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Heat Transfer - Engineering

Q1:

A metal wire of 0.01 m dia and thermal conductivity 200 W/m.K is exposed to a fluid stream with a convective heat transfer coefficient of 100 W/m2.K. The Biot number is

A 5.6

B 0.025

C 3.5

D 0.0035

ANS:B - 0.025

The Biot number (Bi) is a dimensionless number used in heat transfer calculations that represents the ratio of internal thermal resistance to external thermal resistance for a solid experiencing convection. It's calculated as the ratio of the convective heat transfer resistance to the conductive heat transfer resistance. The formula for the Biot number (Bi) is: Bi=ℎBi=khL​ Where:

  • ℎh is the convective heat transfer coefficient (W/m²·K)
  • L is the characteristic length (m)
  • k is the thermal conductivity of the material (W/m·K)
Given:
  • Diameter of the wire, =0.01d=0.01 m (which will be used as the characteristic length)
  • Thermal conductivity, =200k=200 W/m·K
  • Convective heat transfer coefficient, ℎ=100h=100 W/m²·K
Plugging the values into the formula: Bi=100×0.01200=12=0.5Bi=200100×0.01​=21​=0.5 So, the Biot number is 0.5. None of the provided options match this result. Would you like to recheck the options?