Heat and Mass Transfer Thermal conductivity of solid metals with rise in temperature normally Decreases Remain constant May increase or decrease depending on temperature Increases Decreases Remain constant May increase or decrease depending on temperature Increases 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 The critical thickness of insulation for a sphere is k/h₀ 2k/h₀ h₀/2k h₀/k k/h₀ 2k/h₀ h₀/2k h₀/k ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer The thermal diffusivities for gases are generally More than those for solids More than those for liquids Less than those for liquids Dependent on the viscosity More than those for solids More than those for liquids Less than those for liquids Dependent on the viscosity ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer 40% of incident radiant energy on the surface of a thermally transparent body is reflected back. If the transmissivity of the body be 0.15, then the emissivity of surface is 0.4 0.55 0.75 0.45 0.4 0.55 0.75 0.45 ANSWER DOWNLOAD EXAMIANS APP
Heat and Mass Transfer Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity) h = kρ/S h = k/ ρS h = S/ρk h = ρS/k h = kρ/S h = k/ ρS h = S/ρk h = ρS/k ANSWER DOWNLOAD EXAMIANS APP
EXAMIANS