Heat and Mass Transfer Thermal diffusivity is Used as mathematical model A dimensionless parameter Function of temperature A physical property of the material Used as mathematical model A dimensionless parameter Function of temperature A physical property of the material ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer Total emissivity of polished silver compared to black body is Very much lower Same More or less same Higher Very much lower Same More or less same Higher ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer Thermal conductivity of air with rise in temperature Remain constant Decreases Increases May increase or decrease depending on temperature Remain constant Decreases Increases May increase or decrease depending on temperature ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer The heat transfer by conduction through a thick cylinder (Q) is given by (where T₁ = Higher temperature, T₂ = Lower temperature, r₁ = Inside radius, r₂ = Outside radius, l = Length of cylinder, and k = Thermal conductivity) Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁) Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁) Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁) Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)] Q = [2π (T₁ - T₂)]/2.3 lk log (r₂/r₁) Q = = 2πlk/2.3 (T₁ - T₂) log (r₂/r₁) Q = [2πlk (T₁ - T₂)]/2.3 log (r₂/r₁) Q = 2.3 log (r₂/r₁)/[2πlk (T₁ - T₂)] ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h₁, h₂ and h₃ respectively. The average heat transfer coefficient for the cube is (h₁.h₂.h₃)1/3 1/h₁ + 1/h₂ + 1/h₃ h₁ + h₂ + h₃ None of these (h₁.h₂.h₃)1/3 1/h₁ + 1/h₂ + 1/h₃ h₁ + h₂ + h₃ None of these ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer The heat transfer takes place according to Second law of thermodynamics First law of thermodynamics Kirchhoff's law Zeroth law of thermodynamics Second law of thermodynamics First law of thermodynamics Kirchhoff's law Zeroth law of thermodynamics ANSWER DOWNLOAD EXAMIANS APP
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