Heat Flux and
Heat Transfer | Thermal
Conductivity Diffusivity and Heat Capacity | Thermal
Sensors | Dictionary
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Dictionary
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Jump
directly to the following terms:
Heat Flux
| Heat Flux Sensor
| Heat transfer
| Medium
| Heat conduction
| Convective flux
| Radiative flux
| Thermal conductivity
| Thermal diffusivity
| Soil heat flux
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Heat Flux
Also know as thermal flux,
thermal flow, warmefluss, warmestromdichte (German),
flux thermique (French), flusso
thermico (Italian).
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Energy flowing through a certain imaginary
surface of 1 m2 in one second. Vector quantity. Usually the flow in one
dominant direction is considered. Unit: W/m2. The energy can be transported
by means of conduction, convection or radiation.
Usually the measurement of heat flux is done using a solid state sensor, in which case
the flow is locally converted to a conductive heat flux (heat flux at the surface of a
wall), or altogether interrupted (radiation measurement by means of a radiation sensor).
See also Thermal Sensors or Heat Flux. |
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Heat flux sensor
Also known as heat flux
plate, heat flux microsensor, carmeflussplatte (German),
capteur de flux thermique,
fluxmetre, (French), flussimetro (Italian), TNO heat flux sensor (brand name), REBS Q7
(brand name), Hukseflux HFP 01 (brand name).
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A sensor with which the heat flux is
measured. Usually the sensor consists of a differential temperature sensor, incorporated
in a medium of constant properties. The shape usually is flat. The sensor is mounted in or
on the object of interest, and usually generates an output that is proportional to the
local heat flux perpendicular to the sensor surface. See also Thermal Sensors
or Heat
Flux & Transfer
and Products. |
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Heat Transfer
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Heat is transferred by
convection, conduction and radiation.
Examples in daily life: a strong source of radiative
transfer is the sun. Convection plays a large role in controlling body
temperature. Convective transfer is strongly related to wind speed.
Conduction transports heat through the wall of a
building. |
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Medium
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The material in which the sensor is
located. The thermal properties of the medium can influence the accuracy of the
measurement. |
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Heat conduction
Also known as flux
conductif.
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Transport of heat through solid media is
taking place either by radiation, if the material is transparent in the particular
spectral range, or by conduction. |
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Convective flux
Also know as flux
convectif (French).
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Transport of heat in gasses can take place
by conduction, radiation of convection. The conduction is usually negligible, unless very
short distances are involved. Gasses are transparent to most radiation. If energy is
transported by flowing gas, this is called heat convection. Convection is often induced by
density differences that are caused by temperature differences. In conditions without
forced flow, a gas exchanges energy with a solid object at a rate of 5 W/m2/C
(C temperature difference between the objects). In forced flows, the
transfer becomes larger. In physics handbooks this is expressed by means
of a transfer coefficient. In indoor situations, the transfer coefficient
varies from 5 W/m2/C (at zero wind speed) to 9 W/m2/C
at 1 m/s. The transfer coefficient can be measured using HFP01SC
or TP01. |
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Radiative flux
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Objects of a certain temperature irradiate
heat. The transport between two objects of radiative heat depends on the temperatures and
the spectral properties. As a rule of thumb, at a temperature of around 20 degrees C, the
energy exchange between two blackbodies is 5 W/m2/C. |
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Thermal conductivity |
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Material property, expressing the
resistance of a material to energy transport in a semi-static situation. Expressed in
W/m.K. Energy per second transported through the medium per square meter, when a
temperature gradient of 1K/m is forced upon the medium. See also Thermal Conductivity and
Products. |
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Thermal diffusivity |
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Material property, expressing the speed of
temperature change of a medium when exposed to changes in the thermal environment. The
thermal diffusivity is inversely proportional to the heat capacity and proportional to the
thermal conductivity. Expressed in m2/s. See also Thermal Conductivity. |
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Soil heat flux Also known as boden
warmefluss (German), flux thermique du sol (French), flusso thermico nel Suolo (Italian). |
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The heat flux through the soil is an
important parameter in energy balance studies. The scientific disciplines that study this
phenomenon are mainly meteorology and climatology. See also Meteorology.
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