Recirculating systems functions

Flush the system to remove dust and major debris. Recirculate detergent or alkali cleaner at elevated temperatures to remove grease or oil. Flush and recirculate an acid at elevated temperatures to dissolve any ferrous particles in the system. Flush with water of the same quality as will be used in service. The cleaning procedure shall be validated by making chemical analysis of surface residues. System functional checkout... 

Next, we define a parallel set of NPD function in continuous flow recirculating systems. We restrict our discussion to steady flow systems. Here, as in the case of RTD, we distinguish between external and internal NPD functions. We define fk and 4 as the fraction of exiting volumetric flow rate and the fraction of material volume, respectively, that have experienced exactly k passages in the specified region of the system. The respective cumulative distribution functions, and /, the means of the distributions, the variances, and the moments of distributions, parallel the definitions given for the batch system. 

Passage times and distribution of passage times in recirculating systems were first considered by Shinnar et al. (64) in their analysis of RTD in closed-loop systems. The most important such system is that of blood circulation, but the analysis cited is also relevant to engineering systems such as fluidized-bed reactors. The main objective of this work was the analysis of tracer experiments in recirculating systems. The renewal theory discussed by Cox (65) served as the theoretical framework for their analysis. Both Shinnar et al. (64), and later Mann and Crosby (66) and Mann et al. (67) have shown that the NPD functions can be evaluated from the passage time distribution function, which in turn can be obtained from the renewal theory. 

Figure 7. Fat surface area of the protein-stabilized emulsions as a function of power consumption after emulsification with a valve homogenizer using 10 passes through the recirculating system ( ll,)...

MARS A new therapeutic option that could improve renal function and prolong survival, especially in risk patients to TIPS, can be found in the molecular adsorbent recirculating system (MARS). It represents a cell-free liver dialysis technique and enables the selective removal of albumin-bound substances using an albumin-enriched dialysate fluid. Significant improvements for different biochemical and clinical parameters as well as a 30-day prolongation of survival were reported. (40) (s. p. 385)... 

Using this approach, corrosion potentials have been calculated for various components in the heat-transport circuit of a BWR, as shown in Fig. 19, as a function of the concentration of hydrogen added to the feedwater. The calculations predict that the lower plenums and recirculation systems of many BWRs can be protected by hydrogen water chemistry, but that those components that are exposed to high radiation fields and/or high concentration of radiolysis products cannot be protected, at least under full-power operating conditions. Similar calculations have been carried out [46] for in-vessel materials in PWRs, in order to explore the susceptibility of various components to intergranular fracture. 

The function of the reactor water recirculation system (Figure 3.8) is to circulate the required coolant through the reactor core. The system consists of two loops external to the reactor vessel, each containing a pump with a directly coupled water-cooled (air-water) motor, a flow control valve, and two shutoff valves. 

An understanding of the environment of an open recirculating system is very important, as the cooling tower functions as an "air scrubber". Pollutants from the air can be ... 

Many studies were performed with the use of plate count techniques. Experience demonstrates that the concentration of microorganisms in the cooling water depends on many parameters and is site-specific. However, the normal functioning of cooling water system is reported when bacterial counts are below 10 colony-forming units (cfu) per milliliter of cooling water in open recirculating systems, 10" cfu/ml in closed systems or 400 cfu/ml in a makeup supply (Drew, 1994). 

Research has also been focused on the need for inhibitors that will function adequately in recirculated systems made up of a variety of metals (and perh s nonmetals as well). Typical systems of this type include jacket water cooler circuits, which may include cast iron parts, copper-bound gaskets, lead-tin or silver solder joints, and brass or aluminum heat exchanger tubes or both. The inhibitive system must provide protection for all the different metals and not stimulate galvanic aaion between them. Films that may be deposited must be sufficiently thin so heat transfer is not seriously reduced. 

Air cleaning (dust collection) can be cost effective for LVHV systems handling valuable dusts. Care must be taken when handling potentially toxic dusts from air cleaners. Regular, routine reconditioning of fabric filters (e.g., by automatic shaking or pneumatic pulsing) is impottant. This can be accomplished on a set maintenance schedule or as a function of pressure drop across the fabric filter. It is not recommended to recirculate airflow back to the workplace because of the low air volume and potential hazards in the event of filter failures. 

These systems can be inside large halls and may have no fixed limits for their influence, except for some parts of the system (inlet device surface, etc.) They can also be situated inside small rooms, where walls, floors, and ceilings are the natural boundaries. The systems usually consist of one exhaust hood and one supply inlet, which interact. There are also special combinations, as two or more inlets and one exhaust hood, or one supply inlet and two or more exhausts. All of these combinations need careful design and an accurate relation between supply and exhaust flow rates and velocities. Some systems also need stable temperature conditions to function properly. All combinations are dependent on having a defined contaminant concentration in the inlet air. This usually implies clean supply air, but some systems may use recirculated air with or without cleaning. 

Embedded in such models, in which variations were developed [12] are further detailed. The laminar burning velocity is expressed as a function of fuel type, fuel/ air ratio, level of exhaust gas recirculation, pressure, temperature, etc. Furthermore, submodels have been developed to describe the impact of engine speed, port-flow control systems, in-cylinder gross-flow motion (i.e., swirl, tumble, squish), and turbulent fluctuations u. Thus, with a wider knowledge base of the parametric impact of external variables, successful modeling of... 

The quantity of deposit control water treatment chemical required to be added to a cooling system per unit time (and hence the cost of the chemical program) is a function of the volume of makeup water added to the system and the cycles of concentration, or concentration factor of dissolved solids within the recirculating water. 

Almost all open recirculating cooling water systems operate within a pH range of 6.5 to 9.5. Occasionally this may be as low as 6.0 or as high as 10.0. Typically, however, water treatment programs are designed to function within only a narrow pH band of 0.5 to 1.0 pH unit or less. The specific... 

The first term on the right hand side of Eq. (1) gives the amount of particles of / th size at the moment of time tn which neither moved forwards nor broke during one time step of simulation. The second term represents those particles of the same size that moved backwards from the second section. The third term expresses the amount of particles that remained in the first section and have broken from some size higher than x, to that subinterval of size. Term ai(tn) denotes the amount of particles of the / th size that freshly enters the system. Finally, the last term ( Vf - Vb) f(xi-( 1/2)) p(yj, Xi, tn-d) is the fraction of particles of the /th size that left the mill at the moment of time tn-d and was classified by the classifier to recycle into the mill for further grinding. Here, function ///,. 0 < x/j, = t (x,) < 1, describes the operation of the classifier, whilst parameter d denotes the discrete time delay in the recirculation line. 

The key to smooth operation of a CFB system is the effective control of the solids recirculation rate to the riser. The solids flow control device serves two major functions, namely, sealing riser gas flow to the downcomer and controlling solids circulation rate. Both mechanical valves or feeders (see Figs. 10.1(a) and (d)) and nonmechanical valves (see Figs. 10.1(b) and (c)) are used to perform these functions. Typical mechanical valves are rotary, screw, butterfly, and sliding valves. Nonmechanical valves include L-valves, J-valves (see Chapter 8), V-valves, seal pots, and their variations. Blowers and compressors are commonly used as the gas suppliers. Operating characteristics of these gas suppliers which are directly associated with the dynamics and instability of the riser operation must be considered (see 10.3.3.2). 

---