The split of vertical annular flow at a large diameter T junction

Measurements and observations have been made of the split of gas—liquid flow at a T junction where the main pipe was vertical and the side arm horizontal. All three pipes connecting to the junction were of 0.125 m dia. The gas and liquid flow rates were chosen to ensure annular flow in the inlet pipe. The resulting data have been compared with existing models.     

The split of stratified gas–liquid flow at a small diameter T-junction

The present work reports a study of phase split at a horizontal T-junction with main and side branches of 0.005 m diameters. The experiments were confined to the stratified flow pattern and the effects of phase velocities and pressure on the split were examined. The results were also compared with those reported for larger T-junctions. The side arm take-off tends to be richer in the gas phase with increase in pressure under all flow conditions. The reason has been attributed to the complex effect of pressure on the interface position (characterised by the dimensionless liquid height, h/D) which in turn determines the gas and liquid momentum.     

Phase split of nitrogen/non-Newtonian fluid two-phase flow at a micro-T-junction

An experimental investigation has been undertaken to understand the phase split of nitrogen gas/non-Newtonian liquid two-phase flow passing through a 0.5 mm T-junction that oriented horizontally. Four different liquids, including water and aqueous solutions of carboxymethyl cellulose (CMC) with different mass concentrations of 0.1, 0.2 and 0.3 wt%, were employed. Rheology experiments showed that different from water, CMC solutions in this study are pseudoplastic non-Newtonian fluid whose viscosity decreases with increasing the shear rate. The inlet flow patterns were observed to be slug flow, slug–annular flow and annular flow. The fraction of liquid taken off at the side arm for nitrogen gas/non-Newtonian liquid systems is found to be higher than that for nitrogen gas/Newtonian liquid systems in all inlet flow patterns. In addition, with increasing the pseudoplasticity of the liquid phase, the side arm liquid taken off increases, but the increasing degree varies with each flow pattern. For annular flow, the increasing degree is much greater than those for slug and slug–annular flows.     

Flow pattern,void fraction and pressure drop of refrigerant two-phase flow in a horizontal pipe—II: Analysis of frictional pressure drop

Two-phase flow in horizontal pipe was analyzed with simplified models for annular and stratified flow. The velocity profiles for the liquid and gas phase were described with the Prandtl mixing length. From this analysis, the frictional pressure drop was calculated with the modified Baker map for flow pattern transition. The intermediate region, i.e. wavy flow, was interpolated between annular and stratified flow. Comparison of this analysis with existing experimental data of refrigerants showed good agreement.     

Air-water two-phase flow in a helically coiled tube

Air-water flow has been studied in a helically coiled tube. The flow pattern transition between stratified and annular flow was examined, and a series of measurements were then taken in the annular flow regime. Local values of the liquid film thickness and liquid film flowrate around the tube periphery were obtained. The variations of these values around the periphery was similar. For most of the cases studied the liquid film flow rate was greatest on the inside of tbe bend, but in some results a subsidiary peak at the outside position was also obtained. There was little net entrained flow because of the centrifugal forces tending to deposit drops very quickly. Attempts to use correlations developed in vertical annular flow at a local position on the tube periphery were not very successful.     

Studies on two-phase co-current air/non-Newtonian shear-thinning fluid flows in inclined smooth pipes

In this work, co-current flow characteristics of air/non-Newtonian liquid systems in inclined smooth pipes are studied experimentally and theoretically using transparent tubes of 20, 40 and 60 mm in diameter. Each tube includes two 10 m long pipe branches connected by a U-bend that is capable of being inclined to any angle, from a completely horizontal to a fully vertical position. The flow rate of each phase is varied over a wide range. The studied flow phenomena are bubbly flow, stratified flow, plug flow, slug flow, churn flow and annular flow. These are observed and recorded by a high-speed camera over a wide range of operating conditions. The effects of the liquid phase properties, the inclination angle and the pipe diameter on two-phase flow characteristics are systematically studied. The Heywood–Charles model for horizontal flow was modified to accommodate stratified flow in inclined pipes, taking into account the average void fraction and pressure drop of the mixture flow of a gas/non-Newtonian liquid. The pressure drop gradient model of Taitel and Barnea for a gas/Newtonian liquid slug flow was extended to include liquids possessing shear-thinning flow behaviour in inclined pipes. The comparison of the predicted values with the experimental data shows that the models presented here provide a reasonable estimate of the average void fraction and the corresponding pressure drop for the mixture flow of a gas/non-Newtonian liquid.     

Experimental investigation of two-phase flow splitting in an equal-sided impacting tee junction with inclined outlets

Phase-distribution data have been generated for two-phase (air-water) flow splitting at an impacting tee junction with a horizontal inlet and inclined outlets. This investigation also considered the possibility of full separation at the junction and the effect of the outlet angle of inclination on partial separation at various inlet conditions. A flow loop with the ability to incline the outlets from horizontal to vertical was constructed. The operating conditions were as follows: test section inside diameter (D) of 13.5 mm, nominal junction pressure (P_s) of 200 kPa (abs), near ambient temperature (T_s), inlet superficial gas velocities (J_G1) ranging from 2.0 to 40 m/s, inlet superficial liquid velocities (J_L1) ranging from 0.01 to 0.18 m/s, inlet qualities (x₁) ranging from 0.1 to 0.9, mass split ratios (W₃/W₁) from 0 to 1.0, and inlet flow regimes of stratified, wavy, and annular. The data reveal that the degree of maldistribution of the phases depended on the inlet conditions, the mass split ratio at the junction, and the inclination angle of the outlets.     

The rivulet flow pattern during oil–water horizontal flow through a 12 mm pipe

The present study reports the hydrodynamics of the rivulet pattern during oil–water flow through a 12 mm horizontal acrylic pipe. The interfacial distribution has been observed visually and characterized from signals obtained from an optical probe as well as by isokinetic sampling. The probability density function (PDF) and fast Fourier transform (FFT) of the signals have provided an understanding of the flow configuration. The experiments have revealed that although rivulet flow is a typical separated flow pattern, it has different characteristics as compared to the stratified and annular flow patterns. The holdup and pressure drop under such conditions have been compared with the drift flux model for horizontal flow as well as the two-fluid model as proposed by Brauner and Maron [9] for liquid–liquid flows.     

Phase split of liquid–liquid two-phase flow at a horizontal T-junction

This paper provides data on the split of liquid/liquid two-phase flow at a horizontal T-junction. Phase maldistribution was measured for kerosene–water flow at the T-junction with equal pipe diameters of 67.4 mm. Data were taken with both stratified flow with a mixture at interface and dispersed flows approaching the junction. The degree of phase maldistribution was not very great but preferential emergence of either phase from the side-arm was observed depending on the flow rates of the two-phases. There are similarities with the limited split data from liquid/solid flows and the degree of separation is seen to depend on the dispersed/continuous phase density ratio. The data were compared to predictions from the correlation by Seeger et al. The Seeger equation gives but reasonable agreement.     

Liquid film circumferential asymmetry prediction in horizontal annular two-phase flow

This study considers the prediction of the degree of asymmetry in the circumferential distribution of the liquid film in the tube cross section of horizontal annular gas–liquid two-phase flow, endemic of the lower region of this flow regime near the stratified-wavy flow transition boundary. Focusing on disturbance waves as the predominant mechanism for transporting the liquid in the annular film from the bottom to the top of the tube to counterbalance the draining effect of gravity, a new prediction method for the degree of asymmetry in the annular liquid film is proposed that outperforms existing correlations. Flow pattern maps for horizontal gas–liquid two-phase flow of frequent use in the design of evaporators and condensers can thus be explicitly updated to account for both symmetric and asymmetric annular flows. The underlying experimental database contains 184 measured liquid film circumferential profiles, corresponding to 1276 local liquid film thickness measurements collected from 15 different literature studies for tube diameters from 8.15 mm to 95.3 mm.     

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.     

Flow-excited acoustic resonances of coaxial side-branches in an annular duct

This paper investigates the aeroacoustic response of an annular duct with closed coaxial side-branches, and examines the effect of several passive countermeasures on the resonance intensity. The investigated geometry is inspired by the design of the Roll-Posts in the Rolls-Royce LiftSystem^® engine, which is currently being developed for the Lockheed Martin Joint Strike Fighter (JSF^®) aircraft. The effects of design parameters, such as diameter ratio, branch length ratio and thickness of the annular flow on the frequency and resonance intensity of the first acoustic mode are studied experimentally. Numerical simulations of the acoustic mode shapes and frequencies are also performed. The annular flow has been found to excite several acoustic modes, the strongest in all cases being the first acoustic mode, which consists of a quarter wavelength along the length of each branch. The ratios of the branch length and diameter, with respect to the main duct diameter, have been found to have strong effects on the frequency of the acoustic modes.     

Equal quality distribution of gas–liquid two-phase flow by partial separation method

This paper proposes a new method for equal quality distribution of gas–liquid two-phase flow by partial separate-phase distribution with a dual-header distributor. The upper and liquid (lower) headers are interconnected with five vertical downward arms. A gas–liquid two-phase mixture enters the distributor from the upper header where most of the liquid of the mixture is removed through the downward arms into the liquid header. Hence, firstly, the remaining gas-rich fluid can be uniformly distributed into the outlet branches, and then secondly, the liquid collected in the liquid header can be uniformly re-distributed into the individual outlet branches. Because both distribution processes are conducted in the condition of single or near single-phase flow, mal-distribution of the two-phase flow is essentially eliminated, and a satisfactory equal quality distribution of gas–liquid two-phase flow is reached. Experiments were conducted in an air–water two-phase flow test loop. The inner diameter of the inlet pipe was 60 mm, the superficial velocity ranges of gas and liquid were 3–32 m/s and 0.02–0.17 m/s respectively, and the quality ranged from 0.02 to 0.44. The flow pattern in the inlet pipe included stratified flow, wavy stratified, slug flow, and annular flow. The experimental results showed that this new method could significantly improve the distribution performance of the two-phase flow. The maximum quality deviation between each outlet branch and the inlet pipe is less than ±1% under the conditions of stratified, wavy stratified and slug flows in the upper header, and less than ±5% in annular flow.     

The flow of a rigid core surrounded by an annular liquid layer through a horizontal tube

A theoretical investigation has been made of the flow of a rigid core surrounded by an annular liquid layer through a horizontal tube. Special emphasis is placed on the question how the gravity force on the core, caused by a possible density difference between the core and the annular layer, is counterbalanced.Shell Research N.V.     

Two-phase stratified flow splitting at a T-jun

The objective of this study is to investigate, experimentally and theoretically, two-phase splitting under stratified wavy flow conditions at a regular horizontal T -junction with an inclined branch arm.

Experimental data have been acquired with the side arm at horizontal conditions, downward inclination angles of −5, −10, −25, −40 and −60°, and upward inclinations of 1, 5, 10, 20, and 35° from the horizontal. The data reveal that gravity forces have a significant effect on the flow splitting. For downward inclination of the side arm more liquid is diverted into the branch arm, as compared to the case in which the side arm was horizontal. All the liquid was found to be diverted into the branch arm when the branch arm inclination was increased to −60°. For upward inclination angles a significant amount of the inlet gas has to be diverted into the side arm in order to get any liquid to flow into that arm. However, once liquid has started flowing, not much more additional gas has to be diverted into the side arm to get all of the liquid to flow into the branch. At 35° almost all the gas has to be diverted for any liquid flow into the branch.

A mechanistic model has been developed for the prediction of the splitting phenomenon for both the horizontal and the downward orientations of the side arm. The model is based on the momentum equations applied for the separation streamlines of the gas phase and the liquid phase. Very good agreement is observed between the prediction of the model and the data acquired for all the cases.     

Non Newtonian annular alloy solidification in mould

The annular solidification of an aluminium–silicon alloy in a graphite mould with a geometry consisting of horizontal concentric cylinders is studied numerically. The analysis incorporates the behavior of non-Newtonian, pseudoplastic (n?=?0.2), Newtonian (n?=?1), and dilatant (n?=?1.5) fluids. The fluid mechanics and heat transfer coupled with a transient model of convection diffusion are solved using the finite volume method and the SIMPLE algorithm. Solidification is described in terms of a liquid fraction of a phase change that varies linearly with temperature. The final results make it possible to infer that the fluid dynamics and heat transfer of solidification in an annular geometry are affected by the non-Newtonian nature of the fluid, speeding up the process when the fluid is pseudoplastic.     

Measurements and observations of the split of annular flow at a vertical T-junction

Measurements and observations have been made when annular flow divides at a vertical T. This work has extended earlier experiments in covering the entire range of take off. From the observations and measurements, three ways in which the liquid can be diverted into the side arm have been identified. A modification of an earlier model has been produced which correctly allows for two of the three phenomena.     

An analytical approach to estimate local liquid heights in horizontal diabatic slug flow

As the intermittent (slug) flow pattern was recently shown to be, along with the stratified flow regime, responsible for circumferential anisothermality of horizontal steam generating tubes operating at moderate steam qualities, the ability to estimate the local liquid levels in such tubes and to compare them with the position of the circumferentially maximum value of the externally applied heat loading appears to be of great practical importance for boiler designers. While the procedure of the estimation of minimum liquid heights (h_L) in horizontal stratified flows was suggested in previous papers, this study presents an analytical approach for engineering evaluations of h_L in the horizontal, diabatic slug flow pattern. It is, importantly, shown that the use of the stratified flow-based approach to evaluate h_L in slug flows results in the overestimation of actual liquid heights which may be detrimental for boiler tubes, especially under circumferentially nonuniform heat loading.     

Use of hydrodynamic cavitation for volatile removal compound

Hydrodynamic cavitation and its feasibility for volatile compound removal in enclosed channels is discussed in this paper. Very high Reynolds numbers are needed to rupture liquid by decreasing its pressure below its saturated vapour pressure. Hence, a simple stratified flow, at which the two phases separate, is precluded in vertical and horizontal tubes, where turbulence stresses will be much larger than the buoyant forces. The most probable flow regime at this high turbulence regime is a bubble- or annular flow, where the volatile matter tends to concentrate in the centre of the pipe because of the lift force resulting from the unequal flow of the viscous liquid around the bubbles in the presence of the pipe wall. Therefore, boiling the volatile matter for volatile compound removal is not enough if hydrodynamic cavitation is pursued. The attainable efficiency must also be assessed. An expression for the volatile removal efficiency and the main parameters affecting this efficiency were derived by utilising a simplified geometrical and physical model. The efficiency was found to approximate a power law as a function of the volatile concentration and its strong dependence on the size of the volatile bubble reasonably well. This result implied the need of bubble growth and the limitation of the process for highly concentrate compounds to a few percent concentrations. With regard to energetic requirements, both thermal and hydrodynamic cavitations are quantitatively similar. Furthermore, the choice of one or another corresponds more to the kind of energy source available.     

An analysis of film flow and its application to condensation in a horizontal tube

An analysis is presented for turbulent flow in a liquid film which is being dragged along a horizontal tube by an axial shear at the film surface. While being dragged along, the film drains down the wall due to gravity. The analysis can be applied to a number of horizontal, annular, gas-liquid flow problems and an example is given here of its use in analysing condensation in a horizontal tube. For this problem, the predictions show limited agreement with the little experimental data presently available.