Deck 13: Concepts in Heat Transfer

Question 1

Condensing film co-efficient for steam on horizontal tubes ranges from 5000 to 15000 Kcal/hr.m².°C. Condensation of vapor is carried out inside the tube in a shell and tube heat exchanger, when the

A)Higher condensing film co-efficient is desired
B)Condensate is corrosive in nature
C)Lower pressure drop through the exchanger is desired
D)Temperature of the incoming vapor is very high

Answer 1

Condensate is corrosive in nature

Question 2

Viscosity of gases __________ with increase in temperature.

A)Increase very rapidly
B)Increase slowly
C)Decrease slowly
D)Remain unaffected

Answer 2

Increase slowly

Question 3

In case of surface condensers, a straight line is obtained on plotting 1/U vs. __________ on an ordinary graph paper.

A)1/V?^-0.8
B)V??^-0.8
C)V^-2
D)1/ V^-2

Answer 3

1/V?^-0.8

Question 4

A cube, sphere & a thin circular plate (all having same mass and made of same material) are all heated to 300°C and allowed to cool in natural air. Which one will cool the slowest?

A)Cube
B)Plate
C)Sphere
D)All will cool at the same rate

Question 5

A steel sphere of radius 0.1 m at 400°K is immersed in an oil at 300°K. If the centre of the sphere reaches 350°K in 20 minutes, how long will it take for a 0.05 m radius steel sphere to reach the same temperature (at the centre) under identical conditions? Assume that the conductive heat transfer co-efficient is infinitely large.

A)5 minutes
B)10 minutes
C)20 minutes
D)40 minutes

Question 6

Which of the following material has lest value of thermal diffusivity?

A)Aluminium
B)Rubber
C)Lead
D)Mercury
E)Iron

Question 7

For a opaque body

A)reflectivity = 0
B)absorptivity = reflectivity = 1
C)37,500 kg
D)absorptivity + reflectivity = 1
E)absorptivity = 0

Question 8

In which case the value of thermal conductivity drops with rising temperature

A)Methane
B)Benzene
C)Carbondioxide
D)Ammonia
E)None of the above

Question 9

Which of the following is used as entrainer in acetic acid - water separation?

A)Butyl acetate
B)Methyl alcohol
C)Benzene.
D)Phosphorous
E)Hexane

Question 10

Which of the following provides maximum contact surface for a liquid vapour system?

A)Wetted wall column
B)Packed tower
C)Sieve plant column
D)Benzene.
E)Bubble cap tower

Question 11

The lower temperature limit for mercury thermometer is

A)Absolute zero
B)0°F
C)- 39°F
D)0°C
E)100°C

Question 12

Cork is a good insulator because

A)It is porous
B)Its density is low
C)It is flexible
D)It can be powdered
E)It can be cast into rolls

Question 13

The value of thermal conductivity of water at room temperature is expected to be

A)0.05 kcal/m-hr-°C
B)0.5 kcal/m-hr-°C
C)0.001 kcal/m-hr-°C
D)1.0 kcal/m-hr-°C
E)1.5 kcal/m-hr-°C

Question 14

The coefficient of linear expansion of a solid is L. The volume V of a cube of this solid on being heated by 1?C will change by

A)VL
B)VL/3
C)3 VL
D)37,500 kg
E)3L

Question 15

The unit of thermal conductivity in S.I. units is

A)KJ/m-hr-°K
B)KJ/m-hr°C
C)W/m°K
D)W/m-hr°C
E)W/m-hr-°K

Question 16

Two rods one of copper and the other of mild steel, both of diameter 20 mm and length 250 mm are coated with a uniform layer of wax all around. These rods are placed vertically in a boiling water bath with 200 mm, length of each rod projecting outside. If the melting point of wax is 10?C, then

A)equal quantity of wax will meet on the two rods
B)more wax will melt on copper rod as compared to mild steel rod
C)37,500 kg
D)nothing can be predioted as the data is insufficient
E)more wax will melt on mild steel rod as compared to copper rod

Question 17

Oxygen boils at -183°C, this temperature is

A)- 215°F
B)- 361°F
C)- 227°F
D)- 329°F
E)-398°F

Question 18

Heat is transferred from an electric bulb mainly by

A)Conduction, convection and radiation.
B)Radiation
C)Convection and conduction
D)Convection
E)Conduction

Question 19

The average value of thermal conductivity for air at 20°C is about

A)0.11
B)0.011
C)0.022
D)None of the above
E)Nichrome

Question 20

A vapour containing liquid particles to the extent of 50% by the volume is known as

A)Saturate vapour
B)Superheated vapour
C)Super saturated liwuid
D)Wet vapour
E)Saturated liquid

Question 21

Ice is slippery when a man walks on it for

A)There is no friction
B)Increase of pressure causes it to melt
C)It is very chill
D)Its surface is smooth
E)It has lubricating qualities

Question 22

The total solar radiation incident on a body is 1000 kcal/min. The body reflects 400 kcal/min. If the transmissivity of the surface will be

A)0.85
B)0.3
C)0.45
D)0.15
E)0.4

Question 23

The nature of flow of a fluid inside a tube i.e., whether it is turbulent or laminar, is ascertained by

A)Viscosity of fluid
B)Flow velocity
C)Surface conditions
D)Tube size
E)Reynolds number

Question 24

When metallic surfaces are oxidized the emissivity

A)Depends on the temperature
B)Depends on other factors
C)Decreases
D)Does not change
E)Increases

Question 25

For which fluid combination the value of overall heat transfer coefficient will be least?

A)Alcohol condensers
B)Air to heavy tars
C)Feed water heaters
D)37,500 kg
E)Air condensers

Question 26

The rate of heat flow between a solid wall and a fluid (in contact with a solid wall) is given by

A)Wein's Law
B)Kirchhoff's law
C)Newton-Rikhman's Law
D)None of the above
E)Nichrome

Question 27

Radio active nuclear waste is treated in

A)Pulsed column extractor
B)Mixer settler extractor
C)Sieve plate extraction column
D)Bollman extractor
E)None of the above

Question 28

In which case does the thermal conductivity increase from left to right?

A)Aluminium, silver, copper
B)37,500 kg
C)Aluminium, copper, silver
D)Silver, copper, aluminium
E)Copper, silver, aluminium

Question 29

If two systems are being compared on the basis of temperature and heat flux, the similarity being considered is

A)37,500 kg
B)thermal similarity
C)dynamic similarity
D)geometrical similarity
E)kinematic similarity

Question 30

Thermal conductivity of air at room temperature in kcal/m-hr-°C is nearly

A)0.1
B)0.001
C)0.005
D)0.05
E)0.01

Question 31

Steam traps are used to

A)Heat steam
B)Remove condensate
C)Balance the pressure
D)Regulate the flow
E)Add moisture

Question 32

-40°C is equivalent to

A)- 40°K
B)172°R
C)- 40°F
D)273°K
E)500°R

Question 33

The temperature inside a furnace is generally measured by

A)Mercury thermometer
B)Alcohol thermometer
C)Gas thermometer
D)Optical pyrometer
E)Any of the above

Question 34

At all wavelengths and temperatures the monochromatic emissivity of a white body is equal to

A)Zero
B)Unity
C)0.1 to 0.5
D)0.5
E)0.5 to 1

Question 35

If the bubbles formed on a submerged hot surface get absorbed in the mass of liquid, the process of boiling is termed as

A)Nucleate boiling
B)Film boiling
C)Pool boiling
D)Any of the above
E)None of the above

Question 36

The rate of radiant energy, which is emitted by a surface at any temperature and in small wavelength is found from the known rate of energy, which under the same condition would be emitted from a black surface by multiplying with the absorptivity. Above enunciation is known as

A)Planck's law
B)Kirchhoff's law
C)Stefan Boltzman law
D)Lambert rule
E)None of the above

Question 37

A radiation shield should have

A)low reflectivity
B)high reflectivity
C)high emissivity
D)None of the above
E)37,500 kg

Question 38

In heat exchanger design, one transfer unit means

A)Condition when the change in temperature of 1°C numerically equals the average driving force.
B)The equivalent length of tubes in case the heat exchange was for a temperature difference of 1°C
C)One fluid exchanging with another fluid of the same chemical composition
D)The section of heat exchanger where heat transfer surface area is one square metre
E)The section of heat exchanger which will cause temperature drop of one degree centigrade

Question 39

A 1-2 heat exchanger means

A)Single pass on shell side and double pass on tube side
B)Single pass on tube side and double pass on shell side
C)Two tubes of hot fluid pass through one tube of cold tube
D)Single liquid cools two liwuids at different temperatures
E)Two tubes of cold fluid pass through one tube of hot fluid

Question 40

When a body is in thermal equilibrium with its surroundings, the absorptivity and the emissivity of the body are same. This Law is known as

A)Wein's Law
B)Kirchhoff's law
C)Stefan Boltzmann's law
D)None of the above
E)Nichrome

Question 41

The process of separation of solutes of different molecular sizes in a liquid solution by use of a sutable membrane is known as

A)Hyper sorption
B)Leaching
C)Adsorption
D)Dialysis
E)Distillation

Question 42

The propose of using multiple pass heat exchangers is to

A)Increase pressure drop
B)Increase the rate of heat transfer
C)Neutralise viscous friction
D)Reduce pressure drop
E)Reduce fluid flow friction losses

Question 43

The range of diffusivity of gases in cm²/sec at atmospheric pressure is

A)10 to 5
B)More than 10
C)5 to 1
D)Less than 1
E)1

Question 44

Four identical copper cubes are painted with different paints. Now if all the cubes are heated to the same temperature and are left in vacuum, which cube will lose heat more rapidly? The colours of the cubes are

A)Pale blue
B)37,500 kg
C)Shiny black
D)Dull red
E)shiny white

Question 45

In case of ideal mono-atomic gas, the ratio of specific heats would be

A)1.4
B)1.33
C)1.41
D)1.67
E)1

Question 46

Thermal conductivity of glass wool depends on

A)Composition
B)Density
C)Porosity
D)Structure
E)All of the above

Question 47

The average value of thermal conductivity for water at 20°C is about

A)0.13
B)0.32
C)0.51
D)None of the above
E)Nichrome

Question 48

Which one of the following is a very good insulator?

A)A hard wood board
B)A porcelain sheet
C)An asbestos sheet
D)Saw dust
E)None of the above

Question 49

A device for transferring heat from one fluid to another is known as

A)Lead
B)Heat exchanger
C)Radiation
D)Condenser
E)Evaporator

Question 50

Which insulating material is suitable for low temperature applications?

A)85% magnesia
B)Diatomaceous earth
C)Fused alumina bricks
D)Cork
E)Asbestos paper

Question 51

Steady state heat transfer occurs when

A)The flow of heat is uniform
B)The flow of heat is uniformly increasing
C)The flow of heat is uniformly decreasing
D)The flow of heat is negligible
E)The flow of heat is independent of time

Question 52

Which of the following material has thermal conductivity closest to silver?

A)Steel
B)37,500 kg
C)Aluminium
D)Brass
E)Copper

Question 53

A constant gas thermometer is based on

A)Avogadro's law
B)Graham's law
C)Charle's law
D)Boyle's law
E)37,500 kg

Question 54

Thermal conductivity of liquids can be determined by

A)Guarded plate method
B)Searles method
C)Laby and Hercus method
D)Any of the above
E)None of the above

Question 55

The temperature of sun can be measured using a

A)radiation pyrometer
B)platinum resistance thermometer
C)standard thermometer
D)mercury thermometer
E)37,500 kg

Question 56

Any of the following could be the unit for Stefan Boltzmann constant EXCEPT

A)cal / cm²-sec-K⁴
B)BTU/ft2-hr-R⁴
C)W / m²K⁴
D)37,500 kg
E)erg / cm-K⁴

Question 57

Which one of the following approximates to the black body condition?

A)Ice
B)Water
C)Lamp black
D)All of the above
E)None of the above

Question 58

Heat is shown to be closely related to

A)Energy
B)Momentum
C)Temperature
D)Waveform
E)A fluid

Question 59

Which of the following method is used for finding the thermal conductivity of rubber?

A)Lec's disc method
B)Searles method
C)Cylindrical shell method
D)Laby and Hercus method
E)Any of the above

Question 60

The ratio of thermal conductivity of copper to that of brass is nearly

A)37,500 kg
B)8
C)4
D)2

Question 61

The relation between the emissive and absorptive power of a surface is developed under

A)Electrical analogy
B)Stefan-Baltzmann's law
C)Planck's law
D)Kirchhoff's law
E)Law of radiations

Question 62

In air prelieater for boiler heat is least transferred by

A)Convection
B)Conduction, convection and radiation.
C)Conduction and convection
D)Conduction
E)Radiation

Question 63

The rate of heat loss through a furnace wall is 1000 kcal per hour when inside temperature is 1000°C and outside wall temperature is 500°C. What should be the wall thickness in case the thermal conductivity of wall material is 0.5 kcal/m-hr°C

A)25 cm
B)12.5 cm
C)50 cm
D)60 cm
E)40 cm

Question 64

Non-isotropic conductivity is exhibited in case of

A)Steel
B)Wood
C)Copper
D)Lead
E)Brass

Question 65

What energy transformation takes place when ice and salt mixture is converted into water

A)Heat energy to sensible heat
B)Kinetic energy to heat energy
C)Heat energy to latent heat
D)Heat energy to potential energy
E)Heat energy to kinetic energy

Question 66

The rate of energy stored in the wall will be

A)50 kcal/sec
B)50 kcal/min
C)200 kcal/min
D)50 kcal/hr
E)200 kcal/hr

Question 67

Pyrometer which react to all wavelengths of incident radiant energy are known as

A)Multicolour pyrometers
B)Total radiation pyrometers
C)Polarising pyrometers
D)Optical pyrometers
E)Ddisappearing filament type pyrometers

Question 68

A relationship between the temperature of a black body and the wavelength at which the maximum value of monochromatic emission power occurs, is established under

A)D' lambert's rule
B)Stefan-Bolzmann's law
C)Planck's law
D)Wein's displacement law
E)Kirchhoff's law

Question 69

In case of white body, absorptivity is

A)Between 0 to 0.5
B)1
C)Zero
D)More than 0.5
E)37,500 kg

Question 70

Two parallel opposed, infinite black planes are maintained at 300°C and 400°C respectively. If the temperature difference is doubled by increasing the temperature from 400°C to 500°C, the heat exchange rate will increase by a factor of about

A)2.5
B)5.5
C)8.75
D)6.25
E)4.5

Question 71

The overall co-efficients of heat transfer is used in the problems of

A)convection
B)conduction
C)radiation
D)conduction and convection
E)Nichrome

Question 72

Identity the correct statement

A)Only some substances emit radiation
B)A substance will emit radiation at a particular wavelength only
C)Quality and quantity of radiation depends on the properties of the material only
D)All substances emit radiation the quality and quantity depends on the absolute temperature and the properties of the material composing the radiating body
E)Bodies black in colour are known as black bodies

Question 73

Baffles are provided in heat exchangers to

A)Provide better mechanical strength
B)Reduce heat transfer rate
C)Reduce vibrations
D)Increase heat transfer rate
E)Remove dirt

Question 74

Heat sensitive liquids are connected

A)By using insulated vessels
B)By using low intensity heating
C)By using deoxidisers
D)By using small quantities
E)By using vacuum

Question 75

Which sample of concrete may be expected to have highest value of thermal conductivity

A)Dry concrete having 0.4% rein-forcement
B)Concrete having 10% moisture by volume
C)Concrete having 10% meisture by volume and 0.4% reinforcement
D)Dry concrete
E)Concrete having 10% moisture by volume and 0.6% reinforcement