Hukseflux BLK Series User manual

Copyright by Hukseflux | manual v2214 | www.hukseflux.com | [e-mail]
USER MANUAL BLK -GLD
STICKER SERIES
Black and gold stickers for measuring
convective and radiative heat flux separately
Hukseflux
Thermal Sensors

BLK - GLD sticker series manual v2214 2/47
Cautionary statements
Cautionary statements are subdivided into four categories: danger, warning, caution and
notice according to the severity of the risk.
DANGER
Failure to comply with a danger statement will lead to death or serious
physical injuries.
WARNING
Failure to comply with a warning statement may lead to risk of death or
serious physical injuries.
CAUTION
Failure to comply with a caution statement may lead to risk of minor or
moderate physical injuries.
NOTICE
Failure to comply with a notice may lead to damage to equipment or may
compromise reliable operation of the instrument.

BLK - GLD sticker series manual v2214 3/47
Contents
Cautionary statements 2
Contents 3
List of symbols 4
Introduction 5
1Ordering and checking at delivery 8
1.1 Ordering BLK – GLD stickers 8
1.2 Included items 10
2Instrument principle and theory 11
2.1 Introduction 11
2.2 Normal use: moderate-accuracy and comparative measurements 13
3Advanced use: high-accuracy measurements 14
3.1 Introduction 14
3.2 Spectral properties of BLK and GLD stickers 14
3.3 BLK and GLD sensors on the same heat sink 16
3.4 BLK and GLD sensors at different temperatures 20
3.5 Surface temperature correction at high flux levels 21
3.6 Optional correction for sensor temperature dependence 23
3.7 Working with high colour temperature sources; the Sun, Xenon lamps 24
4Examples of BLK and GLD in use 25
4.1 Outgoing radiation heat flux on metallic / reflective surfaces 25
4.2 Sources covering part of the sensor field of view; the view factor 26
4.3 Heat flux measurement to characterise ovens, thermal profiling 28
5Specifications of BLK – GLD sticker series 32
5.1 Specifications of BLK – GLD stickers 32
5.2 Dimensions of BLK – GLD stickers 34
6Installation of BLK – GLD sticker series 36
6.1 Application procedure 36
6.2 Site selection and sensor installation 38
7Maintenance and trouble shooting 40
7.1 Recommended maintenance and quality assurance 40
7.2 Trouble shooting 42
7.3 Calibration and on-site checks 42
8Appendices 43
8.1 Reflection versus wavelength and source temperature 43
8.2 EU declaration of conformity 46

BLK - GLD sticker series manual v2214 4/47
List of symbols
Quantities Symbol Unit
Heat flux ΦW/m²
Voltage U V
Sensitivity S V/(W/m2)
Temperature T °C or K
Temperature dependence of sensitivity TD %/K
Thermal resistance per unit area Rthermal,A K/(W/m²)
Heat transfer coefficient by convection Ctr (W/m2)/K
Area A m2
Reflection factor r -
Absorbance α-
Emissivity ε-
Stefan-Boltzmann constant: 5.67 x 10-8 σW/m²·K4
Optical view factor f -
Angle of incidence θ°
Solid angle SA sr
Subscripts
Property of sensor sensor
Property of heat sink sink
Property of a radiative source source
Measured radiative heat flux radiative
Measured convective heat flux convective
Sensor with black sticker BLK
Sensor with gold sticker GLD
Property of ambient air air
Property of ambient environment ambient
Total total
Emitted radiative flux emitted
Incoming radiative flux at the sensor position incoming
Absorbed radiative flux absorbed
Reflected radiative flux reflected
Abbreviations
Ultraviolet UV
Visible light VIS
Near-infrared NIR
Far-infrared FIR

BLK - GLD sticker series manual v2214 5/47
Introduction
Heat flux measurement is a powerful tool to gain insights into processes involving
thermal energy. Heat is transported to an object by convection and radiation. Studying
thermal processes, the cause of temperature changes or heat transport, you may wish to
separate radiative and convective heat flux. This is now possible with the BLK – GLD
sticker series, designed to be used with a wide range of our market-leading heat flux
sensors. The BLK black stickers absorb all radiation and are sensitive to both radiative
and convective heat flux, while the GLD gold reflective stickers reflect all radiation and
are sensitive to convective heat flux only. Applying BLK and GLD stickers, on two
separate heat flux sensors, makes it possible to calculate the contributions of radiative
and convective heat flux:
Φradiative + Φconvective =Φtotal = ΦBLK
Φconvective = ΦGLD
Φradiative = ΦBLK −ΦGLD
BLK – GLD stickers have unique features and benefits:
•makes it possible to perform convective and radiative heat flux measurements
•available as accessory for the five models of the FHF05 series and HFP01 heat flux
sensors
•designed to be applied by the user
Figure 0.1 From left to right: model FHF05-50X50 heat flux sensor, FHF05-50X50 with
BLK-50X50 sticker, and FHF05-50X50 with GLD-50X50 sticker. BLK – GLD stickers are also
available for other dimensions of the FHF05 series and HFP01 heat flux sensors. The BLK
black absorbing stickers will absorb all radiation and are sensitive to both radiative and
convective heat flux, while the GLD gold reflective stickers reflect all radiation and are
sensitive to convective heat flux only.

BLK - GLD sticker series manual v2214 6/47
Figure 0.2 Working with BLK - GLD stickers: measuring the radiative and convective
heat fluxes on an espresso machine.
BLK – GLD stickers are easy to use:
They are designed to be applied by the user but can optionally also be pre-applied at the
factory. Applying a sticker to a heat flux sensor does not change the sensitivity of the
sensor, so no additional calibration is required. Using the reliable measurement technology
behind our heat flux sensors, separating convective and radiative heat flux has never been
easier.
Figure 0.3 BLK – GLD sticker series is a range of accessories for use with Hukseflux heat
flux sensors of the FHF05 series and HFP01. The stickers have matching sizes and are
designed to be applied by the user to the sensor.

BLK - GLD sticker series manual v2214 7/47
There is restriction to use BLK and GLD stickers: in particular if there is a notable amount
of solar radiation, the GDL sticker will absorb a significant part of it.
NOTICE
Treat BLK and GLD stickers with care. Avoid abrasive action. Clean gently with
soft cloth and if needed with demi-water. The gold layer of the GLD sticker is
extremely thin and may easily be rubbed off.
NOTICE
The GLD sticker will not perfectly reflect radiation from sources with
blackbody temperature higher than 4000 K. Solar radiation is in this category.
When in doubt, consult this manual or Hukseflux.
See also:
•BLK – GLD sticker application instruction video on our YouTube channel
•FHF05 series general-purpose heat flux sensor
•FHF05SC series a self-calibrating version of the FHF05 series
•model HFP01 for increased sensitivity
•heater HTR02 series, for calibration and verification of performance of FHF-type
sensors
•view our complete range of heat flux sensors
Figure 0.4 Overview of BLK-GLD stickers series: black absorbing stickers and gold
reflective stickers matching FHF05 series and HFP01 heat flux sensors. They are designed
to be applied by the user but can optionally also be pre-applied at the factory. The figure
shows, from left to right, the stickers GLD and BLK on FHF05-10X10, FHF05-15X30,
FHF05-50X50, FHF05-15X85 and FHF05-85X85. BLK-GLD sticker series is also available
for model HFP01 and FHF05SC series.

BLK - GLD sticker series manual v2214 8/47
1Ordering and checking at delivery
1.1 Ordering BLK – GLD stickers
The BLK – GLD sticker series is a range of accessories for use with Hukseflux heat flux
sensors of FHF05(SC) series and HFP01.
The ordering codes of the different versions in the series are BLK-10X10, BLK-15X30, BLK-
50X50, BLK-15X85, BLK-85x85, BLK-80, GLD-10X10, GLD-15X30, GLD-50X50, GLD-
15X85, GLD-85X85 and GLD-80.
Table 1.1.1 Overview of versions in the BLK – GLD sticker series
BLK versions
BLK-10X10
Black absorbing sticker to measure convective + radiative heat flux, to be used
with FHF05(SC)-10X10 heat flux sensors
BLK-15X30
Black absorbing sticker to measure convective + radiative heat flux, to be used
with FHF05(SC)-15X30 heat flux sensors
BLK-50X50
Black absorbing sticker to measure convective + radiative heat flux, to be used
with FHF05(SC)-50X50 heat flux sensors
BLK-15X85
Black absorbing sticker to measure convective + radiative heat flux, to be used
with FHF05(SC)-15X85 heat flux sensors
BLK-85X85
Black absorbing sticker to measure convective + radiative heat flux, to be used
with FHF05(SC)-85X85 heat flux sensors
BLK-80
Black absorbing sticker to measure convective + radiative heat flux, to be used
with HFP01 heat flux sensor
GLD versions
GLD-10X10
Gold reflective sticker to measure convective heat flux only, to be used with
FHF05(SC)-10X10 heat flux sensors
GLD-15X30
Gold reflective sticker to measure convective heat flux only to be used with
FHF05(SC)-1530 heat flux sensors
GLD-50X50
Gold reflective sticker to measure convective heat flux only, to be used with
FHF05(SC)-50X50 heat flux sensors
GLD-15X85
Gold reflective sticker to measure convective heat flux only, to be used with
FHF05(SC)-15X85 heat flux sensors
GLD-85X85
Gold reflexive sticker to measure convective heat flux only, to be used with
FHF05-85X85 heat flux sensors
GLD-80
Gold reflective sticker to measure convective heat flux only, to be used with
HFP01 heat flux sensor
A common option is:

BLK - GLD sticker series manual v2214 9/47
•pre-application of the sticker to the sensor(s) of your choice at the factory
When opting for pre-application at the factory, please use the following ordering code:
product code sensor with cable length indicated + product code sticker
example: HFP01-05-GLD-80
for model HFP01 with 5 meters of cable and a pre-applied gold sticker

BLK - GLD sticker series manual v2214 10/47
1.2 Included items
Arriving at the customer, the delivery should include:
•BLK – GLD sticker version(s) as ordered
•application procedure instruction sheet
•prostrated IPA (Isopropyl Alcohol) wipe
See the instruction sheet included with your delivery, the instruction movie on our
YouTube channel or Section 4.1 of this manual for instructions how to apply the BLK –
GLD stickers to your sensor.
When opting for pre-applied BLK – GLD stickers, the delivery should include:
•heat flux sensor with sticker applied, with cable of the length as ordered
•product certificate matching the instrument serial number
Figure 1.2.1 GLD and BLK stickers pre-applied to their matching sensors at the factory

BLK - GLD sticker series manual v2214 11/47
2Instrument principle and theory
2.1 Introduction
BLK and GLD stickers series are accessories to FHF05 series and HFP01 heat flux
sensors. These stickers allow the heat flux sensors to be used to separately measure
radiative and convective heat flux.
As a first approximation, BLK black stickers absorb all radiation, as Figure 2.1 shows.
Figure 2.1.1 BLK black stickers absorb all radiation
In contrast to BLK black stickers, GLD gold stickers as a first approximation reflect all
radiation.
Figure 2.1.2 GLD gold stickers reflect all radiation

BLK - GLD sticker series manual v2214 12/47
BLK black stickers are sensitive both to radiative and convective heat flux, whereas GLD
gold stickers, reflecting all radiation, are sensitive to convective heat flux only. See
Figure 2.1.3.
Figure 2.1.3 Both BLK and GLD stickers are sensitive to convective heat flux
Summarising, radiative and convective heat flux are absorbed by the black sticker. The
absorbed heat flows through the heat flux sensor, creating a temperature difference
across the thermopile detector inside the heat flux sensor. This thermopile generates a
small voltage proportional to the sum of the radiative and convective heat flux.
Radiative heat flux is reflected by the gold sticker, convective heat flux is absorbed. The
absorbed heat flows through the heat flux sensor, generating a small voltage
proportional to the convective heat flux.
The proportionality factor, the ratio of heat flux sensor output voltage to heat flux, is
called the sensitivity Sin V/(W/m²). This is determined individually for the heat flux
sensor by calibration and reported on its product certificate.
Applying a sticker to a heat flux sensor does not change the sensitivity of the heat flux
sensor.

BLK - GLD sticker series manual v2214 13/47
2.2 Normal use: moderate-accuracy and comparative
measurements
As a first approximation, you may assume that both sensors are at the same
temperature and have perfect absorption and emission. This approach leads to
moderate-accuracy results. These may be sufficient for the average user.
This moderate-accuracy approach is also often used to compare two situations, for
example with a source switched [on] or [off]. Furthermore, it is useful to estimate
orders of magnitude of heat flux as a starting point for high-accuracy measurements.
For moderate-accuracy measurements the following formulas are used:
Φradiative + Φconvective =Φtotal = ΦBLK (2.1.1)
Φconvective = ΦGLD (2.1.2)
Φradiative = ΦBLK −ΦGLD (2.1.3)
The heat flux Φ in W/m² passing through- and measured by a heat flux sensor is
Φ = U/S (2.1.4)
where [U] is the heat flux sensor voltage output, and [S] the sensitivity found on the
sensor calibration certificate.
Chapter 3 explains what should be done to attain a high-accuracy measurement.

BLK - GLD sticker series manual v2214 14/47
3Advanced use: high-accuracy
measurements
3.1 Introduction
The following sections explain what should be done to attain a high-accuracy
measurement with BLK and GLD stickers.
For high accuracy measurement it is essential to understand that:
•absorption and reflection of both BLK and GLD stickers may not be perfect
•a sensor with a BLK black sticker not only receives radiation, but also emits radiation
depending on its own temperature. What is measured is the net result of incoming
and emitted radiation
•the surface temperature of a sensor is not the same as the measured temperature.
The difference between the measured sensor body and heat sink temperature
depends on the heat flux. The difference can be calculated from temperature, heat
flux and thermal resistance of the sensor. At high heat fluxes this temperature
difference is significant.
•the sensitivity of a heat flux sensor is not a constant. It changes with temperature.
Calibration is performed at 20 °C. At operating temperatures far away from the
calibration temperature, you may compensate for this effect.
•radiation of high colour-temperature sources is not perfectly reflected by the GLD
sensor
Section 3.2 gives more details on the BLK and GLD spectral properties. The further
sections treat typical mathematical treatment of measurement results to compensate for
the above effects.
3.2 Spectral properties of BLK and GLD stickers
In high accuracy measurement you may correct for non-perfect absorption and emission.
This section gives the numbers to work with. See also the appendix on the subject.
3.2.1 Reflection
In an ideal scenario, a black sticker reflects no radiation across all wavelengths and a
gold sticker reflects all radiation across all wavelengths. In reality, the reflection of both
stickers depends on the wavelength of the incoming radiation.
The BLK black sticker has an average reflection of 3 % (rBLK = 0.03) in the UV, visible,
near-infrared and far-infrared spectrum.
The GLD gold sticker has a reflection of about 35 % (rGLD = 0.35) in the UV spectrum,
which increases through the visible spectrum to an average reflection value of 98 %
(rBLK = 0.98) in the near-infrared and the far-infrared.

BLK - GLD sticker series manual v2214 15/47
Figure 3.2.1.1 BLK and GLD reflection factors as a function of wavelength
Typical values of the average reflection factors for common radiation sources are given in
table 2.2.1.1.
For more details on spectral properties of the stickers, see the Appendix on the subject.
Table 3.2.1.1 Typical reflection factor for common radiation sources
RADIATION SOURCE
rBLK
rGLD
UV radiation
0.02
0.35
Solar radiation, Xenon lamps
(colour temperature 6000 K)
0.02
0.80
Halogen and infrared lamps, industrial heaters
(colour temperature < 4000 K)
0.03
0.97
Low temperature infrared sources such as radiant heaters,
stoves, 300 to 600 ˚C
0.05
0.99
Objects at room temperature, - 40 to + 70 ˚C
0.11
0.99
3.2.2 absorption and emissivity
In certain applications, absorption and emissivity are the relevant spectral properties
instead of reflection.
Absorption α is the amount of energy absorbed by an object.
αBLK = 1 - rBLK
αGLD = 1 - rGLD
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
02000 4000 6000 8000 10000 12000 14000 16000 18000 20000
reflection factor
wavelength [nm]
GLD
BLK

BLK - GLD sticker series manual v2214 16/47
Emittance is the amount of thermal energy emitted by an object. Numerically, emissivity
is the same as absorption.
εBLK = αBLK
εGLD = αGLD
Table 3.2.2.1 Typical absorption factors for common radiation sources
RADIATION SOURCE
αBLK
αGLD
UV radiation
0.98
0.65
Solar radiation, Xenon lamps
(colour temperature 6000 K)
0.98
0.20
Halogen and infrared lamps, industrial heaters
(colour temperature < 4000 K)
0.97
0.03
Low temperature infrared sources such as radiant heaters,
stoves, 300 to 600 ˚C
0.95
0.01
Objects at room temperature, - 40 to + 70 ˚C
0.89
0.01
3.3 BLK and GLD sensors on the same heat sink
If possible, we recommend mounting the two sensors, BLK and GLD, on the same heat
sink. This makes analysis easy because they then have - at least approximately, which is
sufficient - the same temperature, and thus:
TBLK = TGLD (3.3.1)
To measure radiative and convective heat flux, preferably:
•apply a BLK black sticker on a first heat flux sensor
•apply a GLD gold sticker on another heat flux sensor
•place the two heat flux sensors side by side, on the same heat sink so that they have
the same heat sink (and sensor) temperature.
•a heat sink may be a metal plate, for example an aluminium plate of at least 1 mm
thickness, or, in case a larger heat capacity is required, a thicker plate. We then
assume there is no significant temperature difference of the heat sink between
sensors (difference < 2 ˚C)

BLK - GLD sticker series manual v2214 17/47
Measure:
•Tamb, ambient air temperature
•TGLD, the heat sink temperature
•ΦBLK , heat flux measured by the black heat flux sensor (output voltage divided by
sensitivity)
•ΦGLD , heat flux measured by the gold heat flux sensor (output voltage divided by
sensitivity)
Typical boundary conditions to keep in mind are:
•valid measurements require steady state conditions: temperature and flux do not
change
•no solar radiation or other sources with high colour temperature (see the section on
working with high temperature sources / solar radiation)
•heat fluxes below a level that surface temperature significantly increases (see the
section on correction of sensor surface temperature)
•spectral corrections are made based on the tables in the section about spectral
properties)
•sensor temperatures at a level that temperature dependence is not corrected (see
appendix on temperature dependence)
Applying a sticker does not alter the working principle of the heat flux sensor. The
original sensitivity S, as specified on the sensor calibration certificate, is still valid.
For most VIS, IR and FIR radiation sources the GLD sticker is a perfect reflector. This
does not apply to solar and Xenon lamp sources (see tables in 3.2). In case the sources
have a low colour temperature, lower than 1000 ˚C, we assume that the reflection factor
of GLD, while actually 0.99, is 1. See the section on sources with high colour
temperature and the appendix on reflection and absorption how to deal with exceptional
sources.
rGLD = 1 (3.3.2)
The heat flux Φ in W/m² passing through- and measured by a heat flux sensor is
Φ = U/S (3.3.3)
where [U] is the heat flux sensor voltage output, and [S] the sensitivity found on the
sensor calibration certificate.

BLK - GLD sticker series manual v2214 18/47
3.3.1 Measurement of convective flux
The purpose is to calculate the convective heat flux Φconvective:
•transferred by ambient air at a certain temperature and speed
•to an object at the heat flux sensor location
•to an object at the heat flux sensor temperature
•to an object in the heat flux sensor plane (same surface orientation)
The heat flux due to convection is measured by the GLD sensor.
Φconvective =ΦGLD = UGLD/SGLD (3.3.1.1)
3.3.2 Characterising a convective source: Tair and heat transfer coefficient Ctr
Properties of a convective source properties are the convective ambient air temperature
Tair and the convective heat transfer coefficient Ctr. Knowing Ctr, the convective heat
transfer to a similarly oriented surface in the same airflow may be calculated.
Note that the convective heat transfer coefficient Ctr is not a function of the sensor
temperature, because the Φconvective is proportional to the difference (Tair - TGLD). Ctr is a
function of:
•air speed and
•the interaction of the sensor surface with the air (orientation of the surface).
Ctr = Φconvective/(Tair - TGLD) (3.3.2.1)
Expected measured values of the heat transfer coefficient for air are between 5 to 20
W/(m²∙K) for natural thermal convection and up to 100 W/(m²∙K) for forced convection.
The convective heat transfer to a similarly oriented surface in the same airflow is:
Φconvective, surface =Ctr∙(Tair - Tsurface) (3.3.2.2)
3.3.3 Measurement of incoming radiative flux
The purpose is to calculate the radiative heat flux Φincoming
•emitted by the source
•incoming to an object at the heat flux sensor location
•to an object in the heat flux sensor plane (same surface orientation)

BLK - GLD sticker series manual v2214 19/47
As a first approximation we assume that the heat transfer by convection to the BLK and
GLD sensors is identical, because their surface temperatures are the same, see 2.3.1.
Φconvective = Φconvective BLK = Φconvective GLD (3.3.3.1)
The measured radiative flux ΦBLK is a net heat flux consisting of incoming flux from the
source, corrected for the absorption of the BLK coating αBLK, incoming for incoming radiation
Φincoming from the source at Tsource minus the (blackbody) radiation emitted by the sensor
at TBLK, corrected for the emission of the BLK coating, εBLK, emitted.
The net heat flux by radiation as measured by the BLK sensor
Φradiative BLK = ΦBLK - Φconvective GLD = (UBLK/SBLK) – (UGLD/SGLD) (3.3.3.2)
and
Φradiative BLK = αBLK, incoming∙Φincoming - σ∙εBLK, emitted∙(TBLK +273)4(3.3.3.3)
This gives us the following formula to calculate the incoming flux:
Φincoming = (Φradiative BLK + σ∙εBLK, emitted∙(TBLK +273)4)/αBLK, incoming (3.3.3.4)
3.3.3.1 Example 1: working around room temperature:
Consider the following boundary conditions:
-40 ˚C < TBLK, Tsource < 70 ˚C (3.3.3.1.1)
We assume (see appendix on absorption and reflection):
εBLK, emitted = αBLK, incoming = 0.89 (3.3.3.1.2)
so that
Φincoming = 1.12∙Φradiative BLK + σ∙(TBLK + 273)4(3.3.3.1.3)
3.3.3.2 Example 2: sensor at room temperature and a uniform infra-red source
Consider the following boundary conditions:
-40 ˚C < TBLK < 70 ˚C, (3.3.3.2.1)
300 ˚C < Tsource < 600 ˚C (3.3.3.2.2)

BLK - GLD sticker series manual v2214 20/47
We assume:
εBLK, emitted = 0.89 (3.3.3.2.3)
αBLK, incoming = 0.95 (3.3.3.2.4)
and
Φincoming = (1.05∙Φradiative BLK + 0.94∙σ∙(TBLK + 273)4(3.3.3.2.5)
3.3.4 Characterising a radiative source: Tblackbody equivalent blackbody
temperature
The equivalent blackbody source temperature assumes that the heat flux sensors face
•an imaginary, uniform blackbody source
•over its full 180˚ field of view angle (or more correctly: 2Πsr solid angle)
•with an emission of 1
εsource = 1 (3.3.4.1)
The heat exchange is described by:
σ∙εsource∙(Tblackbody + 273)4
= (Φradiative + σ∙εBLK, emitted∙(TBLK + 273)4)/αBLK, incoming (3.3.4.2)
The equivalent blackbody source temperature is:
Tblackbody =
((Φradiative + σ∙εBLK, emitted∙(TBLK + 273)4)/(σ∙εsource∙αBLK, incoming))1/4 - 273 (3.3.4.3)
3.4 BLK and GLD sensors at different temperatures
In case TBLK and TGLD differ by more than 2˚C, this may have a significant impact on
convective exchange:
|TBLK - TGLD| > 2 (3.4.1)
equation 3.3.3.2 must be corrected for differences in convective heat flux:
Φradiative= ΦBLK - Φconvective GLD
= (UBLK/SBLK) – (UGLD/SGLD)∙((Tair – TBLK)/(Tair - TGLD)) (3.4.2)
From then on, the other equations of 3.3.3 may be used, possibly with the optional
corrections of 3.5 and 3.6.