2300_les02

# 2300_les02 - I Concepts and Definitions F Properties of a...

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1 lesson 2 I. Concepts and Definitions F. Properties of a system (we use them to calculate changes in energy) 1. A property is a characteristic of a system that can be given a numerical value without considering the history of the system. Examples include T, P, ρ , velocity, E, U, volume (we can only measure T, P, velocity, mass, volume) 2. Examples and definitions a. pressure, P b. density, ρ 2 5 () 1 1 1 101325 1.01325 14.696 11 0 force exerted by fluid P unit area N P pascal Pa m atm Pa bar psia bar Pa = == = = = 3 m kg , V m volume mass = = ρ (1-4) lesson 2 I. Concepts and Definitions c. atmospheric pressure (absolute) = P atm d. gage pressure = P gage = P abs -P atm (1-15) e. absolute pressure = P abs = P atm + P gage f. vacuum pressure = P vac = P atm abs (1-16) g. specific volume = v = 1/ ρ = Vol/mass, m 3 /kg h. intensive properties are independent of the size of the system: T, e, P, ρ , specific volume (v), u. The units on e are kJ/kg . i. extensive properties depend on the size of the system: actual volume (V), E, m, U. The units on E are kJ . Example . The pressure gage attached to the air storage tank of a compressor reads 100 psi. If the atmospheric pressure of the surroundings is 14.7 psi, what is the absolute pressure in the tank? (Answer: 114.7 psia) p Stiff metal tube Bourdon tube gage gives P gage.

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2 lesson 2 I. Concepts and Definitions Example . You are designing a snorkel that will allow you to remain submerged in water at a depth of 1 m. Discuss any problems you might experience in using this device.
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2300_les02 - I Concepts and Definitions F Properties of a...

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