Vestimentary insulation

The vestimentary insulation is the thermo isolation which the Vêtement S. get.

One of the roles of clothing is indeed to protect from the bad weather, and in particular from the cold. They are also useful to be protected from heat, in particular for the professions related to fire (Métallurgie, firemen).

Mechanisms of insulation

There are three modes of Transfer of heat: the conduction (heat transfers per contact), the Convection (movements of air) and the Radiation.

The Air has a very weak thermal Conductivité, but on the other hand, it is very mobile. There are thus two essential components in protection against the cold:

to cut the wind, to prevent it from driving out the layer of hot air which one constituted;
to maintain a layer of air motionless, by trapping it by wire (Wool, Fur, natural Pilosity…).

The third element is the moisture. Indeed, water is a good thermal driver (it is used besides as liquid coolant in the systems of central heating and the nuclear plants, and to cool the Brûlure S). If clothing is wet - by perspiration, the rain, an immersion - water will replace the air between wire of clothing and it will occur escapes by conduction.

The thermo isolation is thus optimal with three layers of clothing:

a layer close to the body, for the Hygiene (changes more frequently than the remainder of clothing), and whose role is to evacuate perspiration, so that it does not remain in contact with the skin;
a layer external with fine grid, Wind-cutter, in general fine; if there is a risk of bad weather, it is ideally a clothing Imperméable, the ideal being a textile stopping the water drops but letting pass the Steam, which makes it possible to evacuate the Sueur (for example Gore-Tex);

between the two, a “thick” layer which traps air and prevents the contact between the skin and the layer wind-cutter (this one being fine, it takes the temperature of outside quickly).

The three layers of air between the skin and clothing play also a part of insulation. Thus, if clothing is tight (for example by the straps of a backpack), the insulation is less good at these places.

Units

The clo is a unit measuring the thermo isolation used for the Vêtement S ( cloths in English).

1 clo = 0,155 K · m ²/W

It is the insulation which makes it possible a person at rest to maintain the thermal balance in an atmosphere with 21 °C (70 °F). Above, the person perspires, below, it feels the cold.

One uses also the togs

1 togs = 0,1 m ²·K/W ≈ 0,645 clo

1 clo = 1,55 togs

The word “ togs ” is a word of English slang, the equivalent of “clothes”. It comes from the Dutch tuig and from the German tög .

Equation with dimensions

A person produces heat by her Métabolisme (at the time of the contraction of a Muscle, approximately 15% of the energy are used for the movement and 85% of energy are used to produce heat), with a power P per body unit of area of approximately:

60 W/m ² at rest;
120 W/m ² for a slow walk;
180 W/m ² for a fast walk.

The escapes of heat are proportional to the difference between the temperature of the body and the outside temperature, from where the term in Kelvin.

Thermal temperature of balance

The temperature of environment T to which the body is with thermal balance depends on the power P produced by the body and on the insulation R . The empirical formula, in °C, is:

T = 31 - P · R

in international units. If R is in clo, the formula becomes

T = 31 - 0,155· P · R

Some examples

; Insulation of clothing

summer clothing shorts and barechested: 0,4 clo;
held of Ski: 2 clo;
light polar equipment: 3 clo;
heavy polar equipment: 4 clo;
polar sleeping bag: 8 clo.

; Temperature of balance

nobody in summer clothing at rest ( P = 60 W/m ², R = 0,4 clo): T = +27 °C;
heavy polar equipment at rest ( P = 60 W/m ², R = 4 clo): T = -6 °C;
slow walk out of light polar equipment ( P = 120 W/m ², R = 3 clo): T = -25 °C;
sleep in a polar sleeping bag ( P = 48 W/m ², R = 8 clo): T = -28 °C;
fast walk out of heavy polar equipment ( P = 180 W/m ², R = 4 clo): T = -80 °C.

See too

wind Cooling

External bonds

How Many? With Dictionary off Units off Measurement, Russ Rowlett, University of North Carolina, Chapel Hill

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