




Problemsolving strategy: effects of heat transfer
 Examine the situation to determine what type of heat transfer is involved.
 Identify the type(s) of heat transfer—conduction, convection, or radiation.
 Identify exactly what needs to be determined in the problem (identify the unknowns). A written list is useful.
 Make a list of what is given or what can be inferred from the problem as stated (identify the knowns).
 Solve the appropriate equation for the quantity to be determined (the unknown).
 For conduction, use the equation
$P=\frac{kA\text{\Delta}T}{d}$ .
[link] lists thermal conductivities. For convection, determine the amount of matter moved and the equation
$Q=mc\text{\Delta}T$ , along with
$Q=m{L}_{\text{f}}$ or
$Q=m{L}_{\text{V}}$ if a substance changes phase. For radiation, the equation
${P}_{\text{net}}=\sigma eA\left({T}_{2}{}^{4}{T}_{1}{}^{4}\right)$ gives the net heat transfer rate.
 Substitute the knowns along with their units into the appropriate equation and obtain numerical solutions complete with units.
 Check the answer to see if it is reasonable. Does it make sense?
Check Your Understanding How much greater is the rate of heat radiation when a body is at the temperature
$40\phantom{\rule{0.2em}{0ex}}\text{\xb0}\text{C}$ than when it is at the temperature
$20\phantom{\rule{0.2em}{0ex}}\text{\xb0}\text{C}$ ?
The radiated heat is proportional to the fourth power of the
absolute temperature . Because
${T}_{1}=293\phantom{\rule{0.2em}{0ex}}\text{K}$ and
${T}_{2}=313\phantom{\rule{0.2em}{0ex}}\text{K}$ , the rate of heat transfer increases by about 30% of the original rate.
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Source:
OpenStax, University physics volume 2. OpenStax CNX. Oct 06, 2016 Download for free at http://cnx.org/content/col12074/1.3
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