ASTM C1041-85(2001)
(Practice)Standard Practice for In-Situ Measurements of Heat Flux in Industrial Thermal Insulation Using Heat Flux Transducers
Standard Practice for In-Situ Measurements of Heat Flux in Industrial Thermal Insulation Using Heat Flux Transducers
SCOPE
1.1 This practice covers the in-situ measurement of heat flux through industrial thermal insulation using a heat flux transducer (HFT).
1.2 This practice estimates the thermal transport properties of thermal insulation materials in-situ in field applications under pseudo steady-state conditions. It is not intended that this practice should be used as a substitute for more precise laboratory procedures such as Test Methods C 177, C 335, or C 518.
1.3 This practice is limited by the relatively small area that can be covered by an HFT and by the transient effects of environmental conditions.
1.4 Temperature limitations shall be as specified by the manufacturer of the HFT.
1.5 While accurate values of heat flux are highly depend-ent upon proper calibrations under the conditions of use, manufacturer's calibrations may be used with confidence for comparative work between similar materials, aging, or other conditions of use.
Note 1—Further information may be found in the literature (1-6).
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
General Information
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Standards Content (Sample)
Designation: C 1041 – 85 (Reapproved 2001)
Standard Practice for
In-Situ Measurements of Heat Flux in Industrial Thermal
Insulation Using Heat Flux Transducers
This standard is issued under the fixed designation C 1041; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope C 518 Test Method for Steady-State Thermal Transmission
Properties by Means of the Heat Flow Meter Apparatus
1.1 This practice covers the in-situ measurement of heat flux
E 220 Method for Calibration of Thermocouples by Com-
through industrial thermal insulation using a heat flux trans-
parison Techniques
ducer (HFT).
E 230 Temperature Electromotive Force (EMF) Tables for
1.2 This practice estimates the thermal transport properties
Standardized Thermocouples
of thermal insulation materials in-situ in field applications
2.2 Other Standards:
under pseudo steady-state conditions. It is not intended that this
ASHRAE Standard 101-1981; Application of Infrared
practice should be used as a substitute for more precise
Sensing Devices to the Assessment of Building Heat Loss
laboratory procedures such as Test Methods C 177, C 335, or
Characteristics
C 518.
ISO/TC 163/SC 1WG N31E Thermal Insulation—
1.3 This practice is limited by the relatively small area that
Qualitative Detection of Thermal Irregularities in Building
can be covered by an HFT and by the transient effects of
Envelopes—Infrared Method
environmental conditions.
1.4 Temperature limitations shall be as specified by the
3. Terminology
manufacturer of the HFT.
3.1 Definitions:
1.5 While accurate values of heat flux are highly depend-ent
3.1.1 heat flux transducer (HFT)—a rigid or flexible trans-
upon proper calibrations under the conditions of use, manufac-
ducer in a durable housing comprised of a thermopile or
turer’s calibrations may be used with confidence for compara-
equivalent for sensing the temperature drop across a thin
tive work between similar materials, aging, or other conditions
thermal resistance layer which gives a voltage output propor-
of use.
tional to the heat flux through the transducer.
NOTE 1—Further information may be found in the literature (1-6).
3.1.1.1 belt HFT—a heat flux transducer having a belt-like
1.6 This standard does not purport to address all of the configuration such that the unit can be wrapped helically
around a section of pipe insulation (see Fig. 1).
safety concerns, if any, associated with its use. It is the
responsibility of the user of this standard to establish appro- 3.1.1.2 spot HFT—a small heat flux transducer having a
round, square, rectangular or other configuration for the
priate safety and health practices and determine the applica-
bility of regulatory limitations prior to use. sensitive area (see Fig. 1).
3.1.2 pseudo steady state of HFT—the criterion for pseudo
2. Referenced Documents
steady-state condition is that the average HFT reading over two
2.1 ASTM Standards: consecutive 5-min periods does not differ by more than 2 %.
C 168 Terminology Relating to Thermal Insulation Since the time constant of an HFT is typically less than or of
C 177 Test Method for Steady-State Heat Flux Measure- the order of 1 min, using a time interval of 5 min ensures that
ments and Thermal Transmission Properties by Means of the transient effects in the HFT are averaged.
the Guarded-Hot-Plate Apparatus 3.2 Symbols:Symbols:
C 335 Test Method for Steady-State Heat Transfer Proper- 3.2.1 Q—heat flow, W (Btu/h).
3 2 2
ties of Horizontal Pipe Insulation 3.2.2 q—heat flux, W/m (Btu/h·ft ).
3.2.3 C—overall conductance of the insulated section,
2 2
W/m ·K (Btu/h·ft · °F).
This practice is under the jurisdiction of ASTM Committee C16 on Thermal 3.2.4 t —process surface temperature,° C(°F).
Insulation and is the direct responsibility of Subcommittee C16.30 on Thermal
Measurement.
Current edition approved July 26, 1985. Published September 1985. Annual Book of ASTM Standards, Vol 14.03.
2 5
The boldface numbers in parentheses refer to the list of references at the end of Available from ASHRAE, Inc., 1791 Tullie Circle NE, Atlanta, GA 30329.
this standard. Available from International Standards Organization, 1 Rue de Varembe, Case
Annual Book of ASTM Standards, Vol 04.06. Postale 56, CH-1211, Geneva 20, Switzerland.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
C 1041
because modest changes in ambient conditions have but
minimal effects on HFT output.
5.5 While it would be ideal for the HFT and attachment
system to have zero thermal resistance, this factor is insignifi-
cant to the measured result if kept to 5 % or less of the
resistance of the insulating section being tested.
6. Apparatus
6.1 Heat Flux Transducer, as described in 3.1.1.
6.2 Voltmeter/Recorder—A voltage-measuring recording
instrument accurate to within 0.5 % of the lowest HFT output
anticipated during the test. An integrating voltmeter is even
more appropriate for reading the output of the HFT.
6.3 Temperature Sensor—A thermocouple or other device
of a type suitable for the temperatures being measured.
6.3.1 For measuring the temperature of an insulated surface,
such as a pipe under insulation, a 1.5-mm diameter or smaller,
flexible ungrounded thermocouple probe 500 mm long is
recommended.
6.3.2 For measuring the temperature of surfaces that can be
NOTE 1—Belt wraps around exterior; shim slips under jacketing (spot easily accessed, 24 gage or smaller, bare bead thermocouples
HFT).
or equivalent shall be used.
FIG. 1 Flexible Heat Flux Transducers for Pipes
6.4 Attachment Materials—Pressure-sensitive adhesive
tape, elastic bands, straps, mastic, grease, or other means may
3.2.5 t —insulation inside surface temperature. For pur-
be used to hold the HFT in place on the test surface.
poses of this standard, t and t shall be considered to be
0 1
6.5 Thermal Contact Materials—Patching cement, silicone
identical.
grease, heat sink grease, silicone sealant, room temperature
3.2.6 t —insulation outside surface temperature,° C (°F).
vulcanizing elastomer, thermally conducting epoxy, or con-
3.2.7 R—areal resistance of the insulating section,
formable pads may be used to provide maximum contact
2 2
m · K h·ft ·°F between the test surface and the HFT where applicable. The
S D (1)
W Btu thermal coupler should not add to or reduce the resistance of
the system such that the temperature patterns of heat flows are
3.2.8 l (k)—apparent thermal conductivity, W/m·K
significantly changed. This could be measured by surface
(Btu·in·h·ft ·°F).
temperature probes or infrared measurement devices.
3.2.9 D—thickness of test section, m (in.).
6.6 Surfacing Materials—Coating, films, or foils to adjust
3.2.10 r —outer radius of pipe insulation, m (in.).
the surface emittance of the HFT to match the radiant charac-
3.2.11 r —inner radius of pipe insulation, m (in.).
teristics of the test surface.
3.2.12 r —outer radius of pipe, m (in.).
3.2.13 V—HFT output in millivolts or other chosen unit.
7. Calibrations
4. Summary of Practice
7.1 HFT must be calibrated under the conditions of use; for
example, a calibration under aluminum jacketing on a test
4.1 This practice is a guide to the proper use of heat flux
setup in accordance with Test Method C 335, would be proper
transducers for estimating the thermal transport properties of
for calibration of an HFT for subsequent testing under similar
thermal insulation in-situ in field applications under pseudo
conditions.
steady-state conditions.
7.2 Calibrate HFT to national reference standards in accor-
5. Significance and Use
dance with Test Methods C 177, C 335, or C 518. A calibration
5.1 The major contribution of this practice is that it enables curve showing q/V versus insulation surface temperature (ex-
a measurement of the real-time energy loss or gain through a pected to be the HFT temperature) shall be developed covering
chosen surface of an existing process insulation with minimal the intended range of operating temperatures and heat fluxes.
disturbance to the heat flux through the insulating body.
7.2.1 The following is an example of calibration under use
5.2 The primary use of this practice will be for the in-situ conditions (pipe insulated with preformed insulation and jack-
estimation of thermal transport properties of industrial insula- eted with aluminum):
tion such as used on pipes, tanks, ovens, and boilers, operating 7.2.1.1 Set up the apparatus in accordance with Test Method
under normal process conditions. C 335 with preformed insulation, jacketed with aluminum
5.3 Errors attributable to heat flow measurements over a jacket in the same condition as that to be tested.
small area or short term testing can be misleading and this 7.2.1.2 Establish steady-state at test temperature (3.1.2).
practice is intended to minimize such errors. 7.2.1.3 Insert flexible HFT under jacket, near the center of
5.4 Insulation processes with large temperature differences the insulation section. The jacket should be lifted enough to
across the insulation are best suited to HFT measurements provide guidance in placing the HFT away from all joints in the
C 1041
insulation section. (When a belt HFT is being calibrated, it must be made. If the HFT is not long enough to wrap
must be wrapped in a tight helix around the center of the completely around the test section, connect additional belts in
insulation section with the appropriate side, foil or gray to series until a full wrap is made. Any helical lap of the belt past
match emittance, exposed. Attach the strap to the belt, pulling full circle should be on the side of the test section, not at the top
and rubbing the belt into close contact with the insulation or bottom. Do not overwrap a flexible HFT because compres-
section, making sure that the lap of the belt is on the side of the sion may cause a change in calibration.
pipe.) 8.3 Thermocouple Placement:
7.2.1.4 Insert a bare temperature sensor about 50 mm away 8.3.1 Measure the process surface temperature by inserting
from the HFT. After calibrating the belt HFT, place the sensor a thermocouple probe as described in 6.3.1 such that the probe
between the belt and the insulation surface to measure surface lies against the process surface for 150 mm (6 in.) or more. For
temperature. purposes of inserting the probe, pierce the insulation with an
7.2.1.5 Read pseudo steady-state electrical output of HFT ice pick or other means at an angle of 30° or less to the plane
and temperature at both surfaces of the insulation. Since the of the surface to be measured. The correct insertion of the
output of the HFT will fluctuate under most conditions, a probe should show the maximum DT across the insulation.
graphical or integrated average of the output of the HFT must 8.3.1.1 If the process system has built-in temperature-
be made. measuring capabilities in good repair and calibration the output
7.2.1.6 Utilizing q, as may be calculated from Test Method from such devices may be usable in place of a temperature
C 335 data, determine the calibration value for the HFT in q/V probe.
for at least 3 insulation surface temperatures. 8.3.2 A bare bead thermocouple should be inserted under
7.2.1.7 Plot calibration value (q/V) versus insulation surface the jacket to measure the surface temperature of the insulation
temperature (7.2.1.6). near the HFT (see 7.2.1.4).
7.3 Calibrate the thermocouple in accordance with Test 8.3.3 When the HFT is installed on a surface rather than
Method E 220. under a jacket (or other cover), measure the surface tempera-
ture of the insulation near the HFT by taping a bare bead
8. Test Section and HFT and Temperature Sensor
thermocouple to the insulation surface (6.3.2) such that at least
Placement Guidelines
100 mm of the thermocouple is in contact with the surface. The
8.1 Test Section:
emittance of the tape should match that of the insulation
8.1.1 Selection of the test sections must be appropriate and
surface within 60.2 (see 8.2.2).
consistent with the test objectives. Several test sections may be
9. HFT and Temperature Data Points
needed.
8.1.2 Infrared scanning is an appropriate way to identify 9.1 The output from the HFT shall be recorded with a
relative surface uniformity conditions so that the HFT may be
suitable recorder such that pseudo steady-state (3.1.2) may be
placed to measure the thermal transport properties of a repre-
observed when attained. Depending on exact environmental
sentative area.
conditions, the recorder usually traces a “band” of data which
8.1.3 Test sections must be amenable to attachment of the
must be averaged graphically.
HFT with good thermal coupling and with minimal disturbance
9.2 As an alternative to recording the output of the HFT, an
of normal heat transfer.
integrating voltmeter may be used. While the exact conditions
8.2 HFT Placement:
to be utilized will depend upon the capabilities of the voltmeter
8.2.1 Where block or pipe insulation is being tested, place a
at hand, it is suggested that short integration periods be
spot HFT preferably under the jacketing material near the
averaged over sequential 5-min intervals to determine when
center of a formed section of material. Avoid placement on
pseudo steady-state (3.1.2) is achieved.
joints in insulation or laps in jacketing unless joint loss is being
9.3 Temperature readings shall be taken when the HFT
evaluated.
reading comes to pseudo steady-state as defined in 3.1.2.
8.2.2 When a spot HFT is surface-mounted, it may be
9.4 Multiple location data points must be taken and aver-
attached by using an adhesive two-sided tape, heat transfer
aged.
grease, or other appropriate means. The emittance of the HFT
10. Procedure
must match the surface as closely as possible. With one
transducer an error of 0.01 at the 0.05 emittance level displaces 10.1 Select an appropriate test area and install HFT and
the reading by 3.5 %. An error of 0.1 at the 0.5 emittance level temperature sensors in accordance with Section 8.
displaces the reading by 3.5 %. 10.2 Shield the HFT from direct solar radiation unless solar
8.2.3 Use a belt HFT for obtaining system thermal perfor- gain is intended as a factor in the study.
mance data of block or pipe insulation, including heat loss 10.3 Connect the HFT to the recorder or integrating volt-
from large joints. When the belt HFT is mounted on reflective meter and take readings until pseudo steady-state is achieved in
insulation jacketing, it should have the foil side exposed; when accordance with Section 9.
it is mounted on a surface with high emittance, the gray side 10.4 Measure the surface temperature of the insulation near
must b
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