Question Set 14 – Mechanical Engineering

Question Set 14

Question No. 1

Which furnace burns low ash fusion coal and retains most of the coal ash in the slag?

Cyclone furnace.

Question No. 2

How the thickness of thermal boundary layer and thickness of hydrodynamic boundary layer related?

Ratio of their thickness = (Prandtl number) – (1/3).

Question No. 3

What is the effect of friction on flow of steam through a nozzle?

To decrease both mass flow rate and wetness of steam.

Question No. 4

What is the function of Scoop in BFP (Boiler Feed Water Pump) in Thermal Power Station?

The Function of Scoop tube is regulating the varying amount of oil level in the coupling during operation of infinite variable speed.

Question No. 5

In the Thermal Power Plant why Deaerator (D/A) placed on height?

To build a Very high pressure and the temperature for a boiler feed water pump and it discharge high pressure water to the boiler. And to provide the required Net Positive Suction Head (NPSH) for the BFW pump and to serve as a storage tank to ensure a continuous supply of feed water during rapid changes in BFP.

Question No. 6

In orifice why the Pressure and Temperature are decreases?

Orifice is a small hole like a nozzle. When a high pressure fluid passes through the orifice,

Pressure gets reduced suddenly and the velocity of the fluid gets increased. Also the heat transfer rate increases. We know that Heat transfer rate is directly proportional to the difference in temperature, Area and the Heat transfer coefficient. Heat transfer Coefficient remains constant for a fluid at a particular temperature.

Q= KA (T1-T2)

If the heat transfer rate increases, it seems the difference in temperature gets increased. There is no way in reduction of inlet temperature of the orifice. As a result, the outlet temperature of the orifice gets reduced. Hence the pressure and temperature gets reduced when it passes through orifice

Question No. 7

Why gas turbine power plant needs efficient compressor?

Because a large portion of turbine work is eaten away by compressor and its inefficiency will affect net power output and cost of generation.

Question No. 8

Why rockets using liquid hydrogen have higher specific impulse compared to liquid hydrocarbon?

Liquid hydrogen has higher burning velocity.

Question No. 9

Why axial flow compressor is preferred for gas turbines for aeroplanes?

Because it has low frontal area.

Question No. 10

What is the difference between gas turbine and a steam turbine?