Difference between revisions of "Pump sampling in unidirectional and oscillatory flow"

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Peristaltic pumps have proven to be very efficient in coastal conditions.
 
Peristaltic pumps have proven to be very efficient in coastal conditions.
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==Photographs and Figures==
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[[Image:H5632figure2.jpg|thumb|left|Fig.1: Sampling error related to intake velocity]]
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Revision as of 08:50, 11 June 2007

Pump sampling in oscillatory flow (coastal flow)

Pump sampling is an attractive method for concentration measurements in coastal conditions because a relatively long sampling period can be used which is of essential importance to obtain a reliable time-averaged value. The sampling period should be rather long (15 min) in irregular wave conditions (at least 100 waves). A problem of sampling in conditions with irregular waves is that the magnitude and direction of the fluid velocity is changing continuously. This complicates the principle of isokinetic sampling in the flow direction. A workable alternative may be the method of normal (or transverse) sampling, which means that the intake nozzle of the sampler is situated normal to the plane of fluid velocity. Bosman et al (1987) studied the sampling error related to the orientation of the intake nozzle, because they were interested in pump sampling under wave conditions. They found that a transverse pumping direction yields good results. The intake nozzle is directed downward or normal to the plane of orbital motion. Figure 1 shows the ratio c/co as a function of the ratio u/uo and the nozzle orientation for 170 um-sediment (c = measured concentration, co = original concentration, u = intake velocity, uo = local ambient velocity). For transverse orientation (90°) and ratio of u/uo> 2, the c/co-ratio is about 0.7 to 0.8 which means a systematic error of 20% to 30% in the measured concentration. Similar results were obtained for 220 um, 280 um, 360 um and 450 um-sediment. This systematic error can be corrected for.

Peristaltic pumps have proven to be very efficient in coastal conditions.


Photographs and Figures

Fig.1: Sampling error related to intake velocity


















References

Antsyferov, S.M., Basinski, T. and Pykhov, N.V., 1983. Measurements of Coastal Suspended Sediment Concentrations. Coastal Engineering, 7, Elsevier Publishers, Amsterdam, The Netherlands.

Bosman, J.J., Velden, E.T.J.M., van der and Hulsbergen, C.H., 1987. Sediment Concentration Measurement by Transverse Suction. Coastal Engineering, Vol. 11, p. 353-370.



See also

Other contributions of Leo van Rijn

articles with parts of the manual


External links

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