s levels o 22.9 An endurance athletic event is cond ditions are extremely stress
ID: 1770177 • Letter: S
Question
s levels o 22.9 An endurance athletic event is cond ditions are extremely stressful, the d 45 °C. One of the participants in the event. tempet sorb 1.1 litre of water per hour through the a, i lose water through perspiration fasterthahotole latent heat of vaporisation of water at the perature is 2440 kJ kg-1 ed when the dry-bulb temperature this if partici ant's skin Determine the maximum rate at which he perspiration without becoming dehydrated. heanoutareconveventnloss he can reject hea by (a) The athlete has a surface area of 1.8 m2 transfer coefficient, including convection and bracha 22 Wm2 K-1. During the endurance e ture is 37°C. Determine the rate of heatainos e convection and radiation alone, not including the e perspiration. and his (b) his skin e efflect o (e) The table above shows the metabolic rate of the thies ing different activities. Assume this is the same as the of production of thermal energy in his body. Determine b maximum sustainable metabolic rate for the athlete the endurance event without any temperature rise. Whz is the most vigorous activity that could be sustained unde these conditions? the athlete has sufficient water to perspire and evapore 1.1 kg per hour and on this occasion he intends to run wit a metabolic rate of 800 W. What is the maximum dry temperature at which he could do this sustainably,assur ing his skin temperature is 37 °C? (d) Suppose the event is rescheduled for a cooler day. AgaiExplanation / Answer
a)
Athlete can perspire at a rate 1.1 l/hr. Taking density of water as 1kg/l, the mass of water lost is 1.1 kg/hr
Heat given out Q = mL for vaporization
Q = 1.1 * 2440 = 2684 kJ/hr = 2684000/3600 W = 745.5 W
b)
Rate of heat gained = surface heat transfer coefficient * area * temperature difference
= 22 * 1.8 * (45-37) = 316.8 W
c)
For no temperature rise heat gained = heat lost
heat due to metabolism + heat convection/radiation = heat lost by perpiration
heat due to metabolism = 745.5 - 316.8 = 428.7 W (Ans)
d)
heat due to metabolism + heat convection/radiation = heat lost by perpiration
800 + 22 * 1.8 * ( T -37) = 745.5
T = 35.6 deg C (Ans)
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