured at a wind velocity of 5 m/s (10 knots) will be approximately twice as high at 1 m/s (2 knots). An excess temperature measured at 8 m/s (16 knots) will be 2.5 times as high at 1 m/s (2 knots). This correction factor, which is based on empirical measurements, is usually applicable up to 8 m/s (16 knots).

There are, however, cases when you have to inspect even if the wind is stronger than 8 m/s (16 knots). There are many windy places in the world, islands, mountains, and so on but it is important to know that overheated components found would have shown a considerably higher temperature at a lower wind speed. The empirical correction factor can be listed.

The measured overheating multiplied by the correction factor gives the excess temperature with no wind, that is, at 1 m/s (2 knots).
 


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