Heat Transfer Mechanical Objective Questions Answers PDF

Heat Transfer Mechanical Objective Questions Answers PDF

 

1. Thermal diffusivity of a substance is.
(a) proportional to thermal conductivity
(b) inversely proportional to k
(c) proportional to (k)
(d) inversely proportional to k2
(e) none of the above.

Answer:A
2. Thermal conductivity of glass-wool varies from sample to sample because of variation in
(a) composition
(b) density
(c) porosity
(d) structure
(e) all of the above.

Answer:E
3. Thermal conductivity of a material may be defined as the
(a) the quantity of heat flowing in one second through one cm cube of material when opposite faces ^re maintained at a temperature difference of 1°C
(b) the quantity of heat flowing in one second through a slab of the material of area one cm square, thickness 1 cm when its faces differ in temperature by 1°C
(c) The unit area thickness takes place during the single time when the unity of a temperature is maintained on opposite charges.
(d) all of the above
(e) none of the above.

Answer:D
4. Which of the following has maximum value of thermal conductivity
(a) aluminium
(b) steel
(c) brass
(d) copper
(e) lead.

Answer:A
5. Moisture would find its way into insulation by vapour pressure unless it is prevented by
(a) a high thickness of insulation
(b) high vapour pressure
(c) less thermal conductivity insulator
(d) a vapour seal
(e) all of the above.

Answer:D
6. Heat is transferred by all three modes of transfer, viz, conduction, convection and radiation in
(a) electric heater
(b) steam condenser
(c) melting of ice
(d) refrigerator condenser coils
(e) boiler.

Answer:E
7. 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 companies emit radiation from the perfect zero
(d) In most cases, the heat transfer is performed by a combination of circulation, circulation and radiation
(e) the rate of heat transfer depends on thermal conductivity and temperature difference.

Answer:C
8. The temperatures will be two-pronged temperature Q1 / Q2 ratio at the same height as their ATj-2K2 conductivities
(a) 1
(b) 0.5
(c) 2
(d) 0.25
(e) 4.0

Answer:C
9. Unit of thermal diffusivity is
(a) m2/hr
(b) m2/hr°C
(c) kcal/m2 hr
(d) kcal/m.hr°C
(e) kcal/m2 hr°C.

Answer:A
10. Thermal conductivity of wood depends on
(a) moisture
(b) density
(c) temperature
(d) all of the above
(e) none of the above.

Answer:D
11. In convection heat transfer from hot flue gases to water tube, even though flow may be turbulent, a laminar flow region (boundary layer of film) exists close to the tube. The heat transfer through this film takes place by
(a) convection
(b) radiation
(c) conduction
(d) both convection and conduction
(e) none of the above.

Answer:C
12. Film coefficient is defined as Inside diameter of tube
(a) Equivalent thickness of film
(b) Thermal conductivity Equivalent thickness of film Specific heat x Viscosity
(c) Thermal conductivity Molecular diffusivity of momentum Thermal diffusivity
(d) Film coefficient x Inside diameter Thermal conductivity
(e) none of the above.

Answer:B
13. Heat conducted through a unit area and unit thick face per unit time when the temperature difference between opposite faces is unity is called?
(a) thermal resistance
(b) thermal coefficient
(c) temperature gradient
(d) thermal conductivity
(e) heat-transfer.

Answer:D
14. The rate of energy emission from unit surface area through unit solid angle, along a normal to the surface, is known as
(a) emissivity
(b) transmissivity
(c) reflectivity
(d) the intensity of radiation
(e) absorptivity.

Answer:D
15. Emissivity of a white polished body in comparison to a black body is
(a) higher
(b) lower
(c) same
(d) depends upon the shape of the body
(e) none of the above.

Answer:B
16. The insulation ability of an insulator with the presence of moisture would
(a) increase
(b) decrease
(c) remain unaffected
(d) may increase/decrease depending on temperature and thickness of insulation
(e) none of the above.

Answer:B
17. When heat is Transferred by molecular collision, it is referred to as heat transfer by
(a) conduction
(b) convection
(c) radiation
(d) scattering
(e) convection and radiation.

Answer:B
18. Heat transfer in liquid and gases takes place by
(a) conduction
(b) convection
(c) radiation
(d) conduction and convection
(e) convection and radiation.

Answer:B
19. Which of the following is the case of heat transfer by radiation
(a) blast furnace
(b) heating of the building
(c) cooling of parts in the furnace
(d) heat received by a person from the fireplace
(e) all of the above.

Answer:D
20. Heat is closely related to
(a) liquids
(b) energy
(c) temperature
(d) entropy
(e) enthalpy.

Answer:C
21. When heat is transferred from hot body to cold body, in a straight line, without affecting the intervening medium, it is referred as heat transfer by
(a) conduction
(b) convection
(c) radiation
(d) conduction and convection
(e) convection and radiation.

Answer:C
22. Sensible 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
(e) convert saturated steam into dry steam.

Answer:C
23. A steam pipe is to be insulated by two insulating materials put over each other. For best results
(a) better insulation should be put over the pipe and better one over it
(b) inferior insulation should be put over the pipe and better one over it
(c) both may be put in any order
(d) whether to put inferior OIL over the pipe or the better one would depend on steam temperature
(e) unpredictable.

Answer:A

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