This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 11048-2008 Textiles — Physiological effects — Measurement of thermal and water-vapour resistance under steady-state conditions and the following main technical changes have been made with respect to GB/T 11048-2008:
——The standard name has been modified as "Textiles — Physiological effects — Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded-hotplate test) ";
——The description of Type A and Type B instruments in the scope of Chapter 1 has been deleted (Chapter 1 of 2008 edition);
——The terms and definitions of "clo" and "thermal conductivity" in Chapter 2 have been deleted (2.5 and 2.6 of 2008 edition);
——The "k thermal conductivity" and "d material thickness" in the symbols and units of Chapter 3 have been deleted (Chapter 3 of 2008 edition);
——The Type B instrument — static plate method and its related clauses in the original standard have been deleted (5.2 and 8.2 of 2008 edition);
——The schematic diagram of thermal retaining ring and bottom plate in the original Figure 3 has been deleted (Figure 3 of 2008 edition);
——The calculation of other indexes in 7.5 has been deleted (7.5 of Edition 2008);
——The Annex D "Guidance on the test specimen assembly for materials prone to swelling" has been added (see Annex D).
This standard has been redrafted and modified in relation to ISO 11092: 2014 Textiles — Physiological effects — Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded-hotplate test).
The technical differences of this standard from ISO 11092:2014 are as follows:
——The supplementary explanation of scope in Chapter 1 of the international standards has been adjusted to "Note";
——The expression of "with 3 significant figures reserved for result" has been added to the relevant calculations in Chapter 7;
——The Annex C "Verification of Instruments" has been added, and the Annex C in ISO 11092: 2014 has been postponed and adjusted to Annex D.
This standard was proposed by China National Textile and Apparel Council.
This standard is under the jurisdiction of the National Technical Committee on Textiles of Standardization Administration of China (SAC/TC 209).
The previous editions of the standard replaced by this standard are as follows:
——GB/T 11048-1989 and GB/T 11048-2008.
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Introduction
The physical properties of textile materials which contribute to physiological comfort involve a complex combination of heat and mass transfer. Each may occur separately or simultaneously. They are time-dependent, and may be considered in steady-state or transient conditions.
Thermal resistance is the net result of the combination of radiant, conductive and convective heat transfer, and its value depends on the contribution of each to the total heat transfer. Although it is an intrinsic property of the textile material, its measured value may change through the conditions of test due to the interaction of parameters such as radiant heat transfer with the surroundings.
Several methods exist which may be used to measure heat and moisture properties of textiles, each of which is specific to one or the other and relies on certain assumptions for its interpretation.
The sweating guarded-hotplate (often referred to as the "skin model") described in this International Standard is intended to simulate the heat and mass transfer processes which occur next to human skin. Measurements involving one or both processes may be carried out either separately or simultaneously using a variety of environmental conditions. Hence transport properties measured with this apparatus can be made to simulate different wear and environmental situations in both transient and steady-states. In this Standard only steady-state conditions are selected.
Textiles — Physiological effects — Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded-hotplate test)
1 Scope
This Standard specifies methods for the measurement of the thermal resistance and water-vapour resistance, under steady-state conditions.
This standard is applicable to all kinds of textile fabrics and their products, and coatings, leather and multilayer assemblies may be implemented with reference.
Note 1: The application of this measurement technique is restricted to a maximum thermal resistance and water-vapour resistance which depend on the dimensions and construction of the apparatus used (e.g. 2m2·K/W and 700m2·Pa/W respectively, for the minimum specifications of the equipment referred to in this Standard).
Note 2: The test conditions used in this Standard are not intended to represent specific comfort situations, and performance specifications in relation to physiological comfort are not stated.
2 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
2.1
thermal resistance
Rct
temperature difference between the two faces of a material divided by the resultant heat flux per unit area in the direction of the gradient
Note 1: The dry heat flux may consist of one or more conductive, convective and radiant components.
Note 2: Thermal resistance is expressed in square metres kelvin per watt (m2·K/W).
2.2
water-vapour resistance
Ret
water-vapour pressure difference between the two faces of a material divided by the resultant evaporative heat flux per unit area in the direction of the gradient
Note 1: The evaporative heat flux may consist of both diffusive and convective components.
Note 2: Water-vapour resistance is expressed in square metres pascal per watt (m2·Pa/W).
2.3
water-vapour permeability index
imt
ratio of thermal and water-vapour resistances in accordance with Formula (1):
i_mt=(S×R_ct)/R_et (1)
where,
S=60Pa/K.
Note: imt is dimensionless, and has values between 0 and 1. imt= 0 implies that the material is water-vapour impermeable, that is, it has infinite water-vapour resistance; imt= 1 has both the thermal resistance and water-vapour resistance of an air layer of the same thickness.
2.4
water-vapour permeability
Wd
characteristic of a textile material or composite depending on water-vapour resistance and temperature in accordance with Formula (2):
W_d=1/(R_et×Φ_(T_m ) ) (2)
where,
Φ_(T_m )——the latent heat of vaporization of water at the temperature Tm of the measuring unit, Φ_(T_m )＝0.627W·h/g at Tm = 35°C.
Note: Water-vapour permeability is expressed in grams per square metre hour pascal [g/(m2·h·Pa)].
3 Symbols
For the purposes of this document, the following symbols apply.
Rct——the thermal resistance, m2·K/W;
Ret——the water-vapour resistance, m2·Pa/W;
imt——the water-vapour permeability index, dimensionless;
Rct0——the apparatus constant, m2·K/W, for the measurement of thermal resistance Rct;
Ret0——the apparatus constant, m2·Pa/W, for the measurement of water vapour resistance Ret;
Wd——the water-vapour permeability, g/(m2·h·Pa);
Φ_(T_m )——the latent heat of vaporization of water at the temperature Tm, W·h/g;
A——the area of the measuring unit, m2;
Ta——the air temperature in the test enclosure, °C;
Tm——the temperature of the measuring unit, °C;
Ts——the temperature of the thermal guard, °C;
pa——the water-vapour partial pressure (of the air in the test enclosure at temperature Ta), Pa;
pm——the saturation water-vapour partial pressure (at the surface of the measuring unit at temperature Tm), Pa;
va——the speed of air above the surface of the test specimen, m/s;
sv——the standard deviation of air speed va, m/s;
R.H.——the relative humidity, %;
H——the heating power supplied to the measuring unit, W;
?Hc——the correction term for heating power for the measurement of thermal resistance;
?He——the correction term for heating power for the measurement of water-vapour resistance;
α——the slope of the correction line for the calculation of ?Hc;
β——the slope of the correction line for the calculation of ?He.
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4 Principle
Cover the specimen on a test plate, the test plate, its surrounding thermal guard and the bottom protection plate can keep constant temperature, so that the heat of the test plate can only be lost through the specimen, and the air may flow parallel to the upper surface of the specimen. For the determination of thermal resistance, the heat flux through the test specimen is measured after steady-state conditions have been reached.
The technique described in this Standard enables the thermal resistance Rct of a material to be determined by subtracting the thermal resistance of the boundary air layer above the surface of the test apparatus from that of a test specimen plus boundary air layer, both measured under the same conditions.
For the determination of water-vapour resistance, a porous measuring unit is covered by a water-vapour permeable but liquid-water impermeable membrane. Water fed to the measuring unit evaporates and passes through the membrane as vapour, so that no liquid water contacts the test specimen. With the test specimen placed on the membrane, the heat flux required to maintain a constant temperature at the plate is a measure of the rate of water evaporation, and from this the water-vapour resistance of the test specimen is determined.
The technique described in this Standard enables the water-vapour resistance Ret of a material to be determined by subtracting the water-vapour resistance of the boundary air layer above the surface of the test apparatus from that of a test specimen plus boundary air layer, both measured under the same conditions.
5 Apparatuses
5.1 Measuring unit, with temperature and water supply control
The measuring unit consists of a metal plate approximately 3mm thick with a minimum area of 0.04m2 (e.g. a square with each side 200mm in length) fixed to a conductive metal block containing an electrical heating element (see Figure 1). For the measurement of water-vapour resistance, the metal plate (1) must be porous. It is surrounded by a thermal guard which is in turn located in a measuring table.
The coefficient of radiant emissivity of the plate surface shall be greater than 0.35, measured at 20°C between the wavelengths 8μm to 14μm, with the primary beam perpendicular to the plate surface and the reflection hemispherical.
Channels are machined into the face of the heating element block where it contacts the porous plate to enable water to be fed from a dosing device into the measuring unit.
The position of the measuring unit with respect to the measuring table shall be adjustable, so that the upper surface of test specimens placed on it can be made coplanar with the measuring table.
Heat losses from the wiring to the measuring unit or to its temperature measuring device shall be minimized, e.g. by leading as much wiring as possible along the inner face of the thermal guard.
The temperature controller, including the temperature sensor of the measuring unit, shall maintain the temperature Tm of the measuring unit constant to within ±0.1°C. The heating power H shall be measurable by means of a suitable device to within ±2% over the whole of its usable range.
Water is supplied to the surface of the porous metal plate by a dosing device such as a motor-driven burette. The dosing device is activated by a switch which senses when the level of water in the plate falls more than approximately 1.0mm below the plate surface, in order to maintain a constant rate of evaporation. The level switch is mechanically connected to the measuring unit.
Before entering the measuring unit, the water shall be preheated to the temperature of the measuring unit. This can be achieved by passing it through tubes in the thermal guard before it enters the measuring unit.
Foreword i
Introduction iii
1 Scope
2 Terms and definitions
3 Symbols
4 Principle
5 Apparatuses
6 Test specimens
7 Tests
8 Precision of results
9 Test report
Annex A (Normative) Mounting procedure for specimens containing loose filling materials or having uneven thickness
Annex B (Normative) Determination of correction terms for heating power
Annex C (Normative) Check of instruments
Annex D (Informative) Guidance on test specimen assembly for materials prone to swelling
