Liquid Velocity Research Articles

Comparative Study of Air–Water and Air–Oil Frictional Pressure Drops in Horizontal Pipe Flow

Experimental data for frictional pressure drop using both air–water and air–oil mixtures are reported, compared and used to evaluate predictive methods. The data were gathered using the 2-inch (54.8 mm) flow loop of the multiphase flow facility at the National University of Singapore. Experiments were carried out over a wide range of flow conditions of superficial liquid and gas velocities that were varied from 0.05 to 1.5 m/s and 2 to 23 m/s, respectively. Pressure drops were measured using pressure transducers and a differential pressure (DP) cell. A hitherto unreported finding was achieved, as the pressure drop in air–oil flow can be lower than that in air–water flow for the higher range of flow conditions. Using flow visualization to explain this phenomenon, it was found that it is related to the higher liquid holdup that occurs in the case of air–oil around the annular flow transition and the resulting interfacial friction. This additional key finding can have applications in flow assurance to improve the efficiency of oil and gas transportation in pipelines. Models and correlations from the open literature were tested against the present data.

Experimental heat transfer analysis of the effects of thermophysical properties on PCM at freezing conditions employing Particle Image Velocimetry

Cold chain logistics of fresh produce distribution are facing new challenges owing to the increasing consumer demand, often traveling long distances, and facing temperature variations during storage and distribution stages. Nowadays, solutions for improving food preservation by searching effective energy storage strategies, such as the use of PCM, are capturing more interest. Nevertheless, most studies are focused on organic PCM with ambient temperature melting points analyses. This leaves an important research gap in the experimentation of other types of eutectic materials with melting points below 0 °C, something of great interest for food preservation in the refrigeration industry. Velocity vector field and heat transfer via natural convection in a small cavity filled with two different PCM at below 0 °C conditions were experimentally investigated employing temperature measurements and Particle Image Velocimetry. In this regard, brine (18.8 wt%) and ethylene glycol-water (EGW) blend (30.5 wt%) PCM with equal melting temperature, but different thermophysical properties, were selected to compare their thermal behavior. It was investigated the effects of thermophysical properties such as density, specific heat capacity, thermal conductivity, and viscosity on melting front, heat transfer and flow patterns through the evaluation of liquid fraction, heat storage, Nu, Gr, Ra, and velocity field. The maximum Nu value for brine was almost the double of that of EGW. Pr values of EGW were in average 1.88 times higher than those of brine. Besides, Gr and Ra values of brine were in average 7.23 and 3.97 higher than those of EGW, respectively.

Interfacial heat transfer and melt-front evolution at a Fractal Cantor structured interface under various PCM melting conditions

With the aim to investigate heat transfer characteristics of PCM on micro-textured hot surface, this study numerically investigates the heat transfer process of PCM at fractal Cantor structured surfaces using the total enthalpy-based lattice Boltzmann method, which is partly validated by experimental testing. The thermal slip length and liquid velocity distribution are assessed as evaluation criteria. Results show that Fractal Cantor structure can significantly stimulate localized thermal convection, thereby reducing the average thermal slip length from 0.3 mm to approximately 0.14 mm. When the Fourier number exceeds 0.1, both thermal conduction and convection should be considered within the melted layer. With the fractal level increasing, a more uniform melt-front evolution can be observed, consequently, minimizing the total melting time by 500 s with the fractal level of 3. Elevating Ste and gravity can significantly increase the flow rate of liquid PCM by augmenting superheat degree and buoyancy effect, thereby enhancing convective heat transfer strength and reducing thermal slip length. According to the orthogonal design, though the fractal level demonstrates minimal range values for both maximum velocity and Rayleigh number, it elevates the sensitivity to the variation of boundary conditions. Ste yields the most significant enhancement in heat transfer performance.

INVESTIGATION OF THE TRANSFORMATION OF MODEL PETROLEUM RAW MATERIALS UNDER CRACKING CONDITIONS OVER A REGENERATED SPENT HYDROTREATMENT CATALYST

The physicochemical properties and catalytic activity of regenerated spent aluminium-cobalt-molybdenum hydrotreatment catalyst have been investigated under cracking conditions in the model systems n-dodecane - toluene and decalin - toluene - n-hexane. A series of experiments to study the catalytic activity of the sample was carried out using a flow-type laboratory installation within the temperature range 430-470 °C, nitrogen pressure 1.6 MPa, liquid hourly space velocity 0.5-3.0 h-1. The directions of transformation were determined for paraffin and naphthenic hydrocarbons by means of gas chromatography - mass spectrometry. Paraffin hydrocarbons enter into cracking, isomerisation and compaction reactions. Naphthenic hydrocarbons are transformed into the products of isomerisation, dehydrogenation and compaction. Predominant dehydrogenation of decalin with the formation of naphthalene and hydrogen is observed in the system under investigation. A positive role of hydrogen in thermodestructive processing of heavy oil residues is observed due to the hydrogenation of nonlinear olefin hydrocarbons and aromatic hydrocarbon intermediates, which decreases the rate of coke formation. The corresponding reaction rate constants were calculated, and the results were analysed. Conclusions are drawn about the prospects of introducing a regenerated spent hydrotreatment catalyst into the procedure of thermodestructive processing of heavy oil residues.

Design and performance optimization of diesel engine waste heat recovery methanol reforming hydrogen generation system

Abstract A shell-and-tube Methanol Steam Reformer (MSR) system was designed for diesel engines. The effects of structural and operational parameters of the spiral baffles in the methanol reformer on heat transfer and hydrogen production performance were investigated. Additionally, a multi-objective optimization using response surface methodology was conducted to study the interactive effects of spacing and thickness, as well as liquid hourly space velocity and steam–methanol ratio, on the methanol conversion rate, hydrogen concentration and hydrogen production. The results indicated that reducing the baffle spacing and increasing the baffle thickness further improved heat transfer efficiency. Optimal conditions were achieved at a spacing of 30 mm and a thickness of 2 mm, resulting in a methanol conversion rate of 64.2 %. Increasing the steam–methanol ratio from 0.5 to 2 increased the methanol conversion rate from 50.6 % to 79.7 %, with a subsequent decrease in hydrogen concentration. Increasing the liquid hourly space velocity from 635 h−1 to 1905 h−1 significantly reduced the methanol conversion rate from 94.5 % to 64.2 %, but the hydrogen production increased from 0.111 mol/s to 0.228 mol/s. Optimization results indicate that the liquid hourly space velocity and steam–methanol ratio have a greater influence on the hydrogen production efficiency of the methanol reformer.

Bubble oscillations at low frequency ultrasound for biological applications

Bubbles oscillating in the presence of ultrasound is commonly employed in biomedical applications for drug delivery, ultrasound enhanced thrombolysis, and the transport and manipulation of cells. This is possible because bubbles tend to interact with the ultrasound to undergo periodic shape changes known as shape-mode oscillation, concomitant with the generation of liquid agitation or streaming. This phenomenon is examined both experimentally and theoretically on a single bubble at a frequency of (45 ± 1) kHz. Effects of ultrasonic frequency and power on the flowfield were explored. Experiments revealed different trends in the development of liquid streaming velocities at different acoustic forcing conditions (5.53, 6.80 and 7.02 Vpp), with lowest (0.5 mm/s) and highest (1.1 mm/s) values of time-averaged mean streaming velocity occurring at 6.80 Vpp and 7.02 Vpp, respectively. Simulations captured the simultaneous evolution of bubble-shapes that helped create flow vortices in the liquid surrounding the bubble. These vortices collectively responsible in generating signature patterns in the liquid for a dominant shape-mode of the bubble, and could also generate localised shear stresses for practical application. The velocity and pressure profiles in the liquid around the bubble confirmed the connection of the applied and reflected soundwaves in driving this phenomenon.

Design and optimizing the liquid distributor of a rotating packed bed by the analysis of liquid flow behavior

Rotating packed beds (RPBs) have been widely applied in multiphase systems. When handling some extreme operating condition systems, finding a suitable pump to provide pressure to force the feeding liquid to be evenly distributed by the distributor of the RPB is very costly. In this work, we designed new liquid distributors by using the kinetic energy of the rotating shaft as driving force to obtain uniform distribution. The performance of the liquid distribution has been investigated in terms of liquid flow behavior, liquid velocity, and impacting angle (α). Compared with bar and cantboard distributors, the radlamelle liquid distributor had the best distribution performance. By further optimization of the radlamelle structure, the left-hand wheel had better dispersion performance with α varying from 24.3 to 79.1°. This new liquid distributor without pump pressure expands the applications of the RPB in ultra-low or high temperature and high pressure operating conditions.

Global dynamics and topology of two-phase mixing layer flow through simultaneous gas and liquid velocity measurements

This study reports the first time-resolved particle image velocimetry characterization of a planar two-phase mixing layer flow, whose velocity field is measured simultaneously in gas and liquid streams. Two parallel air and water flows meet downstream of a splitter plate, giving rise to an initially spanwise invariant configuration. The aim is to elucidate further the mechanisms leading to the flow breakup in gas-assisted atomization. The complete experimental characterization of the velocity field represents a database that could be used in data-driven reduced-order models to investigate the global behaviour of the flow system. After the analysis of a selected reference case, a parametric study of the flow behaviour is performed by varying the liquid ( $Re_l$ ) and gas ( $Re_g$ ) Reynolds numbers, and as a consequence also the gas-to-liquid dynamic pressure ratio ( $M$ ), shedding light on both time-averaged (mean) and unsteady velocity fields. In the reference case, it is shown that the mean flow exhibits a wake region just downstream of the splitter plate, followed by the development of a mixing layer. By increasing both $Re_l$ and $Re_g$ , the streamwise extent of the wake decreases and eventually vanishes, the flow resulting in a pure mixing layer regime. The spectral analysis of the normal-to-flow velocity fluctuations outlines different flow regimes by variation of the governing parameters, giving more insights into the global characteristics of the flow field. As a major result, it is found that at high $Re_g$ and $M$ values, the velocity fluctuations are characterized by low-frequency temporal oscillations synchronized in several locations within the flow field, which suggest the presence of a global mode of instability. The proper orthogonal decomposition of velocity fluctuations, performed in both gas and liquid phases, reveals finally that the synchronized oscillations are associated with a low-frequency dominant flapping mode of the gas–liquid interface. Higher-order modes correspond to interfacial wave structures travelling with the so-called Dimotakis velocity. For lower gas Reynolds numbers, the leading modes describe higher frequency fingers shedding at the interface.

An experimental and simulation study on the velocity distribution of the falling film on a horizontal tube in jet mode

The velocity characteristics of falling film on horizontal tube affect the heat transfer efficiency. To date, experimental studies on velocity distribution of liquid film on tube surface are very scarce. In this paper, the mean velocity of liquid film is measured using particle tracking velocimetry (PTV). A simulation is also conducted to investigate the flow characteristics of falling film. Results show that the spreading of liquid film undergoes two stages: circular spreading and circumferential flow. In circumferential direction, the liquid film tangential velocity shows different law in planes of L* = 0–0.3 and L* = 0.4/0.5. The tangential velocity decreases and then increases as axial distance increases. Simulation results agree well with the experimental results within experimental angle range. The liquid film axial velocity is always zero at L* = 0. When L* = 0.1–0.5, the axial velocity decreases as circumferential angle increases and gradually tends toward zero.

Hydrodynamics and mass transfer performance of microbubble flow in the bubble column with a contraction section

Bubble columns have many applications in the biochemical, petrochemical, and metallurgical industries. The gas-liquid system composed of microbubbles is characterized by significant phase interfacial area, high mass transfer efficiency, fast dissolution rate, strong adsorption capacity, and long self-sustaining time. This paper investigated the performance of pressurized dissolved gas microbubble generation (PDG) using a Venturi tube as the releaser using a plug-in online imaging instrument. The hydrodynamic and mass transfer characteristics of the microbubble flow generated by PDG in a bubbling column with a contraction section (BCS) were then investigated. One of the primary studies was the effect of the contraction section on the flow performance of the bubbles, the mass transfer performance, and the aeration efficiency of the PDG versus the throat inlet Venturi bubble generator (VBG). The results show that the initial bubble Sauter mean diameter is essentially constant with dissolved gas pressure, and the bubble size distribution(BSD) is similar. The bubble stream passing through the contraction section exhibits two different BSD at the center and side walls of the BCS outlet section. Microbubbles in the inlet section in the absence of external forces almost do not occur in bubble coalescence. The flow of bubbles in the contraction section is subject to a slight coalescence effect. The diameter of bubbles in the contraction section is mainly larger than 20 μm. In the contraction section, coalescence occurs mainly at the side wall. The way of occurrence is adsorption coalescence and collision coalescence. The bubbles move in a gradually confined space with a high degree of interference with each other's bubbles, and the liquid linear velocity acts as an ‘external force’ that benefits the flow of the bubbles out of the confined space. The standard aeration efficiency of PDG is 3–11 times higher than that of the VBG. At 0.3 MPa, the highest standard aeration efficiency for the PDG method was between 0.18 and 0.64 kgO2/kW∙h.

Experimental study on leakage characteristics of gas-liquid two-phase flow in a horizontal pipe

Oil and gas pipeline leakage accidents caused by aging and third-party damage have increased, resulting in polluting the ecological environment and jeopardizing life and property safety. A detailed and systematic investigation on the leak characteristics of oil and gas two-phase pipelines is significantly urgent. The leak experiments were performed on a horizontal tube with a diameter of 32 mm. There was a 3 mm round leakage hole at the bottom of the tube. The distance of the leakage hole from the pipe inlet was 4.8 m. Three inlet flow patterns, including stratified flow, slug flow, and annular flow via adjusting the gas superficial velocity (1.73 m/s ≤ USG ≤ 24.19 m/s) and liquid superficial velocity (0.017 m/s ≤ USL ≤ 0.415 m/s), were obtained. The conclusions point out that the type of leakage, whether it is mainly liquid or both gas and liquid, depends on the USG. The degree of phase separation in stratified flow is the greatest among the three inlet flow patterns, with a maximal phase separation efficiency (η) of 0.403. Slug flow has the least phase separation degree. Interestingly, the η is directly proportional to the inlet mass fraction only for slug flow. The harmonic frequency that appeared in the power spectral density curves for the pressure difference of leakage hole in slug flow, indicates that leakage is not a standard periodic event. The liquid velocity loss is primarily related to the gas leakage mechanism. These findings can provide new insights into two-phase pipeline leak detection and accident consequence prediction.

Purification of lipid oil using ion exchange resins

AbstractOil upgrading technologies for fuel production from second-generation feedstocks require pretreatments, such as the removal of ash metals in crude oil, to improve the catalytic performance in the process. The aim of this work was to purify lipid crude oil, derived from black soldier fly larvae (BSFL), from calcium by dry washing using ion exchange resins. Commercially available ion exchange resins suitable for organic liquids, namely GF 202 and Amberlyst 15DRY (AL 15), were selected for the purification experiments. The lipid material dissolved in nonanoic acid in different concentrations of mixtures was passed through a resin-filled plug-flow reactor at 50 °C and 75 °C with a liquid hourly space velocity (LHSV) of 4 h−1. The oil samples were analyzed for calcium using inductively coupled plasma-optical emission spectrometry, while the resin surfaces were examined by scanning electron microscopy. AL 15 showed a better overall performance and led to a case where over 99% of calcium was removed. Graphical abstract

Soft measurement model for wet gas flow rate based on ultrasonic and differential pressure sensing

Non-separation measurement of gas–liquid two-phase flow is of great significance to industrial production and theoretical research on two-phase flow. In this paper, a soft measurement method of wet gas flow rate based on ultrasonic and differential pressure (DP) sensors is proposed. A total of 129 sets of experimental data are obtained in DN50 horizontal pipe, the superficial velocity of gas and liquid ranging from 5 m s−1 to 33 m s−1 and 0.015 m s−1 to 0.6 m s−1, respectively. Ten feature parameters of ultrasonic signals such as the time difference between two echoes and kurtosis factor are proposed from time and frequency domain. As well as the power spectral density, mean value and standard deviation value are analyzed based on DP signals. Furthermore, the Spearman correlation coefficient is introduced to evaluate these feature parameters quantitatively. And nine parameters which are highly correlated to gas–liquid flow rate are selected as the inputs of the soft measurement model. Finally, Decision Tree, least square support vector machines and artificial neural network (ANN) models are established through training with the experimental data. Comparison results show that ANN has the lowest prediction errors on the test set, with the mean absolute percentage errors of 1.49% and 3.2% for gas and liquid, respectively.

Intensification of a microbial electrolysis cell for biohydrogen production

Hydrogen can be the fuel of the future, and there are multiple approaches for its production and storage. Most hydrogen production comes from non-renewable sources, primarily natural gas reforming, which is efficient but unsustainable. Microbial electrolysis cells (MEC) are alternative developing technologies that exploit conductor-like properties of electrogenic bacteria to both oxidize organic contaminants and get protons reduced in a cathode, thus producing hydrogen. Here, the aim is to design a model-based optimization framework to intensify the MEC efficiency. The constructed process model is proposed by considering transport phenomena, microbial kinetics, and a secondary current distribution model to estimate steady-state reactor performance and electrical efficiency. The results show a value of 25 % for electrical efficiency as hydrogen recovered. Global sensitivity analysis was performed and determined a strong dependency on inlet liquid velocity, and a built-in, gradient-free optimization algorithm was implemented to the model to maximize electrical efficiency under a defined range of inlet liquid velocity, inlet substrate concentration, and applied voltage. The proposed model predicts a maximum increase of efficiency of about 267 % by increasing inlet velocity and substrate concentration. Intensification of the cell's performance can be greatly achieved when halving hydraulic retention time and by having a more concentrated feed.

A novel recurrence-based approach for investigating multiphase flow dynamics in bubble column reactors.

In chemical industries, multiphase flows in a bubble column reactor are frequently observed. The nonlinearity associated with bubble hydrodynamics, such as bubble-bubble and bubble-liquid interactions, gives rise to complex spatiotemporal patterns with increased gas or liquid velocities, which are extremely difficult to model and predict. In the current study, we propose a new, computationally efficient recurrence-based approach involving the angular separation between suitably defined state vectors and implement it on the experimental multiphase flow variables. The experimental dataset that consists of image frames obtained using a high-speed imaging system is generated by varying air and water flow rates in a bubble column reactor setup. The recurrence plots using the new approach are compared with those derived from conventional recurrence, considering standard benchmark problems. Further, using the recurrence plots and recurrence quantification from the new recurrence methodology, we discover a transition from a high recurrence state to a complex regime with very low recurrence for an increase in airflow rate. Determinism exhibits a rise for the decrease in airflow rate. A sharp decline in determinism and laminarity, signifying the quick shift to complex dynamics, is more prominent for spatial recurrence than temporal recurrence, indicating that the rise in airflow rate significantly impacts the spatial location of bubbles. We identify three regimes that appeared as distinct clusters in the determinism-laminarity plane. The bubbly regime, characterized by high values of determinism and laminarity, is separated by an intermediate regime from the slug flow regime, which has low determinism and laminarity.

New correlation of the subcooled flow boiling heat transfer coefficient for hybrid micro/nanostructured surfaces with high heat flux incidence

Surfaces manipulated with micro/nanostructures have great potential for imparting high heat removal capacity to heat transfer equipment under high heat flux incidence. However, few correlations of heat transfer coefficients have been developed based on high-heat flux experiments of subcooled flow boiling with nano- and microstructured surfaces, which may limit the further application of this technique in industrial engineering. Aiming at recently developed hybrid micro/nanostructured surfaces for subcooled flow boiling performance enhancement, a series of experiments with different surface structure scale specifications, flow conditions, and heat flux incidence ranges were conducted. In total, 530 experimental data points were obtained with heat fluxes ranging from 3.4 to 13.1 MW/m2, pressures from 0.5 to 1.5 MPa, liquid velocities from 1 to 5 m/s, inlet temperatures from 303.15 to 323.15 K, and structured surfaces with wire apertures of 250, 125, and 58 μm. The 28 existing correlations based on smooth surfaces and structured surfaces failed to predict these experimental data. A new enhancement factor-type correlation model, which included four dimensionless numbers that specialized in the effects of the span dimension and depth dimension of the target hybrid micro/nanostructured surfaces, was developed and shown to have good prediction accuracy and a considerable degree of application adaptability, with a mean absolute deviation of 5.7%.

Impact of ion-specific interactions on laser-induced liquid microjet generation

Jet velocity and jet power are the crucial parameters that govern the release profile of drugs/vaccines in needle-free injection systems, where salts are considered as one of the essential constituents of drugs/vaccines as adjuvants. However, the impact of salts on the generation of laser-induced liquid microjets that have shown tremendous potential for drug delivery has remained unexplored. Here, we have investigated the influence of Hofmeister ions on the velocity of laser-induced liquid jets in rhodamine 6G (Rh6G) dye solution. A comprehensive experimental approach is adopted to find out the values of the liquid microjet velocity by varying the parameters, such as input energy of the laser beam, concentrations of the dye, and specific Hofmeister ions in the aqueous solution. From our experimental findings, it is observed that the presence of ions significantly influences the jet velocity that follows the Hofmeister series: SO42−>I−>SCN−. This, in turn, governs the ion-specific penetration depth of liquid jets as simulated for the model soft tissues. The observed Hofmeister trend in the jet velocity values showcases the possible specific-ion interactions between anions and Rh6G molecules in the aqueous solution. Our detailed experimental findings on ion-specific jet velocity and jet power could be beneficial in designing needle-free drug delivery systems with controlled penetration depths.

Dynamic behaviors of a bubble near a rectangular wall with a bulge

In this paper, the cavitation bubble dynamics near a rectangular wall with a bulge are theoretically investigated. High-speed photography is employed to provide experimental verification of the theoretical results. Through a series of conformal transformations and the image method, the analytical description of how this complex wall configuration affects the bubble is shown to be equivalent to the superposition of eight virtual bubbles. The physical meaning of the eight virtual bubbles can be divided into four groups, corresponding to the influence of the left wall, the bottom wall, the angle formed by the two flat walls, and the bulge. The influence of the bulge on the liquid velocity distribution, as well as the intensity and direction of the Kelvin impulse exerted on the bubble, is explored for cases in which the bubble is located at symmetric and asymmetric positions. The main findings are given as follows: During the bubble collapse, a high-velocity area of the liquid exists to the side of the bubble farthest from the bulge, and three stagnation points with three low-velocity areas appear on the bulge surface. The bulge mainly influences the impulse intensity when the bubble is located near the symmetric position. The existence of the bulge causes the impulse angle to attain a minimum as the distance between the bubble and the bulge increases. For a larger bulge radius, the changes in the impulse angle become more complicated as the bubble position angle increases.

Theoretical and experimental investigation of a bubble collapsing near an asymmetric hydrofoil

In the present paper, the restricted cavitation bubble dynamics near an asymmetric Joukowsky hydrofoil are investigated theoretically and experimentally. This investigation employs the conformal transformation, the image method, and the Kelvin impulse model, together with high-speed photographic experiments. The characteristics of bubble collapse deformation and bubble wall movement are analyzed qualitatively and quantitatively, and the spatial distributions of the liquid velocity and Kelvin impulse are revealed by theoretical predictions. The main conclusions include (1) the bubble collapse deformations can be divided into three typical cases: penetrating deformation (mostly occurs when γ<2 with γ defined as the bubble-hydrofoil dimensionless distance), triangular depression (mostly occurs when 2<γ<4), and arc-shaped depression (mostly occurs when γ>4). (2) The impulse acting on the bubble is governed by a point source and a point sink, which is dominant, and the impulse is inversely correlated with the bubble-hydrofoil distance, which corresponds to the experimental results. (3) The Kelvin impulse exhibits different distributions at the tail, head, and middle regions of the hydrofoil, and the impulse angle remains basically unchanged in the concave region of the asymmetric hydrofoils (i.e., the range of 240°<θz<350° with θz defined as the bubble position angle).

On the Macrosegregation of Continuous Casting of High Carbon Steel Billet with Strand Reduction Process

A mathematical model of the macrosegregation of continuous cast high carbon steel billet was developed based upon a representative volume element, considering the flow of enriched liquid, solidification rate, and solidification shrinkage as well. It was found that a lower casting velocity, higher cooling intensity, and shorter solidification interval positively contributed to the inhibition of macrosegregation in a continuously cast billet when a mechanical reduction process was not applied. A numerical expression for the relative flow velocity of liquid was further proposed incorporating such aspects as casting velocity, densities of different phases, and the variation of cross section areas as well. The analysis based on this numerical expression indicated that the overall effect of the reduction process on the macrosegregation of billets depended not only on the reduction zone but also on the reduction amount and its distribution for the active reduction rolls. The test results of further practical plant trials demonstrated a reasonable agreement with the predictions obtained from the proposed numerical model, indicating the reliability of this analysis model to be employed for the continuous casting of high carbon steel billet with strand reduction process.