Βασικές Εννοιες Ενέργειας. Εισαγωγή. Το λεξιλόγιο της Ενέργειας Επισκόπηση μονάδων Βασικές έννοιες Θερμοδυναμικής Σύστημα Κατάσταση Διεργασία Κύκλος Εννοιες Θερμοκρασίας και Κλίμακες Θερμοκρασίας, Πίεσης, Μετρήσεις. Θερμοδυναμική.
Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.
of matter is under study.
The portion of the internal energy of a system associated with the
The seven fundamental dimensions and their
units in SI (International System).
Pressure is defined as the force exerted by a fluid per unit area.
Units in SI are Pa=N/m2. The pressure unit Pascal is too small for pressure encountered in practice.
Therefore, kPa and MPa are commonly used.
Units in British are : psf = lbf/ft2, psi = lbf/in2
You have to convert from psi to psf ( 144 in2 = 1 ft2)
Absolute pressure, is measured relative to absolute vacuum (i.e., absolute zero pressure.)
Gauge pressure, is measured relative to atmospheric pressure
Variation of Pressure with Depth
The pressure variation in a constant density fluid is given as
P + Z = constant
Or P1+ Z1 = P2 + Z2
Z is the vertical coordinate ( positive upward).
is the specific weight of fluids, (N/m3)
For small to moderate distances, the variation of pressure with height is negligible for gases because of their low density.
Pressure at a Point
Pressure Variation in horizontal planes
Pressure is constant in horizontal planes provided the fluid does not change. ( this leads to Pascal’s principle.)
Noting that P1 = P2, the area ratio A2/A1 is called the ideal mechanical advantage. Using a hydraulic car jack with A2/A1 = 10, a person can lift a 1000-kg car by applying a force just 100 kg (= 908 N).
A device based on P + Z = constant is called a manometer (Right), and it is commonly used to measure small and moderate pressure differences.
P2 = Patm + h
The length or the cross-sectional area of the tube has no effect on the height of the fluid column of a barometer.
When solving problems, we will assume the given information to be accurate to at least 3 significant digits. Therefore, if the length of a pipe is given to be 40 m, we will assume it to be 40.0 m in order to justify using 3 significant digits in the final results.
A result with more significant digits than that of given data falsely implies more accuracy.