MDME: MANUFACTURING, DESIGN, MECHANICAL ENGINEERING

FLUID POWER


The Bernoulli equation now includes the input of energy from a pump (or loss of energy through a turbine).

SmartBoard Notes: Adobe Fluid_Power.pdf OneNote 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 = rho g H


where:
P = power (W)
mass flowrate = 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.
Hence power (W) due to fluid can often be simplified to the following;

When pressure head is the only factor, the amount of power is given by;

P = p volume flowrate

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).

Bernoulli equation

H = power Head (+ for pumps, - for turbine/actuator)

Bernoulli chart with power




Questions

Homework Assignment: Kinksy new edition
Do all questions; Chapter 12: Fluid Power
12.1 to 12.15 (page 261-265)

Do all questions.
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