71. Define a black surface.

A black surface is the perfect emitter and absorber of radiation. It is an idealized concept ( no surface is exactly black surface ), and the characteristics of real surfaces are compared to that of an ideal black surface.

72. What is internal energy generation? Give examples where internal energy generation occurs.

Internal energy generation is the generation of heat within a body by a chemical, electrical, or nuclear process.

Examples are the heating of nuclear fuel rod (due to fission within the rod), the heating of electrical wires (due to the conversion of electrical to heat energy), microwave heating and the generation of heat within the Earth. The heat generated in each case is being converted from some other form of energy.

73. What is the difference between diffusion and radiation heat transfer?

Diffusion heat transfer is due to random molecular motion. Neighboring molecules move randomly and transfer energy between on another – however there is no bulk motion. Radiation heat transfer, on the other hand, is the transport of heat energy by electromagnetic waves. All bodies emit thermal radiation. In particular, notice that unlike diffusion, radiation heat transfer does not require a medium and is thus the only mode of heat transfer in space. The time scale for radiative heat transfer is much smaller than diffusive heat transfer.

74. What is wet bulb temperature (WBT) ?

The wet bulb temperature of air is also measured by the ordinary thermometer, but the only difference is that the bulb of the thermometer is covered by the wet cloth. Temperature of the ordinary air measured by the thermometer when it is covered by wet cloth or wick is called as the wet bulb temperature, commonly referred to as WBT.

75. What is forced and natural convection?

Heat transfer using movement of fluids is called convection. In natural convection, the flow is induced by the differences between fluid densities which result due to temperature changes. Force convection uses externally induced flow, such as wind.(external force or velocity)

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76. What HVAC?

Heating, Ventilation and Air conditioning

HVAC is an technology which is used to provide indoor air comfort as well as vehicle air comfort.

77. What is Newtons Law of Cooling?

Newton’s law of cooling states that the rate of change of the temperature of an object is proportional to the difference between its own temperature and the ambient temperature.

78. What is the difference between Wrought iron, Cast iron and pig iron?

Wrought iron contains less than 0.1% carbon and this is a product of pudding furnace.

Cast iron is produced from cupola furnace. It contains (2.5 to 4) % carbon in combined or free state.

Pig iron is an iron carbon alloy contains (3.8 to 4.7)% carbon along with impurities like manganese, sulphur and phosphorous. It is a product of blast furnace.

79. How does carbon affects the properties of steel?

If carbon content is higher the degree of hardness is more and the melting point is lower, If carbon percentage is lower it is easy to forging and forge welding.

80. Define the following properties of metal: (a) Fusibility (b) Stiffness (c) Ductility.

:- Fusibility :- It is the property of metal due to which a metal becomes fluid when it is heated.

:- Stiffness :- It is the property of metal due to which a metal is capable of resisting deflection due to an externally applied load.

:- Ductility :- It is the property of metal due to which a metal can be drawn into the form of wires without rupture.