IESL Part I key terms

The water content remaining in soil after excess water has drained away by gravity, usually one to three days after rain or irrigation. It represents the upper limit of water readily available to plant roots.

The soil moisture level below which plants can no longer extract water and remain wilted even after rewetting. It marks the lower limit of plant-available water in the root zone.

The amount of water held in soil between field capacity and permanent wilting point that crops can actually use. It depends on texture and organic matter and guides how much irrigation to apply.

Deciding when and how much water to apply to a crop, based on soil moisture, evapotranspiration, or plant indicators. Good scheduling avoids both under-watering stress and wasteful deep percolation losses.

The combined loss of water from soil evaporation and plant transpiration to the atmosphere. Reference values are used to estimate crop water demand and size irrigation systems.

The total quantity of exchangeable positive ions a soil can hold on clay and organic matter surfaces. Higher values mean better nutrient retention and buffering against fertilizer leaching.

The fraction of applied irrigation water that must drain below the root zone to keep soil salinity below a level that harms the crop. It rises with the salt content of the irrigation water.

The overall rate of heat transfer through a building element per unit area per degree of temperature difference, expressed in W/m2K. Lower values indicate better thermal insulation of walls, roofs, or glazing.

A path of higher heat conduction through a building envelope, such as a steel lintel or concrete slab edge, that bypasses insulation. It lowers effective R-value and can cause local condensation.

The temperature to which moist air must be cooled, at constant pressure, for water vapour to begin condensing. Surfaces colder than the dew point risk condensation and mould growth.

A graph relating dry-bulb temperature, wet-bulb temperature, humidity ratio, relative humidity, and enthalpy of moist air. Engineers use it to analyse air-conditioning and ventilation processes.

The ratio of useful heating or cooling delivered by a heat pump to the electrical energy it consumes. Values above one are possible because the device moves heat rather than generating it.

Dividing a building into zones with fire-resisting walls, floors, and doors to limit the spread of fire and smoke. It protects escape routes and gives occupants time to evacuate.

The gradual reduction in soil volume caused by squeezing out pore water under sustained load, typical of saturated clays. It continues over years and must be predicted for structures on soft ground.

The stress carried by the soil skeleton, equal to total stress minus pore water pressure. It governs soil strength and compressibility, so rising groundwater reduces stability.

The maximum pressure a soil or rock foundation can support without shear failure or excessive settlement. Designers compare it with applied footing pressure and apply a factor of safety.

A simple field test measuring the drop in height of fresh concrete in a standard cone, indicating workability. Results guide adjustments to water content before placing and compacting.

The mass of water divided by the mass of cement in a concrete mix. Lower ratios increase strength and durability but reduce workability, so admixtures are often used.

An accounting of material entering, leaving, and accumulating within a process boundary, based on conservation of mass. It is the first step in sizing equipment and checking process performance.

An accounting of all energy entering, leaving, and accumulating in a system, including heat, work, and enthalpy changes. It supports utility sizing and efficiency analysis in process design.

A single physical processing step such as distillation, filtration, or drying that transforms material without changing its chemical identity. Complex plants are designed by combining these standard steps.

A device that transfers thermal energy between two fluids at different temperatures without mixing them. Common types include shell-and-tube and plate units, rated by overall heat transfer coefficient.

A dimensionless ratio of inertial to viscous forces in a flowing fluid, used to predict whether flow is laminar or turbulent. It determines friction factors and heat transfer correlations.

The ratio of real power to apparent power in an alternating-current circuit, equal to the cosine of the phase angle. Low values increase current and losses, so utilities may penalise them.

A method of expressing voltages, currents, impedances, and powers as fractions of chosen base values. It simplifies fault and load-flow calculations across transformer voltage levels.

A static device that changes alternating voltage and current levels through magnetically coupled windings. It enables efficient transmission at high voltage and distribution at safe utilisation levels.

A sensing device that detects abnormal currents, voltages, or frequencies and commands a circuit breaker to trip. Correct coordination isolates faults while keeping healthy sections energised.

A stability test for feedback systems that examines the open-loop frequency response around the critical point minus one. It indicates closed-loop stability and the gain and phase margins available.

A pair of graphs showing magnitude and phase of a system's frequency response against logarithmic frequency. Engineers read gain margin and phase margin from it to judge closed-loop stability.

A feedback controller that combines proportional, integral, and derivative action on the error signal. Each term trades speed, steady-state accuracy, and damping, and gains must be tuned.

The rule that a signal must be sampled at more than twice its highest frequency component to be reconstructed without error. Violation causes aliasing, so anti-alias filters precede converters.

The error introduced when a continuous signal is rounded to discrete digital levels by an analogue-to-digital converter. Its magnitude falls as resolution in bits increases.

A 32-bit pattern that separates the network portion of an IPv4 address from the host portion. It determines which destinations are local and which must be reached through a router.

Classless Inter-Domain Routing notation that writes an address block as a prefix length, such as /24. It allows flexible allocation of address space and efficient route aggregation.

A seven-layer reference framework describing how network functions are partitioned, from physical transmission up to applications. It helps engineers isolate faults and match protocols to layers.

Mechanisms in the Transmission Control Protocol that adjust sending rate in response to network congestion signals such as loss or delay. They aim to share bandwidth fairly without collapse.

The maximum theoretical efficiency of a heat engine operating between two reservoir temperatures, equal to one minus the ratio of absolute cold to hot temperature. No real cycle exceeds it.

The ideal cycle describing steam power plants, comprising pump, boiler, turbine, and condenser processes. Efficiency improvements include reheating and regenerative feedwater heating.

A thermodynamic property measuring the dispersal of energy in a system; it increases in any real spontaneous process. It sets the direction of heat flow and limits achievable work.