Hot:17292013-08-29 02:04:44 From: FTD Automation Instruments
One :the characteristics of liquid flow measurement in large diameter pipelines
The less pressure loss, the better for the largediameter pipelines.
Generally reducing pipeline in some part of pipeto improve velocity is not allowed.
2 velocity is generally very high.
Economic flow velocity is selected in New designinstallation line.
Low velocity will increase line investment; high velocitywill cause power loss greatly increased, hence the cost of operation; Both ofthem are not economical.
But some aged road improves the flow velocity dueto the needs of the production.
Dirt, silt, etc, in the fluid can be easilydeposited because of low velocity
The wetted parts of the flow meter should be cleanedwhen designing.
4 Large requirements for measuring range.
The flow in the pipelines varies a lot during day and night, winter and summer, as many as 10 ~ 20 times; some air conditioning water even stopped running in some reasons. Therefore, this water flow meterrequires wide flow range.
5.High demand for protection level
Most of large diameter pipelines are buried tosave a space, in the north, it is also the need of antifreeze.
So the flow meters are mostly installed in thepipeline where there is instrument borehole.
Flow meters can be submerged because of rain, pipelineleakage or well leakage, we should consider it when designing. IP68 protectionlevel flow meter should be used.
Two, the flow meter selection
1 Electromagnetic flowmeter.
Electromagnetic flowmeters occupies an extremelyimportant position inlarge diameter water flow measurement, it has the following characteristics.
A. no moving parts, high reliability, goodlong-term stability.
B. no additional resistance.
It has special important significance to largediameter flowmeters.
C. High accuracy in flow measurement.
The accuracy can achieve - 0.3% of the R at thespeed of 1 m/s.
D. Large Turndown ratio.
Theturn down ratio can reach 40:1, measurable range can reach 200:1.
e. low demand for Straight pipe section
For large diameter pipeline, it is also veryimportant.
A variety of flow meters requirements 30 D beforeand after of the pipe; For the pipe diameter above 1m, , it means that it should have straight pipe morethan 30 m which inmost cases is difficult to satisfy.
F. Electromagnetic flow meters have large sizes, DN3000electromagnetic flow meters can be provided to satisfy the needs of largediameter water flow measurement.
G. Electromagnetic flow meters have IP68protection level.
h. The shortcoming is the high price level, andthe price will grow highly for large diameters.
Even so, some factories are willing to spend moneyto choose electromagnetic flowmeter for its high accuracy , for example waterfactory, finished product water and source water metering.
2 Ultrasonic flowmeter.
Ultrasonic flowmeter occupies an importantposition in large diameter pipeline flow measurement, the reasons are asfollows.
A. ultrasonic flowmeters are clamping mounted, andhas little relationship with the pipe line. It can be used in the largediameter pipelines.
B. ultrasonic flowmeter can get measurementaccuracy with the pipe diameter, pipe diameter is larger, likely to get higheraccuracy.
Some suppliers can provide multi-channeltime-difference ultrasonic flowmeter, the accuracy can reach to 0.15, but theprice increase correspondingly.
C. Ultrasonic flowmeter can measure conductiveliquid and non- conductive liquid.
Now some companies equip some handheld( timedifference methods) Ultrasonic flowmeter for large pipelines; generally theyget good result.
When the DN ≥ 150 mm,v ≥0.3m/s, theaccuracy can reach - 2% R.
3 Insert electromagnetic flowmeter.
The electromagnetic flow meter used in largediameter pipeline , but the price is more expensive, therefore, insertelectromagnetic flowmeter will become popular when accuracy demand is not sohigh.