Unformatted text preview: HW 11 Solution 1) A small fan pulls air through a duct and across and electrical resistor where the air is heated. Given that the density of air is 1.20 kg/m3 at the inlet and 1.05kg/m3 at the exit, determine the percent increase in air velocity as it flows through the duct. 2) Nitrogen gas at 50°C and 200 kPa is flowing in a pipe 50mm in diameter at 0.05kg/s. The gas encounters a partially closed valve. If there is a pressure drop of 30 kPa across the valve and assuming no temperature change, determine (a) the inlet velocity and (b) the velocity exiting the pipe after the valve. 3) Two steady flows of air enter a control volume shown below. Inlet (1) is at 350 kPa, 250°C, and flows at 0.025 kg/s. The other inlet (2) enters at 450kPa and 15°C. A single flow exits the control volume at 100 kPa and 40°C. During the process 1kW of heat is rejected while 4kW of work is produced. What is the mass flow of the second inlet? 4) A 25,000 gallon pool is being filled with water (T = 90 F) by a fire hose. If the volumetric flow rate of the fire hose is 11 butts per hour, what is the mass flow rate of the water? Starting from conservation of mass and applying assumptions, how long will it take to fill the pool? 5) When analyzing steady flow systems why is it common practice to neglect the mechanical energy terms (ke and pe) ? The potential energy can be neglected due to most common control volumes being horizontal. The kinetic energy term is negligible because it makes up a fraction of a percent of the total energy of the system. ...
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 Summer '07
 RAMUSSEN
 Fluid Dynamics, Thermodynamics, Energy, Kinetic Energy, Mass, partially closed valve

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