EN 11092:2015

TEXTILES. PHYSIOLOGICAL EFFECTS. MEASUREMENT OF THERMAL RESISTANCE AND WATER VAPOR RESISTANCE IN STEADY CONDITIONS

OBJECT AND SCOPE

Thermal resistance is the net result of the combination of heat transfer by convection, conduction and radiation, and its value depends on the contribution of each of them to the total heat transfer. Although it is an intrinsic property of the textile material, its measured value can change with test conditions, due to the interaction of parameters, such as radiant heat transfer with the environment.

The sweat-protected hot plate method (often referred to as the “skin model”) described in this International Standard is designed to simulate the heat and mass transfer processes that occur near human skin.

The application of this measurement technique is limited to maximum values of thermal resistance and resistance to water vapour, which depend on the dimensions and construction of the device used.

TERMS AND DEFINITIONS

Thermal resistance, Rct:
The temperature difference between the two faces of a material, divided by the resulting heat flux per unit area in the direction of the gradient.
Water vapor resistance, Ret:
The difference in water vapor pressure between the two faces of a material divided by the resulting evaporative heat flux per unit area in the direction of the gradient.
Water vapor permeability index, imt:
Relationship between thermal resistance and water vapour.
Water vapor permeability, Wd:
Characteristic of a textile material, or composite, which depends on its resistance to water vapor and to temperature.

EQUIPMENT

Measuring unit, with temperature and water supply control, consisting of a metal plate about 3 mm thick, fixed on a conductive metal block containing a heating element containing an electric heating element. For the measurement of water vapor resistance, the metal plate must be porous. It is surrounded by a heat shield, itself located in an opening of a measuring table.

TEST TUBES

Thick materials < 5 mm
From each material to be tested, a minimum of three specimens must be cut and tested.
Before the test, the specimens must be conditioned for at least 12 hours, at 20° C 65% RH in the case of Ret and 35° C 40% RH in the case of RET.

Thick materials >5 mm
Specimens included in this category require a special test procedure to avoid the loss of heat or water vapor through their edges and conditioning for 24 hours under the conditions specified in the previous point.

TEST PROCEDURE

In the values of thermal and water vapor resistance, measured with the device described in this International Standard, the intrinsic constants of the device are included.

To determine water vapor resistance, an electrically heated porous plate is coated with a membrane that is impermeable to liquid water but permeable to water vapor. The water supplied to the heating plate evaporates and passes through the membrane as vapor, so the liquid water does not come into contact with the test tube. With the specimen placed on the membrane, the heat flux required to maintain the plate at a constant temperature is a measure of the degree of water evaporation and from there the water vapor resistance of the plate. specimen is determined.

ASSEMBLY OF THE TEST SPECIMENS ON THE MEASURING UNIT
The test pieces shall be placed so that they lie flat in the measuring unit, with the side that normally faces the human body, towards the measuring unit.
Bubbles and wrinkles in the test piece, or air gaps between the test piece and the measuring unit must be avoided.

MEASUREMENT OF THERMAL RESISTANCE, Rct
The temperature of the measurement unit, Tm, is set at 35°C and the air temperature, Ta, is set at 20°C, with an RH of 65%. The air velocity, va, is set to 1 m/s.

MEASUREMENT OF THE RESISTANCE TO WATER VAPOR, Ret
For the measurement of resistance to water vapor, a cellophane membrane impermeable to liquid water, but permeable to water vapor shall be placed on top of the surface of the measuring unit.