Biot Number

Written by Jerry Ratzlaff on . Posted in Dimensionless Numbers

Biot Number, abbreviated as Bi, a dimensionless number, is the ratio of internal thermal resistance of solid to fluid thermal resistance.  This is used for heat transfer between fluids and solids.


Biot Number formula

\(\large{ Bi=\frac{h \; l_c}{k}  }\) 
Symbol English Metric
\(\large{ Bi }\) = biot number \(\large{dimensionless}\)
\(\large{ l_c }\) = characteristic length \(\large{ft}\) \(\large{m}\)
\(\large{ h }\) = heat transfer coefficient of film coefficient or convective heat transfer coefficient \(\large{\frac{Btu}{hr-ft^2-F}}\)  \(\large{\frac{W}{m^2-K}}\)
\(\large{ k }\) = thermal conductivity of the body \(\large{\frac{Btu-ft}{hr-ft^2-F}}\)  \(\large{\frac{W}{m-K}}\)


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Tags: Heat Transfer Equations