Mechanical Engineering & Thermodynamics

• Mechanical engineering is a diverse field focused on the design, construction, and operation of machinery and mechanical systems.
• It uses physics and material science for the analysis, design, manufacturing, and maintenance of mechanical systems.
• Mechanical engineers are employed in automotive, aerospace, manufacturing, energy, and robotics industries, among others.
• Key areas in mechanical engineering are thermodynamics, fluid mechanics, heat transfer, mechanics of materials, manufacturing, and control systems.

Thermodynamics

• Thermodynamics studies energy and its transformations.
• It examines the relationships between heat, work, and energy, and the laws governing these interactions.
• The fundamental laws of thermodynamics include:
  • Zeroth Law: If two systems are in thermal equilibrium with a third, they are in thermal equilibrium with each other.
  • First Law: Energy is conserved; it can only be converted from one form to another (ΔU = Q - W, where ΔU is the change in internal energy, Q is the heat added, and W is the work done).
  • Second Law: The total entropy of an isolated system increases or remains constant in ideal cases (ΔS ≥ 0, where ΔS is the change in entropy).
  • Third Law: As temperature nears absolute zero, the entropy of a system approaches a minimum or zero.
• Thermodynamic properties are temperature (T), pressure (P), volume (V), internal energy (U), enthalpy (H), entropy (S), and Gibbs free energy (G).
• Thermodynamic processes are isothermal (constant temperature), isobaric (constant pressure), isochoric (constant volume), and adiabatic (no heat exchange).
• Thermodynamic cycles like the Carnot, Otto, and Diesel cycles help in analyzing the performance of heat engines and refrigerators.

Fluid Mechanics

• Fluid mechanics studies fluids (liquids and gases) and their behavior under different conditions.
• It includes fluid statics (fluids at rest) and fluid dynamics (fluids in motion).
• Key fluid properties are density (ρ), viscosity (μ), surface tension (σ), and compressibility (β).
• Fluid statics studies pressure distribution in fluids at rest, where pressure equals force divided by area and increases with depth (P = ρgh, where P is pressure, ρ is density, g is gravitational acceleration, and h is depth).
• Buoyancy is the upward force a fluid exerts on an immersed object, and Archimedes' principle states this force equals the weight of the displaced fluid.
• Fluid dynamics involves the study of fluids in motion.
• Viscosity measures a fluid's resistance to flow.
• Laminar flow features smooth, orderly fluid layers, while turbulent flow is chaotic and irregular.
• The Reynolds number (Re) predicts whether flow will be laminar or turbulent, using the formula Re = (ρvL)/μ, where ρ is density, v is velocity, L is a characteristic length, and μ is dynamic viscosity.
• Bernoulli's equation relates pressure, velocity, and height for an ideal fluid in steady flow: P + (1/2)ρv^2 + ρgh = constant (P = pressure, v = fluid velocity, ρ = fluid density, h = height).
• The Continuity equation is A1V1 = A2V2 for incompressible fluids in a closed system.

Material Science

• Material science is an interdisciplinary field studying the relationship between material structure and properties.
• It involves designing and discovering new materials.
• Material properties of interest include:
  • Mechanical properties (strength, hardness, ductility)
  • Thermal properties (thermal conductivity, specific heat)
  • Electrical properties (conductivity, resistivity)
  • Chemical properties (corrosion resistance)
• Common material types are metals, ceramics, polymers, and composites.
• Metals are strong, ductile, and electrically conductive.
• Ceramics are hard, brittle, and resistant to high temperatures and corrosion.
• Polymers are organic, consisting of long chains of repeating units (monomers).
• Composites are made from two or more materials with significantly different physical or chemical properties.
• Material structure, from atomic to macroscopic levels, influences its properties.
• The crystal structure of metals impacts their mechanical properties.
• The microstructure of a material includes grain size, grain boundaries, and phases.
• Heat treatment can alter a material's microstructure and properties.

Mechanics of Materials

• Mechanics of materials (or strength of materials) studies the behavior of solid materials under stress and strain.
• Stress is force per unit area (σ = F/A, where σ is stress, F is force, and A is area).
• Strain is the deformation of a material caused by stress (ε = ΔL/L, where ε is strain, ΔL is change in length, and L is original length).
• Hooke's Law states that stress is proportional to strain within the elastic limit (σ = Eε, where E is Young's modulus).
• Types of stress include tensile (pulling), compressive (pushing), shear (tangential), and torsional (twisting).
• Poisson's ratio (ν) is the ratio of lateral strain to axial strain.
• Shear modulus (G) is the ratio of shear stress to shear strain.
• Bending occurs when a material is subjected to a moment.
• Torsion is the twisting of an object due to applied torque.
• Failure criteria, like yield strength and ultimate tensile strength, predict material failure under stress.
• Fatigue is the weakening of a material from repeated loading and unloading.
• Creep is the time-dependent deformation of a material under constant stress at high temperatures.