Closed recirculating system

Figure 8-3 Three basic types of cooling water systems. Top the once-through system where the cooling water is used once and then discharged. Middle the open recirculation system where the water is cooled and recycled through a system in which it comes in direct contact with air. Bottom a closed recirculation system where the water is cooled and recycled without coming in direct contact with the atmosphere.

The closed recirculation system (see Fig. 8-3) is used when it is necessary or economical to produce cooling water at a temperature below that feasible with an open system, or it is important to prevent foreign matter from getting into the water.14 Here secondary heat exchangers are used to remove the energy. The only water loss is due to leaks, and since it is an isolated system, any water pretreating that is required is minimal. 

Because of the independence of stages it is easy to evaluate what happens to the C curve when tanks are added or subtracted. Thus this model becomes useful in treating recycle flow and closed recirculation systems. Let us briefly look at these applications. 

Closed Recirculation System. If we introduce a 8 signal into an N stage system, as shown in Fig. 14.5, the recorder will measure tracer as it flows by the first time, the second time, and so on. In other words it measures tracer which has passed through tanks, tanks, and so on. In fact it measures the superposition of all these signals. 

This form of curve is encountered in closed recirculation systems in which tracer is broken down and removed by a first-order process, or in systems using... 

In order to compare the catalytic action of SOuj LrOi with that of H-mordenite (H-Mor), the reaction of pentane was performed in a closed recirculation system. The changes of product yields against reaction time are shown in Figure 17.4 [135]. The reaction rate with S04/Zr02 at 0°C is almost constant during the reaction, and the main product is isopentane, with small amounts of isobutane and hexanes being detected. 

The configuration depicted in Fig.4.3-5 comprises of two interacting reactors forming a closed recirculation system. The pulse introduced into reactor 1 is distributed at steady state between reactors 1 and 2. 

Modem adiabatic calorimeters employ a technique whereby the enthalpy of vaporization is measured under conditions in which a measured amount of electrical energy is supplied to a heater immersed in the sample to compensate for the heat absorbed by the substance during the evaporation and hence the temperature is kept constant. The main differences among adiabatic calorimeters are that the vapour flows out of the calorimeter at atmospheric pressure (those of Mathews and Fehlandt [65]), into a vacuum, [67,69-71] into a gas stream [68], or into a closed recirculation system with continuous fluid flow [66]. 

The third example of the reactor is a closed recirculation system, as displayed in Fig. 9.3c. The gases in the system (typically, 300-1,000 cm ) can be recirculated by a circulating pump with a speed >3 cm /s to attain homogeneous gas mixing in the system. All valves are made of grease-less valves, or of Pyrex glass sealed with... 

Table 61 summarizes the protection procedures for closed recirculating systems. 

Before any remedial action can be taken, it is necessary to identify the t) e of bacteria involved in corrosion. Aeration of water in a closed recirculating system reduces the activity of anerobic bacteria. Chlorination and treatment with biocides help control populations of some bacteria, though they are not effective in all cases. Also, the bacteriocides fail to reach the areas underneath deposits where the bacteria thrive. Coating a buried structure with tar, enamel, plastic, or the like is often an effective means to... 

Nitrites are not effective inhibitors. The presence of chloride and sulfate ions can damage the protective film formed by nitrites. They are often blended with borax in closed recirculating system. 

They protect solder and aluminum. They are not very effective and limited to use only in closes recirculating systems. 

Cooling water systems may be either recirculating or once-through types. In closed recirculating systems, oxygen can be excluded, and corrosion often can be controlled by adjusting the pH to an alkaline value. 

Recirculating systems are more easily controlled by inhibitors since higher concentrations can be applied because the water is reused. Sodium chromate or sodium nitrite are both effective in all-steel, closed recirculating systems. 

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