Counterflow Of Water Research Articles

Results of experimental studies of changes in the level and heating of the main condensate in mixing-type LPH

In the thermal circuits of domestic steam turbines, mixing-type low-pressure heaters (LPH) with free-flow jet water distribution and counter-flow of water and steam are widely used. The choice of the counterflow variant of the media movement ensures the most efficient heat transfer. However, the technical problem of ensuring reliable operation of LPH in the entire range of design loads of TPP and NPP power units is still relevant.During the commissioning and operation of mixing-type LPH in 800÷1200 MW turbines of TPP and NPP, the presence of metal knocks in the zone of the check valve, hydraulic shocks in the heating section were revealed. A priori, these phenomena indicated design flaws in LPH or manufacturing defects in their production. Research carried out by NPO CKTI specialists showed that periodic hydraulic shocks in the heating section and metal knocks occur as a result of uneven distribution around the circumference of the main condensate and steam supply. This leads to a breakdown of the check valve and the destruction of perforated plates and off-design heating of water in the volume of the annular LPH water chamber. To clarify the causes of the damage, develop recommendations for the reconstruction of the apparatus and further account for the design, two series of experimental studies were carried out on mixing-type heaters of 800 MW turbine units PNSV-2000-1 and PNSV-2000-2 manufactured at PJSC Krasny Kotelshchik. The purpose of the experimental studies was to determine the change in the water level in the water chamber and the heating of the main condensate in the elements of the heating compartment during normal operation of the power unit at loads of 400÷850 MW. Based on the results of the research, the method for calculating the mixing-type LPH has been refined, taking into account the revealed non-uniformity of water heating in the water chamber, recommendations for their reconstruction have been developed and implemented.

Computational and experimental investigation of condensation flow patterns and heat transfer in parallel rectangular micro-channels

This study explores experimentally and computationally fluid flow and heat transfer characteristics of FC-72 condensation along a cooling module containing multiple 1 mm × 1 mm square channels. The module is cooled along its underside by a counterflow of water. The computational portion of the study adopts the VOF method and Lee interfacial phase change model, and is executed using ANSYS FLUENT. Computed are dominant flow patterns as well as spatial variations of both bottom wall temperature and fluid temperature for FC-72 mass velocities ranging from 68 to 367 kg/m2s. The computed flow patterns show good agreement with those captured experimentally using high-speed video. Captured correctly are dominant smooth-annular, wavy-annular, transition, slug, bubbly, and pure liquid flow patterns. And predicted variations of wall temperature show good agreement between computational results, with average deviation ranging from 1.46% to 6.81%. The computational method is capable of predicting fluid temperature, which cannot be measured experimentally in a small channel. Detailed spatial variations of fluid temperature are provided both perpendicular to the bottom wall and along the channel. These variations show close correspondence with axial spans of the dominant flow patterns.

Mechanism of counterflows and circulation cells in swirling flows

This paper reviews counterflows, double counterflows, and circulation cells in swirling flows and argues that all these seeming paradoxical phenomena can be caused by a common swirl- decay mechanism (SDM). It is shown that SDM explains (a) the counterflow of water and oil in hydrocyclones, (b) the elongated counterflow of hot and cold air in vortex tubes, and (c) the double counterflow occurring in vortex combustion chambers. SDM also explains the development and disappearance of circulation cells, often referred to as vortex breakdown bubbles, in sealed cylindrical containers where the flow is driven by rotation of one end disk. In a few words, SDM is the following. The balance of the centrifugal force and the radial gradient of pressure in a fast- swirling flow results in that pressure at the rotation axis is smaller than pressure at the periphery. If swirl decays downstream, pressure grows along the axis. This axial gradient of pressure decelerates the near-axis flow and can reverse it thus developing a local or global counterflow. It is shown that SDM also works in two-fluid flows modeling vortex bioreactors.

Conditions for Obtaining “Thick” Amorphous Wires by the Ulitovsky–Taylor Method

The existing methods for obtaining amorphous wires of large diameters from a melt are considered. The advantages of the Ulitovsky–Taylor method for obtaining amorphous wires in a wide range of diameters with stable geometric characteristics are underlined. The factors that affect the process of obtaining “thick” amorphous wires by a continuous version of the Ulitovsky–Taylor method are analyzed. It is demonstrated why it is necessary to use alloys with a high glass-forming ability and with melting temperatures of 950–1150°C. The practicability of introducing technological additives (Nb, Mo, Cr, etc.) is justified. It is noted that, to ensure a continuous process of producing a “thick” wire, it is necessary to use a high-purity precursor with stable geometric parameters. A variant of a quenching device is proposed for cooling a melt jet with a counterflow of water. The technique for removing the glass cover is based on elastic bending of the metal core and brittle cracking of glass. The technology for producing “thick” wires was tested. Long wires with diameter of 50–200 μm with a high set of properties were manufactured.

Numerical and Experimental Investigation of Heat Transfer Enhancement in Double Pipe Heat Exchanger

This study included two parts, one of them experimental work and the other the Artificial Neural Networks (ANN) application. For the first part, a heat exchanger of double pipe with counter flow of water were used. This heat exchanger included a semicircular disc baffles attached on the outer surface of the inner tube fitted with twisted tape. The second part used to determine the transfer functions effect and training algorithms on the experimental work. The heat exchanger outer tube material was made from iron of (0.054 m and 0.05 m) outer and inner diameters respectively also inner tube material was copper of (0.022 m and 0.02 m) outer and inner diameters respectively. The dimensions of baffles were with (22 mm, 11 mm and 1 mm) outer radius, inner radius, and depth respectively while baffles space was 150 mm. the types of twisted tape for the inner tube were plain twisted tape (PTT), twisted tape with circular ring CRT and wire nail-twisted tape (WN-TT). The ratio of twist was y = 5. The results show that the errors in all cases for Nusselt number and factor of friction not exceed 5%.

Analytical and experimental determination of slug flow parameters, pressure drop and heat transfer coefficient in micro-channel condensation

This paper investigates slug flow associated with condensation along a module containing 10 of 29.9-cm long micro-channels having 1×1-mm2 cross section. Using FC-72 as condensing fluid, which is cooled by water counterflow, experiments are performed to measure pressure drop as well as detailed temperature variations along the condensation module. Using high speed video, the flow is shown to consist of a series of unit cells, each comprised of a liquid slug and an elongated bubble. New interfacial instability theory is developed to describe the transition from annular flow to slug flow and obtain analytical expressions for bubble and slug lengths for the most upstream unit cell. Also presented is a new theoretical model for slug flow that is used to determine axial variations of bubble, slug and unit cell lengths. These lengths are used to evaluate axial variations of the local heat transfer coefficient, which are accurately predicted using the new model. Additionally, pressure drop data show good agreement with predictions of a recent universal correlation approach for condensation in small channels.

A Microstructured Fiber with Defined Borosilicate Regions to Produce a Radial Micronozzle Array for Nanoelectrospray Ionization.

This work highlights the possibility of using microstructured fibres with predefined doped regions to produce functional microstructures at a fibre facet with differential chemical etching. A specially designed silica microstructured fibre (MSF) that possesses specific boron-doped silica regions was fabricated for the purpose of generating a radial micronozzle array. The MSF was drawn from a preform comprising pure silica capillaries surrounded by boron-doped silica rods. Different etching rates of the boron-doped and silica regions at the fiber facet produces raised nozzles where the silica capillaries were placed. Fabrication parameters were explored in relation to the fidelity and protrusion length of the nozzle. Using etching alone, the nozzle protrusion length was limited, and the inner diameter of the channels in the array is expanded. However with the addition of a protective water counter flow, nozzle protrusion is increased to 60 μm with a limited increase in hole diameter. The radial micronozzle array generated nine individual electrosprays which were characterized using spray current measurements and related to theoretical prediction. Signal enhancement for the higher charge state ions for two peptides showed a substantial signal enhancement compared to conventional emitter technology.

Experimental Investigation of Flow Condensation in Microgravity

Future manned space missions are expected to greatly increase the space vehicle's size, weight, and heat dissipation requirements. An effective means to reducing both size and weight is to replace single-phase thermal management systems with two-phase counterparts that capitalize upon both latent and sensible heat of the coolant rather than sensible heat alone. This shift is expected to yield orders of magnitude enhancements in flow boiling and condensation heat transfer coefficients. A major challenge to this shift is a lack of reliable tools for accurate prediction of two-phase pressure drop and heat transfer coefficient in reduced gravity. Developing such tools will require a sophisticated experimental facility to enable investigators to perform both flow boiling and condensation experiments in microgravity in pursuit of reliable databases. This study will discuss the development of the Flow Boiling and Condensation Experiment (FBCE) for the International Space Station (ISS), which was initiated in 2012 in collaboration between Purdue University and NASA Glenn Research Center. This facility was recently tested in parabolic flight to acquire condensation data for FC-72 in microgravity, aided by high-speed video analysis of interfacial structure of the condensation film. The condensation is achieved by rejecting heat to a counter flow of water, and experiments were performed at different mass velocities of FC-72 and water and different FC-72 inlet qualities. It is shown that the film flow varies from smooth-laminar to wavy-laminar and ultimately turbulent with increasing FC-72 mass velocity. The heat transfer coefficient is highest near the inlet of the condensation tube, where the film is thinnest, and decreases monotonically along the tube, except for high FC-72 mass velocities, where the heat transfer coefficient is enhanced downstream. This enhancement is attributed to both turbulence and increased interfacial waviness. One-ge correlations are shown to predict the average condensation heat transfer coefficient with varying degrees of success, and a recent correlation is identified for its superior predictive capability, evidenced by a mean absolute error of 21.7%.

Numerical modeling of counter-current condensation in a Black Liquor Gasification plant

Pressurized Entrained flow High Temperature Black Liquor Gasification is a novel technique to recover the inorganic chemicals and available energy in black liquor originating from kraft pulping. The gasifier has a direct quench that quickly cools the raw syngas when it leaves the hot reactor by spraying the gas with a water solution. As a result, the raw syngas becomes saturated with steam. Typically the gasifier operates at 30 bar which corresponds to a dew point of about 235 °C and a steam concentration in the saturated syngas that is about 3 times higher than the total concentration of the other species in the syngas. After the quench cooler the syngas is passed through a counter-current condenser where the raw syngas is cooled and most of the steam is condensed. The condenser consists of several vertical tubes where reflux condensation occurs inside the tubes due to water cooling of the tubes on the shell-side. A large part of the condensation takes place inside the tubes on the wall and results in a counterflow of water driven by gravity through the counter current condenser. In this study a computational fluid dynamics model is developed for the two-phase fluid flow on the tube-side of the condenser and for the single phase flow of the shell-side. The two-phase flow was treated using an Euler–Euler formulation with closure correlations for heat flux, condensation rate and pressure drop inside the tubes. The single-phase model for the shell side uses closure correlations for the heat flux and pressure drop. Predictions of the model are compared with results from experimental measurements in a condenser used in a 3 MW Black Liquor Gasification development plant. The results are in good agreement with the limited experimental data that has been collected in the experimental gasifier. However, more validation data is necessary before a definite conclusion can be drawn about the predictive capability of the code.

Cavitation interaction between fluid counterflows

Some features of self-oscillatory regimes for the cavitation interaction of coaxial water and annular gas jets with a water counterflow are studied. The dependencies of the self-oscillation frequency, the maximum displacement of a cavity toward the incident flow, and the displacement amplitude on the pipe diameter and the Froude number are found. A conclusion on the onset of self-oscillations is substantiated. The possibility of a significant increase in the counterflow range due to the gas injection in the vicinity of the counterflow is shown.

Flow condensation in parallel micro-channels – Part 2: Heat transfer results and correlation technique

This second part of a two-part study concerns heat transfer characteristics for FC-72 condensing along parallel, square micro-channels with a hydraulic diameter of 1 mm, which were formed in the top surface of a solid copper plate. Heat from the condensing flow was rejected to a counter flow of water through channels brazed to the underside of the copper plate. The FC-72 condensation heat transfer coefficient was highest near the channel inlet, where the annual liquid film is thinnest. The heat transfer coefficient decreased along the micro-channel because of the film thickening and eventual collapse of the annular regime. Notable heat transfer enhancement was observed for annular flow regions of the micro-channel associated with interfacial waves. Comparing the present data to predictions of previous annular condensation heat transfer correlations shows correlations intended for macro-channels generally provide better predictions than correlations intended specifically for mini/micro-channels. A new condensation heat transfer coefficient correlation is proposed for annular condensation heat transfer in mini/micro-channels. The new correlation shows excellent predictive capability based on both the present FC-72 data and a large database for mini/micro-channel flows amassed from eight previous sources.

Flow condensation in parallel micro-channels – Part 1: Experimental results and assessment of pressure drop correlations

In this first part of a two-part study, experiments were performed to investigate condensation of FC-72 along parallel, square micro-channels with a hydraulic diameter of 1 mm and a length of 29.9 cm, which were formed in the top surface of a solid copper plate. The condensation was achieved by rejecting heat to a counter flow of water through channels brazed to the underside of the copper plate. The FC-72 entered the micro-channels slightly superheated, and operating conditions included FC-72 mass velocities of 68–367 kg/m 2 s, FC-72 saturation temperatures of 57.2–62.3 °C, and water mass flow rates of 3–6 g/s. Using high-speed video imaging and photomicrographic techniques, five distinct flow regimes were identified: smooth-annular, wavy-annular, transition, slug, and bubbly, with the smooth-annular and wavy-annular regimes being most prevalent. A detailed pressure model is presented which includes all components of pressure drop across the micro-channel. Different sub-models for the frictional and accelerational pressure gradients are examined using the homogenous equilibrium model (with different two-phase friction factor relations) as well as previous macro-channel and mini/micro-channel separated flow correlations. Unexpectedly, the homogenous flow model provided far more accurate predictions of pressure drop than the separated flow models. Among the separated flow models, better predictions were achieved with those for adiabatic and mini/micro-channels than those for flow boiling and macro-channels.

Theoretical model for annular flow condensation in rectangular micro-channels

This study examines the pressure drop and heat transfer characteristics of annular condensation in rectangular micro-channels with three-sided cooling walls. A theoretical control-volume-based model is proposed based on the assumptions of smooth interface between the annular liquid film and vapor core, and uniform film thickness around the channel’s circumference. Mass and momentum conservation are applied to control volumes encompassing the liquid film and the vapor core separately. The model accounts for interfacial suppression of turbulent eddies due to surface tension with the aid of a new eddy diffusivity model specifically tailored to shear-driven turbulent films. The model predictions are compared with experimental pressure drop and heat transfer data for annular condensation of FC-72 along 1 × 1 mm 2 parallel channels. The condensation is achieved by rejecting heat to a counterflow of water. The data span FC-72 mass velocities of 248–367 kg/m 2 s, saturation temperatures of 57.8–62.3 °C, qualities of 0.23–1.0, and water mass flow rates of 3–6 g/s. The data are also compared to predictions of previous separated flow mini/micro-channel and macro-channel correlations. While some of the previous correlations do provide good predictions of the average heat transfer coefficient, they fail to capture axial variation of the local heat transfer coefficient along the channel. The new model accurately captures the pressure drop and heat transfer coefficient data in both magnitude and trend, evidenced by mean absolute error values of 3.6% and 9.3%, respectively.

Rapid Multiphase Flow Dynamics Mapped by Single‐Shot MRI Velocimetry

A new, fast magnetic resonance imaging (MRI) method is described and applied to map flow fields in systems with internal velocities rapidly varying along the streamlines. While conventional MRI techniques encode the velocity information in a preparatory period prior to the imaging acquisition module, our technique repeatedly refreshes the velocity encoding during a single-shot imaging sequence. In this way, the maximum acceleration responsible for velocity variation of the molecules is increased by up to two orders of magnitude compared to standard procedures. Besides being compatible with high acceleration, this pulse sequence is suited to acquiring in a single scan the multiple velocity images required to construct a full velocity vector map. The power of this new methodology is demonstrated by following the internal dynamics of toluene droplets levitating in a counterflow of water during mass transfer of acetone from the water phase into the drop in the presence of surface-active impurities. The dramatic reduction in measurement time allows visualization for the first time of the important impact of even small concentrations of acetone on accumulation of surfactants at the drop's surface.

Simulation of Heat and Water Counterflow in Unsaturated Compacted Bentonite

Abstract An engineer-scaled experiment, KENTEX is being performed at the Korea Atomic Energy Research Institute to study the thermal, hydraulic, and mechanical (THM) processes occurring in the engi...

Relaxation dynamics of water-immersed granular avalanches

We study water-immersed granular avalanches in a long rectangular cell of small thickness. By video means, both the angle of the granular pile and the velocity profiles of the grains across the depth are recorded as a function of time. These measurements give access to the instantaneous granular flux. By inclining the pile at initial angles larger than the maximum angle of stability, avalanches are triggered and last for a long time, up to several hours for small grains, during which both the slope angle and the granular flux relax slowly. We show that the relaxation is quasi-steady so that there is no inertia: the relaxation at a given time is controlled only by the slope angle at that time. This allows us to adapt a frictional model developed recently for dry or water-immersed grains flowing in stationary conditions. This model succeeds well in reproducing our unsteady avalanche flows, namely the flowing layer thickness, the granular flux and the temporal relaxation of the slope. When a water counter-flow is applied along the pile, the granular avalanches are slowed down and behave as if granular friction were increased by an amount proportional to the water flow. All these findings are also reproduced well with the same friction model by taking into account the additional fluid force.

Effect of NAPL film stability on the dissolution of residual wetting NAPL in porous media: A pore-scale modeling study

Wettability profoundly affects not only the initial distribution of residual NAPL contaminants in natural soils, but also their subsequent dissolution in a flowing aqueous phase. Under conditions of preferential NAPL wettability, the residual NAPL phase is found within the smaller pores and in the form of continuous corner filaments and thick films on pore walls. Such films expose a much greater interfacial area for mass transfer than would be exposed by the same amount of non-wetting NAPL. Importantly, capillary and hydraulic continuity of NAPL filaments and thick films is essential for sustaining NAPL–water counterflow during the course of NAPL dissolution in flowing groundwater—a mechanism which maintains and even increases the interfacial area for mass transfer. Continued dissolution results in gradual thinning of the NAPL films, which may become unstable and rupture causing disconnection of the residual NAPL in the form of clusters. Using a pore network simulator, we demonstrate that NAPL film instability drastically modifies the microscopic configuration of residual NAPL, and hence the local hydrodynamic conditions and interfacial area for mass transfer, with concomitant effects on macroscopically observable quantities, such as the aqueous effluent concentration and the fractional NAPL recovery with time. These results strongly suggest that the disjoining pressure of NAPL films may exert an important, and hitherto unaccounted, control on the dissolution behaviour of a residual NAPL phase in oil wet systems.

A polyaminoquinone film for dopamine entrapment and delivery

Dopamine uptake and release was investigated with a quinone-containing conducting film, poly(5-amino-1,4-naphthoquinone) (PANQ), used for its intrinsic cation-exchange properties. The good electroactivity of this film in aqueous medium leads to interesting values of dopamine uptake, up to 100 nmol cm−2 in a 300 nm thick film. The uptake and release mechanisms indicate a water counterflow during the doping process and competition with protons. The incorporated dopamine can be released by applying an oxidative potential, and such a film has possibilities as a dopamine vector for in vivo applications.

Laminar cooling of pseudoplastic fluids flowing through cylindrical horizontal pipes

We present results concerning heat transfer for pseudoplastic fluids flowing inside cylindrical tubes. The fluids are cooled by an external turbulent counterflow of water. A method is developed to evaluate the values of the local heat exchange coefficients. The variations of the associated Nusselt numbers can be approached using the dimensionless axial abscissa X + = ( 2z/D )/Pe. Experimentation shows that the Nusselt numbers remain slightly dependent on the difference between the inlet temperature of the pseudoplastic fluid T e and the wall temperatures T w ( z ). This last phenomenum, attributed to the variations of consistency K and rheological index n with temperature, can be linked to the evolutions of the axial velocity profiles, experimentally determined by laser Doppler anemometry. A very simple correlation Nu(z) = 1.15(3 n + 1)/(4 n ) 1/3 1−0.008[ T e − T w ( z )[ X + −0.36 seem to be acceptable in our experimental range. Comparisons with numerical predictions are also proposed.

The kinetics and mechanism of caffeine infusion from coffee: The hindrance factor in intra‐bean diffusion

AbstractGreen and medium‐roast Kenyan arabica coffees were ground and sieved, and the 0·85–1·8 mm size fractions partially converted into two water‐swollen forms by an appropriate series of treatments. The first form still contained a mix of coffee solubles, the second only caffeine. The rates of caffeine infusion into water at 80°C were then measured for the dry coffee and for the two water‐swollen preparations. The caffeine was extracted two to three times faster from the solute‐free water‐swollen preparation than from the dry material Analysis of the results showed that counterflow of water the swelling of coffee particles, caffeine association with other solubes and physical restraints within the bean matrix all contribute to the low diffusion coefficient of caffeine inside the coffee particles. The behaviour of the green and the medium roast coffees was surprisingly similar.