Heat Transfer and Psychrometry Vocabulary

Vocabulary flashcards covering core definitions and terms from heat transfer and psychrometry lecture notes.

Overall coefficient of heat transfer

The rate of heat transfer that is governed by all three processes of conduction, radiation, and convection, depending on the particular configuration of the equipment involved.

Hypothermia

Also known as Systemic Cold Stress, it is the condition of having an abnormally low deep body or 'core' temperature, occurring below $35^\circ\text{C}$.

Enthalpy

The sum of the sensible internal energy and pressure energy of the dry air and water vapour components of an air/water vapour mixture, expressed in $\text{kJ/kg}$ dry air.

Microbiological fouling

An accumulation of biological micro-organisms in the tubes, including bacteria, algae, and fungi.

Sigma heat/energy

The enthalpy of the air/water vapour mixture minus the enthalpy of the water vapour in the liquid phase at the wet bulb temperature, expressed in $\text{kJ/kg}$ dry air.

Factors affecting radiation heat transfer rate

The difference between the fourth powers of the absolute temperatures of the two exchanging surfaces, the area of the smaller of the two surfaces, and the emissivity and view factor.

Symptoms of condenser tube fouling

Reduced duty of the condenser, increase in condenser pressure, and increase in load on the compressor.

Dry-bulb temperature ($t_{db}$)

A measure of sensible internal energy indicated by a conventional thermometer, expressed in $^\circ\text{C}$.

Wet-bulb temperature ($t_{wb}$)

A measure of the evaporative capacity of the air when used together with dry-bulb temperature, indicated by a thermometer whose bulb is covered by a wetted wick of cotton and exposed to an air flow of $3\,\text{m/s}$.

Atmospheric air

A mixture of dry air and water vapour.

Dew-point temperature ($t_{dp}$)

The temperature to which a quantity of air must be cooled at constant pressure for the condensation of water to begin, at which point the air is $100\%$ humid or saturated.

Partial pressure ($P_a$ or $P_v$)

The pressure that dry air or water vapour in a sample of atmospheric air would exert on the walls of the container if it alone were present at constant temperature, measured in $\text{kPa}$.

Total pressure ($T_p$)

The sum of the partial pressures of dry air and water vapour in a quantity of atmospheric air, expressed as $T_p = P_a + P_v$ in $\text{kPa}$.

Vapour pressure ($P_v$)

The partial pressure of the $\text{H}_2\text{O}$ vapour present in atmospheric air, which is known as saturated vapour pressure (SVP) when the sample is saturated.