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The vapour recirculation apparatus of Moodley [2002] was modified, reconstructed, and commissioned in order to be used in the acquisition of high-pressure vapour-liquid equilibrium (HPVLE) data at low temperatures. The original equipment of Moodley [2002] was modified with the aim of achieving the desired operating temperature range which the original equipment was unable to achieve. Major modifications were carried out on the cooling circuit allowing the equipment to reach temperatures as low as -30°C, a significant improvement to the original equipments minimum attainable temperature of -5°C. Modifications were also successfully carried out on the vapour recirculation pump of Moodley [2002], which failed when operated over extended periods at high pressures thus enabling the equipment to operate at pressures up to 10.0 bar, an improvement on the previous pressure operating limit of 6.9 bar. The operating limits of the equipment were tested through measurement of pure-component vapour-pressures of isopentane at temperatures between -14 and +27.9°C and pressures up to 10.1 bar and on propane at temperatures between -30.1 and +26.0°C and pressures up to 9.7 bar. The isopentane vapour-pressure measurements had an average deviation of ±0.49% when compared to literature data while the propane vapour-measurements had a maximum average deviation of ±0.35% when compared to literature data indicating that the equipment was capable of measuring accurate vapour-pressure data at temperatures down to -30°C and pressures up to 10.0 bar. The equipment was thereafter used in the acquisition of binary HPVLE data. Considerable time was spent developing and practicing the techniques used in the binary HPVLE measurements. Binary measurements were performed on the test system propane + 1- propanol at 19.9°C. To gain more confidence in the binary HPVLE measurements another test system, propane + isopentane was selected and binary HPVLE measurements were performed at 25°C and 0°C. The equipment was able to reproduce relatively accurate binary HPVLE results for the test systems at the selected isotherms. The equipment was thereafter used in the acquisition of a new set of binary HPVLE data for the propane + isopentane system at -10°C however owing to time constraints and chemical availability the acquisition of a complete set of data was not possible. The binary HPVLE data was thereafter regressed via the direct method. The Peng-Robinson (PR) equation of state (EOS) and the Soave-Redlich-Kwong (SRK) EOS were each coupled with the Mathias Copeman alpha function together with the Wong-Sandler mixing rule and the NRTL local composition model and applied to the binary systems at each of the isotherms investigated. Regressed data showed a relatively good agreement with measured experimental data for both binary systems investigated at all of the isotherms except the new -10°C isotherm of the propane + isopentane system. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2010.

Highway subsoils in cold countries are subject to increased thermal conductivity, disruption of natural moisture circulation as well as dynamic loading and application of de-icing chemicals in the winter months. In this work, the moisture mass transfer in a state of vapour flow and the de-icing chemical migration were considered during unidirectional freezing. The moisture mass transfer in a gaseous state was previously widely neglected in the exploration of frost heave. To conduct freeze-thaw cycles with increased lengths of soil samples and a modified slow freezing technique, an environmental chamber of nine samples capacity was designed. Supplying the non-saline samples with either 11 or 22 g/L sodium chloride solution signified chemical mass transport over the sample length and a significant change in temperature-moisture distribution when compared to deionised water supplied test results. The presented conceptual model with vapour mass transfer was based on the thermodynamic equilibrium of vapour density with temperature change and the phase transition to ice during thermal energy withdrawal. Compared to the widely used coupled heat-mass models, the vapour flow based model clearly explained the driving forces and presented a much easier algorithm for calculation. The de-icing chemical displacement was explained as the migration of the dissolved ions together with hygroscopic water transport, which in turn, was driven by cryosuction forces. The reduction of hydraulic conductivity during the secondary salinisation with sodium chloride was caused by chemical osmosis, which tended to equalise the solute concentration in pore water over the sample length. The research outcomes indicate a significant contribution to the future perspectives on frost heave modelling and prognosis. Further research could extend this work by inclusion of the vapour mass transfer in quantitative analysis for soil freezing. The effect of secondary salinisation should be also foreseen in the long term prognosis for highway subsoils exploitation.