Torque Calculation without a gauge

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Discussion Overview

The discussion focuses on measuring shaft power of a vertical turbine using dead weight blocks, exploring methods for torque calculation and the effects of load on turbine RPM. The context includes theoretical calculations and practical applications related to turbine performance.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • One participant suggests measuring torque using a dead weight and lever arm setup, proposing that torque can be calculated as dead weight multiplied by the length of the lever arm.
  • Another participant questions the consistency of a previous statement regarding torque generation without load, asserting that torque cannot exist without a load on the turbine.
  • A participant provides a detailed calculation of torque based on water pressure and flow rate, presenting values for force, torque, angular velocity, and power, and seeks validation of their calculations.
  • Another participant challenges the calculation of force, suggesting that it should be derived from pressure and flow rate instead, leading to a different power output estimation.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between load and torque generation, with some asserting that torque cannot exist without load, while others provide calculations that suggest otherwise. There is no consensus on the correctness of the torque calculation or the appropriate method for determining power output.

Contextual Notes

Participants reference various assumptions, such as the relationship between torque and RPM under load conditions, and the dependence of calculations on specific definitions of force and power. The discussion highlights the complexity of accurately measuring and calculating turbine performance.

Who May Find This Useful

Individuals interested in turbine mechanics, power calculations in fluid dynamics, and those seeking to understand the implications of load on turbine performance may find this discussion relevant.

dilipbhanu
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Hi
How can I measure, shaft power (watts or HP) of a vertical turbine using dead weight blocks

Turbine diameter - 18 inches
RPM - 450 ( Zero Load)
 
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Mount generator casing on bearings so it can rotate through a small angle.
Fix lever arm to generator casing.
Add rope from lever arm over pulley to dead weight.
Measure rpm an convert to angular velocity

Dead weight * length of lever arm = torque

Power = torque * angular velocity
 
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Thanks a ton. A little more help.

My Turbine is a reaction turbine of 6 inch diameter. It rotates at 2500 RPM generating 15N.m of Torque. The mentioned RPM is measured for shaft rotating (without coupling it to any other machine). Once a Generator is coupled, what will be the final RPM. Will the RPM reduce ? If yes, is there a formula to calculate the final RPM ?
 
dilipbhanu said:
My Turbine is a reaction turbine of 6 inch diameter. It rotates at 2500 RPM generating 15N.m of Torque. The mentioned RPM is measured for shaft rotating (without coupling it to any other machine).

That statement is inconsistent. If there is no load on the turbine it cannot generate any torque (or power for that matter).

What usually/sometimes happens is that as you increase the load the torque increases and the rpm reduces. If you use the right units.. Power = Torque * rpm. So you really need a graph of Torque vs rpm to workout the best operating point (peak power) for the turbine.

Perhaps 2500rpm @ 15N.m is the max power operating point?
 
Last edited:
The RPM has been read with a non contact tachometer, while the Torque has been calculated theatrically based on the input forces (Water Pressure and Flowrate)

Motive fluid = Water
Pump Gauge Pressure = 29.86 PSI
Flow rate = Water leaving the turbine = 10LPS @ 19.70 m/s (linear Velocity)

Force = 10*19.697 = 196.95 Newtons
Turbine radius (arm length) = 3 inches ( 0.0762 meters)

Torque = 196.95*0.0762 = 15 N.m
Angular Velocity = 258.49 rad/sec
RPM = 2468

Power = Toque*rad/sec = 15*258.49 = 3877 Watts

Is my Torque calculation correct or have i missed something.
 
Perhaps I miss understand your calculation but force isn't mass * velocity.

It might be easier to use...

Power = pressure * flow rate

..to calculate the power available.

Which I make 2058 Watts.

If the turbine utput isn't connected to anything then this isn't the output power. It's the power needed to spin the turbine with no load. Eg its the power loss.
 

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