# Practice Test: Question Set - 24

**1. The film thickness for laminar film condensation on vertical surface __________ from top to bottom.**

- (A) Cumulatively
increases

- (B) Cumulatively
decreases

- (C) Remain constant

- (D) And the surface
conductance increase

**2. 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/m**

^{2}.K. The Biot number is- (A) 5.6

- (B) 0.025

- (C) 3.5

- (D) 0.0035

**3. __________ paint has the minimum absorption co-efficient.**

- (A) Black

- (B) White lead

- (C) Grey

- (D) Light cream

**4. The value of Stefan-Boltzmann constant in SI unit is**

- (A) 5.6697 × 10

^{-8}W/m

^{2}.°K

^{4}

- (B) 0.1714 × 10

^{-8}W/m

^{2}.°K

^{4}

- (C) 5.6697 × 10

^{-8}kcal/m

^{2}. °K

^{4}

- (D) 0.1714 × 10

^{-8}kcal/m

^{2}. °K

^{4}

**5. For shell and tube heat exchanger, with increasing heat transfer area, the purchased cost per unit heat transfer area**

- (A) Increases

- (B) Decreases

- (C) Remain constant

- (D) Passes through a
maxima

**6. What is the thermal conductivity of a perfect heat insulator?**

- (A) Zero

- (B) One

- (C) ∞

- (D) Between 0 and ∞

**7. Mode of heat transfer in which the fluid moves under the influence of changes in fluid pressure produced by external work is called**

- (A) Radiation

- (B) Natural convection

- (C) Forced
convection

- (D) Conduction

**8. The ratio of momentum diffusivity to thermal diffusivity is the __________ number.**

- (A) Prandtl

- (B) Nusselt

- (C) Stanton

- (D) Grashoff

**9. Steam traps are provided in steam carrying pipelines to**

- (A) Condense steam

- (B) Release excess steam
pressure by bleeding steam

- (C) Remove condensate and
inert gases

- (D) None of these

**10. A metal ball of radius 0.1 m at a uniform temperature of 90°C is left in air at 30°C. The density and the specific heat of the metal are 3000 kg/m**

^{3}and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m^{2}.K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60°C is- (A) 555

- (B) 55.5

- (C) 0.55

- (D) 0.15

**11. Kirchoff’s law applies to __________ radiation.**

- (A) Total

- (B) Monochromatic

- (C) Both (a) & (b)

- (D) Neither (a) nor (b)

**12. Heat transfer occurs by natural convection because change in temperature causes difference in**

- (A) Viscosity

- (B) Density

- (C) Thermal
conductivity

- (D) Heat
capacity

**13. Log mean temperature difference (LMTD) cannot be used, if**

- (A) Heat transfer
co-efficient over the entire heat exchanger is not constant

- (B) There exists an
unsteady state

- (C) The heat capacity is
not constant and there is a phase change

- (D) None of these

**14. The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (Δ**

*T*) between wall and outside bulk. The proportionality is given as- (A) (Δ

*T*)

^{1/4}

- (B) (Δ

*T*)

^{1/2}

- (C) (Δ

*T*)

^{5/4}

- (D) (Δ

*T*)

^{3/4}

**15. Pick out the wrong statement.**

- (A) In case of heat
transfer by purely forced convection,

*G*/

_{R}*R*

_{e}^{2}≤ 1

- (B) The equivalent
diameter of heat transfer for a duct of square cross-section (having each side
as '

*x*') is equal to 4

*x*

- (C) Distillation process
is not the same as evaporation

- (D) The effectiveness of
nucleate boiling depends basically on the ease with which the bubbles are
formed and detached from the heating surface

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