Flash conditions

FIG. 8-78 Generic depictions of average pressure at subsequent cross sections throughout a control valve, FiS selected for illustration are 0,9 and 0,63 for low and high recovery, respectively. Internal pressure in the high-recovery valve is shown as a dashed line for flashing conditions [Pg.788]

Step 5. Read the convergence pressure (ordinate) at the temperature (abscissa) corresponding to that of the desired flash conditions, from Figure 8-3A [79]. 

Liquid ammonia is stored in a tank at 24°C and a pressure of 1.4 X 106 Pa. A pipe of diameter 0.0945 m breaks off a short distance from the vessel (the tank), allowing the flashing ammonia to escape. The saturation vapor pressure of liquid ammonia at this temperature is 0.968 X 106 Pa, and its density is 603 kg/m3. Determine the mass flow rate through the leak. Equilibrium flashing conditions can be assumed. 

Equation 4-91 applies for the case of equilibrium flashing conditions. Assume a discharge coefficient of 0.61. Then... 

On combining these equations and introducing j8 = V/F, the fraction vaporized, the flash condition becomes... 

A computer algorithm has been developed for making multi-component mixture calculations to predict (a) thermodynamic properties of liquid and vapor phases (b) bubble point, dew point, and flash conditions (c) multiple flashes, condensations, compression, and expansion operations and (d) separations by distillation and absorption. 

Figure 2. Reaction of MnHb (15/xM, monomer) with NO ( 70fiM) ( ) after full flash photolysis of MnHbNO (O) after partial photolysis of MnHbNO. The actual OD excursion upon partial flash was only 15 % that upon full flash, but excursions in the lower curve are scaled to give the same initial AA as after full flash. Conditions are as in Figure 1, but the path length is 2 mm (25).

Fittings, pipe, resistances, 95, 98-100 Fixed bed solid catalysis, 596 name reactor, 573 Flash conditions, 375-377 example, 378... 

The method described here is based on the vapor-liquid equilibrium relationships given in handbooks available from the Gas Processors Suppliers Association. This technique will handle flash calculations with feed streams containing up to 15 components. As an added feature, the calculation will check the feed composition at flash conditions for dew point or bubble point condition (i.e., whether the feed is either all vapor or all liquid). These checks are done before the flash calculations are started. If the feed is above the dew point or below the bubble point, an appropriate message is displayed on the computer screen. A default value for R (L/V) = 1.0 is used to start the iterative process. 

The main variables associated with phase relationships include the overall composition, Z , temperature, pressure, liquid composition, X , vapor composition, F, vapor mole fraction, /, and heat transferred, Q. A process in which Z, and two other independent variables are set, and equilibrium separation of the phases is allowed to take place, is called a flash operation. A general flash operation is shown in Figure 2.4. A feed stream initially at conditions T, and P, is controlled so that its final conditions satisfy two specifications. The feed is of fixed rate and composition, F and Z . A heat duty, Q, may be added to or removed from the system as required. The feed is flashed to generate a vapor product with flow rate Ft r and a liquid product with flow rate F(1 -1 /), where / is the vapor mole fraction at flash conditions and P. In general, tj/ may be equal to zero or one or any value in between. The enthalpies of the vapor and liquid products are H2 and /Z2> respectively. The type of flash operation... 

The specified variables are the final temperature and pressure, T2 and P2- The dependent variables are the vapor fraction, t /, the liquid and vapor compositions, X, and the total enthalpy of the two phases, /Z2 + H, and the heat duty, Q. The term isothermal should not be interpreted to imply that the transition from initial conditions to final conditions is at constant temperature is, in general, different from T. It simply means that within the flash drum the temperature, as well as the pressure, is fixed. The heat duty required to bring about the final conditions is equal to the enthalpy change, Q = (Hj + 2) - i> where is the enthalpy at and P,. Isothermal flash conditions may be represented by a point ( 2, P2) on tbs phase envelope diagram. It is clearly possible that this point may fall either within the phase envelope or outside it, in which case the system would be all vapor or all liquid (or dense phase). A flash drum operating at such conditions would have a single product and no phase separation would take place. In a single-phase situation, the dependent variables are the properties of the vapor or liquid product. The liquid or vapor composition is, of course, identical to the feed or overall composition, Z,. Note that any set of temperature and pressure specifications is feasible. 

The vapor phase at the flash conditions is assumed to behave as an ideal gas. Hence, the /(-value of water relative to the hydrocarbon liquid is written as... 

According to analysis and consideration detailed above for photoinitiated polymerization, it may now be concluded that Rp or [M ] can be varied by varying the frequei of blinking. Under otherwise comparable conditions, the average rate (Rp) at different flashing conditions with the same / is related to the steady-state Rp)s as... 

As noted, both vapor and liquid products are withdrawn from the flash chamber of Fig. 5.3-3. This means that the flash conditions must lie between the dew point and the bubble point of the feed mixture and thel the conditions of the Gibbs phase rule must be met. 

Anthracene photodimers have been investigated extensively. A study of the photodissociation of the dimer of 9-methylanthracene, under both steady-state and flash conditions, suggests that the process occurs through an excited singlet... 

Brown and York [11] investigated many aspects of flashing phenomenon. He used Freon-11 and water as the working liquids. He measured droplet sizes at different flashing conditions, and predicted the following correlation for the droplet size with degree of superheat and Weber number. 

Fig. 1. EPR spectra of the iron-sulfur centers in thylakoids (left) and flash-induced absorption changes at 698 nm in PS 1-200 (right). Samples were preincubated with 50% (v/v) EG at 25 C (a), 58 C (b) and 70°C for 5 min. EPR experimental conditions temperature, 8K microwave frecjuency and power of 9.69 GHz and 100 mW, respectively gain 1.0 x 10 modulation amplitude, 20 G Scan width, 3,200-4,200 time constant, 320 mS reaction mixture, 0.1 M glycine-0.1 M amino methyl propanediol-NaOH (pH 10.0) 50 juM mehyi viologen, 50 pM DCPIP, 0.7% (w/v) sodium dithionite and thylakoids (2 mg chl/ml). Flash conditions temperature, 15 C reaction mixture, 10 pM DCPIP 1 mM sodium ascorbate, 100 mM sorbitol, 10 mm NaCI 50 mM Tricine-NaOH (pH 7.8) and PS 1-200.

Arc-extinguishing plastics are materials that give off a gas that has arc-extinguishing properties under flash conditions. 

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