Circulation, water/currents

Impressed-current systems for power stations are somewhat more sophisticated than those required for pipelines or marine structures inasmuch that a large number of items of plant, with a wide range of current requirements, are protected by one transformer-rectifier. Each section of every water box in order to provide even current distribution requires one or more anodes. In the case of a large circulating water pump as many as 30 anodes may be required to provide the current distribution necessary. Three types of system should be considered as follows ... 

Manually Controlled System A manually controlled system comprises one or more transformer-rectifiers each with its associated control panels which supply the d.c. to the various anodes installed in the water box spaces. Each transformer-rectifier is provided with its own control panel where each anode is provided with a fuse, shunt and variable resistor. These enable the current to each anode to be adjusted as required. Reference cells should be provided in order to monitor the cathodic protection system. In the case of a major power station, one transformer-rectifier and associated control panel should be provided for separate protection of screens, circulating water pumps and for each main condenser and associated equipment. 

When coolers or condensers are shut-down but remain full of water, the amount of current required to maintain satisfactory cathodic protection is considerably reduced. If the current is not reduced over-protection occurs and excessive amounts of chlorine can be generated which would tend to accumulate in the upper section of the water boxes causing considerable corrosion, not only to the water boxes, but also possibly to the tubes. To ensure against this a stand-by condition should be included on the control panel which effectively reduces the current required under shut-down conditions. This control is effected by a limit switch fitted to the outlet valve of the condenser or cooler concerned. It is impossible to determine exact requirements for the protection of circulating water systems in advance and it is normal to adjust the current to provide protection during commissioning. 

A tubular type reactor was used in this experiment as shown in Fig. 2. Two copper electrodes with an area of 100 cm2 each were set in parallel with a gap of 3.5 cm. In order to diminish the eddy current in the gas flow, Teflon inserts were set in a tubular reactor as shown in Fig. 2. The bottom electrode was cooled by circulating water. The temperature of water was almost 19 °C throughout this experiment. 

Figures 6 and 7 show a modem Langmuir film balance and its arrangement inside a Puffer-Hubbard temperature-controlled cabinet (63). Inside the cabinet, the film balance is protected further from circulating air currents by a Plexiglass case. At the bottom of the Teflon trough lies a serpentine glass coil through which water from a thermoregulator is circulated to help control subphase temperature.

Electrical System. The conductors in the hose-cable carry power and control signals down to the underwater vehicle and return information. The drive-pump motor is powered by three-phase, 220 V carried down three paired conductors. The solenoid valve, which controls the clean pump, is energized by 24 V direct current (DC), which is controlled on deck. The submersible pump that circulates water through in situ sensors uses 110 V alternating current (AC) power from the hose-cable. 

The resistance of membranes can be measured by AC impedance methods [85,86], using the four-point-probe technique. The test membrane is placed in a cell consisting of two Pt-foil electrodes, spaced 3 cm apart, to feed the current to a sample of 3 x 1 cm and two platinum needles placed 1 cm apart, to measure the potential drop (see Fig. 4.3.26). The cell is placed in a vessel maintained at constant temperature by circulating water. The impedance measurements are then carried out at 1-10 kHz using a frequency-response analyzer (e.g., Solatron Model 1255HF frequency analyzer). After ensuring that there are no parasitic processes (from the phase angle measurements, which should be zero), one can measure the resistance directly. The membrane resistance can also be obtained directly from the real part of the impedance (see typical data in Fig. 4.3.27). 

Because of a high water level, high water discharge and water circulation (main current along the left riverbank), no regularity in plankton distribution from the sur-... 

The piezoelectric coefficients d, and d, do not cancel each other, as we saw previously with the shear piezoelectric biopolymers, but contribute to a small but finite value of tensile piezoelectricity. The tensile piezoelectric coefficient, d, can be measured with a Berlincourt piezometer [38]. The pyroelectric response can be measured with an apparatus in which the temperature is altered at 0.5°/min by circulating water and the pyroelectric current is measured using a low-impedance current amplifier [39]. 

The circulating water pumps circulate the cooling water from the pump basin to the main condenser and back through two supply and return pipes that are below grade (ground level). Supply to the pump basin will depend on the specific site requirements, currently assumed to be sea water cooling, but could include cooling towers. 

Cooling towers dissipate tremendous quantities of heat into the atmosphere through the process of humidification. Water circulated counter-currently to a stream of air is reduced in temperature owing to the fact... 

The soils generated from the sealed digging methods currently used are listed in Table 3. The soil water sealed method disperses the soil in circulating water. The sand and gravel are separated by sifting and the fine particles, such as silt and clay, are separated by solid-liquid separation into dehydrated cakes. Hence, these soils can be carried by truck and need no further modifications. 

In water flooding, the same types of inhibitors as described for primary production are currently used. The most effective and most frequently used are the quaternary ions of the fatty or the imidazoline types. They are also good bactericides and dispersive agents. Combination of amino-methylene phosphonate and zinc salts have been used successftdly in circulating water systems and have provided more effective protection than the inorganic phosphate-zinc salts. Organic sulfonates have recently been introduced into practice. 

Air which passes over a heated surface expands, becomes lighter and warmer and rises, being replaced by descending cooler air. These circulating currents of air are called convection currents. In circulating, the warm air gives up some of its heat to the surfaces over which it passes and so warms a room and its contents. The same process takes place in water. The immersion heater in a water vessel such as that shown in Fig. 3.60 heats up the water in contact with the heater element which rises and is replaced by cold water, which then heats up and rises and so on. This process sets up circulating convection currents in the water which heats up the contents of the whole vessel. 

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