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Thermodynamics help.

Thermodynamics help.
by liam_wilson on 04/19/04 at 08:23:21

Any help please.

A high pressure floor cleaner has 2 high pressure nozzles on each end of a 450mm rotating bar.
It is connected to a pump by means of a 15 metre long 8mm diameter hosepipe. (8mm bore)
The pressure in the hosepipe to the rotating bar is 155bar.
The maximum flow rate is 25litres/min.

From this I need to:
Determine the power input to the motor driving the pump.
Determine the exit velocity from the nozzle, and the force it produces.
Using maximum flow rate determine the velocity in the delivery pipe and from this the friction and other loses.
Apply bernoulli's equation between the pump inlet and a point just before the rotating bar entry.

I have very little knowledge on this subject and have searched the net to no avail. I have tried to work out reynolds number for the moody chart but I don't understand what to do.
If possible any equations in the areas above would help a great deal. ???

Re: Thermodynamics help.
by liam_wilson on 04/19/04 at 15:32:05

From this I have points 2 & half of 3.
Please anybody I am getting to the point of jacking it all in >:(

Re: Thermodynamics help.
by Robert Fogt on 04/19/04 at 21:12:56

Well the power input to the motor driving the pump should be easy to figure out.

P = V * I

I am assuming there is no watt rating on the motor, hopefully there is a current rating.  Just multiply Volts * Amps.

If not you'll need to break out your good'ole Volt/Amp meter and measure it. I doubt it is possible to calculate the power used by the pressure or flowrate of the hoses.

I wont be able to help much with your other questions. But here is a link on Bernoulli's Equation. Though no doubt you don't need more information, but assistance in calculating it.


Re: Thermodynamics help.
by liam_wilson on 04/20/04 at 03:19:26

Thanks for the response.
Unfortunatly this is an assignment on paper no actual pump or motor.
I have not been given and ratings for the motor.
The equation given is:

P (power required watts) = E per kg * mass flow rate.

The other equation I have for Reynolds number is:

Re = Velocity * diameter/ Viscosity

This is where I feel I am going wrong I get an answer of around 66 but from this I dont know how to get a friction factor from a moody chart? ???

Re: Thermodynamics help.
by Robert Fogt on 04/20/04 at 11:35:12

Here is a online automated calculator for getting the friction factor from a moody chart.


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