⚙️ Basic Mechanical Engineering Solved Paper 2024
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B.Tech. I-Semester (Main/Back) Exam - 2024
Subject: Basic Mechanical Engineering
Code: 1FY3-07 / 1E3107
PART - A (Short Answer Questions)
Q.1 State the Zeroth law of thermodynamics.
Zeroth law states that if two thermodynamic systems are each in thermal equilibrium with a third system, then they are also in thermal equilibrium with each other. This forms the fundamental basis for temperature measurement.
Q.2 Discuss the two important properties of Steam.
1. Dryness Fraction (x): Ratio of the mass of dry steam to the total mass of wet steam.
2. Specific Enthalpy (h): Total heat content stored per unit mass of steam.
2. Specific Enthalpy (h): Total heat content stored per unit mass of steam.
Q.3 What are the main components of IC engine?
Main components include: Cylinder block, Piston, Connecting rod, Crankshaft, Spark plug/Fuel injector, Valves (Inlet & Exhaust), and Flywheel.
Q.4 What is meant by priming in centrifugal pumps?
Priming is the operation of filling the suction pipe, casing, and pump chamber completely with liquid to remove trapped air before starting the pump.
Q.5 Define the performance measure of a refrigerator and a heat pump.
Both are measured by Coefficient of Performance (COP):
• Refrigerator: COPR = QL / Wnet
• Heat Pump: COPHP = QH / Wnet = COPR + 1
• Refrigerator: COPR = QL / Wnet
• Heat Pump: COPHP = QH / Wnet = COPR + 1
Q.6 Why gear drive is called as positive drive?
Gear drive is called a positive drive because teeth mesh directly with each other, eliminating any possibility of slip or creep and ensuring a exact velocity ratio.
Q.7 List the different fields of mechanical engineering.
Thermal Engineering, Design Engineering, Manufacturing/Production Engineering, Robotics, Mechatronics, Automotive Engineering, and Fluid Mechanics.
Q.8 What is the difference between open belt and cross belt?
• Open Belt Drive: Connects parallel shafts rotating in the same direction with a larger arc of contact.
• Cross Belt Drive: Connects parallel shafts rotating in opposite directions with greater lap angle and higher power capacity.
• Cross Belt Drive: Connects parallel shafts rotating in opposite directions with greater lap angle and higher power capacity.
Q.9 Give the name of four types of patterns.
1. Single piece pattern
2. Split pattern (Two-piece)
3. Match plate pattern
4. Gated pattern
2. Split pattern (Two-piece)
3. Match plate pattern
4. Gated pattern
Q.10 What is 18:4:1 steel? State its application.
It is a standard High-Speed Steel (HSS) containing 18% Tungsten, 4% Chromium, and 1% Vanadium. Used for high-speed cutting tools like drills, lathe tools, taps, and milling cutters.
PART - B (Analytical / Problem Solving)
Q.1 Explain the second law of thermodynamics. Is it possible for a heat engine to operate without rejecting any waste heat to a low temperature reservoir? Explain.
Kelvin-Planck Statement: It is impossible to construct a device operating in a cycle that absorbs heat from a single reservoir and delivers an equivalent amount of work.
Clausius Statement: Heat cannot flow spontaneously from a colder body to a hotter body without external work input.
Possibility: No, it is impossible for a heat engine to operate without rejecting waste heat. According to the Kelvin-Planck statement, a heat engine must interact with at least two thermal reservoirs (source and sink) to produce net work continuous cycle.
Clausius Statement: Heat cannot flow spontaneously from a colder body to a hotter body without external work input.
Possibility: No, it is impossible for a heat engine to operate without rejecting waste heat. According to the Kelvin-Planck statement, a heat engine must interact with at least two thermal reservoirs (source and sink) to produce net work continuous cycle.
Q.2 Discuss the classification of the Steam Boilers. Explain the working of any boiler with the neat sketch.
Classification of Steam Boilers:
- Based on Content in Tubes: Fire-tube vs. Water-tube boilers.
- Based on Axis: Horizontal, Vertical, or Inclined.
- Based on Pressure: Low pressure (< 80 bar) vs. High pressure (> 80 bar).
- Based on Circulation: Natural vs. Forced circulation.
Q.3 Derive an expression for the air standard efficiency of Otto cycle. Draw neat P-V and T-S diagrams.
Otto Cycle Processes:
1-2: Isentropic Compression | 2-3: Constant Volume Heat Addition
3-4: Isentropic Expansion | 4-1: Constant Volume Heat Rejection
Heat added: Qin = m · cv (T3 - T2)
Heat rejected: Qout = m · cv (T4 - T1)
Efficiency: η = 1 - (Qout / Qin) = 1 - (T4 - T1) / (T3 - T2)
Using compression ratio r = V1 / V2 and relation T2 / T1 = T3 / T4 = rγ-1:
1-2: Isentropic Compression | 2-3: Constant Volume Heat Addition
3-4: Isentropic Expansion | 4-1: Constant Volume Heat Rejection
Heat added: Qin = m · cv (T3 - T2)
Heat rejected: Qout = m · cv (T4 - T1)
Efficiency: η = 1 - (Qout / Qin) = 1 - (T4 - T1) / (T3 - T2)
Using compression ratio r = V1 / V2 and relation T2 / T1 = T3 / T4 = rγ-1:
ηOtto = 1 - (1 / rγ-1)
Q.4 Differentiate among the welding, brazing and soldering.
| Feature | Welding | Brazing | Soldering |
|---|---|---|---|
| Temperature | High (> 1000°C) | Medium (> 450°C) | Low (< 450°C) |
| Melting Base Metal | Yes | No | No |
| Filler Metal | Same/Similar to base metal | Non-ferrous alloy (Spelter) | Lead-Tin alloy (Solder) |
| Joint Strength | Very High | Moderate | Low |
Q.5 Compare the working of two stroke and four stroke Internal Combustion Engine.
| Parameter | 4-Stroke Engine | 2-Stroke Engine |
|---|---|---|
| Power Cycles | 1 power stroke in 2 revolutions | 1 power stroke in 1 revolution |
| Valves/Ports | Valves operated by camshaft | Ports covered/uncovered by piston |
| Flywheel Size | Heavy flywheel required | Lighter flywheel required |
| Thermal Efficiency | High | Low (due to scavenging losses) |
Q.6 Derive an expression for the ratio of tensions in a V-belt drive.
In a V-belt running in a groove with semi-groove angle β:
Normal reaction on groove sides: 2 RN sin β = R (Where R is total radial reaction).
Frictional force: F = 2 μ RN = μ R / sin β.
Substituting effective coefficient of friction μ' = μ / sin β in standard flat belt derivation dT / T = μ' dθ:
Normal reaction on groove sides: 2 RN sin β = R (Where R is total radial reaction).
Frictional force: F = 2 μ RN = μ R / sin β.
Substituting effective coefficient of friction μ' = μ / sin β in standard flat belt derivation dT / T = μ' dθ:
ln(T1 / T2) = (μ · θ) / sin β ⇒ T1 / T2 = e(μ · θ / sin β)
Q.7 Discuss the following manufacturing processes: (a) Rolling (b) Extrusion
(a) Rolling: Metal forming process where raw stock is passed through one or more pairs of opposing rotating rolls to reduce thickness and make uniform cross-sections (sheets, rails, I-beams).
(b) Extrusion: Process where metal billet is forcibly squeezed through a shaped die opening using a ram to create continuous long objects of uniform profile (tubes, rods, channel sections).
(b) Extrusion: Process where metal billet is forcibly squeezed through a shaped die opening using a ram to create continuous long objects of uniform profile (tubes, rods, channel sections).
PART - C (Descriptive / Analytical / Design)
Q.1 Explain the oxy-acetylene gas welding and metal arc welding with neat sketches. Also state their applications.
1. Oxy-Acetylene Gas Welding:
Uses thermal energy generated by combusting Acetylene (C2H2) and Oxygen (O2) at ~3200°C to melt filler rod and base metal.
• Applications: Sheet metal fabrication, pipe joining, repair works.
2. Shielded Metal Arc Welding (SMAW):
Creates an electric arc between a consumable flux-coated electrode and base metal. Heat generated melts metal, and flux coating produces shielding gas to prevent atmospheric contamination.
• Applications: Heavy structural steelwork, pressure vessels, shipbuilding.
Uses thermal energy generated by combusting Acetylene (C2H2) and Oxygen (O2) at ~3200°C to melt filler rod and base metal.
• Applications: Sheet metal fabrication, pipe joining, repair works.
2. Shielded Metal Arc Welding (SMAW):
Creates an electric arc between a consumable flux-coated electrode and base metal. Heat generated melts metal, and flux coating produces shielding gas to prevent atmospheric contamination.
• Applications: Heavy structural steelwork, pressure vessels, shipbuilding.
Q.2 Explain the working of a reciprocating pump with neat sketch.
Working of Positive Displacement Reciprocating Pump:
- Suction Stroke: Piston moves outward, creating partial vacuum inside cylinder. Suction valve opens, drawing fluid through suction pipe.
- Delivery Stroke: Piston moves inward, increasing cylinder pressure. Suction valve closes, delivery valve opens, forcing fluid out through delivery pipe.
Q.3 Find the power transmitted by a belt running over a pulley of 500 mm diameter at 300 rpm. The coefficient of friction between the belt and pulley is 0.24, angle of lap is 150° and maximum tension in the belt is 2.45 kN.
Given Data:
Diameter D = 0.5 m, Speed N = 300 rpm, μ = 0.24
Angle of lap θ = 150° = 150 × (π / 180) = 2.618 rad
Maximum Tension T1 = 2.45 kN = 2450 N
Step-by-Step Solution:
1. Linear Velocity: v = (π × D × N) / 60 = (π × 0.5 × 300) / 60 = 7.854 m/s
2. Tension Ratio: T1 / T2 = eμθ = e(0.24 × 2.618) = e0.6283 ≈ 1.874
3. Slack Side Tension: T2 = T1 / 1.874 = 2450 / 1.874 = 1307.36 N
4. Power Transmitted: P = (T1 - T2) × v = (2450 - 1307.36) × 7.854 = 8971.8 W = 8.972 kW
Diameter D = 0.5 m, Speed N = 300 rpm, μ = 0.24
Angle of lap θ = 150° = 150 × (π / 180) = 2.618 rad
Maximum Tension T1 = 2.45 kN = 2450 N
Step-by-Step Solution:
1. Linear Velocity: v = (π × D × N) / 60 = (π × 0.5 × 300) / 60 = 7.854 m/s
2. Tension Ratio: T1 / T2 = eμθ = e(0.24 × 2.618) = e0.6283 ≈ 1.874
3. Slack Side Tension: T2 = T1 / 1.874 = 2450 / 1.874 = 1307.36 N
4. Power Transmitted: P = (T1 - T2) × v = (2450 - 1307.36) × 7.854 = 8971.8 W = 8.972 kW
Q.4 Explain the following: (a) Vapour compression refrigeration cycle (b) Comfort air conditioning
(a) Vapour Compression Refrigeration System (VCRS):
- Compressor: Compresses low-pressure refrigerant vapor to high pressure/temperature.
- Condenser: Rejects heat to surrounding, condensing refrigerant into liquid.
- Expansion Valve: Throttles pressure and temperature of liquid refrigerant.
- Evaporator: Absorbs heat from storage space, vaporizing refrigerant to repeat cycle.
Q.5 Write a short note on any two of the following: (a) Classification of IC engines (b) Forging manufacturing process (c) Various engineering materials and their properties
(a) Classification of IC Engines:
• By Fuel: Petrol, Diesel, CNG, Gas engines.
• By Strokes: 2-Stroke, 4-Stroke engines.
• By Ignition: Spark Ignition (SI), Compression Ignition (CI).
• By Cooling: Air-cooled, Water-cooled engines.
(b) Forging Manufacturing Process:
Forging is a metalworking process where metal is shaped through localized compressive forces applied using hammers, presses, or dies. Classified into Open-die, Closed-die, and Impression-die forging. Produces superior grain flow and mechanical strength.
• By Fuel: Petrol, Diesel, CNG, Gas engines.
• By Strokes: 2-Stroke, 4-Stroke engines.
• By Ignition: Spark Ignition (SI), Compression Ignition (CI).
• By Cooling: Air-cooled, Water-cooled engines.
(b) Forging Manufacturing Process:
Forging is a metalworking process where metal is shaped through localized compressive forces applied using hammers, presses, or dies. Classified into Open-die, Closed-die, and Impression-die forging. Produces superior grain flow and mechanical strength.