Investigation Of Two-phase Flow Research Articles

Influence of Diffusion Angle on Sediment Concentration in Front Inflow Forebay of Pumping Station

Abstract The numerical simulation and field investigation of solid-liquid two-phase flow are carried out in a large-scale forward intake forebay with various diffusion angles at the Jingtaichuan Pumping Irrigation Project in Gansu Province, China. The purpose is to investigate the properties of sediment deposition in the pumping station forebay. The results indicate that the low-sediment concentration area is in the forebay’s centre, whereas the high-sediment is near the two side walls flanks. The sediment concentration increases dramatically from the centre to the sides. Both the high-sediment concentration area and the sediment concentration increase with water depth. The forebay’s narrowing diffusion angle causes the high-concentration area to gradually decrease while the low-concentration area gradually increase. Furthermore, the amount of siltation and sediment deposition efficiency decrease, resulting in a large increase in forebay sediment concentration and sedimentation efficiency. The sediment concentration and water flow velocity reveal a quadratic polynomial relationship. This study can provide a guide and reference for the design and construction of comparable large-scale pumping station forebays.

Film investigation of swirl-vane separator based on Euler grid approximation and coupled film method of Eulerian wall film and volume of fraction method

The movement of multiple liquid droplets within steam flow constitutes a commonplace and noteworthy phenomenon across a spectrum of disciplines, including environmental science, chemical engineering, and energy studies. To simulate the dynamic behavior of these droplets, the methodology of Euler grid approximation, along with the Eulerian wall film (EWF) coupled with the volume-of-fluid (VOF) method, was successfully employed to simulate the steam-liquid separation and liquid film processes within the swirl-vane separator. The trajectory of droplets within the gas phase field was constructed using the Euler grid approximation methodology, while the flow of liquid film formed by droplet–wall collision was modeled based on the coupled EWF and VOF liquid film model. The investigation of two-phase flow and liquid film flow within the swirl-vane separator under high temperature and pressure conditions was conducted utilizing the proposed model, with subsequent analysis of the pertinent characteristics of droplets and liquid film. Specifically, the thickness and velocity of the liquid film significantly increased with the increase in droplet mass flow rate, with larger droplets more prone to concentrate and form stable flow of thick liquid film. The study results may hold significant implications for the design, operation, and optimization of separators.

Energy expenditure in the Z-type plate heat and mass exchanger based on the concept of heat-integrated distillation column

Thermal separation of substances typically involves the use of rectification columns equipped with condensers and reboilers. This conventional method is notably energy-intensive, necessitating substantial heat input to the reboiler and leading to significant waste heat discharge through the condenser into the environment. This paper presents our further study on an innovative alternative technology for thermal separation. The proposed approach involves conducting thermal separation within flow channels of a Heat and Mass Exchanger (HME), which are composed of plates with intricate geometries. In this system, heat distribution is maintained through the diaphragm, i.e., the channel walls, facilitating both heat exchange and simultaneous thermal separation of substances.This paper focuses on both laboratory and numerical investigations of two-phase flow within various channel geometries. Experimentally, four distinct channel designs were examined using an air–water mixture, aiming to identify a new geometry that facilitates countercurrent flow patterns in this challenging substance combination. The experimental phase led to the selection of a channel geometry that demonstrated the most effective countercurrent flow for intensive cases, then used for ethane-ethylene mixture. Subsequently, this selected geometry was subjected to numerical calculations using the mathematical model of the Heat and Mass Exchanger (HME). These calculations encompassed flow dynamics, thermal behavior, and the sizing of the HME, tailored specifically for the newly identified channel geometry.

Solid-liquid particle flow sealing mucus (PFSM) in enhancing coalbed methane (CBM) recovery: Multiple-perspectives analysis and mechanism insights

The paper presents an in-depth investigation of solid-liquid two-phase particle flow sealing mucus (PFSM) for enhanced coalbed methane (CBM) recovery. PFSM is composed of solid waste particles such as fly ash and rubber particles. The PFSM is assessed using multiple-perspectives analysis, which includes measurements of water retention, pressure expansion, rheological characteristics, adhesion, wettability, microscopy and field case studies. Single-factor and multi-factor studies are used to optimize slurry material ratios. The results show that PFSM has outstanding water retention characteristics, with over 80 % retention for 30 days at 30 °C, and impressive expansion performance, with 9.52 % at 0.6 MPa. The shear thinning curve conforms to the Cross model. After 30 s, the final contact angle is 75.17 °, which is about 6 ° smaller than that of cement based materials. Field experiments show that, after applying PFSM, the drainage gas concentration can be improved at least 60 % comparing to other sealing materials. This research findings could offer novel insights into enhancing CBM extraction, indicating potential for safer and more efficient coal mine production.

A comprehensive investigation of two-phase flow in off-design operating condition of ejector performance by using entropy generation analysis

A comprehensive investigation of two-phase flow in off-design operating condition of ejector performance by using entropy generation analysis

Two-phase flow investigation of sewage pumps with different tip clearance via computational fluid dynamics and multi-factor ANOVA

Sewage pumps are widely utilized in various applications, including municipal wastewater treatment plants, industrial processes, and residential sewage systems. These pumps are specifically designed to handle the transportation of mixtures consisting of solid and liquid components, commonly observed as two-phase flow. In this study, semi-open sewage pumps with varying clearance sizes have been examined through adjustment of the geometrical model. Multi-factor analysis of variance is employed to investigate the combined influence of different two-phase flow conditions and tip clearance sizes on the performance of sewage pumps. The results show that the performance of the pump decreases significantly as the clearance size increases. Also, the sensitivity of pump efficiency to variations in tip clearance size is contingent upon the flow rate. Under part-load conditions, both particle concentration and clearance size exhibit a notable effect on efficiency. The two-phase flow will greatly enhance the intensity of the unsteady flow near the inlet and outlet of the semi-open impeller, which is the main reason for the performance degradation of the sewage pump. The findings of this research provide valuable insights for enhancing the hydraulic performance and operational stability of semi-open sewage pumps operating under two-phase flow conditions.

Experimental investigation of two-phase flow in Chevron-type compact plate heat exchangers: A Study on pressure drops and flow regimes visualization

Compact plate heat exchangers are a very promising technology and lately they are being considered for potential use as steam generators in Small Modular Reactors. However, there is a lack of scientific literature on their operation with two-phase flows, especially with non-refrigerant fluids. In this study, we conducted experiments to visualize and measure the pressure drop of a two-phase flow in a Chevron-type Plate Heat Exchanger. An air–water mixture was used in adiabatic conditions as the operating fluid in upward-flow configuration. Visualization was achieved through high-framerate videos. This study covers a wide range of operating conditions, surpassing those documented in existing literature by specifically analyzing also the region of very low mass flux for both phases. The tested conditions ranged from 6 to 365 kg/m2s of water and from 0.02 to 5 kg/m2s of air. Single-phase pressure drops were measured to establish a correlation for the Darcy friction factor. Instead, measurements of the pressure drop in two-phase conditions were processed and presented using a non-dimensional form referred to as the two-phase multiplier. The adoption of a void-fraction model played a crucial role in accurately extrapolating the frictional component of the pressure drop from the measurements, resulting in less scattered data on the Lockhart–Martinelli plot. In addition, the observed flow structures were categorized into distinct regimes (fine-coarse bubbly, Taylor-like bubbly, heterogeneous, partial film, and film flow) based on visual observation and were represented on a flow map. Finally, these data were used to develop new criteria for predicting flow pattern transitions.

Numerical investigation of subcooled two-phase flow and heat transfer characteristics in a liquefied natural gas cargo containment system

The increase demand in liquefied natural gas (LNG) leads to an increase in the import and export of LNG cargo using LNG carriers with composite insulation and double-hull structures for membrane-type storage tanks. Therefore, the transient characteristics of cryogenic heat transfer in LNG cargo containment systems have become important for understanding the physics when LNG vaporizes into the gas phase to minimize the cargo loss of boil-off gas (BOG). However, public papers on fundamental research on long-term computational fluid dynamics (CFD) simulations are still lacking. In the present study, the transient flow behaviors of LNG fluids and the heat transfer characteristics were numerically studied by applying the simplified single-layer insulation in an LNG cargo containment system, based on an initial temperature of TLNG,0 = 110.5 K and saturation temperature of TLNG,sat = 111.5 K in the boundary condition of IGC code. The proposed analysis procedure can serve as a reference for relative comparison of predicted BOG difference in LNG cargo holds.Consequently, the heat transfer mode between the two-phase methane and the solid insulation could be typically classified into two different regimes: (1) a subcooled regime before reaching the saturation temperature from the initial temperature, and (2) a boiling regime after reaching the saturation temperature. In the subcooled regime, the subcooled liquid exhibited bulk flow motion induced by natural convection. The loss rate of LNG mass per time interval was extracted from the best-fit correlations as −0.0448 kg/s at 1 d (105 s) to cool down the insulation system and −0.0072 kg/s at 5 d (5 × 105 s) to reach the LNG saturation temperature. When the predicted value of the loss rate of LNG mass by the CFD simulation was regarded as the generation rate of boil-off gas, it was smaller than the designed value of the boil-off gas of 0.464 kg/s corresponded to boil-off rate (BOR) about 0.2 %/day. In the boiling regime and under sufficiently cooled conditions, the loss rate of LNG mass per time interval did not consistently exceed the BOR value. The liquid flow exhibited a turbulent-like motion despite the relatively low velocity at 10 d (106 s). Especially, the increase in the effective thermal conductivity was a good indicator for distinguishing between the boiling and subcooled regimes.

Modelling of liquid oxygen and nitrogen injection under flashing conditions

The present numerical investigation of two-phase flashing flows examines the injection of liquid oxygen and liquid nitrogen into near-vacuum conditions prevailing in the upper-stage boosters of rocket engines. The predictive capability of a pressure-based solver and a density-based solver, each employing distinct approaches related to the imposed phase-change rate and thermodynamics closure, has been comparatively evaluated. Regarding the pressure-based solver, the departure from thermodynamic equilibrium during phase-change has been taken into account via the implementation of a bubble-dynamics model employing the Hertz-Knudsen equation. In contrast, the density-based solver relies on the adoption of thermodynamic equilibrium while real-fluid thermodynamic properties are assumed by loading tabulated values to the solver. Each thermodynamic property value was calculated in advance by solving the Helmholtz Equation of State (EoS) for a wide range of density and internal energy conditions. Numerical findings have been compared against experimental data available in the literature. The comparison demonstrates the capability of both methodologies in capturing the evolution of cryogenic flashing flow expansion, phase-change, and spray formation. The salient features identified in the numerical results, i.e., the expansion sphere immediately downstream of the injector exit, the bell-shaped topology of the spray, as well as the dependency of the spray cone angle on superheat, are in agreement with experimental measurements. Especially the density-based approach has been proven highly accurate with respect to the steady expanding flow described by a level of superheat in the range of 3 to 245, while also being independent of any parameter tuning.

Artificial intelligence-based entropy generation investigation of two-phase nanofluid flow in a heatsink with pin fins

It is crucial to assess the efficiency of using entropy generation (EYG) in energy-consuming devices. In this article, a study is done on the EYG of laminar water/alumina nanofluid (NFD) in a heatsink (HTK) with circular pin fins. The NFD enters the middle of the HTK and exits around it and passes through the pin fins. The bottom portion of the HTK is subjected to a steady flux, and the temperature of the HTK is lowered by the cold NFD. By changing the diameter and height of pin fins and their distance, the values ​​of thermal EYG (TEYG), frictional EYG (FEYG), and total EYG (TOEYG) are estimated and the contours of temperature and NFD flow are presented. An optimization is performed on the results by using the response surface method (RSM) in the range of the studied variables to obtain minimum amounts of EYG and HTK temperature. The finite element method (FEM) and the two-phase mixture method are utilized to simulate the NFD flow. The findings show that increasing the height of the pin fins decreases thermal and TOEYG while increasing FEYG. Enhancing the distance between the pin fins, leads to a slight decrease in thermal and TOEYG.

Numerical investigations of two-phase flow coupled with species transport in proton exchange membrane fuel cells

A 3D + 1D model is developed to investigate the effect of liquid water in cathode channels on oxygen transportation. The gas-liquid interface is tracked by volume of fluid (VOF) method and the oxygen transportation is solved by a species transport model. It is found that the existence of liquid water in channels can hinder the transportation of oxygen towards catalyst layers. The water coverage is a key factor that affects the oxygen transportation. It is influenced by the droplet numbers, volumes, contact angles and liquid regimes. Compared to the case with 0 droplet, the current densities for the cases with 6 and 12 droplets decrease by 1.4% and 10.6% respectively, for the cases with a droplet volume of 0.05 μL, 0.1 μL, 0.2 μL and 0.3 μL decrease by 1.7%, 3.9%, 9.6% and 14.9% respectively, for the cases with the contact angles of 115°, 125°, 135°, 145° and 155° decrease by 15.2%, 13.8%, 9.6%, 6.6% and 5.3% respectively. Compared to the droplet regime, the current densities of the film regime with the water volume of 1.2 μL and 2.4 μL increase by 3.6% and 9.4% respectively.

Pressure Drop Prediction Model of the Gas-Liquid Stratified Flow Development Section in the Horizontal Pipeline

Abstract The gas phase accelerating beyond the liquid phase caused by gas-liquid slippage cannot be ignored in short horizontal pipelines with undulation and inflow, and there is no method to calculate it. Therefore, a pressure drop prediction model for variable liquid holdup was developed in this paper. The theoretical model calculation results were validated using computational fluid dynamics. The effectiveness of the pressure drop prediction model has been demonstrated. The various pressure drop, liquid holdup, and development length laws were then examined. The findings indicate that: the pressure drop in the developed section of stratified flow is not only the friction pressure drop but also the acceleration pressure drop; the length of the stratified flow development section and pipeline pressure drop are more easily affected by the flowrate than the liquid holdup in the pipe inlet. Using the relevant data from coalbed methane horizontal wells as an example, the L/D of the development section is approximately 40–85 when the inlet flowrate is 0.8–1 m/s, and the inlet liquid holdup is 0.3–0.5. The pressure drop characteristics in the gas-liquid stratified flow development section are obviously different from those in the stable section. The development of a pressure drop prediction model for the stratified flow development section lays the theoretical groundwork for the investigation of gas-liquid two-phase flow in horizontal pipelines with short or undulating and inflow conditions.

Thermal management of GaN HEMT devices using subcooled flow boiling in an embedded manifold microchannel heat sink

Ultra-high heat flux thermal management has been an urgent demand for high electrical performance and reliability of GaN HEMT electronic devices, and direct fabrication of embedded heat sinks have proven to be an effective approach for its thermal management. In this work, a self-developed solver based on OpenFOAM has been employed and verified for numerical investigations of three-dimensional two-phase flow coupled with conjugate heat transfer. An extremely uneven heat source distribution in GaN HEMT is accounted for in the numerical modeling with localized refined mesh. The thermal performance and pressure drop during subcooled flow boiling are investigated and presented considering parametric effects of heat flux, mass velocity, inlet/outlet width ratio, manifold thickness and channel aspect ratio as well as substrate materials. The results indicate that GaN-on-Diamond structure provides a lower thermal resistance and better temperature uniformity, and the superior performance of GaN-on-SiC and GaN-on-Diamond are augmented with increasing heat flux during subcooled flow boiling. Additionally, it can be concluded that maximum temperature and pressure drop decrease with increasing channel height firstly, and then flatten out as the height/width ratio reaches 8 and 6, respectively. The flatten-out relationship between increasing height/width ratio and thermal/hydraulic performance is partly attributed to the balance of decreasing convective heat transfer coefficient and increasing effective area. Besides, flow pattern analysis for high-aspect ratio microchannels shows that hotspots at the bottom of inlet manifold promote the bubble nucleation and bubbles tend to accumulate at the bottom of channels because of nonuniform velocity distribution along the microchannel height.

Experimental Investigation of Regular or Wavy Two-Phase Flow in a Manifold

An experimental study was conducted to investigate the properties of stratified regular or wavy two-phase flow in two parallel separators located after a manifold. A total of 103 experiments with various gas and liquid velocity combinations in three inlet pipes were conducted, including 77 groups of outlet pipe resistance symmetry and 26 groups of outlet pipe resistance asymmetry trials. The experimental results have revealed that when the gas-liquid flow rate is low, the degree of uneven splitting is high, and “extreme” conditions are attained. When the superficial gas velocity is greater than that established in the extreme case, the direction of the liquid-phase displacement is reversed, while that of the gas remains unchanged. Thus, the degree of gas phase bias tends to be mitigated with an increase in the gas velocity, while the uneven splitting degree of liquid approaches 10%. Finally, varying the gas-phase outlet pipe resistance is shown to effectively change the gas-liquid two-phase flow distribution.

Bubble behaviors and flow boiling characteristics in open microchannels with large aspect ratio

Large aspect ratio of microchannels enables the corresponding heat sink possess higher heat transfer capability, however, the generated bubbles tend to rapidly extend forward and backward due to the large aspect ratio of the channels, thereafter blocking the channels, deteriorating the heat dissipation and increasing the pressure loss. Open microchannels have been reported to inhibit the two-phase flow instability due to the existence of extra gap for vapor expansion. However, the visualization of bubble dynamics and characterization of flow boiling behaviors of open microchannels with large aspect ratio are limited. In this study, the open microchannel heat sink with large aspect ratio was proposed and flow boiling tests were conducted at two mass fluxes of 153 and 229 kg/m2·s with the effective heat flux ranging of 180.81–2165.15 kW/m2. The inlet temperatures of the test module were set in the range of 5-85 °C. Visualization results showed that the flow patterns can be classified into bubbly flow, combined bubble flow and stratified slug flow. The flow mode tended to transition to stratified flow as the inlet temperature increased, and the combined bubble flow was found to be absent at high inlet subcooling. The size of the nucleated bubbles increased with the increase of inlet temperature during bubbly flow. The length to width ratio, survival time of nucleated bubbles and the bubble dynamic behaviors were respectively discussed. The heat transfer characteristics and pressure drop were strongly dominated by the two-phase flow patterns. The optimum flow boiling heat transfer was achieved when the flow pattern transitioned to combined bubble flow and early stage of stratified slug flow, during which bubble nucleation and thin liquid film evaporation jointly contributed to the heat dissipation. The pressure drop increased with the increase of inlet subcooling because of the greater liquid viscosity, and the sudden spurt of pressure drop was observed due to the occurrence of stratified slug flow. This work provides a preliminary investigation of two-phase flow boiling performance in large aspect ratio open microchannels, which may provide important insights of bubble dynamics or interfacial mechanics in open microchannel heat sinks.

Research on bubbly to slug flow regime transition of air-water co-current upward flow in vertical rectangular channels with different gap sizes

To investigate the transitional criterion of bubbly to slug flow influenced by gap size in rectangular channels, an experimental investigation of air-water two-phase co-current upward flow has been conducted in adiabatic vertical channels under atmospheric conditions. Experiments were carried out in three channels with different cross-sections of 4 × 66 mm, 6 × 66 mm, 8 × 66 mm, respectively. The superficial velocities are 0≤jg≤20m/s and 0.25≤jf≤3m/s for gas and liquid phase. The range of liquid superficial Reynolds numbers is 1900≤Ref≤42000 which have covered purely laminar flow to turbulent flow. Flow regimes were defined according to photos captured by a high-speed camera and characteristics of void fraction measured by flat electrodes, and a random forest algorithm was used to identify the flow regimes at the transitional region. Results show that with the increase of the gap size, the transition from bubbly to slug flow is delayed, and the regime transitional void fraction changes from 0.17 to 0.25. The mechanisms of random collision, wake entrainment, and turbulence breakup were analyzed according to the experimental phenomena. A new criterion of the bubbly to slug flow regime transition applied in rectangular channels was proposed considering the impact of the gap size.

Numerical investigation of two-phase flow through tube bundles based on the lattice Boltzmann method

In pursuit of stable operation in thermal hydraulic engineering, this paper researches two-phase flow through tube bundles by the lattice Boltzmann method. The single-relaxation-time lattice Boltzmann model and the multicomponent, multiphase pseudo-potential lattice Boltzmann model are adopted. Specifically, the two-phase flow past double-tandem circular cylinders, double-parallel circular cylinders, in-line tube bundles and staggered tube bundles with various spacing ratios is investigated. The vortex variable distribution and vortex shedding law under different working conditions are further compared to obtain the time-averaged drag, oscillating drag and Strouhal number. The variation law of lift coefficient and lift power spectrum with different spacing ratios is revealed. With increasing spacing ratio, the mutual interference between the double-tandem circular cylinders is weakened, the amplitude of the time-averaged drag on the double-parallel circular cylinders is reduced and the lift power spectrum changes from a double-peak distribution to a single-peak structure. The drag and lift of the center column of in-line tube bundles are lower than those on both sides, while the oscillating drag of the odd-row columns of staggered tube bundles is higher than that of even-row columns. These results contribute toward laying a solid foundation for future research on multiphase tube bundle flow issues in nuclear engineering.

CFD investigation of air-oil two-phase flow in oil jet nozzle

In aero-engines applications, nozzle geometric parameters have major effects on the lubricating oil to accurately reach target gears or bearings. To investigate the deviation phenomenon of oil jet flow in the lubrication system, the computational fluid dynamics (CFD) technique integrating with the volume of fluid (VOF) method and SST k- ω turbulence model is adopted to deeply understand the flow characteristics of the nozzle. By leveraging this method, the relationship between nozzle geometry, inlet pressure, jet velocity, and jet deviation are firstly analyzed. The results reveal that a higher average velocity and smaller jet deviation can be determined via adjusting the nozzle geometry. Furthermore, a specific test rig, composed of an oil supply system, target system and data collection system, is set up for oil injection test; experimental outlet velocity and mass flow rate of oil passing through the hole on the target plate are monitored and recorded. The experimental findings compare well with numerical results obtained by the CFD method.

Experimental analysis of pressure drops and heat transfer coefficient during upward two-phase flow of R-134a/R-245fa mixture in an offset-strip finned passage

The current study focuses on an experimental investigation of upward vertical two-phase flow of binary mixtures in complex geometries composed of offset-strip fins. The flow boiling of a mixture containing 52% mol/mol of R-134a and 48% mol/mol of R-245fa was visualized. The ranges of mass flux and heat flux investigated were 11 – 25 kg.m−2.s−1 and 9 – 23 kW.m−2 respectively. The test section is an offset-strip finned passage whose hydraulic diameter is 1.75 mm. The operating pressure ranges from 2 to 5 bar absolute. The temperature glide of the used binary mixture ranges from 14 to 16 °C. Different flow regimes were identified along the test section such as bubbly, slug and annular regimes. The impact of strip-fins and mass flux on flow maps was analysed in this study. The pressure drop was analyzed and the obtained data were gathered to propose a new correlation for R-134a/R-245fa mixture in offset-strip fins. The local heat transfer coefficient was calculated and it has been found that nucleate boiling was the predominant mode of heat transfer.

Investigation of two-phase jet flow from a degassing pipe used for a lake with potential gas-driven eruption

Gas-driven limnic eruption can happen in a lake with an aqueous gas solution that becomes supersaturated due to some reason. In this case, the exsolution of massive gases dissolved in the water could occur in a very short time, resulting in a disaster as happened in the Lake Nyos (Cameroon, Africa) in 1986. Using degassing pipe to artificially release the dissolved gases is a good way to minimize the risk of an eruption. In this study, a transient multi-component gas-liquid two-phase flow model of the degassing pipe used in Lake Nyos has been established and verified with the observed eruption data. The drift flux model has been used for modelling of a transient multi-component gas-liquid flow formed due to the spontaneous exsolution of gases dissolved in the water inside the degassing pipe. The governing equations for the mechanistic drift model include continuity equation for each phase, a single momentum equation for a homogeneous mixture of the fluid, constitutive equations for mass transfer rates between the phases, and the drift velocity formulas. The model considered not only CO2 but also CH4 as dissolved gases. The “chain reaction” conjecture predicted to have the degassing-point migrating downward with time during the transient degassing process is verified by using this model. The relationship between the eruption height and the CO2 concentration at the bottom of the degassing pipe has been simulated in detail. This relationship supplies people with a quick and convenient way to estimate the CO2 concentration in the lake, based on which one can evaluate the risk of lake eruption and hence to formulate or adjust the degassing plan. In addition, the effects of diameter and equivalent roughness of the degassing pipe on the eruption height has been investigated. Meanwhile, the eruption height upper-limit in different lake-depth scenarios has also been determined. Finally, the role of CH4 component in the degassing process has been analyzed. Although the influence of CH4 on eruption height can be neglected in Lake Nyos' case, CH4 as a dissolved gas plays an important role at Lake Kivu. The multi-component gas-liquid flow model developed in this study is useful to study the role of CH4 in the degassing process.