# Using Fluid mechanics to rate power output of an engine.

1. Nov 16, 2013

### siegelaaron94

I trying to come up with a way to measure the power output of an engine using a water pump, And I wanted some one to go over my math and check for flaws in my thoughts. My idea is to measure the flow rate and the pressure of the output of the water pump.

Using this math to solve for power
Power = Fv
Pressure = F/A
R = Av

Pressure*A = F

Power = Pressure*A*v = Pressure*R

2. Nov 16, 2013

### OmCheeto

I believe this will work.

3. Nov 17, 2013

### siegelaaron94

Thanks for responding and the help. Im sure it will work the only thing that I think might be wrong is the way I come up with the force.

4. Nov 17, 2013

### Staff: Mentor

R is volumetric flow rate? That's correct... but then you also need to divide by pump efficiency to get input power.

5. Nov 17, 2013

### OmCheeto

Why do you think your force is wrong?

ps. a belated, welcome to Physics Forums.

6. Nov 18, 2013

### siegelaaron94

I was thinking more of the ideal case. I was also thinking of using a positive displacement pump which i think that would solve that problem, right???

7. Nov 21, 2013

### mrspeedybob

No. There will still be friction between the moving parts of the pump, between the pump and the water, and within the water. All this friction creates heat.
Solving the problem is pretty simple though. Insulate the pump, thus preventing any heat loss through the pump housing. Measure the water temperature at the inlet and outlet of the pump. This, along with the flow rate and the heat capacity of water will tell you how much of the input energy is converted to heat. This heat represents most of the inefficiency of the pump. Add this to the hydraulic energy you already measured and that should be very close to the energy output of your engine.