Lecture 3

Question 1

what is bernoullis equation derived from

Answer 1

forces acting on a fluid element apply newtons 2nd law

Question 2

bernoullis very similar to

Answer 2

first law of thermodynamics

Question 3

assumptions for bernoullis equation

Answer 3

ideal fluid (inviscid) (though modified later to include losses)
steady state
incompressibly
1D uniform flow

Question 4

bernoullis equation

Answer 4

pressure energy + kinectic energy + potential energy = total enery (constant)

Question 5

bernoullis equation pressure formalism

Answer 5

pressure + 0.5densityC^2 + density * g * height = constant

Question 6

for gases what term can cancel out of bernoullis equation and why

Answer 6

potential energy term as density is small therefore can remove

Question 7

fan delivery pressure

Answer 7

pressure straight after fan (anything about deliver is the fluids characteristics straight after the fan)

Question 8

if delivering to large vessel what is velocity in the vessel

Answer 8

0

Question 9

litres to m^3

Answer 9

divide by 1000

Question 10

if velocity increases then

Answer 10

pressure must decrease

Question 11

if cross sectional area increases

Answer 11

velocity decreases

Question 12

cavitation occurs when

Answer 12

pressure gets so low that liquid starts to boil (due to high velocity)

Question 13

SFEE

Answer 13

steady flow energy equation (bernoullis equation with losses)

Question 14

major losses due to

Answer 14

roughness of pipe

Question 15

relative roughness

Answer 15

roughness/diameter

Question 16

SFEE assumptions

Answer 16

incompressible fluid
steady state
2D flow
could be turbulent

Question 17

where do pressure losses come

Answer 17

frictional effects
inertial losses
dissipation of energy by turbulence

Question 18

frictional losses

Answer 18

due to viscosity (low flow rates)

Question 19

inertial losses

Answer 19

movement of the fluid (turbulence high flow rate)

Question 20

work and energy from SFEE

Answer 20

times everything by volume flow rate = heat in + (- work done by the system) or heat in plus work done on the system

Question 21

reservoir

Answer 21

C = 0

Question 22

actual work =

Answer 22

work with no losses / efficiency

Question 23

first law of thermodynamics

Answer 23

energy cannot be created nor destroyed merely converted from one form to another

Question 24

mass flow rate =

Answer 24

density * volume flow rate

Question 25

laminar flow down a pipe use

Answer 25

poiseuille equation which simplifies down to change in pressure = 64/Re

Question 26

volume flow rate symbol

Answer 26

V with dot over the top or Q

Question 27

if working out pressure required to maintain flow rate what must be added

Answer 27

pressure due to major and minor losses plus the pressure needed to accelerate the flow to desired flow rate