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The density of the H2–CO2–CH4–CO–H2O system in the supercritical region of water is significant for analyzing the gasification process of organic substances in the supercritical water. We report density measurements of the quinary system by the isochoric method at 722–930 K and 15.4–30.3 MPa. The upper limit of the expanded uncertainty at 95% confidence for temperature is 0.2 K. The upper limits of the expanded relative uncertainties at 95% confidence for pressure and density are 0.0006 and 0.0125, respectively. The density data were compared with those predicted using the GERG-2008 equation of state. The absolute relative deviations between the calculated and experimental densities are not more than 1.79%. Furthermore, the excess volume of the quinary system decreases monotonically with the increase of temperature in the isochoric process at 722–930 K. The thermal expansion coefficients of the quinary system were also determined.

Modeling the pVT properties of hydrogen mixtures at high temperatures is significant for the development of relevant production and utility systems. In this work, pVT measurements are reported for the H2–CO2–CH4–CO–H2O system at 740–939 K and 18.1–34.7 MPa with an isochoric apparatus. The expanded relative uncertainty (k = 2) of density is less than 0.015. Based on the present and previous pVT data, a virial equation of state (EOS) has been developed at 720–939 K and up to 35 MPa for the quinary system with relative uncertainty (k = 2) at density less than 0.015. The thermal pressure coefficient of the quinary system was calculated from the virial EOS and the comparison with the experimental values indicated that changes in the specific volume and composition of the quinary system existed in each set of measurements. Isochoric heat capacity of the quinary system was also calculated and was compared with the GERG-2008 EOS. The calculated isochoric heat capacities agree with the GERG-2008 EOS within 1.75% above 873 K and up to 35 MPa, while at lower temperatures, the deviations become larger (up to 3.66%).

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The PVT properties of the (H2 + CO2) mixtures and the (H2 + CO2 + CH4) mixtures in the supercritical region of water are significant for making full use of the gas mixtures in the coal and supercritical water gasification. We report PVT measurements of the (0.6005 H2 + 0.3995 CO2), (0.6992 H2 + 0.3008 CO2), and (0.6026 H2 + 0.1948 CO2 + 0.2026 CH4) mixtures (all in mole fractions) at temperature 673 K and pressures of (0.5 to 25) MPa, measured by a modified Burnett method. The upper bounds of the expanded uncertainties at 95% confidence are 0.2 K for temperature, 0.015·p for pressure, and 0.008·ρ for density. The density data were compared with those predicted using the GERG-2008 equation of state. The deviations between the calculated and experimental data are not more than 0.021·ρ. Furthermore, the densities were found in accordance with the weighted average of the components’ existing equations of state using their mole fractions within 0.0076·ρ for all of the mixtures in this work. The second and third virial coefficients were determined at temperature 673 K for hydrogen and all of the mixtures investigated.

A tradeoff between high thermal conductivity and large thermal capacity for most organic phase change materials (PCMs) is of critical significance for the development of many thermal energy storage applications. Herein, unusual composite PCMs with simultaneously enhanced thermal conductivity and thermal capacity were prepared by loading expanded graphite (EG) after natural aging into the paraffin matrix via an integrated blending method for the first time. Of special interest is that the composite PCMs with an EG load as low as 4 wt % exhibited 642% thermal conductivity (4 wt % EG) and 5% (melting) or 7% (freezing) thermal capacity (1 wt % EG), larger than those of pure paraffin. The characterization results revealed that the short wormlike EG rods built a flexible framework in the paraffin matrix during blending, among which smaller exfoliated graphite flakes were cross-linked in space; thus, a highly effective thermal conductive pathway was constructed. Additionally, the alkylated EG surface after natural aging with high lipophilicity contributed to the good paraffin/EG interface compatibility because of similar chemical compositions and the same polarities of paraffin molecules and the EG surface and thus reduced the interface thermal resistance. Meanwhile, the least EG load in paraffin ensured the highest thermal storage density in the whole system. Under this premise, the increased paraffin crystallinity and the strong intermolecular interactions between paraffin and functionalized EG finally resulted in the enhancement of thermal capacity of the composite PCMs. This work provides a new strategy to prepare high-performance PCMs that are available in the real solar thermal storage applications.