BS ISO 20852 pdf free download
BS ISO 20852-2020 pdf free download.Textiles — Determination of the total heat transfer through textiles in simulated environments.
This document specifies the test method for determining the amount of heat transferred through clothing fabrics by the combined dry and evaporative heat emission under simulated and specified conditions. This test method can be used for fabrics, films, coatings, foams and leathers including multilayer assemblies used in hot environment or in activities. The application of this measurement technique is restricted to a maximum amount of total heat transfer which depend on the dimensions and construction of the apparatus used (e.g. about 1 200 W/m 2 for the maximum specifications of the equipment according to ISO 11092).
2 Normative references The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 3696, Water for analytical laboratory use — Specification and test methods
ISO 11092:2014, Textiles — Physiological effects — Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded-hotplate test)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
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3.1 dry heat emission heat transferred by the temperature difference between the two faces of a material divided by the resultant heat flux per unit area in the direction of the gradient in dry state Note 1 to entry: It is a quantity which determines the dry heat flux across a given area in response to a steady applied temperature gradient. 3.2 evaporative heat emission heat transferred by the 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, when evaluated non-isothermally Note 1 to entry: It is a quantity which determines the “latent” evaporative heat flux across a given area in response to a steady applied water-vapour pressure gradient. The evaporative heat flux may consist of condensation as well as diffusive and convective components.
5 Principle This test evaluates two forms of heat transfer which are dry heat and evaporative heat emission. The total heat transfer results from combining both by calculation. Dry heat emission represents the heat loss resulting from the external environment due to the temperature gradient 10 °C and it is drawn from the standardized total thermal resistance of the test specimen and air layer. Evaporative heat emission represents the heat loss resulting from the external environment due to the vapour pressure gradient 3,57 kPa and it is drawn from the standardized total evaporative resistance of the test specimen and air layer
6 Apparatus
6.1 Sweating guarded hot plate test machine, as described in ISO 11092. 7 Materials 7.1 Water For the evaporative resistance measurements, water for analytical laboratory use over grade 3, according to ISO 3696, shall be used to wet the test plate surface. 7.2 Liquid barrier A smooth, water-vapour permeable but liquid-water impermeable cellophane membrane of thickness 10 μm to 50 μm shall be fitted over the porous plate. 8 Test specimens Three test specimens are used. Use test specimens large enough to cover the surface of the hot plate test section and the guard section completely. Remove any undesirable wrinkles from the test specimens. Possible techniques for removing wrinkles include smoothing, free-hanging, pressing, steaming, ironing, and so forth. Allow the test specimens to come into equilibrium with the atmosphere 25 °C, 65 % R.H. of the testing chamber after conditioning them at the same environment for at least 12 h. 9 Test procedure 9.1 Test conditions Maintain the temperature of the test plate, guard section and bottom plate at (35 ± 0,5) °C without fluctuating more than ± 0,1 °C during a test. Air temperature should be (25 ± 0,5) °C and it should maintain the air flowing over the test plate at the same condition without fluctuating more than ± 0,1 °C during a test. Maintain the relative humidity of the air flowing over the plate at (65 ± 4) % R.H. during the test. Set the air velocity 1 m/s. Maintain the same air velocity for all calibrations and tests, and without fluctuating more than ± 0,1 m/s over the duration of the test measurement.BS ISO 20852 pdf download.
