BIO Heat Loss During Breathing. In very cold weather a significant mechanism for heat loss by the human body is energy expended in warming the air taken into the lungs with each breath. (a) On a cold winter day when the temperature is – 20o C, what amount of heat is needed to warm to body temperature (37o C) the 0.50 L of air exchanged with each breath? Assume that the specific heat of air is 1020 J/kg ? K and that 1.0 L of air has mass 1.3 X 10-3 kg. (b) How much heat is lost per hour if the respiration rate is 20 breaths per minute?

Solution 28E Introduction The heat supplied to increase temperature is given by Q = mcT Step 1 The density of the air, as given in this problem is = 1.3 ×kg/L So the mass of 0.5 L of air is m = V = (0.5 L)(1.3 × kg/L) = 0.65 × 103 kg Specific heat of the air is c = 1020 J/kg · K And the temperature change is T = 37°C ( 20°C) = 57°C Hence the energy supplied to the air is Q = (0.65 × 103 kg)(1020 J/kg · K)(57°C) = 37.8 J