Deck 15: Heat Transfer and Thermodynamics

Question 1

Tea pots are highly polished

A)So that they may not conduct heat from outside
B)So that they may absorb all radiation from outside
C)To make them attractive to look at
D)Because porcelain takes high polish
E)None of the above

Answer 1

So that they may absorb all radiation from outside

Question 2

A shpere, a cube and a disc all of the same material, quality and volume are heated to 900K and left in air. Which of these will have the lowest rate of cooling

A)Sphere
B)All will have the same rate of cooling
C)Disc
D)Cube
E)37,500 kg

Answer 2

Sphere

Question 3

The overall co-efficient of heat transfer is expressed as

A)kcal/hr
B)kcal/m/hr
C)kcal/m²/hr/°C
D)None of the above
E)Nichrome

Answer 3

kcal/m²/hr/°C

Question 4

A fur coat on an animal will help the animal to be

A)Warm in summer
B)Safe in rains
C)Cool in summer
D)Warm in winter
E)Cool in winter

Question 5

The wagelength of X-rays is

A)6 to 100000 micron
B)0.4 to 0.8 micron
C)0.8 to 400 micron
D)0.1 to 0.4 micron
E)0.014 to 0.018 micron

Question 6

There are two spheres of copper the ratio of their radii being 1 : 3 both at the same temperature. The ration of heat contents will be

A)1 ; 81
B)1 ; 9
C)1 ; 3
D)1 ; 1
E)1 ; 27

Question 7

Which dimensionless number can be used for convective heat transfer?

A)Mach number
B)37,500 kg
C)Graetz number
D)Froude number
E)Nusselt number

Question 8

Essential requirement for the transfer of heat from one body to another is

A)Both bodies must be solids
B)Both bodies must be in contact
C)Temperatures of the two bodies must be different
D)One of the bodies must have internal source of heat generation
E)All of the above

Question 9

The ratio of specific heats of a gas is 1.4 and the value of specific heat at constant pressure is 7.0 cal/mole °C. The difference between specific heat at constant presure and specific heat at constant volume will be

A)1.4
B)5
C)1/1.4
D)1.7
E)2

Question 10

The reflectance of a black body is

A)less than 1.0
B)37,500 kg
C)infinite
D)one
E)zero

Question 11

A dimensionless heat transfer coefficient which gives a measure of the ratio of the heat transfer rate to the rate at which heat would be conducted within the fluid under a temperature gradient is known as

A)Stanton number
B)Reynolds number
C)Nusselt number
D)Grashoff number
E)Peclet number

Question 12

If thermal conductivity of a material of wall varies as ko (1 -t ). The temperature at the centre of the wall will be

A)Same as in case of constant thermal conductivity
B)More than that in case of constant thermal conductivity
C)Less than that in case of constant thermal conductivity
D)Depends on other factors
E)None of the above

Question 13

Dynamic similarity is the similarity of

A)Shape
B)Forces
C)Velocities
D)Effective dimensions
E)None of the above

Question 14

Which of the following is an example of absorption?

A)Extraction of sugarcane juice
B)Dechlorination of water
C)Removal of oil from cake
D)Removal of moisture from gasoline
E)None of the above

Question 15

The sensible heat of hot industrial gases can be recovered by a

A)Regenerator
B)Recuperator.
C)Either of (A) and (B) above
D)None of the above
E)None of the above.

Question 16

For glass wool the thermal conductivity varies from sample to sample because of variations in

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

Question 17

Metals are good conductors of heat because

A)They contain free electrons
B)Their atoms are relatively far apart
C)Their atoms collide frequently
D)They have reflecting surfaces
E)None of the above

Question 18

Which one of the following cannot be unit of thermal conductivity?

A)Kcal/m-hr°C
B)cal/c,-sec°K
C)BTU/ft-h°F
D)CHU/ft-hr°C
E)Watt / m² K

Question 19

A body cools from 80°C to 70°C in 10 minutes. The time taken by the body for further cooling to 60°C will be

A)5 minutes
B)7 minutes
C)10 minutes
D)More than 10 minutes
E)Less than 10 minutes

Question 20

Calorific value of Indian coal is

A)5700 kcal/kg
B)9600 kcal/kg
C)Nichrome
D)3300 kcal/kg
E)2000 kcal/kg

Question 21

The statement that the emissivity and absorptivity of a surface is surrounded by its own temperature are the same for both monochromatic and total radiation, is known as

A)Kirchhoff's law
B)Lambert law
C)Stefan Boltzman low
D)D'Alembert's rule
E)Law of emissivity

Question 22

Emissivity and absorptivity of a surface are equal for radiation

A)37,500 kg
B)in ultraviolet region
C)in radio frequency range
D)with equal temperature and wavelength
E)infrared region

Question 23

The equation m x T = constant represents

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

Question 24

The face temperatures of a flat wall are 650°C and 450°C respectively and the thermal conductivity of wall material is 0.30 kcal/m-hr-°C. For a wall thickness of 20 cm, the rate of heat conduction per square meter of wall area will be

A)37,500 kg
B)300 kcal/hr
C)600 kcal/hr
D)3000 kcal/hr
E)150 kcal/hr

Question 25

Pipes are insulated so that

A)There is minimum corrosion
B)Heat loss from the surface is minimized
C)They can withstand higher fluid pressures
D)Vibrations resulting from fluid flow are minimized
E)They may not break under pressure

Question 26

The value of Stefan Boltzmann's constant in kcal-m²-hr-K⁴ is

A)0.174 x 10^-8
B)0.567 x 10^-4
C)4.87 x 10^-8
D)56.7 x 10^-9
E)1.335 x 10^-12

Question 27

An isotherm is a graph

A)Showing pressure volume changes at constant temperature
B)Connecting points of equal pressure
C)Constant temperature
D)Connecting points of equal temperature
E)Showing product of pressure and volume against pressure

Question 28

A non-dimensional number which generally finds application in mass transfer problems is

A)Stanton number
B)Weber number
C)Grashoff number
D)Mach number
E)Graetz number

Question 29

The mass of water vapour per kg of the pressure of saturated vapour at the air is known as

A)Specific humidity
B)Relative humidity
C)Molar humidity
D)Humidity ratio
E)None of the above

Question 30

Unsaturated vapours

A)Do not obey gas laws
B)Obey Boyle's law and not Boyles law
C)Fully obey gas laws
D)Superheated vapour
E)Partly obey gas laws depending upon the degree of unsaturation

Question 31

Four balls made of lead, glass, brass and iron made of same size, are heated to 100°C. They are simultaneously placed on a sheet of paraffin nearly 5 mm thick. Which ball will drop first?

A)Lead
B)Glass
C)37,500 kg
D)Iron
E)Brass

Question 32

Kinematic viscosity indicates

A)heat energy transport through conduction
B)37,500 kg
C)heat evergy transport through convection
D)conversion of momentum into heat energy
E)momentum transport by molecular friction

Question 33

A piece of metal with a circular hole is heated. If the metal expands on heating the diameter of the hole will

A)Increase
B)Decrease
C)Increase or decrease depending upon the diameter of the whole
D)Increase or decrease depending on the kind of the metal
E)None of the above

Question 34

Four rods with different radii 'r' and length 'l' are used to connect to reservoirs of heat at different temperature. Which one of them with conduct most heat?

A)r = 1 cm, l = 1m
B)r = 2 cm, l =
C)r = 2 cm, l = 2m
D)r =
E)37,500 kg

Question 35

Which type of heat exchanger an automobile radiator is?

A)Recuperator type
B)Counter flow type
C)Cross flow type
D)Regenerator type
E)Parallel flow type

Question 36

The wavelength for maximum emissive power is given by

A)Stefan Boltzman's law
B)Wein's law
C)Fourier's law
D)Kirchhoff's law
E)Planck's law

Question 37

The emissivity of a body will be equal to absorptivity when

A)Body is in thermal equilibrium
B)Temperature of body is rising
C)Temperature of body is falling
D)Body is at low temperature
E)Body is at high temperature

Question 38

In constant volume Hydrogen gas Thermometer, a correction has to be applied, because

A)Hydrogen is impure
B)Expansion of Hydrogen is non-linear
C)Density of mercury changes
D)None of the above
E)Optical pyrometer

Question 39

All substances emit radiation, the quality and quantity depending upon the absolute temperature and the properties of the material composing the radiating body. The above statement is known as the statement of

A)Stefan-Bolzmann's law
B)Kirchhoff's law
C)Planck's law
D)D Alambert's rule
E)Law of radiation

Question 40

The unit of thermal conductivity in M.K.S. unit is

A)kcal/m/°C
B)kcal/m/sec°C
C)kcal/m²/°C sec
D)None of the above
E)Nichrome

Question 41

Radiation heats transfer between two surfaces can be reduced by

A)Preheating the surfaces closer together
B)Introducing radiation shield between the surfaces
C)Polishing the surface
D)37,500 kg
E)Bringing the surfaces closer together

Question 42

Thermal diffusivity is

A)A function of temperature
B)A mathematical formula only
C)A dimensionless parameter
D)A configuration for heat conduction
E)A physical property of the material

Question 43

In a thermal power plant, cooling towers are used to cool

A)steam
B)condensed wate
C)circulating
D)All of the above
E)37,500 kg

Question 44

A steam pipe is to be insulated by two insulating materials put over each other. For best results

A)Better matt. Over pipe and inferior over it
B)Inferior matt. Over pipe and better over it
C)Can be in any order
D)None of the above
E)Nichrome

Question 45

The rate of heat flow from a 50 mm thick wall of material having thermal conductivity of 40 W/m°C for a temperature difference of 10°C will be

A)800 W/m² - hr
B)200 W/m² - hr
C)2000 W/m² - hr
D)80 W/m² - hr
E)8000 W/m² - hr

Question 46

All temperatures above the freezing point of gold are usually determined by

A)Thermo couple
B)Gas thermometer
C)Optical pyrometer
D)Resistance bridge
E)Any of the above

Question 47

Two large closely spaced concentric spheres (both of which are perfect black body radiators) are maintained at temperatures of 127°C and ² 7°C respectively. The space in between the two spheres is evacuated. Taking Stefan Boltzmann constant as 5.67 x 10⁸ watt m²K the rate of radiation in watts per sq. m between the two spheres is approximately

A)992
B)762
C)37,500 kg
D)852
E)666

Question 48

A body cools from 90°C to 80°C in 5 minutes. Under the same external conditions to cool from 80°C to 70°C the body will take

A)2.5 minutes
B)Cannot be predicted
C)5 minutes
D)More than 5 minutes
E)4 minutes

Question 49

Maximum heat transfer rate can be expected in case of

A)Turbulent flow
B)Co-current flow
C)Laminar flow
D)Counter current flow
E)Heat transfer rate is independent of nature of flow