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of radiation) at the heat transfer by radiation is greater the lower the temperature of
surfaces, that is surround a person, and determined by using the Stefan-Boltzmann
law:
T 4 T 4
q rad . C 0 F 1 1 2 1 2 , (5.4)
100 100
4
2 o
where С – reduced (special) radiation (emissivity) coefficient, W/m · K ;
0
2
F – area of the surface, that emits radiant flux, m ;
1
γ – coefficient of exposure (irradiation), that depends on the location and
1-2
sizes of surfaces F і F and shows the percentage (part) of the radiant flux, that
2
1
falls on the part of a surface F , from the total flow emitted by the surface F ;
2
1
Т , Т – respectively, average surface temperature of the human body and
2
1
o
clothing and the average temperature of surrounding surfaces, K.
For practical calculations in the range of subject’s temperature, which
surrounds the man (10 ... 60°C) the reduced radiation coefficient equals to
2 o
4
С =4,9W/m · K . Irradiation coefficient γ is usually taken equal to 1,0. In this
1-2
0
case, the values of radiant flux mainly depends on the emissivity factor (“degree of
blackness”) and temperature of objects that surround person.
Heat release through evaporation is given by following equation:
q s. g. G r , (5.5)
where G – amount of moisture that is released and evaporates, kg/s;
r – latent heat from the evaporation of moisture that is released, J/kg.
Data about sweating depends on air temperature and physical activity of
human and vary widely. Thus, at the air temperature 30°C person, who is not
engaged in physical labor, has sweating near 2g/min, and when doing hard work
this value increases to 9,5g/min.
Heat release through respiration is defined by:
q V p .v . C t t 2 , (5.6)
1
b
where V – “pulmonary ventilation” – volume of air, that is inhaled by a person
p.v.
3
per time unit, m /s;
3
ρ – density of inhaled air, kg/m ;
С – reduced heat (thermal) capacity of inhaled air, J/kg·˚С;
t , t – respectively, temperature of inhaled and exhaled air, °С.
2
1
4 TASK OF CLASS
4.1 Before meeting on class, students should study basic theory of
methodology of determination of the human thermal state. All students are
expected to come to class alert and ready to participate in discussion.
4.2 Students in the classroom at the request of a teacher give answers on the
questions.
4.3 Then the students should solve the problems and tasks (should determine
the biology heat production and compare its value with environment heat
production; construct a graph of the dependence of heat transfer perceived by
31
