Abstract
This paper presents results from an investigation of the two phase flow, especially liquid ingas phase, in most mainly used flow meter in steam industry namely differential pressuremeter is investigated. As in general, a flowmeter is designed and employed to measure flowrate of single phase fluid. There are many types of meter available in the market characterizeby their working principles, installed conditions and measured fluid. All meters representtheir accuracies under the single phase flow condition. However, when they are working inunusual conditions especially under multiphase flow, most meters lose their accuraciessignificantly even there is small amount of second phase introduced into the system. Tounderstand the deteriorated performance of the meter under two phase flow, additional studyon the effect the second phase on the meter is required.The laboratory experiment is set up to simulate the wet steam by flowing compressed airin the 2 inch pipe. Water droplet is generated by pressurized water flowing through a nozzleand then spayed into the system in range of 25% maximum by mass fraction. The signal fromeach flowmeter is collected by digital computer and analyzed using FFT and power spectrumdensity. The results show that the presence of the second phase in the system causes highfrequency fluctuation and causes significant error on meter reading. Flow manufacturersalways add low-pass filter circuit to remove this high frequency signal, however, this papershows that the high frequency signal in specific region is useful as it can be use to estimatedthe percentage of the second phase in the main phase system.
Highlights
Steam referred to vaporized water known as working fluid is widely used in many process applications
Air mass flow rate is calculated by measuring volume flow rate by vortex flowmeter, line pressure and temperature simultaneously while water mass flow rate was measured by a coriolis meter with accuracy better than ±0.1% FSD simulated steam quality can be calculated by equation (1)
The results from FFT shows that the amplitude of sensor signal in a specific frequency range (60–250 Hz) increases proportionally to water injected mass flow rate
Summary
Steam referred to vaporized water known as working fluid is widely used in many process applications. The pressure is reduced at the point of use, if necessary This arrangement makes installation easier and less expensive than for some other heat transfer fluids. Offline technique [3] is available by sampling steam sampled from live line process and separated water content from steam calculated its quality. Those methods are complicated, time consuming and expensive. This work presents the straightforward technique to measure quality of steam by using the signal available from a conventional flowmeter installed in the process applying signal analysis technique to discover the relation between high frequency fluctuation and percentage of water droplet in the pipe [4]
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