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Multiple choice question for engineering

Set 1

1. Regarding one dimensional heat transfer, choose the correct statement
a) Steady- f (x), Unsteady- f (x, t)
b) Steady- f (x, t), Unsteady- f (x)
c) Steady- f (x, y, t), Unsteady- f (x)
d) Steady- f (y, z), Unsteady- f (y)

View Answer

Answer: d [Reason:] In case of one dimensional heat flow steady state is a function of x coordinate only while unsteady state is a function of x coordinate and time only.

2. Which statement is true regarding steady state condition?
a) There is a variation in temperature in the course of time
b) Heat exchange is constant
c) It is a function of space and time coordinates
d) Internal energy of the system changes

View Answer

Answer: b [Reason:] Heat influx is always equal to heat efflux. It is a function of space coordinates only.

3. Which of the following is an example of steady state heat transfer?
a) Boilers and turbines
b) Cooling of I.C engine
c) Chilling effect of cold wind on a warm body
d) Electric bulb cools down by the surrounding atmosphere

View Answer

Answer: d [Reason:] System is a perfect black body.

4. Heat transfer in a long, hollow cylinder which is maintained at uniform but different temperatures on its inner and outer surfaces may be assumed to be taking place in which direction?
a) Axial only
b) Unpredictable
c) Radial only
d) No heat transfer takes place

View Answer

Answer: c [Reason:] Ambient temperature is uniform on the periphery of cylinder and temperature is uniform. So it takes place in radial direction only.

5. Heat transfer takes place according to which law?
a) Newton’s law of cooling
b) Second law of thermodynamics
c) Newton’s second law of motion
d) First law of thermodynamics

View Answer

Answer: b [Reason:] Second law states about heat transfer between source and sink.

6. Heat transfer takes place in liquids and gases is essentially due to
a) Radiation
b) Conduction
c) Convection
d) Conduction as well as convection

View Answer

Answer: c [Reason:] Convection is a process by which thermal energy is transferred between solid and fluid flowing through it.

7. The appropriate rate equation for convective heat transfer between a surface and adjacent fluid is prescribed by
a) Newton’s first law
b) Wein’s displacement law
c) Kirchhoff’s law
d) Newton’s law of cooling

View Answer

Answer: d [Reason:] The rate equation used to describe the mechanism of convection is called Newton’s law of cooling when the solid surface is cooled by fluid.

8. Identify the wrong statement
a) The process of heat transfer is an irreversible process
b) For heat exchange, a temperature gradient must exist
c) A material medium is not necessary for heat transmission
d) Heat flow doesn’t depends on temperature

View Answer

Answer: d [Reason:] Heat flows from higher to lower temperature.

9. During a cold winter season, a person prefers to sit near a fire. Which of the following modes of heat transfer provides him the maximum heat?
a) Conduction from the fire
b) If it is near the fire, convection sounds good
c) Convection and radiation together
d) Radiation will provide quick warmth

View Answer

Answer: d [Reason:] Heat transfer by radiation can occur between two bodies even when they are separated by a medium colder than both of them.

10. Most unsteady heat flow occurs
a) Through the walls of the refrigerator
b) During annealing of castings
c) Through the walls of the furnace
d) Through lagged pipe carrying steam

View Answer

Answer: b [Reason:] Under steady state condition, with time there is a change in temperature i.e. temperature field is a function of space and time.

Set 2

1. The Stefan-Boltzmann constant has units of
a) kcal/m2 hr K4
b) kcal/m hr K4
c) kcal/hr K4
d) kcal/m2 K4

View Answer

Answer: a [Reason:] According to Stefan-Boltzmann law, q = α A T4.

2. According to Stefan-Boltzmann law of thermal radiation
a) q = α A T
b) q = α A T4
c) q = α A T3
d) q = α A T5

View Answer

Answer: b [Reason:] α is Stefan-Boltzmann constant whose value is 5.67 * 10 -8 W/m2 K4.

3. Calculate the radiant flux density from a black surface at 400 degree Celsius?
a) 1631.7 W/m2
b) 31.7 W/m2
c) 631.7 W/m2
d) 11631.7 W/m2

View Answer

Answer: d [Reason:] E = σ T4 = 5.67 * 10 –8 (400 + 273)4 = 11631.7 W/m2.

4. If the emitted radiant energy is to be doubled, to what temperature surface of black body needs to be raised? Take radiant flux density as 11631.7 W/m 2.
a) 894.4 K
b) 200.4 K
c) 800.3 K
d) 600.4 K

View Answer

Answer: d [Reason:] 2(11631.7) = 5.67 * 10 –8 T 4.

5. A furnace having inside temperature of 2250 has a glass circular viewing of 6 cm diameter. If the transmissivity of glass is 0.08, make calculations for the heat loss from the glass window due to radiation
a) 234.54 W
b) 652.32 W
c) 328.53 W
d) 762.32 W

View Answer

Answer: c [Reason:] Q = σ A T4 (t) = 328.53 W.

6. The value of radiation coefficient or the Stefan-Boltzmann constant is
a) 5.67 * 10 -8 W/m2 K4
b) 5.67 * 10 -7 W/m2 K4
c) 5.67 * 10 -6 W/m2 K4
d) 5.67 * 10 -5 W/m2 K4

View Answer

Answer: a [Reason:] q = α A T4.

7. Measurements were made of the monochromatic absorptivity and monochromatic hemispherical irradiation incident on an opaque surface, and the variation of these parameters with wavelength may be approximated by the result shown below. Determine the total hemispherical absorptivity
heat-transfer-questions-answers-stefan-boltzman-law-q7
a) 0.557
b) 0.667
c) 0.777
d) 0.887

View Answer

Answer: b [Reason:] Incident flux = 800(8 – 2) – 4800 W/m2. Absorptivity = 3200/4800 = 0.667.

8. What is the wavelength band for Ultraviolet rays?
a) 1 * 10 -6 to 3.9 * 10 -1 micron meter
b) 1 * 10 -4 to 3.9 * 10 -1 micron meter
c) 2 * 10 -3 to 3.9 * 10 -1 micron meter
d) 1 * 10 -2 to 3.9 * 10 -1 micron meter

View Answer

Answer: d [Reason:] This is the maximum and minimum wavelength for Ultraviolet rays.

9. A black body of total area 0.045 m2 is completely enclosed in a space bounded by 5 cm thick walls. The walls have a surface area 0.5 m 2 and thermal conductivity 1.07 W/ m K. If the inner surface of the enveloping wall is to be maintained at 215 degree Celsius and the outer wall surface at 30 degree Celsius, calculate the temperature of the black body
a) 547.3 K
b) 287.4 K
c) 955.9 K
d) 222.2 K

View Answer

Answer: c [Reason:] Q r = σ A (T b4 – Tw4), Q c = k A d t/δ = 1979.5 W. So temperature of black body is 955.9 K.

10. What is the wavelength band for solar radiation?
a) 1 * 10 -1 to 3 micron meter
b) 1 * 10 -1 to 2 micron meter
c) 1 * 10 -1 to 1 micron meter
d) 1 * 10 -1 to 10 micron meter

View Answer

Answer: a [Reason:] This is the maximum and minimum wavelength for solar radiation.

Set 3

1. What is the dimension of heat?
a) M L T -2
b) M L 2 T -2
c) M L 2 T -1
d) M L 2 T

View Answer

Answer: b [Reason:] Unit of heat is Joule. It is a form of energy that can be transferred from an object of high temperature to the lower one.

2. What is the dimension of dynamic viscosity?
a) M L -1 T -1
b) L -1 T -1
c) M L -2 T -1
d) M L -1 T -2

View Answer

Answer: a [Reason:] Unit of dynamic viscosity is kg/meter second. It is defined as a quantity measuring the force needed to overcome internal friction of a moving liquid.

3. What is the dimension of kinematic viscosity?
a) M L 2T -2
b) L 2T -2
c) L 2T -1
d) M L 2T -1

View Answer

Answer: c [Reason:] Unit of kinematic viscosity is m2/s. It is defined as dynamic viscosity per unit density.

4. What is the dimension of energy?
a) M L 2 T -2
b) M L 2 T -1
c) M L 1 T -2
d) M L T -2

View Answer

Answer: a [Reason:] Unit of energy is m N. It is a form of energy that can be transferred from one object to another.

5. What is the dimension of force?
a) M L T -1
b) L T -2
c) M T -2
d) M L T -2

View Answer

Answer: d [Reason:] Unit of force is N. It is a push or pull that can stop a moving object.

6. What is the dimension of density?
a) M L -3 T
b) M L -3
c) M L -3 T 2
d) M L -2

View Answer

Answer: b [Reason:] Unit of density is kg/m3. It is defined as mass per unit volume.

7. What is the dimension of acceleration?
a) M L T -2
b) L T -4
c) M L T -1
d) L T -2

View Answer

Answer: d [Reason:] Unit of acceleration is m/s2. It is defined as force per unit mass.

8. What is the dimension of specific heat?
a) L T -1 α -1
b) M L T -1 α -1
c) L T -2 α -1
d) M L T -2 α -1

View Answer

Answer: c [Reason:] Unit of specific heat is k J/kg K. The specific heat is the amount of heat per unit mass required to raise the temperature by one degree celsius.

9. What is the dimension of thermal conductivity?
a) M L T -3 α -1
b) M L T -3
c) M L T -2 α -1
d) M L T -3 α -2

View Answer

Answer: a [Reason:] Unit of thermal conductivity is W/m K. It is the amount of heat per unit time per unit area that can be conducted through a plate of unit thickness of a given material.

10. What is the dimension of gravity?
a) M L T -2
b) L T -2
c) M L T -1
d) L T -4

View Answer

Answer: b [Reason:] Unit of gravity is m/s2. It is a force that attracts a body towards itself.

Set 4

1. Which field is set up when a fluid flows past a heated or cold surface?
a) Energy
b) Temperature
c) Mass
d) Time

View Answer

Answer: b [Reason:] The temperature field encompasses a very small region of fluid.

2. The zone or thin layer wherein the temperature field exists is called the
a) Single boundary layer
b) Multi boundary layer
c) Hydrodynamic boundary layer
d) Thermal boundary layer

View Answer

Answer: d [Reason:] It is known as thermal boundary layer. The temperature gradient results due to heat exchange between the plate and the fluid.

3. The thickness of thermal boundary layer is arbitrarily defined as the distance from the plate surface at which
a) t S – t/t S – t INFINITY = 0.34
b) t S – t/t S – t INFINITY = 0.10
c) t S – t/t S – t INFINITY = 0.99
d) t S – t/t S – t INFINITY = 0.87

View Answer

Answer: c [Reason:] It should be 0.99. The convection of energy reduces the outward conduction in the fluid and consequently the temperature gradient decreases away from the surface.

4. The convection of energy reduces the outward conduction in the fluid so temperature gradient
a) Decreases
b) Increases
c) Constant
d) Becomes twice

View Answer

Answer: a [Reason:] The temperature gradient is infinite at the leading edge and approaches zero as the layer develops downstream.

5. The velocity profile of the hydrodynamic boundary layer is dependent upon
a) Time
b) Viscosity
c) Temperature
d) Mass

View Answer

Answer: b [Reason:] It depends upon viscosity as the fluid velocity varies from zero at the solid surface to the velocity of free stream flow at a certain distance away from the solid surface.

6. Consider an elemental control volume for mass balance continuity equation. Which one of the following is correct?
heat-transfer-questions-answers-thermal-boundary-equation-q6
a) Value of 1 is 2 v + d u/d x (d y)
b) Value of 2 is u + d u/d y (d x)
c) Value of 1 is v + d u/d x (d y)
d) Value of 2 is 2 u + d v/d x (d x)

View Answer

Answer: c [Reason:] The flow velocity changes in the direction of x axis and the rate of change is d u/d x.

7. Which is true for two dimensional boundary layer?
a) d u/d x – d v/d y = 1
b) d u/d x – d v/d y = 0
c) d u/d x + d v/d y = 1
d) d u/d x + d v/d y = 0

View Answer

Answer: d [Reason:] This a two dimensional general equation. This equation also represents the continuity equation.

8. The differential energy equation for flow past a flat plate is given by
a) u d t/d x + v d t/d y = µ/p c (d u/d y) 2 + k d 2 t/p c d y 2
b) u d t/d x + v d t/d y = µ/p c (d u/d y) + k d 2 t/p c d y 2
c) u d t/d x + v d t/d y = k d 2 t/p c d y 2 + µ/p c (d u/d y) -2
d) u d t/d x + v d t/d y = µ/p c (d u/d y) -1 + k d 2 t/p c d y 2

View Answer

Answer: a [Reason:] Here heat generation due to viscous effects is not neglected.

9. The assumptions for thermal boundary layer are
(i) Steady compressible flow
(ii) Negligible body forces, viscous heating and conduction in the flow direction
(iii) Constant fluid properties evaluated at the film temperature
Identify the correct option
a) 1 and 3
b) 1, 2 and 3
c) 2 and 3
d) 1 and 2

View Answer

Answer: c [Reason:] It is steady incompressible flow. The temperature of the fluid changes from a minimum at the plate surface to the temperature of the mainstream at a certain distance from the surface.

10. The relationship between the thermal and hydrodynamic boundary layer thickness is governed by the
a) Peclet number
b) Prandtl number
c) Stanton number
d) Fourier number

View Answer

Answer: b [Reason:] It is governed by the Prandtl number, which is indicative of the relative ability of the fluid to diffuse momentum and internal energy by molecular mechanisms.

Set 5

1. Thermal conductivity is defined as the heat flow per unit time
a) When temperature gradient is unity
b) Across the wall with no temperature
c) Through a unit thickness of the wall
d) Across unit area where temperature gradient is unity

View Answer

Answer: d [Reason:] Thermal conductivity of a material is because of migration of free electrons and lattice vibrational waves.

2. Mark the matter with least value of thermal conductivity
a) Air
b) Water
c) Ash
d) Window glass

View Answer

Answer: a [Reason:] For air it is .024 W/ m degree i.e. lowest.

3. Which one of the following forms of water have the highest value of thermal conductivity?
a) Boiling water
b) Steam
c) Solid ice
d) Melting ice

View Answer

Answer: c [Reason:] For ice it is 2.25 W/m degree i.e. maximum.

4. The average thermal conductivities of water and air conform to the ratio
a) 50:1
b) 25:1
c) 5:1
d) 15:1

View Answer

Answer: b [Reason:] For water it is 0.55-0.7 W/m degree and for air it is .024 W/m degree.

5. Identify the very good insulator
a) Saw dust
b) Cork
c) Asbestos sheet
d) Glass wool

View Answer

Answer: d [Reason:] Glass wool has lowest thermal conductivity of 0.03 W/m degree amongst given option.

6. Most metals are good conductor of heat because of
a) Transport of energy
b) Free electrons and frequent collision of atoms
c) Lattice defects
d) Capacity to absorb energy

View Answer

Answer: b [Reason:] For good conductors there must be electrons that are free to move.

7. Heat conduction in gases is due to
a) Elastic impact of molecules
b) Movement of electrons
c) EM Waves
d) Mixing of gases

View Answer

Answer: a [Reason:] If there is elastic collision then after sometime molecules regain its natural position.

8. The heat energy propagation due to conduction heat transfer will be minimum for
a) Lead
b) Water
c) Air
d) Copper

View Answer

Answer: c [Reason:] It is because air has lowest value of thermal conductivity amongst given options.

9. Cork is a good insulator because
a) It is flexible
b) It can be powdered
c) Low density
d) It is porous

View Answer

Answer: d [Reason:] Cork has thermal conductivity in the range of 0.05-0.10 which is very low so it can be porous.

10. Choose the false statement
a) For pure metal thermal conductivity is more
b) Thermal conductivity decreases with increase in the density of the substance
c) Thermal conductivity of dry material is lower than that of damp material
d) Heat treatment causes variation in thermal conductivity

View Answer

Answer: b [Reason:] Thermal conductivity increase with increase in density of substance.