Isobaric Critical Exponents: Test of Analyticity Against NIST Reference Data

초록

Finite systems may undergo first or second order phase transitions under not isovolumetric but isobaric condition. The "analyticity" of a finite-system partition function has been argued to imply universal values for isobaric critical exponents, alpha(P), beta(P), and gamma(P). Here we test this prediction by analyzing NIST REFPROP data for twenty major molecules, including H2O, CO2, O-2, etc. We report they are consistent with the prediction for temperature range, 10(-5) < vertical bar T/T-c-1 vertical bar < 10(-3). For each molecule, there appears to exist a characteristic natural number, n = 2, 3, 4, 5, 6, which determines all the critical exponents for T < T-c as alpha(P) = gamma(P) = n/n+1 and beta(P) = delta(-1) = 1/n+1. For the opposite T > T-c, all the fluids seem to indicate the universal value of n = 2.

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