(SEM VI) THEORY EXAMINATION 2017-18 FLUID MACHINERY

Fluid Machinery (NME-021)

Complete Section-Wise Explanation – B.Tech Semester VI

Introduction to the Subject

Fluid Machinery deals with machines that either convert hydraulic energy into mechanical energy (like turbines) or convert mechanical energy into hydraulic energy (like pumps). This subject is extremely important because it connects fluid mechanics theory with real engineering applications such as power plants, irrigation systems, water supply, hydropower generation, and industrial pumping systems.

The subject mainly focuses on:

Hydraulic turbines (Pelton, Francis, Kaplan)

Centrifugal and reciprocating pumps

Governing of turbines

Cavitation and draft tubes

Characteristic curves

Jet impact and momentum theory

Similarity laws and model analysis

The question paper is divided into three sections: A, B, and C, and all sections must be attempted as per the instructions.

SECTION A – Basic Concepts & Definitions

Pattern:
Attempt all questions
10 questions × 2 marks = 20 marks

Nature of Section A

Section A tests your basic understanding of definitions and concepts. Answers should be short, direct, and technically correct. This section is highly scoring if fundamentals are clear.

Explanation of Section A Questions

Fluid Machines / Hydraulic Machines
Fluid machines are devices that exchange energy between a fluid and a rotating or stationary component. If they convert hydraulic energy into mechanical energy, they are called turbines. If they convert mechanical energy into hydraulic energy, they are called pumps.

Function of Breaking Jet in Pelton Wheel
Breaking jet reduces the velocity of water leaving the buckets. This minimizes loss of kinetic energy and improves efficiency by preventing splashing and interference with incoming jets.

Spiral Casing of Varying Area in Reaction Turbine
The spiral casing has decreasing cross-sectional area so that velocity of water entering the runner remains constant even though discharge reduces along the circumference.

Function of Draft Tube
A draft tube recovers kinetic energy at the runner outlet by converting velocity head into pressure head and allows the turbine to be installed above tailrace level.

Cavitation in Reaction Turbine
Cavitation occurs when local pressure falls below vapor pressure, forming vapor bubbles that collapse violently and damage turbine surfaces.

Volute vs Vortex Casing in Centrifugal Pump
Volute casing gradually increases area to reduce velocity and increase pressure, while vortex casing creates a forced vortex to reduce losses and improve efficiency.

Manometric Head
Manometric head is the net head against which a centrifugal pump works. It includes suction head, delivery head, velocity heads, and losses.

NPSH (Net Positive Suction Head)
NPSH is the minimum pressure head required at pump suction to avoid cavitation.

Positive Displacement Pump
A positive displacement pump delivers a fixed quantity of fluid per cycle regardless of pressure, such as reciprocating pumps.

Slip of Reciprocating Pump
Slip is the difference between theoretical discharge and actual discharge, expressed as a percentage of theoretical discharge.

 SECTION B – Theory & Numerical Applications

Pattern:
Attempt any three questions
3 × 10 marks = 30 marks

Nature of Section B

This section tests derivations, conceptual understanding, and numerical ability. Answers should be written in paragraph form, with equations and assumptions clearly stated.

Explanation of Section B Questions

Moment of Momentum Equation

This question involves deriving the equation based on Newton’s second law for rotating systems. It states that the torque exerted on a fluid is equal to the rate of change of angular momentum. This equation is fundamental in analyzing turbines and pumps, especially for calculating work done by water on runner blades.

Characteristic Curves of Hydraulic Turbines

Characteristic curves show the relationship between discharge, speed, efficiency, and power under different operating conditions. These curves help in selecting suitable turbines, predicting performance, and understanding part-load behavior.

Kaplan Turbine Numerical

This numerical applies velocity triangles and similarity laws. You calculate runner diameter using speed and flow ratios, then determine specific speed, which indicates the type and suitability of the turbine.

Centrifugal Pump Model Analysis

This question uses model–prototype similarity laws. Discharge, speed, and suction lift of the model are calculated using scale ratios. Cavitation considerations using vapour pressure and atmospheric pressure are also included.

Air Lift Pump

An air lift pump works by injecting compressed air into a vertical pipe, reducing density of the air-water mixture and causing upward flow. It is commonly used where sand or corrosive fluids are present.

SECTION C – Advanced Theory & Problem Solving

Pattern:
Attempt any one part from each question
5 questions × 10 marks = 50 marks

This section has the highest weightage and decides overall performance.

Question 3

Jet Impact on Inclined Plate (Numerical)

This problem applies momentum theory. First, force on the stationary plate is calculated using change in velocity. Then, for a moving plate, relative velocity is used to calculate force, power developed, and efficiency of the jet.

Governing of Pelton Wheel

Governing refers to maintaining constant turbine speed under varying load. In Pelton turbines, governing is achieved using spear and deflector mechanism, which controls water flow without sudden pressure changes.

Question 4

Characteristic Curves (Theory)

This is a repeated and important theory question explaining main characteristic curves, operating characteristic curves, and constant head curves for turbines.

Unit Quantities Numerical

This problem uses unit speed, unit discharge, and unit power concepts to predict turbine performance under different heads using similarity laws.

Question 5

Classification of Hydraulic Turbines

Turbines are classified based on energy available, direction of flow, head, speed, and specific speed. Explanation must include impulse and reaction turbines with examples.

Kaplan Turbine Efficiency Numerical

This numerical involves calculating overall efficiency using power output, head, draft tube efficiency, and vacuum gauge reading.

Question 6

Centrifugal Pump Numerical

This is a core pump design problem involving velocity triangles. Power required, manometric efficiency, and minimum starting speed are calculated using Euler’s equation.

Priming of Centrifugal Pump

Priming is the process of removing air from suction pipe and casing before starting. A self-priming pump automatically removes air without external priming.

Question 7

Indicator Diagram

An indicator diagram shows pressure variation inside a cylinder during one cycle. An ideal indicator diagram represents theoretical performance without losses.

Reciprocating Pump – Separation Condition Numerical

This problem checks cavitation avoidance. Maximum safe speed is calculated so that pressure in suction or delivery pipe does not fall below separation pressure.