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This paper discusses the extension of an optical liquid film thickness measurement technique to characterize liquid film flow rate in wavy thin liquid film flow. The technique, based on laser refractometry, is used to measure wave height, shape, frequency, and velocity. A two-zone model to process the measured wave characteristics is used to estimate the liquid film flow rate. The method is validated in a falling film facility where easy optical access allows comparisons of the wave velocity measurements with high-speed videos and where the calculated liquid film mass flow rate can be compared with actual measurements. The paper provides a framework for analyzing time-resolved film thickness data using multizone models in more complex liquid film flows, such as in two-phase annular flow. [ABSTRACT FROM AUTHOR]

This paper presents a method for machining an annular groove on the inner wall of a steel tube by ball spinning. Based on spatial analytic geometry theory and assumptions about radial helical feed, the process utilizes a simplified expression of boundary curves of radial and tangential contact area between ball and workpiece. Through curve integration, the equations of radial and tangential contact areas for calculating ball-spinning force have been obtained. Based on results from calculation examples, this paper discusses the relationships between spinning depth, ball diameter, spinning feed, and ball-spinning force. The comparison of calculation results between the analytical model and the finite element method has been supplied, and the validity of the model has been certified. [ABSTRACT FROM AUTHOR]

Most of the current studies focus on the moving heat source model of straight wheel. However, these cannot be applied to calculate the cup wheel grinding temperature field, especially for the grinding processes performed with an adaptive end-effector. Based on the moving heat method and the principle of heat source superposition, the analytical thermal model of annular moving heat source for large surface workpiece is deduced. According to the parameters of the grinding instance, the numerical model is established by the finite element method for comparison and validating in this paper. The comparison results show that the characteristics of temperature distribution predicted by the analytical model and the numerical model agree very well. Two evident peak temperatures in grinding zone appear at both edges at the back of the grinding wheel in the feed direction, and test results with different grinding parameters show the relative errors do not exceed 19%. The feasibility of the analytical model and the numerical model based on different mathematical foundations is mutually validated. In the view of the non-uniform features of temperature distribution, especially the location of the peak temperature values, there are some reasonable explanations and analyses in this paper. [ABSTRACT FROM AUTHOR]

Two-phase (gas–liquid) flow in vertical pipes has been one of the interests of industrial applications such as power plants, nuclear reactors, boilers, gas well exploration and so on. One of the problems usually encountered in the gas well exploration industries is liquid loading: a condition where the gas velocity is not high enough to carry all the liquid generated in the gas wells. During normal operation, flow in the gas wells shows characteristics of annular flow regime. However, as the gas wells mature, the gas velocities reduce (below a critical value) and gradually lead to the onset of liquid loading (film reversal). At this point, flow in the gas well presents features of churn flow. Thus, during the film reversal point, the liquid film tends to increase in thickness and part of it starts to flow downwards. This paper first summarizes the available mechanistic and numerical models related to liquid loading and then reviews the application of CFD techniques to liquid loading modeling in vertical pipes. Most of the methodologies discussed here focus on annular and churn flow due to the limited information on the application of CFD techniques to liquid loading modeling and the onset of film reversal occurs during the transition from annular flow to churn flow which can lead to liquid loading as observed experimentally by many researchers. It was concluded from the available literature related to liquid loading that a detailed understanding of the fluid flow behavior during liquid loading is not yet fully available and prediction methods of this phenomenon are still rather incipient. Directions for good CFD modeling of these important phenomena are presented in the present paper. [ABSTRACT FROM AUTHOR]

With the excellent heat and mass transfer performance, the annular flow has been widely employed in industries. The study on the flow characteristics distribution of annular flow is the basis for revealing the flow mechanism and improving the performance. In this paper, based on the non-invasive planar laser-induced fluorescence technology, the circumferential characteristics of liquid film in horizontal annular flow and wavy flow are investigated. The circumferential film thickness and entrainment concentration are measured by the image processing. The spatial–temporal flow structure is reconstructed, and the cross-correlation analysis is conducted. The results show that the liquid entrainment and deposition phenomena contribute to the liquid film formation near the top of the pipe. In addition, a model which predicts the circumferential film thickness according to Froude number and circumferential angle is established. [ABSTRACT FROM AUTHOR]

The annular coaxial nozzle has good convergence and is widely used in laser melting deposition (LMD). In this paper, a new-type annular coaxial nozzle is developed, which can transform four-channel powder flow into annular distribution through the internal channel to obtain a more uniform distribution of powder in the circumferential direction. A three-dimensional computational fluid dynamics (CFD) numerical model is established. The dynamic behavior of Fe-based powder is described by discrete phase model (DPM). The influence of gas on powder particles is described by two-way turbulence coupling model. The convergence and transport characteristics of the nozzle are revealed. The accuracy of CFD model is verified by powder feeding experiment, and the deposition performance of powder nozzle is verified by single-track deposition experiment. The results show that the nozzle can provide stable powder feeding and excellent convergence characteristics. The powder flow is converged in a "Y" shape on the longitudinal section. The higher the powder concentration at the focal plane of the nozzle, the smaller the aspect ratio of single-track coating. The powder utilization rate of the nozzle can reach 76.97%. [ABSTRACT FROM AUTHOR]

The wavy structure of a liquid film sheared by high-velocity gas flow with droplet entrainment from the film surface has been investigated. The paper presents an analysis of methods for measuring the local fluid film thickness and a review of classical concepts of the wave hydrodynamics of annular dispersed flow obtained in early studies using rather crude methods. A systematic description of the structure, evolution, and interaction of waves of various types is given based on an analysis of high-resolution spatio-temporal records of film thickness obtained by laser-induced fluorescence. The results are compared with the results of recent experiments, and the necessity of revising some classical concepts is shown. Directions for further research are suggested. [ABSTRACT FROM AUTHOR]

Under time-varying loads, thermoelectric devices are prone to failure due to fatigue accumulation. The fatigue life of annular thermoelectric generators (ATEGs) has not yet been studied. The primary goal of this paper is to numerically investigate the fracture parameters and fatigue life of ATEG legs with central cracks. When there are central circumferential and radial cracks, the effects of temperature difference on the stress intensity factor (SIF) at the crack tip and fatigue life of the ATEG are investigated in the case of specific geometry. The results show that, in the temperature range 300–550 K, while the SIF at the fracture tip increases as the temperature difference increases, none of its values exceed the critical SIF, which prevents crack propagation. Nonetheless, the thermal cycling load can cause fatigue fracture and crack propagation in the legs, and a greater temperature difference shortens the service life of the ATEG. Furthermore, when the temperature difference is 50 K, the ATEG with a central radial crack have an 18.7% longer lifetime than the ATEG with a central circumferential crack. The findings will provide a theoretical foundation and recommendations for long-term reliable application of ATEGs in waste heat recovery. [ABSTRACT FROM AUTHOR]

A high-speed backlight system was adopted to investigate the evolution process of the inside-out-gas (IOG) effervescent atomizer and subsequent influence on spray morphology. The results show that bubble flow and annular flow are the most obvious flow patterns when the liquid flow rate is 20 g/s. During the transition from bubble to annular flow, slug flow occurred at gas–liquid mass ratio (GLR) of 3.2%. The annular flow was observed when the GLR further increased to 6.4%. In particular, when the mixing chamber is in a large bubble flow, an annular flow can still be formed at the orifice for the small exit diameter. For the annular flow, a relatively stable spray cone angle was observed. On the contrary, the slug flow has a greater oscillation for the spray cone angle. It was found that bubble flow in the orifice has little effect on atomization effect. For the spray cone angle, the oscillation in the slug flow is larger. Furthermore, the effects of GLR and liquid injection pressure drop are carefully considered in the empirical formula fitting compared to the widely used empirical formula. The empirical formula of the discharge coefficient of the effervescent atomizer is fitted, which provides fast data support for engineering applications. [ABSTRACT FROM AUTHOR]

This paper develops mathematical models for a proposed production logging tool, which uses capacitance sensors to measure liquid annulus thickness and liquid type for a primarily gas-carrying wellbore. A semi-analytical method is devised which uses Fourier analysis to account for the complicated system geometry and reduces the problem to singular integral equations over a sensor electrode. Approximate solutions of these integral equations give expressions for capacitance, which is calculated for different liquids and varying liquid annuli thicknesses and electrode positions. These results are compared with capacitance values found using COMSOL Multiphysics, a finite element package. Good agreement is obtained between these two methods, with a discrepancy range of 1-8 %. Capacitance values obtained range from 32 to 93 pF/m, and sensitivity is estimated to range from 0.8 to 60 %, depending mainly on the proximity of the electrode to the liquid and also on the permittivity and thickness of the liquid layer. Practical implications of the study are also discussed. Realistically useful measurements, where ~0.2 mm of liquid is detectable, can potentially be made using an electrode 4-6 mm away from the inner wellbore wall. [ABSTRACT FROM AUTHOR]

To investigate the boiling characteristics of flow outside the R410A tube under swaying conditions, this article conducts numerical simulation and experimental research on the flow boiling heat transfer of R410A outside a horizontal tube. The results show that when the swing frequency increased from 0.2 to 2 Hz, the sway amplitude is 0.03 m, the heat flux on the inner wall of the runner remains unchanged, and the mass flow rate increases from 85 to 170 kg/(m2·s), which makes the heat transfer coefficient of the working fluid in the annular area increases significantly. Keeping the inlet mass flow rate unchanged, the heat flux on the inner wall of the flow channel increases from 25 to 35 kW/m2, the heat transfer coefficient of the working fluid in the annular area has also improved, but under high heat flux conditions, the working fluid is evaporated and dried, its heat transfer coefficient increases less than in low heat flux conditions. When the sway amplitude increases from 0.02 to 0.07 m, the sway frequency is 0.2 Hz and 2 Hz respectively, and the heat transfer coefficient of the working fluid shows a downward trend as a whole. The studies provide a reference for heat exchanger design suitable for offshore swaying conditions. [ABSTRACT FROM AUTHOR]

Wavy structure of liquid film in annular gas–liquid flow without liquid entrainment consists of fast long-living primary waves and slow short-living secondary waves. In present paper, results of spectral analysis of this wavy structure are presented. Application of high-speed LIF technique allowed us to perform such analysis in both spatial and temporal domains. Power spectra in both domains are characterized by one-humped shape with long exponential tail. Influence of gas velocity, liquid Reynolds number, liquid viscosity and pipe diameter on frequency of the waves is investigated. When gravity effect is much lesser than the shear stress, similarity of power spectra at different gas velocities is observed. Using combination of spectral analysis and identification of characteristic lines of primary waves, frequency of generation of secondary waves by primary waves is measured. [ABSTRACT FROM AUTHOR]

Using a newly developed experimental setup, the features and advantages of an autothermal single-casing atmospheric subbituminous coal fluidized bed air-blown gasifier, combining a combustion and gasification section, and mixing the dispersed phase (inert material, char) and heat exchange between them through an annular transfer device, have been revealed. To increase the efficiency of the gasifier, an experimental-computational method was developed find the conditions for optimal operation, combining changing the annular flow's geometry and regulating the primary air for gasification. A simple and reliable multizone thermodynamic calculation model makes it possible to predict the composition of char and syngas in the gasification section with acceptable accuracy. This method confirmed that a two-section fluidized bed gasifier can provide efficient gasification of solid fuels and is suitable for use in small-scale cogeneration plants. Syngas with a heating value of 3.6–4.5 MJ/m3 and CGE of 38.2%–42.3% was obtained in the experimental setup without optimizing the primary air flow rate. With optimization, the indicators increased to the heating value of syngas of 5.20–5.34 MJ/m3 and CGE of 42.5%–50.0%. With heat regeneration of 0.8, CGE increases to 70%. [ABSTRACT FROM AUTHOR]

A new concept of simulation modeling of dynamic systems is developed. The basic notions and terms of the concept are outlined, as well as the principles of creating a simulation model of a physical process. The proposed concept is applied to the problem of modeling the process of developing a volatile oil formation operated by a rod pump in the pump–drill hole–formation system. The developed computer simulation model, taking into account the presence of the annular space and the fluid flow between the annular space and the lifting pipe, is used to study the operation process. Full filling of the rod pump cylinder does not always coincide with the maximum flow rate of the drill hole. The coincidence of the maxima of filling the cylinder and pump delivery is a condition for the optimal mode. The optimal mode can only be achieved by switching to the periodic mode of operation of the pump. It is established that in order to switch to a periodic mode, a condition is necessary when, at maximum flow, the maximum filling of the pump cylinder cannot be achieved. [ABSTRACT FROM AUTHOR]

The Air-Core-Liquid-Ring (ACLR) atomizer is an innovative internal-mixing pneumatic atomization technique, suitable for energy-efficient spray drying of highly viscous liquid feeds, with high solid contents. However, pneumatic atomizers such as the ACLR can suffer from unstable internal flow conditions, which may lead to a wide variation in the droplet diameter obtained. Therefore, the internal flow conditions of an ACLR-atomizer needs to be properly studied and comprehended. With that in mind, a computational fluid dynamic (CFD) model was implemented and tested with experimental data collected for different air pressures and liquid feed viscosities. The model used can predict average lamella thickness with a relative error of less than 10%, when compared to experimental results, although some degree of artificial dampening of the flow instabilities occurs at high viscosities and low pressures. These instabilities have to be investigated in more detail from both the numerical side, by further refining the CFD model to capture the moment-to-moment behavior of the flow, as well as on the experimental side, by studying the instability development at higher recording speeds. [ABSTRACT FROM AUTHOR]

The formation of gas condensate near the wellbore affects the gas liquid two-phase flow between the pores. It may occur in the path between two pores depending on the thermodynamic conditions of the single-phase gas flow, two-phase gas liquid annular flow or the closed path of condensate in the throat. To model the behavior of gas condensate in a network of pores, relative permeability and naturally pressure drop should be calculated. This study obtained the flow characteristics (pressure drop) between the pores at different physical and geometric conditions using computational fluid dynamics (CFD). CFD is time-consuming, so its results were transferred to an artificial neural network (ANN) model and the ANN model was trained. The CFD was replaced with the ANN model for calculating the pressure drop. In addition, instead of utilizing empirical correlations to compute the accurate value of condensate formed in throats' corners at every time step, the flash calculation using Esmaeilzadeh–Roshanfekr equation of state was performed, and closed throats were specified. This accurately estimates gas and condensate distribution in the pore network. Furthermore, the value of condensate that transferred to the adjacent throats was computed using Poiseuille's law. The results showed that the proposed ANN-based proxy model could promote the calculation speed in gas condensate simulation, considering the dynamic change of relative permeability curves as a function of gas condensate saturation. Also, it was found that the relative permeability obtained by the proposed model is in good agreement with the experimental data. By entering the fractures pattern in the network model and predicting the relative permeability of gas and condensate by the proposed method, the role of fractures in gas condensate production in such reservoirs could be predicted. Dynamic changes due to the relative permeability of gas and condensate as a function of saturation can be entered into the reservoir simulation to optimize inertia and positive coupling phenomena to maximized condensate production in gas condensate reservoir. [ABSTRACT FROM AUTHOR]

A semi-analytic solution for the elastic/plastic distribution stress and strain in a thin annular disc subject to pressure over its inner radius is presented. It is assumed that a pressure-dependent yield criterion and its associated flow rule are valid in the plastic zone. Thus, the material is plastically compressible, which is a distinguished feature of the solution. Also, in contrast to most studies on elastic/plastic deformation of thin plates and discs under plane stress conditions, the flow theory of plasticity is adopted in conjunction with a smooth yield surface. Numerical methods are only necessary to evaluate ordinary integrals and to solve simple transcendental equations. It is shown that the stress path is not proportional and, therefore, the application of deformation theories of plasticity widely used to calculate the distribution of stresses and strains in thin plates and discs is not justified. [ABSTRACT FROM AUTHOR]

In this study, a numerical simulation is used to show the physics of a coupled forced perturbation and liquid jet in the presence of a low-velocity coaxial gas flow. The volume of fluid (VOF) approach is employed to capture the liquid–gas interface. A sinusoidal velocity with a finite frequency and amplitude is applied at the liquid jet inlet to define a forced perturbation. An annular gas flow with a velocity lower than that of the liquid jet is imposed to examine its influence on the liquid jet breakup mechanism. The annular gas flow is modulated by the sinusoidal velocity inlet, and the effect of this flow on the liquid jet breakup mechanism is analyzed. Different ratios of the gas velocity to liquid velocity are studied. The results indicate that the low-velocity gas flow can considerably affect the behavior of the liquid jet, and this effect becomes more significant as the amplitude of the forced perturbation increases. [ABSTRACT FROM AUTHOR]

The ability to accurately predict the forces on an aerofoil in real-time when large flow variations occur is important for a wide range of applications such as, for example, for improving the manoeuvrability and control of small aerial and underwater vehicles. Closed-form analytical formulations are only available for small flow fluctuations, which limits their applicability to gentle manoeuvres. Here we investigate large-amplitude, asymmetric pitching motions of a NACA 0018 aerofoil at a Reynolds number of 3.2 × 10 4 using time-resolved force and velocity field measurements. We adapt the linear theory of Theodorsen and unsteady thin-aerofoil theory to accurately predict the lift on the aerofoil even when the flow is massively separated and the kinematics is non-sinusoidal. The accuracy of the models is remarkably good, including when large leading-edge vortices are present, but decreases when the leading and trailing edge vortices have a strong interaction. In such scenarios, however, discrepancies between the theoretically predicted and the measured lift are shown to be due to vortex lift that is calculated using the impulse theory. Based on these results, we propose a new limiting criterion for Theodorsen's theory for a pitching aerofoil: when a coherent trailing-edge vortex is formed and it advects at a significantly slower streamwise velocity than the freestream velocity. This result is important because it extends significantly the conditions where the forces can be confidently predicted with Theodorsen's formulation, and paves the way to the development of low-order models for high-amplitude manoeuvres characterised by massive separation. [ABSTRACT FROM AUTHOR]

An X-ray microtomography (µCT) system was adapted so that 3D scans of fixed horizontal or vertical test sections can be performed. The mobile µCT system has been applied to measure the local, time-averaged volume fraction distribution of developing annular air-water flow in a horizontal pipe with µm spatial resolution. Based on the volume fraction data the liquid film thickness profile is computed and the accumulation, stripping and renewal of the annular liquid film at a circular orifice is studied. The development length of the annular flow downstream of the orifice is evaluated based on the integral volume fraction and the change of the film thickness profile along the pipe axis. Both parameters give a consistent result, indicating that liquid film renewal can be judged based on integral measurement techniques in this case. Further, the detailed 3D data enables the validation of computational fluid dynamics codes based on phase-averaged variables such as the Euler-Euler approach. [ABSTRACT FROM AUTHOR]

Bottom-hole flowing pressure and pump intake pressure (PIP) are important parameters to optimize the performance of oil wells. In recent years, downhole sensors are becoming widely used in electrical submersible pump systems to measure these pressures. However, it is still rare to use downhole sensors in sucker rod and progressive cavity pumped wells. In this study, two correlations were developed to calculate bottom-hole flowing pressure and PIP from readily available field data. The two correlations do not require measurements of buildup tests, but they rely on measuring the dynamic fluid level and estimating fluid gradient correction factor using either (1) the tubing gas flow rate or (2) the annular gas flow rate. Then, the PIP is calculated by the summation of either (1) the tubing pressure plus the tubing gaseous liquid column pressure or (2) the casing pressure, annular gas column pressure and the annular gaseous liquid column pressure. The correlations were developed using 419 field data points (389 points for training and 30 for testing) of wide range for each input parameter. Using the training data, the mean absolute percentage deviation (MAPD) between the calculated and measured PIPs is 25% and 20% for the first and second correlations, respectively. However, the testing data showed MAPD of 33% and 12% for the first and second correlations, respectively. The accuracy of these correlations is significantly higher than that of the previously available methods, and the correlations require simpler input. Such study is an original contribution to calculate the PIP with improved accuracy and without downhole pressures sensors. [ABSTRACT FROM AUTHOR]

In this work we present a mathematical model for the flow of two fluids (micropolar and Newtonian) through concentric cylinders having porous space of different permeability. The Poiseuille flow of micropolar fluid takes place in core region while Newtonian fluid in the annular region of concentric cylinders respectively. An analytical expression of velocity, flow rate, micro rotational velocity, wall shear stress for the flows of two-fluid through concentric cylinders have been evaluated. We also discuss the case of Newtonian-Newtonian fluid flow through concentric porous cylinders having different permeability. The significant effect of permeability parameter, micropolar fluid parameters, flow parameters on the velocity profile, flow rate and wall shear stress have been analyzed graphically. The model is applicable for the process of extraction of crude oil through the porous pipes, blood flow through arteries, and filtration process etc. [ABSTRACT FROM AUTHOR]

Experimental work has been conducted to study the influence of gas injection on the phase inversion between oil and water flowing in a vertical pipe. A vertical transparent pipe test section line of 40 mm ID and 50 cm length was used. The test fluids used were synthetic oil and filtered tap water. Measurements were taken for mixture velocity, superficial water velocity, superficial gas velocity, and input superficial oil velocity ranging from 0.4 to 3 m/s, 0.18 to 2 m/s, 0 to 0.9 m/s, and 0 to 1.1 m/s. Most of the experiments were conducted more than two times, and the reproducibility of the experiments was quite good. Special attention was given to the effect of oil and water concentration where phase inversion took place with and without gas injection. The results showed that the phase inversion point was close to water fraction of ~ 30%, for both water friction direction changes (from water to oil or from oil to water) and that the effective viscosity increases once the mixture velocity increases. On the other hand, the results with gas injection showed that gas injection had no effect on the oil or water concentration where phase inversion occurred. Furthermore, the study investigated the effect of gas–oil–water superficial velocity on the total pressure gradient in the vertical pipe. It was found that the total pressure gradient was fast and increased at high superficial gas velocity but was slow at low superficial gas velocity. When the superficial oil velocity increased, the total pressure gradient approached the pressure gradient of an oil–water two-phase flow. The obtained results were compared with few correlations found in the literature, and the comparison showed that the uncertainty of the flow pattern transition peak in this study is very low. [ABSTRACT FROM AUTHOR]

The Navier-Stokes equations were used to carry out the numerical modeling of chemically reactive gas flow in an annular flow chamber. The model was based on laws of conservation of mass, momentum, and energy for nonstationary two-dimensional compressible gas flow in the case of axial symmetry with a tangential component of the gas velocity. Viscosity, thermal conductivity, and turbulence were taken into account. Fuel and oxidizer were fed into the chamber separately, and heat release in the chemical reaction zone was largely determined by the rate of turbulent mixing of the gas components. The possibility of burning out of the mixture in the chamber was demonstrated numerically. Detonation failure can occur if reagents temporarily cease to be fed into the chamber, which can be caused by high pressure in the reaction zone. With short combustion chamber lengths, there are the underburning of fuel and the release of unreacted hydrogen into the atmosphere. [ABSTRACT FROM AUTHOR]

In this research, the nonlinear local and nonlocal analysis of an annular sector plate is studied and solved based on a new modified higher-order shear deformation theory. Due to the shortcomings of HSDT in the two-dimensional nonlinear analysis, it is modified by eliminating the defects, and a comprehensive theory is presented for analyzing the mechanical behavior of an annular sector sheet in general form. The strain field is developed by considering the von Karman assumptions and also the nonlocal theory of Eringen from which the classical local analysis can be deduced conveniently by neglecting the small-scale effects. Whereas the annular sector plate is assumed, the sector, annular/circular, rectangular and solid circular plates can be simulated. Afterward, the nonlocal constitutive equations are derived and solved by using the two-dimensional SAPM (Dastjerdi et al. in Compos B Eng 98, 78-87, 2016). Moreover, a combination of the extended Kantorovich method and one-dimensional SAPM is applied. Since the presented theory is relatively new and similar studying was not available in order to compare the results, a comparison is done with the results of lower-order theories. Finally, the effect of various parameters, such as boundary conditions, different theories, nonlocal and local analyses, loading and the size of the plate, on the mechanical behavior of an annular sector plate are investigated. [ABSTRACT FROM AUTHOR]

One of the fundamental questions that must be addressed in the effective design and operation of pipeline lubrication of heavy oil is; 'how much time will be needed to restart a blocked core annular flow (CAF) line after shutdown due to fouling or pump failures', if the pipe is to be cleaned using water only. In this work, laboratory results of shutdown and restart experiments of high-viscous oil conducted in a 5.5-m-long PVC horizontal pipe with internal diameter of 26 mm are first presented. A new correlation for the prediction of the restart time of a shutdown core annular flow line is then formulated. The predictive capabilities of the correlation are checked against measured restart time and pressure drop evolution data. Somewhat high but still reasonable predictions are obtained. The restart time correlation, together with the associated correlations formulated as well, can be of practical importance during the engineering design of high-viscous oil pipeline transportation facility for predicting restart process. [ABSTRACT FROM AUTHOR]

The present work is a continuation of experimental investigations conducted at the Moscow Power Engineering Institute (MPEI) on heat-transfer intensification. Brief descriptions of the working section and structure of intensifiers are given and their basic geometric parameters are enumerated. New systematized experimental data on the coefficients of hydraulic resistance and heat transfer in the regime of single-phase convection are given in an extended range of regime parameters and geometric characteristics of the intensifiers. Considerable increase in the heat-transfer coefficient as a function of the geometric characteristics of the intensifier has been established experimentally. The values of the relative fin height, at which these are the maxima of heat transfer and hydraulic resistance, have been established. Calculated dependences for the coefficient of hydraulic resistance and heat transfer have been obtained. [ABSTRACT FROM AUTHOR]

Considering thermal loads, dynamics and stability of an outer cylindrical shell conveying swirling fluid in the annulus between the inner shell-type body and the outer shell are investigated by the travelling wave approach. Shell motions are considered based on Donnell-type shell theory. The fluid forces are described by means of the potential flow theory, and thermal loads are determined by the thermo-elastic theory. The numerical analyses are conducted by a zero-level contour method. The study shows the effects of annular gaps and boundary conditions on stability of shells. The influences of angular flow on the critical axial velocity and axial flow on the critical annular velocity are discussed. Moreover, the thermal loads decrease the critical flow velocity markedly and the critical temperature rise is found. [ABSTRACT FROM AUTHOR]

The interfacial jetting phenomena of coaxial air-assisted water jets are studied using high-speed digital camera. Here, an inner round air jet is injected into annular water sheet spray. The experimental photographs show that the outside interface of liquid sheet shoots out large numbers of violent ligaments at high air velocity. The ligament velocity, ligament angle, ligament diameter, fragment size, and distribution are measured and analyzed. There are two kinds of ligament evolution that are breakup and contraction. An empirical model is also proposed for the ligament evolution process. At last, we obtain the criterion of critical Weber number on the ligament breakup based on the experimental results. This suggestion agrees well with the experimental data. [ABSTRACT FROM AUTHOR]

An overview of a measurement method for liquid film thickness in annular flows based on cold neutron imaging is given here. Neutron imaging being a non-intrusive, contactless method is attractive option for two-phase flow investigations offering an excellent contrast. It can provide with information at a high spatial resolution on the flow structure, like the thickness of the liquid film in annular flows. The method has been optimized, and its performance, regarding bias, statistical accuracy, upper and lower detection limits, has been thoroughly quantified using computational tools and measurement results. The technique has been developed based on nuclear fuel bundle models; however, it is applicable practically to annular flows in any arbitrary flow channel geometry of interest. [ABSTRACT FROM AUTHOR]