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In order to ascertain the effects of atmospheric pressure on developmental characteristics and the stability of AEA (air-entraining agent) solution bubbles, AEA solution experiments and AEA solution bubble experiments were, respectively, conducted in Peking (50 m, 101.2 kPa) and Lhasa (3,650 m, 63.1 kPa). Surface tensions and inflection-point concentrations were tested based on AEA solutions, whilst developmental characteristics, thicknesses and elastic coefficients of liquid films were tested based on air bubbles of AEA solutions. The study involved three types of AEAs, which were TM-O, 226A, and 226S. The experimental results show that initial sizes of TM-O, 226A, and 226S are, respectively, increased by 43.5%, 17.5%, and 3.8%. With the decrease of ambient pressure, the drainage rate and the drainage index of AEA solution bubbles increase. Interference experiments show that the liquid film thicknesses of all tested AEA solution bubbles are in micron scales. When the atmospheric pressure decreases from 101.2 to 63.1 kPa, the liquid film thicknesses of three types of AEA solutions decrease in various degrees; and film elasticities at critical thicknesses increase. Liquid film of 226S solution bubbles is the most stable, presenting as a minimum thickness variation. It should be noted that elastic coefficient of liquid film only represents the level at critical thickness, thus it can not be applied as the only evaluating indicator of bubble stability. For a type of AEA, factors affecting the stability of its bubbles under low atmospheric pressure include initial bubbles size, liquid film thickness, liquid film elasticity, ambient temperature, etc. [ABSTRACT FROM AUTHOR]

Conventional conductivity methods for measuring the void fraction in gas-liquid multiphase systems are typically affected by accuracy problems due to the presence of fluid flow and salinity. This study presents a novel approach for determining the void fraction based on a reciprocating dynamic conductivity probe used to measure the liquid film thickness under forced annular-flow conditions. The measurement system comprises a cyclone, a conductivity probe, a probe reciprocating device, and a data acquisition and processing system. This method ensures that the flow pattern is adjusted to a forced annular flow, thereby minimizing the influence of complex and variable gas-liquid flow patterns on the measurement results; Moreover, it determines the liquid film thickness solely according to circuit connectivity rather than specific conductivity values, thereby mitigating the impact of salinity. The reliability of the measurement system is demonstrated through laboratory experiments. The experimental results indicate that, in a range of gas phase superficial velocities 5–20 m/s and liquid phase superficial velocities 0.079–0.48 m/s, the maximum measurement deviation for the void fraction is 4.23%. [ABSTRACT FROM AUTHOR]

In this work, numerical simulations are performed to predict two-phase annular flow of refrigerant R245fa inside a 3.4 mm diameter vertical channel. The VOF (Volume of Fluid) method implemented in an OpenFOAM solver is used to accurately track the vapor-liquid interface. A 2D axisymmetric domain is considered and the Adaptive Mesh Refinement (AMR) method is applied to the cells near the liquid/vapor interface. The Reynolds-Averaged Navier Stokes (RANS) equations are solved and the k-ω SST model is adopted for turbulence modelling in both the liquid and vapor phase. Simulations are used to calculate instantaneous and mean values of the liquid film thickness at mass flux G = 100 kg m-2 s-1 and vapor quality ranging between 0.2 and 0.85. Numerical results are compared against measurements of the liquid film thickness taken during vertical annular downflow. Previous works from the literature and the deviations observed between present numerical and experimental results suggest the need for turbulence damping at the vapor-liquid interface by adding a source term in the ω equation. The simulations show that a low value of the turbulence damping parameter (e.g. 1) causes the average liquid film thickness to increase by 25 %–52 % compared to the non-damped scenario. The interface presents large amplitude disturbance waves in the non-damped case, whereas small ripple waves are predicted when turbulence damping is introduced. Furthermore, the difference between the application of a symmetric and asymmetric treatment for the source term is analysed. From the comparison between experimental data and numerical simulations, it emerges that the value of the correct damping source term to be applied is strictly dependent on the vapor quality.

This study investigates wave-stratified flow in a horizontal pipe at high pressure, and flow characteristics are obtained, such as flow pattern map, liquid film thickness, and pressure drop. Compared with a flow pattern map of a gas-liquid two-phase flow carried out at atmosphere, stratified flow zone is depressed with increasing system pressure and the critical gas superficial velocity decreases for smooth-wave-stratified flow transition, while the critical liquid superficial velocity increases for stratified-intermittent transition. On one hand, the compressed air results in an increase in momentum transfer between gas and liquid phases, which accounts for the smaller gas superficial velocity that is encountered in both smooth-wave and stratified-annular flow transition at higher pressure. One the other hand, it slows down the liquid below the crest, and it makes the interface wave crest unstable and split for the vortex shedding behind the wave crest, which accounts for flow regime transition in gas-liquid two-phase flows in pipelines. As a result, stratified-intermittent flow transition is depressed and delayed. The pressure influence on the liquid film profile is analyzed, and relationships between film thickness and dimensionless numbers are studied, such as liquid Weber number and gas Weber number. Friction factors on different interfaces at high pressure are studied, and new empirical formulas are deduced. [ABSTRACT FROM AUTHOR]

Centrifugal granulation technology using a spinning cup opens a potential way to recycle steel slag that is currently difficult to reuse. The objective of this research was to study the flow characteristics of a molten slag–metal mixture that was produced during smelting reduction in molten steel slag, passing over a spinning cup, so as to explore the feasibility of using centrifugal granulation technology to treat the steel slag. This was achieved by developing and implementing a computational fluid dynamics (CFD) model that incorporated free-surface multiphase flow to predict the thickness of the liquid slag film at the edge of the spinning cup (slag film thickness for short), which was an important parameter for estimating the size of the slag particles resulting from centrifugal granulation of the molten slag–metal mixture. The influences of various relevant parameters, including spinning cup diameter, slag feeding rate, cup spinning speed, etc., on the slag film thickness were analyzed. Additionally, hot experiments on centrifugal granulation of a molten slag–metal mixture were conducted to verify the results of the numerical simulations. The experimental results indicated a progressive reduction in the Sauter mean diameter of the slag particles as the metallic iron content in the slag increased. Specifically, when the iron content rose from 5% to 15% at a cup spinning speed of 2500 RPM, the Sauter mean diameter decreased by 13.77%. The numerical simulation results showed that the slag film thickness had a positive relationship to the slag feeding rate but a negative relationship to the spinning cup diameter and the cup spinning speed. Furthermore, the ratio between the mean slag particle diameter and the slag film thickness decreased nearly linearly with the increase in the metallic iron content in slag, with the average ratio being approximately 4.25, and this relationship was useful for estimating the slag particle size from the slag film thickness. Therefore, the present research results can provide theoretical guidance for the industrial application of spinning cup centrifugal granulation technology to effectively treat and recycle steel slags. [ABSTRACT FROM AUTHOR]

The falling film heat exchanger over horizontal tubes has the advantages of high heat and mass transfer efficiency, low resistance, simple structure and so on. It is widely used in traditional fields such as chemical industry and field of energy conservation and emission reduction of energy utilization. Complex coupling flow and heat and mass transfer processes are occured in falling film heat exchanger. The progress of experimental and numerical simulation research methods was reviewed. The multiple influences of different operating parameters ( such as gas temperature, gas flow direction, gas flow rate, solution flow rate, solution temperature, solution concentration, internal media flow rate and temperature) and structural parameters (such as tube diameter and tube spacing) on flow characteristics of falling film over horizontal tubes were reviewed, such as intertube flow pattern, liquid film thickness and wettability, etc. And the influence rules on the performance of heat exchangers such as evaporative heat transfer characteristics and absorptive heat and mass transfer characteristics were reviewed, including the overall performance and local fine characteristics, which provided theoretical support for improving the performance optimization of falling film heat exchangers over horizontal tubes. It was pointed out that the coupling effects of multi-dimensional local flow and heat and mass transfer performance under different gas flow characteristics and multi-factor interaction as well as strengthening heat transfer means will be there search direction of falling film heat exchangers over horizontal tube in the future. [ABSTRACT FROM AUTHOR]

This study reports the effects of the grid spacer with mixing vane (MV) on gas velocity for air single-phase flow and liquid film thickness for air-water two-phase annular flow in a 3 × 3 rod bundle channel. To investigate the effects of the shape of the spacers, three kinds of spacers were installed into the channel: spacer without MV (without MV), spacer with four MVs (4-MV30), and spacer with two MVs (2-MV30). The 4-MV30 and 2-MV30 had vanes that were inclined 30 deg from the vertical axis. Gas velocity was measured with a hot-wire anemometer and liquid film thickness was measured with the constant electric current method. From the gas velocity measurement, it was found that the irregularities in the velocity distribution became smaller toward downstream of the spacer. For the 2-MV30, the flow distribution was asymmetric and the flow was biased. From the liquid film thickness measurement, it was found that the liquid film thickness became thicker downstream of the spacer. [ABSTRACT FROM AUTHOR]

Traditional conductivity method for measuring the liquid-holding of gas-liquid two-phase flow is often affected by the flow pattern and salinity, resulting in reduced measurement accuracy and range. To overcome these limitations, a method for measuring liquid holdup using a reciprocating dynamic conductivity probe under forced annular flow conditions has been proposed. The measurement device consists of a cyclone, conductivity probe, automatic probe reciprocating system, and data acquisition and processing system. On the one hand, this measurement method adjusts the flow pattern to a forced annular flow, so that the measurement results are not affected by the complex and variable gas-liquid flow patterns. On the other hand, the thickness of the liquid film is determined solely based on the circuit's on-off, without relying on the specific conductivity, thus overcoming the influence of mineralization on the measurement results. Numerical simulations were used to determine that the dynamic conductivity sensor should be located approximately 6D downstream of the swirl generator for measuring the liquid film, in which D is the measurement of the inner diameter of the pipe section. Laboratory experiments were conducted to verify the feasibility of the device, and the results show that within the experimental parameter range of gas phase superficial velocities of 5 ~ 20 m/ s and liquid phase superficial velocities of 0. 079 ~ 0. 48 m/ s, the maximum deviation of liquid holdup is 10. 45% . [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.)

Liquid films are an important part of liquid metal granulation in the process of centrifugal spray forming. The size of the granulated particles has an important influence on the density, grain size and microstructure uniformity of the deposited blanks. The particle size is closely related to the flow characteristics of liquid films. Therefore, enhancing our understanding of the flow characteristics of liquid films can provide guidance for forming blanks. In this study, force analysis of a liquid film on the surface of a high-speed rotating centrifugal disc used in centrifugal spray-forming technology was carried out using D'Alembert's principle and Newton's law of viscosity. Then, combined with the principle of mass conservation, a theoretical model of the smooth flow of the liquid metal film was established. The experimental values obtained by Leshev were compared with our values to verify the correctness and accuracy of the model. Through the model, the influencing factors of the liquid film flow were obtained, such as the centrifugal disc speed, centrifugal disc radius, inlet volume flow rate and kinematic viscosity. Taking A390 aluminum alloy as the research object, the influence of the process parameters on the thickness, velocity and trajectory of the liquid film was revealed theoretically, and the relationship between the process parameters and the trajectory length and liquid film thickness was clarified. Modeling and analysis can not only help us to understand the flow of a liquid film, but also help us to predict the relevant parameters, which is convenient for the accurate and rapid regulation of the process to obtain the desired flow parameters. Therefore, the research content of this paper is of great significance for the preparation of billets with a uniform microstructure and excellent mechanical properties. [ABSTRACT FROM AUTHOR]

This study investigates wave-stratified flow in a horizontal pipe at high pressure, and flow characteristics are obtained, such as flow pattern map, liquid film thickness, and pressure drop. Compared with a flow pattern map of a gas-liquid two-phase flow carried out at atmosphere, stratified flow zone is depressed with increasing system pressure and the critical gas superficial velocity decreases for smooth-wave-stratified flow transition, while the critical liquid superficial velocity increases for stratified-intermittent transition. On one hand, the compressed air results in an increase in momentum transfer between gas and liquid phases, which accounts for the smaller gas superficial velocity that is encountered in both smooth-wave and stratified-annular flow transition at higher pressure. One the other hand, it slows down the liquid below the crest, and it makes the interface wave crest unstable and split for the vortex shedding behind the wave crest, which accounts for flow regime transition in gas-liquid two-phase flows in pipelines. As a result, stratified-intermittent flow transition is depressed and delayed. The pressure influence on the liquid film profile is analyzed, and relationships between film thickness and dimensionless numbers are studied, such as liquid Weber number and gas Weber number. Friction factors on different interfaces at high pressure are studied, and new empirical formulas are deduced.

Falling film flow is critical in the shell-side heat transfer performance of spiral-wound heat exchangers, and the wettability of the tube surface has a significant effect on the falling film flow characteristics. Therefore, a three-dimensional numerical model with two rows of tubes was established to study the influence of surface wettability on the liquid film distribution outside the tubes of a spiral wound heat exchanger. The transient spreading characteristics of the liquid film under different wettabilities were studied, the thickness of the liquid film along the axial and circumferential directions of the tube surface was quantitatively measured, and the effects of the tube spacing and Reynolds number on the flow characteristics of the falling film were analyzed. The results indicate that for the upper half-tube, increasing the contact angle to a certain extent is beneficial for improving the uniform distribution of the liquid film, whereas for the lower half-tube, decreasing the contact angle can suppress the fluctuation of the liquid film. The influence of the contact angle on the axial spreading of the liquid film was greater than that in the circumferential direction. When the contact angle does not exceed 30°, increasing Re can improve the wetting ratio, otherwise, increasing Re number has a limited effect on improving the wetting ratio. A smaller tube spacing can increase the thickness of the liquid film outside the tube. When the tube spacing changed from 4 mm to 8 mm, the average liquid film thicknesses of the circular, elliptical and egg-shaped tube decreased by 4%, 30.7% and 59.6% respectively. • A 3D falling film flow model of SWHE was established to study the effect of wettability. • Appropriately increasing the contact angle can improve the local liquid film distribution. • Increasing the Re number has limited effect on the wetting ratio at large contact angles. • Smaller tube spacing can increase the thickness of the liquid film on the tube surface. [ABSTRACT FROM AUTHOR]

Horizontal tube falling film evaporator is widely used in seawater desalination and chemical industry. A three-dimensional numerical model was established, and the heat transfer characteristics of falling film evaporation process outside the horizontal tube were numerically simulated using volume of fluid(VOF)method and user defined function (UDF )program. The effects of different tube spacing, spray density, evaporation temperature and tube diameter on the liquid film thickness and average heat transfer coefficient of smooth tube and enhanced tube were deeply studied. The simulation results show that under the same conditions, the average heat transfer coefficient of the strengthened tube is significantly higher than that of the smooth tube. It can be seen that optimizing the heat transfer surface structure based on the bionics principle can effectively improve the heat transfer efficiency of falling film evaporation outside the horizontal tube. The average heat transfer coefficients of the smooth tube and the strengthened tube increased with the increase of evaporation temperature, and increased first and then decreased with the increase of spray density. The average heat transfer coefficients of smooth tubes and strengthened tubes increase with the increase of tube spacing, and increase first and then decrease with the increase of spray density. The average heat transfer coefficient of heat exchange tube increases with the increase of evaporation temperature, and then decreases with the increase of spray density. [ABSTRACT FROM AUTHOR]

A 3D falling film flow model outside the horizontal tube is established to study the influence of the liquid column impact the wall on the liquid film thickness distribution. It is found that the liquid film thickness fluctuates significantly at 0°–60° in single liquid column, and the minimum thickness appears. In the jet flow, there is a critical value of 70° due to the liquid film fluctuation. The liquid film thickness change before 70° was negatively correlated with Reynolds number and positively correlated after 70°. And the fluctuation amplitude negatively correlates with the Reynolds number. [ABSTRACT FROM AUTHOR]

Falling film evaporation is the core heat transfer mode of spiral-wound heat exchangers used in the liquefaction process of natural gas. In order to study the impact of different Reynolds numbers, outer diameters and spacings of pipeline on the parameters of the falling film flow of alkane media, such as the flow pattern and liquid film thickness, numerical simulation study of falling film flow was performed with the coupling model based on the VOF and Level Set two-phase flow models. Meanwhile, the numerical simulation model was verified by setting a visual experimental device. In addition, the calculating equation of liquid film thickness applicable to the alkane media was obtained by fitting based on the numerical simulation results. According to the results, the Reynolds number and the outer diameter of pipeline have great influence on the distribution of liquid film thickness. In the case that the outer diameter of pipeline is 4 mm, the liquid film thickness of falling film flow is uniform with poor stability at great Reynolds number (340–1 700). In general, the research results could provide theoretical guidance to the design and the safe and efficient operation of spiral-wound heat exchangers during the liquefaction of natural gas.

• The collision dynamics between viscous droplets and heated particles are studied. • The particle undergoes the greatest temperature drop in bubble-breakup mode. • Each collision dynamic mechanism is quantitatively analyzed and detailed. • Six different collision patterns are identified based on Re-T and We-T. • Particle temperature drives collision behavior with Re over 100 and We over 55. The collision process involving droplets and heated particles has gained significant attention due to its wide industrial relevance. This study utilizes a high-speed photography to investigate the collision dynamics between viscous droplets and heated particles. The research identifies six distinct collision patterns. In the bubble-breakup mode, the particle experiences the greatest temperature drop, resulting in the most substantial heat transfer. The particle temperature plays a crucial role in determining collision behavior when the Reynolds number exceeds 100 and the Weber number exceeds 55. The maximum spreading area demonstrates a linear relationship with the Weber number, while it reaches a peak and stabilizes with Reynolds numbers in the deposition regime. Contact angle fluctuations are caused by the instability of the contact line. The liquid film thickness exhibits linear and power growth phases, followed by a rapid decrease in the bubble-breakup regime. While the branch-breakup pattern sees smaller fragmented droplet sizes, the atomization-breakup pattern sees flow velocity rise with both Reynolds and Weber numbers. The predicted wavelength of the disturbance in the atomization regime, based on Rayleigh-Taylor instability theory, aligns well with the experimental measurements. The residence time correlates positively with the Weber number. [ABSTRACT FROM AUTHOR]

Liquid films are an important part of liquid metal granulation in the process of centrifugal spray forming. The size of the granulated particles has an important influence on the density, grain size and microstructure uniformity of the deposited blanks. The particle size is closely related to the flow characteristics of liquid films. Therefore, enhancing our understanding of the flow characteristics of liquid films can provide guidance for forming blanks. In this study, force analysis of a liquid film on the surface of a high-speed rotating centrifugal disc used in centrifugal spray-forming technology was carried out using D’Alembert’s principle and Newton’s law of viscosity. Then, combined with the principle of mass conservation, a theoretical model of the smooth flow of the liquid metal film was established. The experimental values obtained by Leshev were compared with our values to verify the correctness and accuracy of the model. Through the model, the influencing factors of the liquid film flow were obtained, such as the centrifugal disc speed, centrifugal disc radius, inlet volume flow rate and kinematic viscosity. Taking A390 aluminum alloy as the research object, the influence of the process parameters on the thickness, velocity and trajectory of the liquid film was revealed theoretically, and the relationship between the process parameters and the trajectory length and liquid film thickness was clarified. Modeling and analysis can not only help us to understand the flow of a liquid film, but also help us to predict the relevant parameters, which is convenient for the accurate and rapid regulation of the process to obtain the desired flow parameters. Therefore, the research content of this paper is of great significance for the preparation of billets with a uniform microstructure and excellent mechanical properties.

In recent years, several gas-phase odor biosensors have been developed. Sensitive cells and multiple sensing elements were investigated for enhancing the performance of those biosensors. The thickness of the liquid layer that covers the cells, however, has rarely been so far explored. Recently we utilized the feedback control method to maintain a constant liquid film. Now we intended to step further about the alteration and estimation of this liquid film. Here, we developed a gas phase odor biosensor with variable liquid film thickness. The liquid layer thickness change was reflected as the impedance change between two electrodes. Thinner liquid film always resulted in greater response and faster peak time. For realizing such a thin liquid film state, withdrawing the buffer solution step by step was more preferred. Furthermore, the sample concentration dependency curves under normal and thin liquid layer conditions proved thin liquid film improved response evidently. Moreover, the weakened stability caused by thin liquid film was explained. Finally, we calculated the liquid film thickness according to the feedback control signal and validated the estimation result by manual operation. It revealed a steady liquid film thinner than 100 $\mu \text{m}$ was implemented in this system. This study demonstrated the advantages of thin liquid layer and provided an access to estimation and fine adjustment of liquid film thickness in gas phase odor biosensors. [ABSTRACT FROM AUTHOR]

After the Fukushima nuclear accident, the safety of spent fuel pool has attracted much attention. Under extreme accident conditions, the spent fuel pool may lose make-up water and cooling for a long time, causing the water level in the spent fuel pool to drop, resulting in excessive temperature of spent fuel rods, even damage to fuel assemblies and leakage of radioactive substances, come into being serious safety problems. In order to avoid this safety problem, the third generation nuclear power plants, such as AP1000 and CAP1400, introduced spray cooling system. Under the condition of spraying, the liquid film flow characteristics on spent fuel rods is an important factor affecting the cooling effect, which has not been studied in detail by domestic and foreign scholars. Too large or too small spray flow rate may lead to the rupture of the liquid film on the spent fuel rod. Therefore, it is necessary to study the flow characteristics of the liquid film on the spent fuel rod. In this paper, optical method was used to study the time and space variation of liquid film thickness formed by spray cooling of single spent fuel rod at different Reynolds numbers. The liquid film image was captured by CCD camera, and the clear liquid film thickness image and good coincidence data were obtained after processing. Using the obtained data, the fluctuation images of liquid film at different Reynolds numbers at fixed positions of spent fuel rod and at different positions of spent fuel rod at fixed Reynolds numbers were drawn. In addition, the variation trend of time-averaged liquid film thickness on spent fuel rod at different Reynolds numbers was obtained. The experimental results show that when Reynolds number is in the range of 608-7 538, the maximum value of transient liquid film thickness is 2.36 mm, which occurs when Reynolds number is 7 085. With the increase of Reynolds number, the time mean liquid film thickness will increase, and the amplitude of liquid film fluctuation will also increase. Along the rod direction, with the increase of the distance from the top of the rod, the liquid film thickness will gradually decrease and become stable, and as the Reynolds number increases, the stable part will appear farther from the top of the rod. The research on the flow characteristics of single rod coolant film of spent fuel lays a foundation for determining the minimum spray flow rate with effective cooling capacity.

This paper seeks to decipher the exact relationship between the liquid film thickness and the hydrodynamics of gas-liquid slug flows. An instantaneous measurement system is developed by integrating the laser focus displacement meter (LFDM) and high-speed camera to characterize the temporal evolution of the liquid film and the dynamic characteristics of continuous slug flows. A glass tube with internal diameter of 0.75 mm is used and the tested ranges of superficial gas and liquid velocities are 0.01–1.2 m/s and 0.01–0.09 m/s respectively. The non-zero signals of LFDM representing the bubble slug flows changed from regular periodic intervals to chaotic fluctuations when slug-annular flow pattern appears. The dominant frequencies of the periodic intermittent slug flows increased from about 0.5–2 Hz to nearly 10–20 Hz as the superficial gas velocity rised from 0.025 to 0.78 m/s. The bubble and liquid slug lengths calculated by the time interval of liquid film thickness and bubble velocity correlated well with the empirical model. Meantime, the average value of void fraction derived from the calculation of transient liquid film thickness shows a linear growth with the gas holdup ratio. [ABSTRACT FROM AUTHOR]

The liquid film formed around the inner walls of a small horizontal circular pipe often exhibits non-uniform distributions circumferentially, where the film is thinner at the top surface than the bottom one. Even with this known phenomenon, the problem remains a challenging task for Computational Fluid Dynamics (CFD) to predict the liquid film formation on the pipe walls, mainly due to inaccurate two-phase flow models that can induce an undesirable 'dry-out' phenomenon. Therefore, in this study, a user-defined function subroutine (ANNULAR-UDF) is developed and applied for CFD modelling of an 8.8 mm diameter horizontal pipe, in order to capture transient flow behaviour, flow pattern formation and evolving process and other characteristics in validation against experiments. It is found that CFD modelling is able to capture the liquid phase friction pressure drop about maximum of 30% in deviation, consistent to the correlated experimental data by applying an empirical correlation of Chisholm. Due to the gravity effect, the liquid film is generally thicker at the bottom wall than at the top wall and this trend can be further enhanced by increasing the superficial air–water velocity ratios. These findings could be valuable for HVAC industry applications, where some desirable annular flow features are necessary to retain to achieve high efficiency of heat transfer performance. [ABSTRACT FROM AUTHOR]

• A theoretical model of liquid film thickness during flow boiling for non-circular microchannels has been proposed. • This new model considers the effects of evaporation, shear force and transversal flow. • Numerical calculations are performed to investigate the temporal variations of transient liquid film thickness. Liquid film thickness is a dominant feature for understanding boiling heat transfer mechanism in microscale slug flow. Flow boiling in circular microchannels has been extensively studied. Microchannels with non-circular cross-section are more common in industrial applications, but there have been few studies on such complex cross-sections. In the present study, the transient liquid film thickness during flow boiling in non-circular microchannels was experimentally investigated by a laser confocal displacement meter. Non-circular tubes with inner dimension of 0.39 × 0.39, 0.5 × 0.5, 0.6 × 0.6, 0.7 × 0.7 and 0.3 × 0.8 mm2 were used for the test section, and water and ethanol were used as working fluids. The variation of liquid film thickness under adiabatic condition in non-circular microchannels was analyzed and an empirical correlation was proposed for predicting initial liquid film thickness. On this basis, a new theoretical model for liquid film thickness variation under flow boiling in non-circular microchannels was developed, considering the effects of evaporation, shear force and transversal flow. [ABSTRACT FROM AUTHOR]

A two-phase flow measuring device whose measurement system does not disturb the flow pattern, real-time measurement, and non-destructive measurement or non-intrusive model is a typical tool for an ideal situation. One measuring instrument that meets these criteria is an ultrasonic flow meter. Ultrasonic sensors can measure the velocity of fluid flow in pipelines. It has the advantage of high accuracy and reproducibility and does not make direct physical contact with the fluid in the pipe. Low fabrication costs and fast response make ultrasonic flowmeters widely used for two-phase flow measurements in both horizontal and vertical orientations. The void fraction or liquid holdup and velocity are the two most essential parameters for flow monitoring. The Time of Flight (ToF) method is mainly used for measurements in several ultrasonic flowmeter methods. In the present manuscript, the introductory section of this review explains the advantages of using the Time of Flight (ToF) method and its basic principles. This review also discusses research on measuring velocity and flow rate, differences in intrusive and non-intrusive measurement methods, parameters that affect ultrasonic measurements, and finally, measuring film thickness using non-intrusive methods. • The mass flow rate of two-phase flow is measured using a non-intrusive ultrasonic flowmeter. • The velocity of each phase and the void fraction or the liquid hold-up are two important parameters to be determined for two-phase flow mass flow rate measurement. • The Time of Flight (ToF) method and its basic principles, advantages are discussed in detail. • The comparison of flow patterns characterization using echo amplitude ratio method and other existing methods such as PDF (Probability Distribution Function), PSD (Power Spectral Density) and DWT (Discrete Wavelet Transform) is proposed. [ABSTRACT FROM AUTHOR]

The objective of this study was to reduce the uncertainties of correlations for flow characteristics in vertical pipes under flooding at the top end. The void fraction α, pressure gradient dP/dz, and countercurrent flow limitation (CCFL) were previously measured with diameter D = 40 mm and working fluid of air and water. The wall friction and interfacial friction factors (fw and fi) were obtained based on the annular flow model, and CCFL and fw were evaluated in detail. Hence, attention was turned to detailed evaluations of α and fi. Liquid film thickness δ and interfacial friction factor fi for smooth film (SF) due to flooding at the top end were obtained using the previously derived fw correlation and existing dP/dz data with D = 20 to 50.8 mm and pressure P = 0.1 to 4.1 MPa, and empirical correlations for δ and fi were derived. The δ term was well expressed by a function of the liquid Reynolds number ReL, and the uncertainty of the δ correlation was ±0.0062 for α = 0.87 to 0.98. fi was expressed by a function of δ/L (where L is the Laplace length) or the Kutateladze parameter KG*, the dimensionless diameter D* (=D/L), and the density ratio of the gas and liquid phases ρG/ρL. The applicability of the derived correlations to conditions of D = 300 mm and P = 7 MPa was evaluated, and the fi correlation was modified based on fi values computed with the δ correlation. The drift-flux parameters for SF were also considered. [ABSTRACT FROM AUTHOR]

The present study has evaluated the solidification and liquation cracks of GTD-111 superalloy by pulsed Nd:YAG laser techniques. For this purpose, samples were subjected to different temperatures under the conditions of heat treatment (1120, 1200 and, 1230 °C), pre-cooling (−30 and 0 °C), and pre-heating (100 and 200 °C). The Rosenthal equation was used for calculation of mushy zone (MZ), partially-melted zone (PMZ), and heat-affected zone (HAZ). The values of the temperature gradient (G) and welding cooling rate (G × R) were calculated using the Rosenthal equation. The results showed that by reducing the temperature of the sample before welding (from 200 to −30 °C), the G (from 3763.5 to 5821.5 °C/mm) and the G × R (from 31,237 to 48,310.2 °C/s) increased. Experimental test results were in agreement with Rosenthal's numerical results. Microstructural studies have shown that both solidification and liquation cracks are minimized by reducing the pre-cold temperature. This is attributed to the reduction in the segregation of alloying elements and the reduction in the volume of the weld pool. Further studies of the microstructure revealed that there was a correlation between the thickness of the grain boundary (GB) liquid and the formation of cracks. In this way, if the liquation material is from γ–γ′ eutectic and M3B2 boride, increasing the liquid film thickness (LFT) increases the sensitivity to cracking (Eq. (5) in the text), and if the liquation material is from γ′ phase and MC carbide, increasing the LFT reduces the sensitivity to cracking due to increased stress release.

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.)

Falling film evaporative heat exchangers are extensively used in processing industries; broad areas of application being refrigeration, desalination and food processing industries. The fundamental aspect of this type of heat transfer process is to extract the process heat in the form of latent heat by liquid which is sprayed over the surface of the process tubes. Formation of liquid film over a fully wetted horizontal round tube of falling film evaporator has been numerically simulated here. Two numerical approaches, Volume of Fluid (VOF) technique and the Eulerian multiphase model are applied to compare their results. The effect of varying flow and geometrical parameters on the film thickness is investigated. Two horizontal tubes of diameter 19.05mm and 25.04mm with three different uniform spacing have been selected for simulation. Film Reynolds numbers 650, 950 and 1250 are considered for the above set of parameters. Ii is observed that the geometrical and flow parameters considerably influence the film thickness. Transient analysis of the film formation has been carried out and parameters like pathline of liquid film and the velocity profile have been obtained for understanding the flow behavior in a better manner. All the simulated results agree well with the published data. [ABSTRACT FROM AUTHOR]

In order to evaluate effects of water levels in the upper tank hut on flow characteristics in a vertical pipe under flooding at its top end, counter-current flow limitation (CCFL characteristics), void fraction and pressure gradient were measured for counter-current flows of air and water in a vertical pipe with the diameter of 40 mm at hut = 200 and 300 mm in addition to data at hut = 100 mm measured in our previous study, and the wall and interfacial friction factors were obtained from the data. As a result, the falling water flow rate decreased with increasing hut, and a Wallis-type CCFL correlation with the Kutateladze parameters was derived as a function of hut. With increasing hut, the thickness of the falling water film decreased due to decrease in the falling water flow rate, and the wall and interfacial friction factors decreased due to decrease in the water film thickness. The annular flow model with correlations for CCFL, and the wall and interfacial friction factors could predict the effects of hut on the liquid volume fraction αL and the transition from αL decrease regime to αL increase regime with increasing the gas volumetric flux. [ABSTRACT FROM AUTHOR]

Taylor bubble/slug flow is a type of multiphase flow that is predominant in many natural and industrial applications. A thorough understanding of two phase flows and void fraction measurement is essential to understand thermal hydraulic behavior during accident conditions in nuclear reactors. The performance of mini-reactors/microreactors and microthrusters requires a complete knowledge on shape and size of the void fraction distribution, which governs the flow characteristics in mini-channels/microchannels. The present study focuses on analyzing the signal characteristics of two IR transceivers simultaneously during two-phase bubble/slug regime having varying liquid film thickness. The transceivers are positioned at 90° and 0° to the axis of a tube of 1.5 mm diameter and 2.5 mm thickness. The experimental signal output is compared with the results obtained from a numerical model developed using COMSOL Multiphysics package. The present study exposes the critical parameters that need to be considered while developing a 3D reconstruction methodology based on IR transceivers for volumetric void fraction measurement. [ABSTRACT FROM AUTHOR]

In horizontal annular flow, the high gas velocity leads to the strong randomness, rapidity and complexity of the structure and dynamic characteristics of gas-liquid interfacial wave. As one of the important parameters to describe the interfacial wave, the liquid film thickness is significant to study the hydrodynamic characteristics of the gas-liquid two-phase flow. In this paper, the ultrasonic echo resonance main frequency (UERMF) method and the ultrasonic reference signal elimination (URSE) method are compared by numerical simulation method. The minimum liquid film thickness measured by these two methods are 0.3 mm and 0.01 mm, respectively. Experiments are conducted on a stainless steel test section with an inner diameter of 50.0 mm to study annular air-water flow under five different pressure conditions (from 0.1 MPa to 0.7 MPa). The experimental data is processed using the URSE method to analyze the characteristics of the liquid film under different operating conditions. In addition, based on the aforementioned experimental dataset, a comparison is made regarding the performance of existing predictive correlations. It is found that the existing correlations have certain limitations in capturing the variations of liquid film thickness in annular flow, particularly at high pressures and for different pipe diameters. Therefore, a new liquid film thickness correlation suitable for different system pressures and pipe diameters is proposed. By expanding the range of fitted data points (220 data points), the 95 % relative error of improved model is within ±25 % error band for all available data (authors' and literature). The mean absolute percentage error (MAPE) is 11.08 %. The improved correlation has the applicability and extrapolation for different system pressure and pipe diameter conditions. • Numerical simulations confirm higher accuracy of URSE method. • Experiments under different pressures are conducted in horizontal annular flow. • Experimental results are compared and analyzed with existing predicted correlation. • A liquid film thickness correlation under different pressure and diameter is proposed. • The new model is validated by comparing with real flow experimental data. [ABSTRACT FROM AUTHOR]

• Quantitative characterization of the liquid film in downward vertical annular flow (DVAF) was presented • Tests were conducted in an apparatus with 26-mm ID and 14-m length using air-water as working fluids. • The downstream evolution of the flow was evaluated at two test sections placed at 90D and 335D from the flow inlet • A non-intrusive, dual ring-shaped conductance sensor is used to measure the liquid film features • Correlations to predict the main parameters of the unit wave in DVAF is proposed Experiments in downward vertical air-water annular flow in a 26-mm ID, 14-m length pipe were conducted to analyze and improve the understanding of the main characteristics of the liquid film thickness. The downstream evolution of the flow was analyzed at two test sections placed at 90D and 335D from the flow inlet. A non-intrusive conductance sensor and a high-speed camera were deployed to measure the characteristics of the liquid film in the test sections. Thirty-five combinations of superficial air and water velocities were investigated, ranging from 0 m/s to 20 m/s and 0.05 m/s to 0.25 m/s, respectively. The analysis of the liquid film thickness time series provided quantitative features such as the average film thickness, liquid film roughness, velocity, frequency, amplitude, length and the appearance of the disturbance waves. Individual identification of the disturbance waves was performed to investigate the velocity and frequency concerning the distribution of the waves and their interaction. Moreover, variations for all annular flow characteristics were observed in the flow direction and new correlations to estimate the main parameters of the unit wave in DVAF are proposed. [Display omitted] [ABSTRACT FROM AUTHOR]

The problem of laminar film condensation from binary vapours mixture with the presence of non-condensable gas (air) flowing in a vertical tube is numerically investigated. The set of the non-linear parabolic equations expressing the mass conservation, momentum, energy, and species diffusion in both phases with the boundary conditions are resolved by using a finite difference numerical scheme. A comparative study between the results obtained for three cases (water-ethanol-air, water-methanol-air, and ethanol-methanol-air) under the same conditions is made. The impact of varying the wall temperature, the inlet vapour mass fractions, and the inlet liquid mass flow rate on the conjugate the heat and mass transfer during the condensation of the studied mixtures are examined. It is found that the condensation of water-methanol-air corresponds to a higher latent heat flux QL2 and accumulated condensation rate Mr2 when compared with water-ethanol-air and ethanol-methanol-air. Moreover, the nature of the fluid plays an important role in the heat and mass exchanges.

The liquid film formed around the inner walls of a small horizontal circular pipe often exhibits non-uniform distributions circumferentially, where the film is thinner at the top surface than the bottom one. Even with this known phenomenon, the problem remains a challenging task for Computational Fluid Dynamics (CFD) to predict the liquid film formation on the pipe walls, mainly due to inaccurate two-phase flow models that can induce an undesirable ‘dry-out’ phenomenon. Therefore, in this study, a user-defined function subroutine (ANNULAR-UDF) is developed and applied for CFD modelling of an 8.8 mm diameter horizontal pipe, in order to capture transient flow behaviour, flow pattern formation and evolving process and other characteristics in validation against experiments. It is found that CFD modelling is able to capture the liquid phase friction pressure drop about maximum of 30% in deviation, consistent to the correlated experimental data by applying an empirical correlation of Chisholm. Due to the gravity effect, the liquid film is generally thicker at the bottom wall than at the top wall and this trend can be further enhanced by increasing the superficial air–water velocity ratios. These findings could be valuable for HVAC industry applications, where some desirable annular flow features are necessary to retain to achieve high efficiency of heat transfer performance.

Liquid film thickness is an important parameter for predicting phase change heat transfer in pulsating heat pipes (PHPs). This study experimentally evaluated the liquid film thickness formed during the oscillation of the liquid column within PHPs. The liquid column was oscillated sinusoidally under various oscillating conditions to simulate the flow phenomena. The average thickness of the liquid film formed during the oscillations was determined by comparing the oscillation amplitudes of the tip of the liquid column with and without the liquid film. It was confirmed that the average thickness of the liquid film varied with the capillary number for each working liquid (water, ethanol, and FC-40). The characteristic velocity of the capillary number was the time-average velocity of the tip of the liquid column, which was derived by assuming that the tip of the liquid column oscillated sinusoidally. Additionally, the average liquid film thicknesses during the liquid column oscillations were evaluated according to the correlations for various flow conditions proposed in previous studies. In this evaluation, the velocity and acceleration values obtained by assuming that the tip of the liquid column oscillated sinusoidally were determined based on the experimental results. This evaluation demonstrated the acceleration effect, thereby indicating that the acceleration made the liquid film thinner when the capillary number was higher than the threshold of the capillary number for each working liquid. Finally, empirical correlations with and without the acceleration effect were proposed for the average liquid film thickness of oscillating flows in terms of capillary and Laplace numbers. It was demonstrated that the proposed correlations could predict the average liquid film thickness within the range of approximately ±15 % accuracy.

The aim of this study is to examine experimentally the thickness variations of a falling film on plain and hydrophilic horizontal tube evaporator surfaces in order to enhance the performance of the horizontal tube evaporators. The hydrophilic surfaces are acquired by exposing them to plasma irradiation for a 120 s time period. A test loop has been installed, and by using electrical film thickness measuring devices, the distributions of the formed liquid thickness layer around the hot plain and hydrophilic surfaces are determined at different operating conditions. By analyzing the experimental data, the present results show that the film thickness around the hydrophilic tube changes with the same pattern around the plain tube. The film distribution along the peripheral angle is non-symmetrical, minimum film thickness values are more likely to appear at a different angular position of 90°–120° under various conditions. The film thickness is significantly decreased for hydrophilic surfaces. The film thickness mainly increases as the flow rate increases, while it decreases as the tube diameter increases, the evaporation pressure increases, the inlet water subcooling increases, and tube surface temperature increases. The feeder height has a minor influence on the film thickness. Comparison between the current results and results acquired by another researcher is in good agreement between 2.0% and 18%. [ABSTRACT FROM AUTHOR]

Falling film microreactors have contributed to the pursuit of process intensification strategies and have, over the years, been recognized for their potential in performing demanding reactions. In the last few decades, modifications in the measurement techniques and operational parameters of these microstructured devices have been the focus of many research studies with a common target on process improvement. In this work, we present a review dedicated to falling film microreactors, focusing on the recent advances in their design and operation, with particular emphasis on mass transfer enhancement. Analysis of the recent techniques for the measurement of mass transfer as well as the operational parameters used and their effect on the target objective, particularly in the liquid phase (being the limiting phase reactant), are included in the review. The relationship between the hydrodynamics of falling thin liquid films and the microreactor design, the discrepancies between measured and model results, the major challenges, and the future outlook for these promising microreactors are also presented. [ABSTRACT FROM AUTHOR]

In this study, the liquid film thickness of swirling annular flow has been measured by parallel conductivity probes. The differences of the liquid film between vertically downward swirling annular flow and straight flow have been investigated. A theoretical model for predicting the liquid film thickness in the swirling annular flow without decaying has been developed. The predicted liquid film thickness of 93.2% data points is within ±10% relative error band. The results prove that the model proposed in this study has satisfactory accuracy.

BackgroundWith the development of thorium molten salt reactor nuclear energy system (TMSR) from experimental reactor to research, demonstration and commercial reactor, its shafting evolved into the slender flexible rotor supported by submerged bearing. High temperature molten-salt pump is the main power device of TMSR, its stability and reliability are critical to the submerged bearing support characteristics.PurposeThis study aims to analyze bearing eccentricity on support characteristics of high temperature molten-salt pump for TMSR.MethodsThe numerical simulation method in Beperf module of DyRoBeS software was used for the theoretical calculation and analysis of the submerged bearing. Combined with experimental verification, the influences of various eccentricity on the supporting characteristics of the bearing were studied.ResultsThe results show that the eccentricity of the bearing decreases with the increase of rotational speed. With the augmentation of eccentricity, the orthogonal stiffness and damping of the bearing is increasing continuously, so are the cross stiffness and damping. Conversely, the thickness of minimum liquid film reduces continuously. The bearing pressure ends up with zero and zero gradient due to the attenuation of the minimum liquid film thickness when the eccentricity is greater than 0.6.ConclusionsIt is verified that the liquid membrane invalidation brings about serious wear of the bearing in actual operation, and this study provides theoretical guidance and experimental data support for the design of the submerged bearings of ultra-high temperature long shaft molten-salt pump.

We have been developing the ultrasonic liquid film sensor to measure the liquid film thickness under high-temperature and high-pressure conditions of Boiling Water Reactors (BWRs), focusing on thin film thickness in pre-/post-dryout. The liquid film sensor utilizes Time-of-Flight (ToF) detection based on the ultrasonic pulse-echo method. To detect the ToF from output ultrasonic signal of the liquid film sensor, the waveform subtraction in the time domain has been used as conventional method. However, subtracting signals in the time domain has some concerns for the ToF detection under actual steam-water conditions; e.g. a calibration test is forced to be carefully conducted in the single-phase flow. In the present study, we improved signal-processing performance for the liquid film measurement using cepstral subtraction method. In this method, the ToF was directly detected from convoluted waveforms by calculating cepstrum from Fourier transform and logarithm spectrum. Moreover, avoiding noise effect on the cepstrum was achieved by subtracting mean cepstrum in the qufrency domain; because multiple waveforms were acquired from repetition pulsing of ultrasonic signals at the same experiment, the noise effect could be removed due to unsteady characteristics of liquid film flow. In this study, the basic principle of the cepstral subtraction method was confirmed by a calculation test using simulated ultrasonic signals. Assuming the additive white Gaussian noise with average noise power of -90dB, the maximum error between input thickness and output thickness was 21% in the range of liquid film thickness of 0.008-0.300mm. Furthermore, the time-series liquid-film thickness was measured from actual signals acquired under BWRs' operating conditions at temperature of 286°C and pressure of 7MPa. Comparing to the thickness processed from the conventional time-domain subtraction method, the processed results of cepstral subtraction method showed good agreement. Consequently, we confirmed appropriateness of the cepstral subtraction method for the liquid film sensor under high-temperature and high-pressure conditions. [ABSTRACT FROM AUTHOR]

The discussion initiated by a brief message by Prof. E.D. Fedorovich allows for briefly recalling the evolution of ideas about the nature of the boiling crisis. Although the hydrodynamic model of the crisis, due to its clarity and simplicity of the calculation formula that follows from it, remains the most popular among specialists, experiments of the last 10–15 years confirm that this model objectively has no relation to nucleate boiling of a liquid. In most modern studies, an irreversible increase in the area of dry spots on the heating surface is taken as the cause of the crisis. A quantitative model based on this hypothesis was proposed by the author in 1988. However, in the absence of a rigorous mathematical description of the nucleate boiling process, any model in this area is approximate and long life is guaranteed for discussions about the mechanisms of the boiling crisis. [ABSTRACT FROM AUTHOR]

The corrugated plate dryer is an important steam-water separation device in the steam generator in the secondary loop of a light water reactor. It is essential to understand its steam-water separation mechanism. Most studies have shown that the separation efficiency of the corrugated plate is related to the thickness of the liquid film on the wall of the corrugated plate. We have studied the relationship between the thickness of the liquid film and the critical airflow velocity of the corrugated plate. At present, scholars mostly use the image method, ultrasonic method, and capacitance method to measure the thickness of thin liquid film. We have analyzed the application of these three methods in liquid film thickness measurement. Some important examples are listed. The results show that the capacitance method is recommended for liquid film thickness measurement experiments, whereas its accuracy is not particularly high. To pursue the higher accuracy, the image method is recommended. Planar laser-induced fluorescence (PLIF) technology is the first choice among image methods. The ultrasonic method is applicable in the case that the measurement data are large.