Fluids- TAME and Pumps

Question 1

Formula for angular momentum

Answer 1

O=rmv

r is distance from centre of rotation

Question 2

Formula for angular momentum flux

Answer 2

O•=rm•v

Dots are above letter

Question 3

Torque and angular momentum equation

Answer 3

T=(rm•v)out-(rm•v)in

Can be summations as well is multiple components to system.

Question 4

How to work out torque generated by sprinkler

Answer 4

Need to get velocity of each jet by subtracting velocity of nozzle from velocity of jet relative to nozzle. Find torque generated by each nozzle using TAME. Multiply by number of nozzles to get overall torque.

Question 5

How to compute bending moments caused by jets of fluid

Answer 5

F=m•V to find force caused by jet. Weight of pipes is sometimes important. Due moments about the point you are interested in.

Question 6

Describe energy transfer in a pump

Answer 6

Energy supplied to them and they transfer most of it to the fluid. Increase in fluid energy usually felt as an increase in the pressure of the fluid

Question 7

Positive displacement pump

Answer 7

Fluid directed into a closed volume. Energy transfer to the fluid accomplished by movement of the boundary of the closed volume thereby sucking fluid in or squeezing fluid out.

Question 8

Dynamic pumps

Answer 8

Involve rotating blades which impart momentum to the fluid

Question 9

Three types of flow from a rotary (dynamic) pump

Answer 9

Centrifugal (outlet flow perpendicular to inlet flow)
Mixed (outlet flow at an angle to inlet flow)
Axial flow (outlet flow parallel to inlet flow)

Question 10

Compare fans, blowers and compressors in terms of pressure difference and volume flow rate they cause

Answer 10

Fan has high flow rate but low pressure. Compressor has high pressure but low flow rate. Blower is in between for both.

Question 11

Free delivery

Answer 11

The flow rate that occurs through a pump when the net head is 0. This is the maximum volume flow rate.

Question 12

Shutoff head

Answer 12

The net head that occurs when the volume flow rate is zero. Achieved when the outlet port of the pump is blocked off. Head is large but V is 0.

Question 13

Pump characteristic curve

Answer 13

Head as a function of volume flow rate. At Q=0, H is shutoff head. At H=0, Q is free delivery. Curve down from left to right getting steeper as you go.

Question 14

System curve

Answer 14

Like an exponential curve. Head against volume flow rate. Y intercept at the height you want the system to lift the water by and is required for 0 flow rate. As flow increases so do major head losses so the pump needs to provide a greater head.

Question 15

How to find operating point (duty point) of system

Answer 15

Draw characteristic curve and system curve on same graph. Where curves intersect is at the operating conditions

Question 16

Mechanical efficiency of a pump formula

Answer 16

ρgHQ/ωTs

Ts is torque of shaft

Question 17

How to find best efficiency point (BEP)

Answer 17

Plot efficiency against flow rate graph based on points provided. Do line of best fit to see where peak is.

Question 18

How does the head and maximum volume flow rate produced vary when pumps are connected in series?

Answer 18

Head produced is the some of the heads produced by each individual pump. The volume flow rate is just the same as the pump that produces the highest flow rate would achieve.

Question 19

How does the head and maximum volume flow rate produced vary when pumps are connected in parallel?

Answer 19

The volume flow rate is the sum of what each individual pump would achieve. The head produced is just the same as the one that produces the most would cause.

Question 20

What are centrifugal pumps good for?

Answer 20

Producing a high pressure

Question 21

Describe the velocity triangles for a centrifugal pump

Answer 21

At inside edge looking at edge of blade: Vr1 tangential to blade and u1 parallel to tangent of inner radius circle (equal to ωr1), V1 completes triangle.
At outside edge: Vr2 tangential to blade and u2 parallel to tangent of inner radius circle (equal to ωr2), V2 completes triangle.
Angle α between V and u. Angle β between Vr and u.
r subscript means relative to edge of blade.

Question 22

Formula for power provided to fluid by centrifugal pump

Answer 22

ρQ(V2Cos(α2)u2-V1Cos(α1)u1)

Question 23

What can be said about a flow of fluid relative to the blade of a pump?

Answer 23

It is always tangential to the blade

Question 24

Formula for head provided by a centrifugal pump

Answer 24

1/g(V2Cos(α2)u2-V1Cos(α1)u1)

Question 25

What happens to formula for head provided by centrifugal pump when α1 is set to 90?

Answer 25

H=V2Cos(α2)u2/g

Question 26

What are axial pumps good for?

Answer 26

Providing a large flow rate

Question 27

Describe the velocity triangles at an axial blade looking at blade edge

Answer 27

Like looking at side of fan facing right.
Left edge: Vr1 tangential to blade, u1 parallel to vertical motion of blade, V1 completes triangle.
Right edge: Vr2 tangential to blade u2 parallel to vertical motion of blade, V2 completes triangle.
α between u and V, β between u and Vr. u1=u2=u

Question 28

Formula for head produced by axial pump

Answer 28

u^2/g-uVn/g(Cot(α1)+Cot(β2))

Where Vn is horizontal velocity of fluid

Question 29

What happens to formula for head produced by axial pump when α1 equals 0?

Answer 29

Cotα1 term is removed.

Question 30

What do stator blades do?

Answer 30

They are stationary vanes that redirect the fluid, often to send it tangential to the rotating blades of the pump.