Trickle Flow Research Articles

An experimental investigation of various trickle collector structures to enhance solar water heater efficiency

This study aimed to enhance the efficiency of the solar water heater (SWH) due to the increasing demand of renewable energy. It compared use three different solar collector models, namely Model A (square-shaped polycarbonate), Model B (v-corrugated zinc), and Model C (trapezoidal aluminium) to identify the most cost-effective configuration. The models were subjected to experiments in real operating conditions during the summer season in Indonesia. Various parameters, including solar radiation intensity, wind speed, inlet and outlet temperatures, and flow rate, were measured every 10 min from morning to afternoon. Additionally, the study employed a trickle and one-way flow rate system. The results showed that Model B achieved the highest total efficiency at 50%, followed by Models A and C at 47% and 34%, respectively. The 120 Lph flow rate exhibited better performance in absorbing useful heat energy than the 240 Lph flow rate. Based on these findings, all three models were recommended for the household-scale SWH applications. Model A showed the most promising economic value but had a shorter lifespan due to the tendency of polycarbonate to deform. In contrast, Model B and Model C, using zinc and aluminium, offered longer lifespans.

Experimental development of packing structures in a gas-particle trickle flow heat exchanger for application in concentrating solar tower systems

Ceramic particles represent a viable alternative as heat transfer and storage medium in concentrating solar tower systems. The particles are heated in solar-receivers close to 1000 °C. To utilize the stored energy in the particles, an air-particle direct-contact trickle-flow heat exchanger has been identified as suitable for this task. To date, no design recommendations exist that identify an optimized packing structure capable of providing a high particle volume fraction and a uniform spatial particle density distribution for a given grain type. Consequently, an experimental selection process is presented in this work to assess various packing structures for a given grain type in a trickle-flow reactor. The experiments were conducted with countercurrent flowing air at ambient conditions and 1 mm bauxite particles. A variety of packing structures were investigated at varying media flow rates. For each flow condition, the particle volume fraction was determined, as well as the particle distribution in a separate analysis. The cold experiments yielded a clear image of a preferred packing geometry, which will be discussed in detail. The results will serve as the basis for further hot experiments and thermal performance analysis in future work, where the packing geometry can be refined iteratively if necessary.

Magnetic resonance imaging of trickle flow

AbstractTrickle bed reactors (TBR) are widely used in the chemical industries. These reactors involve gas and liquid flow through a catalyst‐packed bed. For optimal TBR performance, it is crucial to achieve a uniform distribution of gas and liquid among the catalyst particles. However, in multitubular reactors with slender tubes, flow maldistribution near the tube walls is a common issue. Therefore, a comprehensive understanding of local phase and flow distribution is essential for designing and operating reactors with slender tubes. This article employs Magnetic Resonance Imaging (MRI) to characterize the three‐dimensional distribution of the two‐phase trickle flow within a slender tube. Three quantities are characterized: gas‐liquid‐solid distribution, particle wetting efficiency, and the flow field. Structure and flow MRI images are processed to calculate these quantities. Additionally, a novel postprocessing technique is introduced to determine the liquid distribution over individual particle surfaces. This distribution is determined at several axial and radial positions.

Predicting Temperature and Humidity in Roadway with Water Trickling Using Principal Component Analysis-Long Short-Term Memory-Genetic Algorithm Method

The heat dissipated from high geo-temperature underground surrounding rocks is the main heat source of working faces, while thermal water upwelling and trickling into the roadway will notably deteriorate the mine’s climate and thermal comfort. Predicting airflow temperature and relative humidity (RH) is conductive to intelligent control of air conditioning cooling and ventilation regulation. To accommodate this issue, an intelligent technique was proposed, integrating a genetic algorithm (GA) and long short-term memory (LSTM) based on rock temperature, inlet air temperature, water temperature, water flow rate, RH, and ventilation time. A total of 21 input features including over 200 pieces of data were collected from an independently developed modeling roadway to construct a dataset. Principal component analysis (PCA) was conducted to reduce features, and GA was used to tune the LSTM and PCA-LSTM architectures for best performance. The following research results were yielded. The proposed PCA-LSTM-GA model is more reliable and efficient than the single LSTM model or hybrid LSTM-GA model in predicting the air temperature Tfout and humidity RHout at the end of the water trickling roadway. The importance scores (ISs) indicate that Tfout is mainly influenced by the surrounding rock temperature (IS 0.661) and the inlet air temperature (IS 0.264). While RHout is primarily influenced by the rock temperature in the water trickling section (IS 0.577), the inlet air temperature (IS 0.187), and the trickling water temperature and flow rate (total IS 0.136), and it has an evident time effect. In addition, we developed relevant equipment and provided engineering practice methods to use the machine learning model. The proposed model, which can predict the mine microclimate, serves to facilitate coal and geothermal resource co-mining as well as thermal hazard control.

Guard of hydrotreating catalysts of oil fractions from solid particulates: experimental studies and calculation

A study was made of the efficiency of trapping solid microparticulates contained in diesel fuel for catalyst loading – an analogue of an industrial package of guard beds of hydroprocesses. The package of catalysts consisted of catalyst granules ranked by shape and size: segmented rings, hollow cylinders of two standard sizes and trilobe shape. The experiments were carried out in the trickle flow regime with a constant ensemble of microparticulates – iron scale with a size of 5 to 150 μm at the inlet of the catalysts loading. It was found that the penetration coefficient of the catalysts loading of the guard beds did not change significantly (K ≈ 0.985) during the experiment. At the same time, a linear increase in the pressure drop on the catalysts loading of the guard beds with a height of 17 cm from 220 to 408 Pa was observed which occurred as a result of the trapping of solid microparticulates by the catalyst granules. The theoretical estimate of the initial pressure drop (228 Pa) coincides with the experimental data (220 Pa) with good accuracy.

A new approach to model the fluid dynamics in sandwich packings

Abstract Sandwich packings represent new separation column internals, with a potential to intensify mass transfer. They comprise two conventional structured packings with different specific geometrical surface areas. In this work, the complex fluid dynamics in sandwich packings is modeled using a novel approach based on a one-dimensional, steady momentum balance of the liquid and gas phases. The interactions between the three present phases (gas, liquid, and solid) are considered by closures incorporated into the momentum balance. The formulation of these closures is derived from two fluid-dynamic analogies for the film and froth flow patterns. The adjustable parameters in the closures are regressed for the film flow using dry pressure drop measurements and liquid hold-up data in trickle flow conditions. For the froth flow, the tuning parameters are fitted to overall pressure drop measurements and local liquid hold-up data acquired from ultra-fast X-ray tomography (UFXCT). The model predicts liquid hold-up and pressure drop data with an average relative deviation of 16.4 % and 19 %, respectively. Compared to previous fluid dynamic models for sandwich packings, the number of adjustable parameters could be reduced while maintaining comparable accuracy.

Forces governing the dynamics of liquid spreading in packed beds

Liquid spreading through a randomly packed particle-resolved bed influenced by capillary or inertial ($AB_s \sim 1$), and gravitational force (moderately ($AB_s \sim 0.1$) and strongly ($AB_s \sim 0.01$)) is investigated using the volume-of-fluid simulations. The relative contribution of governing forces at different stages of spreading is analysed using the time evolution of Weber ($We_I$) and$AB_I$numbers. We show that the dynamics of liquid spreading at$AB_s \sim 1$is primarily governed by the inertial force in the beginning ($AB_I > 1$,$We_I > 1$) followed by the capillary force at$t/t^* \sim 1$. This interplay of governing forces leads to inertia- and capillary-induced bubble entrapments at the void scale and promote lateral liquid spreading. When the$AB_s \sim 0.1$, the$t/t^*$for which the flow is governed by inertial ($AB_I > 1$,$We_I > 1$) and capillary forces ($AB_I > 1$,$We_I < 1$) decreases and the relative contribution of gravitational force is substantial at large$t/t^*$($AB_I < 1$). This force balance leads to unified-void filling characterised by negligible bubble trapping and results in a decrease in the lateral spreading. Further decrease in the$AB_s$to${\sim } 0.01$results in liquid spreading primarily governed by gravitational force ($AB_I < 1$) with small contribution of inertial and capillary forces at the very beginning leading to trickling flow and a further decrease in lateral spreading. Finally, a regime map is proposed, which provides the relationship between different forces, void-scale events, and the resultant liquid spreading at$t/t^* \sim 1$.

A novel trickle bed electrochemical reactor design for efficient hydrogen peroxide production

A specific and environmentally benign electrochemical reactor that combines the property of gas diffusion electrode (GDE) with trickling flow property in trickle bed electrochemical reactor (TBER) is designed for intensive hydrogen peroxide (H2O2) production. Compared with other reactors a significant feature of this reactor is the capability to uniformly distribute the oxygen gas all over the cathode bed avoiding oxygen gas transport limitations, electrode limited area, and continuous electrolyte leakage. This reactor consists of two plates as anodes and two porous layers composed of carbon black and polytetrafluoroethylene (C-PTFE) mixture that are pasted on two stainless steel meshes(SSM) to form cathode beds (C-PTFE-SSM). The cathodes are placed on both cathode frame sides which were designed to comprise two separated cathodes. The oxygen gas can flow easily through the space between cathodes and diffuses to the solid-liquid interface to be electrochemically reduced to form H2O2. H2O2 was in situ electrosynthesized in an alkaline solution by the oxygen electrochemical reduction on the cathode surface. All operating conditions that affect the process were systematically investigated. The highest concentration of H2O2 of 46.56 mM was achieved in 40 min and 1.0 V at room temperature, whereas at 0 °C the generated peroxide was 57.86 mM. This significant performance is attributed to the uniform oxygen distribution on the electrode bed making an easy access for gas transport to the electrolyte-cathode interface. The low temperature increases oxygen solubility which increases the production rate as well. Power consumption was also estimated and found to be 4 kWh/kg which is economically beneficial. At different applied cell voltages and best-operating conditions, a kinetic study was conducted for H2O2 electrosynthesized.

Fixed Bed Continuous Hydrogenations in Trickle Flow Mode: A Pharmaceutical Industry Perspective

Fixed Bed Continuous Hydrogenations in Trickle Flow Mode: A Pharmaceutical Industry Perspective

Flow regimes in a gas–liquid–solid three‐phase moving bed

AbstractThe gas–liquid–solid three‐phase moving beds could supply a potential solution for multiphase reactions with catalyst easily deactivated, and the flow regimes in it were studied by optical method and pressure drop measurement. Results showed that taking the trickle flow as the initial flow regime, the flow channels were more obvious as the particle velocity increased. When the initial flow regimes were pulse flow and bubble flow respectively, the pulse‐to‐trickle and bubble‐to‐pulse flow transitions mainly occurred at moderate‐to‐high particle velocities (0.01–0.04 m s−1under conditions used in this work). Moreover, the flow regime map in the three‐phase moving bed was constructed and shown that the region of trickle flow increased and the region of bubble flow decreased. Finally, the application of three‐phase moving beds was discussed, and it could be suitable for those reactions, which had to operate in the pulse flow, bubble flow, and transition zone.

Analysis and estimation of gas-liquid flow pattern in packed bed compact tubular reactors

One of the factors that influence the performance of packed bed reactors is the flow pattern, and many flow pattern maps have been reported so far. In this study, a gas-liquid flow pattern map of a packed bed compact reactor, which is being increasingly used in the flow synthesis of functional chemicals, was constructed, and two types of flow patterns, trickle flow and pulse flow, were identified. In addition, an estimation method was developed to distinguish the trickle flow and pulse flow from differential pressure or voltage when the flow inside the reactor cannot be visually recognized from the outside. The effects of the liquid flow rate and the slug formation frequency at the mixer on the pulsation frequency, which is a parameter in reaction optimization, were examined. As a result, it was shown that the pulsation frequency increases as the liquid flow rate increases under a fixed gas flow rate and that the pulsation frequency and the slug formation frequency do not always match due to the possibility of coalescence of the gas and liquid slugs at the reactor inlet.

Flow regime transition and liquid distribution in a 3D concurrent downflow three-phase moving bed

Based on a cold-flow experimental setup, the transition between trickle flow and pulse flow in a 3D concurrent downflow three-phase moving bed is investigated by the standard deviation of pressure drop and visual observations. Results show that at a constant gas flow rate, the trickle-to-pulse transition shifts to a higher liquid flow rate with the increasing solid flow rate because the particle moving inhibits the formation of local liquid blockage. Furthermore, an empirical model is proposed to fit the trickle-to-pulse transition boundary by correlating the dynamic liquid holdup at the boundary with the gas Reynolds number, the particle velocity, and the relative viscosity. Finally, the effects of the particle moving on the liquid distribution are investigated, which shows that the particle moving makes the liquid distribution more uniform when the solid flow rate is smaller than a certain value. But further increasing the solid flow rate, the liquid distribution becomes uneven.

Comprehensive numerical assessment of molten iron–slag trickle flow and gas countercurrent in complex coke bed by Eulerian–Lagrangian approach

The transient behavior of immiscible two-liquid interfaces initiated by molten iron–slag trickle flow was investigated using a Lagrangian particle-based smoothed particle hydrodynamics (SPH) model to track the movements of both liquid phases directly. The transient behavior of the associated gas flow was simulated using a Eulerian grid-based model dependent on the gas permeability characteristics exhibited by the molten iron–slag counterflow. As an example of the assessments conducted, the sliding behavior of molten iron down the slag surface at different between-phase interfacial tensions was observed in the unsteady state. While the effect of wetting between the molten slag and coke on the gas flow was found to be insignificant, decreasing the liquid–liquid interfacial tension promoted mixing between the two liquids, which in turn hindered the rapid dropping of the molten iron and resulted in a significant stagnation of gas flow.

Enhanced weathering to capture atmospheric carbon dioxide: Modeling of a trickle‐bed reactor

AbstractEnhanced weathering (EW) of alkaline minerals can potentially capture CO2 from the atmosphere at gigaton scale, but the reactor design presents great challenges. We model EW with fresh water in a counter‐current trickle flow packed bed batch of 1–10 mm calcite particles. Weathering kinetics are integrated with the mass transfer of CO2 incorporating transfer enhancement by chemical reaction. To avoid flooding, flow rates must be reduced as the particles shrink due to EW. The capture rate is mainly limited by slow transfer of CO2 from gas to liquid although slow dissolution of calcite can also play a role in certain circumstances. A bed height of at least 7–8 m is required to provide sufficient residence time. The results highlight the need to improve capture rate and reduce energy and water consumption, possibly through enriching the feed with CO2 and further chemical acceleration of the mass transfer.

Some Methods of a Change in the Trickle Flow Structure during the Water Dispersion by Flat-Plate Jet Nozzles

Consideration is given to the possibility of the control of the structure of the trickle flow by using flat-plate jet nozzles for the elliptic shape of the surface of the spray zone. This research paper gives consideration to the data of experimental investigations of the water-air dispersed water during the internal mixture formation in the flat-plate nozzle as applied to the cooling of the ingot between the rollers in continuous steel casting machines. In this case, the water flow rate per nozzle and the water concentration can be reduced ten times. As a result, the ingot cooling intensity is reduced and the probability of the crack nucleation on the ingot surface is decreased. This research paper gives also the data of the experimental research carried out for a more efficient use of flat-plate nozzles when cooling the casting roller before its polishing and when heating it before charging the mill stand. It was shown that the intercrossing of trickle flows produced by two flat-plate jet nozzles arranged at an angle relative to each other results in the four-time increase in the spray zone surface area and the surface spray density is reduced two times. The analogous problem was solved using the kinetic energy of the disintegrating water film and the drops after these leave the flat-plate nozzle for the additional splitting when passing through the metal gauze. It turned out that the spray zone was increased threefold and the surface spray density was decreased two times. The trickle flow structure control options in question with the use of flat-plate nozzles contribute to the improved quality of the ingots, decreased water consumption, reduced number of the nozzles and their simplified arrangement on the collectors.

A numerical study of the mechanism of liquid film spread and distribution on spherical particles including wall effects

Studies to elucidate the mechanism of liquid film flow have been carried out for many years, but the results are still inadequate. Because of random packing, several problems frequently appear in the near-wall region. Therefore, in this study, the liquid film thickness and its spreading behavior were fully investigated using FLUENT v17.1, to unveil the mechanism of the trickle flow, including wall effects. As a quantification, the coefficient of variation (COV) was used to represent the degree of liquid film equilibrium. The results show that trickle flow on the sphere can be roughly separated into three flow stages in which the features of the films are nearly identical. The wall effect, which plays a key role in the poor distribution of the films, is only available if the interstice is lesser than liquid film thickness. To alleviate wall effects, an intermediate velocity of surrounding gas flow is required.

Numerical Simulation of Coexisting Solid-liquid Slag Trickle Flow in a Coke Bed by the SPH Method with a Non-Newtonian Fluid Model

Numerical Simulation of Coexisting Solid-liquid Slag Trickle Flow in a Coke Bed by the SPH Method with a Non-Newtonian Fluid Model

Liquid hydrogen line chilldown experiments at high Reynolds numbers. II. Analysis

This paper presents in-depth analysis of the recently conducted high Reynolds (Re) number liquid hydrogen (LH2) transfer line chilldown experiments at NASA Glenn Research Center. Vertically upward trickle and pulse flow chilldown tests were conducted over a wide range of LH2 liquid temperatures (20.3 K – 24.2 K) and mass flow rates (0.0012 – 0.036 kg/s) typical of a proposed cryogenic propellant depot. Two-phase flow mapping is used to correlate flow visualization with LH2 stream temperature profiles. Thermodynamic state diagrams, reverse boiling curves, and heat transfer coefficients are used to explain the evolution of the chill down process at various locations. Analysis reveals stark differences in behavior between skin and stream temperature measurements due to annular flow and bubbly flow dominated cooling. Analysis also shows that hydrogen chilldown at high Re numbers promotes better mixing and thus more liquid contact along the wall earlier on, in comparison to chilldown with other fluids like nitrogen where classical inverted annular flow boiling is incurred.

Heterogeneous Catalytic Ozonation of Phenol over Iron-based Catalysts in a Trickle Bed Reactor

The use of continuous reactors for heterogeneous catalytic ozonation is yet to be investigated in order to develop a viable technology for industrial applications. This paper presents hydrodynamic and degradation studies on the use of a co-current down flow trickle bed reactor for heterogeneous catalytic ozonation of phenol (as model pollutant) over Fe-Diatomite pellets and Fe-coated glass beads. It was found that the reactor can operate under trickle or pulsing flow regimes, promoting mass transfer augmentation. Residence time distribution data, fitted with n-CSTR and axial dispersion (ADM) models, showed low axial dispersion and high flow distribution. Just the Fe-diatomite pellets showed important phenol adsorption (16 %). Degradation experiments demonstrated that phenol conversion was substantial when using both catalysts, up to 19,7 % pollutant conversion with liquid-phase space times of just 6 s. Compared to direct ozonation, the use of the Fe-diatomite pellets and Fe-coated glass beads enhanced the reactor performance by 48 % and 23 %, respectively. It was confirmed that mass transfer is an important factor that restricts this reaction system performance; consequently, further improvement in mass transport rate is necessary for system optimization.

Numerical Study of Binary Trickle Flow of Liquid Iron and Molten Slag in Coke Bed by Smoothed Particle Hydrodynamics

In the bottom region of blast furnaces during the ironmaking process, the liquid iron and molten slag drip into the coke bed by the action of gravity. In this study, a practical multi-interfacial smoothed particle hydrodynamics (SPH) simulation is carried out to track the complex liquid transient dripping behavior involving two immiscible phases in the coke bed. Numerical simulations were performed for different conditions corresponding to different values of wettability force between molten slag and cokes. The predicted dripping velocity changes and interfacial shape were investigated. The relaxation of the surface force of liquid iron plays a significant role in the dripping rate; i.e., the molten slag on the cokes acts as a lubricant against liquid iron flow. If the attractive force between the coke and slag is smaller than the gravitational force, the slag then drops together with the liquid iron. When the attractive force between the coke and slag becomes dominant, the iron-slag interface will be preferentially detached. These results indicate that transient interface morphology is formed by the balance between the momentum of the melt and the force acting on each interface.