Thermal precision: advantages and applications of heat

Thermal precision: advantages and applications of
heat flux sensors
Heat flux sensors offer a variety of advantages like dynamic measurements with ultra high resolution of thermal energies. Until
recently, thermal sensors could not be manufactured with the necessary specs for the mass market. With greenTEG’s gSKIN® sensor
a cost-effective and reliable heat flux sensor is now available.
Dynamic high-resolution thermal measurements
gSKIN® thermal sensors measure
dynamic thermal influences in the
form of heat fluxes or temperature
differences. They offer ultra-high
resolution of thermal parameters.
Temperature differences of 10 μK as
well as heat fluxes below 0.05 W/m2
can be resolved.
Heat flux is the rate of heat energy passing through a surface. Depending on the exact definition of heat flux, its unit
can be expressed as either W/m2 or W. Temperature differences in a given system induce a heat flux. The induced heat
flux always flows from the hot to the cold side. Heat fluxes
occur everywhere.
In contrast to temperature sensors, gSKIN® sensors are
able to measure this heat flux (dynamic) instead of the thermal status (which is temperature). More information about
heat flux measurement can be found at [1].
gSKIN® sensors are based on the Seebeck-Effect. The sensors contain a large amount of active piles made of an optimized semiconductor compound. Each pile generates a
voltage in the nV to µV range. This voltage is proportional
to the temperature difference and the heat flux flowing
through it. By connecting the piles in series, the small voltages are added up and allow for a larger signal and a precise
read-out. The key features of greenTEG’s heat flux sensors
are:
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Ultra-high resolution of thermal energies and temperature differences (< 0.05 W/m2 / < 10 µW / < 10 µK)
Integration via soldering, gluing or clamping
Broad range: -150 kW/m2 to 150 kW/m2
Minimal invasiveness & thickness
Ultra-low noise based on low impedance
Highly homogeneous across surface
Until recently, heat flux sensors were only available as large
devices. They could not be manufactured according to mass
market requirements. A high price per sensor unit prevented large volume applications.
Where are gSKIN® thermal sensors applied?
gSKIN® thermal sensors are applied in a variety of settings
and applications.
Flow monitoring
Today’s calorimetric mass flow sensors use temperature
sensors as the core sensing element. While this type of
mass flow sensor is tried and tested, it is nonetheless not
the most cost-effective solution. Mass flow sensors can be
improved by addressing the two main concerns of temperature-based mass flow sensors:
a) Manufacturing high precision mass flow sensors
requires the use of two high resolution temperature
sensors (in the mK range). These temperature sensors
are very expensive and must be handled with care. This
results in a more complex and expensive manufacturing process. In contrast, gSKIN® sensors are much more
robust and deliver the same level of resolution.
b) Temperature-based mass flow sensors are invasive
sensors: typically two temperature probes are inserted
into the fluid to be measured. These probes create local
turbulences which distort the measurement. While
these turbulences can be controlled to some extent, it
is preferable to not create the turbulences in the first
place. Using gSKIN® sensors as the core sensing element gives the possibility to manufacture non-invasive
mass flow sensors.
Core body temperature monitoring
The core body temperature is an important parameter
when making assessments of the human body’s state. The
information can be used in a variety of applications:
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Performance optimization for athletes
Monitoring in incubators for prematurely born children
Alert functions for people working in dangerous environments (e.g. firefighters)
In these and other applications, it is crucial to get reliable
data of the core body temperature. Most of today’s measurement concepts use only temperature sensors to do this.
These methods give a good approximation, but cannot
measure the core temperature directly (unless inserted in
the human body). A method for measuring core body tem-
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perature using one gSKIN® Heat Flux Sensor and one temperature sensor is described at [2]
Precision Systems
Thermal influences are present in all systems and limit the
achievable precision e.g. by inducing thermal expansion.
In order to compensate for these effects, it is important to
measure the thermal influences.
The current approach to control thermal effects is based on
multi-parameter models. These models are derived empirically, and are used to measure and predict thermal influences. The most common parameters in such models are
temperatures at various locations in the system and situational information (e.g. power consumption of motor).
A certain compensation of thermal effects is accomplished
with this method. However, in applications like dosing systems, positioning systems, lithography, bonding systems,
and metrology systems, higher measurement precision and
robustness towards external factors like changing ambient
temperature is required to obtain a satisfactory compensation. This is where heat flux sensors provide clear advantages.
Ressources
[1] http://www.greenteg.com/heat-flux-sensor/definitionof-heat-flux
[2] http://www.greenteg.com/heat-flux-sensor/mass-flowmeasurement
[3] http://www.greenteg.com/heat-flux-sensor/u-valuemeasurement
Contact
greenTEG AG
Technoparkstr. 1
8005 Zurich
Switzerland
www.greenTEG.com
[email protected]
+41 44 632 04 20
A company providing metrology solutions increased the
precision of their product by a factor of four with gSKIN®
Heat Flux Sensors.
Building Intelligence
Thermal energy enters buildings mainly from the heating
system and from solar irradiation. The energy exchange
between the building and the outside is focused through
the roof, walls, windows and thermal bridges e.g. balconies,
into the soil and through exchange of ambient air. Every
building is a complex thermal system and to optimize it (for
example to reduce heating costs), precise data is necessary.
Within the field of building physics, the gSKIN® Heat Flux
Sensor is used to:
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Compare the amount of heat transferred through different walls or the same type of walls, but located in
buildings with different weather patterns.
Calculate the thermal conductivity (U-value) of walls
and find out if you have a well-insulated building. More
detailed information about U-value Measurements is
available at [3].
Quantify the energy balance of a room: How much
energy is coming from the heating and where is this
energy lost?
Analyze the thermal behavior of rooms and buildings
at different temperature levels.
Raise the efficiency of thermal building automation.
Like temperature sensors, heat flux sensors can be applied
in many more applications. They need to be easy to integrate and cost-effective. Both factors have been achieved
with greenTEG’s products.
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