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The use of an actual column of mercury to measure pressure normally requires correction for the density of mercury at the actual temperature and the sometimes significant variation of gravity with location, and may be further corrected to take account of the density of the measured air, water or other fluid.
The absolute pressure of 10 to 40 mmHg in the vacuum column is most often achieved by using multiple stages of steam jet ejectors. [16] Many industries, other than the petroleum refining industry, use vacuum distillation on a much smaller scale.
Mercury is a useful material to use in a manometer because of its high density. This means that a much shorter column is needed compared to water. [ 2 ] For instance, the pressure represented by a column of 100 mm of water is just under 7.4 mm of mercury ( mmHg ).
So, for example, pressure head might be written "742.2 mm Hg" or "4.2 in H 2 O at 59 °F" for measurements taken with mercury or water as the manometric fluid respectively. The word "gauge" or "vacuum" may be added to such a measurement to distinguish between a pressure above or below the atmospheric pressure.
Technical literature can be confusing because many authors fail to explain whether they are using the ideal gas constant R, or the specific gas constant R s. The relationship between the two constants is R s = R / m, where m is the molecular mass of the gas. The US Standard Atmosphere (USSA) uses 8.31432 m 3 ·Pa/(mol·K) as the value of R.
Research has shown that drinking beetroot juice can help lower your systolic blood pressure by four to five mmHg. Try adding beetroot juice to your diet, and if you buy store-bought juice, make ...
For example, if the original fluid was water and we replaced it with mercury at the same pressure, we would expect to see a rather different value for pressure head. In fact the specific weight of water is 9.8 kN/m 3 and the specific weight of mercury is 133 kN/m 3 .
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