Diploma Thermal Engineering 1 Important Questions three marks questions & answers – Unit – 1

Diploma Thermal Engineering 1 Important Questions

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We are adding Diploma Thermal Engineering 1 important questions for the Unit -1 Additionally we add answers for these questions. The Highlighted questions are important questions

Department : Mechanical Engineering

Scheme : N

Subject: 4020340, Thermal Engineering – 1

Unit – 1 BASICS OF THERMODYNAMICS AND THERMODYNAMIC PROCESSES OF PERFECT GASES

THREE MARKS QUESTIONS & ANSWERS

1. Define Mass

• Mass is the amount of matter contained in an object, and does not depends on gravity.
• Mass is measured in grams or kilograms.
• Therefore it is denoted by letter ‘W’ and its unit is Kg.

2. Define Weight

• Weight is the amount of mass of an object, and it’s dependent upon gravity.
• It is denoted by letter ‘W’ and Its unit is Newton.
• Mathematically, W = m g . Where, ‘g’ is the acceleration due to gravity in m/s2

3. Define Force

• Force According to Newton’s second law of motion, the applied force or impressed force is directly proportional to the rate of change of momentum.
• It is denoted by letter ‘F’. Its unit is Newton (N). Mathematically, F = Mass x Acceleration F = m a
• Note: 1N = 1kg-m/s2

4. Define Volume

• Volume is defined as the ratio of mass to density.
• It is also defined as the space occupied by the mass. Its unit is m3 .
• It is denoted by ‘V’. Mathematically,
• Note: 1000 c.c = 1 litre = 0.001m3

5. Define Density

• The amount of matter (mass) in a given amount of space (volume)
• Density is defined as mass per unit volume.
• Its unit is kg/m3 . It is denoted by ‘ρ’. It is also known as mass density or specific mass.

6. What is Specific Weight?

• Specific Weight Specific weight is defined as the weight per unit volume.
• Its unit is N/m3 . It is denoted by ‘w’.
• It is also known as weight density. Mathematically, w = 𝑾 𝒗 = ρ g . . .(W = mg &ρ = m/v)

7. Define Specific Gravity

• Specific gravity is defined as the ratio of density of given liquid to the density of a standard fluid (water).
• It has no unit. It is denoted by ‘s’. It is also known as relative density.
• Note: Density of water (ρw) = 1000 kg/m3

8. What do you mean by Specific Volume?

• The volume occupied by unit mass is known as specific volume.
• Its unit is m3 /kg. It is denoted by ‘vs’. Mathematically, vs = 𝑽 𝒎
• Therefore, it is the reciprocal of density, i.e. v = 1/ρ

9. Define Pressure

• Pressure is defined as the normal force per unit area of the surface.
• The unit of pressure depends upon the units of force and area.
• Its unit is N/m2 , Pascal (Pa) and bar.
• It is denoted by ‘p’. Mathematically, p = 𝑭 𝑨 Note: 1 bar = 1×105 N/m2 = 100 kN/m2 = 0.1 MN/ m2 . 1Pa = 1 N/m2 1kPa= 1 kN/m²

10. What is Gauge Pressure and Absolute pressure?

• The reading of the pressure gage is known as gauge pressure, while the actual pressure is called absolute pressure.
• Mathematically,
• For pressures above atmospheric, Absolute pressure = Atmospheric pressure + Gauge pressure
• For pressures below atmospheric, the gauge pressure will be negative.
• This negative pressure is known as vacuum pressure.
• Mathematically, Absolute pressure = Atmospheric pressure – Vacuum pressure
• Note: pabs = patm + pg
• pabs = patm – pv
• Patm= 760 mm of Hg = 1.01325 bar = 1.01325 x 105 N/m2 = 101.325 kN/m2

11. Define Temperature

• Temperature is the amount of heat in a system.
• Temperature is defined as the degree of hotness or coldness of a body.
• The unit of temperature measurement is degree. It is denoted by ‘T’

12. What is standard temperature?

Standard Temperature and Pressure (S.T.P) The temperature and pressure of any gas, under standard atmospheric conditions, is taken as 15°C (288 K) and 760 mm of Hg respectively

13. Explain Normal temperature.

Normal Temperature and Pressure (N.T.P) The conditions of temperature and pressure at 0°C (273 K) temperature and 760 mm of Hg pressure are termed as normal temperature and pressure

14. Define Heat

• Heat is a form of energy. It can be transferred from one body to another due to the difference of temperature.
• Heat is defined as the energy transferred, without transfer of mass, across the boundary of a system because of a temperature difference between the system and the surroundings. It is expressed in Joule (J). It is usually represented by ‘Q’.

15. What is Specific Heat Capacity?

• Specific Heat at Capacity at Constant Volume It is defined as the amount of heat required to raise or lower the temperature of a unit mass of any substance through one degree when the volume remains constant. Its unit is kJ/kgK. It is denoted by ‘Cv’. Q = m .Cv .dT
• Specific Heat at Capacity at Constant Pressure It is defined as the amount of heat required to raise or lower the temperature of a unit mass of any substance through one degree when the pressure remains constant. Its unit is kJ/kgK. It is denoted by ‘Cp’. Q = m .Cp.dT

Note:

• Cp– Cv = R
• Cp value of water = 4.189 kJ/kgK
• Cp value of air = 1.005 kJ/kgK
• Cv value of air = 0.718 kJ/kgK
• R (Gas Constant) = 0.287 kJ/kgK

16. Define Power

• Power may be defined as the rate of doing work or work done per unit time.
• Its unit is Nm/s or J/s or watt.

17. What is Internal Energy?

• Internal energy (U) is the energy possessed by a body or a system due to its molecular arrangement and motion of the molecules.
• It is usually represented by U.

18. Define First Law of Thermodynamics.

• Law of Conservation of Energy states that, “The energy can neither be created nor destroyed, though it can be transformed from one form to any other form, in which the energy can exist”.

19. Define Thermodynamic System

The thermodynamic system (simply known as system) may be defined as a definite area or a space where some thermodynamic process is taking place.

20. What is Surroundings?

Everything outside of the system which affects the behavior of the system is called surroundings

21. What is a boundary?

• Boundary The system and surroundings are separated by the system boundary.
• It may be real or imaginary.

22. What are the types of thermodynamic systems?

There are three Types of thermodynamic systems:

1. 1. Closed system (Non flow process)
   2. Open system (flow process)
   3. Isolated system

 

23.  Explain Closed System.

• In a closed system or non-flow system, Energy crosses the system boundary in the form of heat and work, but there is no mass transfer.
• Example: Gas contained in the cylinder

 

24. What is an open system?

• In an open system or flow system or control volume system, both energy and mass (heat and work) cross the boundary of the system
• Examples: Air compressor, flow through nozzles and turbines

25. What is an isolated system?

In an isolated system no mass and no energy crosses the boundary of the system.

Example: Thermal flask and insulated gas container

26. What is Intensive propery?

• Intensive or Intrinsic properties: These are the properties which are independent of the mass of the system.
• Examples: Temperature, pressure, velocity, density, specific heat etc.

27. Define Extensive Properties?

• Extensive or Extrinsic properties: These are the properties which are dependent on the mass of the system

• Examples: volume / mass = specific volume Enthalpy / mass = Specific enthalpy

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