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Dimensionless numbers (or characteristic numbers) have an important role in analyzing the behavior of fluids and their flow as well as in other transport phenomena. [1] They include the Reynolds and the Mach numbers, which describe as ratios the relative magnitude of fluid and physical system characteristics, such as density, viscosity, speed of sound, and flow speed.
In many engineering applications the local flow velocity vector field is not known in every point and the only accessible velocity is the bulk velocity or average flow velocity ¯ (with the usual dimension of length per time), defined as the quotient between the volume flow rate ˙ (with dimension of cubed length per time) and the cross sectional area (with dimension of square length):
When converting oil density to specific gravity using the above definition, it is important to use the correct density of water, according to the standard conditions used when the measurement was made. The official density of water at 60 °F according to the 2008 edition of ASTM D1250 is 999.016 kg/m 3. [2] The 1980 value is 999.012 kg/m 3. [3]
ρ (Greek letter rho) is the fluid mass density (e.g. in kg/m 3), and; u is the flow speed in m/s. It can be thought of as the fluid's kinetic energy per unit volume. For incompressible flow, the dynamic pressure of a fluid is the difference between its total pressure and static pressure. From Bernoulli's law, dynamic pressure is given by
Water is the most common heat transfer fluid because of its economy, high heat capacity and favorable transport properties. However, the useful temperature range is restricted by freezing below 0 °C and boiling at elevated temperatures depending on the system pressure .
[4] [5] [6] A generalized model of the flow distribution in channel networks of planar fuel cells. [6] Similar to Ohm's law, the pressure drop is assumed to be proportional to the flow rates. The relationship of pressure drop, flow rate and flow resistance is described as Q 2 = ∆P/R. f = 64/Re for laminar flow where Re is the Reynolds number.
This will result in another viscosity value if the fluid is a non-Newtonian fluid such as paint, but it will give the same viscosity value for a Newtonian fluid such as water, petroleum oil or gas. If another parameter like temperature, T {\displaystyle T} , is changed, and the experiment is repeated with the same force, a new value for ...
where is the density of the fluid, is the average velocity in the pipe, is the friction factor from the Moody chart, is the length of the pipe and is the pipe diameter. The chart plots Darcy–Weisbach friction factor f D {\displaystyle f_{D}} against Reynolds number Re for a variety of relative roughnesses, the ratio of the mean height of ...