Page 35 - Fluid mechanics, heat transfer, and mass transfer

FLUID MECHANICS BASICS
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& Closed U-tube manometers are used with mercury as
manometric fluid, to directly measure absolute pres-
sure P of a fluid, provided that the space between the
closed end and mercury is perfect vacuum.
. Name some fluids used as manometric liquids.
& Low freezing point fluids are used for cold weather
climates and outdoor use. High-temperature fluids
are used for higher temperature environments. Indi-
cating fluid specific gravity (density), options range
from 0.827 Red Oil to 13.54 Mercury. Higher specific
gravity liquids can be used to increase the measure-
ment range of any glass tube manometer.
& Mercury is used for larger DP measurements and oils
for small pressure differences.
. What is a two-liquid manometer? What are its
applications?
& A two-liquid manometer, a highly sensitive device,
is used for measuring small pressure differences.
Figure 1.11 shows a two-liquid manometer.
Aneroid barograph.
. What is a differential U-tube manometer?
FIGURE 1.9
& A differential U-tube manometer is used for mea-
& Aneroid barometers are the heart of altimeters used in
suring pressure difference between two points of a
modern aviation.
closed system such as a head-type flow meter.
. What is an aneroid barograph? Illustrate by means of a
. How does Bourdon tube (pressure gauge) work? Does it
diagram. indicate absolute pressure?
& A pen at the end of a lever attached to the aneroid
& Bourdon tubes are hollow, cross-sectional beryllium,
moves up and down according to pressure changes copper, or steel tubes, shaped into a three-quarter
and records the pressure on the graph paper wrapped circle.
around the cylinder, which slowly rotates.
& It is a thin-walled tube with wall thicknesses in the
& Figure 1.9 illustrates an aneroid barograph.
range of 0.25–1.25 mm (0.01–0.05 in.) that is flat-
. Name and illustrate different types of manometers. tened diametrically on opposite sides to produce a
& U-tube, inclined, and two-liquid types of man- cross-sectional area elliptical in shape, having two
ometers are in common use. These are illustrated in long flat sides and two short round sides. The tube is

Figure 1.10. bent lengthwise into an arc of a circle of 270–300 .

FIGURE 1.10 Different types of manometers.