Approximate thermal calculation of clothing

 

G. M. Kondrat'ev [6] proposed equations for the approximate calculation of thermal comfort of clothing:

R = 0,175 I; (1) I = 0.15 x ((33 - t a)/N) - 5,7/α; (2) N = 0.78 x M/100, (3) where R is the total thermal resistance of clothing in m2 · h · grad/kcal; N - index of the heat load of clothing; the larger N, the harder the body to fight a cold; I - thermal insulation value of clothing; the more I have, the warmer clothes, M heat production of the human body (metabolism) kcal/h (the value of M for various conditions are taken according to the physiologists)*1; α - heat transfer coefficient from the outer surface of the clothing to the environment, kcal/m2 · h · deg.*2; 33 is a constant surface temperature of skin, you need to feel comfortable 'With it;t - temperature of the human environment, 'S;

Using the equations of Professor G. M. Kondratyev, possible to determine the thermal resistance R must have clothes that provide a sense of comfort with the known heat production M and the state of the environment t and α.

Consider one suggested by G. M. Kondratyev [6] examples of an approximate thermal calculation of clothing.

Example. To determine the thermal resistance of clothing for a slow walk at low temperature t = + 10'C in windless cloudy weather.

For these conditions it is possible to make the heat transfer coefficient α = 10 kcal/m2 · h · deg. Metabolism, according to physiologists, M = 200 kcal/h

According to the formula (3) find the value of N: N = 0.78 x M/100 = 200/100 x 0,78 = 1,56.

By the formula (2) find the value of I is: I = 0.15 x ((33 - t a)/N) - 5,7/α = 0.15 x ((33 - 10)/1,56) - 5,7/10 = 1,64.

Given the fitness of the subject, can I reduce to 1.5, then the total thermal resistance of clothing R is R = 0.175 in the I = 0,175 x 1.5 = 0,26 m2 · h · deg/cal.

The next step after determine the required thermal resistance in the design of thermal protective clothing is the solution to the question, how to get clothing with a thermal resistance.

Set of clothes is a multi-layer "package", including products (underwear, shirt, jacket, coat) and the air gap between them. In addition, individual products themselves are multi-layer "package" consisting of tissues of the top, lining and gasket. The amount of air strata in such a small package, as the layers bonded to each other. In the package formed by the products of several types, the value of air layers is more significant.High thermal insulation properties of air to "inert" state forced to take into account the air gap in determining the thermal resistance of clothing.

The total thermal resistance of clothing Rсум*3, by definition of G. M. Kondratyev, represents the equivalent of re by*surface and RP ⁴ * ⁵ thermal resistances [6] Rсум = re by + RP. (4) For the simplest single layer of clothing is the same equation can be represented as follows [7]: Rсум = δ/ λв + δт/ λт + 1/ α, (5) where δ is the average thickness of the air layer between clothing and human skin, mm; λв - coefficient of thermal conductivity of air, kcal/m2 · h · ° δт - average fabric thickness, mm; λт - coefficient of thermal conductivity of tissue, kcal/m2 · h · grad; α - heat transfer coefficient, kcal/m2 · h · deg.

The first two terms represent the value of equivalent thermal resistance, and the last - surface thermal resistance.

For clothing package, this equation will have the form [7]

 

where

the amount of thermal resistance n air layers in clothing;

- the sum of the thermal resistances of the m layers of fabrics within the clothes.

The solution to this equation is a very difficult task due to the fact that all the components in it are the variables.

The first term - thermal resistance of air layers depends on the size of the air gap and air conduction. The maximum thermal resistance of clothing is achieved by the inertia of the air, i.e. when the heat is transferred only by conduction. It was established [9] that the inertia of the air depends on the thickness of the air gap. In layers of thickness greater than 1.27 cm, due to the difference in temperature, the natural circulation of air. The thermal resistance of the air gap, and hence the total thermal resistance of clothing decreases.Putting on the clothing of one type to another causes a certain pressure, the outer layers of clothing on the inside, the deformation of the tissues and reduction of air layers. Reducing air layer occurs is greater the lower the elastic properties of clothing materials. According to [7], the value of air layers in the set of clothes put on the person, ranges from 0 to 0.5 - 0.6 cm, i.e. considerably less than the value of 1.27 cm.

To establish quantitative values of thermal resistance of air layers in a "package" of clothing necessary for special studies.

The second term is the thermal resistance of fabrics and other materials is determined primarily by the number contained in the pores and fibers of still air. The amount of air depends on the thickness, porosity and volumetric weight fabrics. The more the thickness of the fabric, less bulk density and more porosity, the more closely the fabric of the 'perfect' insulator - air inert*⁶.

Technical and aesthetic requirements for clothing fabrics, as well as their efficiency determines the border thickness change and volumetric weight of the materials. According to P. A. Kolesnikov [4], the thickness of most linen fabrics ranges from 0.1 to 0.5 mm, dress is from 0.1 to 1.9 mm, suiting from 0.5 to 1.9 mm. Thickness of overcoat fabrics is quite varied (from 0.1 to 5.5 mm), but the greater part of these tissues (90%) it is equal to from 0.5 to 3.6 mm, the Volume weight of fabrics varies from 0,108 to 0,479 g/cm3, coefficient of thermal conductivity λ from a to 0,070 0,033 kcal/m2 · h · deg.

L. I., Tretyakov [7] calculated the second term in the equation the total thermal resistance, assuming that the set of clothes consists of the best thermal insulation in respect of fabrics: linen, flannel, shirts of calico, woolen jacket with satin lining and woolen coat on twill silk lining. The calculation showed that when the thickness of the "package" of clothing 1.3 cm is provided by a thermal resistance equal 0,360 m2 · h · deg/cal.

When designing clothing with high insulating properties is a great place assign special insulated strips. Thus, the use in the above set is a cotton strip with a thickness of 10 mm will increase the thermal resistance of the package 0,350 m2 · h · grad/kcal and will bring it to 0,710 m2 · h · deg/cal.

Resistance clothing is changing due to natural and forced (moving people) air circulation, while warm air is removed through the "package", and the cold comes in clothing from the environment. The thermal resistance of clothing even more decreases in wind conditions. According to [8], the thermal resistance of clothing materials can be reduced by moving ambient air 3.5 - 4 times.

The decrease in thermal resistance depends on the air permeability of the "package" of clothes; the greater the permeability, the lower the thermal resistance. Therefore, in the design process, heatproof clothes, special attention must be paid to increasing the thermal resistance by reducing air permeability of the "package" of clothes and heat loss by convection.

In this regard, the importance of rational design of heat-protective clothing: blind fasteners, cap details, use vetrostojkie linings and coatings, etc. [4].

The third term the total thermal resistance of clothing - the surface resistance is determined by the heat transfer coefficient. The heat transfer coefficient is equal to the sum of heat transfer coefficients by convection and radiation: aconv. + Arad. Change the first depends mainly on the velocity of the air and structural shapes of clothes (curvature factor). The radiation component of the heat transfer coefficient depends on the temperature difference between the surface of the clothing and environment, as well as the degree of blackness of the surface of the garment. The tissue corresponds to a high degree of blackness, about 80 - 85% [6].

According to foreign hygienists Barton and Edholm[9], the surface thermal resistance of clothing under different conditions is 0,036 - 0,144 m2 · h · deg/cal.

The proportion of individual components of total thermal resistance of clothing, as you can see, varies. The indisputable leading role is the equivalent thermal resistance of the "package" of clothing.

The maximum value of the equivalent thermal resistance depends on the maximum thickness of the "package". According hygienists [9], this thickness should not exceed 4 cm*⁷, which corresponds to the equivalent thermal resistance of approximately 1,000 m2 · h · deg/cal.

Considering the underwear and dress or suit in a set of warm clothes as permanent components of thermal resistance which is approximately equal to 0.1 m2 · h · grad/kcal, the calculation of the specific thermal protective clothing is simplified and reduces to determining the total thermal resistance only clothing.

To do this, according to the formulas (1 - 3) find the required value of thermal resistance of clothing (R), which can ensure human comfort under appropriate conditions the activities of the human body (M) environmental conditions (t, α).

Substituting the value of the total thermal resistance in equation (6), by selection of the user to determine what the "package" of clothing will provide the desired thermal resistance.

Thermal protective clothing should be designed taking into account the climatic conditions of various regions of the USSR and varying intensity of labor.

P. A. Kolesnikov [4] details the requirements for clothing in each of the 6 climatic regions, which medical climatology divides the entire territory of the USSR. As described in his book data, thermal protective clothing must have a thermal resistance of 0.27 m2 · h · deg/cal for the mild winter (summer coat or cloak and suit) to 1.08 m2 · h · grad/kcal, for a very severe winter (Arctic insulated clothing). For a moderately cold winter, the thermal resistance of clothing must be equal to 0,45 - 0,54 m2 · h · deg/cal.

When selecting "packages" of clothing you can use indicative data on the thermal resistance of certain types of clothing, is given in [4], which ranges from 0.5 (light summer dress) to b,0 KLO (Arctic insulated clothing) (1 CLO = 0,18 m2 · h · grad/kcal). Suit and cloak have a thermal resistance by an average of 1.5 CLO, light coats of 2.0 - 2.5 CLO, winter coat - 3,0, Clos [4].

 

Principles of selection "package" heat-resistant clothing

 

The most efficient heat-protective clothing is considered to be the fur clothing. High thermal insulation properties of fur are subject to low permeability of its membrane (the permeability of fur in most cases does not exceed 1 l/m2 · sec) and a significant thickness of air gap formed by the hairline.

However, the raw materials of the fur are limited, the cost is high, so the focus is only on the fur in the manufacture of heat-shielding clothes can not. The bulk of the thermal clothing is made from long fabrics and other materials Semenovich.

Modern heat-protective clothing is a complex structure and consists of several layers: the top fabric, insulating layer (wool, batting, etc.) and lining.

Analysis of the insulating properties of modern winter clothing, held TSNIISHP [10], shows that it has in some cases significant drawbacks: a large consumption of materials, a significant weight reduction of thermal resistance in the process of operation due to stall cotton pads and their thickness. For some areas of the country with cold climate its thermal insulation properties existing clothing is clearly insufficient.

Low thermal insulation properties of winter clothing due to a large extent its great breathability, which reaches, according to P. A. Kolesnikov [4], 40 - 50 l/m2 · sec. Therefore, to improve the thermal properties of winter clothing, you must find the means to reduce its air permeability. Breathability used still tissue top, cotton pads and cotton batting is very large and ranges for most fabrics at the top (78%) in the range of 50 to 250 l/m2 · h, and cotton pads and cotton batting from 90 to 100 l/m2 · h or more.

Attempts to reduce the permeability and increase thermal resistance of winter clothing due to the increase in the thickness and increase the density of the fabric top lead to unjustified increase in the weight and cost of these tissues, but do not give the desired results.

Studies [10, 11, 13] led to the conclusion that to create a rational design of the "package" thermal insulation of clothing is impossible without a revision of the requirements of its individual layers.

Based on the fact that the heat-shielding functions of different layers vary, their structure and physico-mechanical properties should also be different.

From top fabric (the coating) does not require high thermal insulation properties; it should be beautiful, lightweight, durable, nesminaemoy, with minimal water absorption.

Currently successfully used as tissue top lightweight wool and wool blend fabrics loose structures, and various cotton fabrics (reps), woven fabrics of synthetic fibres (kapron, lavsan, etc.) and nesminaemoy with water repellent finishing (impregnation). This can significantly reduce the need for wool fabrics.

The second layer in winter the clothing should be light, soft, cheap vetrostojkie strip, have low permeability and the required strength.

The need to vetrostojkie the strip is eliminated, if the fabric top use a thin and dense fabric having sufficiently low air permeability (within 6 - 10 l/m2 · sec).

The third layer actually insulation, thermal protective clothing should have sufficient thickness, low thermal conductivity, high elasticity in compression, to be light, porous and hygroscopic. The thickness of the insulating strip should be different depending on the climatic conditions, time of year (autumn - winter), working conditions, age of consumers and clothing designs.

Insulation gaskets are used mainly for production of winter clothes. However, their application can be greatly expanded. When selecting a thin and light strip can be used for light coats, ski suits, childrens clothing, etc. the Difference between spring, autumn and winter coat will be only in the thickness of the insulating strip.

The next layer of clothes - lining - must have a smooth surface with a low coefficient of friction so clothes can be easily put on and remove, and improved resistance to dry and wet friction.

Thus, the task of choosing rational "package" thermal protective clothing is to achieve the greatest possible thermal resistance at the smallest possible thickness and weight of the package.

One of the main structural elements of thermal protective clothing, as noted, are insulating gaskets. The rational structure of heat-insulating gasket is still insufficiently studied. Existing research allow to formulate two basic requirements for the insulation strips: the stability of a given thickness, and the presence of a stationary layer of air inside the pad. TSNIISHP together with other research institutions conducted a lot of research work [10] on the selection of a rational heat-insulating gaskets.The most acceptable were a new kind of plastic porous material - polyurethane foam (foam rubber)*⁸.

The foam has good hygienic properties, water vapor permeability, air permeability, high heat resistance and elasticity in compression thickness (foam virtually desminagem).

The foam has a very high porosity, and the pores closed, so that at a small volumetric weight he may have a lower air permeability than the other insulating strip.

The foam is not affected by moth, easy to clean from dirt, frost (up to - 50' C), has significant absorption, but the filter dries quickly.

Clothing made with strips of foam has almost twice as less weight and higher thermal insulation properties than conventional heatproof clothing that was found during the tests in conditions of wind speeds of 8 m/sec.

Comparative data on the above mentioned properties of the foam and other insulating strips, as well as "packages" of winter clothing are given in table. V-1.

 

The foam found in the present application not only in the form of strips, but also duplicated (glued together) with fabric upper and knit.

Cotton and nylon fabric, lined with foam, widely used for the manufacture of men's and women's winter coats and short coats, sporty jackets. Studies of the properties of these tissues [12] showed that thermal properties are not inferior Drapes and bobriki used as fabrics of top for manufacturing winter, spring and autumn coat [13].

 

The weight of clothes

 

On human health has a significant impact weight clothing: heavy clothing causes fatigue from her aching shoulders and reduced efficiency.

In the absence of special requirements to weight of clothes she should weigh as little as possible. This is achieved by reducing the area of parts and the use of materials with lower bulk density (light weight wool and wool blend fabrics, fabrics of synthetic fibers, new heat insulating strips, etc.). The weight of the clothing of different species varies greatly (table. V-2).

The table shows that the average weight of men's winter clothing in 2.5 times and winter women three times more summer.

Weight men's clothing is almost two times more than women.

B. F. Tserevitinov [14] it is estimated that in relation to body weight weight of winter clothes is on average: men - 1/9 females 1/12 in summer, respectively, 1/22 and 1/39.

Especially heavy winter fur clothing. Weight women's fur coat reaches 4.0 to 4.7 kg.

Winter clothes for children is not very different from the clothes of the adults, and in relation to the child's body weight even more difficult. Thus, the weight of fur coats to the average body weight of women is approximately 1/24, while in children 1/12 - 1/16. The great weight of clothing with great mobility and underdeveloped muscles in children leads to a rapid fatigue of the whole body. Therefore, for children to create a light winter clothing is even more important than for adults.

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*1 According to the G. M. Kondratiev [6], the heat production of the body varies widely from 60 kcal/h (sleep) up to 660 kcal/h (most intense muscular effort).

*2 the heat transfer Coefficient, according to G. M. Kondratiev [6], taking from of 7.15 kcal/m2 · h · grad (in calm weather or with normal natural ventilation inside the building) to 45 kcal/m2 · h · grad or above in a strong wind.

*3 Total thermal resistance is called impedance clothing package corresponding to the transition of heat from the skin to the external environment [4].

*⁴ Equivalent thermal resistance is the sum of heat resistances of air layers and layers of materials included in the package clothing.

*⁵ Surface thermal resistance - the resistance to heat transmission from the outer surface of the garment to the external environment - the reciprocal the heat transfer coefficient RP = 1/ α.

*⁶ Coefficient of thermal conductivity fixed (inert air) equal 0,00083 kcal/cm · sec · deg.

*⁷ Thickness of <package" winter modern clothing with a cotton strip is 1.2 - 3.0 cm [4].

*⁸ Clothing industry uses foam in the form of paintings with a width of 100 cm and a length of 15 - 17 m.

 

LITERATURE

 

4. Kolesnikov P. A. Thermal insulation properties of clothing. Publishing house "Light industry", 1965.

6. Kondrat'ev, G. M. Approximate calculation of thermal clothing. Proceedings of the TSNIISHP, 1957, No. 6.

7. Tretyakova L. I. On the thermal calculation of clothing. Izvestiya vuzov, Technology of light industry, 1962, No. 6.

8. Tretyakova L. I. Study of thermal properties of cotton pads. Izvestiya vuzov, Technology of light industry, 1958, No. 1.

9. Barton and Edholm. People in cold conditions. Vol IL, Moscow, 1957.

10. Kolesnikov P. A., Gushchin K. G. Comparative analysis of thermal insulation materials of clothing. Research works TSNIISHP, 1962, № 10.

11. Performance properties of fabrics and modern methods of their assessment, under the General editorship of P. A. Kolesnikova. Wasteheat, 1960.

12. Mikhailov S. M., Shangina, V. F., the Use of fabrics, doubled with foam rubber, in the manufacture of clothing, 5Курн. "Sewing promyshlennosti", 1962, № 2.

13. Kolesnikov P. A. principles of construction of a rational heat-protective clothing, LDNTP, 1961.

14. Tserevitinov B. F. Scientific bases of commodity science of fur products. Thesis, MTILP, 1965.