Deck 14: Components of Radiation From Flames

Question 1

Which rays have the least wavelength?

A)Ultraviolet
B)Cosmic rays
C)Irifrared
D)X-rays
E)Radio

Answer 1

Cosmic rays

Question 2

Ditus Boelter equation is applicable in case of fluids flowing in

A)Laminar region
B)Turbulent region
C)Transition region
D)Any of the above
E)None of the above

Answer 2

Turbulent region

Question 3

Transmission of heat by molecular collision is

A)Scattering
B)Transmission
C)Radiation
D)Convection
E)Conduction

Answer 3

Convection

Question 4

The emissive power of a body depends on

A)Nature of body
B)Temperature of body
C)Physical nature
D)All of the above
E)None of the above

Question 5

Floating heads are provided in heat exchangers to

A)Facilitate maintenance
B)Regulate the flow
C)Increase the pressure drop
D)Avoid deformation of tubes due to thermal expansion
E)Reduce the pressure drop

Question 6

The transfer of heat in case of radiation takes place by means of

A)Heated particles of the medium
B)Electromagnetic waves
C)Thermal energy of the source
D)None of the above
E)37,500 kg

Question 7

In case of liquids and gases, the heat transfer takes place according to

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

Question 8

Which of the following has the highest value of the thermal conductivity

A)Wood
B)Asbestos
C)Nichrome
D)Clay
E)Refractory brick

Question 9

Which of the following is wrong

A)Black surfaces are better absorbers than white ones
B)Black surfaces are better radiators than white ones
C)Rough surfaces are better radiators than smooth surfaces
D)37,500 kg
E)Highly polished mirror like surfaces are very good radiators

Question 10

Which of the following are generally diathermanous?

A)Solids
B)Liquids
C)Gases
D)All of the above
E)37,500 kg

Question 11

Longest wavelength

A)Ultraviolet rays
B)Infrared rays
C)Gamma rays
D)X-rays
E)Radio waves

Question 12

All bodies above absolute zero temperature emit radiation". Above statement is based on

A)D'Alambert's rule
B)Wein's law
C)Stefan law
D)Planck's law
E)Prevost theory

Question 13

Which one of the following will radiate heat to a large extent?

A)White polished surface
B)White rough surface
C)Black rough surface
D)Black polished surface
E)None of the above

Question 14

In a cooling tower which mode of heat transfer plays insignificant role?

A)Evaporative cooling
B)Convective cooling
C)Radiaion
D)All of the above
E)37,500 kg

Question 15

A dimensionless number which is the ratio of kinematic viscosity to thermal diffusivity is known as

A)Grashoff number
B)Reynolds number
C)Prandtl number
D)Pacelet number
E)Nusselt number

Question 16

There metal walls of same cross-sectional area having thermal conductivity in the ratio 1 : 2 : 4 transfer heat at the rate of 15000 kcal/hr. For same thickness of wall, the temperature deop will be in the ratio

A)1 ; 2 ; 4
B)1 :
C)4 ; 2 ; 1
D)1 ; 1 ; 1

Question 17

Formation of fog is due to

A)High pressure
B)Humidity
C)Temperature fall of atmosphere
D)Low pressure
E)Night showers

Question 18

The radiation from flames consists of

A)Continuous radiation from burning soot particles of microscopic and submicroscopic dimensions
B)Radiation from suspended larger particles of coal, coke or ash contributing to flame luminosity
C)Infrared radiation from water vapour and carboundioxide
D)Non-equilibrium radiation associated with the combustion process
E)All of the above

Question 19

In a shell and tube heat exchanger, the corrosive liquid is normally passed through

A)Shell side.
B)Tube side
C)Either of (A) and (B) above
D)None of the above
E)None of the above.

Question 20

DBA = DAB, in case of

A)Stagnet diffusion
B)Equimolar counter diffusion
C)Either of (A) and (B) above
D)None of the above
E)2.6 cm²/sec

Question 21

Unsaturated vapours

A)Do not obey gas laws
B)Fully obey gas laws
C)Obey Boyle's law but not Charle's law
D)Partly obey gas laws depending upon the degree of unsaturations
E)None of the above

Question 22

A substance above critical temperature exists as

A)Solid
B)Liquid
C)Wet vapour
D)Gas
E)Dry vapour

Question 23

Which dimensionless number indicates the relative strength of the buoyant to viscous forces?

A)Froude's number
B)37,500 kg
C)Prandtl number
D)Weber number
E)Grashoff number

Question 24

In case the hydrodynamic and thermal boundary layers are identical for a fluid flowing over a heated plate

A)The value of Prandtl number must be 0.5
B)The plate surface must be smooth
C)The plate must be of low thermal conductivity
D)The value of Prandtl number thust be 1
E)The value of Prandtl number must be zero

Question 25

A high value of Prandtl number indicates

A)rapid diffusion of momentum by viscous action compared to diffusion of energy
B)relative heat transfer by conduction to convection
C)rapid heat transfer by forced convection to natural convection
D)None of the above
E)37,500 kg

Question 26

Elongation of a rod when heated

A)Is proportional to original length
B)Is proportional to length
C)Is inversely proportional to linear strain
D)Is inversely proportional to original length
E)Does not depend on its length

Question 27

A dimensionless number which is the ratio of mass heat flow rate to the heat flow rate by conduction under a unit temperature gradient and through a thickness L is known as

A)Nusselt number
B)Prandtl number
C)Weber number
D)Grashof number
E)Peclet number

Question 28

The surface temperatures of a flat wall are 650°C and 450°C respectively and the thermal conductivity of the wall material is 0.30 kcal/m-hr-°C. The heat flux for a wall of 20 cm thickness will be

A)60 kcal/m²-hr
B)600 kcal/m²-hr
C)120 kcal/m²-hr
D)300 kcal/m²-hr
E)450 kcal/m²-hr

Question 29

Which of the following is a minimum boiling azeotrope?

A)Acetone-chloroform
B)Molasses-water
C)Benzene-toluene
D)Iso-butanol-water
E)Carbon disulphide-acetone

Question 30

In a psychrometric chart the abscissa represents

A)Specific humidity
B)Relative humidity
C)Enthalpy
D)Dry bulb temperature
E)Wet bulb temperature

Question 31

For handling severely scaling liquids which of the following evaporator will be preferred?

A)Horizontal tube type
B)Long vertical tube type
C)Agitated film type
D)Short vertical tube
E)None of the above

Question 32

The factor which affects nucleate pool boiling is

A)Material of heating surface
B)Surface condition of heating surface
C)Physical properties of liquid
D)Pressure
E)All of the above

Question 33

If the amount of radiant energy received per unit area per second from the sun is measured at the Earth, Mars and Jupiter it will be

A)in the decreasing order - Jupiter, Mars, Earth
B)in the increasing order - Jupiter, Mars, Earth
C)identical on all the three planets
D)37,500 kg
E)in the increasing order - Earth, Mars, Jupiter

Question 34

Two bodies one hot and the other cold are kept in vacuum. What will happen to the temperature of the hot body after sometime?

A)Increases due to convection
B)Remains the same
C)Decreases due to convection
D)Increases due to radiation
E)Decreases due to radiation

Question 35

Transformer oil having kinematic viscosity of 3.66 x 10-6 m²/s flows through a tube 8 mm diameter at velocity of 0.6 m/s. The value of Reynolds number of flow would be

A)1510
B)1625
C)1000
D)1310
E)1415

Question 36

The thermal conductivity of wood depends upon

A)Density
B)Moisture content
C)Temperature
D)All of the above
E)None of the above

Question 37

In case of natural covection, the Nusselt number is function of

A)Reynolds number
B)Reynolds number and Prandtl number
C)Grashof's number and Prandtl number
D)Weber number and Mach number
E)None of the above

Question 38

Transient heat flow occurs in

A)Cooling of casting
B)Heating and cooling of buildings due to sun
C)Electric conductors carrying current
D)Melting of ice
E)Insulated pipes carrying superheated steam

Question 39

If thermal conductivity of aluminium is say 100 units at 0°C, the thermal conductivity at 500°C will be closer to

A)37,500 kg
B)100 units
C)20 units
D)140 units
E)50 units

Question 40

The highest value of thermal conductivity is expected for

A)Solid ice
B)Water
C)Melting ice
D)Steam
E)Boiling water

Question 41

If the roof of a house is painted with a shiny metallic paint, the temperature inside will

A)Rise
B)Fall
C)Remain unchanged
D)Depends on other factors
E)None of the above

Question 42

Plank's law of radiation is applicable to

A)Radiation of any kind
B)Temperature radiation
C)Monochromatic radiation
D)Thermal radiation
E)None of the above

Question 43

Diffusion coefficient of water into air at 26°C is nearly

A)5.2 cm²/s
B)2.6 cm²/sec
C)0.026 cm²/s
D)2.6 cm²/s
E)0.26 cm²/s

Question 44

A wall has two layers A and B, each made of a different material. Both the layers have the same thickness. The thermal conductivity of material of A is twice that of B. Under the thermal equilibrium the temperature difference across the wall is 30°C. The temperature drops in layers A and B will be respectively

A)15°C and 15°C
B)cannot be predicated
C)37,500 kg
D)10°C and ² 0°C
E)20°C and 10°C

Question 45

Hydrogen cannot be liquefied at room temperature because

A)it is a diatomic gas
B)its critical temperature is less than the room temperature
C)37,500 kg
D)it has low density
E)it has high specific heat

Question 46

Ablation heat transfer method is used on

A)nuclear war heads
B)submarines
C)37,500 kg
D)satellites
E)rockets

Question 47

In case of a body transparent to thermal radiation

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

Question 48

The phenomenon of boiling the milk in an open container when milk spills over the vessel is termed as

A)Film boiling
B)Pool boiling
C)Sub-cooled boiling
D)Interface evaporation
E)Nuclear boiling

Question 49

A hollow sphere with uniform interior temperature and a small hole behaves very nearly as a

A)White body
B)Transparent body
C)Opaque body
D)Black body
E)Grey body

Question 50

If a body reflects entire radiation incident on it, then it is known as

A)White body
B)Black body
C)Grey body
D)Transparent body
E)Opaque body