Vapor density ratio

An alternative correlation in terms of flow quality x and liquid-to-vapor density ratio (p,/pg) is given by Steiner and Taborek [259] as follows ... 

Vapor density ratio is the measure of the relative density of the pure vapor or gas when compared to air for the purposes of fire protection applications. Technically it is the weight of the vapor per unit volume at any given temperature and pressure. Vapors with a vapor density ratio of greater than 1.0 are heavier than air and will follow the surface of the ground and may accumulate until they are dissipated by some means and are generally considered more of a hazard. Vapors with a vapor density less than 1.0 wiU rise into the atmosphere, the lower the density the faster they will rise, and are considered relatively less hazardous since they may dissipate and disperse... 

The preceding equations, which have assumed that both the air and the water vapor benave as ideal gases, are sufficiently accurate for most engineering calculations. If it is desired to remove the restriction that water vapor oehave as an ideal gas, the aclual density ratio should be used in place of the molecular-weight ratio in Eqs. (12-5) and (12-6). 

The trapping efficiency of polymeric, microporous adsorbents [e.g., polystyrene, polyurethane foam (PUF), Tenax] for compound vapors will be affected by compound vapor density (i. e., equilibrium vapor pressure). The free energy change required in the transition from the vapor state to the condensed state (e.g., on an adsorbent) is known as the adsorption potential (calories per mole), and this potential is proportional to the ratio of saturation to equilibrium vapor pressure. This means that changes in vapor density (equilibrium vapor pressure) for very volatile compounds, or for compounds that are gases under ambient conditions, can have a dramatic effect on the trapping efficiency for polymeric microporous adsorbents. 

Vapor density is the ratio of the density of any gas or vapor to the density of air, under the same conditions of temperature and pressure. It is a measure of how heavy the vapor is in relation to the same volume of air. Vapor density helps in estimating how long an agent will persist in valleys and depressions. The higher the vapor density, the longer the vapor will linger in low-lying areas. 

In desert areas of southern California fruit are often injured but leaves are seldom injured by sulfur dust. In coastal areas fruit burn is less marked but leaf burn may be acute. Where the air-vapor density is high, leaf temperatures in the sun may sometimes become higher than fruit temperatures. The leaf, a better absorber of radiation and a better radiator than the fruit, has a higher surface-mass ratio and appears to be very sensitive to the heat trap effect of high vapor density its temperature changes with great rapidity, but fruit temperature may lag until the danger period is passed (18). 

For the CHF condition for two-phase crossflow on the shell side of horizontal tube bundles, few investigations have been conducted. Katto et al. (1987) reported CHF data on a uniformly heated cylinder in a crossflow of saturated liquid over a wide range of vapor-to-liquid density ratios. Recently, Dykas and Jensen (1992) and Leroux and Jensen (1992) obtained the CHF condition on individual tubes in a 5 X 27 bundle with known mass flux and quality. At qualities greater than zero, they found that the CHF data are a complex function of mass flux, local quality, pressure level, and bundle geometry. 

Katto, Y., S. Yokoya, S. Miake, and M. Taniguchi, 1987, CHF on a Uniformly Heated Cylinder in a Crossflow of Saturated Liquid over a Very Wide Range of Vapor-to-Liquid Density Ratio, Int. J. Heat Mass Transfer 30.1971-1977. (5)... 

Vapor density The vapor density of a substance is defined as the ratio of the mass of vapor per unit volume. An equation for estimating vapor density is readily derived from a varied form of the ideal gas law ... 

The specific vapor density, Pv, is simply the ratio of the vapor density of the substance to that of air under the same pressure and temperature. According to Weast (1986), the vapor density of diy air at 20 °C and 760 mmHg is 1.204 g/L. At 25 °C, the vapor density of air decreases slightly to 1.184 g/L. Calculated specific vapor densities are reported relative to air (set equal to 1) oidy for compounds that are liquids at room temperature (i.e., 20-25 °C). 

Vapor Density (vap d). This value expresses the ratio of the density/of a vapor to the density of air. The vapors of most flammable liquids are heavier than air, thus they can readily flow into low areas, excavations and similar localities. Hence, ventilating outlets in a plant should be located near ground level. 

For ambient pressures suflBciently less than the critical pressure of the fuel, the droplet remains in the liquid phase throughout its lifetime. The large liquid-to-gas density ratio then implies that the liquid droplet possesses large thermal and mass inertia compared with the gas phase subsequently the gas-phase processes can be assumed to be quasi-steady. This assumption has been found to be very accurate even at moderate pressures (28), For near-critical or super-critical vaporization occurring typically in rocket motors and diesel engines, unsteady gas-phase analyses are required (29-34,85). 

For illustrative purposes, we exhibit temperature and vapor density profiles along the line connecting sphere centers for two water drops growing imder a supersaturation ratio of 1.05 at atmospheric pressure and 27°C ambient temperature these profiles are shown in Figures 1 and 2. Also in Figures 3 and 4, the profiles for a water drop and an inert sphere are shown. It may be of some interest to use the present generalized formalism to treat thermophoretic and diffusiophoretic forces between spheres. 

Figure 2. Vapor density vs. distance (Z) along line-of-centers for two water drops of equal radii (20 fi). Supersaturation ratio, 1.05 ambient temperature,...

The ratio of the pressures of the two gases at a given temperature will be inversely proportional to the ratio of the vapor densities at unit pressure, which in turn is proportional to the ratio of molecular weights. 

Souders and Brown introduced the relationship C%ax = KV JD / D — Dv), a modified kinetic energy ratio to correlate limiting entrainment rates for various systems. In this relationship V is the vapor velocity is the vapor density and Dj is the liquid density. 

Check design flexibility. The minimum vapor for no leakage through the tray is deflned by the vapor kinetic energy to liquid density ratio, E ... 

Figure 7-10. Plots of tray spacing, vs. ratio of surface tension to vapor density. By permission of Nutter Engineering.

CALCULATE THE RATIO OF SURFACE TENSION TO THE VAPOR DENSITY, X... 

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