# Practice Test: Question Set - 03

**1. The interchange factor for radiation heat transfer from surface '**

*x*' to surface '*y*' in case of an infinite parallel planes with emissivities ε_{x}& ε_{y}is given by- (A) ε

_{x}+ ε

_{y}

- (B) ε

_{x}. ε

_{y}

- (C) 1/ε

_{x}+ 1/ε

_{y}

- (D) (ε

_{x}+ ε

_{y})/( ε

_{x}+ ε

_{y}- ε

_{x}. ε

_{y})

**2. If the thermal conductivity of a wall material is independent of temperature, the steady state temperature distribution in the very large thin plane wall having steady, uniform surface temperature follows __________ law.**

- (A) Parabolic

- (B) Hyperbolic

- (C) Linear

- (D) Logarithmic

**3. With increase in temperature, the thermal conductivity of a gas**

- (A) Increases

- (B) Decreases

- (C) Remain same

- (D) May increase or decrease depending on the type of gas

**4. Grashoff number is given by**

- (A)

*gD*

^{3}.β.Δtρ

^{2}/μ

^{2}

- (B)

*gD*

^{2}βΔtρ/μ

^{2}

- (C)

*gD*

^{2}βΔtP

^{2}μ

- (D)

*gD*

^{3}βΔtP

^{2}/μ

**5. Which area is used in case of heat flow by conduction through a cylinder?**

- (A) Logarithmic mean area

- (B) Arithmetic mean area

- (C) Geometric mean area

- (D) None of these

**6. Pick out the wrong statement.**

- (A) Heat transfer from a hot body to cold body by the emission of heat
waves is called radiation

- (B) Filmwise condensation takes place on non-wettable surfaces

- (C) The boiling point of a solution is affected by liquid head as well
as boiling point elevation

- (D) None of these

**7. Choose the correct equation.**

- (A)

*Nu*= (

*Re*) (

*Pr*) (

*Gz*)

- (B)

*Nu*= (

*Re*) (

*Pr*) (

*St*)

- (C)

*Nu*= (

*Re*) (

*Pr*)

- (D)

*Nu*= (

*Pr*) (

*St*)

**8. In a heat exchanger, the rate of heat transfer from the hot fluid to the cold fluid**

- (A) Varies directly as the area and the LMTD

- (B) Directly proportional to LMTD and inversely proportional to the area

- (C) Varies as square of the area

- (D) None of these

**9. Pick out the wrong statement.**

- (A) 'Solvates' are chemical compounds formed by solute with their
solvents. When water is the solvent, then it is called a 'hydrate'

- (B) In heat exchanger calculations (Δt) weighted is used in place of Δt,
when it involves more than one sequence of heating or cooling i.e.,
desuperheating & condensation or condensation & sub-cooling

- (C) Heat transfer co-efficient during nucleate boiling is not influenced
by the agitation imparted

- (D) In case of short tube vertical evaporators, area of central downtake
is about 50 to 100% of the total tube cross-sectional area

**10. For what value of Prandtl number,**

*St*=*f*/2?- (A) 1.5

- (B) 1

- (C) > 1

- (D) < 1

**11. The rate of emission of radiation by a body does not depend upon the**

- (A) Wavelength of radiation

- (B) Surface temperature of the body

- (C) Nature of the surface

- (D) Shape and porosity of the body

**12. Heat sensitive materials can be concentrated in an evaporator employing**

- (A) Vacuum

- (B) High pressure

- (C) High residence time

- (D) None of these

**13. In a cooling tower, water becomes cool by**

- (A) Loosing sensible heat

- (B) Heat transfer to surroundings

- (C) Vaporization due to heat loss to air

- (D) Loosing latent heat

**14. Conductance is given by (where,**

*x*= thickness,*A*= heat flow area,*K*= thermal conductivity.)- (A)

*x*/

*KA*

- (B)

*KA*/

*x*

- (C)

*K*/

*Ax*

- (D)

*A*/

*Kx*

**15. Out of the following four assumptions used in the derivation of the equation for LMTD**

**[**

*LMTD*= (∆*t*- ∆_{1}*t*)/ln(∆_{2}*t*/∆_{1}*t*)], which one is subject to the largest deviation in practice ?_{2}- (A) Constant overall heat transfer co-efficient

- (B) Constant rate of fluid flow

- (C) Constant specific heat

- (D) No partial phase change in the system

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