Flow measurements current meter

Gup and Vane Anemometers. A number of flow meter designs use a rotating element kept in motion by the kinetic energy of the flowing stream such that the speed is a measure of fluid velocity. In general, these meters, if used to measure wind velocity, are called anemometers if used for open-channel Hquids, current meters and if used for closed pipes, turbine flow meters. 

Current Meters. Various vane designs have been adapted for open-channel flow measurement. The rotating element is partially immersed and rotates rather like a water wheel. Operation is similar to that of vane anemometers. 

If we were to place a zero-resistance meter between the two electrodes, we could monitor the amount of charge that flows. Such a meter would be called an ammeter if it measured the current, or a coulometer if it measured the charge. (In practice, most modem meters are multi-function devices and can measure both, changing from one function to another at the flick of a switch.)... 

The dominant fate process for chloroform in surface waters is volatilization. Chloroform present in surface water is expected to volatilize rapidly to the atmosphere. An experimental half-disappearance range of 18-25 minutes has been measured for volatilization of chloroform from a 1 ppm solution with a depth of 6.5 cm that was stirred with a shallow pitch propeller at 200 rpm at 25 °C under still air ( 0.2 mph air currents) (Dilling 1977 Dilling et al. 1975). Using the Henry s law constant, a half-life of 3.5 hours was calculated for volatilization from a model river 1 meter deep flowing at 1 meter/second, with a wind velocity of 3 m/second, and neglecting adsorption to sediment (Lyman et al. 1982). A half-life of 44 hours was estimated for volatilization from a model pond using EXAMS (1988). 

The flow in the river can be obtained by several methods. A direet measurement of river veloeity and cross-sectional area at a specific location can provide an estimate of the flow at that loeation and time. River veloeities are measured either directly by current meters or indirectly by tracking the time for objects in the water to travel a given distance. Since the velocity of a river varies with width and depth due to frictional effects, the mean vertical velocity must be estimated. 

Figure 18-4 Change in cell potential after passage of current until equilibrium is reached. In (a), the high-resistance voltmeter prevents any significant electron flow, and the full open circuit cell potential is measured. For the concentrations shown this is + 0.412 V. In (b), the voltmeter is replaced with a low-resistance current meter, and the cell discharges with time until eventually equilibrium is reached. In (c), after equilibrium is reached, the cell potential is again measured with a voltmeter and is found to be 0.000 V. The concentrations in the cell are now those at equilibrium as shown.

The specific conductance (SpC) of Fox tributary is 4510 /rS/cm. The flow of Caddo Creek measured by current meter is 6.63 cfs (ft /s). Above its confluence with Fox tributary the specific conductance of Caddo Creek is 2010 fiS/cm, whereas 500 ft below this confluence at a distance sufficient to assure complete mixing of both waters, the SpC of Caddo Creek is 2130 fiS/cm. Compute the flow of Fox tributary. 

In an early study of oceanic bottom water flow within the C-C F.Z., Johnson (1972) deployed free-fall bottom current meters in an area north of the Clipperton Fracture Zone where substantial sediment erosion was known to occur. The limited data showed that the bottom currents were generally slow (<10 cm see ) but fluctuated markedly due to a strong semi-diurnal tidal component. It was also established that the currents flowed mainly to the east with minor variations due to topographic effects. In addition, data from a 14-day record of bottom current measurements taken at 210 m above the sea floor revealed an averge bottom water flow of 2.0 cm sec in an ENE direction with peak velocities of up to 16.5 cm sec at semidiurnal periods. These data showed that peak velocities of bottom water transport were strong enough to erode and transport sediment in the area (Amos et al. 1977). 

Currently NGPL has 14 flow measurement systems in service. Four of them are on the TR All. BLAZER system. A data acquisition, control and flow calculation program is operating successfully at Natural Meter in Beatrice, Nebraska. 

Current meters are hydrodynamic instruments with rotating vanes or buckets. The speed of their rotation is proportional to the flow velocity. The forerunners of current meters were the paddle wheels developed in the early 18 century. These were applied by Francesco Domenico Michelotti (1710-1777) in 1767, or by Pierre-Louis Du Buat (1734-1809) in 1786. There are two principal types of current meters, namely the screw and the cup types. The first was conceived by the famous British engineer Robert Hooke in 1783 to measure wind velocity with four vanes similar to a windmill. This type was developed by Reinhard Woltman (1757-1837) in 1790, Andre Baumgarten (1808-1859), Albert Ott (1847-1895), Alphonse Fteley (1837-1903) and Haskell, among many others. The other type meter has several cups on spokes rotating around an axis oriented transverse to the current. These anemometers were first applied around 1850 to measure wind velocities, and then were developed by Theodore Gunville Ellis (1829-1883), or William G. Price (1853-1928) to record flow velocity in rivers. 

When the current is measured in an electric circuit, the observation is the flow of charge for a period of time. The base unit of current, the ampere (A), is a combined unit defined as one coulomb per second 1 A = 1 C s . Devices called amp-meters (or ammeters) measure current. If a known current passes through a circuit for a known time, the charge can be easily calculated. 

Recent tests by other workers Gust et al, 1994) seem to indicate that the flow around and inside sediment traps may have considerable effects on the trap collection efficiency at shallow depths, whereas the deep-ocean traps appear to collect the actual flux. We recommend, therefore, to equip the instruments with current meters, and depth and tilt sensors. This allows a description of the dynamics of the hydrographical field and its effects on mooring line motions as well as on the excursions of traps from the vertical position, and may even offer the basis for corrections of hydrodynamic biases in particle flux measurements. 

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