欧洲必威体育精装版流体力学课件第三章.pdfVIP

Chapter 3: Pressure and Fluid Statics Pressure Pressure is defined as a normal force exerted by a fluid per unit area. 2 Units of pressure are N/m , which is called a pascal (Pa). Since the unit Pa is too small for pressures encountered in practice, kilopascal (1 kPa = 103 Pa) and megapascal (1 MPa = 106 Pa) are commonly used. 2 Other units include bar, atm, kgf/cm , 2 lbf/in =psi. Meccanica dei Fluidi I 2 Chapter 3: Pressure and Fluid Statics Absolute, gage, and vacuum pressures Actual pressure at a give point is called the absolute pressure. Most pressure-measuring devices are calibrated to read zero in the atmosphere, and therefore indicate gage pressure, P =P - P . gage abs atm Pressure below atmospheric pressure are called vacuum pressure, Pvac=Patm - Pabs . Meccanica dei Fluidi I 3 Chapter 3: Pressure and Fluid Statics Absolute, gage, and vacuum pressures Meccanica dei Fluidi I 4 Chapter 3: Pressure and Fluid Statics Pressure at a Point Pressure at any point in a fluid is the same in all directions. Pressure has a magnitude, but not a specific direction, and thus it is a scalar quantity. When Dz 0 P = P = P 1 2 3 Meccanica dei Fluidi I 5 Chapter 3: Pressure and Fluid Statics Variation of Pressure with Depth In the presence of a gravitational field, pressure increases with depth because more fluid rests on deeper laye