Heat Transfer Miscellaneous
 For a glass plate transmissivity and reflectivity are specified as 0.86 and 0.08 respectively, the absorptivity of the glass plate is

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τ = 0.86
ρ = 0.08
α = ?
α + τ + ρ = 1
α + 0.86 + 0.08 = 1
α = 0.06Correct Option: D
τ = 0.86
ρ = 0.08
α = ?
α + τ + ρ = 1
α + 0.86 + 0.08 = 1
α = 0.06
 Water (Prandtl number = 6) flows over a flat plate which is heated over the entire length. Which one of the following relationship between the hydrodynamic boundary layer thickness (δ) and thermal boundary layer thickness (δ_{t}) is true

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δ = ( Pr )^{n} δ_{t}
Here, Pr = 6 > 1or δ > 1 δ_{t}
∴ δ > δ_{t}Correct Option: B
δ = ( Pr )^{n} δ_{t}
Here, Pr = 6 > 1or δ > 1 δ_{t}
∴ δ > δ_{t}
 For air near atmospheric condition flowing over a flat plate the laminar thermal boundary layer is thicker than hydrodynamic boundary layer

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The given statement is False.
At near atmospheric or ambient condition,
Pr = 1, i.e., δ = δ_{t}Correct Option: C
The given statement is False.
At near atmospheric or ambient condition,
Pr = 1, i.e., δ = δ_{t}
 A fluid flowing over a flat plate has the following properties: dynamic viscosity = 25 × 10^{–6} kg/ ms, specific heat = 2.0 kJ/kgK, thermal conductivity 0.05 W/mK. The hydrodynamic boundary layer thickness is measured to be 0.5 mm. The thickness of the thermal boundary layer would be

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Pr = μC_{p} K = 25 × 10^{6} × 2 × 10^{3} = 1 0.05 ⇒ δ = 1 δ_{t}
Now , δ = 0.5 mm
∴ δ = δ_{t} = 0.5 mmCorrect Option: B
Pr = μC_{p} K = 25 × 10^{6} × 2 × 10^{3} = 1 0.05 ⇒ δ = 1 δ_{t}
Now , δ = 0.5 mm
∴ δ = δ_{t} = 0.5 mm
 For the fluid flowing over a flat plate with Prandtl number greater than unity, the thermal boundary layer for laminar forced convection.

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Pr^{1 / 3} = δ , if Pr > 1 , it means δ < δ_{t} δ_{t} Correct Option: A
Pr^{1 / 3} = δ , if Pr > 1 , it means δ < δ_{t} δ_{t}