Heat transfer coefficient for soils

[noroc]

What are the limit values for the coefficient of heat transfer for soils?<br>I am trying to calculate if have a forest fire (very dry native soil), how much is the soil temperature 2 ft. bellow surface?<br>Thanks<br>

 

[DonLeffingwellPE]

The heat transfer coefficient will depend on the properties of the air near the surface of the earth. You will need to estimate the temperature of the air to the get the air properties. Then you will need to assume or know an air velocity to estimate h. For the heat conduction into the earth, you will need to know the thermal properties of the soil.<br>Units below are in Btu, hr, ft, and lbm<br>Dusinberre G.M. Heat Transfer Calculations by Finite Differences International Textbook Company&nbsp;&nbsp;&nbsp;Scranton, PENN 1961<br>gives the following properties as typical above 8 ft of depth:<br>k = .21 Btu/hr-ft-F<br>density = 70 lbm/ft^3<br>cp = .2 Btu/lbm-F<br>alpha = .015 ft^2/hr<br><br>Schneider P.J. Conduction Heat Transfer Addison-Wesley Publishing Company Reading, MA 1955<br><br>Gives&nbsp;&nbsp;the following<br>k = ..325 <br>density = 100<br>cp = .5<br><br>Good Luck <br>Don<br><A HREF="mailto:dleffingwell@snet.net">dleffingwell@snet.net</A><br>

 

[subjectin]

I recall locating soil thermal conductivity properties through the Oak Ridge National Lab. Try the database search at

http://www.ornl.gov.

Also, I would suggest locating or speaking to someone knowledgable in geothermal heat pump system. It would be worth a try. Good luck

 

[dcasto]

Nothing to add on the engineering side, but here's a real story. There was a major pipeline rupture and fire in a location where my company had buried lines. After the fire was out we went to the site. Steel poles that held our aluminum signs were melted to puddles and the lignum signs were &quot;vaporized&quot; leaving a metallic shine to the ground. The land once green looked like Mars. Across the area where mounds of dirt about 6&quot; above the normal level. We kicked these mounds and about 3&quot; of the soil had become baked clay. Under these mounds were our favorite things, fire ants, alive and well. The extreme heat had created nearly a perfect insulation firebrick.