Compressors_ Gas Turbines And Jet Engines — Part 1 MCQs with Explanations

The compression ratio is simply the ratio of the absolute stage discharge pressure to the absolute stage suction pressure. The compression ratio for the compressor is always More than unity.

The hottest point in a gas turbine is between ~ to i of the blade height. The hottest component is the turbine blades, in particular the first-stage turbine inlet guide vanes, which are the most forward part of the exhaust section of the engine, which is the section exposed to the hot exhaust gases.

Temperature of gases at end of compression as compared to exhaust gases in a gas turbine is lower

The maximum temperature in a gas turbine is 700°C

Jet propulsion is the propulsion of an object in one direction, produced by ejecting a jet of fluid in the opposite direction. By Newton's third law, the moving body is propelled in the opposite direction to the jet.

The fuel consumption in gas turbines is accounted for by Lower heating value

The indicated work per unit mass of air delivered is Not affected by clearance volume

Gas turbine plant is smallest and lightest for generating a given amount of power

In jet engines, for the efficient production of large power, fuel is burnt in an atmosphere of compressed air

Gas turbine blades are given a rake In the direction of motion of blades

Rotary compressors are suitable for Large discharge at low pressure

An air compressor may be controlled by -Throttle control - Clearance control - Blow off control

The degree of reaction of an axial flow turbine is the ratio of isentropic temperature drop in a blade row to the Total temperature drop in the stage. The degree of reaction contributes to the stage efficiency and thus used as a design parameter. Stages having 50% degree of reaction are used where the pressure drop is equally shared by the stator and the rotor for a turbine.

The net work input required for compressor with increase in clearance volume remains same

A compressor's volumetric efficiency (V) is defined by the ratio of the actual volume of gas that it could suck if there was no such thing as clearance volume. Therefore, a compressor with less clearance volume should be more volumetrically efficient.

Volumetric efficiency of a compressor with clearance volume Decreases with increase in compression ratio

Compression efficiency is compared against Isothermal compression

Choke/Stonewall point Choking is the condition which occurs in the compressor in which it operates at very high mass flow rate and flow through the compressor can't be further increased as mach number at some part of the compressor reach to unity

Reheating in a multistage expansion gas turbine Decreases compressor work.

The work ratio of simple gas turbine cycle depends on - Pressure ratio - Maximum cycle temperature - Minimum cycle temperature

The ideal efficiency of simple gas turbine cycle depends on Pressure ratio

There is a certain pressure ratio (optimum) for a gas turbine at which its thermal efficiency is maximum. With increase in turbine temperature, the value of pressure ratio for the peak efficiency would Increase

The ratio of the air-indicated horsepower to the indicated horsepower in a power cylinder, in the case of compression driven by steam or internal-combustion engines, and to the brake horsepower delivered to the shaft in the case of a power-driven machine.

Ratio of indicated H.P. and brake H.P. is known as Mechanical efficiency

Given Data: Output power = 300 kW Efficiency = 20% = 0.2 Efficiency = Output power / Input power Input power = Output power / Efficiency Input power = 300 / 0.2 Input power = 1500 kW Therefore, heat supplied is 1500 kW.

Reheating is applied in a gas turbine in such a way that it increases the turbine work without increasing the compressor work or melting the turbine materials. When a gas turbine plant has a high pressure and low pressure turbine a reheater can be applied successfully.

In axial flow compressor, exit flow angle deviation from the blade angle is a function of Blade camber and incidence angle

Indicated Power is defined as the power developed by combustion of fuel inside the engine cylinder. It is always more than brake power and is given by, Therefore, the difference between ip and bp indicates the power loss in the mechanical components of engine due to friction.

To avoid moisture troubles, the compressed air main line should Drop gradually towards the point of use

The ratio of the discharge pressure to the inlet pressure of air is called Compression ratio

A machine used to raise the pressure of air is called Compressor

The efficiency of jet engine is Higher at high altitudes

The volume of air delivered in a medium capacity air compressor per unit time is 0.15 to 5 m 3 /s

The inter-cooler pressure, for minimum work required, for a two stage reciprocating air compressor, is given by $${{\text{p}}_2} = \sqrt {{{\text{p}}_1} \times {{\text{p}}_2}} .$$ Where p 1 = Intake pressure of air, p 2 = Inter-cooler pressure and p 3 = Delivery pressure of air.

Atmospheric pressure is 1.03 kg/cm and vapour pressure is 0.03 kg/cm. The air pressure will be 1.00 kg/cm 2 .

For perfect intercooling in a three stage compressor $$\frac{{{{\text{p}}_2}}}{{{{\text{p}}_1}}} = \frac{{{{\text{p}}_3}}}{{{{\text{p}}_2}}} = \frac{{{{\text{p}}_4}}}{{{{\text{p}}_3}}}$$

For perfect intercooling in a two stage compressor $$\frac{{{{\text{p}}_2}}}{{{{\text{p}}_1}}} = \frac{{{{\text{p}}_3}}}{{{{\text{p}}_2}}}$$

The weight per horse power ratio for gas in Turbine as compared to I.C. engine and steam turbine is lower

The volume of air sucked by the compressor during its suction stroke is called Swept volume

So, in a compressor, first additional kinetic energy is imparted to the fluid with the help of a rotating impeller. ... So like this, pressure of a fluid is increased in a centrifugal compressor. So basically it works on the principle of conversation of kinetic energy into pressure energy.