TEMPERATURE AND PRESSURE MEASUREMENTS
Thermodynamics
Pabs = Patm + Pgauge
(1-9)
Pabs = Patm - Pvac
(1-10)
Patm is atmospheric pressure, which is also called the barometric pressure. Pgauge is the gauge
pressure, and Pvac is vacuum. Once again, the following examples relating the various pressures
will be helpful in understanding the idea of gauge versus absolute pressures.
Example 1: Pressure Relationships
How deep can a diver descend in ocean water (density = 64 lbm/ft3) without damaging
his watch, which will withstand an absolute pressure of 80 psia? (P = density • height)
Solution:
Assume:
Patm
= 14.7 psia
Pabs
= Patm + Pgauge
80 psia = 14.7 + Pgauge
Pgauge
= (80 - 14.7) = 65.3 psig
Pgauge
= density height = rH
(65.3)(144 in2/ft2) = (64 lbm/ft3)H
H
= (65.3)(144)/(64)
H
= 146.9 ft
HT-01
Page 10
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