# Practice Test: Question Set - 04

**1. LMTD can't be used as such without a correction factor for the**

- (A) Multipass heat exchanger

- (B) Baffled heat exchanger

- (C) Condensation of mixed vapor in a condenser

- (D) All (a) (b) and (c)

**2. What is the logarithmic mean of r**

_{1}and r_{2}?- (A) (

*r*

_{1}-

*r*

_{2})/

*ln*(

*r*

_{1}/

*r*

_{2})

- (B) (

*r*

_{1}-

*r*

_{2})/

*ln*(

*r*

_{2}/

*r*

_{1})

- (C) (

*r*

_{2}-

*r*

_{1})/

*ln*(

*r*

_{1}/

*r*

_{2})

- (D) (

*r*

_{1}-

*r*

_{2})/-

*ln*(

*r*

_{1}/

*r*

_{2})

**3. In a heat exchanger with steam outside the tubes, a liquid gets heated to 45°C, when its flow velocity in the tubes is 2 m/s. If the flow velocity is reduced to 1 m/s, other things remaining the same, the temperature of the exit liquid will be**

- (A) Less than 45°C

- (B) More than 45°C

- (C) Equal to 45°C

- (D) Initially decreases and remains constant thereafter

**4. The Nusselt number for fully developed (both thermally and hydrodynamically) laminar flow through a circular pipe, where the wall heat flux is constant, is**

- (A) 2.36

- (B) 4.36

- (C) 120.36

- (D) Dependent on

*N*only

_{Re}**5. Heat flux, as defined in heat flow is analogous to __________ in electricity flow.**

- (A) Current

- (B) Voltage

- (C) Resistance

- (D) None of these

**6. The overall resistance for heat transfer through a series of flat resistance, is the __________ of the resistances.**

- (A) Average

- (B) Geometric mean

- (C) Product

- (D) Sum

**7. The driving potential for the crystal growth during crystallization is the __________ of the solution.**

- (A) Concentration

- (B) Viscosity

- (C) Super-saturation

- (D) Density

**8. Heat transfer co-efficient equation for forced convection,**

*Nu*= 0.023*R*_{e}^{0.8}.*P*, is not valid, if the value of_{r}^{n}- (A)

*n*= 0.4 is used for heating

- (B)

*n*= 0.3 is used for cooling

- (C) Reynolds number for the flow involved is > 10000

- (D) Reynolds number for the flow involved is < 2100

**9. For flow over a flat plate, the ratio of thermal boundary layer thickness, '**

*xt*' and hydrodynamic boundary layer thickness '*x*' is equal to (where,*N*= Prandtl number)_{Pr}- (A)

*N*

_{Pr}- (B)

*N*

_{Pr}^{1/3}

- (C)

*N*

_{Pr}^{-1}

- (D)

*N*

_{Pr}^{-1/3}

**10. In a shell and tube heat exchanger, putting a longitudinal baffle across the shell, forces the shell side fluid to pass __________ through the heat exchanger.**

- (A) Once

- (B) Twice

- (C) Thrice

- (D) Four times

**11. An ejector is used to**

- (A) Increase pressure

- (B) Increase temperature

- (C) Remove condensate

- (D) None of these

**12. In a forward feed multiple effect evaporator, the pressure is**

- (A) Highest in last effect

- (B) Lowest in last effect

- (C) Same in all effects

- (D) Dependent on the number of effects

**13. In a laboratory test run, the rate of drying was found to be 0.5 x 10**

^{-3}kg/m^{2}.s, when the moisture content reduced from 0.4 to 0.1 on dry basis. The critical moisture content of the material is 0.08 on a dry basis. A tray dryer is used to dry 100 kg (dry basis) of the same material under identical conditions. The surface area of the material is 0.04 m^{2}/kg of dry solid. The time required (in seconds) to reduce the moisture content of the solids from 0.3 to 0.2 (dry basis) is- (A) 2000

- (B) 4000

- (C) 5000

- (D) 6000

**14. With increase in temperature, the thermal conductivity of most liquids**

- (A) Increases

- (B) Decreases

- (C) Remain same

- (D) First increases upto a certain temperature and then becomes constant

**15. Peclet number (**

*Pe*) is given by- (A)

*Pe*=

*Re*.

*Pr*

- (B)

*Pe*=

*Re*/

*P*

_{r}- (C)

*P*=

_{e}*P*/

_{r}*R*

_{e}- (D)

*Pe*=

*Nu*.

*Re*

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