Asymmetry of the vapor–liquid coexistence curve: The asymptotic behavior of the "diameter"

Abstract

We analyze, without resort to any model field-mixing scheme, the leading temperature-dependent term in the 'diameter' of the coexistence curve asymptotically close to the vapor-liquid critical point. For this purpose, we use a simple non-parametric equation of state which we develop by meeting several general requirements. Namely, we require that the desired equation (1) lead to correct asymptotic behavior for a limited number of the fluid's parameters along selected thermodynamic paths, (2) reveal a Van der Waals loop below the critical point, and (3) be consistent with a rigorous definition of the isothermal compressibility in the critical region. For the temperature interval in question, the proposed equation approximates experimental data with an accuracy comparable to those given by Schofield's parametric equation and by other authors' equations. The desired term is obtained by applying the Maxwell rule to the equation and can be represented as D 2β |τ | 2β , where |τ | = |T − Tc|/Tc and β is the critical exponent for the order parameter. The amplitude D 2β is determined explicitly for the volume-temperature and entropy-temperature planes.

Crossover parametric equation of state for asymmetric fluids

“…In addition, the temperature behaviour of the coexistence diameter predicted by mentioned equation of state was studied. In summary, the deviation obtained using ECPM is smaller than that given by the equation proposed by Sushko et al [13] in a wider region, it should be mentioned that they have used a different source of data.…”

“…Recently, Sushko et al [13] studied the temperature behaviour of the coexistence curve diameter within a mixing-model-free approach. By using the amplitudes reported in Ref.…”

“…By using the amplitudes reported in Ref. [13] 6 the diameter d v = (V l +V g )/2V c , whereV l ,V g andV c are liquid, gas and critical molar volume respectively was calculated by the Sushko approach and its deviation with the NIST data was compared with the deviation of d v obtained from our extended crossover parametric equation of state in the same region and the same source of correlated data (The NIST data). The results are presented in Fig.…”

“…We have applied this equation to CO 2 and N 2 fluids. Also, we have investigated the temperature behaviour of the coexistence diameter predicted by the extended parametric equation of state and comparison has been made with a recent work for N 2 [13].…”

Experimental observation of triple correlations in fluids

“…As one of the ways for evaluating c ′ in the fluctuation region, we can use the asymptotic equation of state [29] π(τ, ω) = Mτ + 1 2Γ 0…”