Heat and Mass Transfer - Set 03 - ObjectiveBooks

# Practice Test: Question Set - 03

1. Temperature of steam at around 540°C can be measured by
(A) Thermometer
(B) Thermistor
(C) Thermocouple
(D) None of these

2. Thermal diffusivity of a substance is
(A) Directly proportional to the thermal conductivity
(B) Inversely proportional to density of substance
(C) Inversely proportional to specific heat
(D) All of the above

3. Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
(A) 0.002
(B) 0.02
(C) 0.01
(D) 0.1

4. Fouling factor is used
(A) In heat exchanger design as a safety factor
(B) In case of Newtonian fluids
(C) When a liquid exchanges heat with a gas
(D) None of the above

5. The time constant of a thermocouple is
(A) The time taken to attain the final temperature to be measured
(B) The time taken to attain 50% of the value of initial temperature difference
(C) The time taken to attain 63.2% of the value of initial temperature difference
(D) Determined by the time taken to reach 100°C from 0°C

6. The natural convection air cooled condensers are used in
(A) Domestic refrigerators
(B) Water coolers
(C) Room air conditioners
(D) All of these

7. Thermal conductivity of air with rise in temperature
(A) Increases
(B) Decreases
(C) Remain constant
(D) May increase or decrease depending on temperature

8. A heat exchanger with heat transfer surface area A and overall heat transfer coefficient U handles two fluids of heat capacities Cmax and Cmin. The number of transfer units (NTU) used in the analysis of heat exchanger is specified as
(A) A.Cmin/U
(B) U/A.Cmin
(C) A.U.Cmin
(D) A.U/Cmin

9. Heat flows from one body to other when they have
(A) Different heat contents
(B) Different specific heat
(C) Different atomic structure
(D) Different temperatures

10. Thermal diffusivity of a substance is given by (where h = Thermal diffusivity, ρ = Density of substance, S = Specific heat, and k = Thermal conductivity)
(A) h = k/ ρS
(B) h = ρS/k
(C) h = S/ρk
(D) h = kρ/S

11. The concept of overall coefficient of heat transfer is used in heat transfer problems of
(A) Conduction
(B) Convection
(D) Conduction and convection

12. The use of heat exchangers is made in
(B) Condensers and boilers in steam plants
(C) Condensers and evaporators in refrigeration and air conditioning units
(D) All of the above

13. In heat transfer, conductance equals conductivity (kcal/hr/sq.m/°C/cm) divided by
(A) Hr (time)
(B) Sq. m (area)
(C) °C (temperature)
(D) K.cal (heat)

14. In a heat exchanger with one fluid evaporating or condensing, the surface area required is least in
(A) Parallel flow
(B) Counter flow
(C) Cross flow
(D) All of these

15. The amount of heat flow through a body by conduction is
(A) Directly proportional to the surface area of the body
(B) Directly proportional to the temperature difference on the two faces of the body
(C) Dependent upon the material of the body
(D) All of the above

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