EN ISO 22975-1:2016
(Main)Solar energy - Collector components and materials - Part 1: Evacuated tubes - Durability and performance (ISO 22975-1:2016)
Solar energy - Collector components and materials - Part 1: Evacuated tubes - Durability and performance (ISO 22975-1:2016)
ISO 22975-1:2016 specifies definitions and test methods for materials, durability and performance of evacuated tubes.
ISO 22975-1:2016 is applicable to all types of evacuated tubes.
Solarenergie - Kollektorbauteile und -materialien - Teil 1: Vakuumröhren - Beständigkeit und Leistungsfähigkeit (ISO 22975-1:2016)
Dieser Teil von ISO 22975 legt Begriffe und Prüfverfahren für die Materialien sowie die Beständigkeit und Leistungsfähigkeit von Vakuumröhren fest.
Dieser Teil von ISO 22975 ist auf alle Arten von Vakuumröhren anwendbar.
Énergie solaire - Composants et matériaux du collecteur - Partie 1: Tubes sous vide - Durabilité et performance (ISO 22975-1:2016)
ISO 22975-1:2016 spécifie les définitions et les méthodes d'essai pour les matériaux, la durabilité et la performance des tubes sous vide.
ISO 22975-1:2016 est applicable à tous les types de tubes sous vide.
Sončna energija - Sestavni deli in materiali sprejemnikov sončne energije - 1. del: Vakuumske cevi - Trajnost in zmogljivost (ISO 22975-1:2016)
Področje uporabe predlaganega standarda je spodbuditev uskladitve nacionalnih specifikacij in zahtev glede trajnosti in zmogljivosti vakuumskih cevi, vključno s pogoji ter preskusnimi metodami za materiale, trajnost in zmogljivost vakuumskih cevi.
General Information
Standards Content (Sample)
SLOVENSKI STANDARD
01-januar-2017
6RQþQDHQHUJLMD6HVWDYQLGHOLLQPDWHULDOLVSUHMHPQLNRYVRQþQHHQHUJLMHGHO
9DNXXPVNHFHYL7UDMQRVWLQ]PRJOMLYRVW ,62
Solar energy - Collector components and materials - Part 1: Evacuated tubes - Durability
and performance (ISO 22975-1:2016)
Solarenergie - Kollektorbauteile und -materialien - Teil 1: Vakuumröhren - Beständigkeit
und Leistungsfähigkeit (ISO 22975-1:2016)
Energie solaire - Composants et matériaux du collecteur - Partie 1: Tubes sous vide -
Durabilité et performance (ISO 22975-1:2016)
Ta slovenski standard je istoveten z: EN ISO 22975-1:2016
ICS:
27.160 6RQþQDHQHUJLMD Solar energy engineering
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
EN ISO 22975-1
EUROPEAN STANDARD
NORME EUROPÉENNE
October 2016
EUROPÄISCHE NORM
ICS 27.160
English Version
Solar energy - Collector components and materials - Part 1:
Evacuated tubes - Durability and performance (ISO 22975-
1:2016)
Énergie solaire - Composants et matériaux du Solarenergie - Kollektorbauteile und -materialien - Teil
collecteur - Partie 1: Tubes sous vide - Durabilité et 1: Vakuumröhren - Beständigkeit und
performance (ISO 22975-1:2016) Leistungsfähigkeit (ISO 22975-1:2016)
This European Standard was approved by CEN on 12 September 2016.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania,
Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels
© 2016 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 22975-1:2016 E
worldwide for CEN national Members.
Contents Page
European foreword . 3
European foreword
This document (EN ISO 22975-1:2016) has been prepared by Technical Committee ISO/TC 180 "Solar
energy" in collaboration with Technical Committee CEN/TC 312 “Thermal solar systems and
components” the secretariat of which is held by ELOT.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by April 2017, and conflicting national standards shall be
withdrawn at the latest by April 2017.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN [and/or CENELEC] shall not be held responsible for identifying any or all such patent
rights.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia,
France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta,
Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Turkey and the United Kingdom.
Endorsement notice
The text of ISO 22975-1:2016 has been approved by CEN as EN ISO 22975-1:2016 without any
modification.
INTERNATIONAL ISO
STANDARD 22975-1
First edition
2016-10-01
Solar energy — Collector components
and materials —
Part 1:
Evacuated tubes — Durability and
performance
Énergie solaire — Composants et matériaux du collecteur —
Partie 1: Tubes sous vide — Durabilité et performance
Reference number
ISO 22975-1:2016(E)
©
ISO 2016
ISO 22975-1:2016(E)
© ISO 2016, Published in Switzerland
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form
or by any means, electronic or mechanical, including photocopying, or posting on the internet or an intranet, without prior
written permission. Permission can be requested from either ISO at the address below or ISO’s member body in the country of
the requester.
ISO copyright office
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CH-1214 Vernier, Geneva, Switzerland
Tel. +41 22 749 01 11
Fax +41 22 749 09 47
copyright@iso.org
www.iso.org
ii © ISO 2016 – All rights reserved
ISO 22975-1:2016(E)
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification and test list . 2
5 Testing of material . 3
5.1 Inspection for stones and knots . 3
5.1.1 General. 3
5.1.2 Test conditions. 3
5.1.3 Apparatus . 3
5.1.4 Procedure . 3
5.1.5 Results . 4
5.2 Inspection for scratches . 4
5.2.1 General. 4
5.2.2 Test conditions. 4
5.2.3 Apparatus . 4
5.2.4 Procedure . 4
5.2.5 Results . 5
5.3 Testing of solar transmittance . 5
5.3.1 General. 5
5.3.2 Test conditions and apparatus . 5
5.3.3 Procedure . 5
5.3.4 Results . 5
5.4 Testing of solar absorptance . 5
5.4.1 General. 5
5.4.2 Test conditions and apparatus . 5
5.4.3 Procedure . 5
5.4.4 Results . 6
5.5 Testing of hemispherical emittance . 6
5.5.1 General. 6
5.5.2 Test conditions. 6
5.5.3 Apparatus and procedure . 6
5.5.4 Results . 7
6 Durability testing of evacuated tube . 7
6.1 Vacuum performance . 7
6.1.1 General. 7
6.1.2 Test conditions and apparatus . 7
6.1.3 Procedure . 8
6.1.4 Results . 8
6.2 Resistance to thermal shock . 8
6.2.1 General. 8
6.2.2 Test conditions and apparatus . 9
6.2.3 Procedure . 9
6.2.4 Results . 9
6.3 Resistance to impact . 9
6.3.1 General. 9
6.3.2 Principle . 9
6.3.3 Procedure . 9
6.3.4 Results . 9
6.4 Resistance to internal pressure .10
6.4.1 General.10
ISO 22975-1:2016(E)
6.4.2 Test conditions and apparatus .10
6.4.3 Procedure .10
6.4.4 Results .10
7 Performance testing of evacuated tube .10
7.1 Tests for determination the exposure parameter .10
7.1.1 General.10
7.1.2 Test conditions.11
7.1.3 Apparatus .11
7.1.4 Procedure .12
7.1.5 Results .13
7.2 Tests for determination of sum of solar irradiation for temperature increase of
double-glass evacuated tube .13
7.2.1 General.13
7.2.2 Test conditions.13
7.2.3 Apparatus .13
7.2.4 Procedure and results .13
7.3 Tests to determine the average heat loss coefficient of a double-glass evacuated tube .13
7.3.1 General.13
7.3.2 Test conditions.14
7.3.3 Apparatus .14
7.3.4 Procedure .14
7.3.5 Results .15
Annex A (informative) Configuration schemes of evacuated tubes .16
Annex B (normative) Test report .18
Annex C (normative) Determination of the external surface area of absorber tube for
double-glass evacuated tubes .25
Bibliography .27
iv © ISO 2016 – All rights reserved
ISO 22975-1:2016(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment,
as well as information about ISO’s adherence to the World Trade Organization (WTO) principles in the
Technical Barriers to Trade (TBT) see the following URL: www.iso.org/iso/foreword.html.
The committee responsible for this document is ISO/TC 180, Solar energy.
ISO 22975 consists of the following parts, under the general title Solar energy — Collector components
and materials:
— Part 1: Evacuated tubes — Durability and performance
— Part 2: Heat-pipes for solar thermal application — Durability and performance
— Part 3: Absorber surface durability
The following parts are under preparation:
— Part 5: Insulation material durability and performance
ISO 22975-1:2016(E)
Introduction
This part of ISO 22975 is applicable to all categories of evacuated tubes, including double-glass
evacuated tubes and glass-metal sealed evacuated tubes.
This part of ISO 22975 provides test methods for inspecting stones and knots in envelope glass tubes.
This part of ISO 22975 also provides test methods for determining durability of evacuated tubes,
including vacuum performance, thermal shock resistance, external impact resistance and internal
pressure resistance. For each durability test, this part of ISO 22975 specifies general, apparatus,
procedure and results of the test.
This part of ISO 22975 also provides test methods for measuring performance of evacuated tubes,
including exposure parameter, solar irradiation for temperature increase of double-glass evacuated
tube and average heat loss coefficient. For each performance test, principle, test conditions, apparatus,
procedure and results of the test are specified.
vi © ISO 2016 – All rights reserved
INTERNATIONAL STANDARD ISO 22975-1:2016(E)
Solar energy — Collector components and materials —
Part 1:
Evacuated tubes — Durability and performance
1 Scope
This part of ISO 22975 specifies definitions and test methods for materials, durability and performance
of evacuated tubes.
This part of ISO 22975 is applicable to all types of evacuated tubes.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and are
indispensable for its application. For dated references, only the edition cited applies. For undated
references, the latest edition of the referenced document (including any amendments) applies.
ISO 9488, Solar energy — Vocabulary
ISO 9845-1, Solar energy — Reference solar spectral irradiance at the ground at different receiving
conditions — Part 1: Direct normal and hemispherical solar irradiance for air mass 1,5
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 9488 and the following apply.
3.1
double-glass evacuated tube
component of an evacuated tube solar collector, of which both the inner tube and the envelope tube are
made of glass
3.2
glass-metal sealed evacuated tube
component of an evacuated tube solar collector, in which the absorber is affixed to a metal fluid channel,
that is sealed into the envelope glass tube through a specific glass-metal sealing process
3.3
stone
opaque inclusions in the glass of the evacuated tube
3.4
knot
transparent inclusions in the glass of the evacuated tube
3.5
scratch
abraded area where the surface of the glass is torn or worn off
3.6
vacuum jacket
space between envelope glass tube and absorber in an evacuated tube, wherein air pressure is
sufficiently low that thermal conduction and convection of air can be ignored
ISO 22975-1:2016(E)
3.7
stagnation
state where no working fluid passes through the evacuated tube and the temperature of the evacuated
tube is determined by the solar irradiance
3.8
exposure temperature
maximum temperature at an accessible part of an evacuated tube with specified irradiance under
stagnation (3.7) conditions
Note 1 to entry: For double glass evacuated tubes, the temperature with only air in the tube is measured. For
direct flow tubes, the measurement is done in the air-filled flow channel within the vacuum tube. For glass-metal
sealed tubes with heat pipe, the well-insulated condenser surface temperature is measured.
3.9
exposure parameter
ratio of the difference between exposure temperature (3.8) and ambient temperature to the solar
irradiance
3.10
sum of solar irradiation for temperature increase
sum of solar irradiation for a certain preset temperature rise range of the water in a double-glass
evacuated tube (3.1)
Note 1 to entry: This term applies only to double-glass evacuated tubes.
3.11
average heat loss coefficient
ratio of heat loss per m² defined external surface area of absorber tube, without irradiance, to
temperature difference between water content of vacuum tube and ambient air
Note 1 to entry: This term applies only to double-glass evacuated tubes (3.1).
4 Classification and test list
According to material category of absorber, evacuated tubes can be substantially classified into two types:
a) double-glass evacuated tube, see Figure A.1;
b) glass-metal sealed evacuated tube, see Figure A.2.
Tests for the two categories of evacuated tubes are summarized in Table 1.
Table 1 — Test list
Category of evacuated tube Test
Double-glass, Glass-metal sealed 5.1 Inspection for stones and knots
Double-glass, Glass-metal sealed 5.2 Inspection for scratches
Double-glass, Glass-metal sealed 5.3 Testing of solar transmittance
Double-glass 5.4 Testing of solar absorptance
Double-glass 5.5 Testing of hemispherical emittance
Double-glass 6.1 Vacuum performance
Double-glass 6.2 Resistance to thermal shock
Double-glass, Glass-metal sealed 6.3 Resistance to Impact
Double-glass, Glass-metal sealed direct flow 6.4 Resistance to internal pressure
2 © ISO 2016 – All rights reserved
ISO 22975-1:2016(E)
Table 1 (continued)
Category of evacuated tube Test
Double-glass, Glass-metal sealed 5.1 Inspection for stones and knots
7.1 Tests for determination of exposure
Double-glass, Glass-metal sealed
parameter
7.2 Tests for determination of sum of solar
Double-glass irradiation for temperature increase of
double-glass evacuated tube
7.3 Tests for determination the average heat loss
Double-glass
coefficient of double-glass evacuated tube
5 Testing of material
5.1 Inspection for stones and knots
5.1.1 General
This test is intended to check the uniformity of the tube glass by visual inspection.
5.1.2 Test conditions
The test room/table for taking observations shall have a minimum illuminance of 1 500 lx.
5.1.3 Apparatus
The dimension measurement instrument shall have an accuracy of ±0,1 mm.
5.1.4 Procedure
a) Draw two lines with permanent marker or other non-invasive marking method with thickness no
more than 0,5 mm on the surface of tube along the axial direction, such that the surface is split into
two equal parts.
b) With one part upward, count and separately record for this part the numbers of the following:
— stones with size not over 1 mm;
— stones with size over 1 mm;
— knots with size not over 1,0 mm;
— knots with size between 1,5 mm and 2,0 mm;
— knots with size over 2,0 mm;
— cracks around the stones and knots.
c) Turn the other part of the tube upward and repeat Step b).
d) Sum the values from Steps b) and c) for each category of stone, knot or crack.
e) Draw another pair of lines parallel with the first pair of lines, ensuring that the distance between
lines is 1/4 of the perimeter. Erase the first pair of lines and count and record the stones, knots and
cracks again as in Steps b) to d).
f) For each category of stone, knot or crack, take the larger of the values recorded in Steps d) and e) as
the result.
ISO 22975-1:2016(E)
5.1.5 Results
Report the following values:
a) the number of stones with size not over 1 mm, per unit area of the tube;
b) the number of stones with size over 1 mm on the whole tube;
c) the total number of stones on the whole tube;
d) the number of knots with size not over 1,0 mm, per unit area of the tube;
e) the number of knots with size between 1,5 mm and 2,0 mm on the whole tube;
f) the number of knots with size over 2,0 mm on the whole tube;
g) the number of cracks on the whole tube.
5.2 Inspection for scratches
5.2.1 General
This test will check and record the scratches on the tube by visual inspection.
NOTE The presence of scratches is one of the main reasons for tubes being broken.
5.2.2 Test conditions
The test room/table for taking observations shall have a minimum illuminance of 1 500 lx.
5.2.3 Apparatus
The dimension measurement instrument shall have an accuracy of ±0,1 mm.
5.2.4 Procedure
a) Draw two lines with permanent marker or other non-invasive marking method with the thickness
no more than 0,5 mm on the surface of tube along the axial direction, such that the surface is split
into two equal parts.
b) With one part upward, count and separately record for this part:
— the number of scratches not longer than 100 mm;
— the number of scratches longer than 100 mm;
— the total length of all scratches.
c) Turn the other part of the tube upward and repeat Step b).
d) Sum the respective values from Steps b) and c).
e) Draw another pair of lines parallel with the first pair of lines, ensuring that the distance between
lines is 1/4 of the perimeter. Erase the first pair of lines, count and record the scratches again as in
Steps b) to d).
f) Take the larger value of each of the quantities recorded in Steps d) and e) as the results.
4 © ISO 2016 – All rights reserved
ISO 22975-1:2016(E)
5.2.5 Results
Report the following values:
a) the number of scratches not longer than 100 mm on the whole tube;
b) the number of scratches longer than 100 mm on the whole tube;
c) the total length of all scratches on the whole tube.
5.3 Testing of solar transmittance
5.3.1 General
This test will determine the solar transmittance (AM1.5) of the envelope glass tube.
5.3.2 Test conditions and apparatus
This test shall use a spectrophotometer with a wavelength accuracy of ±1 nm, resolution of 0,1 nm,
range of 0,3 μm to 2,5 μm and an integrating-sphere unit. The measuring spot of the spectrophotometer
and the opening of the integrating sphere shall be sized to ensure that the curvature of the tube has no
influence on the result.
5.3.3 Procedure
The solar transmittance of a sample piece of the envelope tube is tested twice. In the first test, place
the sample into the measuring spot with the light incident on the concave surface and measure the
transmittance of the sample with the spectrophotometer for solar spectral irradiance according to
ISO 9845-1. In the second test, place the sample into the measuring spot with the light incident on the
convex surface and measure the transmittance of the sample with the spectrophotometer for solar
spectral irradiance according to ISO 9845-1.
5.3.4 Results
The transmittance for solar spectral irradiance according to ISO 9845-1 shall be reported for both
measurements and the mean value of the two measurements.
5.4 Testing of solar absorptance
5.4.1 General
This test will determine the solar absorptance (AM1.5) of selective absorbing coating of a double-glass
evacuated tube. This test is applicable for double glass evacuated tubes only.
5.4.2 Test conditions and apparatus
This test shall use a spectrophotometer with a wavelength accuracy of ±1 nm, resolution of 0,1 nm,
range of 0,3 μm to 2,5 μm and an integrating-sphere unit. The measuring spot of the spectrophotometer
and the opening of the integrating sphere shall be sized to ensure that the curvature of the tube has no
influence on the result.
5.4.3 Procedure
Two samples of the solar selective surface shall be taken; one from a position 150 mm distant from the
open end of the tube and one from the middle of the tube. For each sample, position the sample into
the measuring spot with the light incident on the convex surface and measure the reflectance for solar
spectral irradiance according to ISO 9845-1.
ISO 22975-1:2016(E)
5.4.4 Results
Calculate and report the solar absorptance for each sample from the measured reflectance and the
mean of these two absorptance results.
5.5 Testing of hemispherical emittance
5.5.1 General
This test will determine the hemispherical emittance of selective absorbing coating of a double-glass
evacuated tube.
5.5.2 Test conditions
The hemispherical emittance of the selective absorbing coating on the outside of the inner glass tube
of an double-glass evacuated tube is determined by steady state calorimetry at a temperature of
80 °C ± 5 °C.
-2
NOTE The gas pressure in the vacuum jacket is typically around 5 × 10 Pa, so the conduction of gas
molecules can be ignored.
The hemispherical emittance of the selective surface ε is as given in Formula (1):
h
q
IU
s
ε = = (1)
h
4 4
q
σAT −T
b
( )
11 2
where
I is the current of heater, A;
U is the voltage of heater, V;
A is the reference area of the outside of inner glass tube, m ;
-8 -2 -4
σ is the Stefan-Boltzmann constant, 5,67 × 10 W·m K ;
T is the temperature of heater at steady state, K;
T is the temperature of cooling water, K;
-2
q is the emissive power density of selective absorbing surface, W·m ;
s
-2
q is the emissive power density of black body, W·m .
b
5.5.3 Apparatus and procedure
A double-glass evacuated tube is placed into a water-cooled jacket and heating elements are inserted
into the tube. The heating elements consist of the central main heater and the compensating heaters at
the ends of the main heater.
The heater elements are contained within three segments of ceramic tube which fit within the
inner glass absorber tube. Temperature sensors are attached to each ceramic element allowing the
temperature of each to be measured and controlled independently. The temperature sensor in the inner
tubes shall be recorded to a standard uncertainty of 0,2 K. The power dissipated in the central heater
required to maintain the absorber tube at a chosen constant temperature is used to evaluate average
heat loss of the heater. The outer segments are maintained at the same temperature as the central
segment by means of independent power inputs, to prevent longitudinal heat flow. Consequently, only
radial dissipation of the power need to be considered. The glass envelope is enclosed in a water cooled
jacket and its temperature is thus maintained at 20 °C.
6 © ISO 2016 – All rights reserved
ISO 22975-1:2016(E)
Operate the apparatus until the heaters have stabilised at a temperature of 80 °C ± 5 °C. Determine the
voltage, U, and current, I, supplied to the main heater. Determine the reference area, A , of the outer
surface of inner glass tube in direct contact with the main heater. Calculate the hemispherical emittance
in accordance with Formula (1).
For test apparatus, see Figure 1.
Key
1 temperature (T1) sensor of cooling water 8 inlet of cooling water
2 outlet of cooling water 9 cooling water
3 inner glass tube 10 sealing flanges of water cooled jacket
4 envelope glass tube 11 amperemeter
5 water cooled jacket 12 voltmeter
6 temperature (T2) sensor of central heater 13 central heater
7 wires of central heater 14 auxiliary heater
Figure 1 — Test apparatus for hemispherical emittance
5.5.4 Results
The test report shall record the hemispherical emittance of a solar selective absorbing coating ε .
h
6 Durability testing of evacuated tube
6.1 Vacuum performance
6.1.1 General
This test is intended to assess, for a double-glass evacuated tube, the air pressure of the vacuum jacket
and the disappearance percentage in axial length of the getter mirror after the tube is heated for 48 h at
a temperature of 350 °C ± 5 °C.
6.1.2 Test conditions and apparatus
The air pressure of the vacuum jacket is assessed using a spark leak detector in a darkened room or
enclosure.
For assessment of the disappearance percentage in axial length of the getter mirror of a double-glass
evacuated tube, a heating rod shall heat up the inner tube without direct contact with the glass. The
ISO 22975-1:2016(E)
heating rod shall have a length not less than 90 % of the tube length and the end of the tube shall be
well insulated. The temperature within the tube shall be measured using a temperature sensor in the
middle of the tube close to the tube wall, to a standard uncertainty of 1 K. the temperature in the inner
tubes shall be kept at 350 °C ± 5 °C for 48 h.
6.1.3 Procedure
With a new tube, apply testing with the spark leak detector to assess air pressure of vacuum jacket in
the evacuated tubes in dark condition. Make qualitative judgments according to the appearance of the
discharge.
For a double-glass evacuated tube, the spark leak detector shall be aimed at the open end of the tube
where no selective coating is on the inner glass tube. Turn on the spark leak detector in dark condition,
record the test results. If the tube is not leaky, the glass surface shows weak fluorescence. Otherwise,
if the glow discharge appears in the tube, sparks penetrate on the glass surface or sparks are divergent
whereas no fluorescence on the glass surface, the tube is leaky.
Repeat the spark leak detector test with a second tube.
For the disappearance percentage test, the following procedure shall be used with a new tube.
a) Determine the axial length, L , of the getter mirror, from the point at the closed end of the tube
where outside diameter is 15 mm to the getter mirror edge. Six measurements shall be made,
equally spaced around the circumference of the tube, and averaged to give the length value.
b) Insert the heating rod into the evacuated tube.
c) Maintain the inner glass tube at a temperature of 350 °C ± 5 °C for 48 h and record the air
temperature in the inner tube during this period.
d) After the tube has cooled to room temperature, determine the axial length, L , of the getter mirror,
in accordance with Step a).
6.1.4 Results
The appearance of the discharge, when the tubes are tested by the spark leakage detector, shall be
reported.
For a double-glass evacuated tube, the disappearance percentage in axial length of the getter mirror
shall be calculated according to Formula (2) and reported.
LL−
R = ×100 (2)
L
where
R is the disappearance percentage in axial length of the getter mirror, %;
L is the axial length of the getter mirror before heating, mm;
L is the axial length of the getter mirror after heating, mm.
6.2 Resistance to thermal shock
6.2.1 General
This test is intended to assess the capability of an evacuated tube to withstand thermal shocks without
failure. This test applies to double glass evacuated tubes.
8 © ISO 2016 – All rights reserved
ISO 22975-1:2016(E)
6.2.2 Test conditions and apparatus
This test uses an ice-water mixture bath at a temperature not higher than 0 °C and a hot water bath at a
temperature above 90 °C. For both baths, the temperature shall be stable within ±0,5 °C.
6.2.3 Procedure
a) Insert the open end of evacuated tube into the ice-water mixture bath to a depth not less than
100 mm for 1 min.
b) Remove the tube from ice-water mixture bath and immediately insert it into hot water bath to a
depth not less than 100 mm for 1 min.
c) Remove the tube from hot water bath and immediately insert it again into ice-water mixture bath
to a depth not less than 100 mm for 1 min.
d) Repeat Steps b) and c) three times.
6.2.4 Results
Record any damage to the evacuated tube and the temperature of the testing baths during the testing.
6.3 Resistance to impact
6.3.1 General
This test is intended to assess the extent to which an evacuated tube can withstand the effects of heavy
impacts caused by hailstones.
6.3.2 Principle
A steel ball is dropped onto the evacuated tube from specified heights. The impact energy is gradually
increased by increasing the height up to a maximum of 2,0 m, until either the tube breaks or the
manufacturer’s specified maximum height is reached.
6.3.3 Procedure
a) Mount both ends of collector tube horizontally on a support that is stiff enough so that there is
negligible distortion or deflection at the time of impact.
b) Drop a steel ball with a mass of 150 g ± 10 g vertically onto a point 75 mm from one end of the tube,
in a direction normal to the tube axis, from a height of 0,4 m or other minimum height specified
by the manufacturer of the tube. The height of drop is the vertical distance between the point of
release and the horizontal plane containing the point of impact.
c) Repeat Step b) once, with the point of impact moved by a few millimetres from all previous points
of impact.
d) Repeat Steps b) and c) with the ball dropped onto a point 75 mm from the other end of the tube.
e) Repeat Steps b), c) and d) with the ball dropped successively from heights of 0,6 m, 0,8 m, 1,0 m,
1,2 m, 1,4 m, 1,6 m, 1,8 m and 2,0 m. The test is terminated if the tube is destroyed or if the height
exceeds the maximum specified by the manufacturer of the tube.
6.3.4 Results
All points of impact shall be reported and illustrated by means of
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