Abrupt inlet outlet

Favored locations for erosion-corrosion are areas exposed to high-flow velocities or turbulence. Tees, bends, elbows (Fig. 11.5), pumps, valves (Fig. 11.6), and inlet and outlet tube ends of heat exchangers (Fig. 11.7) can be affected. Turbulence may be created downstream of crevices, ledges (Fig. 11.8), abrupt cross-section changes, deposits, corrosion products, and other obstructions that change laminar flow to turbulent flow. 

Open end vessel One in which there are no discontinuities (abrupt changes) in concentration at die inlet and outlet where bodi bulk and dispersion flow occur. The boundary condidons are C = when z = 0 and 6C/6z = 0 when z =... 

Fig. 27. Abrupt contraction cell for flow visualization, birefringence and degradation measurements A inlet (from a peristaltic pump of a pressurized reservoir B outlet (atmospheric pressure or partial vacuum) C interchangeable metallic nozzle with a sapphire tip D capillary flow meter E glass window for flow visualization AP pressure drop (from pressure transducers)...

Fig. 56. Schematic representation of the convergent flow apparatus < > = 180° (abrupt contraction), 14° or 5° (conical inlet)

Example 14.1 shows how an isothermal CSTR with first-order reaction responds to an abrupt change in inlet concentration. The outlet concentration moves from an initial steady state to a final steady state in a gradual fashion. If the inlet concentration is returned to its original value, the outlet concentration returns to its original value. If the time period for an input disturbance is small, the outlet response is small. The magnitude of the outlet disturbance will never be larger than the magnitude of the inlet disturbance. The system is stable. Indeed, it is open-loop stable, which means that steady-state operation can be achieved without resort to a feedback control system. This is the usual but not inevitable case for isothermal reactors. 

These devices are employed for fine powders (40-400 im) and also coarser particles. In the Franken or Vandenhoek inertial separators [13,14] (Fig. 4a) particle-air mixture enters from the top and falls down in the inlet pipe. The air turns abruptly to the outlet pipe inclined by about 45-50° and carries the fine particles. Coarse fraction proceeds straight down because of high inertia towards the discharge pipe. On its way this material undergoes repeated separation in a secondary air flow carrying fines into a curvilinear chamber. Then they exit via the outlet pipe with blades mounted for better air distribution. These classifiers, manufactured by Buell Co., are used for separation of pulverized limestone at cut size of 150 pra with feeds from a few pounds to 600 t/h [15], In the Buell s variant of this device [14] blades have different angles to increase the efficiency. Such devices were used for separation of 15-1000 pm particles. 

When the valve switches from nitrogen to air, the flow of gas will change abruptly if the vent line and reactor line are inadequately equilibrated the pressure at both exits of the four-way valve must be equalized. This may be accomplished by a back pressure regulator. Whereas a pressure regulator reduces the supply pressure at the inlet to a lower pressure at the outlet, a back pressure regulator throttles the flow downstream to maintain the inlet pressure. A needle valve or a back pressure regulator is required at the vent line to match the pressure across the reactor, process lines, and analytical equipment. 

In operation a liqnid circulates as shown in Figure 2. When the inlet valve 4 opens a portion of gas is injected in form of gas bubbles to the liquid. When the bubbles reach the outlet valve 5 it abruptly closes. The liquid keeps on moving and compresses the bubbles generating pressure and temperature optimal for chemical reactions. Then the valve 5 opens resulting in die eiqiansion and coohng of the reaction products and recovery of the compression energy. 

At the inlet of the reactor, the concentration of a tracer is abruptly changed at time t = 0. In practice, the stepwise change should be faster than a hundreds of the space time in the reactor < O.Olr). The response of the system at the reactor outlet is measured. The momentary tracer concentration c t) is referred to the constant inlet concentration Cg. The response curve is thus dimensionless and is designated as an f-curve according to Danckwerts [2, 3] it thus has values between 0 and 1 (see Figure 3.2) and corresponds to the cumulative curve of the RTD. 

Compared to PFR in which the concentration of A changes gradually from inlet to outlet through the reactor volume, in the CSTR, the concentration of A drops abruptly from to C fat the reactor inlet and remains constant at C,iy throughout the reactor volume. In an ideal PFR, although decreases in the axial direction, its value remains constant in the radial direction. 

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