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The critical heat flux (CHF) is a vital parameter influencing the safety and efficiency of reactor cores. In this study, the Eulerian two-fluid model coupled with the extended wall boiling model in STAR-CCM+ was employed to simulate the departure from nucleate boiling (DNB) phenomenon in a 5 × 5 pressurized water reactor (PWR) fuel rod bundle channel with spacer grids under non-uniform heating conditions. The transition in boiling curves was used as the criterion of DNB occurrence, while the temperature distribution of rod surfaces was utilized for CHF location predictions. The predicted CHF value and CHF location exhibited good agreement with the experimental data. The deviation between calculated and experimental CHF values was within 15% and the deviation between predicted and experimental CHF locations was within one grid-to-grid span length. The results of this study suggested good prospects for the application of two-phase CFD model in predicting CHF in fuel assemblies with spacer grids. [ABSTRACT FROM AUTHOR]

Metallic foams have become a cutting-edge solution for many thermal management problems. These are of interest by thermal research community because of the cellular structure and have gas-filled pores inside a metal matrix. Due to the uniqueness in their structure, they exhibit good performance in boiling heat transfer because of the properties such as higher specific surface area, large number of nucleation sites, wettability characteristics, and capillary action. The boiling heat transfer over metal foam is a complex phenomenon, greatly affected by the thickness, porosity, and pores per inch (PPI) of metal foam along with the thermo-physical properties of the foam and boiling liquid. By thoroughly examining recent research investigations, the paper explains the impact of open-cell metal foams on pool boiling of different liquids such as water, refrigerants, organic liquids, and dielectric liquids. This paper reviews the complexity and various influencing factors involved in flow boiling through metal foam in tubes. It also highlights findings that show metal foam significantly enhances jet impingement boiling heat transfer. Moreover, the discussion on gradient metal foams, offering insights into their potential to enhance boiling heat transfer. The comprehensive review also encompasses numerical modeling studies, such as the lattice Boltzmann method, contributing to a deeper understanding of the intricate flow and heat transfer characteristics within channels filled with metal foam. [ABSTRACT FROM AUTHOR]

Counter-current imbibition can improve the recovery efficiency of complex fractured reservoirs, but there are few studies on the pore-scale mechanism and the factors affecting the recovery efficiency. This paper attempts to track the microscopic oil–water imbibition process through phase field method simulation, revealing the distribution characteristics of oil and water phases at different stages, as well as the sudden change characteristics of pressure and velocity at the instant of oil film rupture. Then, the influence of fracture aperture, capillary number and viscosity ratio on oil recovery efficiency is discussed. Results indicate that the microscopic imbibition process can be divided into 4 stages: the oil film forms after oil–water contact, then the oil film ruptures to form oil droplets, then the oil–water line moves outward from the large pore, and finally the oil droplets gather to discharge from the fracture. It is also found that there will be sudden changes at the moment of oil film rupture, the pressure drops sharply and the velocity increases sharply. Moreover, there exists a critical fracture aperture which is approximately 10 times the average pore size, and if the fracture is smaller than the critical fracture aperture, a dead oil zone occurs, which affects recovery. Additionally, LogM-LogCa stability diagram is constructed which is mainly dominated by viscous forces, capillary forces. As the capillary number increases, the recovery efficiency shows an overall decreasing trend. When the viscosity ratio was greater than 10, there was no significant change in the recovery efficiency, influenced by the weakening of the dominant role of viscous forces. New findings are beneficial to enhancing the recovery efficiency of low permeability reservoirs. [ABSTRACT FROM AUTHOR]

Mathematical modelling of pressure, temperature, and velocity distribution of two-phase flow in a producing gas well is an important phenomena in the management, design, and dynamic analysis of the wells. Many studies in producing gas wells focuses mostly on single phase gas flow during production but pressure traverses in two-phase flow differs from single phase due to the differential flow rates of the different phases and using single phase model may result to insufficient prediction leading to premature closure of wells. This work considered a one-dimensional timedependent homogeneous model which represents a system of partial differential equations to describe mathematically the transient two-phase gas-liquid mixture flow in a producing well. The numerical solution of the mathematical model, which consists conservation of mass, momentum, and energy equations based on finite difference technique in the implicit scheme has been applied. PVT correlation is used in estimating the thermodynamic and transport properties of the fluids. From the results obtained, it was observed that Joule-Thomson affect sensitively in the prediction of pressure and other flow parameters which agreed with existing work. The curves obtained reflect the gas flowing law which can provide technical reliance and dynamic analysis of multiphase producing gas wells. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Harbin University of Science & Technology is the property of Journal of Harbin University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The critical heat flux (CHF) is a vital parameter influencing the safety and efficiency of reactor cores. In this study, the Eulerian two-fluid model coupled with the extended wall boiling model in STAR-CCM+ was employed to simulate the departure from nucleate boiling (DNB) phenomenon in a 5 × 5 pressurized water reactor (PWR) fuel rod bundle channel with spacer grids under non-uniform heating conditions. The transition in boiling curves was used as the criterion of DNB occurrence, while the temperature distribution of rod surfaces was utilized for CHF location predictions. The predicted CHF value and CHF location exhibited good agreement with the experimental data. The deviation between calculated and experimental CHF values was within 15% and the deviation between predicted and experimental CHF locations was within one grid-to-grid span length. The results of this study suggested good prospects for the application of two-phase CFD model in predicting CHF in fuel assemblies with spacer grids.

Simulation of subsurface energy system involves multi-physical processes such as thermal, hydraulical, and mechanical (THM) processes, and requires a so-called THM coupled modeling approach. THM coupled modeling is commonly performed in geothermal energy production. However, for hydrocarbon extraction, we need to consider multiphase flow additionally. In this paper, we describe a three-dimensional numerical model of nonisothermal two-phase flow in the deformable porous medium by integrating governing equations of two-phase mixture in the porous media flow in the reservoir. To account for inter-woven impacts in subsurface conditions, we introduced a temperature-dependent fluid viscosity and a fluid density along with a strain-dependent reservoir permeability. Subsequently, we performed numerical experiments of a ten-year water flooding process employing the open-source parallelized code, OpenGeoSys. We considered different well patterns with colder water injection in realistic scenarios. Our results demonstrate that our model can simulate complex interactions of temperature, pore pressure, subsurface stress and water saturation simultaneously to evaluate the recovery performance. High temperature can promote fluid flow while cold water injection under non-isothermal conditions causes the normal stress reduction by significant thermal stress. Under different well patterns the displacement efficiency will be changed by the relative location between injection and production wells. This finding has provided the important reference for fluid flow and induced stress evolution during hydrocarbon exploitation under the environment of large reservoir depth and high temperature. [ABSTRACT FROM AUTHOR]

The coupling relationship between the deformation field, the diffusion field, and the seepage field is an important factor in fluid transport mechanisms in the long-term coalbed methane (CBM) exploitation process. A mathematical model of gas–water two-phase fluid–structure coupling in a double-porosity medium in coal reservoirs is established in this paper. Taking Hancheng Block, a typical production block in Qinshui Basin, as the geological background critical desorption pressure, reservoir permeability anisotropy is considered in the model. COMSOL Multiphysics (COMSOL_6.0) was used to create the model. The accuracy and rationality of the model were verified by comparing field production data with the results of the simulation. Using the simulation, the influence law of various reservoir geological characteristics parameters (Langmuir strain constant, ratio of critical desorption pressure to reservoir pressure of coal seam (CDPRP), elastic modulus, initial water saturation, Langmuir pressure, etc.) on CBM productivity, reservoir pressure, and permeability ratio was discussed, and a thorough analysis of the factors affecting productivity was obtained using the orthogonal test method. The findings of this study indicate that the change in permeability is the result of the superposition effect of many factors. Different stages of drainage have different primary regulating factors. Rock skeleton stress has a consequence on coal matrix permeability in the early drainage stage, and coal matrix shrinkage is primarily impacted in the later drainage stage. Besides the initial water saturation, other reservoir geological parameters (e.g., CDPRP, Langmuir volume, Langmuir strain constant, elastic modulus) have a strong relationship with productivity. When the value of coal geological parameters increases, the degree of productivity release is higher (as the initial water saturation increases, the production decreases correspondingly). Different coal and rock parameters have varying levels of impact on the drainage stage of CBM wells. The influences of the CDPRP, Langmuir volume, Langmuir strain constant, and elastic modulus on gas production are mainly concentrated in the initial and intermediate drainage stages and begin to fall off during the last drainage stage. Per the multi-factor analysis, the main coal–rock parameters affecting the productivity release are the Langmuir strain constant, followed by the CDPRP and other parameters. The analysis findings can offer theoretical guidance for CBM well selection and layer selection and enhance the block's overall CBM development level. The improved productivity prediction model for CBM, which is based on fluid–structure coupling theory, can offer a new technical benchmark for CBM well productivity prediction. [ABSTRACT FROM AUTHOR]

This study investigates the thermohydraulic characteristics of immiscible two-phase downward flow and heat transfer through porous media in a vertical, cylindrical, and homogeneous porous medium numerically and experimentally. The test section is exposed to a constant wall temperature after filled with spherical beads. Numerical solution of the model is achieved by the finite volume method and applied to a single-phase flow model. The numerical results are experimentally validated according to air/water downward flow, spherical beads, a ratio of particle diameter to pipe radius is 0.412, 0.396 porosity, 0.01 ≤ Re ≤ 500, water to air volume ratio range from 0 to ∞, and saturation ratio from 0 to 1. The results show that the average Nu is nearly constant up to Re = 40. At Re > 100, it is recommended to take inertia and friction effects into account by means of Forchheimer–Brinkman's equation. For single-phase flow (water or air) and two-phase flow mixtures, the local Nu has higher values at the entrance section and decreases as the axial distance increases until it reaches its fully developed value of 4.37 at the end of the thermal entrance length. The comparison between numerical, experimental, and other available previous results shows good agreement and validates the numerical model. [ABSTRACT FROM AUTHOR]

This study examines the influence of hot air flow trajectories within steam generators on their thermal efficiency. Specifically, the investigation focuses on the augmentation of the convection heat transfer coefficient, achieved through enhanced contact efficiency between hot air and water pipes, thereby increasing convective heat. Computational Fluid Dynamics (CFD) served as a preliminary tool for evaluating the thermal dynamics of the steam generator, encompassing the movement of flame and hot air as well as steam generation within the pipes. The introduction of partitions was found to refine the convective heat transfer coefficient in the steam generator, particularly in the inner and outer coils. However, a decrease in the heat transfer coefficient was noted around the vertical cylinder, compared to the configuration without partitions. The inclusion of a single separator in the evaporator generator led to a 29% increase in the total convective heat transfer coefficient, while the utilization of two separators resulted in a 23% increase. These findings highlight the significance of structural modifications in steam generators, specifically through the strategic placement of separators and partitions, in elevating thermal efficiency. [ABSTRACT FROM AUTHOR]

As for two-phase flow in rectangular channels, the flow regimes especially like churn-turbulent and annular flow are significant for the physical problem like Countercurrent Flow Limitation (CCFL). In this study, the rectangular channels with cross-sections of 4 × 66 mm, 6 × 66 mm, 8 × 66 mm are adopted to investigate the flow regimes of air-water vertical upward two phase flow under adiabatic condition. The gas and liquid superficial velocities are 0≤jg≤20m/s and 0.25≤jf≤3m/s respectively which covering bubbly to annular flow. The flow regimes are identified by random forest algorithm and the flow regime maps are obtained. As the results, the transitional void fraction from slug to churn turbulent flow fluctuate from 0.47 to 0.58 which is significantly affected by the dimensional size of channel and flow rate. Besides, the void fraction at transitional points from churn-turbulent (slug) to annular flow are 0.66–0.67, which are independent with the gap size. Furthermore, a new criteria of slug to churn-turbulent flow is established in this study. In addition, by introducing the interfacial force model, the criteria of churn-turbulent (slug) flow to annular flow is verified.

This study presents an experimental investigation centered on the utilization of a solar bubble pump for lifting water. Experimental tests were conducted to analyze the impact of various design and operational parameters. The results revealed a direct proportionality between the maximum height lifted heat flux. Additionally, the experiments demonstrated that increasing the submergence ratio resulted in a higher mass flow of lifted water. Furthermore, a slight increase in tube diameter, while maintaining a constant heat flux and submergence ratio, led to a 22.47% increase in the flow rate when the diameter was increased from 8 mm to 10.21 mm. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Polytechnic is the property of Journal of Polytechnic and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

T-junctions are important structures used in a number of industries to separate gas and liquid. This work studied the effect of the orientation of the side arm on the separation efficiency using a computational fluid dynamics (CFD) approach, and a new mechanical model is developed based on force analysis to predict the liquid carryout threshold. Laboratory experiments from published works are used to verify the CFD simulation and the new model. In this work, the angle of the side arm to the horizontal plane, α , and the angle of the side arm to the main arm's axial direction, β , are investigated. The results show that with increasing β , the liquid carryover threshold increases accordingly, demonstrating that the liquid can be more easily carried to the side arm, while the liquid-carrying performance in the side arm is not sensitive to the inclination angle, β. Hence, in the new model, the inclination angle of is ignored. Experimental data are collected to validate the new model. The results show that this model can accurately predict the liquid carryover threshold, and the relative error is 4.16%. [ABSTRACT FROM AUTHOR]

This study will present a comprehensive review of the two-phase flow boiling heat transfer coefficient of hydrocarbons such as propane (R-290), butane (R-600), iso-butane (R-600a), and ethanol at various experimental conditions. Studying the multiphase flow heat transfer coefficient is crucial for many types of heat transfer equipment to achieve higher efficiency for more compact design and cost reduction. One reason we chose hydrocarbons as refrigerants in this study is that they are of an ozone depletion potential equal to zero (ODP = 0) and a deficient level of direct global warming potential (GWP = 3). Moreover, hydrocarbons' thermodynamic and thermophysical characteristics qualify them to be a strong candidate for more heat transfer applications, initially, by constructing a database for the working fluids using multiple existing experimental work. The current data that this study have collected for the flow boiling spans a wide range of parameters, such as mass flux, heat flux, operating pressure, saturation temperature, etc. Furthermore, by comparing the experimental multiphase heat transfer coefficient database with the anticipated values of each correlation, the prediction performance of 26 correlations found in the literature was assessed. This study allows the best prediction method to be selected based on the minimum deviation of predicted results from the experimental database provided based on the mean absolute error (MAE) calculated from the assessed correlations. The conclusions of such a study can also be helpful for developing more accurate correlation methods for these fluids and improving the prediction of their flow boiling characteristics. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The oil well drilling process is a nonlinear system with transient nature. Conventional drilling is unable to assure safe and cost‐effective operation for fractured, cavernous, and highly permeable carbonate reservoirs, which contain the largest oil reserves worldwide. Concerning drilling technologies, Pressurized Mud Cap Drilling (PMCD) is suitable for the challenging scenario previously mentioned. According to PMCD technique, a sacrificial fluid is injected through the drill string and a light annular mud is pumped in countercurrent through the annulus region (bullheading), without surface return, forcing gas and drilled cuttings back to formation. A two‐phase flow distributed model (Drift Flux Model – DFM) is developed to properly describe the complex nature of the system. Also, an experimental facility, presenting field similarity, is employed to validate the open – closed loop schemes. The main objective of the controller (control reconfiguration with gain scheduling) is to regulate annulus pressure, handling gas kick, drilling fluid losses and inverse response dynamics. Besides, gas injection, migration and bullheading are studied. The simulations, validated through experimental data, highlight the methodology usefulness for field applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Engineering for Thermal Energy & Power / Reneng Dongli Gongcheng is the property of Journal of Engineering for Thermal Energy & Power and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to its advantages, the air lift pump has many applications in real life. Therefore, the present study is dealing with the effect of some parameters on the air lift pump performance. The present study is a continuation of a program started years ago by the fluid mechanics group in Faculty of Engineering, Alexandria University. Beginning by validating the obtained results of the experiment set-up by comparing these experimental results with international accepted sets of data. After that the present experiments shed some lights on the inlet injection region of the air lift pump due to the significant effect of its initial conditions on the pump efficiency. Thus the study directed towards investigating the effect of some parameters including the inlet restrictor resistance, the injection direction and the injector riser diameter. The upward injection technique shows higher peak efficiency of 34.7% compared to 29.7% and 28.9% for downward and side injection respectively while the larger injector inner diameter shows maximum water capacity of 928 kg/h. compared to 823 kg/h. water mass flow rate for the smaller inner diameter injector. In all the above experimental tests, flow visualization is used extensively giving a good agreement with well recognized flow pattern map.

The aim of this study is to investigate the characteristics of gas-non-Newtonian liquids flow patterns in square microchannels. The microchannels that used in this study was made by acrylic material with horizontal orientation and the side length of 8x10-4 m. Water, Air, Carboxymethyl Cellulose 0.2%wt (CMC 0.2%wt) aquoeus solution, and Xanthan Gum 0.2%wt (XG 0.2%wt) aquoeus solution were used in this study as the liquid test. Moreover, nitrogen gas was used as gas test. The liquid superficial velocity was varied of 0.1-1 m/s. Then, the gas superficial velocity variation of 0.26-7.8 m/s. The differential pressure transducer was used in this study to measure the pressure drop, which is occurs in square microchannels. Whereas, The flow patterns were recorded by using the high-speed camera. Furthermore the flow pattern video was analyzed by using image processing method to obtain the flow pattern charcteristics. The two-phase flow pressure drop of all gas-Newtonian/non-Newtonian liquids two-phase flows in this study increase by increasing JL in the same JG. The flow patterns that occur in this study are bubbly, slug, slug-annular and churn. The viscosity and rheological parameter of liquids test influenced the characteristic of flow patterns. The flow patterns in this study were plotted in the flow patterns map and suitable with the flow patterns transisiton lines based on the previous study. Likewise, the experimental pressure drop shows the good agreement with the pressure drop prediction correlation by Kawahara et al. (2011).

Semi-analytic solution representing the time-dependent Couette flow of conducting fluid-particle in a permeable channel is presented in the existence of a magnetic field. The magnetic field is anticipated to be positioned either with the conducting fluid-particle or positioned with the moving wall. Solution to the coupled flow equations is found and given in the Laplace domain. Expressions for fluid-particle velocity and their corresponding skin friction are also found. Influence of a number of flow parameters on flow formation in the permeable channel is demonstrated. Results indicate that, increase in Hartmann number dampens both fluid velocity and particle fluid velocity when the magnetic field is positioned relative to the conducting fluid, while it augments the flow when the magnetic field is positioned relative to the moving plate. In conclusion, it is realized that growing the injection velocity augments the momentum boundary layer yielding an increase in fluid-particle velocity. [ABSTRACT FROM AUTHOR]

The Rothman-Keller colour gradient Lattice Boltzmann Method (LBM) provides a means to simulate two phase flow of immiscible fluids by modelling number densities of two fluids, plus a "recoloring" step that ensures separation of the two fluids. Here, we model an additional number density representing the concentration of an additive to fluid 1 which affects the viscosity of this fluid. The Peclet number – rate of advection to diffusion – is used to set the diffusion coefficient of the concentration. We present tests to demonstrate the method including flow and merging of two adjacent droplets with different additive concentrations, and two-phase flow tests in a 2D porous matrix involving injection of fluid with an additive that increases the viscosity and thus decreases viscous fingering (e.g. a polymer additive). We demonstrate that use of polymers from the start of waterflooding leads to a high saturation of 90% much sooner than when polymers are applied after breakthrough. This work demonstrates that the RK color gradient multiphase LBM can be used to study viscous fingering behavior in porous media in which the injected low viscosity fluid can have its viscosity varied with time by use of an additive. This is both of scientific interest and has economic implications to Enhanced Oil Recovery, in which water–potentially with a polymer additive to increase viscosity– is injected from an injection well into a rock layer saturated with a high viscosity fluid (oil) to help push out the oil into a production well. [ABSTRACT FROM AUTHOR]

Concentrating solar direct-steam-generation (DSG) technology is favored for tying solar energy and water to directly power the energy loop, which is positive in achieving a zero-carbon future. Whereas, the external intermittence of the meteorological irradiation and internal instability of flow boiling pose challenges to the thermohydraulic operation and management. Herein, a light-heat-flow-pattern transient coupled analysis model of parabolic trough collector direct-steam-generation (PTC-DSG) loop was established to figure out the action among the irradiance, thermohydraulic and two-phase flow pattern. The transient flow patterns along the loop were investigated under different irradiance (I), mass flowrate (m in) and inlet temperature (t in) of the loop. The results showed that increasing I and t in temporarily reduces the probability of stratified flow and increasing t in permanently reduces the probability of stratified flow. In all cases, the proportion of intermittent flow to evaporation stage remains almost unchanged (about 11%.), and the heat transfer in superheating stage still needs a long time (253s ∼ 3646s) to recover after the flow stages distribution is stable. More importantly, a quantified management strategy for irradiance -thermohydraulic-flow pattern is built. To achieve a favorable operating state, the inlet mass flow rate m in should be lower than the superheated line ((1.25· I – 6.25)✕10−3 kg s−1) to obtain the superheated steam, and higher than 0.35 kg s−1 to get out of the stratified flow in evaporation stage. When the irradiation is lower than 285 W m−2 for a long time, the start-up and operation is not recommended. [Display omitted] [ABSTRACT FROM AUTHOR]

A second order method and a limited variation WENO numerical scheme are proposed for the Scanning Hysteresis Model (SHM) which describes continuum flows with hysteretic looping fluxes with local memory. The SHM is a nonconservative hyperbolic system with discontinuous coefficients. The limited variation WENO method is fifth order accurate in spatial coordinate and third order accurate in time steps in smooth and monotone regions. The proposed high resolution methods produce the desired solutions more efficiently than the first order upwinding method. These methods are total variation diminishing for the flux, and monotonicity-preserving for the flux and the hysteresis state variable. The flux and the hysteresis state variable produced by these two methods satisfy maximum principle. These two methods also have invariant regions. [ABSTRACT FROM AUTHOR]

This study validates the applicability of the CUPID code for simulating subcooled wall boiling under high-pressure conditions against number of DEBORA tests. In addition, a new numerical technique in which the interfacial momentum non-drag forces are calculated at the cell faces rather than the center is presented. This method reduced the numerical instability often triggered by calculating these terms at the cell center. Simulation results showed good agreement against the experimental data except for the bubble sizes in the bulk. Thus, a new model to calculate the Sauter mean diameter is proposed. Next, the effect of the relationship between the bubble departure diameter (Ddep) and the nucleation site density (N) on the performance of the Wall Heat Flux Partitioning (WHFP) model is investigated. Three correlations for Ddep and two for N are grouped into six combinations. Results by the different combinations show that despite the significant difference in the calculated Ddep, most combinations reasonably predict vapor distribution and liquid temperature. Analysis of the axial propagations of wall boiling parameters shows that the N term stabilizes the inconsistences in Ddep values by following a behavior reflective of Ddep to keep the total energy balance. Moreover, ratio of the heat flux components vary widely along the flow depending on the combinations. These results suggest that separate validation of Ddep correlations may be insufficient since its performance relies on the accompanying N correlations.

• ONB and HTC were measured in a helically coiled tube with a large curvature ratio. • The effects of operating parameters on ONB and HTC were analyzed. • New correlations were proposed for predicting ONB and HTC with higher accuracy. Helically coiled tubes are employed as heat transfer tubes in Once Through Steam Generator (OTSG) of High Temperature Gas-cooled Reactor (HTGR) due to their compact structure, large heat transfer area and excellent thermal expansion adaptability. However, the helical geometry induces centrifugal forces and secondary flows in the tube, resulting in notable differences in flow and heat transfer characteristics compared to that of straight tubes. This study conducted an experimental investigation on the onset of nucleate boiling (ONB) and the subcooled boiling heat transfer coefficient in helically coiled tubes with a large curvature ratio (δ = 0.109). The experimental parameters cover broad ranges. The system pressures are ranging from 3.5 to 7 MPa, mass fluxes are from 300 to 1100 kg/(m2·s) and heat fluxes are from 50 to 600 kW/m2. The experimental results indicate that the ONB can occur even when the average inner wall temperature is below the fluid's saturation temperature. An increase in heat flux advances the ONB, while increases in mass flux and system pressure delay it. Enhancements in both heat flux and mass flux improve the subcooled boiling heat transfer coefficient. Additionally, higher system pressure also increases the heat transfer coefficient, although this effect diminishes as the quality increases. Based on the experimental data and dimensionless analysis, new correlations were proposed for predicting ONB and calculating the subcooled boiling heat transfer coefficient in helically coiled tubes. Both new correlations exhibit more accurate predictive capabilities, with mean absolute percentage error (MAPE) values of 6.20 % and 8.86 %, respectively. [ABSTRACT FROM AUTHOR]

A pulsation heat pipe is an efficient heat pipe used in many engineering applications. This study aims to test the effect of working fluids on the thermal performance of pulsation heat pipe. Seven turned pulsation heat pipes were designed and manufactured from a copper pipe with a 3.5 mm inner diameter. The lengths of an evaporation part, an adiabatic passage, and a condenser part were 300 mm , 210 mm , and 300 mm , respectively. In this study, three different fluids were used as the working fluid: distilled water, methanol, and binary fluid (a mixture of water and methanol) with a 50% filling ratio. Compared to water, the experimental results suggested that methanol had a better thermal performance when used as a working fluid in the PHP . On the other hand, a binary fluid enhanced the lower thermal performance of water ( 29% reduction in the thermal resistance and a 20% increase in the effective thermal conductivity of the PHP ).

In this paper, heat transfer induced in smooth and wavy channels in the presence of two phases (air and steam) was conducted and discussed. Two configurations have been studied according to the geometrical shape of the channel walls. The thermal and hydrodynamic fields in the channel have been predicted using the single‐fluid approach with a solver based on the finite volume method. Explicit formulation of the volume of fluid was used to track the interface between both fluids. The mesh in the wavy channel was treated with a curvilinear mesh grid. Local Nusselt evolution, isothermal distribution, streamlines, and other parameters have been shown at different times of simulation. It was found that weak air phase velocities and wave patterns of the channel walls play a destabilizing role in the interface evolution between both fluid phases. In addition, results show that channels with wavy walls can be an effective solution to ensure higher heat transfer in two‐phase flows. [ABSTRACT FROM AUTHOR]

Pore-scale modeling plays an indispensable role in unveiling the migration mechanism of oil pollutants into the water-saturated soil. Navier Stokes equations and conservation of mass, coupled with the phase field method, are employed to investigate the effect of soil wettability on oil pollutants migration into the soil porous media. The results show that the oil-water interface in the migration process does not advance evenly in three wetting states. When the model system is in oil-wetting state, oil pollutants obviously migrate at a higher speed. Through monitoring the evolution of oil front location and analyzing the velocity distribution vertical to the flow direction at the central axis of the model, the channel corresponding to the peak velocity is the dominant flow channel for the oil pollutants. This study will have the potential ability in obtaining the pore-scale migration regulation of oil pollutions as well as more accurately predicting the pollution range. [ABSTRACT FROM AUTHOR]

Due to its advantages, the air lift pump has many applications in real life. Therefore, the present study is dealing with the effect of some parameters on the air lift pump performance. The present study is a continuation of a program started years ago by the fluid mechanics group in Faculty of Engineering, Alexandria University. Beginning by validating the obtained results of the experiment set-up by comparing these experimental results with international accepted sets of data. After that the present experiments shed some lights on the inlet injection region of the air lift pump due to the significant effect of its initial conditions on the pump efficiency. Thus the study directed towards investigating the effect of some parameters including the inlet restrictor resistance, the injection direction and the injector riser diameter. The upward injection technique shows higher peak efficiency of 34.7% compared to 29.7% and 28.9% for downward and side injection respectively while the larger injector inner diameter shows maximum water capacity of 928 kg/h. compared to 823 kg/h. water mass flow rate for the smaller inner diameter injector. In all the above experimental tests, flow visualization is used extensively giving a good agreement with well recognized flow pattern map. [ABSTRACT FROM AUTHOR]

Fluid flow through layered materials with different wetting behavior is observed in a wide range of applications in biological, environmental and technical systems. Therefore, it is necessary to understand the occuring transport mechanisms of the fluids at the interface between the layered constituents. Of special interest is the water transport in polymer electrolyte membrane fuel cells. Here, it is necessary to understand the transport mechanisms of water throughout the cell constituents especially on the cathode side, where the excess water has to be removed. This is crucial to choose optimal operating conditions and improve the overall cell performance. Pore-scale modeling of gas diffusion layers (GDLs) and gas distributor has been established as a favorable technique to investigate the ongoing processes. Investigating the interface between the hydrophobic porous GDL and the hydrophilic gas distributor, a particular challenge is the combination and interaction of the different material structures and wetting properties at the interface and its influence on the flow. In this paper, a modeling approach is presented which captures the influence of a hydrophilic domain on the flow in a hydrophobic porous domain at the interface between the two domains. A pore-network model is used as the basis of the developed concept which is extended to allow the modeling of mixed-wet interactions at the interface. The functionality of the model is demonstrated using basic example configurations with one and several interface pores and it is applied to a realistic GDL representation in contact with a channel-land structured gas distributor. [ABSTRACT FROM AUTHOR]

We introduce a new concept of dissipative varifold solution to models of two phase compressible viscous fluids. In contrast with the existing approach based on the Young measure description, the new formulation is variational combining the energy and momentum balance in a single inequality. We show the existence of dissipative varifold solutions for a large class of general viscous fluids with non–linear dependence of the viscous stress on the symmetric velocity gradient. [ABSTRACT FROM AUTHOR]

Two-phase pressure drop in the debris has been studied by many researchers concerning the debris cooling characteristics during a severe accident in a nuclear reactor. However, its flow regime transition of the two-phase flow in the debris has not been well understood, which strongly affects the interfacial drag and the pressure drop. Conventional models for gas-liquid two-phase flow pressure drop have not been established to evaluate interfacial drag accurately. In this study, high-speed imaging of a two-dimensional network model was performed to clarify the effect of flow patterns on interfacial drag and pressure drop. Usually, it would not be easy to visualize such two-phase flow behavior in a randomly packed bed due to the reflection/refraction of light and/or overlapping bubbles, even if the test section is made of transparent materials. Therefore, in this study, a test section, which simulates a two-dimensional network of porous structures, was fabricated to avoid overlapping bubbles. The two-phase flow pattern in the porous structure has been identified by high-speed imaging of the two-dimensional network model. The flow regime map based on the flow pattern visualization results is applied to the pressure drop evaluation and it could reduce the overestimation of experimental values. The experimental results suggested that the interfacial drag term should be modified in the gas-liquid two-phase flow pressure drop model.

• Built a condensation two-phase flow and heat transfer experimental system. • Identify the flow regime and develop the flow pattern map in spiral tube. • Exploration of the formation and transformation of flow patterns inside pipes. • A new model for the condensation flow pattern of non-azeotropic refrigerant. The flow patterns have a significant impact on the flow and heat transfer characteristics of the working fluid, making it fundamental for the study of complex two-phase flows. To investigate the condensation flow pattern and flow pattern transformation mechanism with mixed hydrocarbon in a spiral tube, a two-phase flow pattern experimental system was designed. The effects of mass flux (196–540 kg/m−2·s−1), vapor quality (0–1), and operating pressure (2–4 MPa) on flow patterns of methane/ethane/propane/isobutane mixed fluid in spiral tubes were analyzed. The results showed that with the increase in vapor quality, flow patterns such as bubbly flow, intermittent flow, wavy-stratified flow, and annular flow were observed in sequence. Additionally, through a comparative analysis of the experimental observations with existing flow pattern maps, a new flow pattern map tailored for the condensation two-phase flow of mixed hydrocarbon working fluids has been established. Based on the influence of inertial force, surface tension, gravity, shear force and other forces, Martinelli number, Soliman We and Soliman Fr are selected for the development of flow pattern conversion criteria. The new flow pattern map accurately predicts the majority of flow patterns. [ABSTRACT FROM AUTHOR]

Venturi-based differential pressure flow meters have proven to be robust and well suited to measure the flowrate of multiphase flow in combination with other measurement techniques. However, important challenges remain in order to reduce the effect of flow regime dependent measurement uncertainties from non-homogeneous flow. Understanding the complexities of multiphase flow through a Venturi is critical, not only for the Venturi flow measurement but also for the potential implications it might have on adjacent measurements affected by the constriction-induced flow perturbations. In this study, we examine the evolution of multiphase flow through a vertically oriented Venturi situated downstream of a T-bend, with a particular emphasis on the effects this might have on associated measurements within a multiphase metering context. Using Gamma-ray tomography, we conducted measurements at the inlet, throat, outlet, and downstream of the Venturi across a wide range of flow rates and Gas Volume Fractions (GVFs). We evaluated gas fraction (GF), slip, and cross-sectional distribution, quantified using measures of asymmetry and annularity. Our findings suggest that deviations between GF and GVF, relative slip velocity, annularity, and asymmetry are generally less at the outlet and downstream of the Venturi compared to the inlet and throat. Notably, annularity exhibits a greater impact than asymmetry on the estimation of bulk fractions from cord measurements. Overall, the study suggests that there may be more favorable conditions for measurements that require a homogeneous mix and less difference between GF and GVF at the outlet or a short distance downstream of the Venturi. However, despite the inlet results showing larger deviations due to inhomogeneous flow compared to the outlet and downstream, these results demonstrate a more predictable pattern in line with predictive models, offering potential benefits for the application of corrective models. [ABSTRACT FROM AUTHOR]