Pressure, pPressure along with velocity is one of the main parameters in Fluid Dynamics. It is defined as the compressive stress at any point in a fluid at rest. Imagine a thin plate immersed in a fluid at rest. Pressure is the normal force per unit area exerted on the plate. It is brought about by the bombardment of fluid molecules upon the solid surface. Dimensions of pressure are F/L2 which is also called a Pascal. At low speeds fluid flow is caused by pressure differences and gradients than due to pressure itself; the actual pressure level within a fluid becomes less important. But for high speed flows the magnitude of pressure may become important. On the other hand at very low pressures, vaporisation may set in a liquid.
Pressure values read by measuring devices such as a manometer are
the pressure levels above the atmospheric pressure and are called
gauge pressure. When pressure is referred to a vacuum it
becomes an Absolute Pressure being the sum of the gauge
pressure and atmospheric pressure.
Temperature, TTemperature is a measure of the random molecular motion of the fluid at a point. The hotter the fluid the more energy is stored in random motion of molecules.
The unit of temperature is Kelvin (K), as an absolute measure of thermal energy or
Centigrade (oC), as a relative measure with 0 degrees at the freezing point of
water. Velocity, VVelocity of the flow is the average speed of all molecules at a point in the flow at a given time. Velocity is a vector quantity and can be constructed from three scalar components (u,v,w) (horizontal, vertical, forward)
The units of Velocity are m/s in the metric system. (c) Aerospace, Mechanical & Mechatronic Engg. 2005 University of Sydney |
