S2

Question 1

Which area is used in case of heat flow by conduction through a cylinder?

Answer 1

logarithmic mean area

Question 2

Heat transfer by conduction results duet to the transfer of free electrons, kinetic energy, and vibrational energy from one molecule to another. Conduction heat transfer can not take place

Answer 2

between two bodies not in physical contact with each other

Question 3

The dimensionless group in mass transfer that is equivalent to Prandtl number in heat transfer is

Answer 3

Schmidt number

Question 4

Finned tube heat exchangers

Answer 4

**give larger area per tube*&

Question 5

The absorptivity of a grey body at a given temperature _______ with increasing wavelength of radiation.

Answer 5

may increase or decrease; depends on the material

Question 6

Which on gives the monochromatic emissive power for black body radiation?

Answer 6

Planck’s law

Question 7

For what value of Prandtl number, St= f/2?

Answer 7

1

Question 8

In a shell and tube heat exchanger,

Answer 8

the temperature drops in the two fluids and the wall are proportional to individual resistances

Question 9

Dietus-Boelter equation used for the determination of heat transfer coefficient is valid

Answer 9

for fluids in turbulent flow

Question 10

The equation, Nst, corresponds to ______ analogy

Answer 10

Prandtl

Question 11

For large heat transfer area requirement, shell and tube heat exchanger is preferred, because it

Answer 11

All a,b,c

A. Occupies smaller space
B. Is more economical
C. Is easy to operate and maintain

Question 12

Out of the following four assumptions used in the derivation of the equation for LMTD, which one is subject to the largest deviation in practice?

Answer 12

constant rate of fluid flow

Question 13

Heat flux increases with temper drop beyond the Leiden frost point on the plot of heat flux vs. temperature drop for a boiling liquid, because

Answer 13

radiation becomes important

Question 14

Resistance to heat flow by conduction is proportional to

Answer 14

all a,b, and c

A. t
B. 1/density
C. 1/A

Question 15

Temperature profile in steady state heat transfer is

Answer 15

Linear

Question 16

For the same heat load and mass flow rate in the tube side of a shell and tube heat exchanger, one may use multipass on the tube side, because it

Answer 16

increase the overall heat transfer coefficient

Question 17

When vaporization takes place through a blanketing film of gas, the phenomenon is termed as _____ boiling.

Answer 17

film

Question 18

Minimum recommended baffle spacing in a shell and tube heat exchanger is about

Answer 18

0.2D

Question 19

Stefan-Boltzmann law which describes the radiation heat transfer states that, it is proportional to

Answer 19

T^4

Question 20

The Nusselt number for fully developed laminar flow through a circular pipe, where the wall heat flux is constant, is

Answer 20

4.36

Question 21

What is the unit of thermal conductivity?

Answer 21

Kcal/hr.m.degC

Question 22

The thermal radiation emitted by a body is proportional to T^n, where T is its absolute temperature. The value of ‘n’ is exactly 4 for

Answer 22

all bodies

Question 23

It is not preferable to use superheated steam in evaporators, because of its very

Answer 23

low film coefficient

Question 24

It is desired to concentrate a 20% salt solution (20 kg of salt in 100 kg of solution) to a 30% salt solution in an evaporator. Consider a feed of 300 kg/min at 30°C. The boiling point of the solution is 110°C, the latent heat of vaporisation is 2100 kJ/kg and the specific heat of the solution is 4 kJ/kg.K. The rate at which the heat has to be supplied in (kJ/min) to the evaporator is

Answer 24

3.06x10^5 kJ/min

Question 25

LMTD for counterflow and parallel flow heat exchanger will be the same, when the

Answer 25

**cold fluid is heated to a certain temperature by condensing steam (isothermal fluid)**

Question 26

For flow over a flat plate, the ratio of thermal boundary layer thickness, 'xt' and hydrodynamic boundary layer thickness 'x' is equal to (where, NPr = Prandtl number)

Answer 26

**NPr^1/3**

Question 27

The range of electromagnetic spectrum important in heat transfer by radiation is _____ microns

Answer 27

**0.5-50**

Question 28

Use of transverse baffles in a shell and tube heat exchanger is done to increase the

Answer 28

**All a,b,c** A. Rate of heat transfer B. Flow velocity C. Turbulence of shell side fluid

Question 29

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

Answer 29

**All a,b,c** A. Liquid depth over the heating surface B. Solution being evaporated C. Pressure difference between the steam chest and the vapor space above the boiling liquid

Question 30

Economy of multiple effect evaporator depends upon the

Answer 30

**heat balance consideration**

Question 31

The Graetz number is concerned with the

Answer 31

**heat transfer in laminar flow**

Question 32

Solid angle subtended by the finite surface at the radiating element is

Answer 32

**called the angle of vision**

Question 33

Pick out the wrong statement.

Answer 33

**The emissivity of a surface decreases, if it gets corroded by atmospheric environment**

Question 34

In forced convection, the heat transfer depends on

Answer 34

**Re, Pr**

Question 35

With increase in temperature, the thermal conductivity of most liquids

Answer 35

**decreases**

Question 36

Heat transfer by _______ may not necessarily require the presence of a medium.

Answer 36

**radiation**

Question 37

Pick out the CORRECT statement

Answer 37

**Logarithmic mean area is used for calculating the heat flow rte through a thick walled cylinder**

Question 38

In a shell and tube type heat exchanger, the floating tube bundle heat arrangement is used

Answer 38

**in high range of temperature differences**

Question 39

Stefan-Boltzmann law applies to _____ body

Answer 39

**black**

Question 40

The film co-efficient is decreased due to the presence of non-condensing gases in the vapors. The film co-efficient of superheated vapor as compared to that of saturated vapor is

Answer 40

**some**

Question 41

A perfect black body is a perfect _____ of radiation

Answer 41

**both a and b** A. Absorber B. Emitter

Question 42

In case of parallel flow heat exchanger, the lowest temperature theoretically attainable by the hot fluid is _____ the outlet temperature of the cold fluid.

Answer 42

**equal to**

Question 43

An equipment which converts the latent or sensible heat of one fluid into the latent heat of vaporization of another, is called a

Answer 43

**heat exchanger**

Question 44

Which of the following is directly concerned with the heat transfer?

Answer 44

**Grashof number**

Question 45

Pick out the WRONG statement

Answer 45

**With change in temperature, the radiant energy emitted by a black body remains unchanged.**

Question 46

Planck’s distribution law is valid for ____ bodies.

Answer 46

**colored**

Question 47

For hot feed, forward feeding as compared to backward feeding results in ______ economy.

Answer 47

**increased**

Question 48

Radiation energy is emitted by all the substances, which are above

Answer 48

**0 Kelvin**