Liquid Film Flow Rate Research Articles

Drop size measurements for annular two-phase flow in a 20 mm diameter vertical tube

As part of a study on the effect of tube diameter on the mean drop size and liquid film flow rate in annular two-phase flow, data was obtained for the vertical upflow of an air-water system in a 20 mm internal diameter tube, held at a pressure of 1.5 bar and ambient temperature. This complements data taken in earlier experiments on 10 and 32 mm tubes. Increases in the superficial gas velocity caused reductions in the mean drop size whilst increasing the liquid mass flux in all but the lowest gas velocity case, caused the drop size to rise. Comparisons were made between the current drop size data and that from a 10 mm and 32 mm internal diameter tube, for similar conditions of temperature and pressure. The current drop size measurements, which fall between those from earlier work, confirm the dependence of drop size on tube diameter. The performance of several drop size correlations have been tested. Because the correlations do not account for the influence of tube diameter, they fail to predict the drop size data accurately. The influence of gas and liquid flow rate on the measured film flow rate show trends similar to those seen in data from the 10 mm and 32 mm diameter tubes. Models, to calculate the entrained liquid mass flux were tested; good predictions were given.

Rates of atomization and deposition in vertical annular flow

The tracer technique of Quandt has been used to determine the rate of atomization, the rate of deposition and the entrainment for air and water flowing vertically upward in 2.54, 4.20 and 5.72 cm pipes. The rate of atomization was found to vary linearly with gas velocity and liquid film flow rate. The rate of deposition varies linearly with droplet concentration at low concentrations but is insensitive to changes in droplet concentration at high concentrations.

Burnout and distribution of liquid in evaporative channels of various lengths

This paper presents the results of experimental investigations on the distribution of liquid in annular dispersed steam-water upflow in 0.15 and 1.0 m long vertical heated tubes. The effect of heat flux and flow parameters on the distribution of the liquid between the core and the wall liquid film at the end of the heated section and at six points on the 1 m length downstream was investigated. Critical heat flux, liquid film flow rate at burnout and at the onset of annular dispersed flow with subcooled water fed to the heated channel inlet was measured. The rate of total liquid film entrainment relative to the heating is presented.

A Study on Instability of Falling Liquid Film in a Countercurrent Annular-Mist Two-Phase Flow

Stability of liquid film in a counter-current two-phase flow of falling liquid film and upward mist flow, which is generated by spraying the liquid into gas flow, in a vertical pipe have been investigated both experimentally and theoretically. The liquid film flow rate, pressure drop, and interfacial wave velocity were measured for vapor-water and air-water systems. It is shown that, with increasing the spray flow rate under the condition of constant gas-phase velocity, the falling liquid film becomes unstable due to the impact of droplets flowing upward. With the onset of instability, flow reversal of liquid film, entrainment of droplets, and rapid increase of pressure drop occur. This instability occurs even in a stable range of conventional flooding correlation for a counter-current two-phase flow. Based on comparison between experimental results for a vapor-water system at a pressure lower then the atmospheric pressure, and an air-water system at the atmospheric pressure, the droplets' impingement effect on the stability of liquid film is correlated with the ratio of the momentum of the colliding droplets on the liquid film to the interfacial shear stress. A theoretical analysis on the stability of liquid film impinged by droplets is made. Nonlinear stability of a finite-amplitude interfacial wave is treated in the analysis. The theory predicts the existence of a stable finite-amplitude interfacial wave. It also predicts that the flow becomes unstable with increasing the gas velocity and the momentum of impinging droplets. The stability limit predicted by the analysis agrees well with the experimental results.

Characteristics of response of a carburetted SI engine under transient driving conditions. 2nd report Behavior of liquid fuel film in an intake manifold.

This study was made of the transient fuel supply characteristicis in an intake system of a carburetted SI engine under transient driving conditions, through both theoretical analysis and experimental work. The results show that an increase in air velocity is not always accompanied with an increase in liquid fuel film velocity. The thickness of the liquid fuel film increases with the delay of time up to a certain value. The increasing ratio of liquid film flow rate grows with the rise of the acceleration rate finally approaching a certain value. The rapid acceleration of the engine causes an accumulation of liquid fuel film in the intake manifold, and consequently, an insufficient supply of fuel into the combustion chamber. The air fuel ratio in the combustion chamber increases with the time delay, and reaches a maximum which is out of the combustible range of the mixture immediately after the beginning of acceleration.

Interfacial drag and film height for vertical annular flow

AbstractNew measurements are presented for film height and pressure drop for vertical gas‐liquid annular flows. Improved methods for predicting the film height and interfacial friction factor are developed for situations in which the liquid film flow rate is known.

Studies of Swirling Annular-mist Two-phase Flow : 2nd Report, Analysis of Liquid Film Flowrate Along a Tube

The liquid film flowrate along a tube (40 mm ID, 5 m length) in swirling downward annular-mist air-water flows, induced by different swirlers at the inlet of the test tube in each run, was measured. The effects of the angle of torsion and length of swirlers, the gas velocity, and the liquid flowrate on the liquid film flowrate along the tube were clarified by experiments. A theoretical analysis of the liquid film flowrate at an outlet of swirler and along a tube was conducted. The calculated results agreed well with the experimental results.

Droplet transfer in two-phase annular flow

The tracer method, adopted by a number of experiments for the measurement of the rate of liquid interchange between the wall layer and the dispersed phase in a fully developed annular flow, has been critically examined on the basis of a more accurate description of the flow behavior of entrained droplets. The results obtained indicate that this experimental technique can give reliable results in a wide range of flow conditions when the experiments are properly designed. Present measurements of the interchange show that the dimensionless deposition coefficient is a function of the concentration of entrained droplets. This effect appears to be due to the dependence on concentration of droplet size. The rate of entrainment is proportional to the liquid film flowrate and to the gas velocity squared.

Entrainment in condensing annular flow

Experiments were carried out on low pressure, steam-water, condensing annular flow in a 38.1 mm i.d. horizontal tube. The velocity of the steam at inlet was in the range 97–186 m/s. Measurements of the liquid film flow rate at the end of the test section, which arose as a result of condensation, entrainment, and deposition, were made by extracting the film through a porous sinter bush. The liquid flow rate in the vapour core at exit was deduced from these measurements together with a heat balance on the condenser section. These results were compared with three correlations for entrainment developed from air-water studies. On the basis of the experimental data available, there was sufficient agreement in one case to warrant further investigation.

Rewetting of a hot surface by a falling liquid film

An experimental study is made on rewetting of a hot stainless steel tube by a Freon 113 liquid film at atmospheric pressure. The effects of liquid film flow rate, initial wall temperature and wall thickness on the wet front velocity are presented. Applying the temperature variation measured at the wall surface, a two-dimensional conduction equation in the wall is solved numerically to derive the boiling curve, i.e. the relation between the surface heat flux and the wall superheat. The result indicates that the intensive heat transfer to the liquid film behind the wet front is performed by transition and nucleate boiling, that the boiling curve is little affected by liquid film flow rate, initial wall temperature and wall thickness, and that the maximum heat flux is about twice the critical heat flux predicted for the pool boiling system.

Studies of Swirling Annular-Mist Two-Phase Flow : 2nd Report, Analysis of Liquid Film Flowrate along a Tube

Studies of Swirling Annular-Mist Two-Phase Flow : 2nd Report, Analysis of Liquid Film Flowrate along a Tube

The Scale-Up and Limitation of Physical Oxygen Transfer in Rotating Biological Contractors

Three different sized laboratory scale Rotating Biological Contactor (RBC) units were constructed to study the controlling factors of physical oxygen transfer. Physical parameters were identified and evaluated by the volumetric oxygen transfer coefficient (KLa) from non-steady state clean water tests. The controlling factor was found to be the liquid film flow rate per unit volume and the function could be practically expressed as w1.5 D0.5 S−1. The turbulene effect on the free water surface and subsurface volume becomes comparatively less significant as the disk size increases. The data indicated that the physical oxygen transfer contribution to the biological treatment oxygen requirement became less significant than oxygen transfer through other mechanisms as the disk size increases.

Dryout Heat Flux and Size of Entrained Drops in a Flow Boiling System

Boiling heat transfer experiments are performed on a Freon 113 upward flow in a uniformly heated tube, and the liquid film flow rate and the size of drops entrained in the vapor core are measured at the exit end of the heated tube. The exit film flow rate at the critical heat flux condition is near to zero in a range of low heat fluxes, but it shows a trend to increase with increasing heat flux over a certain value. An empirical equation for the arithmetical mean diameter of the entrained drops is proposed, and it has been shown that the size distribution of drops can be suitably described by a gamma distribution.

Critical heat flux and exit film flow rate in a flow boiling system

Critical heat flux and liquid film flow rate at exit end of the test tube are measured with Freon 113 upward flow in a uniformly heated tube. The exit film flow rate at the critical heat flux condition is near to zero in all cases of the exit qualities higher than 50%, however, the exit film flow rate tends to increase as the heat flux is increased and the exit quality decreases less than 50%. A correlation is proposed for the critical condition with high heat fluxes, suggesting that the liquid film separation from the heated surface by vapor generation takes an important part of the critical phenomenon.

Critical heat flux and droplet entrainment rate in boiling of falling liquid films

Measurements of critical heat flux and rate of droplet entrainment due to bubble bursting are made with boiling liquid films flowing downwards on the outside surface of a uniformly heated vertical tube. The critical condition occurs first at the exit end of the heating section. The critical heat flux shows three types of characteristics by increasing the liquid film flow rate at the exit end of the heating section. The data are expressed in terms of the film flow rate and the film Weber number at the exit end. The relationship between the droplet entrainment rate and the evaporation rate of the film is also discussed.

Experimental Study of Countercurrent Steam Condensation

An experimental study of steam condensation on subcooled liquid films in countercurrent flow has been conducted in a small inclined test apparatus having a rectangular cross-section. Condensation heat transfer coefficients were determined and the dependence on steam and water flow rates, the degree of subcooling, and test section inclination were all studied. The results were correlated in terms of local parameters for the complete penetration and bypass regions. It was found that the local Nusselt number increases with steam and liquid Reynolds numbers and liquid Prandtl number when no bypass occurs. In the bypass region the Nusselt number drops sharply due to the strong effects of the reduced liquid film flow rate. It is shown that the local heat transfer coefficient may be related to the turbulence intensity in the liquid film which suggests that a general turbulence-centered model can be constructed.

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.

Heat transfer to falling liquid films and film breakdown—II: Saturated liquid films with nucleate boiling

A series of boiling heat-transfer experiments is performed on saturated water films flowing on an inner tube of a vertically arranged annulus at atmospheric pressure. Data on heat-transfer coefficient and liquid droplet rate entrained by boiling are presented in a range of heat fluxes up to film breakdown. Taking into account characteristics of the droplet rate, variation of liquid film flow rate along the heating surface and film breakdown conditions are discussed.

Studies of Liquid Film Flow in Two-Phase Annular and Annular-Mist Flow Regions : (Part 2, Upflow in a Vertical Tube)

Experimental data are presented on the pressure drop, mean liquid film thickness, state of gas-liquid interface and droplet entrainment for upward annular-mist two phase flow in a vertical tube. Using these data, the relations between the shear stress at gas-liquid interface, the liquid film flow rate and the mean film thickness are investigated, and the characteristics of the mean film thickness with respect to the film Reynolds number are revealed by comparing with the analytical predictions for laminar and turbulent films. A heat transfer experiment is also performed and the results are compared with the analytical values of heat transfer coefficient for laminar and turbulent film flow. On the basis of the experimental data of heat transfer coefficient, the nondimensional thickness of the laminar sublayer of liquid film is calculated for both upflow and downflow, and correlated with the nondimensional film thickness. The result represents the difference in flow state between the upflow film and the downflow film.

Studies of Liquid Film Flow in Two-Phase Annular and Annular-Mist Flow Regions : (Part 1, Downflow in a Vertical Tube)

Experimental data are presented on the pressure drop, mean liquid film thickness, state of gas-liquid interface and droplet entrainment for upward annular-mist two phase flow in a vertical tube. Using these data, the relations between the shear stress at gas-liquid interface, the liquid film flow rate and the mean film thickness are investigated, and the characteristics of the mean film thickness with respect to the film Reynolds number are revealed by comparing with the analytical predictions for laminar and turbulent films. A heat transfer experiment is also performed and the results are compared with the analytical values of heat transfer coefficient for laminar and turbulent film flow. On the basis of the experimental data of heat transfer coefficient, the nondimensional thickness of the laminar sublayer of liquid film is calculated for both upflow and downflow, and correlated with the nondimensional film thickness. The result represents the difference in flow state between the upflow film and the downflow film.