2007, Piran, Slovenia

Figure 2. Difference in heat transfer
with and without the heat lamp for the
indicated manikin sections and helmets
without visors, with standard deviations
shown, and ordered according to the
total value.
Manikins
Figure 3. The same as Fig. 2, with the
visors mounted on the helmets. Note
that the ordering has changed, due to
the variable effects of the visors.
of significant correlation, and suggests that the face is equally well shielded by most visors in
this configuration, and in general has a limited exposure to the impinging heat flow. It is
clear that for helmet 28 changing the visor position had a minor effect in the given lighting
configuration, whereas for helmet 16 there is a significant difference between the two
positions (p < 0.005). Since 16u and 16s show no significant difference (as is the case for 16d
and 16i), the Al foil played no significant or relevant role on the heat transfer in these cases,
suggesting that the heating of the passing air by the visor was unimportant.
Focusing first on the helmet without a visor, many helmets which deliver a large convective
heat transfer (Brühwiler et al., 2006) allow more radiant flow to penetrate to the scalp, and
vice versa, illustrating a fundamental conflict in optimizing helmets for net heat transfer.
Figs. 2 & 3 also indicate that the major influence on the variations in overall transmission of
radiant flow through the helmet is the scalp section, pointing to the importance of vents in that
section. The transmitted radiant flow is physically expected to be proportional to the manikin
surface area visible through the helmet, ignoring reflection from odd surfaces and the angular
variations. Thus the present ensemble encompasses a span varying over a factor of three in
vent area presented to the heat lamp, or from about 0.7 to 2.4 W (see Fig. 2, scalp section).
Forced convection is expected to be much more sensitive to the overall structure of the vents
and surrounding area (Brühwiler et al., 2006). Fig. 4 illustrates that this correlation can be
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