Tricky Heat Transfer Multiple choice Questions and Answers pdf

1. At constant temperature, the thenual conductivities of gases with rise in pressure
o increase
o remain unchanged
o may increase or decrease; depends on the pressure
o decrease
Ans: D

2. Fruit juice (a heat sensitive material) can be concentrated in a ________ evaporator
o high pressure
o falling film
o long tube
o none of these
Ans: B

3. In an interphase heat transfer process, the equilibrium state corresponds to equality of temperature in the two phases, while the condition for equilibrium in an interphase mass transfer process is equality of
o activity co-efficients
o concentrations
o chemical potentials
o mass transfer co-efficients
Ans: B

4. Low thermal conductivity of heat insulating materials is due to its
o high specific heat
o dense structure
o high proportion of air space
o none of these
Ans: C

5. Value of Nusselt number [Nu = (hD/k)] for the heat transfer by conduction from a droplet or a spherical particle to a surrounding stagnant film is
o 0.5
o 21
o 10
o 100
Ans: B

6. Tubes are held between top and bottom tube sheets in Calenderia type evaporator by keeping
o both the tube sheets fixed I
o both the tube sheets floating
o the top tube sheet fixed and the bottom tube-sheet floating
D. the top tube sheet floating and bottom tube sheet fixed
Ans: A

7. Small scale evaporation is done in a
o condenser
o heat exchanger
o steam jacketed kettle
o multiple effect evaporator
Ans: C

8. With increase in temperature, the total emissivitv of conductors
o increases
o decreases
o remains same
o decreases linearly
Ans: A

9. Loss of heat from untagged steam pipe to the ambient air is by
o radiation
o conduction
o convection
o all of above
Ans: D

10. Heat transfer by conduction in the turbulent core of a fluid flowing through a heated pipe is negligible, if the value of Prandtl number is
o 0.2
o 0.4
o o.6
o o.8
Ans: C