FLUID POWER
The Bernoulli equation now includes the input of energy from a pump (or loss of energy through a turbine).
SmartBoard Notes: Fluid_Power.pdf Fluid_Power.one
Image | Video Lesson Description and Link | Duration | Date | Download |
Fluid Power | 20:40 min | 20140819 |
Fluid Power (20 mins)
Fluid Power
Pump: Increases or adds fluid power
Turbine: Decreases or uses up fluid power.
The amount of power is given by;
P = g H
where:
P = power (W)
= mass
flow rate (kg/s)
H = total head of fluid (m). This is only the Head that changes through the pump/turbine (eg This is usually pressure head).
Pressure Head Only
- If a pump (or turbine) has same diameter inlet and outlet (which is normal) then there is no change in velocity - so velocity head terms cancel out.
- If the outlet of the pump/turbine is approximately the same elevation as the inlet then there is no change in potential head - so potential head terms cancel out.
- Pressure head can be so much greater than velocity head or potential head (e.g. hydraulics), that only pressure needs to be considered.
When pressure head is the only factor, the amount of power is given by;
P = p
where:
P = power (W)
= volume flow
rate or volumetric flow rate (m3/s).
p = pressure change between inlet and outlet (Pa)
Efficiency
Fluid machinery (pumps and turbines) convert fluid power Pf to mechanical power P or visa versa. Many (most) fluid machinery can work as either a motor or a pump (for example a motor could drive a pump, or a pump could generate electricity if the motor can act as a generator)Where: Mechanical power is P=Fv (linear) or P=Tω (rotary).
A turbine, fluid motor, ram, cylinder, fluid actuator: Converts fluid power Pf to mechanical power P
A pump: Converts mechanical power P to fluid power Pf.
Efficiency is the ratio of output power to input power.
η = output power / input power
For a turbine:
η = output power P / input power Pf
For a pump:
η = output power Pf / input power P
Bernoulli with Power
Steady flow means the mass flowrate is constant. (constant kg/s).
H = power Head (+ for pumps, - for turbine/actuator)
Questions
Homework Assignment: Kinksy new editionDo all questions; Chapter 12: Fluid Power
12.1 to 12.15 (page 261-265)
Do all questions.