Download presentation

Presentation is loading. Please wait.

Published byBreonna Blanford Modified over 2 years ago

1
Conservation laws • Laws of conservation of mass, energy, and momentum. • Conservation laws are first applied to a fixed quantity of matter called a closed system or just a system, and then extended to regions in space called control volumes. • The conservation relations are also called balance equations since any conserved quantity must balance during a process.

2
**Continuity Equation Conservation of mass for a system**

Time rate of change of the system mass =0 For a system and a fixed nondeforming control volume that are coincident at an instant of time ,with B - mass and b=1 we see at Figure 5.1 (p. 194) System and control volume at three different instances of time. (a) System and control volume at time t – δt. (b) System and control volume at time t, coincident condition. (c) System and control volume at time t + δt.

3
• Time rate of change of the mass of the system = time rate of change in the mass of the control volume + net rate of flow of mass through control surface. • Time rate of change in the mass of the control volume = • Net rate of flow of mass through control surface = • For steady flow, • Net mass flow rate through the control surface = where m mass flow rate( slug/s;kg /s)

4
Continuity Equation • Conservation of mass: for a fixed, non deforming control volume • More commonly used: • Average velocity:

6
Example 1 • Seawater flows steadily through a simple conical-shaped nozzle. If the nozzle exit velocity =20 m/s, determine the minimum pumping capacity in m3/s.

7
Example 2 • Airflows steadily between two sections in a long straight portion of 4-in diameter pipe. The uniformly distributed temperature and pressure at each section are given. If the average air velocity at section (2) is 100 ft/s, calculate the average air velocity at section (1).

8
Example 3 Moist air enters a dehumidifier at the rate of 22 slugs/hr. Determine the mass flow rate of the dry air and the water vapor leaving the dehumidifier.

9
Example 4 A bathtub is being filled with water from a faucet. The rate of flow from the faucet is steady at 9 gal/min. The tub volume is approximated by a rectangular space.

10
Figure E5.5b (p. 199)

11
**Moving, Non deforming Control Volume**

V = W +VCV V= absolute velocity, V W= relative velocity of fluid seen by an observer moving with the control volume velocity, Vcv Continuity equation for a moving non-deforming control volume

12
**Example 5. An airplane moves forward at a speed of 971 km/hr**

Example 5. An airplane moves forward at a speed of 971 km/hr. The frontal intake area of the jet engine is 0.80 m2, and the entering air density is kg/m3. A stationary observer determines that relative to the earth, the jet engine exhaust gases moves away from the engine with a speed of 1050 km/hr. The engine exhaust area is m2, and the exhaust gas density is kg/m3. Estimate the mass flow arte of fuel into the engine in kg/hr.

Similar presentations

Presentation is loading. Please wait....

OK

Lecture# 9 MASS AND ENERGY ANALYSIS OF CONTROL VOLUMES

Lecture# 9 MASS AND ENERGY ANALYSIS OF CONTROL VOLUMES

© 2017 SlidePlayer.com Inc.

All rights reserved.

Ads by Google

Ppt on conservation of electricity Ovary anatomy and physiology ppt on cells Ppt on standing order crossword Converter word para ppt online Ppt on law against child marriage Ppt on switching network design Ppt on california academy of sciences Ppt on solid waste management in india Ppt on mind reading computer system By appt only movie device