BUILT-UP BACK PRESSURE

A pressure existing at the outlet of a pressure relief device occasioned by the flow through that particular device into a discharge system, as well as contributing flow from other sources into the same discharge system.

built_up_back_pressure pressure device flow discharge pressure_relief_device relief

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DIRECTIVITY FACTOR

The ratio of radiated sound intensity at a remote point on the principal axis of a loudspeaker or other transducer, to the average intensity of the sound transmitted through a sphere passing through the remote point and concentric with the transducer; the frequency must be stated.
The ratio of the square of the voltage produced by sound waves arriving parallel to the principal axis of a microphone or other receiving transducer, to the mean square of the voltage that would be produced if sound waves having the same frequency and mean-square pressure were arriving simultaneously from all directions with random phase; the frequency must be stated.

sound square ratio point principal average sphere pressure directivity_factor frequency voltage mean parallel axis

LIFTING DEVICE

A device to manually open a pressure relief valve by decreasing the spring loading in order to determine if the valve is in working order.

lifting_device working open pressure_relief_valve pressure relief relief_valve loading spring valve device

LEAK TEST PRESSURE

The inlet pressure used for a standard quantitative seat leakage test.

leak_test_pressure pressure inlet leakage standard

KNUDSEN VACUUM GAGE

Device to measure negative gas pressures; a rotatable vane is moved by the pressure of heated molecules, proportionately to the concentration of molecules in the system.

knudsen_vacuum_gage pressure gas vane device concentration measure

KIRCHHOFF'S EQUATIONS

Equations which state that the partial derivative of the change of enthalpy (or of internal energy) during a reaction, with respect to temperature, at constant pressure (or volume) equals the change in heat capacity at constant pressure (or volume).

kirchhoff's_equations pressure heat_capacity constant heat capacity internal enthalpy state

KILOBAR

A unit of pressure equal to 1000 bars (100 megapascals). Abbreviated kb.

kilobar pressure unit

KELVIN EQUATION

An equation giving the increase in vapor pressure of a substance which accompanies an increase in curvature of its surface; the equation describes the greater rate of evaporation of a small liquid droplet as compared to that of a larger one, and the greater solubility of small solid particles as compared to that of larger particles.

kelvin_equation pressure vapor_pressure rate substance evaporation vapor liquid curvature particles solid

JOULE-THOMSON COEFFICIENT

The ratio of the temperature change to the pressure change of a gas undergoing isenthalpic expansion.

joule-thomson_coefficient pressure ratio gas temperature

JOULE'S LAW

1. The law that when electricity flows through a substance, the rate of evolution of heat in watts equals the resistance of the substance in ohms times the square of the current in amperes. 2. The law that at constant temperature the internal energy of a gas tends to a finite limit, independent of volume, as the pressure tends to zero.

joule's_law pressure constant current constant_temperature heat rate substance square internal gas resistance

ISOTHERMAL CALORIMETER ISOTENISCOPE

An instrument for measuring the vapor pressure of a liquid, consisting of a U tube containing the liquid, one arm of which connects with a closed vessel containing the same liquid, while the other connects with a pressure gage where the pressure is adjusted until the levels in the arms of the U tube are equal.

isothermal_calorimeter_isoteniscope pressure tube vapor_pressure vessel vapor instrument gage pressure_gage arm closed

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