Engineering Fundamentals: An Introduction to Engineering, 4th ed.c

276 Chapter 10 Force and Force-Related Parameters

The absolute pressure is related to the gauge pressure according to

(a) For a city located at sea level,Patmospheric14.69 psi 14.7 psi,

(b) We can use Table 10.4 to look up the standard atmospheric pressure for a city located

in Colorado with an elevation of 1500 m. The atmospheric pressure at an elevation of 1500 m

isPatmospheric84.55 kPa.

Example 10.11 A vacuum pressure gauge monitoring the pressure inside a container reads 200 mmHg

vacuum. What are the gauge and absolute pressures? Express results in pascals.

The stated vacuum pressure is the gauge pressure, and to convert its units from milli-

meters of mercury to pascal, we use the conversion factor 1 mmHg133.3 Pa. This results in

The absolute pressure is related to the gauge pressure according to

Note that the negative gauge pressure indicates vacuum, or a pressure below atmospheric level.

Vapor Pressure of a Liquid

You may already know from your everyday experience that under the same surrounding con-

ditions some fluids evaporate faster than others do. For example, if you were to leave a pan of

water and a pan of alcohol side by side in a room, the alcohol would evaporate and leave the

pan long before you would notice any changes in the level of water. That is because the alcohol

Pabsolute26,660101,32574,665 Pa

PabsolutePgaugePatmospheric

Pgauge 200 1 mm#Hg2a

133.3 Pa

1 mm#Hg

b26,660 Pa

Pabsolute325,875 1 Pa2a

1 psi

6895 Pa

b47.3 psi

325.875 kPa

Pabsolute241,32584,550325,875 Pa

Pgauge35.0 1 psi2a

6895 Pa

1 psi

b241,325 Pa

342,680 Pa342.68 kPa

Pabsolute49.7 1 psi2a

6895 Pa

1 psi

b

Pabsolute35.0 psi14.7 psi49.7 psi

PabsolutePgaugePatmospheric

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