Practice Problems_Exam 3

# Practice Problems_Exam 3 - Practice Problems Exam 3 1 Heat...

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Practice Problems – Exam 3 1. Heat Loss During Breathing Estimate heat loss during breathing. Assume that a normal person inspires about 6 L/min of bone dry air at 20 º C. Assume that expired air is saturated with warm vapor and is at 37 º C. The molecular weight of air is 28.9 g/mol and the density of air is 0.0012 g/cm 3 . The molal humidity for saturated water vapor at 37 º C is 6.7%; therefore, when saturated, there are approximately 0.041 g of water per 1 g of dry air. The enthalpy change involved with heating air from 20 º C to 37 º C is 494 J/mol and the enthalpy change associated with the vaporization of water to saturated air is 577 cal/g. Heat lost due to respiration _________________________ Atomic weights: H = 1, C = 12, N = 14, O = 16 1 atm = 101.3 kPa 1 cal = 4.814 J 1 N/m 2 = Pa 1 J = 1 N/m 1000 cm 3 = 1 L = 0.001 m 3 Gravitational acceleration = 9.81 m/s 2 = 32.174 ft/s 2 Gas constant = 8.314 m 3 ·Pa/(mol·K) = 8.314 J/(mol·K) = 0.08206 L·atm/(mol·K) Heat of fusion of pure ice: 6009.5 J/mol Heat of vaporization of pure water: 40656.0 J/mol 6 L/min saturated air, 37ºC 6 L/min dry air, 20ºC 3 1 2 Water from nasal tissue Lungs Heat lost due to respiration

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2. Hydroelectric Power Suppose that water from a reservoir flowing into a hydroelectric power plant has a velocity of 1.0 m/s. After flowing through the plant, the water enters a
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Practice Problems_Exam 3 - Practice Problems Exam 3 1 Heat...

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