ISO 11092 pdf download – Textiles – Physiological effects —Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded- hotplate test).
4 Principle
The specimen to he tested is placed on an electrically heated plate with conditioned air ducted to flow across and parallel to its upper surface as specified In this International Standard.
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 International Standard enables the thermal resistance Rd 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, an electrically heated porous plate is covered by a water-vapour permeable but liquid-water impermeable membrane. Water fed to the heated plate 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 International Standard enables the water-vapour resistance R1 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 Apparatus
5.1 MeasurIng unlt with temperature and water supply control, consisting of a metal ilate approximately 3 mm thick with a minimum area of 0,04 m2 (e.g. a square with each side 200 mm in length, IJ fixed to a conductive metal block containing an electrical heating element [see EigureJ,, items (I) and (6)J. For the measurement of water-vapour resistance, the metal plate (1) must be porous. It is surrounded by a thermal guard litern (8) of Figure 21 which is in turn located within an opening in a measuring table (11).
The coefficient of radiant ernissivity of the plate surface (1) shall be greater than 0,35, measured at 20 °C between the wavelengths 8 pm to 14 pm, with the primary beam perpendicular to the plate surface and the rellection hemispherical.
Channels are machined into the face of the heating element block (6) where it contacts the porous plate to enable water to be fed from a dosing device (5).
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 should be minimized. e.g. by leading as much wiring as possible along the Inner face of the thermal guard (8).
The temperature controller (3), including the temperature sensor of the measuring unit (2), shall maintain the temperature Tm of the measuring unit (7) constant to within ± 0,1 K. The heating power H shall be measurable by means of a suitable device (4) to within ± 2 % over the whole of its usable range.
7.1.2 Determination Of RCtO
7.1.2.1 DurIng the determination of Rro, the surface of the porous plate is kept constantly moist by means of a water-dosing device (see SJ.). A smooth, water-vapour permeable but liquid-water impermeable cellophane membrane of thickness 10 pm -50 pm shall be fitted over the porous plate.
The cellophane membrane shall be moistened with distilled water and fixed to the measuring plate by appropriate means so that it remains completely free of wrinkles.
The water supplied to the measurIng plate shall be distilled, preferably double-distilled, and reboiled prior to use so that it is free ofgas in order to prevent the tormation of gas bubbles beneath the membrane.
7.1.2.2 Set the temperature of both the measuring unit Tm and the air temperature T at 35 0C Set the air speed i’ to 1 rn/s.
The relative humidity R.Fl. of the air shall be kept constant at 40 %. corresponding to a water-vapour partial pressure p of 2,250 Pa. The water-vapour partial pressure Pm directly at the surface of the measuring unit can be assumed equal to the saturation vapour pressure at the temperature of this surface, i.e. 5,620 Pa. without compromising the accuracy of the test.
Any deviations from the above values of Tm Ta, va and Ri-I. shall be within the limits stated in iiuse. Wait until the measured quantities (Tm, Tj, Ri-I., H) reach steady-state before recording their values.
ISO 11092 pdf download – Textiles – Physiological effects —Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded- hotplate test)
