(SEM V) THEORY EXAMINATION 2024-25 TURBO MACHINES

Subject Code: BME055

Subject Name: Turbo Machines

Course: B.Tech (Semester V)

Maximum Marks: 70

Duration: 3 Hours

Exam Year: 2024–25

Sections: A, B and C

SECTION A – Short Answer Questions (2 × 7 = 14 Marks)

Attempt all questions briefly.

Compare turbomachines with positive-displacement machines.

Define polytropic efficiency.

What is the utilization factor in turbomachines?

What is Parsons’s turbine? Explain its working principle.

Define Net Positive Suction Head (NPSH).

What is manometric efficiency?

Why does slip occur in centrifugal compressors?
 

SECTION B – Medium-Length Questions (7 × 3 = 21 Marks)

Attempt any three.

Define and explain performance parameters and coefficients used in turbomachinery (flow, head, efficiency, power coefficients, etc.).

Derive an expression for polytropic efficiency of a compressor in terms of temperature, pressure, and adiabatic index.

Explain velocity compounding of a multi-stage impulse turbine.

Discuss specific speed and its role in design and selection of hydraulic turbines.

Define slip factor for centrifugal compressor and derive its equation.
 

SECTION C – Long/Analytical Questions (7 × 5 = 35 Marks)

Attempt one part from each question.

Q3. Introduction to Turbomachines

a. Define a turbomachine. With neat sketch, explain its principal parts.
OR
b. Explain the reheat factor during expansion and its effect on efficiency.

Q4. Energy Transfer and Compressors

a. Derive the Euler’s energy equation for turbomachines and state its significance.
OR
b. Explain working of an axial flow compressor with a sketch and discuss its performance characteristics curve.

Q5. Steam and Reaction Turbines

a. Steam at 4.9 bar and 160 °C is supplied to a single-stage impulse turbine at 60 kg/min. It exhausts to a condenser at 0.196 bar. Blade speed = 300 m/s; nozzles at 25°; outlet blade angle = 35°.
Neglecting losses, find (a) theoretical power developed, (b) diagram efficiency, (c) stage efficiency.
OR
b. Explain the principle, construction and working of a reaction turbine.
 

Q6. Hydraulic Turbines and Draft Tubes

a. Explain how losses in draft tube affect pressure at runner exit.
OR
b. A Pelton wheel runs at 300 r.p.m. under a head of 510 m. Jet diameter = 200 mm, deflection = 165°, relative velocity reduction = 15%. Find: (i) water power, (ii) resultant force on bucket, (iii) overall efficiency.
Given: mechanical loss = 3%, Cv=0.98C_v = 0.98Cv​=0.98, speed ratio = 0.46.
 

Q7. Centrifugal Pumps and Compressors

a. Explain the characteristics of a centrifugal pump and describe its characteristic curves (head–discharge, power–discharge, efficiency–discharge).
OR
b. A centrifugal compressor handles 180 kg/min of air at 1 bar and 300 K; suction velocity = 90 m/s; delivery = 2 bar, 400 K, 240 m/s. Find (a) isentropic efficiency, (b) power required, (c) overall efficiency. Given cp=1.005kJ/kg⋅Kc_p = 1.005 kJ/kg·Kcp​=1.005kJ/kg⋅K.
 

Key Topics to Prepare

Classification and comparison of turbomachines vs positive-displacement devices

Polytropic and isentropic efficiencies                    Euler’s energy equation

Velocity and pressure compounding                    Specific speed of turbines and pumps

Slip factor and utilization factor                            Performance curves of centrifugal pumps and compressors

Impulse & reaction turbines, Pelton wheel numericals    Draft tube losses and reheat factor

Study Tips

Practice numericals — turbine power, efficiency, and flow rate problems.

Revise key diagrams: Pelton wheel, impulse turbine stages, axial flow compressor.

Memorize formulas: H=V22gH = \frac{V^2}{2g}H=2gV2​, η=useful energyinput energyη = \frac{\text{useful energy}}{\text{input energy}}η=input energyuseful energy​, polytropic and isentropic relations.

Understand conceptual differences: impulse vs reaction, axial vs radial flow.

Focus on efficiency and losses in turbines, compressors, and pumps.