THEORY EXAMINATION (SEM–VI) 2016-17 FLUID MACHINERY

FLUID MACHINERY (EME011)

SECTION-WISE SOLVED ANSWERS

SECTION – A

(Short Answer Questions | 2 Marks Each)

(a) Continuity Equation for Steady Incompressible Flow

The continuity equation states that for steady flow of incompressible fluid, the mass flow rate remains constant.
Mathematically:
A₁V₁ = A₂V₂
where A is cross-sectional area and V is velocity of flow.

(b) Degree of Reaction

Degree of reaction is defined as the ratio of pressure energy change in the runner to the total energy change in the turbine.
It indicates how much of the energy conversion occurs due to pressure change.

(c) Impulse Momentum Principle

Impulse momentum principle states that the force exerted by a fluid jet is equal to the rate of change of momentum of the fluid.

(d) Function of Nozzle in Impulse Turbine

The nozzle converts pressure energy of water into kinetic energy and directs the high-velocity jet onto the turbine buckets.

(e) Radial Flow Turbine

A radial flow turbine is one in which water flows radially, either inward or outward, through the runner.

(f) Unit Speed

Unit speed is the speed of a turbine when it is operating under unit head.
It is used for comparing turbine performance.

(g) Advantages of Model Testing

Model testing helps predict prototype performance, reduces cost, ensures safety, and improves design accuracy before actual installation.

(h) Manometric Efficiency

Manometric efficiency is the ratio of actual head developed by the pump to the theoretical head imparted by the impeller.

(i) Cause of Acceleration Head

Acceleration head is caused due to the acceleration and retardation of liquid in the suction and delivery pipes of a reciprocating pump.

(j) Hydraulic Intensifier

A hydraulic intensifier is a device used to increase the pressure of liquid by using a large piston area driving a smaller piston.

SECTION – B

(Descriptive Questions | 10 Marks Each)

(a) Simple Accumulator – Working

A simple accumulator consists of a vertical cylinder with a piston loaded with weights. When high-pressure fluid enters the cylinder, it lifts the piston, storing energy. During demand, the stored fluid is released to maintain pressure in the hydraulic system.

(b) Accelerating Head in Reciprocating Pump

Acceleration head is derived by considering SHM of the piston.
It depends on length and area of pipe, angular velocity, and acceleration of liquid.
This head varies during suction and delivery strokes.

(c) Centrifugal Pump – Blade Exit Angle

Given pump parameters are substituted into continuity equation, velocity triangles, and manometric efficiency relation to calculate the impeller exit blade angle.
The result ensures proper energy transfer from impeller to fluid.

(d) Performance Characteristics of Hydraulic Turbine

Performance characteristics include variation of speed, discharge, efficiency, and power with load. These are represented using characteristic curves such as main, operating, and unit curves.

(e) Draft Tube in Reaction Turbine

A draft tube converts kinetic energy at runner exit into pressure energy.
It reduces exit losses and increases overall efficiency of the reaction turbine.

(f) Governing of Pelton Turbine

Governing is achieved by adjusting the flow rate using a spear or needle.
It controls turbine speed under varying loads while maintaining constant head.

(g) Jet Striking a Moving Curved Vane

Using impulse momentum principle, force on the vane and work done per second are calculated by resolving inlet and outlet velocity components in the direction of motion.

(h) Classification of Hydraulic Turbines

Hydraulic turbines are classified based on:                   Type of energy: impulse and reaction

Direction of flow: radial, axial, mixed                             Head: high, medium, low

Specific speed

SECTION – C

(Long Answer Questions | 15 Marks Each)

3) Hydraulic Ram – Working, Efficiencies, Advantages & Limitations

A hydraulic ram works on the principle of water hammer. A large quantity of water falling through a small head lifts a small quantity of water to a greater height.

Efficiencies:

Volumetric efficiency                                                      Overall efficiency

Advantages:
Simple construction, no external power required, low maintenance.

Limitations:
Low efficiency, requires continuous water supply, limited discharge.

4) Reciprocating Pump – Pressure Head Calculation

Given pump data is used to calculate acceleration head and friction head at the beginning, middle, and end of suction stroke using SHM equations.

Cavitation possibility is checked by comparing absolute pressure head with vapour pressure head of water.

5) Centrifugal Pump – Impeller Design

Using given discharge, speed, velocity of flow, blade angle, and head, the impeller diameter and width are calculated.
Corrections for vane thickness and energy recovery are applied to obtain accurate results.