Homework-4

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University Of Arizona *

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230

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Mechanical Engineering

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Feb 20, 2024

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docx

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Thermodynamics - AME 230 Student name : Date : Homework Assignment No 4 I. Indicate whether the following statements are true or false 1. Mass flux is the time rate of mass flow per unit area. A: True B: False 2. For steady-state operation all properties are unchanging in time. A: True B: False 3. Mass flow rate is the product of density, area, and velocity for 1D flow. A: True B: False 4. As velocity decreases in a diffuser, pressure decreases. A: True B: False 5. Volumetric flow rate is expressed in units of kg/s. A: True B: False 6. At steady state, conservation of mass asserts the total rate at which mass enters the control volume equals the total rate at which mass exits. A: True B: False 7. A mixing chamber is a direct-contact heat exchanger A: True B: False 8. As velocity decreases in a diffuser, pressure decreases. A: True B: False 9. For a one-inlet, one-exit control volume at steady state, the mass flow rates at the inlet and exit are equal but the inlet and exit volumetric flow rates may not be equal. A: True B: False 10. Mass flow rate is the time rate of change of mass within the control volume. 1
Thermodynamics - AME 230 A: True B: False 11. The mass rate balance is defined as the sum of all inlet mass flow rates minus the sum of all outlet mass flow rates. A: True B: False 12. For one-dimensional flow, mass flow rate is the product of density, area, and velocity. A: True B: False 13. As velocity decreases in a diffuser, pressure decreases. A: True B: False 14. Flow work is the work done on a flowing stream by a paddle wheel or piston. A: True B: False II. Checking understanding 1. The time rate of mass flow per unit area is called Answer: 2. _________-________means all properties are unchanging in time. 3. A system consists of liquid water in equilibrium with a gaseous mixture of air and water vapor. How many phases are present? Does the system consist of a pure substance? Explain. Answer: 4. Does the red line in the picture below follow a constant pressure? 2
Thermodynamics - AME 230 Answer: 5. A device in which power is developed as a result of a gas or liquid passing through a set of blades attached to a shaft free to rotate. Answer: 6. A device in which work is done on a gas to increase the pressure and/or elevation. Answer: 7. A device in which work is done on a liquid to increase the pressure and/or elevation. Answer: 8. A flow passage of varying cross-sectional area in which the velocity of a gas or liquid increases in the direction of flow. Answer: 9. A flow passage of varying cross-sectional area in which the velocity of a gas or liquid decreases in the direction of flow. Answer: 10. A device where two moving fluid streams exchange heat without mixing. Answer: 11. A flow-restricting device that causes a significant pressure drop in the fluid. Answer: 3
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