Vapor flow volume

Compressors designed to oparata at vary low AT (3°C or lass) hava effi-ciencias that ara not economically attractive. Compressor afficiency tends to peak at AT s of 10 to 15°C. Often multipla-effact vapor comprassion systems ara economical because the vapor flow volume is reduced approximataly as the numbar of effects increases and the compressor AT is the sum of the AT s for all affects. Such applications may result in reduced investment as well as energy consumption. 

Example 7 Radiation in Gases Flue gas containing 6 percent carbon dioxide and 11 percent water vapor by volume (wet basis) flows through the convection bank of an oil tube stiU consisting of rows of 0.102-m (4-in) tubes on 0.203-m (8-in) centers, nine 7.62-m (25-ft) tubes in a row, the rows staggered to put the tubes on equilateral triangular centers. The flue gas enters at 871°C (1144 K, 1600°F) and leaves at 538°C (811 K, 1000°F). The oil flows in a countercurrent direction to the gas and rises from 316 to 427°C (600 to 800°F). Tube surface emissivity is 0.8. What is the average heat-input rate, due to gas radiation alone, per square meter of external tube area ... 

Vapor rate, ft /sec, or ft/sec Vapor flow, lb mol/hr Liquid rate, gpm Superficial gas velocity, ft/sec Molecular volume of gases, obtained by Kopp s Law of additive volumes, cc/gm mole at normal boiling point, see Table 9-44. 

Pressure drops from Dowtherm A heat transfer media flowing in pipes may be calculated from Figure 10-137. The effective lengths of fittings, etc., are shown in Chapter 2 of Volume 1. The vapor flow can be determined from the latent heat data and the condensate flow. With a liquid system, the liquid flow can be determined using the specific heat data. 

In Table 6.7, C is the Martinelli-Chisholm constant, / is the friction factor, /f is the friction factor based on local liquid flow rate, / is the friction factor based on total flow rate as a liquid, G is the mass velocity in the micro-channel, L is the length of micro-channel, P is the pressure, AP is the pressure drop, Ptp,a is the acceleration component of two-phase pressure drop, APtp f is the frictional component of two-phase pressure drop, v is the specific volume, JCe is the thermodynamic equilibrium quality, Xvt is the Martinelli parameter based on laminar liquid-turbulent vapor flow, Xvv is the Martinelli parameter based on laminar liquid-laminar vapor flow, a is the void fraction, ji is the viscosity, p is the density, is the two-phase frictional... 

In this table the parameters are defined as follows Bo is the boiling number, d i is the hydraulic diameter, / is the friction factor, h is the local heat transfer coefficient, k is the thermal conductivity, Nu is the Nusselt number, Pr is the Prandtl number, q is the heat flux, v is the specific volume, X is the Martinelli parameter, Xvt is the Martinelli parameter for laminar liquid-turbulent vapor flow, Xw is the Martinelli parameter for laminar liquid-laminar vapor flow, Xq is thermodynamic equilibrium quality, z is the streamwise coordinate, fi is the viscosity, p is the density, <7 is the surface tension the subscripts are L for saturated fluid, LG for property difference between saturated vapor and saturated liquid, G for saturated vapor, sp for singlephase, and tp for two-phase. 

Ge and Fan (2005) developed a 3-D numerical model based on the level-set method and finite-volume technique to simulate the saturated droplet impact on a superheated flat surface. A 2-D vapor-flow model was coupled with the heat-transfer model to account for the vapor-flow dynamics caused by the Leidenfrost evaporation. The droplet is assumed to be spherical before the collision and the liquid is assumed to be incompressible. 

The products leave the flame at the flame temperature, 7), and water vapor flows in from the water evaporated on the surface and water evaporated in the flame. The control volume excludes the water droplets in the flame which receive heat, q"w, from the flame control volume. As computed in Equation (9.88) for the fraction of water evaporated now in the flame,... 

Vapor-Liquid Gravity Separator Design Fundamentals The critical factors in the performance of a horizontal separator are the vapor residence time and the settling rate of the liquid droplets. However, two other factors enter into the design—the vapor velocity must be limited to avoid liquid entrainment, and there must be sufficient freeboard within the vessel to allow for a feed distributor. For vertical separators, the design is based on a vapor velocity that must be less than the settling velocity of the smallest droplet that is to be collected, with due allowance for turbulence and maldistribution of the feed. The vapor residence time is a function of the vapor flow rate (mass), vapor density, and volume of vapor space in the separator, based on the following ... 

The uncondensed vapors flowing from the tray below, plus the newly vaporized vapors from the reflux, flow to the tray above. The combined molecular weight of vapors is thus reduced. As the molecular weight decreases, the volume of each pound of vapor increases. 

If an increase in the tower-top reflux rate causes the top of the tower to flood, how should the operator respond She should then increase the pumparound flow to reduce the pounds of vapor flow to tray 5, in Fig. 12.4. But suppose this causes the pumparound trays 6, 7, and 8 to flood, because of the extra liquid flow She should increase the cold liquid flow through the pumparound heat exchanger. If this cannot be done, either, then the tower pressure can be increased. This will increase the density of the flowing vapors and shrink the volume of the vapors which the trays must handle. 

And when the volume of a vapor flowing through a tray increases, so does its velocity. Any increase in vapor velocity through a tray results in higher tray pressure drop. And what is it that causes trays to flood Why, it is high tray deck pressure drop. 

Another way to reduce the compressor discharge pressure is to render the refrigerant heavier, or less volatile. Adding isobutane to a propane refrigerant is one common example. Naturally, this will lower the suction pressure to the refrigerant compressor shown in Fig. 22.1, and increase the actual volume of vapor flow. If the compressor is speed-limited, this will not be practical. 

One of the easy and effective approaches for quantifying the polymer volume fraction within films in situ is to use in situ spectroscopic ellipsometry (SE) [49,118, 119, 144], The measurements should be performed in a thermostated cell (Fig. 7) with full control over the solvent vapor atmosphere p/po, where po is the solvent vapor pressure at saturation and p is the actual pressure, which can be adjusted by a combination of the saturated vapor flow and dry nitrogen flow [118, 119], or by the difference between the temperature 7j of the polymer sample and the temperature 72 of the solvent vapor [49, 114, 144],... 

To size control valves for vapors other than steam, use the relation C = W(v2/Ap)ns/63A, where W is vapor flow rate, in lb/h, v2 is specific volume of the vapor at the outlet pressure P2, in ft3/lb ... 

V Total vapor flow (mass or volume units as applicable) ... 

If represents the molar flow rate of component i in the vapor phase, L = L r, the total vapor flow rate, a the interfacial area per unit volume of froth. Ay the froth height, and Afj the active bubbling area, then the component material balance for the vapor phase may be written as... 

Vmax = maximum vapor velocity, ft/s VvEs = horizontal vessel volume, fF WL = liquid flow rate, Ib/h WV = vapor flow rate, Ib/h... 

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