⚙️ Basic Mechanical Engineering Solved Paper 2025
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B.Tech. I-Semester (Main/Back) Exam - 2025
Subject: Basic Mechanical Engineering
Code: 1FY3-07 / 1E3107
PART - A (Short Answer Questions)
Q.1 Explain the open and close system.
- Open System: A thermodynamic system where both mass and energy can transfer across the system boundaries (e.g., turbine, pump).
- Closed System: A thermodynamic system where energy can cross the boundaries, but mass transfer is not allowed (e.g., piston-cylinder without valves).
Q.2 What is the function of foot valve in suction pipe?
A foot valve is a one-way non-return valve fitted at the bottom of the pump's suction pipe to retain liquid inside the pipe, preventing unpriming and keeping the pump primed for continuous operation.
Q.3 Difference between belt drive and rope drive.
- Belt Drive: Suitable for short to medium center distances, uses flat or V-belts, and produces low power transmission capacity.
- Rope Drive: Suitable for long center distances, uses circular ropes running in grooved pulleys, and transmits high power.
Q.4 State the use of piston rings in IC Engines.
1. Compression Rings: Seal the combustion chamber to prevent blow-by gas leakage.
2. Oil Rings: Scrape excess lubricating oil off the cylinder walls to prevent oil burning.
2. Oil Rings: Scrape excess lubricating oil off the cylinder walls to prevent oil burning.
Q.5 Define Ton of refrigeration.
A Ton of Refrigeration (TR) is defined as the amount of heat extraction required to freeze 1 U.S. ton (2000 lbs or 907 kg) of water at 0°C into ice at 0°C in 24 hours. Equivalent to 3.517 kW or 210 kJ/min.
Q.6 Define mechanical energy and thermal energy.
- Mechanical Energy: Sum of potential energy and kinetic energy possessed by a physical body due to its position, state, or macro-motion.
- Thermal Energy: Internal microscopic energy stored within a system caused by the random kinetic motion of its atoms and molecules.
Q.7 What are functioning difference between refrigeration and air conditioning system?
- Refrigeration System: Cools an enclosed space below ambient temperature solely to preserve products/food.
- Air Conditioning System: Simultaneously regulates temperature, humidity, air cleanliness, and circulation for human thermal comfort.
Q.8 Write the comparison between SI and CI engine.
| Parameter | SI Engine (Petrol) | CI Engine (Diesel) |
|---|---|---|
| Fuel & Ignition | Petrol; Spark Plug ignition | Diesel; Compression ignition |
| Compression Ratio | Low (6:1 to 10:1) | High (14:1 to 22:1) |
| Thermodynamic Cycle | Otto Cycle | Diesel Cycle |
Q.9 What is mechanical coupling?
A mechanical coupling is a mechanical device used to permanently connect two rotating shafts together at their ends to transmit torque and rotational power from a driving shaft to a driven shaft.
Q.10 What is pump?
A pump is a mechanical hydraulic machine that converts mechanical energy into hydraulic energy, raising the pressure and head of fluids to transport them from low to high elevation.
PART - B (Analytical / Problem Solving)
Q.1 Write name of various types of power plants and explain any one in detail.
Types of Power Plants: Thermal (Steam), Hydroelectric, Nuclear, Gas Turbine, Diesel, and Solar/Wind Power Plants.
Thermal Power Plant (Steam Power Plant):
Thermal Power Plant (Steam Power Plant):
- Boiler: Water is converted into high-pressure steam by burning coal.
- Steam Turbine: High-pressure steam expands over turbine blades to convert thermal energy into rotational mechanical energy.
- Generator: Coupled to the turbine shaft to convert mechanical rotation into electrical energy.
- Condenser: Exhaust steam from the turbine is condensed back into water for recirculating to the boiler.
Q.2 Explain the working of 4-stroke diesel engine.
1. Suction Stroke: Piston moves from TDC to BDC; only fresh air is drawn into the cylinder via the open inlet valve.
2. Compression Stroke: Both valves close; piston moves from BDC to TDC, compressing air to high pressure and high temperature.
3. Power/Expansion Stroke: Diesel fuel is sprayed via fuel injector; auto-ignition occurs, driving the piston rapidly from TDC to BDC.
4. Exhaust Stroke: Exhaust valve opens; piston moves from BDC to TDC, pushing burned combustion gases out of the cylinder.
2. Compression Stroke: Both valves close; piston moves from BDC to TDC, compressing air to high pressure and high temperature.
3. Power/Expansion Stroke: Diesel fuel is sprayed via fuel injector; auto-ignition occurs, driving the piston rapidly from TDC to BDC.
4. Exhaust Stroke: Exhaust valve opens; piston moves from BDC to TDC, pushing burned combustion gases out of the cylinder.
Q.3 Describe the construction and working of vapour absorption refrigeration system.
Vapour Absorption Refrigeration System (VARS): Replaces the mechanical compressor of VCRS with a heat-driven assembly (Absorber, Pump, Generator) using NH3-H2O pair.
- Absorber: Low-pressure ammonia vapor from the evaporator is absorbed by weak aqua-ammonia solution.
- Pump: Pumps the strong aqua-ammonia solution to the generator using minimal mechanical work.
- Generator: Thermal heat input boils off high-pressure ammonia vapor, which passes to the condenser.
- Expansion Valve & Evaporator: Liquid ammonia expands and absorbs heat from the refrigerated space, repeating the refrigeration cycle.
Q.4 Describe the metal casting process with suitable diagrams.
Metal Casting Steps:
- Pattern Making: Fabricating a replica model of the desired casting out of wood, metal, or plastic.
- Mould Preparation: Packing foundry sand around the pattern in two mould boxes: Cope (top) and Drag (bottom).
- Core Placement: Placing sand cores inside the mould cavity if hollow features are needed.
- Pouring & Solidification: Molten metal is poured through a sprue into the mould cavity and left to cool and solidify.
- Shakeout & Cleaning: Breaking the sand mould, removing runners/risers, and finishing the final cast component.
Q.5 Explain construction and working of a typical centrifugal pump with a sketch.
Constructional Elements:
- Impeller: Rotating wheel fitted with backward curved vanes mounted on a shaft.
- Casing: Air-tight spiral volute casing surrounding the impeller that converts kinetic energy to pressure energy.
- Suction & Delivery Pipes: Inlet pipe fitted with foot valve and outlet pipe with delivery valve.
Q.6 Write the classification of engineering materials.
Engineering materials are classified into four main categories:
- Metals & Alloys:
- Ferrous Metals: Cast Iron, Mild Steel, Stainless Steel.
- Non-Ferrous Metals: Aluminum, Copper, Brass, Bronze.
- Polymers (Plastics): Thermoplastics (PVC, Polyethylene) and Thermosetting plastics (Bakelite, Epoxy).
- Ceramics: Glass, Brick, Refractories, Cement.
- Composites: Fiber-reinforced plastics (FRP), Concrete, Carbon-fiber composites.
Q.7 Derive the expression for the length of belt for close belt drive.
For a closed belt drive connecting two pulleys of radii R1 and R2 with center distance x:
1. Angle of lap α is given by: sin α = (R1 + R2) / x (approx. (R1 + R2) / x for small angles).
2. Total belt length L = 2 × [Arc length on larger pulley + Straight portion + Arc length on smaller pulley].
3. Substituting geometric arc expressions:
1. Angle of lap α is given by: sin α = (R1 + R2) / x (approx. (R1 + R2) / x for small angles).
2. Total belt length L = 2 × [Arc length on larger pulley + Straight portion + Arc length on smaller pulley].
3. Substituting geometric arc expressions:
L = π(R1 + R2) + 2x + (R1 + R2)2 / x
In terms of diameters (D1 and D2):
L = (π / 2)(D1 + D2) + 2x + (D1 + D2)2 / 4x
PART - C (Descriptive & Numerical Solutions)
Q.1 (a) Define heat treatment. Explain different stages of heat treatment with suitable diagram.
(b) Explain various types of engineering material's properties.
(b) Explain various types of engineering material's properties.
(a) Heat Treatment & Stages:
Heat treatment involves controlled heating and cooling of metals in solid state to modify physical/mechanical properties.
(b) Engineering Material Properties:
Heat treatment involves controlled heating and cooling of metals in solid state to modify physical/mechanical properties.
- Stage 1 (Heating): Heating the metal uniformly up to a specific critical temperature.
- Stage 2 (Soaking): Holding the metal at that temperature to achieve uniform microstructural transformation.
- Stage 3 (Cooling): Controlled cooling to room temperature via quenching (water/oil) or slow furnace cooling.
(b) Engineering Material Properties:
- Strength: Resistance to deformation under applied load.
- Ductility: Ability to draw out into thin wires without fracture.
- Hardness: Resistance to surface scratching, wear, or indentation.
- Toughness: Capacity to absorb impact energy before failure.
Q.2 Explain the following processes in details: (i) Forging (ii) Rolling (iii) Drawing (iv) Extrusion
- (i) Forging: Metal shaping through localized compressive forces applied using hammers or presses (Hot or Cold forging).
- (ii) Rolling: Passing metal ingots between counter-rotating rollers to reduce thickness and yield uniform cross-sections (sheets/plates).
- (iii) Drawing: Pulling a metal wire/rod through a tapered die orifice to reduce cross-section and increase length.
- (iv) Extrusion: Pushing a metal billet through a die opening using a ram to form long continuous shapes (pipes, channels).
Q.3 (a) Belt Power Numerical
(b) Comparison between SI and CI engine
(c) Classification of steam generators
(b) Comparison between SI and CI engine
(c) Classification of steam generators
(a) Numerical Solution:
Given: D = 0.8 m (Radius R = 0.4 m), Speed N = 180 rpm, Angle of lap θ = 165° = 165 × (π / 180) = 2.88 rad, T1 = 2000 N, μ = 0.3.
1. Linear velocity: v = (π × D × N) / 60 = (π × 0.8 × 180) / 60 = 7.54 m/s.
2. Tension ratio: T1 / T2 = eμθ = e(0.3 × 2.88) = e0.864 ≈ 2.373.
3. Slack side tension: T2 = T1 / 2.373 = 2000 / 2.373 = 842.82 N.
4. Power Transmitted: P = (T1 - T2) × v = (2000 - 842.82) × 7.54 = 8725.2 W = 8.725 kW.
(b) SI vs CI Engine: Spark Ignition engines use petrol with homogeneous fuel air mixtures via carburetors/injectors, whereas Compression Ignition engines inject heavy diesel fuel into compressed hot air directly.
(c) Classification of Steam Generators (Boilers):
Given: D = 0.8 m (Radius R = 0.4 m), Speed N = 180 rpm, Angle of lap θ = 165° = 165 × (π / 180) = 2.88 rad, T1 = 2000 N, μ = 0.3.
1. Linear velocity: v = (π × D × N) / 60 = (π × 0.8 × 180) / 60 = 7.54 m/s.
2. Tension ratio: T1 / T2 = eμθ = e(0.3 × 2.88) = e0.864 ≈ 2.373.
3. Slack side tension: T2 = T1 / 2.373 = 2000 / 2.373 = 842.82 N.
4. Power Transmitted: P = (T1 - T2) × v = (2000 - 842.82) × 7.54 = 8725.2 W = 8.725 kW.
(b) SI vs CI Engine: Spark Ignition engines use petrol with homogeneous fuel air mixtures via carburetors/injectors, whereas Compression Ignition engines inject heavy diesel fuel into compressed hot air directly.
(c) Classification of Steam Generators (Boilers):
- Fire-Tube Boilers: Hot gases pass inside tubes surrounded by water (e.g., Lancashire, Cochran Boilers).
- Water-Tube Boilers: Water flows inside tubes surrounded by hot combustion gases (e.g., Babcock & Wilcox Boiler).
Q.4 Classification of gear drives & Derivation of tension ratio for flat and V-belt.
Classification of Gear Drives:
Derivation of Tension Ratio (T1 / T2 = eμθ):
Consider a small element of belt subtending angle dθ over pulley:
1. Resolving forces radially: RN = T · dθ.
2. Resolving forces tangentially: dT = μ RN = μ T · dθ.
3. Integrating between limits T2 to T1 and 0 to θ:
- Parallel Shafts: Spur gear, Helical gear, Rack and Pinion.
- Intersecting Shafts: Bevel gear, Mitre gear.
- Non-Parallel & Non-Intersecting Shafts: Worm and Worm gear, Skew gear.
Derivation of Tension Ratio (T1 / T2 = eμθ):
Consider a small element of belt subtending angle dθ over pulley:
1. Resolving forces radially: RN = T · dθ.
2. Resolving forces tangentially: dT = μ RN = μ T · dθ.
3. Integrating between limits T2 to T1 and 0 to θ:
∫ (dT / T) = μ ∫ dθ ⇒ ln(T1 / T2) = μθ ⇒ T1 / T2 = eμθ
For V-Belts with groove angle 2β:
T1 / T2 = e(μθ / sin β)
Q.5 Explain the joining processes of soldering, brazing and welding. Clearly bring out the differences between them and give specific applications of each type.
Comparison of Joining Processes:
| Feature | Soldering | Brazing | Welding |
|---|---|---|---|
| Operating Temperature | Low (< 450°C) | Medium (> 450°C) | High (> 1000°C) |
| Filler Material | Lead-Tin alloy (Solder) | Copper-Zinc alloy (Spelter) | Similar to parent metal |
| Base Metal Melting | No | No | Yes |
| Joint Strength | Weakest | Medium | Strongest |
| Applications | Printed Circuit Boards (PCB), electronic wiring. | Pipe fittings, heat exchangers, refrigeration coils. | Structural steel frameworks, ship building, pressure vessels. |