Rotameter Head Loss Experiment
Size parameter must be a number (optionally followed by 'px', 'pt' or 'em').
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Overview
A rotameter can be included between the alum stock tank and the constant head tank in the dose controller to verify the flow rate of chemical. The head loss through the rotameter needs to be determined in order to perform an accurate energy balance on the dose controller to provide precise dosing.
Experimental Setup
The head loss through the rotameter was be determined using the setup that is diagrammed in Figure 1. A peristalic pump was used to circulate the fluid at a certain flow rate. Two attenuators were used to minimize the effect of the pulsing from the peristalic pump, and one pressure sensor was used to measure the pressure difference before and after the rotameter.
A ramp function in process controller was used to control the flow rate of the circulating fluid. The flow rate was gradually increased from 8 ml/min to 380 ml/min.
The head loss was be determined by performing an energy balance around the rotameter. The pressure reading from the standing water is subtracted from the measured pressure difference values to cancel out the height term. The resulting pressure difference corresponds directly to head loss of the rotameter.
Results
One experiment looked at the response of the rotameter to flow rates of 8 to 380 mL/min. As seen in Figures 2 and 3, the experimental data fit best to a 0.09 in orifice with a 2 cm offset in pressure. This 2 cm of extra head needed to fit the 0.09 in orifice model has been hypothesized to be caused by the energy needed to lift the ball float.
Size parameter must be a number (optionally followed by 'px', 'pt' or 'em').
Size parameter must be a number (optionally followed by 'px', 'pt' or 'em').
In Figures 2 and 3 there is also a seemingly linear response in the data at low flow rates. Another experiment was performed at 8 to 40 mL/min flow rates to determine if this was indeed linear.
Size parameter must be a number (optionally followed by 'px', 'pt' or 'em').
Size parameter must be a number (optionally followed by 'px', 'pt' or 'em').
From the data, it seems that there is a linear response at low flow rates until about 25-30 mL/min. (All data and results can be found on the attached file.
Conclusions/Future Work
It was concluded that the relationship between head loss and flow rate in the rotameter has an inconsistent relationship. At the lower flow rates, there seems to be a linear relationship until about 25-30 mL where it behaves an orifice with head loss varying with the square of the flow rate.
Also, there seems to be an additional amount of energy needed by the rotameter as seen by the model which adds a 2cm offset to the 0.09 in orifice model. This could be the energy needed to lift the float valve in the rotameter.
If it is desired to use a rotameter, it may be better to use a smaller range rotameter for the lower flow rates. Another experiment could be done to determine whether an orifice relationship can be achieved at the lower flow rates using a different rotameter.
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