【AS澳大利亚标准】AS 1774.14 Refractories and refractory materials— Physical test methods Method.doc

AS 1774.142008AS 1774.142008ISO 8894-2:2007Australian Standard®Refractories and refractory materials Physical test methodsMethod 14: Thermal conductivityThe Standard is downloaded from Standard SharingThis Australian Standard® was prepared by Committee MN-007, Refractories and RefractoryMaterials. It was approved on behalf of the Council of Standards Australia on7 October 2008.This Standard was published on 4 December 2008.The following are represented on Committee MN-007:Australasian Institute of Mining and MetallurgyAustralian Aluminium CouncilAustralian Ceramic SocietyBureau of Steel Manufacturers of AustraliaCSIRO Manufacturing & Materials TechnologyCement Industry FederationInstitute of Refractories EngineersRefractories Manufacturers Association of AustraliaThe University of New South WalesThis Standard was issued in draft form for comment as DR 08160.Standards Australia wishes to acknowledge the participation of the expert individuals that contributed to the development of this Standard through their representation on the Committee and through the public comment period.Keeping Standards up-to-dateAustralian Standards® are living documents that reflect progress in science, technology and systems. To maintain their currency, all Standards are periodically reviewed, and new editions are published. Between editions, amendments may be issued.Standards may also be withdrawn. It is important that readers assure themselves they are using a current Standard, which should include any amendments that may have been published since the Standard was published.Detailed information about Australian Standards, drafts, amendments and new projects can be found by visiting www.standards.org.auStandards Australia welcomes suggestions for improvements, and encourages readers to notify us immediately of any apparent inaccuracies or ambiguities. Contact us via email at mailstandards.org.au, or write to Standards Australia, GPO Box 476, Sydney, NSW 2001.AS 1774.142008Australian Standard®Refractories and refractory materials Physical test methodsMethod 14: Thermal conductivityOriginated as AS R31.141966. Previous edition AS 1774.141992. Second edition 2008.COPYRIGHT© Standards AustraliaAll rights are reserved. No part of this work may be reproduced or copied in any form or by any means, electronic or mechanical, including photocopying, without the written permission of the publisher.Published by Standards Australia GPO Box 476, Sydney, NSW 2001, AustraliaISBN 0 7337 8959 5PREFACEThis Standard was prepared by the Standards Australia Committee MN-007, Refractories and Refractory Materials, to supersede AS 1774.141992, Refractories and refractory materials Physical test methods, Method 14: Thermal conductivity.The objective of this Standard is to provide the refractories industry with an internationally accepted method for the determination of the thermal conductivity of refractory products and materials.This Standard is identical with, and has been reproduced from ISO 8894-2:2007, Refractory materialsDetermination of thermal conductivityPart 2: Hot-wire method (parallel).As this Standard is reproduced from an international standard, the following applies:(a) Its number appears on the cover and title page while the international standard number appears only on the cover.(b) In the source text this part of ISO 8894 should read this Australian Standard.(c) Replace the text in Clause 10, Item b) with a reference to this Australian Standard, i.e. AS 1774.14.(d) A full point substitutes for a comma when referring to a decimal marker.The Standard is downloaded from Standard SharingThe term informative is used to define the application of the annex to which it applies and is only for information and guidance.iiiCONTENTSPage1Scope . 12Terms and definitions. 13Principle . 24Apparatus . 25Test pieces . 46Procedure . 57Assessment of results. 78Calculation and expression of results . 79Precision . 910Test report . 9Annex A (informative) Example of the determination of thermal conductivity. 10Bibliography . 13vThe Standard is downloaded from Standard SharingNOTESwww.standards.org.au© Standards AustraliaAUSTRALIAN STANDARDRefractories and refractory materialsPhysical test methodsMethod 14:Thermal conductivity1ScopeThis part of ISO 8894 describes a hot-wire (parallel) method for the determination of the thermal conductivity of refractory products and materials. It is applicable to dense and insulating shaped products and to powdered or granular materials (see 6.2), for thermal conductivities of less than 25 W/m·K. The limits are imposed by the thermal diffusivity of the test material and therefore by the dimensions of the test pieces; higher thermal conductivities can be measured if larger pieces are used. Electrically conducting materials cannot be measured.NOTE 1The thermal conductivity of products with a hydraulic or chemical bond can be affected by the appreciable amount of water that is retained after hardening or setting and is released on firing. These materials can therefore require pretreatment. The nature and extent of such pretreatment, and the period for which the test piece is held at the measurement temperature as a preliminary to carrying out the test, are details that are outside the scope of this part of ISO 8894 and are agreed between the parties concerned.NOTE 2In general, it is difficult to make measurements on anisotropic materials and the use of this method for such materials is also agreed between the parties concerned.2Terms and definitionsFor the purposes of this document, the following terms and definitions apply.2.1thermal conductivitydensity of heat flow rate divided by the temperature gradientNOTEThermal conductivity is expressed in watts per metre kelvin (W/m·K).2.2thermal diffusivityathermal conductivity divided by the bulk density times the specific heat capacityNOTE 1a = cpwhere is the thermal conductivity;is the bulk density;cpis the specific heat capacity at constant pressure per weight.NOTE 2Thermal diffusivity is expressed in square metres per second (m2s1).15The Standard is downloaded from Standard Sharing2.3 power Prate of energy transferNOTEPower is expressed in watts (W).3PrincipleThe hot-wire method (parallel) is a dynamic measuring procedure based on the determination of the temperature increase against time at a certain location and at a specified distance from a linear heat source embedded between two test pieces.The test pieces are heated in a furnace to a specified temperature and maintained at that temperature. Further local heating is provided by a linear electrical conductor (the hot wire) that is embedded in the test piece and carries an electrical current of known power that is constant in time and along the length of the test piece.A thermocouple is fitted at a specified distance from the hot wire, the thermocouple leads running parallel to the wire (see Figure 1). The increase in temperature as a function of time, measured from the moment the heating current is switched on, is a measure of the thermal conductivity of the material from which the test pieces are made.4Apparatus4.1Furnace, electrically heated, capable of taking one or more test assemblies (see 5.1) up to a maximum temperature of 1 250 °C. The temperature at any two points in the region occupied by the test pieces shall not differ by more than 10 K. The temperature measured on the outside of the test assembly during a test (ofduration about 15 min) shall not vary by more than ± 0,5 K, and shall be known with an accuracy of ± 10 K.4.2Hot wire, preferably of platinum or platinum-rhodium, with a minimum length equivalent to that of thetest piece. The voltage taps should be located in the test piece with a length between the taps of about200 mm known to the nearest ± 0,5 mm.Both ends of the hot wire are attached to the power source and the voltage taps to the digital multimeter (4.5).The wires to the power source may also be a continuation of the hot wire itself and shall have the same diameter as the wire within the assembly. The wires to the digital multimeter shall be of a diameter not greater than that of the hot wire when within the assembly. Leads outside the assembly shall consist of two or more tightly twisted wires of 0,5 mm diameter. The current lead connections external to the furnace shall be made with heavy-gauge cable.4.3Power supply, to the hot wire (4.2), which shall be stabilized a.c. or d.c., but preferably a.c., and shall not vary in power by more than 2 % during the period of measurement.A power supply to the hot wire of at least 250 W/m is required. This is equivalent to 50 W between the voltage taps for a distance of 200 mm.4.4Differential platinum/platinum-rhodium thermocouple, (Type R: platinum 13 % rhodium/platinum thermocouple, or Type S: platinum 10 % rhodium/platinum thermocouple, see Table 1) formed from a measurement thermocouple and a reference thermocouple connected in opposition (see Figure 1). The leadsof the measurement thermocouple shall run parallel to the hot wire at a distance of 15 mm ± 1 mm (seeFigure 2). The output of the reference thermocouple shall be kept stable by placing it between the top outerface of the upper test piece and a cover of the same material as the test piece (see Figure 1). The diameter of the measurement thermocouple wires shall be the same as that of the hot wire and the wires of both thermocouples shall be long enough to extend outside the furnace where connections to the measuring apparatus shall be made by wire of a different type. The external connections of the thermocouple shall be isothermal.An insulating layer may be inserted between the cover and the upper test piece.NOTEBase-metal thermocouples can be used at temperatures below 1 000 °C.www.standards.org.au© Standards AustraliaKey1Cover2Reference thermocouple3Optional insulating layer4Test piece5Measurement circuit6Measurement thermocouple7Test piece8Heating circuit9Voltage tapsFigure 1 Location of heating circuit and measurement circuit (differential thermocouple circuit)Dimensions in millimetresKey1Temperature/time registration device2Cover3Reference thermocouple4Measurement thermocouple5Hot wire6Voltmeter7Ammeter8Power sourcePQ = Hot-wire measurement lengthFigure 2 Measurement arrangementThe Standard is downloaded from Standard Sharing4.5Digital multimeter, used for measuring the current in the hot wire and the voltage drop across it, andcapable of measuring both to an accuracy of at least ± 0,5 %.4.6Data acquisition system, consisting of a temperature-time registration device with a sensitivity of atleast 2 µV/cm or 0,05 µV/digit, or a temperature measurement of 0,01 K or better and with a time resolution better than 0,5 s.4.7Containers, (for use if the test is performed on powdered or granular material), having internal dimensions equal to those of the solid test assembly specified in Clause 5, so that the test assembly shall consist of two sections as specified in 5.1. The bottom container shall have four sides and a base, and the top container shall have four sides only, plus a detachable cover (see Figure 3).Containers should be of a material that will not react with the test piece at the test temperature and should not be electrically conducting.Key1Cover2Reference thermocouple3Containers4Measurement thermocouple5Hot wireFigure 3 Container with hot wire and thermocouple laid on it5Test pieces5.1DimensionsEach test assembly shall consist of two identical test pieces, not less than 200 mm × 100 mm × 50 mm in size.Itisrecommendedthatthesizeofeachtestpiecebe230 mm × 114 mm × 64 mmor230 mm × 114 mm × 76 mm. Standard-size bricks can then be used as the pieces forming the test assembly,subject to the requirements of 5.2.The limits of this method are imposed by the dimensions of the test pieces. With larger test pieces, higher values of thermal conductivity can be measured. The distance between the hot wire and the thermocouple should be extended to the same ratio as the test pieces. For example, with a test piece of230 mm × 180 mm × 95 mm, a thermal conductivity of about 40 W/m·K can be measured.5.2Surface flatnessThe surfaces of the two test pieces forming the test