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The present study examined the microstructure and mechanical properties of ceramic composites based on a kaolin from Djebel Debbagh, northeast Algeria, composed mainly of kaolinite and halloysite with the addition of various amounts of BaCO3. The composites were prepared by high-energy ball milling and sintered at 1100°C and 1200°C for 3 h. The samples sintered at 1200°C without BaCO3were composed mainly of mullite, which disappeared with increasing BaCO3content. X-ray diffraction investigation showed the presence of hexacelsian (BaAl2SiO6and BaAl2Si2O8), which disappeared at BaCO3contents >50 wt.% in favour of barium aluminium and barium silicate phases. At 40 wt.% BaCO3content, the porosity of the composites decreased from 0.7% to 0.1% and the microhardness increased from 7 to 8 GPa, respectively, at 1100°C and 1200°C due to the amorphous phase.

In this study, the two-phase pressure drop of R1234yf refrigerant (as an alternative to R134a) in a smooth horizontal tube is investigated. Tests are carried out and under several conditions of vapor quality (0% to 100%), mass velocity (200, 300 and 400 kg/m²s), heat flux (0, 7 and 14 kW/m²) and evaporation temperatures (20°C and 30°C). The internal diameters tested are 3.2 mm, 4.8 mm, 6.4 mm and 8.0 mm. A comparison of pressure drop between R1234yf and R134a is also carried out. The results demonstrate that the two-phase pressure gradient of R1234yf is approximately 20% lower than that of R134a. The experimental data is compared with 19 correlations from the literature. From this comparison, it is concluded that the experimental data are in accordance with the correlation proposed by Xu and Fang with a mean absolute error of 20% and with approximately 65% of the data predicted within a ± 30% error band.