G - specific weight = weight per unit volume (N/m3, lbf/ft3) R – Density (kg/m3, slug/ft3) Alternatives for density III.Īll of the usual thermodynamic properties are important in fluid mechanics This will be particularly important for problems involving moving control volumes in Ch. NOTE: While not obvious in the basic equation, V n must also be measured relative to any motion at the flow area boundary, i.e., if the flow boundary is moving, V n is measured relative to the moving boundary. Key Point: Note that only the normal component of velocity contributes to flow rate across a boundary. Where Vn is the normal component of velocity at a point on the are a across which fluid flows. However, one of its most important uses in fluid mechanics is to specify both the volume and mass flow rate of a fluid. The basic definition for velocity has been given previously. Two important properties in the study of fluid mechanics are: Review examples on unit conversion in the text. Then convert the final answer to the desired final units. problems, convert all parameters to slug, ft, & s. problems, convert all parameters to kg, m, & s for B.G. Recommendation: In working with problems with complex or mixed system units, at the start of the problem convert all parameters with units to the base units being used in the problem, e.g. Note: We used the following, 1 lbf = 1 slug ft/s2, to obtain the desired units = fluid density*volume flow rate*g*pump head = r Q g hpįor r = 1.928 slug/ft3, Q = 500 gal/min, and hp = 70 ft, Given: Pump power requirements are given by įor a unit system using gc, the manometer equation would be written as Therefore, be careful not to use conventional values for fluid density in English units withoutĪppropriate conversions, e.g., for water: rw = 62.4 lb/ft3 (do not use this system of units, the unit used for mass is the slug and not the lbm. Lbf s /ft2 = (slug ft/s2) s /ft2 = slug/ft s Slug/ft3*ft/s2*ft = (slug ft/s2)/ft2 = lbf/ft2ĭynamic viscosity m N s /m2 = (kg m/s2) s /m2 = kg/m s Manometry r g h kg/m3*m/s2*m = (kg m/s2)/ m2 =N/m2 This will be particularly useful in the following: Rather, in both systems the combination of units for mass * acceleration yields the unit of force, i.e.

This text will use both the International System of Units (S.I.) and British Gravitational System (B.G.).Ī key feature of both is that neither system uses gc. It is used not only to specify flow field characteristics but also to specify flow rate, momentum, and viscous effects for a fluid in motion.

Velocity - The rate of change of position at a point in a flow field. Key Point: The direction of pressure forces will always be perpendicular to the Pressure - The normal stress on any plane through a fluid element at rest. Two important properties in the study of fluid mechanics are: Pressure and Velocity The definition also clearly shows that viscous effects are not considered in the study of fluid statics. (1) fluid statics (fluids at rest), (2) momentum and energy analyses (fluids in motion), and (3) viscous effects and all sections considering pressure forces (effects of fluids on boundaries).įluid - A substance which moves and deforms continuously as a result of an applied shear stress. Note: This definition outlines the key topics in the study of fluids: Fluid Mechanics - Study of fluids at rest, in motion, and the effects of fluids on

Density of water slugft3