t RULES OF THUM FOR MECHANICAL liEH A manual of quick, accurate solutions to everyday mechanical engineering problems J. Edward Pope, Editor RULES OF THUMEI FOR MECHANICAL ENGINEERS Gulf Publishing Company Houston, Texas [...]... It is basically a ratio of convection to conductance: hl N=k Heat transfer r e q k s circulation,therefore, the Grashof number (and heat transfer coefficient)will rise as the buoyancy forces increase and the viscous forces decrease 24 Rules of Thumb for Mechanical Engineers Correlations Heat transfer correlations are empirical relationships They are available for a wide range of configurations.This... the ratio of inertial force to weight: This is particularly important in pipe flows and aircraft model studies The Reynolds number also characterizesdifferent flow regimes (laminar, turbulent, and the transition T i number is useful in the design of spillways, weirs, chanhs nel flows, and ship design 8 Rules of Thumb for Mechanical Engineers Weber Number Weber number is the ratio of inertial forces t... measuring the volume of flow over a specific time Constant Temperature Bath Figure 8 Capillary tube viscometer Figure 9 Rotating viscometer 16 Rules of Thumb for Mechanical Engineers The shear stress z is a function of this torque T Knowing shear stress, the dynamic viscosity may be calculated from Newton’s law of viscosity Td = 2n~3ho OTHER TOPICS Unsteadv Flow Surre and Water Hammer Study of unsteadyflow... v.dv = 0 P (7) When p is either a function of pressure p or is constant, the Euler’s equation can be integrated The most useful relationship, called Bernoulli’s equation, is obtained by integrating Euler’s equation at constant density p 6 Rules of Thumb for Mechanlcal Engineers ~~ Bernoulli’s Equation Bernoulli’s equation can be thought of as a special form of energy balance equation, and it is obtained... Study of open channels is important in the study of river flow and irrigation canals The mechanics of flow in open channels is more complicated than that in pipes and ducts because of the presence of a free surface Unlike closed conduit flow, the specificroughessfactor E for open-channel flows is dependent on the hydraulic state of the channel The flow is called uniform if the cross-section of the... 3), the relations are: Note that for a given specific head and flow rate, two different depths of h are possible The Froude n d e r V/(gh) specifies the f o characteristicsof the channel flow If it is lw less than unity, it is called subcritical, or tranquil, flow If it is more than unity, it is called supercritical, or rapid, flow 12 Rules of Thumb for Mechanical Engineers Flow Through a Siuice Gate... the rate of change of linear momentum inside the control volume plus the net exchange of linear momentum from the control boundary Newton’s second law is used to derive its form: F=-= (mv) L p v d V + cs pw.dA dt (1 1) Moment -of- Momentum Equation The moment -of- momentumequation is obtained by taking the vector cross-product of F detailed above and the position vector r of any point on the line of action,... Reynolds Number The Reynolds number is the ratio of flow momentum rate (i.e., inertia force) to viscous force Prandtl Number The Prandtl number is the ratio of momentum diffusivity to thermal diffusivity of a fluid: Pr=- PCP k It is solely dependent upon the fluid properties: For gases, Pr = 7to 1.0 For water, Pr = 1 to 10 For liquid metals, Pr = 001 to 03 For oils, Pr = 50 to 2000 The Reynolds number... power Therefore, it is not a good investment to spend a lot of time determjningPrandtl number for a gas Just using 85 should be adequate for most analyses Grashof W umber The Grashof number is used to determine the heat transfer coefficient under free convection conditions It is basically a ratio between the buoyancy forces and viscous forces The Nusselt number characterizes the similarity of heat transfer... nondimensional parameters are of great value in fluid mechanics Reynolds Number Reynolds number is the ratio of inertial forces to viscous forces: between the two) through a critical value For example, for the case of flow of fluids in a pipe, a fluid is considered turbulent if R is greater than 2,000 Otherwise, it is taken to be laminar A turbulent flow is characterized by random movement of fluid particles . RULES OF THUMEI FOR MECHANICAL ENGINEERS Gulf Publishing Company Houston, Texas