Biot Number

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	\(\large{\frac{Btu-ft}{hr-ft^2-F}}\)	\(\large{\frac{W}{m-K}}\)