EMERGENCY FLUIDS FINAL

Volume flow rate

the volume of a fluid flowing through a cross section per unit time

conservation of mass principle for a control volume

net mass transfer to or from a CV during a time interval t is equal to the net change in the total mass within the CV during t

mass balance for steady flow

during a steady flow process, the total amount of mass contained within a CV does not change with time

conservation of mass

the total amt. of mass entering a CV is equal to the total amt. of mass leaving it

mechanical energy

the form of energy that can be converted to mechanical work by an ideal mechanical device; kinetic and potential

flow work

pressure force acting on a fluid through a distance

shaft work

the transfer of mechanical energy by a rotating shaft

pump

receives shaft work and transfers it to the fluid as mech. energy

turbine

converts mechanical energy of a fluid to shaft work

0% mech. efficiency

conversion of entire mech. energy input to thermal energy

100% mech efficiency

zero conversion of mech. energy to thermal energy

Bernoulli equation

approximate relation between pressure, velocity, and elevation; is valid in regions of steady, incompressible flow where net frictional forces are negligible; the total pressure along a strealmine is constant

Static pressure

the actual thermodynamic pressure of the fluid

dynamic pressure

pressure rise when the fluid in motion is brough to a stop isentropically

isentropic

adiabatic and reversible process

total pressure

the sum of the static, dynamic, and hydrostatic pressure

hydrostatic pressure

accounts for elevation effects

stagnation pressure

represents the pressure at a point where the fluid is brough to a complete stop isentropically

pitot-static tub

small tube with holes on the side that can be used to measure the dynamic pressure of fluid; can be used for flow speed measurement

limitations of the bernoulli equation

1. must be steady flow

2. negligible viscous effects (no friction)

3. no shaft work

4. incompressible flow

5. negligible heat transfer

6. flow along a streamline

pressure head

height of a fluid column that produces the static pressure P

velocity head

the elevation needed for a fluid to read the velocity V during frictionless free fall

hydraulic grade line

sum of the static pressure and elevation heads

energy grade line

total head of the fluid

laminar flow

smooth streamlines and highly ordered motion

turbulent flow

velocity fluctuations and highly disordered motion

Reynolds number

ratio of inertial forces to viscous forces in the fluid

transitional flow

flow moves between laminar and turbulent

velocity boundary layer region (boundary layer region)

the region of the flow in which the effects of the viscous shearing forces caused by fluid viscosity are felt; changes in viscosity and velocity are significant

irrotational flow region (core region)

the frictional effects are negligible and the velocity remains essentially constant in the radial direction

hydrodynamically fully developed region

the region beyond the entrance region in which the velocity profile is fully developed and remains unchanged

shear stress at pipe wall

related to the slope of the velocity profile at the surface; if velocity profile is constant, shear stress is also constant

pressure loss

a pressure drop due to viscous effects represents an irreversible pressure loss

eddies

disorderly and rapid fluctuations of swirling regions of fluid that define turbulent flow

viscous sublayer

where viscous effects are dominant

buffer layer

where turbulent effects are becoming significant, but the flow is still dominated by viscous effects

overlap (transition) layer

where the turbulent effects are much more significant but still not dominant

outer (turbulent) layer

remaining part of the flow where turbulent effects dominate

relative roughness

ratio of the mean height of pipe roughness to the pipe diameter

colebrook equation

equation to find darcy factor, but only for turbulent flow

Moody chart

graphical tool used to determine the Darcy-Weisbach friction factor

Churchill equation

explicit equation used for any type of flow, any reynolds number, and any roughness

Swamee and Jain

explicit formula to calculate the Darcy-Wiesbach friction factor in fully turbulent flow

head loss

reduction in total head as a fluid flow through a system

parallel pipes

pipes that branch out into two or more and rejoin at a junction downstream; flow rate is the sum of individual pipe flows

Analysis of piping networks is based on two simple principles

1. Conservation of mass throughout the system must be satisfied

2. Pressure drops (and thus head loss) between two junctions must be the same for all path between the two junctions

pump motor efficiency

ratio of the mechanical energy delivered to the fluid by the pump to an electric motor

maximum flow rate (free delivery)

intersection point of the pump head curve with the horizontal axis

maximum head (shutoff head)

intersection of the pump head curve with the vertical axis

operating point

point of intersection between system curve and supply curve; useful head produced by the pump at this point matches the head requirement of the system at that flow rate