Experimental Study Of Hydrodynamics Research Articles

Study of the Effect of Heat Supply on the Hydrodynamics of the Flow and Heat Transfer in Capillary Elements of Mixing Heads Jet Thrusters

The article presents the results of experimental studies of hydrodynamics and those of loobman single-phase and two-phase flows in capillary nozzle elements propellant thrusters and the proposed method of their calculation. An experimental study was performed in capillaries with a sharp entrance edge of the internal diameter of 0.16 and 0.33 mm and a relative length 188 and 161, respectively, in pouring distilled water and acetone in the following range of parameters Reynolds number Re = (0,3 ... 10) · 103, Prandtl number Pr = (2 ... 10), pressure p = (0,1 ... 0,3) MPa, the heat flux q = (0...2)×106 W/m2, the difference of temperature under-heating of liquid Δtn = (5 ... 80)K. The dependences for calculation of single phase boundaries, the undeveloped and the developed surface of the bubble and film key singing of subcooled liquid. It is shown theoretically and experimentally confirmed the virtual absence of areas of undeveloped nucleate boiling in laminar flow. The dependence for calculation of hydraulic resistance and heat transfer in the investigated areas of current. It is shown that in the region of nucleate boiling surface in the flow in capillary tubes, influence of the formed vapor phase on the hydrodynamics and heat transfer substantially higher than in larger diameter pipes.

Experimental assessment of heat and mass transfer of modular nozzles of cooling towers

Data of experimental study of hydrodynamics, heat and mass transfer of modular nozzles of cooling towers and some comparative characteristics of the packed device with nozzles, which have wide industrial application, are given in the article.

THE STUDY OF HYDRODYNAMIC PROCESSES AT THE GAS FLOW FILTRATION THROUGH THE CANDIED FRUITS LAYER

The experimental studies of hydrodynamics of the gas flow filtration through the candied fruits layer, formed by the different methods, were carried out. The particles of studied candied fruits were cylindrical, equally sized, filled the whole container for drying. The main characteristics of the layers were experimentally determined: porosity, equivalent diameter, specific surface. The results of experiments prove the expedience of the candied fruits layer formation of the cylindrical particles with correct form by the method of placing candied fruits vertically “with overlap of channels”. Such method allows provide the insignificant hydraulic resistance of the layer and rather high speed of the gas flow filtration through this layer. It will result in the increase of heat transfer and mass output coefficients, so to the intensification of filtration drying. Such formation method also allows reduce the volume of drying equipment, shorten the time of drying and decrease the energy consumption of process.

Experimental hydrodynamic study of flow through metallic foams: Flow regime transitions and surface roughness influence

The aim of the present work is to study the hydrodynamic behavior of the single phase water flow through three metallic foam samples (i.e. Copper, NiFeAlC, and Inconel) in a plate heat exchanger. These samples have a same pore diameter (1200 µm) and grade (20 PPI), however, the Microscopic images show that the ligament diameter and the surface roughness are different. The effect of the metallic foam surface roughness and the ligament diameter on the pressure drop behavior is analyzed, and the regime transitions from pre-Darcy to turbulent are identified. It is found that more, the metallic foam surface is rough, more the pressure drop is important and the turbulent regime is reached rapidly. The Permeability and Forchheimer parameters were calculated for each flow regime. It is noticed that each fluid regime can exhibit different permeability and Forchheimer coefficient for the same foam sample. The present data were confronted to those available in the literature and a good qualitative and quantitative agreement was obtained.

Numerical and experimental hydrodynamic study of a coolant distributor for grinding applications

ABSTRACTIn grinding, the high frictional energy is converted into heat, which may cause thermal damage and degradation of the wheel and the workpiece. Unwanted thermal effects must thus be reduced, often by external cooling using a curved-duct coolant distributor to match the wheel geometry. The performance of such a system depends strongly on the impinging jet flow properties to ensure efficient sprinkling of the hot spots. The fluid distributor, placed above the workpiece, is pierced with a certain number of identical nozzle fittings, providing multiple jets at the outlet of the nozzles. These jets sprinkle the solids over a given zone and remove the heat by convective transfer. The cooling is hence dependent on the flow structure, meaning the jet diameters, trajectories and velocities, determined up-flow by the distributor design. The present study is devoted to the hydrodynamics aspects of the fluid distributor, aiming to determine the flow-rate distribution at the different orifices and the flow-rate–pressure relationship, for a variety of nozzle diameters and feeding flow rates, under isothermal conditions. A simple hydraulic balance in the device was not able to predict with sufficient accuracy the actual measurements, even when the Venturi effect was accounted for. This discrepancy is due to the curvature of the distributor, inducing secondary flows in interaction with the nozzle outlets, which leads to a rather complex flow pattern. To overcome this issue, a computational fluid dynamics (CFD) tool was used and compared with in situ experiments – global flow rate and pressure measurements were additionally taken with particle image velocimetry (PIV) to gain insight into the local structure. Simulations were performed with a 3D turbulence model for Reynolds numbers up to 100,000. This model provides an efficient tool for coupling with the thermal study at a later step, allowing global sizing and energetic optimization of the grinding process.

Experimental study of hydrodynamics and thermal behavior of a pseudo‐2D spout‐fluidized bed with liquid injection

A novel nonintrusive technique is presented to investigate hydrodynamic and thermal behavior of gas–solid spout‐fluidized beds with liquid injection, by simultaneously capturing visual and infrared images. Experiments were performed in a pseudo‐2D bed with draft plates filled with glass or γ‐alumina particles to investigate the effect of liquid injection and particle properties on the flow characteristics. For the glass particles under dry and wet conditions, time‐averaged particle velocities show similar quasi‐steady‐state behavior. However, under wet conditions, lower particle velocities were observed in both spout and annulus as compared with the dry system. Whereas, γ‐alumina particles do not show considerable variation in the particle velocities under dry and wet conditions and fluidize well at higher liquid injection rates. Additionally, for the glass particles, the particle temperature significantly decreases as compared to the γ‐alumina particles. © 2015 American Institute of Chemical Engineers AIChE J, 61: 1146–1159, 2015

Results of theoretical and experimental studies of hydrodynamics of circulation loops in circulating fluidized bed reactors and systems with interconnected reactors

Problems of the calculation of circulation loops in circulating fluidized bed reactors and systems with interconnected reactors (polygeneration systems for the production of electricity, heat, and useful products and chemical cycles of combustion and gasification of solid fuels)are considered. A method has been developed for the calculation of circulation loop of fuel particles with respect to boilers with circulating fluidized bed (CFB) and systems with interconnected reactors with fluidized bed (FB) and CFB. New dependences for the connection between the fluidizing agent flow (air, gas, and steam) and performance of reactors and for the whole system (solids flow rate, furnace and cyclone pressure drops, and bed level in the riser) are important elements of this method. Experimental studies of hydrodynamics of circulation loops on the aerodynamic unit have been conducted. Experimental values of pressure drop of the horizontal part of the L-valve, which satisfy the calculated dependence, have been obtained.

Experimental hydrodynamic study of gas‐particle dense suspension upward flow for application as new heat transfer and storage fluid

AbstractThis paper focuses on a new concept of Heat Transfer Fluid (HTF) for Concentrating Solar Plants (CSP) applications through fluidized bed. CSP plants with very high concentration (such as solar tower plant technology) offer good efficiencies because of high operating temperatures. CSP efficiency could be greatly increased through more efficient HTF. Molten salts, mineral oils, water and air have some of the following drawbacks: limited range of operating temperatures, corrosiveness, high pressure, low energy storage capacity and toxicity.To replace classical HTF, Dense Particle Suspension (DPS) fluidized with air (approximately 40 % of solid) is proposed. DPS has a volume heat capacity similar to those of liquid HTF, does not need pressurization, is safe, inert and is only limited by the maximal working temperature of the receiver material (1100 K), thus opening new opportunities for high efficiency thermodynamic cycles. This work is the hydrodynamic study of a gas‐solid dense suspension upward flow at ambient temperature, in a vertical 2‐tube bundle of small diameter tubes, which have their bottom immersed in a slightly pressurized fluidized bed (pressure approximately equal to the ratio of the solid weight in a tube over its cross section area). This type of flow is yet implemented in the field of hyper‐dense phase vertical conveying of powders and it is currently under development for solar receivers using dense suspensions of particles as heat transfer and storage medium. This application was patented by Flamant and Hemati in 2010 (France 1058565 (2010) CNRS/INP Toulouse, G. Flamant, H. Hemati; PCT Extension, No. WO 2012/052661 A2), and its development is funded by the European Commission. In this technological breakthrough, the concentrated solar energy is collected, carried and stored directly by the fine particles flowing upward, with a suspension void fraction close to that of a dense fluidized bed. Contrary to circulating fluidized bed “risers”, it offers a good contact area between the wall and the particles.The important hydrodynamic and thermal coupling required a step‐by‐step approach. Ambient flows had to be understood and controlled first. Thus a 2‐pass “cold” mock‐up, each pass composed of two vertical parallel tubes, was built. Pressure drop, solid weight and helium volume fraction measurements demonstrated the ability to handle a regular solid upward flow (imperative here), with solid flow rates from 20 to 130 kg.h−1, with void fractions from 0.57 to 0.63 and with an even distribution of the solid flow rate between the tubes. Moreover, the governing parameters of this flow were established as: the solid feeding flow rate, the fluidization velocity, the solid holdup, the freeboard pressure and the aeration velocity. The secondary air injection, also called “aeration”, is the most important parameter for the stability and the even distribution of the total solid flow rate in the tubes. The 1D modelling of the suspension flow in the tubes was also performed in the flow direction. The flow structure was described using the bubble‐emulsion model formalism, and by adding the solid entrainment by the bubble wake. Predictions of the model are compared with the experimental measurements of driving pressure and axial pressure profile along the tubes.

Thermal exploitation of fruit tree pruning wastes in a novel conical spouted bed combustor

In order to determine the optimum operation conditions for thermal exploitation of fruit-tree pruning wastes in conical spouted bed combustors, operation maps for gas–solid flow regimes have been obtained from the experimental hydrodynamic study of beds of inert material (sand) in conical spouted bed contactors at high temperatures. To this end, minimum spouting and minimum dilute spouting (jet spouted bed) velocities and maximum bed pressure drop have been obtained for different systems. The effects of particle size and gas inlet temperature has been also studied. Combustion of fruit-tree pruning wastes has been successfully carried out in batch mode in a conical spouted bed combustor, with high combustion efficiencies, for gas inlet temperatures from 350 to 550°C. Radial and axial temperature profiles have been measured both in uniform beds of inert material and also in beds composed of mixtures of sand and combusting wastes.

Experimental hydrodynamic study of valve trays

Valve trays column design for gas treatment still relies on empirical correlations developed on pilot units. The available correlations lead to large discrepancies and thus more experimental works are needed. The present hydrodynamic study was carried out on a Plexiglas 1.26m per 0.1905m absorption column containing four V-4 Glitsch valve trays. Water/air system was used at atmospheric pressure and ambient temperature. Liquid rate per weir unit length was varied between 3.2×10−3m3.(m.s)−1 and 24.3×10−3m3.(m.s)−1 and the kinetic gas factor between 0 and 3.5Pa0.5.The following hydrodynamic parameters were determined: tray pressure drop, valves pressure drop, clear liquid height, mean emulsion height and liquid mean hold up on the tray. Correlations for clear liquid height, liquid mean hold up and emulsion height are proposed.Emulsion profiles characterisation was possible due to video records post-processing. Four different behaviours are identified for emulsion profiles according to liquid and gas velocities.Significant behaviour changes on the hydrodynamic parameters allowed the identification of three system limits: dumping, weeping and pre-flooding. Correlations are proposed for these limits and an operational diagram is presented.

Experimental studies of hydrodynamic and mass-transfer properties of coolant flow in VVER fuel assemblies TVSA

The results of experimental studies of the local hydrodynamics and mass transfer of coolant in the characteristic zone of VVER fuel assemblies using mixing lattices of structurally different types are presented. These studies were performed on an aerodynamic stand by the method of impurity diffusion for several experimental scaled models. The studies were performed on a section of self-similar flow, so that the results can be used to convert to natural conditions of coolant flow in the core in regular TVSA. These studies refine the local and mass-transfer characteristics of coolant flow in order to reduce the conservatism in the evaluation of the heat-engineering reliability of the VVER core with TVSA fuel assemblies. The results also comprise a database for verifying CFD codes and programs for cellular calculation of a VVER core.

Hydrodynamics and masstransfer process of rectification in a centrifugal vehicle

The article described and justified by theoretical and experimental study of hydrodynamics and mass transfer in a gas-liquid by centrifugal force, process modeling, development of methods of engineering calculation of highly energy-and resource-saving equipment

Turbulent flow separation and characteristics of heat transfer under unsteady hydrodynamic conditions

Results from an experimental study of hydrodynamics and heat transfer in turbulent separation flow under the conditions of its periodic pulsations are presented. It is found that an essential change occurs in the spatial and timing structure of separation flow under the effect of superimposed unsteadiness. Phenomena involving reduction of the longitudinal dimensions of the separation region and essential enhancement of heat transfer in the separation region of pulsating flow are revealed. The physical mechanism of these phenomena is described.

A Combined Numerical and Experimental Study of Hydrodynamics for an Air-Water External Loop Airlift Reactor

The external loop airlift reactor (ELALR) is a modified bubble column reactor that is composed of two vertical columns that are interconnected with two horizontal tubes and is often preferred over traditional bubble column reactors because they can operate over a wider range of conditions. In the present work, the gas-liquid flow dynamics in an ELALR was simulated using an Eulerian–Eulerian ensemble-averaging method in two-dimensional (2D) and three-dimensional (3D) coordinate systems. The computational fluid dynamics (CFD) simulations were compared to experimental measurements from a 10.2 cm diameter ELALR for superficial gas velocities ranging from 1 cm/s to 20 cm/s. The effect of specifying a mean bubble diameter to represent the gas phase in the CFD modeling was investigated, and 2D and 3D simulations were found to be in good agreement with the experimental data. The ELALR flow regimes were compared for the reactor operating in bubble column, closed vent, and open vent modes, and the 2D simulations qualitatively predicted the behavior of bubble growth in the downcomer. However, it was found that 3D simulations were necessary to capture the physics of the ELALR for gas holdup, bulk density differences, and riser superficial liquid velocity.

Theoretical and experimental studies of hydrodynamics and heat exchange in porous media

This study presents the development of methods of mechanics of heterogeneous systems for complex description of filtration and thermal and mass exchange processes in porous media. Results of theoretical and experimental studies of pyrolysis of natural gas and solid hydrocarbon raw materials and filtration of a mixture of gaseous hydrocarbons through a porous medium are presented.

Experimental Studies of Hydrodynamics and Regime Transition in Bubble Columns

The detailed flow structures in bubble columns with and without internal draught tube have been investigated using the PIV technique. The onsets of transition due to vortex formation and different flow patterns with and without draught tube have been studied using the drift-flux model and the experimentally measured Reynolds stresses. The role of solid particles and liquid viscosity, as well as bubbling orifice configuration on the flow patterns and regime transition has also been studied and discussed. On a etudie par la technique PIV les structures d'ecoulement detaillees dans des colonnes a bulles avec et sans tube d'aspiration interne. L'apparition de la transition due a la formation de vortex et a differents profils d'ecoulement avec et sans tube d'aspiration a ete etudiee a l'aide du modele de flux d'aspiration et des contraintes de Reynolds mesurees experimentalement. On a egalement examine le role des particules solides et de la viscosite du liquide ainsi que de la configuration des orifices de bullage sur les profils d'ecoulement et la transition de regime.

Microfluidic circulatory flows induced by resonant vibration of diaphragms

Piezoelectric elements coupled to thin diaphragms in contact with a fluid chamber are useful to induce fluid motion. These devices are typically operated at the first resonant mode of the coupled piezoelectric/diaphragm composite with low electrical power excitation to achieve large microscale mode shape displacement. Experimental studies of hydrodynamics within the diaphragm coupled chamber at the first and the higher resonant modes have revealed the expected bulk fluid motion associated with the mode shapes, and a coupled set of two complex flow phenomena that drive particle migration to modal nodes and direct bulk flow circulation within the chamber. The phenomena are believed to be acoustic in origin with a focusing force that drives particles to the nodal lines of the mode shapes, and a net directional flow believed to be attributable to acoustic streaming. A diaphragm driven acoustic chamber 6 mm in diameter, 30 μm in depth with 0.2 mm thick lead-zirconate-titanate (PZT) actuator was fabricated for an experimental survey. A quantitative flow field characterization was performed with particle image velocimetry (PIV) using a laser scanning confocal microscope with 2-μm resolution. Complicated in-plane velocity profiles were found near the interface of circulations, where acoustic intensity was considered large. One dominant contributor to observed particle focusing has been associated with flow stagnation regions within the flow chamber. Acoustic streaming regions were successfully identified near the interface between circulation partitions, coincident with particle focusing. Possible applications of the flow phenomena presented include active mixing, pumping, and particle focusing.

Experimental study of hydrodynamics in a flat ohmic cell—impact on fouling by dairy products

This study highlights the link between hydrodynamics and fouling phenomena in a continuous rectangular ohmic cell. The hydrodynamic study was carried out using flow visualisation techniques and particle image velocimetry (PIV). The distribution of deposits in the ohmic cell was investigated by heating an aqueous solution of β-lactoglobulin-xanthan gum mixture. Experimental results show that the deposit distribution on the electrode surfaces is directly related to the flow structures in the ohmic cell.

An experimental study of hydrodynamics of artificial cardiac valves

The results of study of hydrodynamic characteristics of various ACVs in the steady-state and pulse flow modes showed that the flow behind an ACV has an elaborate structure. The PCI method allows determination of the flow structure and its dependence on the design features of the ACV model under study. Such study allows prediction of the valve functioning after implantation. Hydrodynamic characteristics of a new ACV model should be studied with the PCI method in the steady-state flow mode and in various longitudinal sections of the flow channel. The main result of the study of the flow behind the valve in the steady-state flow mode is the maximum flow rate distribution, which is enough to assess the dependence of the ACV hydrodynamic characteristics on the design features of the ACV model under study. The dynamics of changes in the flow structure during the complete cycle of the valve functioning cannot be obtained by this procedure. Therefore, clinical tests of ACV should be preceded by the study of the hydrodynamic characteristics of ACV in the pulse flow mode.

Hydrodynamics, axial mixing and mass transfer in open turbine rotating disc contactor (OTRDC)

AbstractAn experimental study of hydrodynamics, axial mixing and mass transfer has been carried out in a newly developed liquid‐liquid extraction contactor, namely the open turbine rotating disc contactor (OTRDC). It has been established that the OTRDC can be operated with larger holdups of the dispersed phase, larger interfaces and, hence, more efficient mass transfer than the conventional RDC. In correlating axial mixing data, a combined model has been applied in which both the forward mixing due to drop size distribution and the backmixing of droplets are taken into account. The RTD curves of dispersed phase predicted by the model agree well with the experimental data. Comparison of experimental mass transfer data with those predicted by the proposed axial mixing model and the theoretical single drop model shows that they are in good agreement.