the Aviation Dictionary

thermal circulation . thermoelectricity
thermal circulation - The movement of air resulting thermal turbulence - Low-level turbulence (LLT) that
from differential heating.
is produced dry convection (thermals) in the boundary
thermal coefficient of resistance - The amount a
layer.
material's resistance changes with a change in thermal wave - Waves, often but not always marked by
temperature.
cloud streets, that are excited by convection disturbing
an overlying stable layer. Also referred to as
thermal conduction - The transfer of heat energy from
convection waves.
one object to another.
thermals - A rising bubble of warm air. An element of
thermal conductor - A material, such as metal, that can
convection.
easily transfer heat energy.
thermionic - The electron emission caused by an incanthermal
cutout switch - A circuit breaker, or switch,
descent material.
that breaks the circuit at a predetermined temperature.
thermionic current - Current flow in a conductor
thermal decomposition - A chemical action that
caused by heat.
decomposes a material into simpler substances by the
action bf heat.
thermistor - A semiconductor device with a core
material whose electrical resistance changes with a
thermal efficiency - The ratio of the amount of heat
change in temperature.
energy converted into useful work to the amount of
heat energy in the fuel used.
thermoammeter - An instrument for measuring RF
(radio frequency) alternating current in a circuit. The
thermal expansion - The expansion of a substance due
thermoammeter measures the RF alternating current by
to heat.
exposing a thermocouple to the RF energy. As the wire
thermal fatigue - A condition in turbine metals caused heats, it produces a current proportional to the amount
by heating and cooling each time a power setting is of applied heat. This is displayed as current by the
changed.
meter instrument.
thermal index (TI) - In soaring, an index used to
indicate the probability of thermals forming. It is the
temperature, for any given level, of the air parcel
having risen at the dry adiabatic lapse rate (DALR)
subtracted from the ambient temperature. Experience
has shown that a TI should be -2 for thermals to form
and be sufficiently strong for soaring flight.
thermal insulator - Materials such as paper, wood, etc.
that are poor conductors of heat energy.
thermal output - Amount of heat being discharged.
thermal relief valve - A pressure relief valve installed
in a static portion of a hydraulic system to relieve
pressure built up due to heat induced expansion.
thermal runaway - A condition existing in a
nickel-cadmium battery when the cell resistances
become unbalanced because of temperature. The
resistance of some cells decreases and allows the cells
to take more current, which lowers their resistance
even further and creates more current. This action
continues until the battery is seriously damaged,
sometimes exploding.
thermal shock - A stress induced into a system or
component due to a rapid temperature change.
thermal stress cracking - In composites, the crazing
and cracking of some thermoplastic resins from
overexposure to elevated temperatures.
thermal switch - A switch activated by heat.
thermocouple - A temperature measuring system
consisting of two dissimilar metal wires joined at a
temperature sensing point. A current proportional to
the temperature of the junction is produced. In aviation,
thermocouples are generally used as a temperature
sensing device.
thermocouple exhaust temperature probe - A
bimetallic probe, generally of chromel and alumel
alloy, located in an exhaust stream. Heat causes a
milliampere current to flow to a cockpit indicator that
indicates degrees in Celsius.
thermocouple fire detector - A device that produces an
electrical current flow by thermal action and which
ultimately illuminates a cockpit warning signal.
thermocouple oil temperature bulb - A thermocouple
positioned in the oil flow to provide a cockpit indicator
with an oil temperature indication. It is generally made
up of bimetallic materials such as chromel and
constantan.
thermodynamic diagram - A chart presenting isopleths
of pressure, temperature, water vapor content as well as
dry and saturated adiabats. Various forms exist, the
most commonly used in the United States being the
Skew-TILog-P.
thermodynamics - The branch of science that deals
with mechanical actions caused by heat.
thermoelectricity - Electrical energy generated by the
action of heat on the junction of two dissimilar metals.
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