Pump sampling in unidirectional and oscillatory flow
Contents
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.
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
- INTRODUCTION, PROBLEMS AND APPROACHES IN SEDIMENT TRANSPORT MEASUREMENTS
- DEFINITIONS, PROCESSES AND MODELS IN MORPHOLOGY
- PRINCIPLES, STATISTICS AND ERRORS OF MEASURING SEDIMENT TRANSPORT
- COMPUTATION OF SEDIMENT TRANSPORT AND PRESENTATION OF RESULTS
- MEASURING INSTRUMENTS FOR SEDIMENT TRANSPORT
- MEASURING INSTRUMENTS FOR PARTICLE SIZE AND FALL VELOCITY
- MEASURING INSTRUMENTS FOR BED MATERIAL SAMPLING
- LABORATORY AND IN-SITU ANALYSIS OF SAMPLES
- IN-SITU MEASUREMENT OF WET BULK DENSITY
- INSTRUMENTS FOR BED LEVEL DETECTION
- ARGUS VIDEO
- MEASURING INSTRUMENTS FOR FLUID VELOCITY, PRESSURE AND WAVE HEIGHT
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