Initial Liquid Height Research Articles

Experimental study on sloshing mechanical characteristics in a partially filled storage tank

AbstractDue to excellent performance, hydrogen is treated as the most promising energy carrier. However, during the storage of liquid hydrogen, there are still some thorny issues that need to be addressed urgently, such as fluid thermal stratification and sloshing phenomenon. To efficiently grasp fluid sloshing mechanical characteristics, a simple visual sloshing experiment rig was established by using a rectangle transparent water vessel. The variations of the interface shape and the impact force during sloshing were monitored and analyzed. The effects of sloshing frequency, horizontal acceleration, and initial liquid height on fluid sloshing mechanical mechanism were investigated. The results show that when the external sloshing excitation is close to the first order natural frequency, obvious interface fluctuation and large amplitude sloshing force variation are observed. The present work is of significance to strengthen the understanding of fluid sloshing mechanical performance and may lay a solid foundation for fluid sloshing suppression and long‐term storage of cryogenic fuels.

Zero-Net Liquid Flow Simulation Experiment and Flow Law in Casing Annulus Gas-Venting Wells

Under casing annulus gas venting, the annulus of the well is in a special state of zero-net liquid flow (ZNLF), leading to gas production without liquid at the wellhead, resulting in significant holdup issues. Therefore, conventional two-phase flow models cannot be used for calculation. To study the flow characteristics of ZNLF in the annulus of the well, this study established a visual experimental device with a total height of 5.4 m, an outer pipe inner diameter of 140 mm, and an inner pipe outer diameter of 72 mm. The flow characteristics of ZNLF were studied by controlling the casing pressure, initial liquid level, and bottom gas injection rate. The experimental results showed that the flow patterns of ZNLF are mainly bubbly flow and churn flow. Bubbly flow occurred at lower gas rates, while churn flow occurred at higher gas rates. In addition, the experiment found that when the gas injection rate and initial liquid column height were controlled to be the same, the liquid holdup decreased as the casing pressure increased. Analysis of the data patterns indicated that the slip velocity is related to the casing pressure. Based on the experimental results of ZNLF in the annulus, this study established standards for flow pattern transitions, holdup, and a pressure drop calculation model. The model results showed good agreement with the experimental results, with errors not exceeding ±5%.

PIV Experimental Research and Numerical Simulation of the Pigging Process

The initial running speed of the pig during gas–liquid two-phase pipeline pigging can significantly influence the velocities of both gas and liquid phases within the pipeline. However, due to the complexity and limited understanding of these velocity variations, developing an effective operational plan for pigging becomes challenging. To enhance pigging efficiency and effectively seal the pig, it is crucial to monitor the velocity variations in the gas–liquid phase within the pipeline. In this study, an experimental platform was established to facilitate precise observation of these variations. Particle image velocimetry (PIV) technology was employed for a comprehensive understanding of gas–liquid two-phase velocities during pig operation in the pipeline. The experimental results demonstrated that increasing both the velocity and the initial liquid level height of the pig resulted in a corresponding augmentation of velocity fluctuation range. Specifically, at a holdup rate of 30%, there was a 10% reduction in the maximum liquid-phase velocity, while at a holdup rate of 25%, this reduction amounted to 16% compared to the pigging velocity.

Characteristics study of non-equilibrium flash for two-phase expansion based on equivalent expansion experiments

The two-phase expansion inside the expander could be divided into the non-equilibrium flash of superheated liquid and the expansion of the vapor. A higher flash rate would permit higher recovered expansion work. However, it is almost impossible to measure the flash rate inside the expansion chamber. In this paper, an equivalent expansion method s was proposed to study the non-equilibrium flash process for the two-phase expansion. The flash was controlled inside a constant volume flash chamber, which was connected to a vacuum tank to introduce and adjust the flashed vapor rate out of the flash chamber. The flash process inside the chamber was controlled under the working conditions similar to that inside the two-phase expander. By applying the equivalent expansion method, the flash rate could be measured easily. The experiments were carried out with an initial liquid height inside the chamber from 110 to 175 mm, and an initial liquid temperature from 110 to 130 °C with water as the working fluid. The instant flash rate and the PV diagram of the equivalent two-phase expansion were studied. Results showed that the instant flash rate increased and decreased sharply at first, and then the flash became gentle. Thus, the non-equilibrium flash of the two-phase expansion was divided into two stages of the rapid expansion process and the gradual expansion process. It was found that most of the flashed mass was generated during the rapid expansion process. Finally, a non-equilibrium flash model was proposed to simulate the flash process during the two-phase expansion process with the accuracy of ±3.7% predicting the pressure profile and the accuracy of ±2.7% predicting the expansion work.

Numerical Simulation Method for Flash Evaporation with Circulating Water Based on a Modified Lee Model

Flash evaporation processes are widely adopted in the desalination, food processing, waste heat recovery and other industries for heat extraction or product separation. In this paper, a pressure-driven phase transition model is developed by improving the Lee model and combined with the VOF (Volume of Fluid) method to numerically simulate the flash evaporation process. In this modified Lee phase transition model, the driving force for the rates of the local phase transition is calculated using the local temperature and static pressure magnitude. Numerical simulations are carried out in a water-circulating flash chamber and compared with the experimental results to obtain the values of the time relaxation parameters. And the non-equilibrium fraction of the outlet water can be effectively obtained under different conditions of flow rate, inlet temperature and initial liquid level height. The time relaxation factor takes values from 0.195 to 0.43 (Pout,v = 19.9 kPa) and from 0.31 to 0.92 (Pout,v = 31.2 kPa) with increasing superheat. In addition, the model can effectively represent the evolution of the unstable flow flash evaporation from the initial rapid boiling state to dynamic equilibrium.

Experimental investigation on extraction of shallow geothermal energy by flexible two-phase closed thermosyphons: Effect of geometric parameters

This study investigates the thermal performance of three super-long flexible thermosyphons (SFTSs) fabricated using metal corrugated-pipe under shallow geothermal conditions, aiming to uncover enhanced heat-transfer methods applicable to this innovative design. Field tests are conducted for SFTSs, each with a length of 52.5 m, under various cooling conditions in a drilling environment. The effects of evaporator dimensions and corrugated-pipe shape on the start-up and steady-state thermal performance of SFTSs are also discussed. The results indicate that the whole liquid pool of all SFTSs boils during start-up, even with an initial liquid column height of 15 m. The SFTS with the lower-diameter evaporator demonstrates better thermal performance during both start-up and steady-state operations, with an increase of approximately 31.8% in the heat transfer power under optimal conditions within the test parameters. Moreover, the helicon-shaped corrugated-pipe evaporator provides better thermal performance for SFTSs than the U-shaped corrugated-pipe evaporator, thus resulting in an increase in the heat transfer power by approximately 5.5% under optimal conditions. The maximum heat transfer power achieved in this study is approximately 1227 W when the inlet temperature of cooling water is 3 °C and the flow rate of cooling water is 4500 mL/min, demonstrating the potential of super-long flexible thermosyphon in extracting shallow geothermal energy. These results provide valuable insights into the heat-transfer and enhancement mechanisms of geothermal thermosyphons.

Analysis of Liquid Film Evaporation in Porous Particles: Toward Optimal Wick Parameters for Heat Transfer in Heat Pipes

Abstract Evaporation of working fluids inside capillary wicks determines the heat transfer capability of heat pipes. However, the relationship between wick parameters and evaporative heat transfer remains unclear. To establish a correlation between wick parameters of sintered porous particles and evaporation characteristics, a boundary condition model was developed, incorporating wick parameters such as particle radius (R), particle distance (d), apparent contact angle (θa), and initial liquid height (H). In the absence of a significant size effect, the profile of the liquid–vapor interface was determined using the boundary model by numerically solving the augmented Young–Laplace equation. Ammonia was used as an example to investigate evaporation characteristics. The curvature radius of the intrinsic meniscus (Re) was found to serve as a bridging factor between these wick parameters and evaporation characteristics. When Re exceeded 40.3 μm, a limitation in evaporative heat transfer within the thin film region was observed. The relationship between R, d, θa, and H was quantitatively described based on this evaporative heat transfer limit. Furthermore, a nondimensional analysis of the governing equation for the evaporating liquid film profile was conducted, yielding an influencing factor (λ) that governed the thin film profile. The proposed model and its outcomes could offer valuable theoretical insights for the structural design of sintered porous particles, the optimization of surface modification levels, and the determination of the appropriate working fluid charging ratio during the manufacturing process of heat pipes.

Computational fluid dynamics study of gas-liquid mass transfer in concentric tube airlift reactor with helical baffle

This work aims to understand the effect of stationary and rotational helical baffle on gas-liquid mass transfer in concentric tube airlift reactor. A computational fluid dynamics (CFD) method is conducted, and the predicted of overall volumetric mass transfer coefficient (KLa) in concentric tube airlift reactor (0.29 m diameter and 1.5 m initial liquid height) without baffle is validated reasonable agreement with the empirical equations reported in the literatures. The results were simulated basing on this validated model. It indicated that the helical baffle with the same width of riser (40 mm) could increase the KLa by 132∼202% at the superficial gas velocity of 0.00212 m·s−1 when compared with that the airlift reactor without baffle. At the width of helical baffle less than width of riser, the KLa decreased with the decreasing of the width (W) and the rotational speed (n) of helical baffle. When the width of stationary helical baffle is 30 mm, the effect of helical baffle on enhancing mass transfer is negligible. In addition, the KLa decreased with the increasing of the helix pitch (H) of helical baffle and the distance of the lower edge of helical baffle from the bottom of reactor (L).

Numerical simulation of gas holdup in nocoalescence media of industrial-scale bubble column

A bubble column is an industrial-scale wet filtration facility that contains non-coalescence media. To overcome the experimental challenges, numerical simulation was employed to investigate the influence of various factors on the whole gas holdup εt. These include the bubble diameter ds, initial liquid height Hs, column diameter, Dc, the number of bubbling orifices N, and the configuration of bubbling orifices. Two magnitudes of the superficial gas velocity UG, were selected to represent the homogeneous and heterogeneous flow regimes, respectively. The relationship between εt and ds changed within different ds ranges. The proportion of the developing region in the total liquid height is an important factor that influences εt. For an “industrial-scale” column, εt increased with N when N < 49, but becomes insensitive to N when N > 49. The configuration of bubbling orifices significantly influences εt when N > 49. The results of this study show the need to optimize the bubble column and improve the operating performance of filtered containment venting systems.

Coupling model of motion and mass transfer in multicomponent desorption of fine bubbles

Fine bubbles with a diameter less than 1 mm are widely used to intensify the gas–liquid processes since the micro-interface they build can significantly improve the mass transfer of gases to the liquid phase. In this study, a coupled mathematical model of motion and mass transfer of a single fine bubble with multicomponent was established and verified for carbon dioxide desorption. The rising and dissolution behaviors of a single fine bubble with different external pressures and initial diameters were observed using a high-speed imaging technique to evaluate the increasing velocity, Vb, and the mass transfer coefficient, kL. Design indicators such as effective mass transfer height and residence stay time of the bubble have been established to guide the optical selection of initial bubble size and liquid level height (reactor height) for a bubbling reactor's optimal design and operation. The comparison between the theoretical calculations and the experimental results proves that the new model can well describe the movement and multicomponent mass transfer behavior of a single fine bubble in an aqueous solution, and the relative errors are less than 5%.

Flow regimes characteristics of industrial-scale center-rising airlift reactor

• Multiphase fluids in industrial-scale CRALR exhibit unique flow characteristics. • Δ P - u g curves increase stepwise with gradually rising in distributor hole area. • Pressure accumulation and release in large distributor form gas-liquid oscillations. • Increase of the CRALR diameter induces the bubble stream to rotate in advance. • Limit of gas holdup is determined by equipment parameters. Airlift reactors are frequently preferred in biochemical engineering, and related investigations are almost performed using bench-scale reactors. However, in industrial-scale reactors, multiphase fluid usually exhibits unique mixing and transfer behaviors. Therefore, we studied the flow regimes characteristics in an industrial-scale center-rising airlift reactor (CRALR) with a diameter of 1.2 m. The results show that the available jet hole area of the gas distributor gradually increases along with the superficial gas velocity in the plateau range of the total pressure drop. Since the rise in initial liquid height enlarges the available jet hole area, the flow regime can be transformed from a pure heterogeneous regime to other regimes. Meanwhile, the total gas holdup plunges within the transition regime range, which can be interpreted by the gas–liquid oscillations in the gas distributor with a large free gas volume. When the oscillations cannot maintain the small bubble ratio, the rapid transition from a homogeneous regime to heterogeneous regime is affected. Compared with previous results, the bubble stream rotates in advance in the homogeneous regime of the industrial-scale CRALR. The rotational structure helps to reduce the flow resistance and improves the radial bubble distribution. Furthermore, the total gas holdup curves under various operating conditions converge into one curve at which a limit, determined by equipment parameters, is ultimately reached in the course of increasing the superficial gas velocity. It turns out that the fluids have similar hydrodynamic behaviors in flow fields of different scales when the limit is reached.

EFFECTS OF INITIAL LIQUID HEIGHT AND LIQUID VISCOSITY ON TOTAL GAS HOLDUP IN A BUBBLE COLUMN

EFFECTS OF INITIAL LIQUID HEIGHT AND LIQUID VISCOSITY ON TOTAL GAS HOLDUP IN A BUBBLE COLUMN

Continuous removal of ethanol from dilute ethanol-water mixtures using hot microbubbles

Product inhibition is a barrier to many fermentation processes, including bioethanol production, and is responsible for dilute product streams which are energy intensive to purify. The main purpose of this study was to investigate whether hot microbubble stripping could be used to remove ethanol continuously from dilute ethanol–water mixtures expected in a bioreactor and maintain ethanol concentrations below the inhibitory levels for the thermophile Parageobacillus thermoglucosidasius (TM242), that can utilize a range of sugars derived from lignocellulosic biomass. A custom-made microbubble stripping unit that produces clouds of hot microbubbles (~120 °C) by fluidic oscillation was used to remove ethanol from ~2% (v/v) ethanol–water mixtures maintained at 60 °C. Ethanol was continuously added to the unit to simulate microbial metabolism. The initial liquid height and the ethanol addition rate were varied from 10 to 50 mm and 2.1–21.2 g h−1 respectively. In all the experiments, ethanol concentration was maintained well below the inhibition threshold of the target organism (~2% [v/v]). This microbubble stripping unit has the potential to operate in conjunction with a 0.5–1.0 L fermenter to allow an ethanol productivity of 14.9–7.8 g L−1h−1 continuously.

Numerical analysis of liquid fall type gas entrainment in pool-type fast reactor

Argon covering the free surface of the pool-type sodium-cooled fast reactor may be mixed into the coolant in form of entrainment bubbles due to the fluctuation of liquid surface, which introduces positive reactivity to the core, reduces the heat exchange capacity of the core and intermediate heat exchangers (IHXs), and possibly leads to the cavitation of the primary sodium pump (PSP), threatening the safe operation of the reactor. In this study, the computational fluid dynamics (CFD) simulation of liquid sodium fall entrained argon was carried out based on the Volume of Fluid (VOF) interface tracking method to describe the entrainment process in detail, and the influences of geometry size, initial liquid level height and inlet velocity on entrainment were analyzed successively. It was found that the re-submergence velocity, having a linear relation with the re-submergence angle, is the key factor of the liquid fall type gas entrainment. It can be used to judge whether the liquid fall type entrainment occurs conservatively. In addition, the parameters affecting the re-submergence velocity are specifically analyzed from the supplementary cases, according to the results of which, the empirical relation of the re-submergence velocity is obtained. Therefore, the situation of liquid fall type gas entrainment under various working conditions can be predicted numerically.

EFFECTS OF INITIAL LIQUID HEIGHT ON TOTAL AND LOCAL GAS HOLDUPS IN AN AIR-WATER BUBBLE COLUMN

EFFECTS OF INITIAL LIQUID HEIGHT ON TOTAL AND LOCAL GAS HOLDUPS IN AN AIR-WATER BUBBLE COLUMN

Efflux Time for Two Exit Pipe System

Based on integral balances, mathematical equation for efflux time during gravity draining of a Newtonian liquid (below its bubble point) from a large open cylindrical storage tank (Where the flow in the storage tank is essentially laminar) through two exit pipes of same diameter located at the bottom of the vessel (The flow is assumed to be turbulent in each of the exit pipes) is developed. The equation is ultimately simplified and written in dimensionless form. The equation will be of use for arriving at the minimum time required for draining the contents of a cylindrical storage vessel through two exit pipe. The equation is verified with the experi- mental data. A maximum deviation of 19% and an average deviation of 16% are observed. The effect of initial height of liquid on Reynolds' number is also established. It is shown that while draining a liquid from the cylindrical storage tank through exit pipe system, Froude number re- mains constant.

CFD Prediction with Eulerian/Eulerian Approach of SO2 Absorption from Flue Gases in Bubble-Dispersion Tower

Accurate prediction of SO2 absorption efficiency under different physical and chemical parameters is of significant importance for desulfurization of the flue gas. In order to understand the mechanism of SO2 absorption inside a bubble-dispersion tower, a three-dimensional twin Eulerian model together with two-film theory was applied to simulate the flue gas desulfurization processes in a bubble-dispersion tower. After comparing the predicted desulfurization efficiencies by using calculated gas holdup with the experimental parameters, the deviation of simulated model with the measured ones was small. Moreover, it was observed that the larger the fractional hole area, the better desulfurization performance. The bubble tower showed fine adaptability when the superficial gas velocity varies from 0.3 to 0.7 m/s. Also, there was a positive correlation between the SO2 removal ability and the hydrogen ion concentration. Considering the crystallization of calcium sulfite, the PH of slurry tank inside bubble tower is recommended to be set between 5.5 and 6, and the initial CaCO3 mass fraction is suggested to be set around 10–15% under prediction conditions. Moreover, the SO2 absorption capability could be increased by lifting the initial liquid height, while the SO2 removal efficiency would level off when tube insertion depth/column diameter H/D was over 0.128, so the H/D is suggested to be set from 0.08 to 0.128 to achieve high SO2 absorption and avoid soil erosion. It was observed that the smaller the size of bubbles generated in the slurry, the higher SO2 absorption efficiency could be.

Simulation of Gas-Liquid-Solid Three-Phase Flow Process and Particle Removal Characteristics in Liquid Chamber of Scrubbing Tower

In this study, the motion of three phases (gas, liquid, and solid) and characteristics of particle removal inside the liquid chamber of industrial scrubbing tower were studied through unsteady simulations using the VOF-DPM coupled model. The study focused on the motion of dust particles in a three-dimensional computational domain of $$4200\times 8400$$ mm. After the system achieved stability, we obtained a chamber removal ability of 82.0% for a group of particles of different diameters, as well as removal ability for particles of different identical diameters. As the diameter grew from 10 $$\mu$$ m to 500 $$\mu$$ m, the dust removal efficiency increased from 23.1% to 97.2%. Moreover, the particle mass concentration along the height of the chamber was investigated. Based on prediction results, additional simulations were performed to investigate the effect of related parameters, including the inlet gas velocity and the initial liquid level height, on the dust-removal performance of the liquid chamber. The ideal operating parameters were identified, as playing a deciding role in appropriate industrial conditions.

CFD simulation of dynamic heat transfer behaviors in super-long thermosyphons for shallow geothermal application

The use of super-long thermosyphons (TSs) is experimentally proved to allow a higher efficiency in extracting shallow geothermal energy. In this work, transient CFD (Computational Fluid Dynamic) simulation has been carried out for the super-long ammonia geothermal TSs, total length up to 54 m, in order to understand their heat transfer behaviors for thermal performance optimization. The results show that due to the influence of hydrostatic pressure of liquid column, boiling initially starts at the liquid pool surface and then gradually moves downward in start-up. With the initial liquid-column height higher than 10 m, the lower part of liquid pool in TSs would be throughout in quiescent state and make no contribution to heat extraction. At steady state, boiling zone in liquid pool shows a much higher heat transfer efficiency than that of partially-wetted area at the upper part of evaporator. Geothermal TS with 20% filling ratio of ammonia in evaporator, namely the initial liquid column height at 10 m, has the best thermal performance under the simulation test conditions. For super-long geothermal TSs (>50 m) using ammonia as working fluid, it is recommended to fill ammonia as much as possible, but the premise is that the initial height of liquid column must be controlled below 10 m.

Experimental Investigation of the Settling Characteristics of Carbon and Metal Oxide Nanofuels

Fuels dispersed with engineered nanoparticle additives, or nanofuels, are desirable for the vastly different combustion properties such as combustion rate and ignition delay they exhibit compared to base fuels. The stability of such nanofuels over time and under different particle loadings is a very important parameter to consider before they can be put into practical use. Many techniques exist today to analyze suspension stability, which have been developed to analyze water-based nanofluids. Sometimes these techniques can be expensive, and/or require specialized equipment, and/or require a method that is invasive and disturbs the suspension. Present research uses a non-contact, non-invasive, low-cost experimental setup to analyze suspension stability over long periods of time. Nanofuels made from carbon-based nanomaterials (acetylene black, multiwalled carbon nanotubes) and metal oxide nanomaterials (copper oxide, aluminum oxide) with hydrocarbon fuels (canola biodiesel, petrodiesel) have been prepared and their settling rates have been analyzed over the period of three days. It is found that metal oxides go through several metastable states as they settle. The effect of initial concentration and liquid column height is shown. It is hoped that present research showcases the positive traits of the presented technique and will spark further interest in nanofuel stability.