2007, Piran, Slovenia

Air film
Skin surface
Skin layer
δ
-L
Measurement methods
RESULTS
Figure 2 shows the relationship between the skin wet area ratioφ calculated by the above
method and Esk/Emax. The values used for the calculation are listed in Table 1. The Lewis
relation was used to calculate hD, and the value of δ was estimated with the assumption that δ
= D/hD. The value of rc was found from the space occupied by one sweat gland, which was
obtained by dividing the body surface area (1.75 m 2 ) of an average male subject by the
number of sweat glands (2.3 million)(Kuno, 1956). Several combinations of Ta and Ca, were
used for the calculation, and TL was determined to make the mean skin surface temperature
35°C. The results shown in Fig. 2 indicate that Esk/Emax does not change greatly regardless of
air temperature or humidity and remains close to 1 even ifφ 2 Fig. 1 Model of heat and mass transfer from the human
body surface
, which is thought to be the real
wet area, decreases. Because the vapor generated from the wet area diffuses in the film threedimensionally,
the vapor concentration might become almost uniform at a position less than δ
from the skin surface in the y direction when δ is greater than rc. Consequently, the
concentration field in the film would not accurately reflect the skin surface condition. This is
obvious from the results of calculation of vapor the concentration distribution based on the
assumption that φ = 0.25 at a temperature of 30°C and relative humidity of 10%, as shown in
Fig. 3. Figure 4 shows the results of temperature distribution in the skin layer for the same
case. It can also be seen here that, because rc is small, the difference in heat flows of the wet
and dry parts of the skin surface does not have much effect on temperature distribution. If the
mean skin temperatures of the wet and dry parts of the skin surface are calculated by changing
the value of φ from 0.01 to 0.99, the difference between them is only about 1°C at most and is
much greater than that in normal conditions. For this reason, the effect of microscopic
temperature fields on the skin surface on the amount of evaporation is though to be
insignificant.
Table 1 The value used for calculation
D 2.61×10 -5 [m 2 s -1 ]
R v 8.31 [JK -1 mol -1 ]
γ 2.44×10 3 [Jkg -1 ]
h 2.33 [Jm -2 s -1 K -1 ]
λ 0.35 [Jm -1 s -1 K -1 ]
Φ rc rc
y
r
497