On a cool day in April a scantily clothed runner is known to lose heat at a rate of 500 W because of con- vection to the surrounding air at Too = 10°C. The run- ner's skin remains dry and at a temperature of Ts = 30°C. Three months later, the runner is moving at the same speed, but the day is warm and humid with a temperature of Too = 30°C and a relative humidity of ¢oo = 60%. The runner is now drenched in sweat and has a uniform surface temperature of 35°C. Under both conditions constant air properties may be assumed with v = 1.6 X 10-5 m2/s, k = 0.026 W/m · K, Pr = 0.70, and DAB (water vapor-air) = 2.3 X 10-5 m2/s.
(a) What is the rate of water loss due to evaporation on the summer day?
(b) What is the total convective heat loss on the summer day?