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Although turbulent flow is generally needed for good suspension of photocatalysts, lower flow rates are preferred from an economic viewpoint for energy-efficient operation. However, no experimental work has been conducted to reveal how photocatalyst particles move and distribute in a tubular photocatalytic reactor under mild operating conditions, which is critical for reactor design and configuration of the light concentration. In our study, the photocatalyst itself was employed as a tracer particle for Particle Image Velocity (PIV) measurement. PIV combined with a new laser sheet image analysis (LSIA) technology was employed to investigate both the particle velocity and number distribution in the tubular reactor. It was found that, in the inlet, a higher velocity distribution of fluid generally occurred in the lower part of the tube. However, in the middle and outlet regions of the tube, a higher velocity distribution existed in the upper part of the tube. LSIA investigation showed that the transport capacity of the fluid and the initial particle size distribution are two essential factors influencing particle number distribution in the suspension. Regardless of the particle size, the middle part of the reactor holds the maximum number of particles while the outlet has the minimum number of particles. In the inlet, both small and large particles show similar number distribution trends against the flow rate. However, in the middle part of the tube, the number of small particles decreases with the flow rate while the number of the large particles shows the opposite trend. The difference in velocity distribution along the radial direction also significantly affects the particle distribution. One interesting finding is that, regardless of the particle size, the number of particles in the upper part of the tube is always higher than that in centre. Stokes’ drag law and the Saffman lift force were employed to explain this experimental finding. In the last section, the correlation between particle distribution and optical properties was numerically investigated by a modified differential approximation (MDA) method. [ABSTRACT FROM AUTHOR]

• The phase interface in the upstream horizontal section was reconstructed using ECVT. • Upstream interface drop and slugging are induced by the flow in the riser. • Lockhart-Martinelli model is found to be best and is used for improved correlation. • An improved void fraction prediction model is proposed for pipeline-riser systems. • This improved model leads to considerably reduced prediction errors. This paper introduces the application of void fraction prediction models (25 models total) from a simple horizontal pipe to a complex, real pipeline. The flow mechanism in the pipeline-riser system is explained based on the upstream phase interface and differential pressure in the downstream riser. The transition boundaries of "stratified to intermittent flow" and "stratified smooth to stratified wavy flow" in the horizontal section were predicted well by the models based on simple pipes. Electrical capacitance volume tomography was used to obtain the upstream void fraction just before the downstream gas-liquid eruption, α 1 , or during multiple cycles, α 2. The difference between α 1 and α 2 are ranging between −10 % and 5 %. Finally, an improved correlation is proposed based on the model found to be best (Lockhart and Martinelli, with error values (root mean square error (RMSE) and mean absolute percentage error (MAPE)) of about 12 % and 18 %); the corresponding error levels (RMSE and MAPE) amount roughly to 5 % and 10 %, respectively. The improved model also delivers a good prediction for α 1 when separating in two flow regimes. Overall, the finally proposed correlation reads and is found superior in terms of accuracy to all previously published correlations. [ABSTRACT FROM AUTHOR]

• SCW/CO 2 /N 2 mixture injection is proposed for heavy oil recovery. • A core experimental system of SCW/CO 2 /N 2 flooding is developed. • SCW/CO 2 /N 2 flooding is divided into three stages. • CO 2 and N 2 provide the driving force and eliminate gravity override. • SCW/CO 2 /N 2 flooding can both enhance oil recovery and upgrade oil quality. Exploitation of heavy oil is critical for mitigating the energy crisis. However, conventional thermal recovery methods cannot completely exploit the potential of heavy oil owing to its high viscosity and heavy distillates. A new technology is proposed with reference to CO 2 – and N 2 -assisted supercritical water (MGA-SCW) injection for heavy oil recovery. In this study, an experimental apparatus was developed to simulate the MGA-SCW flooding process and test its feasibility. MGA-SCW injection remarkably enhanced oil recovery, increased the oil production rate, and improved the oil quality. For MGA-SCW flooding at 25 MPa and 400 °C, the recovery factor approached 95 %, and the oil viscosity decreased by 32 %; the light distillate fraction (180–350 °C) increased from 11 to 15 %. The dynamic process of MGA-SCW flooding is divided into three stages: pressure difference, thermal, and miscible drives. This technology can be applied to the development and utilization of offshore heavy oil fields. [ABSTRACT FROM AUTHOR]

• The interface wave in the horizontal section before the riser was studied by an ECVT. • Flow regime transition boundaries shift to lower velocities due to the riser. • The period of hydraulic jump is consistent with that of severe slugging flow. • The hydraulic jump upstream is mainly caused by pressure fluctuations of the riser. This paper describes experiments conducted on the gas–liquid two-phase flow characteristics in a pipeline-riser system under 1 MPa. The hydraulic jump phenomenon (HJP) in the upstream horizontal section was quantitatively studied using electrical capacitance volume tomography (ECVT). Flow regime transition boundaries were shifted to lower gas and liquid velocities due to the impact of the riser at the end of the horizontal pipe. The HJP's period is consistent with that of severe slugging flow; additionally, the liquid slug production and the gas–liquid eruption stages always occur before the HJP in the upstream horizontal section. The Pearson correlation coefficient between the HJP upstream and the pressure fluctuations in the three main structures (horizontal, downward, and riser sections), the period consistency, and the sequential relationship between them were analyzed to verify that the pressure fluctuations in the downstream riser were the main cause of the HJP upstream. [ABSTRACT FROM AUTHOR]