Pseudocritical temperature

The pseudocritical temperature of a mixture is obtained by weighting the pseudocritical temperatures and volumes for each component ... 

Chueh s method gives consistently good results for mixtures except in the immediate vicinity of the critical region (T/TCml > 0.93). For the critical region, his procedure was modified by using true critical constants, rather than pseudocritical constants in Eq. (56). For this purpose, he has established a separate correlation of true critical volumes and temperatures (C3). 

For mixtures, a pseudocritical temperature would be used and estimated as the mole fraction average of the critical temperatures of the pure components. 

The Law of Corresponding States has been extended to cover mixtures of gases which are closely related. As was brought out in Chapter 2, obtaining the critical point for multicomponent mixtures is somewhat difficult therefore, pseudocritical temperature and pseudocritical pressure have been invented. 

EXAMPLE 3-8 Calculate the pseudocritical temperature and pseudocritical pressure of the gas given in Example 3-5. Use the critical constants given in Appendix A. 

We will see in Chapter 10 that the composition of a petroleum fluid is often given with all components heavier than hexane lumped together as heptanes plus. Pseudocritical pressures and pseudocritical temperatures for heptanes plus for use in Equations 3-42 can be obtained from Figure 3-10.7... 

Determine values of pseudocritical temperature and pseudocritical pressure for the gas given below. 

Values of pseudocritical temperature and pseudocritical pressure are required in the use of Figure 6-4. Methods presented in Chapter 3, including adjustments for carbon dioxide and hydrogen sulfide, can be used to estimate these properties. 

The above trend is valid for members of a homologous series. For components which are not members of a homologous series, the reverse trend may occur over a limited temperature range, causing relative volatility to increase as the equilibrium temperature is raised [Eq. (1.12)]. However, as temperature is raised further and approaches the critical point, relative volatility eventually diminishes and will reach unity at the pseudocritical point of the mixture. 

The effect of temperature (or pressure 1 on relative volatility is further illustrated in Fig. 1.2b (29). The diagram clearly shows a reduction in relative volatility as pressure is raised and illustrates that relative volatility approaches unify as the pseudocritical point of the mixture is approached. 

The heat transfer to supercritical carbon dioxide was measured in horizontal, vertical and inclined tubes at constant wall temperature for turbulent flow at Re-numbers between 2300 and lxl 05. The influence of the variation of physical properties due to the vicinity of the critical point was examined, as well as the influence of the direction of flow. Therefore most of the measurements were conducted at pseudocritical points. At those supercritical points the behaviour of the physical properties is similar to the behaviour at the critical point, but to a lesser degree. At such points the heat capacity shows a maximum density, viscosity and heat conductivity are changing very fast. [1]... 

Because of the strong variations of the heat capacity and therefore of the local heat transfer coefficient at a pseudocritical point, the LMTD (logarithmic mean temperature difference) cannot be used for the evaluation of all of our measurements. 

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