This document contains lecture notes on fluid mechanics. It defines different types of pressure such as atmospheric, gauge, absolute and vacuum pressure. It discusses the relationship between pressure and depth. It provides an example calculation for determining absolute pressure given gauge and atmospheric pressures. Finally, it lists several practice problems calculating various pressure values.
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Definition of Pressure
Types of Pressure:
a) Atmospheric pressure
b) Gauge pressure
c) Absolute pressure
d) Vacuum pressure
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Source: http://www-mdp.eng.cam.ac.uk/web/library/enginfo/aerothermal_dvd_only/aero/fprops/statics/node13.html
Relation between Pressure and Depth
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Example 1.
A bourdon gauge is attached to a boiler which is located at sea level with a reading pressure of 7 bar.
If atmospheric pressure is 1.013 bar, calculate the absolute pressure in that boiler (in kN.m2
).
𝑃𝐺 = 7 𝑏𝑎𝑟 = 7 𝑥 105
𝑁/𝑚2
𝑃𝑎𝑡𝑚 = 1.013 𝑏𝑎𝑟 = 1.013 𝑥 105
𝑁/𝑚2
𝑃𝑎𝑏𝑠 = 𝑃𝐺 + 𝑃𝑎𝑡𝑚 = (7𝑥 105) + (1.013 𝑥 105) = 8.013 𝑥 105
𝑁/𝑚2
𝑃𝑎𝑏𝑠 = 801.3 𝑘𝑁/𝑚2
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Exercises:
1. What is the pressure gauge of air in the cylinder if the cylinder if the atmospheric gauge is
101.3kN/m2
and absolute pressure is 512 kN/m2
.
2.
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3. Calculate the absolute pressure of air in the compressor cylinder if the pressure gauge is
2500N/m2
. (Assume atmospheric gauge is 101.3 kN/m2
)
4. A pressure gauge is attached to a reservoir containing water which shows value of 20kN/m2
.
Calculate:
i. The pressure head of water, h
ii. The absolute pressure in kN/m2
if the atmospheric pressure is 101.3kN/m2
.
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5. A Bourdon pressure gauge attached to a boiler located at sea level shows a reading pressure of
10bars. If atmospheric pressure is 1.01bars. Determine:
i. The absolute pressure in kN/m2
ii. The pressure head of water, h
