LSAT - Heat & Mass Transfer 1000+ MCQ [Solved] PDF Download

1. Heat is closely related with
A. Liquids
B. Energy
C. Temperature
D. Entropy
Answer : C

2. Which of the following has least value of conductivity?
A. Glass
B. Water
C. Plastic
D. Air
Answer : D

3. Stefan Boltzmann law is applicable for heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and radiation combined
Answer : C

4. The transfer of heat by molecular collision is smallest in
A. Solids
B. Liquids
C. Gases
D. None of these
Answer : C

5. Temperature of steam at around 540°C can be measured by
A. Thermometer
B. Thermistor
C. Thermocouple
D. None of these
Answer : C

6. Heat transfer takes place as per
A. Zeroth law of thermodynamics
B. First law of thermodynamic
C. Second law of the thermodynamics
D. Kirchoff's law
Answer : C

7. An electric cable of aluminium conductor (k = 240 W/mK) is to be insulated with rubber (k = 0.15 W/mK). The cable is to be located in air (h = 6 W/m²). The critical thickness of insulation will be
A. 25 mm
B. 40 mm
C. 160 mm
D. 800 mm
Answer : A

8. The time constant of a thermocouple is
A. The time taken to attain the final temperature to be measured
B. The time taken to attain 50% of the value of initial temperature difference
C. The time taken to attain 63.2% of the value of initial temperature difference
D. Determined by the time taken to reach 100°C from 0°C
Answer : C

9. The rate of heat flow through a body is Q = [kA (T? - T?)]/x. The term x/kA is known as
A. Thermal coefficient
B. Thermal resistance
C. Thermal conductivity
D. None of these
Answer : B

10. Total heat is the heat required to
A. Change vapour into liquid
B. Change liquid into vapour
C. Increase the temperature of a liquid or vapour
D. Convert water into steam and superheat it
Answer : D

11. According to Stefan Boltzmann law, ideal radiators emit radiant energy at a rate proportional to
A. Absolute temperature
B. Square of temperature
C. Fourth power of absolute temperature
D. Fourth power of temperature
Answer : C

12. The amount of radiation mainly depends on
A. Nature of body
B. Temperature of body
C. Type of surface of body
D. All of the above
Answer : D

13. Heat flows from one body to other when they have
A. Different heat contents
B. Different specific heat
C. Different atomic structure
D. Different temperatures
Answer : D

14. Depending on the radiating properties, body will be transparent when
A. P = 0, x = 0 and a = 1
B. P=1, x = 0, and a = 0
C. P = 0, T= 1, and a = 0
D. X = 0, a + p = 1
Answer : C

15. Metals are good conductors of heat because
A. Their atoms collide frequently
B. Their atoms are relatively far apart
C. They contain free electrons
D. They have high density
Answer : A

16. Two balls of same material and finish have their diameters in the ratio of 2: 1 and both are heated to same temperature and allowed to cool by radiation. Rate of cooling by big ball as compared to smaller one will be in the ratio of
A. 1 : 1
B. 2 : 1
C. 1 : 2
D. 4 : 1
Answer : C

17. The expression Q = ? AT⁴ is called
A. Fourier equation
B. Stefan-Boltzmann equation
C. Newton Reichmann equation
D. Joseph-Stefan equation
Answer : B

18. Thermal diffusivity is a
A. Function of temperature
B. Physical property of a substance
C. Dimensionless parameter
D. All of these
Answer : B

19. Which of the following is the case of heat transfer by radiation?
A. Blast furnace
B. Heating of building
C. Cooling of parts in furnace
D. Heat received by a person from fireplace
Answer : D

20. Thermal conductivity of non-metallic amorphous solids with decrease in temperature
A. Increases
B. Decreases
C. Remain constant
D. May increase or decrease depending on temperature
Answer : B

21. According to Wien's law, the wavelength corresponding to maximum energy is proportion to
A. Absolute temperature (T)
B. I²
C. F
D. T
Answer : A

22. Two plates spaced 150 mm apart are maintained at 1000°C and 70°C. The heat transfer will take place mainly by
A. Convection
B. Radiation
C. Forced convection
D. Free convection
Answer : B

23. The critical temperature is the temperature
A. Below which a gas does not obey gas laws
B. Above which a gas may explode
C. Below which a gas is always liquefied
D. Above which a gas will never liquefied
Answer : D

24. Reynolds number (RN) is given by (where h = Film coefficient, l = Linear dimension, V = Velocity of fluid, k = Thermal conductivity, t = Temperature, ? = Density of fluid, cp = Specific heat at constant pressure, and ? = Coefficient of absolute viscosity)
A. RN = hl/k
B. RN = ? cp/k
C. RN = ? V l /?
D. RN = V²/t.cp
Answer : C

25. Absorptivity of a body will be equal to its emissivity
A. At all temperatures
B. At one particular temperature
C. When system is under thermal equilibrium
D. At critical temperature
Answer : C

26. According to Prevost theory of heat exchange
A. It is impossible to transfer heat from low temperature source to t high temperature source
B. Heat transfer by radiation requires no medium
C. All bodies above absolute zero emit radiation
D. Heat transfer in most of the cases takes place by combination of conduction, convection and radiation
Answer : C

27. Thermal conductivity of water ________ with rise in temperature.
A. Remain same
B. Decreases
C. Increases
D. May increase or decrease depending upon temperature
Answer : D

28. The natural convection air cooled condensers are used in
A. Domestic refrigerators
B. Water coolers
C. Room air conditioners
D. All of these
Answer : A

29. Depending on the radiating properties, a body will be white when
A. P = 0, x = 0 and a = 1
B. P=1, T = 0 and a = 0
C. P = 0, x = 1 and a = 0
D. X = 0, a + p = 1 Where a = absorptivity, p = reflectivity, x = transmissivity
Answer : B

30. When heat is transferred from one particle of hot body to another by actual motion of the heated particles, it is referred to as heat transfer by
A. Conduction
B. Convection
C. Radiation
D. Conduction and convection
Answer : A

31. The value of the wavelength for maximum emissive power is given by
A. Wien's law
B. Planck's law
C. Stefan's law
D. Fourier's law
Answer : A

32. In regenerator type heat exchanger, heat transfer takes place by
A. Direct mixing of hot and cold fluids
B. A complete separation between hot and cold fluids
C. Flow of hot and cold fluids alternately over a surface
D. Generation of heat again and again
Answer : C

33. Sensible heat is the heat required to
A. Change vapour into liquid
B. Change liquid into vapour
C. Increase the temperature of a liquid of vapour
D. Convert water into steam and superheat it
Answer : C

34. In counter flow heat exchangers
A. Both the fluids at inlet (of heat exchanger where hot fluid enters) are in their coldest state
B. Both the fluids at inlet are in their hottest state
C. Both the fluids at exit are in their hottest state
D. One fluid is in hottest state and other in coldest state at inlet
Answer : B

35. A cube at high temperature is immersed in a constant temperature bath. It loses heat from its top, bottom and side surfaces with heat transfer coefficients of h?, h? and h? respectively. The average heat transfer coefficient for the cube is
A. h? + h? + h?
B. (h?.h?.h?)1/3
C. 1/h? + 1/h? + 1/h?
D. None of these
Answer : D

36. The product of Reynolds number and Prandtl number is known as
A. Stanton number
B. Biot number
C. Peclet number
D. Grashoff number
Answer : C

37. Moisture would find its way into insulation by vapour pressure unless it is prevented by
A. High thickness of insulation
B. High vapour pressure
C. Less thermal conductivity insulator
D. A vapour seal
Answer : D

38. LMTD in case of counter flow heat exchanger as compared to parallel flow heat exchanger is
A. Higher
B. Lower
C. Same
D. Depends on the area of heat exchanger
Answer : A

39. Which of the following would lead to a reduction in thermal resistance?
A. In conduction, reduction in the thickness of the material and an increase in thermal conductivity.
B. In convection, stirring of the fluid and cleaning the heating surface.
C. In radiation, increasing the temperature and reducing the emissivity.
D. All of the above
Answer : D

40. The process of heat transfer from one particle of the fluid to another by the actual movement of the fluid particles caused by some mechanical means, is known as
A. Conduction
B. Free convection
C. Forced convection
D. Radiation
Answer : C

41. Which of the following has maximum value of thermal conductivity?
A. Aluminium
B. Steel
C. Brass
D. Copper
Answer : A

42. Upto the critical radius of insulation,
A. Added insulation will increase heat loss
B. Added insulation will decrease heat loss
C. Convective heat loss will be less than conductive heat loss
D. Heat flux will decrease
Answer : A

43. Radiation is the process of heat transfer in which heat flows from a ________, in a straight line, without affecting the intervening medium.
A. Cold body to hot body
B. Hot body to cold body
C. Smaller body to larger body
D. Larger body to smaller body
Answer : B

44. When ? is absorptivity, ? is reflectivity and ? is transmissivity, then for a diathermanous body,
A. ? = 1, ? = 0 and ? = 0
B. ? = 0, ? = 1 and ? = 0
C. ? = 0, ? = 0 and ? = 1
D. ? + ? = 1 and ? = 0
Answer : D

45. If the temperature of a solid surface changes from 27°C to 627°C, then its emissive power changes in the ratio of
A. 6
B. 9
C. 27
D. 81
Answer : D

46. Thermal conductivity of air at room temperature in kcal/m hr °C is of the order of
A. 0.002
B. 0.02
C. 0.01
D. 0.1
Answer : B

47. Two long parallel surfaces each of emissivity 0.7 are maintained at different temperatures and accordingly have radiation heat exchange between them. It is desired to reduce 75% of the radiant heat transfer by inserting thin parallel shields of emissivity 1 on both sides. The number of shields should be
A. One
B. Two
C. Three
D. Four
Answer : C

48. Thermal diffusivity is
A. A dimensionless parameter
B. Function of temperature
C. Used as mathematical model
D. A physical property of the material
Answer : D

49. The ratio of surface convection resistance to the internal conduction resistance is known as
A. Grashoff number
B. Biot number
C. Stanton number
D. Prandtl number
Answer : B

50. The process of heat transfer from one particle of the body to another by the actual motion of the heated particles, is called
A. Conduction
B. Convection
C. Radiation
D. None of these
Answer : B