Downward Flow Research Articles

Effect of Distributor on Gas−Liquid Downward Flow in Capillaries

In this study, the effect of tube diameter and type of distributor on the flow patterns during cocurrent, downward, gas−liquid flow has been investigated. The superficial velocities of the liquid phase (water) and the gas phase (air) were varied in the range of 0.01−0.25 m/s and 0.01−0.5 m/s, respectively. For this purpose, capillary tubes of two diameters (1 and 1.89 mm) and two different distributors (conical and Y) were used. Three distinct flow regimes were observed: bubble flow, slug (or Taylor) flow, and liquid-ring flow. Flow transitions were affected by the type of distributor and the size of the capillary. The gas and liquid slug lengths were found to depend on the type of distributor, the capillary diameter, and the superficial fluid velocities. These slug lengths were compared with three published correlations, but none of these were found to be satisfactory. To have general applicability, any future correlation should account for the distributor design. For both distributors and capillary siz...

Buoyancy effects on upward and downward laminar mixed convection heat and mass transfer in a vertical channel

PurposeThe objective of the present study is to investigate numerically the effects of thermal and buoyancy forces on both upward flow (UF) and downward flow (DF) of air in a vertical parallel‐plates channel. The plates are wetted by a thin liquid water film and maintained at a constant temperature lower than that of the air entering the channel.Design/methodology/approachThe solution of the elliptical PDE modeling the flow field is based on the finite volume method.FindingsResults show that buoyancy forces have an important effect on heat and mass transfers. Cases with evaporation and condensation have been investigated for both UF and DF. It has been established that the heat transfer associated with these phase changes (i.e. latent heat transfer) may be more or less important compared with sensible heat transfer. The importance of these transfers depends on the temperature and humidity conditions. On the other hand, flow reversal has been predicted for an UF with a relatively high temperature difference between the incoming air and the walls.Originality/valueContrary to most studies in channel heat and mass transfer with phase change, the mathematical model considers the full elliptical Navier‐Stokes equations. This allows one to compute situations of flow reversal.

Surface Water–Groundwater Connection at the Los Alamos Canyon Weir Site: Part 1. Monitoring Site Installation and Tracer Tests

Following the May 2000 Cerro Grande fire at Los Alamos, NM, surface water control structures were constructed near Los Alamos to mitigate the transport of contaminant‐bearing sediment toward the Rio Grande river due to increased runoff caused by the removal of vegetation by the fire. A low‐head weir was constructed in Los Alamos Canyon, 5 km to the east of Los Alamos, to capture contaminant‐bearing sediments and to allow runoff to pass downstream without significant ponding behind the weir. During construction of the weir, channel alluvium was removed and the underlying fractured basalt was exposed. To monitor any downward transport of contaminants into fractured basalt, and potentially downward to the regional groundwater, three boreholes (one vertical, and two angled) were installed for environmental monitoring. An innovative monitoring system was installed using FLUTe (Santa Fe, NM) liners for both vadose zone and perched groundwater zones. The vertical borehole intersects several perched water zones, and groundwater can be sampled from four ports. One angled borehole has an inflatable liner with sensors to measure relative water content. The second angled borehole was abandoned. Tracer tests were initiated in April 2002 and June 2003 with the application of solutions of potassium bromide and potassium iodide, respectively, onto the basin floor above the weir. The hydrogeologic characterization from drilling the boreholes, in conjunction with groundwater elevation and vadose zone moisture monitoring, and results from the tracer tests show that the subsurface hydrogeology is complex, and surface water and perched groundwater systems are in apparent close communication. Infiltration is rapid, and movement from the surface to the deepest perched zone (at a depth of 78 m) occurs within 8 to 14 d. Downward flow occurs predominantly via fracture flow.

Local Liquid Velocity in Vertical Air-Water Downward Flow

This paper presents an experimental study of local liquid velocity measurement in downward air-water bubbly and slug flows in a 50.8 mm inner-diameter round pipe. The axial liquid velocity and its fluctuations were measured by a laser Doppler anemometry (LDA) system. It was found that the maximum liquid velocity in a downward two-phase flow could occur off the pipe centerline at relatively low liquid flow rates and this observation is consistent with other researchers’ results. The comparisons between the liquid flow rates measured by a magnetic flow meter and those obtained from the local LDA and multi-sensor conductivity probe measurements showed good agreement. In addition, based on the local measurements the distribution parameter and the drift velocity in the drift-flux model were obtained for the current downward flow tests.

Temperature Distribution in a Porous Medium Subjected to Solar Radiative Incidence and Downward Flow: Convective Boundaries

The knowledge of steady-state temperature distribution is known a priori for natural convection stability analysis. The present study determines the temperature profiles in an infinite horizontal layer of fluid filled with saturated porous medium confined between two convective surfaces subjected to external radiative incidence and imposed downward convection. The investigation concentrates on the influences of the thermal boundary condition (Biot number), internal and external Rayleigh numbers, Peclet number, optical thickness, and surface reflectivities. The implications of these factors on fluid stability are addressed in detail.

Temperature Distribution in a Porous Medium with Solar Incidence and Downward Flow

Temperature Distribution in a Porous Medium with Solar Incidence and Downward Flow

면역약침(免疫藥鍼)을 이용(利用)한 방광암(膀胱癌) 치험(治驗) 1례(例)

In oriental medicine bladder cancer had been called `溺血(Hematuria)`, 血淋(Blood Stranguria)`, 濕熱河注(Downward Flow of Damp-heat)` and so on. The symptoms are Hematuria, Oliguria, Lower abdomen pain, febrile sensation and Anemia etc. These are similar to the symptoms of bladder cancer by modem medicine. I have experienced a bladder cancer patient who was diagnosed as stage Ⅲ. She has been treated bladder cancer with Immunity herbal acupuncture and Her clinical and objective symptoms have been better. Therefore I report this results.

605 垂直弾性細管内下降液流中の単一粒子挙動について

605 垂直弾性細管内下降液流中の単一粒子挙動について

Observations of Slug Dissipation in Downward Flow

Detailed observations were made for slug flow in an upward to downward pipeline configuration with 13 capacitance sensors. The results presented in this study are based on four typical tests, which demonstrate the phenomena encountered in slug dissipation. In downward flow, slug frequency decreases with different extent at different flow rates. There is a reduction of slug length after the turning over from upward to downward flow. However, the slug tends to recover its stable length in further downstream development, except for flow that quickly becomes stratified. Growth of the slug length is accomplished by picking up liquid left by the downstream dissipating slug before being fully absorbed by the liquid film. [S0195-0738(00)00503-3]

Subcooled Flow Boiling in Circumferentially Nonuniform and Uniform Heated Vertical Channels With Downward Flow

Results are presented for new experimental data for subcooled flow boiling heat transfer in circumferentially nonuniform (single-side) and uniformly heated tubes. Although the Liu-Winterton correlation had better agreement at low power levels and axial locations, Shah’s correlation had better agreement at higher power levels and at axial locations near the center of the heated length. Both correlations overpredicted the data near the exit. Therefore, additional correlational developmental work is needed for local (axial) flow boiling heat transfer in circumferentially nonuniform heated channels. [S0022-1481(00)00603-4]

Pressure Loss/Gain Boundary of Gas-Liquid Downward Flow in Inclined and Vertical Pipes

Gas-liquid downward flow is frequently encountered in hilly-terrain pipelines, downcomer pipes extending from offshore production platforms to sea floors, and steam injection wells in thermal enhanced recovery operations. Since the gravitational and frictional terms in the total pressure gradient equation for downward flow have opposite signs, gas-liquid downward flow in inclined and vertical pipes may experience either pressure loss or pressure gain, depending on flow rates, pipe geometry, and fluid properties. A mechanistic model for the pressure loss/gain boundary of gas-liquid downward flow in inclined and vertical pipes is developed in this work and is verified with available experimental results. The effects of pipe inclination angle, inside diameter, wall roughness, and fluid physical properties on the pressure loss/gain boundary are presented. [S0195-0738(00)00302-2]

Effects of Upper Plenum on the Critical Heat Flux of Downward Flow

Effects of Upper Plenum on the Critical Heat Flux of Downward Flow

The Onset of Flow Instability for Downward Flow in Vertical Channels

A simple analytical model to predict the onset of Ledinegg instability in vertical channels under downflow conditions has been developed and evaluated. The model divides the flow field into three regions based upon the fluid temperature. The pressure drop is then found by solving an appropriate set of equations for each region. The theoretical results are compared to an extensive set of experimental data covering a range of channel diameters and operating conditions. Agreement is excellent, and the prediction of the velocity at which the minimum point in the demand curve occurs is within 12 percent over the range of experimental results. A parameter, the ratio between the surface heat flux and the heat flux required to achieve saturation at the channel exit for a given flow rate, is found to be a very accurate indicator of the minimum point velocity.

Isothermal Air-Water Two-Phase Up- and Downward Flows in a Vertical Capillary Tube. 2nd Report. Pressure Loss.

Pressure drop was measured for air-water two-phase flow in a vertical capillary tube. Inner diameters of pipes used were 1mm, 2.4mm and 4.9mm. The directions of flow were both vertically upward and downward. Several correlations of pressure loss in two-phase flow, which have been proposed so far, were examined to determine whether or not they are useful for a capillary tube. As a result, it was clarified that those correlations cannot predict the data with high accuracy, especially in the intermittent flow region. Thus we proposed a new. correlation in which the expansion loss of water flow from water film around a large gas bubble to a water slug is taken into consideration. It shows better agreement with the experimental data.

The Effect of Inlet Subcooling on the Critical Heat Flux for Downward Flow With Upstream Compressibility

The Effect of Inlet Subcooling on the Critical Heat Flux for Downward Flow With Upstream Compressibility

Isothermal Air-Water Two-Phase Up-and Downward flows in a Vertical Capillary Tube 1st Report, Flow Pattern and Void Fraction.

Knowledge of two-phase flow in a capillary tube is important to understand flow phenomena in narrow passages, for example, in a compact heat exchanger. The present authors have previously reported the characteristics of flow parameters such as pressure drop, and void fraction as well as flow pattern in an air-water two-phase flow in a horizontal capillary tube. In the present paper, we discuss the effect of flow direction on void fraction and flow patterns in two-phase flow in a vertical capillary tube. Two correlations relating bubble velocity with total volume flux and time-averaged void fraction with gas volume flow quality were proposed.

Numerical Analysis of Heat and Mass Transfer From Horizontal Cylinders in Downward Flow of Air-Water Mist

A numerical analysis is made of heat and mass transfer from horizontal circular cylinders in a downward flow of air/water mist of polydisperse droplets, taking into account the far-upstream droplet size distribution and the blockage effect of the gas phase flow. The effects of the droplet size distribution, temperatures, and liquid-to-gas mass flow ratio upon the liquid film thickness and wall shear stress, velocity, and temperature of the air-water interface, two-phase Nusselt numbers, etc., are examined.

Late Jurassic Paleohydrology of San Juan Basin: Simulated Effects of Variable Transmissivity and Lake Levels: ABSTRACT

A three-dimensional computer model of ground-water flow in the San Juan basin at the end of Morrison Formation time shows that variations in transmissivity and in the level of paleo-Lake T'oo'dichi would have significantly altered the direction of ground-water flow compared to that of surface flow. The model consists of four layers: the (1) Brushy Basin, (2) Westwater Canyon, (3) Salt Wash and Recapture Members of the Morrison, and (4) the San Rafael Group. Paleotopographic slopes were determined from alteration facies thought to indicate variations in extent and depth of the paleoplaya lake. Thicknesses of sandstones and mudstones from approximately 2,000 drill holes were used to estimate transmissivities and conductivities. Simulated results for the lowest paleolake levels and for constant fluid density show that ground water generally would have flowed from highlands on the west, south, and east northward to discharge areas in the lowest part of the basin. Low-permeability lacustrine sediments of the Brushy Basin Shale Member, northward increase in mud/sand ratio in fluvial sediments, east and southeast-trending wedges of thicker fluvial sands, and high lake levels would have partly redirected ground-water flow eastward and tended to cause upwelling and discharge in the southeastern part of the basin andmore » along the paleoshoreline. Downward fluid flow in the basin interior would have required higher fluid density in the center of the basin than at the margins.« less

Sudden Expansion of Gas-solid Two-phase Flow in Vertical Downward Flow

Gas-solid two phase flow in sudden expansion of a vertical downward flow is experimentally examined by using different expansion ratios and different solid particles. The result shows that additional expansion loss takes a negative value when the flux Richardson number exceeds 0.0015 as in horizontal pipes under the condition that the velocity of solid particles is larger than that of air.

Sudden Expansion of Gas-Solid Two-Phase Tube in Vertical Downward Flow

Sudden Expansion of Gas-Solid Two-Phase Tube in Vertical Downward Flow