Q.1
(Cp . μ)/K is termed as the __________ number.
Q.2
Extended heat transfer surface like fins are used to increase the heat transfer rate. Fin efficiency is defined as the ratio of heat transferred across the fin surface to the theoretical heat transfer across an equal area held at the
Q.3
Nusselt number is a function of Prandtl number and __________ number of fluid in natural convection heat transfer.
Q.4
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
Q.5
LMTD can't be used as such without a correction factor for the
Q.6
Economy of an evaporator is influenced by the
Q.7
In regenerative air preheater (as practised in heating of coke ovens), the heat is transferred
Q.8
Which is the most suitable for cold viscous feed?
Q.9
In a forward feed multiple effect evaporator unit
Q.10
Double pipe heat exchangers are preferably useful, when
Q.11
The left face of a one dimensional slab of thickness 0.2 m is maintained at 80°C and the right face is exposed to air at 30°C. The thermal conductivity of the slab is 1.2 W/m.K and the heat transfer co-efficient from the right face is 10 W/m².K. At steady state, the temperature of the right face in °C is
Q.12
Heat flux through several resistances in series in analogous to the current flowing through several
Q.13
The advantage of backward feed multiple effect evaporators over forward feed units is that
Q.14
In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used
Q.15
What is the unit of thermal conductivity ?
Q.16
In forced convection, the Nusselt number is a function of
Q.17
Multiple effect evaporators are commonly used in the manufacture of P. Paper Q. Superphosphate R. Sugar S. Fats
Q.18

Pick out the wrong statement.

  • Orifice baffles are never used in a shell and tube heat exchanger.
  • Pressure drop on the shell side of a heat exchanger depends upon tube pitch also.
  • In a horizontal tube evaporator, surface blanketing by air is avoided.
  • Split ring type and pull through type floating heads are two commonly used floating heads is heat exchangers.
Q.19

Convective heat transfer co-efficient in case of fluid flowing in tubes is not affected by the tube length/diameter ratio, if the flow is in the __________ zone.

  • laminar
  • transition
  • both 'a' & 'b'
  • highly turbulent
Q.20

The actual temperature drop across the heating surface in an evaporator depends on the

  • feed.
  • depth of liquid over heating surface.
  • pressure difference between steam chest and vapour space.
  • all (a), (b) and (c).
Q.21

Which of the following is not used as a medium for high temperature heating ?

  • Dowtherm
  • mercury
  • liquid metal (e.g. molten sodium)
  • fused salts (e.g., an eutectic mixture of 53% KNO3, 40% NaNO2and 7% NaNO3)
Q.22

Presence of a non-condensing gas in a condensing vapour

  • increases the rate of condensation.
  • decreases thermal resistance.
  • is desirable to increase the film co-efficient.
  • none of these.
Q.23

The average heat transfer co-efficient for laminar film condensation on vertical surface is inversely proportional to (where, ΔT = Temperature drop across condensate film )

  • ΔT
  • (ΔT)2
  • (ΔT)1/4
  • (ΔT)3/2
Q.24

Bulk of the convective heat transfer resistance from a hot tube surface to the fluid flowing in it, is

  • in the central core of the fluid.
  • uniformly distributed throughout the fluid.
  • mainly confined to a thin film of fluid near the surface.
  • none of these.
Q.25

The equivalent diameter for pressure drop is __________ that for heat transfer.

  • smaller than
  • greater than
  • equal to
  • not related with
Q.26

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

  • Lewis relationship
  • Nusselt number
  • Kutateladze number
  • Froude number
Q.27

A backward feed multiple effect evaporator is better than forward feed for concentrating cold feed, because it provides

  • higher economy
  • lower capacity
  • both (a) & (b)
  • lower economy
Q.28

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

  • no
  • the least
  • the largest
  • lower
Q.29

Acm dia steam pipe, carrying steam at 180°C, is covered with an insulation (conductivity = 0.6 W/m.°C). It losses heat to the surroundings at 30°C. Assume a heat transfer co-efficient of 0.8 W/m2.°C for heat transfer from surface to the surroundings. Neglect wall resistance of the pipe and film resistance of steam. If the insulation thickness is 2 cms, the rate of heat loss from this insulated pipe will be

  • greater than that for uninsulated steam pipe.
  • less than that of the uninsulated steam pipe.
  • equal to that of the uninsulated steam pipe.
  • less than the steam pipe with 5 cms insulation.
Q.30

The heat flux (from outside to inside) across an insulating wall with thermal conductivity, K= 0.W/m.°K and thickness 0.isW/m2. The temperature of the inside wall is - 5°C. The outside wall temperature is

  • 25°C
  • 30°C
  • 35°C
  • 40°C
Q.31

Thermal conductivity of a conducting solid material depends upon its

  • temperature
  • porosity
  • both (a) & (b)
  • neither (a) nor (b)
Q.32

Pick out the wrong statement.

  • The controlling resistance in case of heating of air by condensing steam is in the air film.
  • The log mean temperature difference (LMTD) for counter flow and parallel flow can be theoretically same when any one of the fluids (hot or cold fluid) passes through the heat exchanger at constant temperature.
  • In case of a 1 - 2 shell and tube heat exchanger, the LMTD correction factor value increases sharply, when a temperature cross occurs.
  • Phase change in case of a pure fluid at a given pressure from liquid to vapor or vice-versa occurs at saturation temperature.
Q.33

Shell side pressure drop in a shell and tube heat exchanger does not depend upon the

  • baffle spacing & shell diameter.
  • tube diameter & pitch.
  • viscosity, density & mass velocity of shell side fluid.
  • none of these.
Q.34

When vaporisation takes place directly at the heating surface, it is called

  • film boiling
  • nucleate boiling
  • vapour binding
  • none of these
Q.35

Hot water (0.m3 /min) enters the tube side of a counter current shell and tube heat exchanger at 80°C and leaves at 50°C. Cold oil (0.m3/min) of densitykg/m3 and specific heat of 2 kJ/kg.K enters at 20°C. The log mean temperature difference in °C is approximately

  • 32
  • 37
  • 45
  • 50
Q.36

The unit of heat transfer co-efficient in SI unit is

  • J/M2°K
  • W/m2°K
  • W/m°K
  • J/m°K
Q.37

Kirchoff s law applies to __________ radiation.

  • total
  • monochromatic
  • both (a) & (b)
  • neither (a) nor (b)
Q.38

In the equation Q = UAΔt; Δt is

  • geometric mean temperature difference.
  • arithmetic mean temperature difference.
  • logarithmic mean temperature difference.
  • the difference of average bulk temperatures of hot and cold fluids.
Q.39

With increase in porosity, the thermal conductivity of a solid substance

  • increases
  • decreases
  • remains unchanged
  • may increase or decrease; depends on the solid
Q.40

Reynold's analogy states that

  • Nst α f
  • Nst α NRe
  • NNu α f
  • NRe α f
Q.41

In a heat exchanger, floating head is provided to

  • facilitate cleaning of the exchanger.
  • increase the heat transfer area.
  • relieve stresses caused by thermal expansion.
  • increase log mean temperature gradient.
Q.42

The number of kg vaporised per kg of steam fed to the evaporator is defined as

  • capacity
  • rate of evaporation
  • economy
  • rate of vaporisation
Q.43

With the increase of temperature, the Col-burn jH factor

  • increases.
  • decreases.
  • remains unchanged.
  • may increase or decrease ; depending on temperature.
Q.44

In case of evaporators, liquid entrainment results primarily due to

  • high vacuum in the evaporator.
  • high evaporation rate.
  • foaming of the solution.
  • high heat transfer rate.
Q.45

Fouling factor

  • is a dimensionless quantity.
  • does not provide a safety factor for design.
  • accounts for additional resistances to heat flow.
  • none of these.
Q.46

Crystal size in a continuous crystalliser depends upon the

  • rate of heat transfer.
  • degree of turbulence.
  • degree of supersaturation.
  • all (a), (b) and (c).
Q.47

For an ideal black body

  • absorptivity = 1
  • reflectivity = 1
  • emissivity = 0
  • transmissivity = 1
Q.48

In Joule's experiment, an insulated container containskg of water initially at 25°C. It is stirred by an agitator, which is made to turn by a slowly falling body weighingkg through a height of 4 m. The process is repeatedtimes. The acceleration due to gravity is 9.8 ms-2. Neglecting the heat capacity of agitator, the temperature of water (in °C) is

  • 40.5
  • 34.4
  • 26.8
  • 25
Q.49

With increase in temperature, the thermal conductivity of non-metallic amorphous solids

  • decreases
  • increases
  • remains constant
  • first decreases upto certain temperature and then increases
Q.50

Leidenfrost point is a term concerned with the

  • condensation of the saturated vapor on a cold surface.
  • concentration of a corrosive solution by evaporation.
  • heat transfer between two highly viscous liquids.
  • boiling of a liquid on a hot surface.
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