Thermodynamics, Fluid Mechanics and Heat Transfer
Core concepts
Understand the first and second laws of thermodynamics, internal energy, enthalpy, entropy, and the ideal gas laws. Know the Carnot cycle, Rankine cycle, Otto and Diesel cycles, and the meaning of thermal efficiency. Study fluid properties: density, viscosity, compressibility, and surface tension. Learn continuity, Bernoulli's equation, momentum, and energy equations, laminar and turbulent flow, Reynolds number, friction losses, and pump and pipe system curves. Understand conduction, convection, and radiation, Fourier's law, Newton's law of cooling, heat exchangers, log mean temperature difference, and overall heat transfer coefficient.
Common traps
Questions often confuse gauge and absolute pressure, or enthalpy with internal energy. Watch for efficiency being calculated with temperatures in degrees Celsius instead of kelvin. Bernoulli's equation applies to steady, incompressible, frictionless flow along a streamline. LMTD must use the correct temperature differences at both ends of the exchanger.
Worked example
A Carnot engine operates between 600 K and 300 K. Efficiency = 1 − Tc/Th = 1 − 300/600 = 0.5, or 50%. Rule of thumb: always convert temperatures to kelvin before calculating thermodynamic efficiency.
Study approach
Practise property tables, cycle efficiency, pipe friction, and heat exchanger calculations. Sketch T-s and p-v diagrams to link processes to equipment.