What I think is: LCM is valid only when the Biot no. is less than 0.1, this puts restrictions on the thermal conductivity of body and the convective coefficient of heat transfer but until now we never put a restriction on the size of body and as logic suggest a very large body cannot be assumed lumped as the spatial invariability of temperature would be difficult to achieve.
Characteristic length, lc = Volume (V) / Surface Area (As) It signifies relative importance of Volume of body with its surface area As lesser the volume & larger the area at a same time will account for significant convection from surface relative to internal heat conduction & storage.. ...& hence the Biot number as Bi is proportional to lc
Wait , Lc did not come from V/As , it came from Fourier's law , when we equated conduction to convection and used KA(Ts1-Ts2)/L = hA(Ts2-Tinf)
Bi = 2.53 is 10^-3 not 10-^4?
t= 5.16 sec approx
t=5.73sec approximately
So clear
what is the physical significance of characteristic length
What I think is:
LCM is valid only when the Biot no. is less than 0.1, this puts restrictions on the thermal conductivity of body and the convective coefficient of heat transfer but until now we never put a restriction on the size of body and as logic suggest a very large body cannot be assumed lumped as the spatial invariability of temperature would be difficult to achieve.
Characteristic length,
lc = Volume (V) / Surface Area (As)
It signifies relative importance of Volume of body with its surface area
As lesser the volume & larger the area at a same time will account for significant convection from surface relative to internal heat conduction & storage.. ...& hence the Biot number as Bi is proportional to lc
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