1)http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/inteng.html#c2
2)http://sol.sci.uop.edu/~jfalward/heattransfer/heattransfer.html
3) http://www.efunda.com/formulae/heat_transfer/conduction/overview_cond.cfm
4) http://apollo.lsc.vsc.edu/classes/met130/notes/chapter3/day_fund2.html
5) http://www.grc.nasa.gov/WWW/K-12/airplane/thermo0.html

6) http://www.physics.sfsu.edu/~lwilliam/111/ch12&13.htm