Taylor flow is a strategy-aimed flow to transfer conventional single-phase into a more efficient two-phase flow resulting in an enhanced momentum/heat/mass transfer rate, as well as a multitude of other advantages. To date, Taylor flow has focused on the processes involving gas–liquid and liquid–liquid two-phase systems in microchannels over a wide range of applications in biomedical, pharmaceutical, industrial, and commercial sectors. Appropriately micro-structured design is, therefore, a key consideration for equipment dealing with transport phenomena. This review paper highlights the hydrodynamic aspects of gas–liquid and liquid–liquid two-phase flows in microchannels. It covers state-of-the-art experimental and numerical methods in the literature for analyzing and simulating slug flows in circular and non-circular microchannels. The review’s main objective is to identify the considerable opportunity for further development of microflows and provide suggestions for researchers in the field. Available correlations proposed for the transition of flow patterns are presented. A review of the literature of flow regime, slug length, and pressure drop is also carried out.

Climate change is one of the biggest environmental, political, economic, technological, and social challenges of the 21st century. Due to ever-increasing fossil fuels costs. The world energy system should be transitioned to renewable energy sources to mitigate greenhouse gas emissions. Solar energy is one of the suitable alternatives to fossil fuel usage. Currently, the most widely available solar technologies are solar photovoltaic (PV) and solar thermal. The integration of these two techniques enables the exploitation of the most significant amount of solar radiation. This combination has led to a hybrid photovoltaic/thermal system (PV/T). Concentrated solar radiation on PV cells, known as concentrated photovoltaic (CPV), effectively decreases PV receivers’ area and harnesses the same quantity of solar radiation. However, the main problem with CPV is the elevated PV surface temperature, which often requires active cooling. This issue can be solved by introducing a Concentrating Photovoltaic Thermal (CPVT) system. In this article, a new CPVT hybrid system based on Point Focus Fresnel Lens (PFFL) and embedded Multi Junction Photovoltaic (MJPV) (GaInP/InGaAs/Ge) cells has been experimentally investigated and numerically modelled under indoor conditions. Experiments and simulations were carried out at different heat transfer fluid (HTF) flow rates and under constant irradiation emitted from a sun simulator. The results indicate that the thermal and electrical performance of the CPVT system improves under the testing conditions, where the total efficiency was 68.7% and 73.5% for the experimental and CFD models, respectively. At the same time, the highest thermal efficiency of the experimental and CFD models was 49.5% and 55.4%, respectively. In contrast, the highest electrical efficiency was 36.5% and 37.1%. Therefore, the CPVT system has an excellent possibility of being competitive with conventional power generation systems.

This study experimentally and numerically investigates the hydrodynamic characteristics and heat transfer of developing and fully developed laminar liquid–liquid Taylor flows. The problem is conducted in circular mini-channels with different diameters subjected to a constant wall temperature boundary condition. An experimental setup is designed employing an open-loop water/oil two-phase nonboiling flow at mini-scale tubing sizes of 1.42, 1.52, and 1.65 mm. Two silicone oils with the dynamic viscosities of 1 and 5 cSt at several volumetric flow rates are used to establish segmented flow. The impacts of the channel diameter, viscosity, and flow rate ratio on the flow pattern, pressure drop, film thickness, and heat transfer rate are discussed. In good agreement with the literature, it is found that the pressure drop generated by the interface increases the total pressure loss by up to 200% compared to the single-phase flow. The results also explain how recirculating regions within the slugs influence the film region and the physics of backflow. Furthermore, introducing segmented water slugs significantly enhances the heat transfer rate as the dimensionless thermal length decreases. A significant relation between the recirculating regions and heat transfer has been demonstrated for the first time.

Flow drag reduction induced by chemical additives, more commonly called drag-reducing agents (DRAs), has been studied for many years, but few studies can manifest the mechanism of this phenomenon. In this paper, a new mathematical model is proposed to predict the upper limit of drag reduction with polymer DRAs in a turbulent pipe flow. The model is based on the classic finitely extensible nonlinear elastic-Peterlin (FENE-P) theory, with the assumption that all vortex structures disappear in the turbulent flow, i.e., complete laminarization is achieved. With this model, the maximum drag reduction by a DRA at a given concentration can be predicted directly with several parameters, i.e., bulk velocity of the fluid, pipe size, and relaxation time of the DRA. Besides, this model indicates that both viscosity and elasticity contribute to the drag reduction: before a critical concentration, both viscosity and elasticity affect the drag reduction positively; after this critical concentration, elasticity still works as before but viscosity affects drag reduction negatively. This study also proposes a correlation format between drag reduction measured in a rheometer and that estimated in a pipeline. This provides a convenient way of pipeline drag reduction estimation with viscosity and modulus of the fluids that can be easily measured in a rheometer.

In this paper, the ice load accumulated on a vertical plate of marine platforms during periodic spray icing in a cold room was investigated experimentally. The mass and thickness of ice formation on the plate along with several parameters such as relative humidity, the front and back surface temperatures of the vertical plate, initial temperature of water, and the spray mass flux impinging on the plate were measured and discussed. Analysis of variance (ANOVA), which is a statistical data analysis method, was utilized to interpret the contribution of the investigated parameters during the icing experiments, comparing the effect of each parameter and their interactions on the quantity of ice accumulated on the vertical plate. The primary analysis of the empirical results illustrates that the ambient temperature, airflow velocity, the distance between the fan and the plate, salinity and the timing of spray events have influences in the icing intensity and the amount of ice formation on the vertical plate. The errors between the average ice thicknesses obtained from two different experimental approaches were from 5 to 20%. For the saline ice formation, the temperature difference between the front and back of the vertical plate was greater than that of the pure ice formed during the spray icing event. The primary experimental results alongside the ANOVA analysis verified that airflow velocity is the most effective parameter, with a high level of interaction for time and temperature.

This paper describes a numerical simulation of the interaction of a single nonlinear wave with a solid vertical surface in three dimensions. A coupled volume of fluid (VOF) and level set method (LSM) is used to simulate the wave-body interaction. A Cartesian-grid method is used to model immersed solid boundaries with constant grid spacing for simplicity and lower storage requirements. Mesh refinement is implemented near the wall boundaries due to the complex behavior of the free surface around the body. The behavior of the wave impact, the water sheet, and the high-speed jet arising from the wave impact are all captured with these methods. The numerical scheme is implemented using parallel computing due to the high central processing unit and memory requirements of this simulation. The maximum wave run-up velocity, instant wave run-up velocity in front of the vertical surface, the sheet break-up length, and the maximum impact pressure are computed for several input wave characteristics. Results are compared with a laboratory experiment that was carried out in a tow tank in which several generated waves were impacted with a fixed flat-shaped plate model. The numerical and experimental data on sheet breakup length are further compared with an analytical linear stability model for a viscous liquid sheet, and good agreement is achieved. The comparison between the numerical model and the experimental measurements of pressure, the wave run-up velocity, and the break-up length in front of the plate model shows good agreement.