HKIE Professional Assessment - Mechanical Discipline flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Carnot efficiency

Maximum theoretical thermal efficiency of a heat engine operating between hot and cold reservoirs at absolute temperatures T_H and T_L, given by 1 − T_L/T_H.

Reynolds number

Dimensionless ratio of inertial to viscous forces, Re = ρVD/μ. Values below about 2,000 indicate laminar pipe flow; above about 4,000 indicate turbulent flow.

Darcy–Weisbach equation

Head loss in a pipe due to friction, h_f = f(L/D)(V²/2g), where f is the friction factor obtained from the Moody chart using Reynolds number and relative roughness.

Euler buckling load

Critical compressive load at which a slender column becomes unstable, P_cr = π²EI/(KL)², where K depends on the end restraint conditions.

Damping ratio

Dimensionless measure of damping in a vibrating system, ζ = c/(2√(km)). A value of 1 represents critical damping; values below 1 produce oscillatory response.

Section modulus

Ratio of second moment of area to distance to the extreme fibre, Z = I/c. Bending stress follows σ = M/Z, so a larger Z reduces stress.

Ashby material index

A derived combination of material properties that captures performance for a given design objective, allowing materials to be ranked for stiffness, strength or mass.

Galvanic corrosion

Accelerated corrosion when two dissimilar metals are coupled in an electrolyte; the less noble metal becomes anodic. Risk rises with greater potential difference and wet conditions.

Tolerance stack-up

Method of combining individual component tolerances to determine assembly variation, using worst-case arithmetic summation or statistical root-sum-square techniques.

Fillet weld throat thickness

The effective load-carrying thickness of a fillet weld, equal to 0.707 times the leg length for a weld with equal legs at 90 degrees.

Ductile-to-brittle transition

Temperature below which a normally ductile steel fractures in a brittle manner. Charpy testing establishes the transition; service temperature should exceed it.

Hydrostatic pressure test

Strength and leak test of pipework or vessels filled with water and pressurised, commonly to 1.5 times design pressure, held for a specified duration with no loss.

Condition monitoring

Predictive maintenance approach using vibration, thermography, oil analysis or performance data to detect developing faults before functional failure occurs.

ISO 20816 vibration zones

Vibration severity classification for rotating machines using RMS velocity in mm/s, with zones A to D indicating new, acceptable, unsatisfactory and unacceptable conditions.

Factory acceptance test

Testing of equipment at the manufacturer's works against specified performance and documentation requirements before shipment; it does not replace site commissioning.

Non-destructive testing methods

Inspection techniques that do not damage the component, including dye penetrant and magnetic particle for surface defects, and ultrasonic and radiographic testing for internal defects.

Fan affinity laws

For a fan or pump, flow varies with speed, head with speed squared, and power with speed cubed, which explains the large energy savings from variable-speed control.

Coefficient of performance

Ratio of useful cooling or heating output to electrical power input for a chiller or heat pump. Higher COP means greater efficiency at the stated operating condition.

Apparatus dew point

The coil surface temperature at which air leaving a cooling coil would be saturated; used with bypass factor to determine supply air condition.

Sensible heat equation

Cooling or heating load for air, Q_s = 1.23 × airflow in L/s × temperature difference in °C, valid for standard air density and specific heat.

Trap seal protection

Requirement in drainage design that each trap retains a water seal, protected by venting or air admittance, to prevent foul air entering the building.

Buildings Ordinance Cap. 123

The principal Hong Kong legislation controlling building works and use, supported by subsidiary regulations and Buildings Department codes of practice for design.

Lifts and Escalators Ordinance

Hong Kong Ordinance Cap. 618 regulating design, installation, maintenance and periodic examination of lifts and escalators by registered contractors and engineers.

Engineers Registration Ordinance

Hong Kong Ordinance Cap. 409 establishing the Engineers Registration Board and the register of registered professional engineers in specified disciplines.

Fire safety code of practice

Hong Kong code covering means of escape, fire resisting construction, means of access and firefighting installations, used to demonstrate compliance with the Buildings Ordinance.

Hierarchy of control

Order of risk control measures: eliminate the hazard, substitute, apply engineering controls, then administrative controls, with personal protective equipment as the last resort.

ALARP principle

Requirement to reduce risk so far as is reasonably practicable, balancing the cost of further control against the reduction in risk achieved.

Confined space entry

Work in an enclosed space requires a permit, atmospheric testing for oxygen, flammable and toxic gases, a standby person and rescue arrangements before entry.

Swiss cheese model

Accident causation model in which failures in multiple defensive layers must align for harm to occur; investigation should address latent system weaknesses, not only front-line error.

Critical path method

Network scheduling technique identifying the longest path through dependent activities, which has zero total float and determines the shortest project duration.

Cost performance index

Earned value metric CPI = EV/AC. A value below 1.0 indicates the project has spent more than the value of work completed, signalling cost overrun.

Liquidated damages

Contractual sum payable for delay, enforceable only if it is a genuine pre-estimate of the employer's loss rather than a punitive penalty.

Whistleblowing duty

Professional obligation to report a serious risk to public safety, escalating internally first and then to the appropriate authority if the concern remains unresolved.