Horizontal Annular Flow Research Articles

Measurement of circumferential and axial liquid film velocities in horizontal annular flow

The mechanism of liquid transport around the inner perimeter of a tube in horizontal annular flow has been experimentally investigated by using a photochromic dye activation technique. The liquid film velocities in circumferential and axial directions were measured by forming a drak spot of dye trace in the liquid film in a non-intrusive manner and recording the subsequent motion of the spot trace with a high-speed video camera. The experiments were conducted in a 5.28 m long horizontal tube with 25.4 mm i.d. at near atmospheric pressure conditions using air and kerosene. Over the ranges of gas and liquid flow rate tested (16 < J G < 40 m/s and 0.04 < J L < 0.1 m/s), the base film was always seen to drain down the tube wall. During the periodic passage of disturbance waves, however, the spot dye trace moved upward indicating the transport of liquid in an upward direction against the force of gravity. The ripples propagating upward over the base film were also observed to transport the liquid upward, however, their contributions were less significant compared to those of the disturbance waves. These results indicate that the liquid is transported to the upper part of the tube by the disturbance waves and not by the secondary gas flow or other mechanisms as previously hypothesized.

Gas-phase secondary flow in horizontal, stratified and annular two-phase flow

Experiments were performed and semi-empirical correlations were developed to both prove the existence of gas-phase secondary flow and to predict annular to stratified transition limits for isothermal and heated horizontal annular two-phase flows in pipes. At the low vapor velocities, where this transition from stratified flow occurs and the entrainment/deposition mechanism is insignificant, secondary flow in the vapor ccore plays the principal role in the full development of the liquid annulus. Direct measurements of secondary flow are presented along with a simple model to correlate its behavior. The secondary flow model is used in conjuction with the fluid mechanics of the film to derive a boundary model for the onset of annular flow in this transition region. The resulting boundary agrees well with both the thermal and isothermal transition data.

Observation of Film in a Horizontal Annular Two-Phase Flow by a Photochromic Dye Activation Method

An experimental study has been conducted to investigate the mechanism of liquid film transport in horizontal annular flow by visualizing the motion of the liquid film on the inner tube wall using a photochromic dye activation method. The captured motion clearly reveals spreading of the liquid during the passage of disturbance waves and constant drainage of the liquid film after the passage of the disturbance waves. The present results support the liquid transport mechanism due to the pumping action of the disturbance waves proposed by Fukano and Ousaka rather than the secondary gas flow or surface wave mechanisms proposed by Laurinat et al. and Jayanti et al.

Corrective technique for numerical prediction of liquid flow rate in annular flow study

AbstractThe computer code FIDAS‐3DT, developed by Power Reactor &amp; Nuclear Fuel Development Corporation of Japan, has been used to solve by the finite‐difference method an air‐water horizontal annular flow problem based on two‐phase, three‐fluid and two‐component velocity modelling. In an attempt to improve the water flow rate results, as compared with those of a reported experiment, several corrections applied to the code are investigated, and the recommended technique is presented.

Relationships between Flow Configuration and Statistical Characteristics of Hold-up and Differential Pressure Fluctuations in Horizontal Annular Two-Phase Flow

Relationships between Flow Configuration and Statistical Characteristics of Hold-up and Differential Pressure Fluctuations in Horizontal Annular Two-Phase Flow

Distribution of Entrainment Flow Rate for Air-Water Annular Two-Phase Flow in a Horizontal Tube

An experimental investigation on the distribution of the entrainment flow rate in a horizontal annular two-phase flow was conducted. In this experiment, the isokinetic sampling probe technique was used for the measurement of the entrained droplet flow rate. It was demonstrated that the distribution of the entrained droplet flow rate was sensitive to the flow configuration, the total entrained droplet flow rate in the gas core was smaller than that of the vertical upward flow and the correlation of the entrainment flow rate proposed by Paleev et al. was superior to that by Wicks et al. Furthermore, a new correlation for the critical flow condition of the onset of droplet entrainment was proposed.

Droplet entrainment and deposition in horizontal annular flow

Local measurements of droplet fluxes, in the core of horizontal annular flow, are employed in order to calculate the liquid concentration distribution as well as the circumferential variation of deposition rate. A relatively simple model is proposed for predicting the above quantities. Terms representing fluxes due to turbulent diffusion and gravitational settling are used in the model. An additional parameter a is introduced and is considered to represent a combination of fluxes; i.e. the net upward flux of droplets responding to turbulence and the flux of droplets that gain high inertia upon atomization. An interpretation is given of average deposition (or atomization) rates obtained from the data, by using detailed information on film thickness properties and by recognizing that only films with a local thickness greater than a critical value can contribute to atomization. The development of a physically realistic correlation for the mean deposition rate is explored.

Axial and Circumferential Film Flow Rate Prediction in a Horizontal Annular Two-Phase Flow Using the FIDAS-3DT Code

Prediction of developing and transient characteristics of circumferential and axial film velocities in a horizontal annular two-phase flow is carried out with the FIDAS-3DT computer code developed in Japan that can provide three-field representation in subchannel flow using the full conservative equations and simple constitutive relations. The specifications are those from a reported air-water experiment in a 3.9m by 32mm diameter pipe. Steady, fully developed axial flow rates seem to be over-predicted compared to the experimental results. A corrective procedure is suggested which takes into account the radial variation in the axial velocity profile.

Time-dependent behaviour of the liquid film in horizontal annular flow

A crucial point still to be established in the prediction of the film thickness distribution in horizontal annular two-phase flow is the mechanism(s) for transporting liquid from the bottom to the top part of the tube. To resolve this issue, the time-dependent behaviour of the liquid film is studied. Wave characteristics such as velocity and frequency are measured around the circumference. It is inferred from the autospectral density functions of film thickness variation that disturbance waves play an important, but as yet unclear, role in the formation of a liquid film in the top part of the tube. A new mechanism, based on the shape of disturbance waves is proposed.

Structure of thin liquid films in gas-liquid horizontal flow

The structure of the liquid film in horizontal annular flow is studied visually using the refractive index matching technique. The liquid film is found to contain significant amount of air bubbles, which are continuously entrained, broken up and released by the rolling motion within the film. A new conceptual picture of the gas-liquid interface is presented.

The prediction of turbulent flows over roughened surfaces and its application to interpretation of mechanisms of horizontal annular flow

It is widely believed that the secondary flow mechanism, namely the generation of secondary flow in the gas phase due to circumferentially varying interfacial roughness, plays an important role in the liquid film distribution in horizontal annular flow. We study this mechanism numerically using the HARWELLFLOW 3D computer program. We use wall functions to account for wall roughness, and verify this approach to comparing our predictions with the data of Nikuradse and Hanjalic &amp; Launder. We then apply the methodology to the prediction of secondary flow in a pipe subjected to differential wall roughness, and show that the contribution of the secondary flow in the gas is hitherto overestimated by up to an order of magnitude.

Film thickness prediction in a horizontal annular two-phase flow

Prediction of developing and transient characteristics of the liquid film in a horizontal annular two-phase flow is carried out using a computer code that provides a three-field representation in subchannel flow. The fully developed steady-state results for film thickness compare satisfactorily with a reported air-water experiment in a pipe 3.9 m long and 32 mm dia. It is concluded that horizontal annular flow modelling may be tractable by the direct application of the conservation equations to mesh cells along the flow.

Prediction of pressure drop during horizontal annular flow boiling of pure and mixed refrigerants

An experimental study on pressure drop during horizontal flow boiling of pure and mixed refrigerants of R22, R114, R12, and R152a is reported. More than 600 pressure drop data are taken for annular flow under uniform heat flux at reduced pressures of 0.08–0.16 (200–800 kPa). The range of heat flux and mass flow rate is 10–45 kW m −2 and 16–46 g s −1 (corresponding to 230–720 kg m −2 s −1 in terms of mass flux). The results are compared against well-known correlations; Bo Pierre's correlation failed to correlate half of the present data while Martinelli and Nelson's correlation overpredicted it by 20%. Pressure drops with both pure and mixed refrigerants, however, are well correlated by Martinelli's parameter, X tt . Furthermore, no composition dependence of pressure drop is found with mixtures. A simple correlation adopting the thermodynamic corresponding states principles is developed with a chart to facilitate the estimation of pressure drop during flow boiling. The prediction agrees with the measured data with a mean deviation of 8.4%.

Condensation from steam—air mixtures in a horizontal annular flow channel

Experiments were performed on the condensation of steam from steam-air mixtures in annular flow at a cooled inner tube. The range of investigation was varied for laminar and turbulent flow for 1.5 × 10 3 ⪕ Re ⪕ 1.3 × 10 4 and inlet concentrations 0.59 ⪕ p steam /p total ⪕ 0.95 . The measurements, performed at an open test loop at p total ≈ 0.96 bar, allowed local heat and mass transfer coefficients to be evaluated for various inlet lengths in the 2 m long annulus. The steam concentration was measured locally inside the annulus with a newly developed dew-point probe. The heat flux was measured locally using the temperature gradient in the cooled inner tube. Near the inlet region the experiments showed a slightly higher heat flux at the bottom of the tube compared to the top, although it is expected to be smaller there owing to a thicker liquid film. Far downstream from the inlet region the heat transfer at the top was higher than at the bottom. The reasons for these effects are discussed, yielding a better understanding of the thermal and fluid processes involved in condensation from vapor-gas mixtures. The measured data allow the development of correlations for predicting the local Nusselt and Sherwood numbers in a horizontal annular-flow chanbel.

Prediction of film thickness distribution in horizontal air-water annular flow.

A theoretical model for predicting the circumferential film thickness distribution in a horizontal annular two-phase flow is presented. It is based upon a two-layer film model which consists of a wave layer and a base film. It differs from Laurinat's and Lin's models in that liquid is transferred in the circumferential direction by the disturbance wave spreading which counteracts the drainage due to gravity and that the effects of induced secondary flow in the gas flow and the surface tension force have minor effects on the formation of the liquid film near the top of the tube cross section. The film thickness distribution predicted by the present model agrees with the experimental data much better than that by Laurinat's model.

Developments in the modelling of horizontal annular two-phase flow

Several authors have considered the extension from vertically upward flow to horizontal flow of a model for annular two-phase flow which allows separate descriptions of liquid droplet deposition and entrainment. However, solutions to the equations which result have either not been obtained or have been found to be mathematically and physically unacceptable. In this paper it is shown how to obtain acceptable solutions. In addition, various physical mechanisms which could improve the model are assessed. Of these it is shown that a variable deposition flux could lead to significant improvement between theory and experiment. A model for the variable deposition flux is then developed and is shown to give results at least in qualitative agreement with known experimental results. The inclusion of the variable deposition rate in the governing equations leads to encouraging results for film thickness and film flowrate distributions.

Observations of drop motion in horizontal annular flow

On etudie plus particulierement les vitesses moyennes des gouttes, leurs trajectoires et la distribution de taille des gouttes

Horizontal annular flow measurements using pulsed photon activation and film thickness distribution modelling

The Pulsed Photon Activation (PPA) technique for the non-intrusive measurements of single and two-phase flows in a horizontal pipe was developed. The advantages of PPA over pulsed neutron activation (PNA) are discussed. Fluid velocity determinations using such a technique were carried out. An interesting subregion of the horizontal annular flow regime was found to have twin-peak PPA activation time profiles. These twin peaks were confirmed to be associated with the film flows on the upper and lower parts of the horizontal pipe, using the directionality of the PPA bremsstrahlung tagging beam. Film thickness measurements around the circumference of horizontal annular flows were also carried out using a resistivity needle probe and analytical models involving droplet exchange and secondary vapor flow pattern were compared with the experimental data.

Measurement of Flow in a Horizontal Pipe Using the Pulsed Photon Activation Technique

The pulsed photon activation (PPA) technique for nonintrusive measurements of singleand two-phase flows in a horizontal pipe is developed. The advantages of PPA over pulsed neutron activation are discussed. Fluid velocity determinations using such a technique are carried out. An interesting subregion of the horizontal annular flow regime is found to have twin peak PPA time profiles. It is confirmed that these twin peaks are associated with the film flows on the upper and lower parts of the horizontal pipe, using the directionality of the PPA bremsstrahlung tagging beam. Fil thickness measurements around the circumference of horizontal annular flows are also carried out using a resistivity needle probe, and analytical models involving droplet exchange and secondary vapor flow pattern are compared with the experimental data.

Film thickness in horizontal annular flow

AbstractFilm thickness in horizontal annular flow in small diameter pipes (8‐12 mm) was measured as a function of circumferential position. In addition a simple analytical model for the prediction of the film thickness at the top and bottom of the pipe is proposed.