Calorimetric heats of mixing per mole, ΔH_x^M, and a solid-liquid phase diagram were obtained for the system water--p-dioxane at 25°C over the entire range of composition. From these data are derived values for the partial molar heat contents, activities and free energies and entropies of mixing. The excess free energy-composition curve, which is roughly parabolic in shape, gives little indication of the extent of interaction in this system. The ΔH_x^M values, however, range from 115 cal./mole endothermic to 142 cal./mole exothermic. A sharp exothermic dip occurs at a mole fraction of 0.143, which corresponds to a ratio of 6.00 water molecules to each dioxane molecule. Minimum values for the freezing points and entropies of mixing also occur at approximately this same composition. Possible short range structures that could contribute to the properties of this system are discussed. ΔH_x^M data were determined calorimetrically for the ternary and the three binary systems that can be formed from carbon tetrachloride (1), cyclohexane (2), and benzene (3). The following analytical equations, in which x_i is the mole fraction of component i, summarize these data: ΔH_12^M = x_1x_2 [ 160.8 / 18.9 (x_1 - x_2) - 20.2(x_1 - x_2)^2 ] 15,25,and 35°c ΔH_13^M = x_1x_3 [ 103.2 / 11.0 (x_1 - x_3) - 13.3(x_1 - x_3)^2 ] 25°C ΔH_13^M = x_1x_3 [ 96 / 4.17 (x_1 - x_3) - 13.19 (x_1 - x_3)^2 ] 10°C ΔH_23^M = x_2x_3 [ 3105 - 7.980 T - (1303-4.370 T) (x_2 - x_3) / (1738 - 5.486 T) (x_2 - x_3)^2 ] 15,25,and 35°C ΔH_123^M = x_1x_2 [ 160.8 / 18.9 (x_1 - x_2) - 20.2 (x_1 - x_2)^2 ] / x_1x_3 [ 103.2 / 11.0 (x_1 - x_3) - 13.3 (x_1 - x_3)^2 ] / x_2x_3 [ 726.0 / 102.4 (x_2 - x_3)^2 ] 25°C Solid-liquid phase equilibria data were also obtained for these systems. This information for the system cyclohexane-benzene, together with the thermal data, made possible the calculation of the partial molar heat contents, L_i, and the excess free energies, ΔF_x^E, and entropies, ΔS_x^E, of mixing per mole as functions of composition. These data are summarized by the following expressions: L_2 = x_3^2 [ (6146 - 17.836T) - (19116-61.368T) x_2 / (20856-65.832T) x_2^2 ] L_3 = x_2^2 [ (3540-9,096T) - (8692-26.408T) x_3 / (20856-65.832T) x_3^2 ] ΔF_x^E = x_2x_3 [ 310.6 / 2.33 (x_2 - x_3) / 40.0 (x_2 - x_3)^2 / 130.8 (x_2 - x_3)^3 ] 25°C TΔS_x^E = x_2x_3 [ 415.4 - 2.33 (x_2 - x_3) / 62.4 (x_2 - x_3)^2 - 130.8 (x_2 - x_3)^3 ] 25°C The system carbon tetrachloride-benzene proved to be especially interesting in that the phase diagram of this "near-to-ideal" system reveals a complex of approximately one benzene molecule to one carbon tetrachloride molecule composition. It is suggested that TT bonding between the electron cloud of the aromatic ring and the empty 3-d shell of chlorine may be responsible for the formation of the compound. Replacing benzene with p-xylene to increase the electron density of the ring enhanced the formation of the complex. On the other hand, either decreasing the electron density of the ring by using nitrobenzene, or decreasing the electronegativity of the chlorine atoms by substituting CHCl_3 for CCl_4 prevented complex formation. The results of this study of carbon tetrachloride-cyclohexane-benzene mixtures seem to indicate that the system carbon tetrachloride-cyclohexane is very nearly ideal, the system carbon tetrachloride-benzene is much more complex than was previously considered, and the high entropy in the system cyolohexane-benzene is probably due partially to volume change on mixing and partially to lack of randomness in the pure benzene.

The effect of the fusion welding process upon the metals being welded is a matter of great interest and has been the subject of much investigation, both theoretical and experimental. The properties of metals are determined by the structure of their crystals (within limits for any given metal), and the crystalline structure is determined by heating and cooling rates. Thus the knowledge of temperatures, and heating and cooling rates, becomes the key to understanding these effects of heating. Since the greatest part of fusion welding is done using a gas torch or an electric arc, the necessary theoretical study is that of a heat source moving across the material. This problem has been invest!- gated and solved analytically for simple conditions and simple shapes, generally greatly idealized. The purpose of this study is to develop an approximate method of predicting temperatures due to a moving heat source in bodies of more complex geometry, with conditions more nearly approaching the actual.

Many thermodynamic properties of materials can be attributed to phonons and their interactions, also known as the Taylor series of the Born-Oppenheimer (BO) energy surface. In this the- sis, we present several novel approaches to computing phonons and their interactions, as well as implementations to predict thermodynamic properties of materials from phonons and phonon interactions. First, we implemented the symmetry analysis technique that allows us to write the Taylor series of the BO energy surface for a material at arbitrary order N using the space group irreducible derivatives, guaranteeing the symmetry of the crystal by construction. Second, we derived the minimum supercell multiplicity equation with which we can compute the smallest possible supercells that can accommodate N given wave vectors, greatly improving the computational efficiency for finite displacements calculations. Third, we implemented 2 branches of finite displacements methodologies, lone irreducible derivatives (LID) and bundled irreducible derivatives (BID), with the former sacrificing efficiency for accuracy and the latter emphasizing on using the least amount of calculations to extract all irreducible derivatives. Additionally, we implemented algorithms to predict materials properties including Grüneisen parameters, phonon linewidth, phonon frequency shift and thermal conductivity using our space group irreducible derivatives. We applied our methods on a wide range of materials, and the comparison against literature demonstrated massive gain on efficiency while maintaining high quality results.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. / The properties-of systems which undergo a metal-insulator (MI) transition are currently being extensively studied. Both the transport and thermodynamic properties of these MI systems show interesting behaviour, particularly near the MI transition. A complete theory to describe MI systems does not yet exist. In the present work the focus is on the thermodynamic properties of MI systems, in particular on the specific heat and susceptibility. The thermodynamic properties in the absence of a magnetic field are now well understood, with models such as the two-fluid model giving a good account of the behaviour. In finite magnetic fields the thermodynamic properties are even more interesting and varied. It is the aim of the present work to develop and test models to explain the effects of applying magnetic fields to MI systems. The focus is mainly on phosphorous doped silicon, and the results are gratifying. The theory should, however, also apply to other similar MI systems. / Andrew Chakane 2018

The goal of this study is to assess the potential of the Stirling engine in alternative energy applications including combined cooling, heating, and power (CCHP) and novel waste heat recovery (WHR) technologies. A first and second law model is developed to quantify Stirling engine performance and realize the crucial parameters in Stirling engine design. In addition, analysis of systems employing the Stirling engine as a prime mover can help justify particular design interests for the engine regarding certain applications. A model of a CCHP system is developed with a Stirling engine prime mover. Sensitivity analysis is performed on the CCHP system to gain a deeper understanding of how each component affects the overall performance of the CCHP system. The main objective of these analyses is to provide information on the feasibility of Stirling CCHP on the basis of primary energy consumption and cost. Finally, the potential of the Stirling engine as a waste heat recovery device is investigated. A thermodynamic model is developed to provide estimates of Stirling engine performance based on an available waste heat stream from any specific heat source, while suggesting practical design constraints on the engine based on bounds from the second law. These results are provided to strengthen the feasibility of the Stirling engine as a bottoming prime mover rather than the central power plant.

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