Reconstruction of the Long-Term Dynamics of Particulate Concentrations and Solid–Liquid Distribution of Radiocesium in Three Severely Contaminated Water Bodies of the Chernobyl Exclusion Zone Based on Current Depth Distribution in Bottom Sediments

Given the importance of understanding long-term dynamics of radionuclides in the environment in general, and major gaps in the knowledge of 137Cs particulate forms in Chernobyl exclusion zone water bodies, three heavily contaminated water bodies (Lakes Glubokoe, Azbuchin, and Chernobyl NPP Cooling Pond) were studied to reconstruct time changes in particulate concentrations of 137Cs and its apparent distribution coefficient Kd, based on 137Cs depth distributions in bottom sediments. Bottom sediment cores collected from deep-water sites of the above water bodies were sliced into 2 cm layers to obtain 137Cs vertical profile. Assuming negligible sediment mixing and allowing for 137Cs strong binding to sediment, each layer of the core was attributed to a specific year of profile formation. Using this method, temporal trends for particulate 137Cs concentrations in the studied water bodies were derived for the first time and they were generally consistent with the semiempirical diffusional model. Based on the back-calculated particulate 137Cs concentrations, and the available long-term monitoring data for dissolved 137Cs, the dynamics of 137Cs solid–liquid distribution were reconstructed. Importantly, just a single sediment core collected from a lake or pond many years after a nuclear accident seems to be sufficient to retrieve long-term dynamics of contamination.

Multiphase Flow in Circular and Triangular Pipes: Examining Flow Characteristics, Sand Erosion and Heat Transfer Via CFD and Experimental Work

Air-water two-phase flow in circular pipes has been studied by many investigators. However, investigations of multiphase flow in non-circular pipes are still very rare. Triangular pipes have found a number of applications, such as multiphase flow conditioning, erosion mitigation in elbows, compact heat exchanges, solar heat collectors, and electronic cooling systems. This work presents a survey of air-water and air-water-sand flow through circular and triangular pipes. The main objective of this investigation is to study the potential effects of triangular pipe geometry on flow patterns, slug frequency, sand erosion in elbows, and heat transfer in multiphase flow. Firstly, twenty-three experiments were performed for horizontal air-water flow. Detailed videos and slug frequency measurements were collected through circular and triangular clear pipes to identify flow patterns and create a database for these pipe configurations. The effect of corners of the triangular pipe on the liquid distribution was investigated using two different orientations of triangular pipe: apex upward and downward and results of triangular pipes were compared to round tubes. Secondly, ultrasonic wall thickness erosion measurements, paint removal studies, and CFD simulations were carried out to investigate the erosion patterns and magnitudes for liquid-sand and liquid-gas-sand flows in circular and triangular elbows with the same radius of curvature and cross-sectional area. Thirdly, heat transfer rates for liquid flows were also simulated for both circular and triangular pipe cross-sections. Although similar flow patterns are observed in circular and triangular pipe configurations, the orientation of the triangular pipes seems to have an effect on the liquid distribution and slug frequency. For higher liquid rates, slug frequencies are consistently lower in the triangular pipe as compared to the circular pipe. Similarly, the triangular elbow offers better flow behavior as compared to circular elbows when investigated numerically with similar flow rates for erosion patterns for both liquid-sand flow and liquid-gas-sand flows. Experimental and CFD results show that erosion in the circular elbow is about three times larger than in the triangular elbow. Paint studies results validated erosion patterns and their relations with particle impacts. Finally, heat transfer to/from triangular pipes is shown to be more efficient than in circular pipes, making them attractive for compact heat exchangers and heat collectors. This paper represents a novel experimental work and CFD simulations to examine the effects of pipe geometries on multiphase flow in pipes with several practical applications. The present results will help to determine the efficiency of utilizing triangular pipes as compared to circular pipes for several important applications and field operations such as reducing slug frequencies of multiphase flow in pipes, and reducing solid particle erosion of elbows, and also increasing the efficiency of heat exchangers.

The effect of microtexture on the liquid flow over the sheets

This work considers the method of the corrugated sheet arrangement near the column wall with the aim to limit liquid fall on the wall and increase liquid concentration in the near-wall area. Experiments were carried out at the corrugated Koch 1Y packing sheets for various liquid flow rates. This report presents experimental results on the character of liquid flow near the edge of corrugated sheets and the effect of the middle sheet shift from the edge of the packing. The ribs of this sheet are directed downward to the edge of the packing. Test was performed for two positions of the middle sheet: to study the effect of microtexture orientation at the sheet, whose ribs are directed downward to the packing edge, on liquid distribution under the packing. Experiments were carried out for liquid flow rates of 1-12 ml/s.

Experiments on the dynamic wetting of growing icicles

The distinctive shape of an icicle is the outcome of a highly non-equilibrium process involving heat and mass transport in the presence of fluid flowing over an evolving topography. It has previously been shown that the ripple patterns with a near universal wavelength that are observed on many icicles are correlated with small levels of impurities in the feed water. Models of icicle shape evolution, and of the origin of the ripple pattern, require a detailed understanding of how liquid water flows over a growing icicle. The impurity effect is not accounted for by any existing model of ripple formation. Here, we explore this flow dynamics using laboratory-grown icicles with a fluorescent dye as an impurity. Contrary to previous models, we find that the ice is incompletely wetted by the liquid phase, and that the whole process is much more stochastic than has been previously assumed. In addition, the presence of impurities modifies the wetting properties of the ice surface, while the emerging topography interacts with the liquid distribution. There is evidence for mixed-phase ice. These observations must inform any successful model of an impurity-driven rippling instability. Our results have general implications for the morphological evolution of many natural, gravity-driven, wet ice growth processes.

Investigation of Huge Wave in Gas-Liquid Two-Phase Churn Flow

Churn flow frequently occurs in power plants, chemical engineering, petroleum, and other industrial applications. Due to its chaotic nature, churn flow has a significant influence on safety and management control. As one of the essential characteristics of churn flow, depth knowledge of the huge wave is crucial for a better understanding churn flow. However, relevant studies on these issues are still in shortage because it is difficult to capture its behaviours experimentally. In this study, we employed the high-speed camera to capture the evolution and properties of huge waves under churn flow conditions in a vertical pipe. The inner diameter of the pipe is 19 mm. Based on the observation, the flooding of the falling film in churn flow is demonstrated to be the slug/churn transition mechanism. Additionally, the liquid distribution in the cross-section of the tube is provided and discussed in detail. Compared with the existing experiment data, we carefully analyze the properties of huge waves, such as frequency and amplitude.

Bed structure and its impact on liquid distribution in a trickle bed reactor

The work reported in this investigation involves the determination of the hydrodynamic properties of the Trickle Bed Reactor which has been loaded in various ways to mark the effect of the loading methodologies employed to pack the catalyst pellets. The bed structure of a packed three-phase reactor is critical to study as it provides the essential contact between the phases and provides the catalytic sites where the reaction takes place. Depending on the structural properties of the bed such as local void structure, liquid distribution, two-phase pressure drop, and holdup of fluids gets affected. The study aims to envelop the catalyst bed characteristics such as the local void structure, the length of the catalyst bed, flow characteristics such as liquid and gas flow rate, and liquid distributor at the top of the catalyst bed to gauge and quantify their effect on the hydrodynamics of a trickle bed reactor.

Reactor Selection for Upgrading Hemicelluloses: Conventional and Miniaturised Reactors for Hydrogenations

This work presents an advanced reactor selection strategy that combines elements of a knowledge-based expert system to reduce the number of feasible reactor configurations with elaborated and automatised process simulations to identify reactor performance parameters. Special focus was given to identify optimal catalyst loadings and favourable conditions for each configuration to enable a fair comparison. The workflow was exemplarily illustrated for the Ru/C-catalysed hydrogenation of arabinose and galactose to the corresponding sugar alcohols. The simulations were performed by using pseudo-2D reactor models implemented in Aspen Custom Modeler® and automatised by using the MS-Excel interface and VBA. The minichannel packings, namely wall-coated minichannel reactor (MCWR), minichannel reactor packed with catalytic particles (MCPR), and minichannel reactor packed with a catalytic open-celled foam (MCFR), outperform the conventional and miniaturised trickle-bed reactors (TBR and MTBR) in terms of space-time yield and catalyst use. However, longer reactor lengths are required to achieve 99% conversion of the sugars in MCWR and MCPR. Considering further technical challenges such as liquid distribution, packing the reactor, as well as the robustness and manufacture of catalysts in a biorefinery environment, miniaturised trickle beds are the most favourable design for a production scenario of galactitol. However, the minichannel configurations will be more advantageous for reaction systems involving consecutive and parallel reactions and highly exothermic systems.