HKIE Professional Assessment - Mechanical Discipline key terms

Energy is conserved: the heat added to a closed system equals the change in its internal energy plus the work it performs. For open systems, enthalpy and flow work replace internal energy.

A thermodynamic property equal to internal energy plus the product of pressure and volume. It conveniently tracks heat transfer in constant-pressure processes such as boilers, condensers and air heating coils.

A control-volume balance stating that mass and energy entering equal mass and energy leaving when conditions do not change with time. It underpins analysis of turbines, pumps, fans and heat exchangers.

The ratio of useful cooling or heating delivered to the work input consumed by a refrigeration or heat-pump cycle. Higher values indicate greater energy efficiency for the same duty.

For steady, incompressible, frictionless flow along a streamline, the sum of pressure head, velocity head and elevation head is constant. It links pressure, speed and height in pipe and duct flow.

A dimensionless ratio of inertial to viscous forces in a flow. It predicts whether flow is laminar or turbulent and governs friction factor selection in pipe and duct design.

A formula expressing head loss in a pipe as a function of friction factor, length, diameter and velocity head. It is the basis for sizing water and air distribution systems.

A plot of applied stress against resulting strain for a material under load. It reveals elastic modulus, yield strength, ultimate strength, ductility and toughness, guiding material selection and safe working stresses.

The stress at which a material begins to deform permanently, typically identified by a small offset from the linear elastic region. Design codes often limit working stress relative to this value.

The ratio of a component's capacity or strength to the maximum expected load or stress. It accounts for uncertainty in loads, material properties, analysis assumptions and consequences of failure.

A frequency at which a structure or machine freely vibrates when disturbed. Operating speeds and excitation frequencies must be kept away from it to avoid amplified resonant response.

A condition in which an excitation frequency matches a system's natural frequency, producing large amplitude vibration. It can cause rapid fatigue damage or catastrophic failure of machinery and structures.

The use of resilient mounts, springs or inertia bases to reduce transmission of vibration between machines and their supporting structure. Selection depends on machine forcing frequency and mount stiffness.

A fluid used in a vapour-compression cycle that absorbs heat by evaporating at low pressure and releases it by condensing at high pressure. Selection considers ozone depletion and global warming potential.

A packaged machine that removes heat from water or air using a refrigeration cycle, producing chilled water for air handling units. Condensers reject the absorbed heat to ambient air or cooling water.

A factory-assembled or built-up unit containing fans, coils, filters and dampers that conditions and distributes air to served spaces. Its performance determines supply airflow, temperature and indoor air quality.

A graphical tool relating dry-bulb temperature, moisture content, relative humidity, enthalpy and specific volume of moist air. It is used to analyse cooling, heating and humidification processes in air conditioning.

An electronic device that adjusts the speed of an electric motor by varying supply frequency or voltage. Applied to pumps and fans, it reduces energy use substantially at part-load conditions.

Relationships stating that fan or pump flow varies with speed, pressure with speed squared and power with speed cubed. They justify variable speed control as a major energy-saving measure.

A systematic review of energy consumption and cost in a building or process, identifying inefficiencies and prioritising improvement measures. Findings support investment decisions and energy performance reporting.

A local regulatory document setting minimum energy efficiency requirements for building services installations such as lighting, air conditioning, electrical and lift systems. Compliance is verified through design submissions and audits.

The process of testing and adjusting installed systems so they perform according to design intent and operational requirements. It includes functional performance tests, documentation and operator training before handover.

A structured test of equipment at the manufacturer's works against specified performance and safety criteria before shipment. Passing it reduces risk of defects appearing during site installation and commissioning.

Scheduled inspection, servicing and replacement of equipment at planned intervals to prevent breakdowns. It extends asset life and supports statutory examination requirements for lifts, boilers and pressure vessels.

Measuring parameters such as vibration, temperature, oil analysis and performance trends to detect developing faults in machinery. It allows maintenance to be planned before failure occurs.

A design philosophy checking that a structure or component will not exceed ultimate states such as collapse or serviceability states such as excessive deflection. Partial safety factors are applied to loads and resistances.

Choosing materials by comparing required properties such as strength, corrosion resistance, temperature capability, machinability and cost against service conditions and applicable standards. Documentation must justify the choice.

Accelerated corrosion occurring when two dissimilar metals are in electrical contact in the presence of an electrolyte. Design should isolate dissimilar materials or select compatible couples to avoid premature failure.

A technique that prevents corrosion of buried or immersed metal by making it the cathode of an electrochemical cell, using sacrificial anodes or an impressed current. It is common for pipelines and tanks.

A structured process identifying hazards, evaluating the likelihood and severity of harm, and defining controls to reduce risk to an acceptable level. Results must be recorded and reviewed as work changes.

A ranked order of risk controls: eliminate the hazard, substitute, use engineering controls, apply administrative controls, then rely on personal protective equipment. Higher-ranked measures are more reliable.

A formal written authorisation controlling high-risk activities such as hot work, confined space entry or isolation of hazardous energy. It records precautions, authorisations and handover before work begins.

A systematic examination of an accident or near miss to establish sequence, immediate and root causes, and corrective actions. The aim is prevention rather than blame, with findings shared and actions tracked.

Planned activities and documented procedures that ensure work consistently meets specified requirements. It differs from inspection, which checks finished output, by focusing on preventing defects.

A scheduling technique identifying the longest sequence of dependent activities that determines project duration. Delays on critical activities delay completion, so management attention focuses there.

A formal instruction changing the scope, quantity or timing of contracted work, with valuation of cost and time effects. It must be issued under the contract to remain valid and auditable.

A situation where an engineer's personal, financial or other interest could improperly influence professional judgement. It must be disclosed promptly and managed, often by withdrawal from the affected decision.

Meeting present needs without compromising the ability of future generations to meet theirs. Engineers apply it through resource efficiency, lifecycle thinking, emissions reduction and whole-life cost analysis.