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PRACTICAL WORK №5

DETERMINATION OF THE HUMAN THERMAL STATE

1 OUTCOMES
Become familiar with the methodology of determination of the human
thermal state.

2 DURATION OF CLASS
The class duration is two academic hours.

3 BASIC THEORY
Normal thermal health occurs when body heat release (biology heat
production) Q is fully perceived by environment Q , i.e. when there is a heat
hb
e
balance. Heat balance equation of "human-environment" is as follows:
Q  q  q cloth .  q rad .  q s .g .  q , (5.1)
. b
. c
hb
where q – convection (heat) due to the flowing of air around the body;
c
q cloth. – heat conduction (diathermancy, thermal conductivity) through
clothing;
q rad. - radiation to the surrounding surface;
q – heat release through sweat glands;
s.g.
q – heat through respiration (air-breathing).
b.
Convective heat transfer is determined by Newton's law:
q  . c  F e t surf . t  amb . , (5.2)
. c
where α – convection heat transfer coefficient (at normal microclimate parameters
c.
2 о
α =4,06W/m · С);
c.
о
t surf. – temperature of the human body's surface, С;
о
t amb. – ambient temperature, С;
F – effective surface of the human body (the size of the effective surface of
е
the body depends on its position in space and is approximately 50–80% of the
geometrical external surface of the human body); for practical calculations is taken
2
F =1,8m .
е
The size (value) and direction of convective heat transfer from the human to
environment is mainly determined by the ambient temperature, atmospheric
pressure, mobility and relative humidity of the air.
Diathermancy (heat conduction) through clothing is determined by the
equation of Fourier:

)
q cloth .  0  F e (t surf .  t amb . , (5.3)
 0
where α – thermal conductivity of the fabrics of clothing of person, W/(m∙°С);
0
∆ – fabric’s thickness of the human clothing, m.
0
Radiation to the surrounding surfaces: thermal energy from the hot body
surface is converted into a radiant energy and transmitted through the air to another
colder surface, where, in turn, is converted again into the heat. Radiant flux (flux
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