Pavement Temperature rise 3

[guying]

Hi,
I have to estimate the temperature rise of an air strip (ashphalt pavement) in the Saharian desert knowing tha the sun provide around 1400 watts per square meters. The purpose is to verify what type of ashphalt to use with Boing 747 (400 tons).
Is there a way to have a good approximation for this?

Thanks

 

[IRstuff]

This is for an airstrip on Saharian desert on Venus? MIL-HDBK-310, which you should have a copy of, lists in Table II, a long-term extreme of 1120 W/m^2. Note that the solar constant, which is the amount of sunlight reaching the Earth's atmosphere is about 1366 W/m^2.

In any case, you'd equate the solar illuminance to the convective, radiative, and conductive heat loss mechanisms, and the result is totally dependent on the assumptions you make. Nonetheless, you can show mathematically, and anecdotally, that the tarmac can get up to the boiling point of water, at least, for about a couple hours a day.

TTFN

FAQ731-376

 

[CarlB]

Don't know about an approximate approach, here's a link to a 2-d finite difference approach:

http://www.mountain-plains.org/pubs/html/mpc-02-136/index.php

Temperatures of over 65 deg C were measured in Saudi Arabia

http://www.kau.edu.sa/Files/320/Researches/47120_18687.pdf

You can probably find lots of measured data, may not need to estimate it unless the design has some unusual features.

 

[IRstuff]

This is for an airstrip on Saharian desert on Venus? MIL-HDBK-310, which you should have a copy of, lists in Table II, a long-term extreme of 1120 W/m^2. Note that the solar constant, which is the amount of sunlight reaching the Earth's atmosphere is about 1366 W/m^2.

In any case, you'd equate the solar illuminance to the convective, radiative, and conductive heat loss mechanisms, and the result is totally dependent on the assumptions you make. Nonetheless, you can show mathematically, and anecdotally, that the tarmac could exceed the boiling point of water, at least, for about an hour a day, using a lumped-element Mathcad model.

TTFN

FAQ731-376

 

[dogtop]

What about an IR thermometer? You could point it to the Highway asphalt of your choice.

HTH

 

[chicopee]

The weight of 400 tons is that of a fully loaded Boing747 landing?

 

[IRstuff]

That would about right for a fully laden 747-400 with about 40% of fuel capacity. About 500 tons on takeoff.

http://en.wikipedia.org/wiki/Boeing_747-400

TTFN

FAQ731-376

 

[guying]

Hi,
Thanks for all the replies.
I know that this seems to be a high value. I've been told it was way too high. But in Tamanrasset, where I was in 2004, a VAG/PNUE meteo station part of a network around the world is measuring in continue solar radiation, direct, global, diffuse and RG8 (I have no clue what that mean). They gave me a 1400 W/m2 value.
The airfield I'm working on now is on a hotter part of the Sahara, reaching 55°C during summer. I was there a month ago and it was 47. Very hot... But there is no measure for that area.
For the B747-400, Boeing manual state a Max Design Takeoff Weight of 875000 pounds for the B747-400 Freighter and 910000 pounds for the 747-400ER.
A lot of weight on hot asphalt.

 

[AllHandlesTaken]

I don't know much about runway design (practically nothing) but I will throw this out:

How about using concrete, rather than a bitumous asphalt?

 

[guying]

One air strip is made of concrete (cementuous) and the other is made of asphalt. It is in the Terms of Reference. Mostly due to cost. Taxiway are all asphalt and parking, where the highest constraint are, all concrete.

 

[IRstuff]

Well, regardless, you're looking at surface temperature exceeding boiling point of water.

With the assumptions I made, 1400 W/m^2 results in 120°C surface temperature.

Link below is to PDF of the Mathcad sheet I used.

TTFN

FAQ731-376

 

[guying]

Wich is very close to what I get (114°C) using what was observed in similar country.
In Tamanrasset, we couldn't pick up a peice of metal left under the sun. It would burn your hand.
Many thanks for your help.

 

[chicopee]

IRStuff, your spreadsheet shows the temperature unit in Kelvin not Celsius. Is that correct?

 

[guying]

chicopee,
On top of the sheet you find °C=K

 

[guying]

And 120°k would be kind of cold for the desert.

 

[IRstuff]

Mathcad 11, which is what I use, natively supports only kelvins and rankines. So long as one remembers that temperature differences are either kelvins or degrees Celcius, all is good.

I try to avoid using the defined degree Celcius in my sheets, since it takes a bunch of keystrokes to create the symbolically pleasing °C.

So, that's why the absolute temperatures required for the blackbody radiation equation use the delta temperature plus 273 K (and yes, I dropped the 0.15K because I was lazy).

Obviously, this isn't my day job, but it's something I can understand enough to be dangerous, and these problems are particularly well-suited to Mathcad's solver function.

TTFN

FAQ731-376