Question 1

A fluid is flowing inside the inner tube of a double pipe heat exchanger with diameter 'd'. For a fixed mass flow rate, the tube side heat transfer co-efficient for turbulent flow conditions is proportional to

Accepted Answer

A)  d0.8
B)  d-0.2
C)  d-1
D)  d-1.8 B

Question 2

The ratio of total radiating power to the absorptivity of the body depends upon the __________ as per Kirchoff?s law.

Accepted Answer

A)  Wavelength of radiation
B)  Nature of the body
C)  Temperature of the body
D)  None of these C

Question 3

For small temperature difference, the heat transfer rate as per Newton's law of cooling is proportional to (where, ?t = excess temperature)

Accepted Answer

A)  ?t
B)  ?t2
C)  ?t3
D)  ?(?t)  A

Question 4

Air is best heated with steam in a heat exchanger of

Accepted Answer

A)  Plate type
B)  Double pipe type with fin on steam side
C)  Double pipe type with fin on air side
D)  Shell and tube type

Question 5

Which of the following is concerned with both heat and mass transfer?

Accepted Answer

A)  Lewis relationship
B)  Nusselt number
C)  Kutateladze number
D)  Froude number

Question 6

What is the steam economy in case of a single effect evaporator system?

Accepted Answer

A)  1
B)  > 1
C)  
D)  0.1

Question 7

Steam side heat transfer co-efficient in an evaporator is in the range of __________ kcal/hr.m2 °C.

Accepted Answer

A)  10-50
B)  100-500
C)  1000-1500
D)  5000-15000

Question 8

Duhring?s rule is important in solving problems on

Accepted Answer

A)  Distillation
B)  Crystallisation
C)  Evaporation
D)  Humidification

Question 9

Pick out the wrong statement.

Accepted Answer

A)  Orifice baffles are never used in a shell and tube heat exchanger
B)  Pressure drop on the shell side of a heat exchanger depends upon tube pitch also
C)  In a horizontal tube evaporator, surface blanketing by air is avoided
D)  Split ring type and pull through type floating heads are two commonly used floating heads is heat exchangers

Question 10

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

Accepted Answer

A)  Prandtl
B)  Nusselt
C)  Stanton
D)  Grashoff

Question 11

Which is the most suitable for the concentration of foamy & frothy liquors?

Accepted Answer

A)  Agitated film evaporator
B)  Long tube vertical evaporator
C)  Open pan evaporator
D)  None of these

Question 12

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/m2 .K. The Biot number is

Accepted Answer

A)  5.6
B)  0.025
C)  3.5
D)  0.0035

Question 13

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

Accepted Answer

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

Question 14

The most conducive surface for dropwise condensation to occur is the __________ surface.

Accepted Answer

A)  Coated
B)  Oily
C)  Glazed & polished
D)  Smooth

Question 15

The main function of baffles provided in a shell and tube heat exchanger is to

Accepted Answer

A)  Facilitate the cleaning of outer tube surface
B)  Enhance turbulence
C)  Hold the tubes in position
D)  All 'a', 'b' & 'c'

Question 16

If air (a non-condensing gas) is present in a condensing vapor stream, it will __________ the condensation rate of vapor.

Accepted Answer

A)  Increase
B)  Decrease
C)  Not affect
D)  Increase the condensing film co-efficient as well as

Question 17

The rate of heat transfer from a vertical plate by natural convection depends upon the temperature differences (?T) between wall and outside bulk. The proportionality is given as

Accepted Answer

A)  (?T)  1/4
B)  (?T)  1/2
C)  (?T)  5/4
D)  (?T)  3/4

Question 18

Controlling heat transfer film co-efficient is the one, which offers __________ resistance to heat transfer.

Accepted Answer

A)  No
B)  The least
C)  The largest
D)  Lower

Question 19

Pick out the wrong statement:

Accepted Answer

A)  The capacity of an evaporator is reduced by the boiling point elevation
B)  Corrosive liquid is normally passed through the tubes in a shell and tube heat exchanger
C)  Steam jet ejector is used for vapor compression in a thermal recompression evaporator
D)  Heat sensitive materials should be concentrated in high pressure evaporators

Question 20

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

Accepted Answer

A)  Radiation
B)  Natural convection
C)  Forced convection
D)  Conduction

Exam 7: Heat Transfer and Heat Exchangers: Part B