Critical points, boiling

Triple point Critical point Boiling point... 

In these equations, the subscripts c, b, and/indicate the critical point, boiling point, and freezing point, respectively the A terms are the contributions of the group to each of the specifieAproperties given in the following table and v, is the number of functional groups of type i in the molecule. 

At low temperatures, using the original function/(T ) could lead to greater error. In Tables 4.11 and 4.12, the results obtained by the Soave method are compared with fitted curves published by the DIPPR for hexane and hexadecane. Note that the differences are less than 5% between the normal boiling point and the critical point but that they are greater at low temperature. The original form of the Soave equation should be used with caution when the vapor pressure of the components is less than 0.1 bar. In these conditions, it leads to underestimating the values for equilibrium coefficients for these components. 

W is simply the amount adsorbed expressed as a liquid volume, and is given by IF = /p where p is the density of the adsorbate in the micropores. At temperatures wdl below the critical point—near the boiling point of the adsorptive, for example—p may be taken as equal to the ordinary density Pi of the bulk liquid adsorptive. 

Properties of Light and Heavy Hydrogen. Vapor pressures from the triple point to the critical point for hydrogen, deuterium, tritium, and the various diatomic combinations are Hsted in Table 1 (15). Data are presented for the equiUbrium and normal states. The equiUbrium state for these substances is the low temperature ortho—para composition existing at 20.39 K, the normal boiling point of normal hydrogen. The normal state is the high (above 200 K) temperature ortho—para composition, which remains essentially constant. 

The Antoine equation does not fit data accurately much above the normal boiling point. Thus, as regression by computer is now standard, more accurate expressions applicable to the critical point have become usable. The entire DIPPR Compilation" is regressed with the modified RiedeP equation (2-28) with constants available for over 1500 compounds. 

The Kellogg and DePriester charts and their subsequent extensions and generahzations use the molar average boiling points of the liquid and vapor phases to represent the composition effect. An alternative measure of composition is the convergence pressure of the system, which is defined as that pressure at which the Kvalues for aU the components in an isothermal mixture converge to unity. It is analogous to the critical point for a pure component in the sense that the two... 

Physical characteristics Molecular weight Vapour density Specific gravity Melting point Boiling point Solubility/miscibility with water Viscosity Particle size size distribution Eoaming/emulsification characteristics Critical temperature/pressure Expansion coefficient Surface tension Joule-Thompson effect Caking properties... 

Gases and Vapors Hydrocarbons Reference Symbols i Chemical Formula Mol. Wt. 1r> 1/7 I a Mol. Wt. Critical Conditions Boiling Point (F) 14,7 Psia Specific Volume Cu ft/lb 14.7 Psia 81 60F (Z Facior Accounted For) Latent Heat of Vaporization (Btu/lb 14.7 Psia) Specific heat Constant Pressure (Cp 60F) Specific heat Constant Volume Specific heat ratio K = Cp/Cv... 

Tb P boiling point temperature a p = lbar, Tm melting temperature at p = lbar, Tti(pti) triple point temperature (pressure), Tct(pCT) critical point temperature (pressure), T p inversion temperature (pressure) L latent heat of vaporization at Tb. 

Table 9.1. Physical properties of hydrogen, methane, and n-heptane at the triple point, the boiling point and the critical point, and under standard conditions...

Supercritical fluids represent a different type of alternative solvent to the others discussed in this book since they are not in the liquid state. A SCF is defined as a substance above its critical temperature (Tc) and pressure (Pc)1, but below the pressure required for condensation to a solid, see Figure 6.1 [1], The last requirement is often omitted since the pressure needed for condensation to occur is usually unpractically high. The critical point represents the highest temperature and pressure at which the substance can exist as a vapour and liquid in equilibrium. Hence, in a closed system, as the boiling point curve is ascended, increasing both temperature and pressure, the liquid becomes less dense due to thermal expansion and the gas becomes denser as the pressure rises. The densities of both phases thus converge until they become identical at the critical point. At this point, the two phases become indistinguishable and a SCF is obtained. 

In this article, we suggest that a modified superheated-liquid model could explain many facts, but the basic premise of the model has never been established in clearly delineated experiments. The simple superheated-liquid model, developed for LNG and water explosions (see Section III), assumes the cold liquid is prevented from boiling on the hot liquid surface and may heat to its limit-of-superheat temperature. At this temperature, homogeneous nucleation results with significant local vaporization in a few microseconds. Such a mechanism has been rejected for molten metal-water interactions since the temperatures of most molten metals studied are above the critical point of water. In such cases, it would be expected that a steam film would encapsulate the water to... 

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