Thermal-Engineering-II

Thermal Engineering - II

• Prepared By: Soumya Ranjan Nayak

• Department of Mechanical Engineering

• Vedang Institute of Technology, Bhubaneswar

CONTENT Overview

1. PERFORMANCE OF I.C ENGINE

2. AIR COMPRESSOR

3. PROPERTIES OF STEAM

4. STEAM GENERATOR

5. STEAM POWER CYCLE

6. HEAT TRANSFER

Performance of I.C Engine

Indicated Power (I.P)

• Defined as the rate of work done on the piston by combustion inside the engine cylinder.

• Determined from indicated diagrams, also called gross power.

• Formula:I.P = Pm × L × A × n/60Where:

• Pm = mean effective pressure (N/m²)

• L = stroke length (m)

• A = cross-sectional area (m²)

• n = working strokes per minute

  • N (for 2-stroke)

  • N/2 (for 4-stroke)

Brake Power (B.P)

• Defined as the net power available at the engine shaft measured by brake and dynamometer.

• Formula:B.P = 2πNF / 60Where:

• F = braking force (N)

• R = effective brake drum radius (m)

• T = torque (N-m)

• N = speed of the engine in r.p.m.

Frictional Power (F.P)

• Defined as the portion of indicated power used to overcome friction.

• Formula:F.P = I.P – B.P

Fuel Consumption

• Mass flow rate of fuel consumed by the engine.

• Calculation Formula:ṁf = Vf × ρf × 3600/ΔtWhere:

• Vf = volume of fuel used (m³)

• ρ = density of fuel (kg/m³)

• Δt = time taken (sec)

Specific Fuel Consumption

• Ratio of mass flow of fuel to power output.

• Brake Specific Fuel Consumption (B.S.F.C):B.S.F.C = ṁf / B.P (kg/kWh)

• Indicated Specific Fuel Consumption (I.S.F.C):I.S.F.C = ṁf / I.P (kg/kWh)

Air Fuel Ratio

• Ratio of mass of air to mass of fuel.

• Ranges:

  • 12-19 for Petrol Engines

  • 20-60 for Diesel Engines

Efficiency Metrics

• Brake Thermal Efficiency:η_bth = ṁf × C.V / B.P * 100

• Indicated Thermal Efficiency:η_ith = ṁf × C.V / I.P * 100

• Mechanical Thermal Efficiency:η_mechanical = B.P / I.P * 100

Air Compressor

• Function: Draws atmospheric air and compresses it to high pressure for various applications.

• Applications include:

  • Air refrigeration

  • Starting heavy-duty diesel engines

  • Operating pneumatic tools and motors

Classification of Air Compressors

Types

1. Single stage vs Multi stage.

2. Single acting vs Double acting.

Important Terms

• Swept Volume (Displacement Volume):Vs = π/4 × D² × LWhere: D = bore diameter, L = stroke length.

• Pressure Ratio:rp = P2/P1

• Free Air Delivered (FAD): Volume of compressor output at standard conditions.

Properties of Steam

Phases of a Pure Substance

• Solids have strong molecular bonds and fixed positions.

• Liquids: Intermediate bonding allows movement.

• Gases: High energy, low interaction.

Process Changes

1. Liquid to Solid

2. Liquid to Gas

3. Gas to Liquid

4. Gas to Solid

Steam Generator

Definition

• Converts water into steam via heat from combustion of fuel.

Classification of Boilers

1. Fire tube vs Water tube

2. Internally vs Externally fired

3. Vertical vs Horizontal

Important Components of the Boiler:

• Steam Stop Valve, Safety Valve, Water Gauge, Pressure Gauge

• Working: Fuel burns, flue gases heat water, resulting in steam production.

Steam Power Cycle

Carnot vs Rankine Cycle

Carnot Cycle Steps

1. Isothermal Expansion

2. Reversible Adiabatic Expansion

3. Isothermal Compression

4. Reversible Adiabatic Compression

Efficiency of Carnot Cycle

Formula:

η_carnot = (T1 - T3) / T1

Heat Transfer

Modes of Heat Transfer

1. Conduction

2. Convection

3. Radiation

Fourier’s Law of Heat Conduction

• Q ∝ A × ΔT/Δx

• Formula:Q = K × A × ΔT/ΔxWhere: K = thermal conductivity

Convective Heat Transfer Coefficient

• Represents heat exchanged per unit temperature difference.

Applications of Heat Exchangers

1. Intercoolers, Preheaters

2. Condensers, Evaporators

3. Automobile radiators

Class Room Problems

• Sample problems include calculating efficiency, power output, specific energy, etc.

Assignments

• Problems on thermodynamic cycles and heat transfer calculations.