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HKIE Professional Assessment - Mechanical Discipline study materials
HKIE Professional Assessment - Mechanical Discipline study resources

HKIE Professional Assessment - Mechanical Discipline: Mechanical engineering science and analysis (thermodynamics, fluid mechanics, mechanics of solids, dynamics and vibrations)

HKIE Professional Assessment - Mechanical Discipline · Work through your exam, one topic at a time.

All guide sections

Mechanical engineering science and analysis (thermodynamics, fluid mechanics, mechanics of solids, dynamics and vibrations)

The paper uses this domain to check whether you can convert first principles into defensible numbers for plant and building services. Expect steady-flow energy balances, pump and fan laws, psychrometric checks, stress in pressure parts and simple vibration/isolation problems. The examiner rewards correct units, stated assumptions and a sanity check.

Core rules and concepts

  • Steady-flow energy: ṁ(h1 + V1²/2 + gz1) + Q = ṁ(h2 + V2²/2 + gz2) + W. For liquids, use ρgQH for hydraulic power.
  • Refrigeration: 1 refrigeration ton (RT) = 3.517 kW. Chiller COP = cooling output / electrical input. Condenser heat rejection = cooling load + compressor input.
  • Pumps and fans: shaft power = ρgQH/η for pumps; air power = QΔp/η for fans. Affinity laws: Q∝N, H∝N², P∝N³.
  • Fluid flow: Darcy–Weisbach hf = f(L/D)(V²/2g); minor losses ΣK(V²/2g). Bernoulli without losses is an idealisation.
  • Solids: thin cylinder hoop stress σ = pr/t; longitudinal stress σ = pr/2t. Bending σ = My/I. Check combined stress and fatigue where cyclic.
  • Vibration: fn = (1/2π)√(k/m). Resonance occurs when excitation frequency approaches fn; isolation is effective only when f/fn > √2.

Worked example

A 500 RT chiller operates at COP 5.5. Find electrical input and condenser heat rejection. Cooling load = 500 × 3.517 = 1,758.5 kW. Input = 1,758.5 / 5.5 = 319.7 kW. Rejection = 1,758.5 + 319.7 = 2,078.2 kW. Reasoning: COP is defined on the cooling effect, so the compressor power is added, not subtracted. The heat rejection is used to size cooling towers and condenser water pumps; a common error is to use the cooling load alone.

Traps that cost marks

  • Mixing gauge and absolute pressure, or kW and RT.
  • Using COP and EER interchangeably without converting units.
  • Applying Bernoulli across a pump or strainer without a head term.
  • Using thin-wall pressure-vessel formulae when t/r is not small.
  • Ignoring part-load performance and fouling margins.