Liquid Entry Research Articles

BPNN-based prediction for the shapes of a petal hole induced by hydrodynamic ram

The attitude angles of a projectile moving through a liquid are important factors that influence the dynamic failure of liquid-filled structures induced by hydrodynamic ram (HRAM). In this study, the effect of the attitude angles of a cylindrical projectile on the shapes of the petal hole in the rear plate of a kerosene-filled tank was investigated through ballistic impact experiments using three-dimensional digital image correlation, finite element simulations, and a back propagation neural network (BPNN). The inclination angle λ characterizing the shapes of the petal hole was related to the projection shapes of the projectile when impacting on the rear plate. The formation of petal-hole shapes was also accompanied by the formation of plastic hinge lines in the rear plate. Additionally, a method combining a BPNN and physical equations that accurately predict the drag coefficient and motion of a projectile moving through a liquid was proposed. A function describing the shapes of the petal hole was provided in the 2D space of the two initial attitude angles. The results provide offer insights into trajectory stability during liquid entry and aid in predicting the dynamic failure mode of a liquid-filled tank induced by HRAM.

Facile preparation of PVDF-HFP/GE tubular nanofiber membranes with 3D surface structure for high efficient continuous oil/water emulsion separation

Polymeric membranes show great potential for treating wastewater containing oil/water emulsions, which can cause serious environmental pollution. In this paper, novel polyvinylidene fluoride-co-hexafluoropropyle/graphene (PVDF-HFP/GE) tubular nanofiber membranes (TNMs) were fabricated by electrospinning and thermal treatment. The prepared TNMs were post-treated under different thermal treatment conditions to obtain 3-dimensional (3D) structures. The effects of thermal treatment time and temperature on membrane structure and performance were investigated by field-emission scanning electron microscopy, hydrophobicity, pore size and distribution, porosity, and liquid entrance pressure. After thermal treatment, more graphene was exposed to the membrane surface, which provided excellent oil/water selective wettability and anti-fouling performance. In addition, the thermally treated TNMs possessed an optimal pore structure and could separate surfactant-stabilized water-in-oil emulsions at high filtration rates (497.5 ±13.3 L·m −2 ·h −1 ) and separation efficiency (>99%). Moreover, the filtration rate and separation efficiency remained constant over 10 filtration cycles, showing that these membranes have great potential for application to practical oil/water separation processes.

Three-layered hollow fiber (HF) membrane and its modification to enhance wetting resistance for membrane distillation (MD)

A three-layered hollow fiber (HF) membrane exhibiting enhanced permeability and wet-resistance was fabricated using polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride–co-chlorotrifluoroethylene) (PVDF–CTFE) simultaneously for membrane distillation (MD). The inner, outer, and middle layers of the membrane were prepared using a macrovoid structure of PVDF–CTFE, the finger-like structure of PVDF, and thin sponge-like structure, respectively. The size of the macrovoid in the inner layer was enlarged and the permeability was enhanced using the polytetrafluoroethylenes (PTFE) as additive. However, the PTFE did not significantly change the liquid entrance pressure (LEP) of the membrane. The LEP and hydrophobicity of the inner layer of HF was increased by grafting pentafluorostyrene (PFS). The prepared membranes were characterized via several analytical tools, and the performance was evaluated using the vacuum MD (VMD) process. With 10% of PTFE, the size of the internal macrovoid increased, thus improving the flux to 137%. When PFS was grafted on the inner layer, the contact angle (CA) and liquid entry pressure (LEP) values increased to 117 and 154%, respectively, that showed an improvement in the wetting resistance. This study showed that the three-layered structure designed using the PTFE and PFS as an additive and grafting, respectively, were successfully fabricated to improve the wetting resistance and permeability.

Muscle activity and kinematics show different responses to recurrent laryngeal nerve lesion in mammal swallowing.

Understanding the interactions between neural and musculoskeletal systems is key to identifying mechanisms of functional failure. Mammalian swallowing is a complex, poorly understood motor process. Lesion of the recurrent laryngeal nerve, a sensory and motor nerve of the upper airway, results in airway protection failure (liquid entry into the airway) during swallowing through an unknown mechanism. We examined how muscle and kinematic changes after recurrent laryngeal nerve lesion relate to airway protection in eight infant pigs. We tested two hypotheses: 1) kinematics and muscle function will both change in response to lesion in swallows with and without airway protection failure, and 2) differences in both kinematics and muscle function will predict whether airway protection failure occurs in lesion and intact pigs. We recorded swallowing with high-speed videofluoroscopy and simultaneous electromyography of oropharyngeal muscles pre- and postrecurrent laryngeal nerve lesion. Lesion changed the relationship between airway protection and timing of tongue and hyoid movements. Changes in onset and duration of hyolaryngeal muscles postlesion were less associated with airway protection outcomes. The tongue and hyoid kinematics all predicted airway protection outcomes differently pre- and postlesion. Onset and duration of activity in only one infrahyoid and one suprahyoid muscle showed a change in predictive relationship pre- and postlesion. Kinematics of the tongue and hyoid more directly reflect changes in airway protections pre- and postlesion than muscle activation patterns. Identifying mechanisms of airway protection failure requires specific functional hypotheses that link neural motor outputs to muscle activation to specific movements.NEW & NOTEWORTHY Kinematic and muscle activity patterns of oropharyngeal structures used in swallowing show different patterns of response to lesion of the recurrent laryngeal nerve. Understanding how muscles act on structures to produce behavior is necessary to understand neural control.

Oropharyngeal Swallowing Dynamic Findings in People with Asthma.

Airflow obstruction in people with asthma, similar to COPD, may interfere with swallowing, increasing the risk of food or liquid entrance into the lower airways, and favoring the uncontrolled disease. To describe the complaints and findings of the oropharyngeal swallowing mechanisms in patients with mild and severe asthma, a cross-sectional study was performed. A total of 135 participants with asthma were studied, of whom 97 had severe asthma and 38 had mild asthma. All subjects answered a questionnaire with demographic information, disease exacerbations, Asthma Control Questionnaire 6 (ACQ6-Juniper 1999), GastroEsophageal Reflux Disease Symptoms Questionnaire (GERD-SQ-Fornari et al. 2004), and Eating Assessment Tool 10 (EAT-10-Gonçalves et al., 2013). The oral and pharyngeal swallowing assessment occurred via videofluoroscopic swallowing evaluation. The age range of the participants was from 19 to 80years, with a predominance of females (78.6%). Uncontrolled asthma was observed in 50 (52%) of the patients with severe asthma and in 11 (29%) of the patients with mild asthma (ACQ6 > 1.5). The GERD-SQ and EAT-10 scores were similar in both groups. In the bivariate analysis, the group with severe asthma presented with more changes when compared to the group with mild asthma in the following events: atypical lingual movement during the swallowing of liquid in the volumes of 5ml (p = 0.003) and 10ml (p = 0.001), and solid (p = 0.009); oral transit time increased in swallowing of liquid in the volumes of 5ml (p = 0.003) and 20ml (p = 0.026); beginning of the pharyngeal swallowing phase below the mandibular ramus (p = 0.003); pharyngeal residue (p = 0.017) of solid consistency; laryngeal penetration of 5ml (p = 0.050) and 20ml (p = 0.032) of liquid; increased transition time between the oral and pharyngeal swallowing phases (p = 0.035) and increased pharyngeal transit time (p = 0.045) of solid consistency. Tracheal aspiration was observed only in the group with severe asthma. After the multivariate analysis, atypical tongue movement maintained a statistically significant difference between the two groups. Oropharyngeal swallowing alternations were frequent in the studied sample and more markedly present in patients with severe asthma. Multivariate regression revealed atypical lingual movement, which was greater in patients with severe asthma. The clinical significance of these findings should be further investigated.

Optimization of nanocomposite membrane for vacuum membrane distillation (VMD) using static and continuous flow cells: Effect of nanoparticles and film thickness

In this study, the effects of incorporation of nanoparticles (NPs), including 7 nm TiO2, 200 nm TiO2, and hydrophilic and hydrophobic SiO2 with a mean diameter in the range of 15–20 nm, and their concentrations on the membrane properties and vacuum membrane distillation (VMD) performance were evaluated. The effect of membrane thickness and support materials were also investigated. The membranes were characterized extensively in terms of water contact angle, liquid entrance pressure of water (LEPw), scanning electron microscopy, surface roughness, and pore size. While the best polyvinylidene fluoride (PVDF) nanocomposite membranes with 200 nm TiO2 NPs were obtained at 2 wt% NPs concentration, the optimal NPs concentration was 5% when 7 nm TiO2 was integrated. Using a nanocomposite membrane containing 2 wt% TiO2 − 200 nm NPs, a VMD flux of 3.2 kg/m2h and a LEPw of 34 psi were obtained with 99.99% salt rejection. Furthermore, it was observed that decreasing the membrane thickness would increase the portion of the finger-like layer in the membrane and reduce the spongy-like layer when hydrophilic NPs were used. Using continuous flow VMD, a flux of 3.1 kg/m2h was obtained with neat PVDF membranes, which was higher than the flux obtained by the static VMD with the same membrane at the same temperature and vacuum pressure. The fluxes of both static and continuous flow cells VMD increased with temperature. Furthermore, it was evident that the continuous flow cell VMD at 2 L per minute yielded higher flux than the static cell VMD at any given temperature, indicating strong effects of turbulence provided in the continuous flow cell VMD.

Design of a novel PVDF-HFP/GE tubular nanofiber membranes for ultrafast and continuous oil/water separation

A novel polyvinylidene fluoride-co-hexafluoropropyle (PVDF-HFP)/graphene (GE) tubular nanofiber membrane (TNM) for application in continuous oil/water separation was firstly fabricated in this study. The obtained PVDF-HFP/GE TNMs showed outstanding mechanical properties due to the reinforcement of polyester braided tube. In addition, the effect of GE concentrations on membrane structure and performance was investigated by field-emission scanning electron microscopy, hydrophobicity, pore size and its distribution, porosity and liquid entrance pressure. The results showed that, the prepared TNMs had ideal membrane structure and performance with moderate addition of GE. When the GE concentration was 0.03 wt%, the obtained TNMs exhibited a superior selective wettability and could achieve separating surfactant- stabilized water-in-oil emulsion with a remarkable separation rate and separation efficiency.

Synergic effects of hydrophilic and hydrophobic nanoparticles on performance of nanocomposite distillation membranes: An experimental and numerical study

Abstract Supported flat sheet nanocomposite polyvinylidenefluoride (PVDF) membranes embedded with hydrophilic TiO2, hydrophobic TiO2, or the combination of them were fabricated via phase inversion process. The membranes were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, atomic force spectroscopy, and the measurement of water contact angle and liquid entry pressure of water and subjected to tests on vacuum membrane distillation (VMD) performance. Addition of appropriate amounts of either hydrophilic or hydrophobic NPs was found to enhance VMD flux but hydrophilic NPs caused significant decrease of liquid entrance pressure of water (LEPw) while hydrophobic particles did not show significant impacts on LEPw. Addition of both hydrophilic and hydrophobic NPs demonstrated synergistic effects in terms of both enhanced flux and LEPw due to their different but complimentary effects on membrane structures. At feed temperature of 27.5 °C, the VMD pure water permeate flux of the composite membrane embedded with 5 wt% hydrophilic TiO2 NPs and 2 wt% of hydrophobic TiO2 NPs (total 7 wt% NPs) was 4.26 kg/m2h with a LEPw of 28 psi, while those of neat PVDF membrane, the membrane embedded with 7 wt% of hydrophilic NP, and the membrane with 7 wt% hydrophobic nanoparticles were 0.335, 3.57, and 1.25 kg/m2 h, respectively, and the LEPw of these membranes were 51, 24 and 47 psi, respectively. It is noted that at 5 wt% addition, the flux of M-L5 (hydrophilic NPs) is 3 times higher than the M-B5 (hydrophobic NPs). Furthermore, by adding another 2 wt% of NPs, flux increment by M-L5-B2 (hydrophobic NPs) is 3.5 times higher than M-L7 (hydrophilic NPs). Therefore, in both the effects combined, the highest flux was achieved by M-L5-B2 indicating synergistic effect of hydrophilic and hydrophobic NPs on the membrane flux. The salt rejection of above 99% could be maintained for 3 h by the membrane in which both hydrophilic and hydrophobic NPs were loaded. Numerical analyses of heat and mass transfer were also carried out to study the impact of hydrophilic and hydrophobic NPs on membrane characteristics.

Study on the effects and properties of PVDF/FEP blend porous membrane

Polyvinylideneflouride (PVDF)/poly(tetrafluoroethylene-co-hexafluoropropylene) (FEP) blend flat-sheet membranes were fabricated by the immerged phase-inversion method. Micro–nanometer scale FEP particles were introduced into PVDF/N,N-dimethylacetamide (DMAc) casting solution. Effects of FEP content on the rheology behavior of casting solution and performances of PVDF/FEP blend membranes were investigated respectively. Results shown that: (1) With FEP content increasing, the viscosity of casting solution decreased while the value of non-Newtonian index n increased. When FEP content was 60wt.%, the value of n reached as high as 0.903 which demonstrated that the casting solution exhibited good Newtonian flowing property; (2) with FEP content increasing, the porosity and permeability of blend membranes increased obviously while the liquid entrance pressure (LEP) decreased. Blend membranes' cross-section morphologies shown that the increase in FEP content aided the formation of a larger and deeper finger-like pore structure; and (3) with FEP content increasing, mechanical strength of blend membranes decreased while the water contact angle increased at first then decreased.

FEP Hollow Fiber Membrane and Its Membrane Distillation Process

The influence of draw ratio on the structure and properties of poly(tetrafluoroethylene-cohexafluoropropylene)(FEP) hollow fiber membrane which was fabricated by melt-spinning stretching(MS) method was investigated in this article.The primary FEP hollow fiber membrane structure was compact while the porous structure occurs after stretching.Furthermore,the increase of membrane draw ratios induced the obvious increase of membrane porosity and the N2flux while the decrease of the liquid entrance pressure(LEP).Meanwhile,the FEP hollow fiber membrane was applied to the vacuum membrane distillation(VMD) process to compared with M-S PP hollow fiber membrane which was the commercial product.The results show that the hydrophobic properties,LEP and mechanical strength of FEP hollow fiber membrane was better than PP hollow fiber membrane.The strong and stable of hydrophobic properties enabled the FEP membrane unpenetrated,which kept the desalination rate maintain up to 99%.The larger inner diameter(about 0.74 mm) of FEP hollow fiber membrane induced the use of internal pressure VMD type which brought about the higher VMD flux when the feed temperature increased.

Multiphase modelling of liquid steel transfer from tundish to curved billet mould by open stream and equipped with SEN

The objective of the present study was to simulate liquid steel flow entry behaviour into a curved billet mould when supplied by an open stream or using a submerged entry nozzle (SEN). For the SEN modelling, nozzle misalignments were considered to determine its effects on the mould flow dynamics. A three-dimensional numerical model in a Cartesian coordinate system was used. For spatial discretisation, a structured mesh was used. For the open stream, two phases (steel–air) were considered in order to study the free surface behaviour. Owing to extreme turbulence, this configuration is useful only for low quality steels. This can be eliminated using a SEN. When the SEN was employed, a multiphase system was also considered (steel–slag–air) to study the free surface stability. However, despite using an aligned SEN, non-symmetric flows are generated, which can be controlled with an appropriated inclination towards the inner radius.

Design and Implementation of Differential Agitators to Maximize Agitating Performance

This research is to design and implement a new kind of agitators called differential agitator. The Differential Agitator is an electro- mechanic set consists of two shafts. The first shaft is the bearing axis while the second shaft is the axis of the quartet upper bearing impellers group and the triple lower group which are called as agitating group. The agitating group is located inside a cylindrical container equipped especially to contain square directors for the liquid entrance and square directors called fixing group for the liquid exit. The fixing group is installed containing the agitating group inside any tank whether from upper or lower position. The agitating process occurs through the agitating group bearing causing a lower pressure over the upper group leading to withdrawing the liquid from the square directors of the liquid entering and consequently the liquid moves to the denser place under the quartet upper group. Then, the liquid moves to the so high pressure area under the agitating group causing the liquid to exit from the square directors in the bottom of the container. For improving efficiency, parametric study and shape optimization has been carried out. A numerical analysis, manufacturing and laboratory experiments were conducted to design and implement the differential agitator. Knowing the material prosperities and the loading conditions, the FEM using ANSYS11 was used to get the optimum design of the geometrical parameters of the differential agitator elements while the experimental test was performed to validate the advantages of the differential agitators to give a high agitation performance of lime in the water as an example. In addition, the experimental work has been done to express the internal container shape in the agitation efficiency. The study ended up with conclusions to maximize agitator performance and optimize the geometrical parameters to be used for manufacturing the differential agitator.

Neutron phase volumetry and temperature observations in an oscillating heat pipe

An experimental investigation on a water filled 6-turn oscillating heat pipe (OHP) was conducted using neutron imaging. Using the neutron images, a method was developed to determine the volume fraction of liquid phase in different portions of the OHP while in operation. The results show that the volume fraction of liquid phase is highly nonuniform once the thermally excited fluid motion starts. Over the heat input range studied, during the steady state oscillating motion in an OHP, the volume fraction distribution of liquid phase was always less than 2.5% in the evaporator and greater than 80% in the condenser. Using this method, the startup behavior, pulsing and pause motions, circulation, and the relationship between the pulsing motion and circulation and temperature variations in the OHP were all determined as well. There is a notable synchronization between the entrance of liquid into the evaporator portion of the heat pipe and temperature oscillations.

Firefighter Burn Injuries

Approximately 100 firefighters suffer fatal injuries annually and tens of thousands receive nonfatal injuries. Many of these injuries require medical attention and restricted activity but may be preventable. This study was designed to elucidate etiology, circumstances, and patterns of firefighter burn injury so that further prevention strategies can be designed. In particular, modification of protective equipment, or turnout gear, is one potential strategy to prevent burn injury. An Institutional Review Board-approved retrospective review was conducted with records of firefighters treated for burn injury from 2005 to 2009. Data collected included age, gender, TBSA, burn depth, anatomic location, total hospital days per patient, etiology, and circumstances of injury. Circumstances of injury were stratified into the following categories: removal/dislodging of equipment, failure of equipment to protect, training errors, and when excessive external temperatures caused patient sweat to boil under the gear. Over the 4-year period, 20 firefighters were treated for burn injury. Mean age was 38.9 ± 8.9 years and 19 of 20 patients were male. Mean burn size was 1.1 ± 2.7% TBSA. Eighteen patients suffered second-degree burns, while two patients suffered first-degree burns. Mean length of hospitalization was 2.45 days. Scald burns were responsible for injury to 13 firefighters (65%). Flame burns caused injury to four patients (20%). Only three patients received contact burns (15%). The face was the site most commonly burned, representing 29% of injuries. The hand/wrist and ears were the next largest groups, with 23 and 16% of the injuries, respectively. Other areas burned included the neck (10%), arm (6.5%), leg (6.5%), knees (3%), shoulders (3%), and head (3%). Finally, the circumstance of injury was evaluated for each patient. Misuse and noncontiguous areas of protective equipment accounted for 14 of the 20 injuries (70%). These burns were caused when hot steam/liquid entered the gear via gaps in the sleeve or face mask. Three patients (15%) received injury due to removal/dislodging of their safety equipment, two patients (10%) suffered their injuries during training exercises when they were not wearing their safety equipment, and the final patient (5%) received burns due to sweat evaporation. Firefighter burn injuries occur to predictable anatomic sites with common injury patterns. Modification and optimization of gear to eliminate gaps that allow steam/hot liquid entry may decrease burn injury. Improving education regarding the use of protective equipment may also be beneficial.

Counter-current gas–liquid flow in a vertical narrow channel—Liquid film characteristics and flooding phenomena

Results are reported of an experimental investigation of gas–liquid counter-current flow in a vertical rectangular channel with 10 mm gap, at rather short distances from liquid entry. Flooding experiments are carried out using air and various liquids (i.e., water, 1.5% and 2.5% aqueous butanol solutions) at liquid Reynolds numbers Re L < 350. Visual observations and fast recordings suggest that the onset of flooding at low Re L (<250) is associated with liquid entrainment from isolated waves, whereas “local bridging” is dominant at the higher Re L examined in this study. Significant reduction of flooding velocities is observed with decreasing interfacial tension, as expected. Instantaneous film thickness measurements show that under conditions approaching flooding, a sharp increase of the mean film thickness, of mean wave amplitude and of the corresponding RMS values takes place. Film thickness power spectra provide evidence that by increasing gas flow the wave structure is significantly affected; e.g., the dominant wave frequency is drastically reduced. These data are complemented by similar statistical information from instantaneous wall shear stress measurements made with an electrochemical technique. Power spectra of film thickness and of shear stress display similarities indicative of the strong effect of waves on wall stress; additional evidence of the drastic changes in the liquid flow field near the wall due to the imposed gas flow, even at conditions below flooding, is provided by the RMS values of the wall stress. A simple model is presented for predicting the mean film thickness and mean wall shear stress under counter-current gas–liquid flow, below critical flooding velocities.

Experiments on Heat Transfer in a Thin Liquid Film Flowing Over a Rotating Disk

An experimental study of heat transfer into a thin liquid film on a rotating heated disk is described. Deionized water was introduced at the center of a heated, horizontal disk with a constant film thickness and uniform radial velocity. Radial distribution of the disk surface temperatures was measured using a thermocouple/slip ring arrangement. Experiments were performed for a range of liquid flow rates between 3.0 lpm and 15.0 lpm. The angular speed of the disk was varied from 0 rpm to 500 rpm. The local heat transfer coefficient was determined based on the heat flux supplied to the disk and the temperature difference between the measured disk surface temperature and the liquid entrance temperature onto the disk. The local heat transfer coefficient was seen to increase with increasing flow rate as well as increasing angular velocity of the disk. Effect of rotation on heat transfer was largest for the lower liquid flow rates with the effect gradually decreasing with increasing liquid flow rates. Semi-empirical correlations are presented in this study for the local and average Nusselt numbers.

Fluid motion through an unsaturated fracture junction

Fluid dynamics in unsaturated fracture intersections were experimentally investigated in a glass fracture‐analog at four different flow rates and compared with theoretical behavior estimates. The experimental system consisted of a vertical fracture that divided into two fracture branches. Visual data of fluid behavior were collected using digital stills and video. Two flow modes were analyzed: film flow and capillary droplets accompanied by snapping rivulets. Even under almost ideal experimental conditions, fluid dynamics at the intersection were extremely complicated and strongly influenced by flow mode, dynamics in the main fracture, contact angle of the advancing meniscus, and the presence of a capillary barrier at the intersection. Film flow moved into one or both branches through a capillary bridge that formed above the intersection. In droplet mode, rivulets reached lengths of up to 70 cm prior to snapping, and often stretched contiguously across the intersection and into both branches while maintaining its connection to the two droplet halves. Transition from droplet to film flow mode was observed at the intersection. There was a strong correlation between the length of the incoming droplet and the potential for a switch to occur. Liquid bridges were observed to form occasionally at the entrance of a fracture branch, which blocked further liquid entry. The temporal nature of these blockages further complicates temporal and spatial variability observed in flow in fracture systems.

Development of counter-current flow limitation model applicable to a sharp-edged liquid entrance

There are many industrial machines that function by operation of multi-phase fluids. Some of them take advantage of the characteristics of counter-current two-phase flow. The maximum flow rates of gas and liquid phases which flow in opposite-directions (counter-current flow) are limited by a phenomenon known as a Counter-Current Flow Limitation (CCFL or flooding). The mass and momentum conservation equations for two phases were established to build a system of first-order partial derivative equations (PDE). A new CCFL model was developed based on the characteristic equation of the first-order PDE system. The present model applies to the case in which a non-uniform flow is developed around a square or sharp-edged entrance of liquid phase. The model can be used to predict the operating-limit of components in which mass and heat transfer are taking place between liquid and gas phases.

Visual observations of flooding in narrow rectangular channels

New flooding data in a vertical rectangular channel with 5 and 10 mm gap between its main parallel plates are reported. Visual observations and fast recordings are made to determine conditions associated with the onset of flooding in the channel. For the 10 mm gap channel a combination of mechanisms, i.e., levitation and upward transportation of laterally coherent or isolated waves, and local wave bridging, appear to be responsible for triggering flooding. The critical flooding velocity is curiously nearly independent of liquid flow rate above film Reynolds number approximately 500. In the 5 mm gap channel and for small Re L, flooding occurs at the liquid entrance, whereas “massive” wave bridging, occurring above the middle of the test section, is the dominant flooding mechanism for relatively higher Re L. Predictions based on small amplitude stability analysis are in good agreement with flooding data from the latter case.

Experimental study of the effect of pipe length and pipe-end geometry on flooding

The onset of flooding is thought to be highly sensitive to the end geometry of the test channel and its high sensitivity is an important cause of data scattering. In the present work, the effect of end geometry on flooding is experimentally investigated. Observation shows that flooding definition also causes the data scattering and that flooding should be classified into two modes according to the location where it occurs. With the sharp liquid entrance geometry, both entrance flooding and exit flooding are able to take place while only exit flooding does when entrance is smooth. In the range of low liquid flow rates, exit flooding always takes place and flooding gas velocities for the same exit geometry are nearly the same regardless of liquid entrance geometry. When air is injected into the test tube through a nozzle, even if the liquid exit is sharp, flooding gas velocities are nearly the same as those with smooth exit geometry. The present experiments show that the length effect is significantly affected by the pipe-end geometry. It is small in the range of low liquid flow rates but becomes significant as the liquid flow rate increases.