98
4 Results and Discussion
• In the 75 kph speed cooling curve, the drop in temperature was very steep as
shown in Fig. 4.24 (brown), and this drop was achieved at a rapid rate initially.
In relation to the 55 kph speed cooling curve, the 75 kph speed cooling curve
shows significant further drop in temperature before it approaches the steady state.
Significant drops in temperature for the road velocity experiments were achieved
because the forced convection at higher speeds allows additional evaporation of
water from the textile liner inside the helmet and contributes to more cooling, as
indicated by the curve shown in the figure.
In addition, it was observed from the figure that at the higher velocities (i.e. 55 and
75 kph) the respective cooling curves show a rapid drop in temperature and reach the
maximum nearer to the half-an-hour mark. Then the drop in temperature gradually
decreases and eventually approaches the steady state.
4.4 Amount of Heat Removed from the Head Form
for Thermal Equilibrium
To analyse and calculate the thermal equilibrium for a motorcyclist riding in tropical
conditions by using the heat loss equations, some assumptions have been made which
are described as shown:
The ambient temperature (T a ) was taken to be 28 °C.
The mean skin temperature (T sk ) was taken to be 34 °C. The dew point temperature
(T dp ) was taken to be 15 °C.
The core body temperature (T c ) was taken to be 37.15 °C
Motorcyclists’ DuBois body area (A d ) for an adult (of weight 70 kg and height
1.73 m) was taken to be 1.84 m
2
The metabolic rate (H) for a motorcyclist in tropical conditions was considered
to be 4 Met which is equivalent to 428.35 W (1 Met = 58.2 W/m
2
× A d , thus 1 Met
= 107.08 W). The mechanical work output for an adult motorcyclist was considered
to be approximately 10% of the metabolic rate (H) that is 42.84 W. The speed of
the motorcyclist was taken as 55 kph (15.28 m/s); h e is the evaporative coefficient
(for 55 kph speed, h e = 8.3 × v
0.5 , v = 15.28 m/s) = 32.44 W/m
2 K [1]; h c is
the convective coefficient (for 55 kph speed, h c = 8.3 × v
0.5 , v = 15.28 m/s) =
32.44 W/m
2 K [1].
4.4.1 Calculations
The equations used for the thermal equilibrium calculations are shown from Eqs. 3.5–
3.12.
4 Results and Discussion
• In the 75 kph speed cooling curve, the drop in temperature was very steep as
shown in Fig. 4.24 (brown), and this drop was achieved at a rapid rate initially.
In relation to the 55 kph speed cooling curve, the 75 kph speed cooling curve
shows significant further drop in temperature before it approaches the steady state.
Significant drops in temperature for the road velocity experiments were achieved
because the forced convection at higher speeds allows additional evaporation of
water from the textile liner inside the helmet and contributes to more cooling, as
indicated by the curve shown in the figure.
In addition, it was observed from the figure that at the higher velocities (i.e. 55 and
75 kph) the respective cooling curves show a rapid drop in temperature and reach the
maximum nearer to the half-an-hour mark. Then the drop in temperature gradually
decreases and eventually approaches the steady state.
4.4 Amount of Heat Removed from the Head Form
for Thermal Equilibrium
To analyse and calculate the thermal equilibrium for a motorcyclist riding in tropical
conditions by using the heat loss equations, some assumptions have been made which
are described as shown:
The ambient temperature (T a ) was taken to be 28 °C.
The mean skin temperature (T sk ) was taken to be 34 °C. The dew point temperature
(T dp ) was taken to be 15 °C.
The core body temperature (T c ) was taken to be 37.15 °C
Motorcyclists’ DuBois body area (A d ) for an adult (of weight 70 kg and height
1.73 m) was taken to be 1.84 m
2
The metabolic rate (H) for a motorcyclist in tropical conditions was considered
to be 4 Met which is equivalent to 428.35 W (1 Met = 58.2 W/m
2
× A d , thus 1 Met
= 107.08 W). The mechanical work output for an adult motorcyclist was considered
to be approximately 10% of the metabolic rate (H) that is 42.84 W. The speed of
the motorcyclist was taken as 55 kph (15.28 m/s); h e is the evaporative coefficient
(for 55 kph speed, h e = 8.3 × v
0.5 , v = 15.28 m/s) = 32.44 W/m
2 K [1]; h c is
the convective coefficient (for 55 kph speed, h c = 8.3 × v
0.5 , v = 15.28 m/s) =
32.44 W/m
2 K [1].
4.4.1 Calculations
The equations used for the thermal equilibrium calculations are shown from Eqs. 3.5–
3.12.