1. Air at 25°C and 1 atm is in fully developed flow at m· = 10-3 kg/s through a 10-mm-diameter circular tube whose inner surface is wetted with water. Determine the tube length required for the water vapor in the air to reach 99% of saturation. The inlet air is dry.
2. A humidifier consists of a bundle of vertical tubes, each of 20-mm diameter, through which dry atmospheric air is in fully developed flow at 10-3 kg/s and 298 K. The inner tube surface is wetted with a water film. Determine the tube length required for the water vapor to reach 99% of saturation. What is the rate at which energy must be supplied to each tube to maintain its temperature at 298 K?