ISO 11092:2014 pdf download – Textiles — Physiological effects —Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded- hotplate test)
ISO 11092:2014 pdf download – Textiles — Physiological effects —Measurement of thermal and water-vapour resistance under steady-state conditions (sweating guarded- hotplate test).
5.3 Test enclosure, into which Is built the measuring unit and thermal guard, and in which the ambient air temperature and humidity are controlled.
The conditioned air shall be ducted so that it flows across and parallel to the upper surface of the measuring unit and thermal guard. The height of the duct above the measuring table shall not be less than 50 mm.
The drift of the temperature Ta of this air (low shall not exceed ± 0,1 K for the duration of a test. For the measurement of thermal resistance and water vapour resistance values below 100 m2’Pa/W, an accuracy of ± 0,5 K is sufficient.
The drift of the relative humidity R.H. of this air flow shall not exceed ± 3 % R.H. for the duraticrn of a test.
This air flow is measured at a point 15 mm above the measuring table over the centre of the uncovered measuring unit and at an air temperature T of 20 °C. The air speed a measured at this point shall have a mean value of 1 rn/s. with the drift not exceeding ± 0.05 rn/s for the duration ofa test.
It is important that at this point the air flow shall have a certain degree of turbulence. expressed by the related variation in air speed Sy/Va of between 0,03 and 0,07, measured at approximately 6 s intervals over a time period of at least 10 mm with an instrument which has a time constant of less than 1 s.
6 Test specimens
6.1 Materials 5 mm thick
Test specimens shall completely cover the surfaces of the measuring unit and thermal guard.
From each material to be tested, a minimum of three test specimens shall be cut and tested.
Before testing. specimens shall be conditioned for a minimum of 12 hat the temperature and humidity specified in either 7.3 or Z4 as appropriate.
6,2 Materials> 5 mm thick
6.2.1 Specimens falling into this category require a special test procedure to avoid loss of heat or water vapour from their edges.
In the measurement of thermal resistance, corrections for thermal edge losses are necessary if the specimen thickness is greater than approximately twice the width b of the thermal guard (see Figure2). The deviation from the linear relationship between thermal resistance and specimen thickness can be determined and corrected by the factor [1+ (R.JR nu,d)J using the measurement of the R1 values for several thicknesses of a homogeneous material such as foam, up to a total thickness d of at least that of the specimen to be tested (see Figure 3).
Check the apparatus constants Rcto and Rto at regular intervals. Where deviations greater than the accuracy of the measuring device occur (see Clause 8), an adjustment shall be made. In most cases a change In Rto or Retü is caused by a deviation in the speed of the air v over the surface of the test specimen. Air speed should be checked at regular Intervals by the technique described in 5.3.
The air flow (both speed and degree of turbulence) over the surface of the test specimen influences the resistance of the boundary layer which adheres to the outer surface of the specimen, and thus influences the test result.
7.2 Assembly of test specimens on the measuring unit
7.2.1 Where appropriate, the orientation of the test specimens with respect to the air flow shall be defined and described in the test report.
The test specimens shall be placed so that they lie flat across the measuring unit, with the side normally facing the human body towards the measuring unit. In the case of multiple layers, specimens shall be arranged and stacked on the measuring unit as on the human body. Water-vapour impermeable adhesive tape or a light metal frame may be used around the edges of the test specimen to keep it flat.
Bubbles and wrinkles in the test specimen, or air gaps between the specimen and measuring unit or between the components of multilayer specimens, shall be prevented provided they are not specific to the surface profile of the specimens.
NOTE Guidance on the test specimen assembly for materials prone to swelling Is given In Annex C.
7.2.2 Normally, test specimens are measured free from stretch or loading and, in the case of multiple layers, without air gaps between layers. However, if a test is carried out under extension or applied pressure or with air gaps, this shall be mentioned in the test report.
7.2.3 With test specimens thicker than 3 mm, the measuring unit shall be lowered so that the outer surface o[the specimen Is flush with the measuring table.
7.3 Measurement of thermal resistance
7.3.1 Set the temperature of the measuring unit Tm at 35°C and the air temperature Ta at 20°C with a relative humidity R.H. of 65 %. Set the air speed Va at 1 m/s. Any deviations from these values shall be within the limits stated in C1aue 5.