Question Set 110

1. Typical Natural Gas Composition is-

Answer:  Typical Natural gas composition includes

Methane – 95 % , Ethane – 3.2 % , Nitrogen – 1 % , CO₂  – 0.5 % , O₂ – 0.02 %

2. Typical Calorific Values for natural gas –

Answer: Higher Heating Value – 52300 kJ/kg or 12500 kcal /kg .  Lower Heating Value – 50000 kJ/kg 0r 11950 kcal/kg

3. What is Hoop Stress and longitudinal stress in a thin walled cylinder?

Answer: When a thin cylinder is subjected to internal pressure longitudinal and hoop stress are observed in the cylinder. Hoop Stress is the circumferential normal stress developed at the tangential direction. Hoop stress acts towards the circumference perpendicular to the length of the cylinder. Longitudinal stress acts along the length of the cylinder.

Hoop stress is expressed as , σ_h = p d / 2 t and longitudinal stress is expressed as σ_l = p d / 4 t.

Here p = internal pressure,

d = internal diameter

t = thickness

4. What is Lateral strain?

Answer: When a body is subjected to longitudinal stress it extends or gets compressed in the direction of the stress (tensile force or compressive force). But it will also get thicket or thinner in the transverse direction. The ratio of this change in the length (breadth for rectangular shape and dia for the circular bar) in the direction perpendicular to the force and the original length is known as lateral strain.

5. What are the differences between elbows and bend? Which has greater head losses?

Answer: Bend and elbow are used for changing the direction of the flow and is attached with the piping system. Bends are simply bends they are generally custom made. On the other hand elbows are well defined engineered bends. Elbows can be have angle 45 or 90 degrees or they can be custom made.

Using Elbows or bends will cause some head losses which is known is minor head loss. If the flow is turbulent in the pipe lines then elbows will have greater head losses than bends. Because in bends it takes lesser time for the fluid to take the turns.

6. What is the function of flywheel?

Answer: The main function of the flywheel is to store kinetic energy in the form of moment of inertia. It also reduces the vibration in the engine and produces an even crank shaft rotational speed.

These are some basic mechanical questions which can be asked in viva-voce or written exam. Next Part is coming up. Stay with us.