Mass Transfer Measurements Research Articles

Power consumption, mixing time, heat and mass transfer measurements for liquid vessels that are mixed using reciprocating multiplates agitators

This work is an extension of previous studies [S. Masiuk, Power consumption measurement in a liquid vessel that is mixed using vibratory agitator, Chem. Eng. J. 75 (1999) 161–165; S. Masiuk, Mixing time for a reciprocating perforated plate agitator, Inż. Chem. Proc. 20 (1999) 601–612; S. Masiuk, Dissolution of solid body in a tubular reactor with reciprocating plate agitator, Chem. Eng. J. 83 (2001) 139–144; S. Masiuk, Heat transfer measurement in a liquid vessel that is mixed using vibratory agitator, Chem. Eng. J. 61 (1996) 107–112] carried out on the reciprocating agitator, in which additional information describing the experimental apparatus and measurements procedure may be found, as well as, dimensionless correlations predicted for agitator with a single plate. The experimental investigation are provided for the explanation of the influence on the power consumption, mixing time, mass and heat transfer of the multiplates low-frequency and high amplitude reciprocating agitators. The maximum power consumption is calculated by multiplying the maximum force acting on the shaft and maximum velocity of the agitator. A thermal-response technique is used for mixing time measurements. The mass transfer coefficient is calculated from a mass balance between a dissolution solid body and its surrounding mixing dilute solution. The heat transfer coefficient from the heating jacket wall to the continuous flow of the mixed liquids is measured by the stabilized heat flow method. The analytical dimensionless equations predicted in the present paper generalize the experimental data without the break through the all regions of flow in a relatively simple and uniform manner.

고정된 터빈 블레이드의 베인에 대한 상대위치 변화가 끝단면 및 슈라우드의 열/물질전달 특성에 미치는 영향

The effect of relative position of the stationary turbine blade for the fixed vane has been investigated on blade tip and shroud heat transfer. The local mass transfer coefficients were measured on the tip and shroud for the blade fixed at six different positions within a pitch. A low speed stationary annular cascade with a single turbine stage was used. The chord length of the tested blade is 150 ㎜ and the mean tip clearance of the blade having flat tip is 2.5% of the blade chord. A naphthalene sublimation technique was used for the detailed mass transfer measurements on the tip and the shroud. The inlet flow Reynolds number based on chord length and incoming flow velocity is fixed to 1.5×10<SUP>5</SUP>. The results show that the incoming flow condition and heat transfer characteristics significantly change when the relative position of the blade changes. On the tip, the size of high heat/mass transfer region along the pressure side varies in the axial direction and the difference of heat transfer coefficient is up to 40% in the upstream region of the tip because the position of flow reattachment changes. On shroud, the effect of tip leakage vortex on the shroud as well as tip gap entering flow changes as the blade position changes. Thus, significantly different heat transfer patterns are observed with various blade positions and the periodic variation of heat transfer is expected with the blade rotation.

MRI Measurement of Heat and Mass Transfer

MRI Measurement of Heat and Mass Transfer

Mass transfer measurements in a non-isothermal bubble column using the uncatalyzed oxidation of sulphite to sulphate

Abstract The volumetric mass transfer coefficient has been determined for a system comprising air and sodium sulphite (0.8 M) in a semibatch bubble column with a diameter of 0.2 m. The superficial gas velocity was varied in the range 0.03–0.2 m/s. The measurements were made at non-isothermal conditions between 19 and 36 °C, and it is shown that if the mass transfer is not chemically enhanced, the absorption rate of oxygen in a sodium sulphite solution will be constant and independent of the temperature. Based on this, it is possible to determine the volumetric mass transfer coefficient without any knowledge of the kinetics of the oxidation of sulphite to sulphate. Furthermore, it is found that the parameter kla/ɛG in the heterogeneous regime for the system is about 0.5, which is in agreement with previous work of an air–water system. It is also shown that the mass transfer coefficient of small bubbles generated by a membrane or by a porous gas sparger is smaller compared to the mass transfer coefficient of larger bubbles formed in a gas sparger with 2 mm holes.

CFD simulations of two stirred tank reactors with stationary catalytic basket

Among the different systems used for laboratory kinetic investigation, stationary catalytic basket stirred tank reactors (SCBSTRs) allow one to study triphasic reactions involving shaped catalyst with large size. The hydrodynamics of these complex reactors is not well known and has been studied experimentally in only a few cases. Despite the difference in the design of two commercial SCBSTRs reported in these works, the local measurements of the liquid–solid mass transfer coefficient inside the catalytic basket revealed the same velocity profile. The aim of the present work is therefore to investigate more accurately the hydrodynamics of the two reactors by means of CFD in order to compare the effect of the blade/baffle hydrodynamic interaction on the flow pattern. Owing to the geometrical complexity of the reactors, the hydrodynamic investigation is based on the k – ε model and the Brinkman–Forsheimer equations. The agreement at the local level with the experimental data (PIV and mass transfer measurements) validates this preliminary work performed with the standard values of the parameters present in the turbulent model and the Brinkman–Forsheimer equations. The simulations reveal in both reactors a ring-shaped vortex around the impeller in the agitation region. The high axial location of its centre induces a reverse flow at the tips of the basket. Owing to the fluid friction in the porous medium, the azimuthal flow in the core region is transformed into a radial flow in the basket where the flow decreases abruptly. Vertical vortices are located at the blade tips and at the downstream face of the baffles or they are located in the basket on both sides of the baffles, depending on the design and the location of the baffles. At the inner radius interface of the basket, the vertical blade impeller induces a rather homogeneous velocity profile, but the pitched blade impeller imposes a high velocity at the plane of symmetry. Therefore the simulations demonstrate that two different local velocity patterns and two different porous media may induce the same mass transfer properties.

A Simple and Inexpensive Technique to Measure Molecular Diffusion Coefficients

The experiment proposed is simple and inexpensive and provides an accurate method for measurement of the molecular diffusion coefficient, D m. It is a novel method that has the added advantage of easily providing data at temperatures and pressures that differ significantly from ambient values. The experimental results for naphthalene in air are in excellent agreement with the experimental values of the molecular diffusion coefficient measured by other authors. Experimental measurements of mass transfer in water were also carried out for a range of the relevant parameters. The soluble spheres used in the experiments were made of either benzoic acid or 2-naphthol, and the ranges of temperatures covered were 293–333 and 293–373 K, respectively. Using the mass transfer theory presented in this work, the molecular diffusion coefficient of the two solutes was determined, and good agreement with literature values was found.

Electrochemical incineration of oxalic acid: Reactivity and engineering parameters

Mass transfer measurements were carried out to test a disk-shaped parallel-plate electrochemical cell, based on a new design. The impinging-jet-cell concept, confined between parallel plates, was adapted to a configuration with one central inlet and several peripheral exit sections, leading to more effective hydrodynamics within the cell. Measurements of mass transfer coefficient were performed using the limiting diffusion current technique based on ferro-cyanide ion oxidation, and overall mass transfer coefficients were correlated to Reynolds numbers ranging from 30 to 200.

베인과 블레이드 사이의 상대위치 변화에 따른 터빈 블레이드 표면에서의 열/물질전달 특성

The present study investigated the effect of relative position of the blade on blade surface heat transfer. The experiments were conducted in a low speed wind tunnel with a stationary annular turbine cascade. The test section has a single turbine stage composed of sixteen guide vanes and blades. The chord length of the blade is 150 mm and the mean tip clearance of the blade is of the blade chord. The Reynolds number based on blade inlet velocity and chord length is and mean turbulence intensity is about . To investigate the effect of relative position of blade, the blade at six different positions in a pitch was examined. For the detailed mass transfer measurements, a naphthalene sublimation technique was used. In general, complex heat transfer characteristics are observed on the blade surface due to various flow characteristics, such as a laminar flow separation, relaminarization, flow acceleration, transition to turbulence and tip leakage vortices. The results show that the blade relative position affects those heat transfer characteristics because the distributions of incoming flow velocity and turbulence intensity are changed. Especially, the heat transfer pattern on the near-tip region is significantly affected by the relative position of the blade because the effect of tip leakage vortex is strongly dependent on the blade position. On the pressure side, the effect of blade position is not so significant as on the suction side surface although the position and the size of the separation bubble are changed.

Local mass transfer measurements in an inclined enclosure at high Rayleigh number

An electrochemical technique is used to study local mass transfer coefficients on surfaces of inclined enclosures over the range 1.1×104 < RaH < 1.4×1010 for a nominal Schmidt number of 2280. Scaling with gcosθ instead of g in the Rayleigh number correlates the data well at low angles of inclination; however, as either the aspect ratio or the angle of inclination increase, the longitudinal density stratification causes the data to deviate from a power law scaling.

Aeration of Large Size Tanks by a Surface Agitator

AbstractA new device has been developed in order to achieve urban or industrial wastewater biological treatment. It has been designed specially for lagoon applications to oxygenate and mix with the same apparatus. The goal is both to achieve a high gas flooding rate and to reach a maximal depth with the bubble plume. Mass transfer measurements have allowed us to choose the most appropriate geometry. Considering the application of the device and the possible use of low‐pressure O2 produced on‐site, the agitation system is located close to the liquid surface and is composed of a gas‐inducing turbine. The role of propellers in addition to the gas‐inducing turbine, as well as the use of baffles and a shell, have been experimentally studied. Numerical simulations (CFD) of the whole apparatus in single‐phase flow have been used to study the influence of the stator part of the geometry.

CFD turbulent modelling of jet impingement and its validation by particle image velocimetry and mass transfer measurements

Heat transfer by initially laminar and transitional submerged, unconfined gaseous jet impingement on a plane target is analyzed numerically and additionally interpreted with the help of associated measurements. Qualitative and quantitative comparisons for three different regimes, in the transitional regime (initially laminar or low turbulence impinging jets) between Re = 1000 and 4000 are presented. A combined experimental approach has first been exploited. By using a Particle Image Velocimetry (PIV), instantaneous flow field data have been extracted and properly averaged to focus on flow field modifications at free-jet interface and along its way to impact and dispersion. Furthermore, a dimensionless local heat transfer Nu is locally assessed by micrometric measurements of ablation depth of a naphthalene film. Finally, the subject configuration has been modelled by a commercial CFD code, allowing to assess its validity. Three turbulence models have been enforced in the present paper, and complete velocity maps and local Nu distributions are presented and compared to the averaged or instantaneous experimental flow field and heat transfer data, helping ascertain on the relative merits of the adopted models.

Experimental study on heat and fluid flow in LNG tank heated from the bottom and the sidewalls

AbstractHeat and fluid flow in a layer heated from the bottom and the sidewalls simulating an underground LNG tank is experimentally studied under high Rayleigh number (7.5×1010&lt;Ra&lt;1.5×1013) conditions by electrochemical mass transfer technique. The experiment yielded the following results. When sidewalls are heated, the heat transfer along the bottom surface is reduced. Heat transfer along sidewalls is independent of bottom heating, and is modeled by an equation for laminar natural convection flow even for Ra&gt;109. Convective flow pattern in the tank is visualized by the Schlieren technique. The results, combined with local mass transfer measurement, show that Sh of the bottom surface is reduced in the area where impinging downward flow exists. It is caused by the suppression of thermal plume formation by the downward flow. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(7): 417–430, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20031

Fluid Flow and Heat Transfer in Air Jet Impingement in Food Processing

ABSTRACT: Air impingement technology is gaining popularity in food-processing operations such as baking, freezing, drying, and toasting. In this article, physical characteristics of impinging jets, such as turbulent mixing in the free jet region, stagnation, boundary-layer formation, recirculation, and their interactions with food products in terms of heat and mass transfer have been reviewed. The discussion includes experimental methods used for measurement of heat and mass transfer for single and multiple slot and circular jets. Procedures used for measurement of heat-transfer coefficient such as lumped sensor method, micro-calorimetric approach, and use of flux sensors are presented. Typical qualitative and quantitative flow-field studies using planar visualization and laser Doppler anemometry have been reviewed. Numerical modeling of air impingement systems is discussed with special consideration of problems arising in food-processing systems.

Membrane-based gas transfer: an environmental engineering laboratory

We propose an educational experience in which students design a membrane gas transfer reactor, construct a bench-scale version in the laboratory, and employ the reactor to measure mass transfer coefficients. The membrane reactor is useful for teaching mass transfer principles because the mass transfer interface is well defined and easily observed. The system can be modeled successfully using straightforward mathematics. The reactor can be designed and constructed by students, using the mathematical model as a basis, providing insight into the physical meaning of model parameters. The proposed membrane system can be readily operated to obtain data that can be employed to develop or modify existing mass transfer correlations. This can provide students with significant insight into the development of mass transfer correlations and how the constants in such correlations are typically determined. These features help promote a deeper understanding of mass transfer principles.

Mass transfer characteristics of corrugated surfaces

The mass transfer characteristics of flat and corrugated electrode surfaces in an electrochemical cell are described. The effect of the distance between the surfaces (electrode to electrode separation) on the mass transport was investigated and empirical correlations are presented. Mass transfer coefficients were determined using the limiting current technique, for the reduction of potassium ferricyanide ion in excess of potassium carbonate. Mass transfer measurements were carried out for a Reynolds number range of 125–3500 and an equivalent diameter range of 2.6–8.6 mm, at a temperature of 20 °C and a Schmidt number of 1469. The data showed that corrugated surfaces enhanced the solid to liquid mass transfer rates, to the extent that characteristics of a turbulent regime were obtained. The smaller inter-electrode gap produced the higher mass transfer rates. Enhancements in mass transfer of up to 30 fold were achieved by using a corrugated surface in place of a flat surface, due to the frequent disruption of the boundary layer imposed by the corrugated design. Through the analogy between heat transfer and mass transfer the data indicates the expected enhancement to be gained for heat transfer to corrugated heat exchanger surfaces with the type of flow studied.

Horizontal Rotating Cylinder—A Compact Apparatus for Studying the Effect of Water Wetting on Carbon Dioxide Corrosion of Mild Steel

Abstract Water wetting is a crucial issue in carbon dioxide (CO2) corrosion of multiphase flow pipelines made from mild steel. This study demonstrates the use of a novel benchtop apparatus, a horizontal rotating cylinder, to study the effect of water wetting on CO2 corrosion of mild steel in two-phase flow. The setup is similar to a standard rotating cylinder except for its horizontal orientation and the presence of two phases—typically water and oil. The apparatus has been tested by using mass-transfer measurements and CO2 corrosion measurements in single-phase water flow. CO2 corrosion measurements were subsequently performed using a water/hexane mixture with water cuts varying between 5% and 50%. While the metal surface was primarily hydrophilic under stagnant conditions, a variety of dynamic water wetting situations was encountered as the water cut and fluid velocity were altered. Threshold velocities were identified at various water cuts when the surface became oil-wet and corrosion stopped.

Flow and Heat Transfer Behavior for a Vortex-Enhanced Interrupted Fin

The potential for enhanced air-side heat transfer in HVAC&amp;R applications has been investigated using combined spanwise and streamwise vorticity. Spanwise vortices were created using an offset-strip fin array, and streamwise vortices were introduced into the flow using delta-wing vortex generators. Mass transfer measurements, obtained using the naphthalene sublimation technique, were used to quantify the heat transfer characteristics of a baseline and enhanced array, and these results were compared to flow visualization and particle image velocimetry measurements of the instantaneous velocity fields. Significant enhancement was observed over portions of the Reynolds number range tested (400⩽Re⩽3700), and a transitional Reynolds number range was identified within which the spanwise and streamwise vortices act to decrease the heat transfer performance of the array.

Mass transfer in sparged and stirred reactors: influence of carbon particles and electrolyte

Mass transfer in multiphase systems is one of the most studied topics in chemical engineering. However, in three-phase systems containing small particles, the mechanisms playing a role in the increased rate of mass transfer compared to two-phase systems without particles, are still not clear. Therefore, mass transfer measurements were carried out in a 2D slurry bubble column reactor (0.015×0.30×2.00 m 3) , a stirred tank reactor with a flat gas–liquid interface, and in a stirred tank reactor with a gas inducing impeller. The rate of mass transfer in these reactors was investigated with various concentrations of active carbon particles (average particle size of 30 μm ), with electrolyte (sodium gluconate), and with combinations of these. In the bubble column, high-speed video recordings were captured from which the bubble size distribution and the specific bubble area were determined. In this way, the specific mass transfer area a gl was determined separately from the mass transfer coefficient k l . Mechanisms proposed in literature to describe mass transfer and mass transfer enhancement in stirred tank reactors and bubble columns are compared. It is shown that the increased rates of mass transfer in the 2D bubble column and in the stirred tank reactor with the gas inducing impeller are completely caused by an increased gas–liquid interfacial area upon addition of carbon particles and electrolyte. It is suggested that an increased level of turbulence at the gas–liquid interface caused by carbon particles accounts for a smaller effective boundary layer thickness and an enhancement of mass transfer in the flat gas–liquid surface stirred tank reactor. However, for the carbon particles used in this study, it is rather unlikely that mass transfer enhancement takes place due to the well-known shuttle or grazing effect.

Flow measurements in micro holes with electrochemical and optical methods

The decreasing feature size of electronic compounds down to the micrometer range is paralleled by an increase in the aspect ratio, worsening all mass transport related processes. In this paper the conditions of liquid flow into micro holes and blind micro vias (BMV) with diameter of 100–300 μm and depth between 100 μm and 1.5 mm are investigated. The flow was induced by surface directed jet flows, visualised by microscopy aided particle image velocimetry (μ-PIV) and correlated with electrochemical mass transfer measurements using the ferro/ferri-hexacyanide redox couple. It was found that the mean flow velocity in the holes and the penetration depth in the blind holes are influenced especially by the roughness of the inner walls and, at a lower scale, by the velocity and the impinging angle of the jet. The results enable the estimation of the mean flow rate in through holes and the penetration depth in BMV at defined hydrodynamic conditions in the bath. This is one of the preconditions for the appropriate engineering of plating lines designed for micro structures.

Local Mass/Heat Transfer on Turbine Blade Near-Tip Surfaces

Local mass transfer measurements on a simulated high-pressure turbine blade are conducted in a linear cascade with tip clearance, using a naphthalene sublimation technique. The effects of tip clearance (0.86–6.90% of chord) are investigated at an exit Reynolds number of 5.8×105 and a low turbulence intensity of 0.2%. The effects of the exit Reynolds number 4−7×105 and the turbulence intensity (0.2 and 12.0%) are also measured for the smallest tip clearance. The effect of tip clearance on the mass transfer on the pressure surface is limited to 10% of the blade height from the tip at smaller tip clearances. At the largest tip clearance high mass transfer rates are induced at 15% of curvilinear distance Sp/C by the strong acceleration of the fluid on the pressure side into the clearance. The effect of tip clearance on the mass transfer is not very evident on the suction surface for curvilinear distance of Ss/C&lt;0.21. However, much higher mass transfer rates are caused downstream of Ss/C≈0.50 by the tip leakage vortex at the smallest tip clearance, while at the largest tip clearance, the average mass transfer is lower than that with zero tip clearance, probably because the strong leakage vortex pushes the passage vortex away from the suction surface. High mainstream turbulence level (12.0%) increases the local mass transfer rates on the pressure surface, while a higher mainstream Reynolds number generates higher local mass transfer rates on both near-tip surfaces.