Hukseflux

Thermal Sensors

MARKET LEADER IN HEAT FLUX MEASUREMENT

Hukseflux – heat flux measurement at the next level
Hukseflux is the global market leader in heat flux measurement. This white paper briefly explains the fundamentals of measuring with heat flux sensors.
It also offers general directions what to watch out for and some, perhaps surprising, applications of heat flux sensors. Would you like to get more information?
Please contact Hukseflux.
Heat flux sensors measure energy flux onto or through a surface in [W/m2]. The heat may be transported by conduction, radiation or convection. All heattransfer is driven by temperature differences, flowing from a hot source to a cold sink. Convective and conductive heat flux is measured by letting thisheat flow through the sensor. Radiative flux is measured using heat flux sensors with black absorbers; the absorber converts radiative to conductiveenergy. Hukseflux started in 1993 designing sensors for measurement of heat flux in soils and through walls. In the course of the years, we have added
specialised sensors and systems for many other applications.
Heat flux sensors manufactured by Hukseflux are optimised for the demands of different applications. The most important variables are:
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rated temperature range
rated heat flux range
sensitivity
response time
chemical resistance, safety requirements
size, shape and spectral properties

Hukseflux heat flux sensors typically employ thermopiles. Thermopiles generate a signal, as a result of the temperature difference between the hot andcold side of the thermopile. The signal is proportional to the heat flux. Thermopiles are passive sensors; they do not require power. The output usually isa small millivolt signal. Pictures show models SBG01 water-cooled heat flux sensor, IHF01 industrial heat flux sensor and FHF02 foil heat flux sensor.

Water-cooled heat flux sensor
for radiative flux

High-temperature all-metal heat fluxsensor (industrial)

Plastic flexible heat flux sensor(general purpose)© Copyright by Hukseflux. Version 2030. Page 1/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com

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MARKET LEADER IN HEAT FLUX MEASUREMENTThermal Sensors

Measurement with a heat flux sensor; what matters most?
On this page, the fundamentals of heat flux measurement are briefly explained. These are general considerations for measuring heat flux.

Thermal contact sensor to heat sink

Representativeness in time and space; average!
A heat flux sensor measures at a certain location. Is this location
representative of what you need to measure? If possible, use a relatively
large sensor, rather than a small one, and consider use of multiple sensors.
Thermal processes often have large time constants; instantaneous
measurements may be misleading. Average to get the full picture.

A small layer of air often forms a major contribution to
the thermal resistance. Make sure that there is good thermal
contact between sensor and environment or heat sink. Avoid airgaps. Use double-sided tapes, welded connections, graphite
sheets. Use Power strips to fill up gaps.
Read our note How to install a heat flux sensor with tips & tricks.

Optical properties
When heat flux sensors also measure radiation, pay attention to
the surface colour. If needed paint the sensor surface. Please mind
that shiny metallic surfaces reflect both infra-red and visible
radiation. Paints may have different colours in the visible range,
but are usually “black” absorbers and at the same time black
emitters in the far-infra-red.

Absolute temperature
Sensors are calibrated at room temperature T CAL. Typicaltemperature dependence is in the order of 0.15 % / K. When
working at high or low temperatures T, ask for the temperaturedependence. Typically, this is a linear correction with (T – T CAL).
Self-calibrating sensors may compensate for temperaturedependence.

Edge effects
A heat flux sensor locally distorts the heat flow
pattern, in particular around the edges of the sensor;
the heat may have a preference to travel through thesensor rather than through the surrounding material.
A passive guard, i.e. a non-sensitive part around thesensor is essential to avoid errors due to edge effects.
On a smaller scale, this effect may again play a role:
see the text block on micro effects.

Sensor thermal
resistance
A heat flux sensor distorts
the local heat flux. In order tominimise this effect, use the sensor
with the lowest possible thermalresistance.

Noise? Pay attention to signal ground
Signals from thermopiles are small DC voltages in the microvolt range. Theseare easily distorted. To guarantee immunity to external sources pay attention togrounding and shielding. A good starting point is to make sure that signal wires
are well insulated from the environment (no possibility for ground loops) andare well protected against humidity ingress (possibly creating electrical contact)

Micro effects – thermal conductivity dependence
In case the thermopile sensor has direct exposure to the environment, there isa risk of so-called micro effects; on a micro scale (scale of the thermopile grid),
the local heat flux gets distorted, and shows a preference to travel though thethermopile. The result is that sensor sensitivity changes as a function of thethermal conductivity of the environment. The calibration is no longer valid. A
thermal spreader, for example using a metal cover, is a proven countermeasure. The heat flux then first meets a metal plate and the thermopile
always has the same thermal environment.

© Copyright by Hukseflux. Version 2030. Page 2/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com

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MARKET LEADER IN HEAT FLUX MEASUREMENT

Thermal Sensors

Heat flux sensors in insulation testing
Hukseflux Thermal Sensors is the global market leader in heat flux measurement. Here are some examples of heat flux sensor application:

In situ study of LNG
tanker insulation
with HFP03 special designClothing thermalperformance
Analysed with FHF02

Insulation ofcar parts
Analysed with FHF02

Building envelope
thermal resistance
Measure it with HFP01
and TRSYSIn situ verificationof airplane insulation
With HFP03

Solar hot water storage
Analysis of system performanceand heat loss with HFP01 andHFP03

Heat loss andinsulation of industrial
installations heat flux
With IHF01 and IHF02

Industrial insulation
performance
Analysed with FHF and IHF
sensors

Heat flux / insulationof home appliances
With HFP01 and FHF02© Copyright by Hukseflux. Version 2030. Page 3/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com

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MARKET LEADER IN HEAT FLUX MEASUREMENT

Thermal Sensors

Heat flux sensors characterising the thermal environment
Hukseflux Thermal Sensors is the global market leader in heat flux measurement. Here are some examples of heat flux sensor application:.

[Indoor climate studies
With HFP01 and TCOMSYS

Server park thermal
management
Analysis of electronics cooling efficiency
by airflow with TCOMSYS and FHF03

Electronics
components heat flux
measurement

Human thermalcomfortmeasurement,
thermal mannequin

Analysed with FHF03

Special equipment made with

Ground surface energy balance
Eddy covariance / Bowen ratio
Soil heat flux measurement in meteorology
with HFP01SC

Bread oven thermal /heat flux profilingWith FHF02

Microclimate in cars
Thermal climate and humanthermal comfort with TCOMSYS

Industrial (aluminiumreduction cell) heat flux
and temperature survey
With IHF01 / IHF02 and ALUSYS,
input for modelling reduction
process and cell behaviour© Copyright by Hukseflux. Version 2030. Page 4/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com

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MARKET LEADER IN HEAT FLUX MEASUREMENT

Thermal Sensors

Heat flux sensors in fire / flammability / high heat flux
Hukseflux Thermal Sensors is the global market leader in heat flux measurement. Here are some examples of heat flux sensor application:

Fire academy / education
Get a better feeling for heat flux levels
With HF02 + LI19

Battery thermal runaway / fireStudy the runaway process and flammability
with FHF03 and SBG01

Forest fireresearchCone calorimetercalibration

Study heat forest firesiSBG01

Calibrate and adjust the heat flux
level with water-cooled SBG01

Welding torch heat
flux measurement
Determining human andequipment exposure toheat sources
With HF03 portable heat flux
sensorStudy heat transfer by flames
with HFS1 and GG01

Full scale fire testing
Study of flame spread with
SBG01 on “full scale wooden
school building fire test”© Copyright by Hukseflux. Version 2030. Page 5/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com

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MARKET LEADER IN HEAT FLUX MEASUREMENT

Thermal SensorsHeat flux sensors in process monitoring & control
Hukseflux Thermal Sensors is the global market leader in heat flux measurement. Here are some examples of heat flux sensor application:

Boiler water wall fouling
Heat flux sensors may be included on the steam tube
surface of boiler tubes! From the trend in heat flux, users
can analyse flame position and fouling of the surface. This isdone with an adapted IHF01. Data are used for sootblower
control / cleaning scheduling

Blast furnace refractory performance
Analysed with NF01 in the shell; improved
emergency response in case of process overheatingor cooling water malfunction

Flare monitoring
Improving safety for equipment andpersonnel. Issue warnings with HF02

Catalytic cracker fouling
measurement
Analysed with HF05 and a meteorologicalstation. Input data are used to schedule
servicing. Fouling translates in lower heat flux

Pharmaceutical vial
freezing / freeze-drying

Solar concentrator boiler heat flux

Control of freeze drying / verify if
sufficient heat is transferred via asurface heat flux measurement

Verify the heat flux level, prevent overheating,with a special IHF01 on the boiler pipe

Ice rink thermal control
Solar radiation
heat flux for PV system
performance assessment
With pyranometer model SR30

Improved with HFP01; heat flux
sensors react faster and have ahigher resolution thantemperature sensors

Plastics and composite
process- and flow front
monitoring
Process monitoring of the flow
front and of the curing process inthe mould with the sensitive NF02

© Copyright by Hukseflux. Version 2030. Page 6/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com

Hukseflux

MARKET LEADER IN HEAT FLUX MEASUREMENT

Thermal Sensors

Heat flux sensors in specialised measurement applications
Hukseflux Thermal Sensors is the global market leader in heat flux measurement. Here are some examples of heat flux sensor application:

S

Solar concentrator heat flux
Water-cooled SBG01 to measure heat fluxof a solar concentrator

Thermal mannequin
Equipped with FHF02

Engine overheating studies
Overheating studies in racecars

Human and animal
metabolism studies
with HFP01 and FHF02

Physics education
Experiments in calorimetry,Stefan-Boltzmann's law ofradiation, heat transferGeothermal heat flux /permafrost melting
Measure at ultra-low heat flux levels
with HFP03 or multiple HFP01’s

Performance evaluationof IR heaters andradiant panels
Using FHF02 and TCOMYS

Solar simulator /climate testing of cars
Using pyranometer SR30 andheat flux sensor FHF02© Copyright by Hukseflux. Version 2030. Page 7/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com

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MARKET LEADER IN HEAT FLUX MEASUREMENT

Thermal Sensors

Heat flux sensors various applications / as OEM component
Hukseflux Thermal Sensors is the global market leader in heat flux measurement. Here are some examples of heat flux sensor application as a component inmeasuring equipment made by other manufacturers than Hukseflux.

Monitoring andcontrol of freeze
dryinglaser power measurement
With adapted FHF02

With FHF02

body core temperature
measurement (zero heat flux
temperature measurement)
With FHF02 and FHF02SC

LED thermal power
calorimeter
Designed for the Zhagi
consortium; TPL01

heat flow meter apparatus
Thermal conductivity measurement of insulationmaterials with an adapted FHF02 at its coreheat flow reaction calorimeterWith adapted FHF01© Copyright by Hukseflux. Version 2030. Page 8/8. For Hukseflux Thermal Sensors go to www.hukseflux.com or e-mail us: info@hukseflux.com