## Heat Transfer Miscellaneous

#### Heat-Transfer

1. The following figure was generated from experimental data relating spectral black body emissive power to wave length at the three temperatures T1, T2 and T3 (T1 > T2 >T3).

The conclusion in that the measurements are

1. Wien's displacement law is not satisfied, i.e., λmax T = C
which tells lower λmax for higher temperature.

##### Correct Option: D

Wien's displacement law is not satisfied, i.e., λmax T = C
which tells lower λmax for higher temperature.

1. For an opaque surface, the absorptivity (α), transmissivity (τ) and reflectivity ρ are related by the equation

1. α + τ + ρ = 1
for opaque surface, τ = 0
∴ α + ρ = 1

##### Correct Option: C

α + τ + ρ = 1
for opaque surface, τ = 0
∴ α + ρ = 1

1. The radiative heat transfer rate per unit area (W/m2) between two plane parallel gray surfaces (emissivity = 0.9) maintained at 400 K and 300 K is (σ = Stefan Boltzmann constant = 5.67 × 10–8 W/m2K4)

1. For plane surfaces

 Q = σ(T14 - T24) A 1 + 1 - 1 ε1 ε2

Here , ε1 = ε2 = 0.9
 Q = 5.67 × 10-8(4004 - 3004) A 1 + 1 - 1 0.9 0.9

 = 8 ∥ .84 w ≈ 812 w m2 m2

##### Correct Option: B

For plane surfaces

 Q = σ(T14 - T24) A 1 + 1 - 1 ε1 ε2

Here , ε1 = ε2 = 0.9
 Q = 5.67 × 10-8(4004 - 3004) A 1 + 1 - 1 0.9 0.9

 = 8 ∥ .84 w ≈ 812 w m2 m2

1. In shell and tube heat exchanger, baffles are mainly used to

1. Baffles are used to deflect the flow.

##### Correct Option: C

Baffles are used to deflect the flow.

1. The practice to use steam on the shell side and water on the tube side in condensers of steam power plant is because

1. Air leaked into the condensor can be easily extracted.

##### Correct Option: D

Air leaked into the condensor can be easily extracted.