Mass Transfer Measurements Research Articles

0807 壁乱流における物質移行係数の計測と電極形状の影響

FAC (flow accelerated corrosion) is a phenomenon that accelerates the wall thinning rate in the flow. Mass transfer coefficient k is one of the important parameters to evaluate pipe wall thinning rate. We measure mass transfer coefficient by electrochemical technique and flow field using stereo PIV in order to observe the relationship between wall thinning and flow field. Based on the previous studies, we can expect that not only flow in the inner layer but also flow in the outer layer affects the mass transfer from the wall surface. Then, we calculate the correlation coefficient of amplitude modulation to observe interaction of inner and outer layer in this study.

Mass transfer measurements and modeling in a microchannel photocatalytic reactor

The main objective of this paper was to evaluate the influence of mass transfer on the photocatalytic efficiency at a low flow rate in the order of several mL per hour. Several continuous flow microchannel reactors have been used to study the degradation of salicylic acid (SA) taken as a model pollutant. The photocatalytic degradation of salicylic acid, under UV illumination of 1.5mWcm−2, was assessed from the outlet concentration measured by liquid chromatography HPLC. It was shown that the degradation of SA by UV was limited by mass transfer. Numerical simulations have allowed establishing a relationship of the Sherwood number valuable for all the microchannel geometries. Computational fluid dynamics with Comsol Multiphysics is useful for predicting the degradation yield for a given geometry of the microreactor. The best representation of the experimental data is obtained by introducing a kinetic law taking into account mass transfer limitation.

Experimental and numerical studies on mass transfer characteristics behind an orifice in a circular pipe for application to pipe-wall thinning

Experimental and numerical studies are carried out to understand the mass transfer characteristics in a circular pipe behind an orifice, which is often encountered in pipe-wall thinning due to flow accelerated corrosion in pipelines of nuclear/fossil power plants. The measurement of mass transfer coefficient is conducted by using benzoic acid dissolution method in a water flow, which allows the measurement of mass transfer behind the orifice in a circular pipe at the Schmidt number near the actual operating condition of the pipeline. The measurement of mass transfer coefficient behind the orifice shows a maximum Sherwood number in the region 1–2 pipe diameters downstream of the orifice due to the flow turbulence, and it decreases gradually in the downstream, which agrees qualitatively with the feature of pipe-wall thinning in the pipeline in literature. The present result indicates that the Sherwood number behind the orifice is greatly increased by increasing the Schmidt number and the Reynolds number, though the geometrical factor, which is the ratio of the thinning rate of the orifice flow with respect to that of the fully developed pipe flow, is weakly dependent of these parameters. It is also found that the experimental Sherwood number profiles and the mean velocity distribution behind the orifice are well reproduced in the numerical simulation by the k–ε model with the empirical modification of high-Schmidt-number flows, though the maximum Sherwood number is slightly overpredicted, reflecting the higher prediction of turbulence energy behind the orifice. These results demonstrate the usefulness of the numerical simulation for predicting the pipe-wall thinning due to the flow accelerated corrosion in the orifice flow.

Natural convection heat transfer in a uniformly heated horizontal pipe

Natural convection heat transfers inside horizontal pipes were measured. The Rayleigh numbers were varied from 6.8 × 108 to 1.5 × 1012, while the Prandtl number was fixed at 2,094. Based on the analogy concept, a copper sulfate electroplating system was adopted to measure mass transfer rates in place of heat transfer rates. Test results using single-piece electrodes were in good agreement with the work of Sarac and Korkut. The angle-dependent mass transfer rates, measured using piecewise electrodes, were compared with the results of studies on natural convection in concentric annuli, and showed similar trends. The experiments were expanded to the turbulent region, and a transition criterion was proposed. Angle-dependent natural convection heat transfer correlations for the laminar and turbulent regions were derived.

Modeling of CO2 dissolution by static mixers using back flow mixing approach with application to geological storage

We propose the application of a back flow cell model for the simulation of supercritical CO2 dissolution in water in static mixers at pressures and temperatures pertinent to geological CO2 storage. Using step tracer injection experiments, the required parameters for calibration of the back flow cell model, such as the number of the cells and the back flow ratio, were obtained. The calibrated model was then verified with the experimental mass transfer measurements at supercritical conditions, and an acceptable agreement was observed. Experimental data of CO2 dissolution in water were regenerated with an average absolute relative deviation of less than 5%. Using the developed model, the optimal operating conditions were determined. The developed model will be useful for the engineering design of CO2 dissolution systems and simulation of supercritical CO2 dissolution in water for geological CO2 storage.

Measuring Mass Transfer on Biodiesel Process by Means of Impedance Measurement

Transesterification is commonly used to produce biodiesel from methylester. In order to control the conversion process is useful to employ process monitoring, in particular monitoring of the mass transfer processes that limits the initial rates of transesterification. Monitoring of these initial stages of the reaction may allow for process optimization. Many methods have been identified to monitor reaction progress. This paper proposes a method to monitor the initial stages of the biodiesel production process using impedance measurement. The impedance measurements presented show the expected sigmoid curves that are associated with mass transfer (mixing) processes taking place during the early stages of the transesterification process.

Ecosystem‐scale measurements of biomass water using cosmic ray neutrons

Accurate estimates of biomass are imperative for understanding the global carbon cycle. However, measurements of biomass and water in the biomass are difficult to obtain at a scale consistent with measurements of mass and energy transfer, ~1 km, leading to substantial uncertainty in dynamic global vegetation models. Here we use a novel cosmic ray neutron method to estimate a stoichiometric predictor of ecosystem‐scale biomass and biomass water equivalent over tens of hectares. We present two experimental studies, one in a ponderosa pine forest and the other in a maize field, where neutron‐derived estimates of biomass water equivalent are compared and found consistent with direct observations. Given the new hectometer scale of nondestructive observation and potential for continuous measurements, we anticipate this technique to be useful to many scientific disciplines.

Heat and Mass Transfer Measurements for Bio-Substrate Drying Processes

The complex process of heat and mass transfer in bio-substrates during convection, vacuum, and thermohygrostat drying was studied. Changes in temperature and moisture content at the center of the wet material were measured before and after the experiment in order to calculate the drying rate (%/h). In the case of convection drying, the inverter frequency within the wind tunnel was set at 10, 20, and 30 Hz (velocities of 2.2, 4, and 6 m/s, respectively). Measurements were then made at 10 and 20 Hz, with temperatures at 50 and 60°C. In the case of vacuum drying, the chamber pressure was set at 0.4, 4.2, and 92 Torr. The thermohygrostat was set at 50°C with humidity levels at 30, 40, and 50%. In conclusion, thermohygrostat is more effective because of the controlled environment, and that drying rate is increased with lower wind velocities and chamber pressures for convection and vacuum drying respectively.

Local mass transfer measurements for corals and other complex geometries using gypsum dissolution

A new method of measuring local mass transfer for highly complex geometries is demonstrated. The method combines gypsum dissolution and X-ray computed tomography (CT). An object coated in gypsum is CT scanned before and after exposure to fluid flow. Digital three-dimensional pre- and post-flow geometries are created using the CT data, and the local dissolution thickness is determined by subtracting the post-flow from the pre-flow object. The method is first demonstrated for cylinders in cross-flow and validated with mass and heat transfer data. The measurements agree with values from correlations reported in the literature when scaled using Reynolds, Sherwood, and Schmidt numbers. The method is then applied to measure local mass transfer for the complex geometry of a 0.75-scale branching scleractinian coral Stylophera pistillata. Local Sherwood numbers vary between nearly zero on the backward facing surfaces of the downstream branches of the coral and nearly 200 at the tips of the branches at the top of the coral. The upstream facing surfaces at radii between 20 and 70 % of the overall radius of the coral experience Sherwood numbers close to 100. The local measurements are integrated to produce a bulk mass transfer coefficient that lies within the range of previous bulk measurements in the literature for similar coral species. With this method, local mass transfer rates can be measured for complex objects in laboratory or natural in situ flow environments. These are geometries for which only bulk measurements were previously possible.

Toward Pipe Wall Thinning Model Development Based on Mass Transfer Coefficient (Simultaneous Measurement of Mass Transfer and Velocity Field)

Toward Pipe Wall Thinning Model Development Based on Mass Transfer Coefficient (Simultaneous Measurement of Mass Transfer and Velocity Field)

Laminar forced convective mass transfer of γ-Al2O3/electrolyte nanofluid in a circular tube

Mass transfer of ferricyanide ions through electrolyte nanofluids in a circular tube was investigated experimentally. Nanofluids consisted of 40 nm γ-Al2O3 nanoparticles suspended in ferri-ferrocyanide and aqueous sodium hydroxide as base fluid. Well known electrochemical limiting diffusion current technique was used to measure mass transfer coefficients. Measurements showed that mass transfer coefficient increased with concentration of nanofluid up to 0.01%. For greater concentrations of nanoparticles in nanofluid mass transfer coefficient decreased with the concentration. The augmentation of mass transfer coefficient for 0.01% nanofluid, was about 16.8% at Re = 1260 relative to the base liquid. Enhancement ratio which is defined as the ratio of the mass transfer coefficient of the nanofluid to the mass transfer coefficient of the base fluid slightly decreases with Reynolds number.

중대사고시 노심용융물의 Rayleigh-Benard 자연대류 예비 실험

원자력발전소 중대사고시 노심용융물의 Rayleigh-Benard 자연대류 문제에 대한 예비실험으로 두 평판 사이의 거리, 측면벽의 유무 및 평판의 기하구조가 열전달에 미치는 영향에 대해 실험적 연구를 수행하였다. 열전달 실험을 대신하여 상사성의 원리를 이용한 황산-황산구리 수용액의 전기도금계를 물질전달계로 채택하였다. 실험은 <TEX>$Ra_s$</TEX>는 <TEX>$1.06{\times}10^7{\sim}2.91{\times}10^{10}$</TEX>의 범위에서 실험적 조건을 변화시켜가며 열전달을 측정하였다. 실험결과 단일 수평평판에서 측정한 열전달은 McAdams의 수평평판 자연대류 열전달 상관식과 일치하였고 두 평판에서 측정한 열전달은 Dropkin과 Somerscales, Globe와 Dropkin의 Rayleigh-Benard 자연대류 열전달 상관식과 매우 유사한 경향을 보였다. 두 평판 사이의 거리가 작을 경우 열전달이 높다가 거리가 증가하면 단일 수평평판에서의 자연대류 열전달과 같아졌다. 평판에 설치된 휜(Fin)은 열전달을 향상시켰다. 모든 경우에서 측면벽이 없는 경우의 열전달이 측면 벽이 있는 경우보다 항상 높았다. Rayleigh-Benard natural convection experiments were carried out as the preliminary experiment to simulate the natural convection of the core melt at the severe accident conditions. This work focused on the influences of plate separation distance(s), the existence of the side walls and crust geometries of upper and lower plates. Based upon the analogy concept, a cupric acid-copper sulfate electroplating system(<TEX>$H_2SO_4-CuSO_4$</TEX>) was employed as the mass transfer system and measurements were made for <TEX>$Ra_s$</TEX> ranging from <TEX>$1.06{\times}10^7$</TEX> to <TEX>$2.91{\times}10^{10}$</TEX>. The test results measured for a single horizontal plate were in good agreement with the correlation reported by McAdams and those for two horizontal plates showed the similar trend to the existing Rayleigh-Benard heat transfer correlations developed by Dropkin and Somerscales, Globe and Dropkin. The measured heat transfer rate decreased with the increasing separation distance between the two plates and became similar to those for a single horizontal plate. Fin arrays mounted on both upper and lower plates enhanced the heat transfer rates. For all cases, the heat transfer rates measured for open side walls are higher than those for closed ones.

The Need for Standardization of Mass Transfer Measurements in Absorption and Desorption

AbstractDie Dimensionierung von Ab‐ und Desorptionskolonnen ist in hohem Maße abhängig von den zugrunde gelegten Stofftransportparametern. In der Literatur zeigen sich teilweise signifikante Abweichungen bei der Bestimmung dieser Stofftransportparameter, wodurch ihre Vergleichbarkeit eingeschränkt ist. Eine standardisierte Vorgehensweise für Stofftransportmessungen in der Absorption ist deshalb erstrebenswert. Es wird gezeigt, wie eine experimentelle Methodik für die Bestimmung volumetrischer Stoffübergangskoeffizienten entwickelt wird. Darauf aufbauend wird eine standardisierte Auswertungsmethodik erarbeitet, die die Auftrennung der volumetrischen Stoffübergangsparameter in phasenspezifische Stofftransportparameter und die effektive Phasengrenzfläche ermöglicht.

Mass Transfer Model of Triethylamine across the n-Decane/Water Interface Derived from Dynamic Interfacial Tension Experiments

This publication presents a detailed experimental and theoretical study of mass transfer of triethylamine (TEA) across the n-decane/water interface. In preliminary investigations, the partition of TEA between n-decane and water is determined. Based on the experimental finding that the dissociation of TEA takes place in the aqueous and in the organic phase, we assume that the interfacial mass transfer is mainly affected by adsorption and desorption of ionized TEA molecules at the liquid/liquid interface. Due to the amphiphilic structure of the dissociated TEA molecules, a dynamic interfacial tension measurement technique can be used to experimentally determine the interfacial mass transport. A model-based approach, which accounts for diffusive mass transport in the finite liquid bulk phases and for adsorption and desorption of ionized TEA molecules at the interface, is employed to analyze the experimental data. In the equilibrium state, the interfacial tension of dissociated TEA at the n-decane/water interface can be adequately described by the Langmuir isotherm. The comparison between the theoretical and the experimental dynamic interfacial tension data reveals that an additional activation energy barrier for adsorption and desorption at the interface has to be regarded to accurately describe the mass transport of TEA from the n-decane phase into the aqueous phase. Corresponding adsorption rate constants can be obtained by fitting the theoretical predictions to the experimental data. Interfacial tension measurements of mass transfer from the aqueous into the organic phase are characterized by interfacial instabilities caused by Marangoni convection, which result in an enhancement of the transfer rate across the interface.

Nitrogen stripping of isopropyl-alcohol and toluene in a falling film micro reactor: Gas side mass transfer experiments and modelling at isothermal conditions

A falling film micro reactor has been investigated as a contactor for a separation process in order to be implemented in fine chemical and pharmaceutical production. Nitrogen stripping of a pure solvent was performed allowing straightforward mass transfer measurements due to the absence of resistance in the liquid side.Two mass transfer models were developed in this study, a semi-analytical one based on the mass balance equations combined with an existing Sherwood correlation for laminar flow in micro channels and a numerical model solving the hydrodynamics and mass transport equations. Very good agreement was found between the two models, which were then compared with experimental data. The experimental values of stripping efficiency agree with the calculated ones with an error of ±15% showing good modelling prediction. The calculated gas side mass transfer coefficients of the investigated micro contactor are in the range of 0.007–0.01ms−1.

Trickle flow liquid–solid mass transfer and wetting efficiency in small diameter columns

AbstractA novel method to simultaneously measure liquid solid mass transfer and external wetting efficiency was employed at column to particle ratios of 10, 6 and 3. Two prewetting procedures representing the upper (Kan) and lower (Levec) hysteresis branches were used. For a multipoint distributor on a Kan prewetted bed wetting efficiency and the specific mass transfer coefficient were almost unaffected by column diameter. The multipoint distributor on a Levec prewetted bed exhibited a decrease in specific mass transfer with decreasing column diameter. Point source experiments resulted in significantly lower wetting and mass transfer measurements with an increasing trend with respect to decreasing column diameter. The results indicate that with proper distribution and prewetting, the effect of column diameter on averaged wetting and liquid–solid mass transfer is almost negligible, a powerful result considering the importance of these parameters on reaction experiments. © 2012 Canadian Society for Chemical Engineering

Computer controlled chamber measurements for clay adherence relevant for potential dioxin exposure through skin

A computer-controlled mechanical chamber was used to control the contact between aluminum sheet samples laden with clay, and cotton sheet samples for the measurement of mass transfer. The contact parameters of pressure (20 to 60 kPa) and time (10 to 70 sec) were varied for 160 multiple experiments of mass soil transfer. Before log transformation the average transfer for ‘First Transfer’ of clay particles was 34.4 ± 6.3 mg/8.97 cm2 while that for ‘Total Transfer’ was 36.1 ± 6.8 mg/8.97 cm2. Second contact, therefore, resulted in an average transfer of 1.70 ± 0.76 mg/8.97 cm2. These values are well above adherence values measured for potting soil and sand as reported for previous experiments using the same methodologies. Based on the univariate analysis and the multiple regression analysis we were able to see some effect of parameters on the clay adherence values. The effect of pressure increases was significant for the higher levels of 50 and 60 kPa. In addition, we observed that increases in temperature were significant for ‘First Transfer,’ and less so for ‘Total Transfer’. Past experiments using potting soil and play sand show high adherence values to human cadaver skin over cotton sample; the same scenario would be expected for clay. This data set can be used to improve estimates of dermal exposure to dioxins found in ball clays often used by artisans in the making of pottery.

Mass Transfer Measurements behind an Orifice in a Circular Pipe Flow for Various Combinations of Swirl Intensity and Orifice Bias

Mass Transfer Measurements behind an Orifice in a Circular Pipe Flow for Various Combinations of Swirl Intensity and Orifice Bias

Introduction to the Feature Articles: Contact Points between Aerosol Science and Measurement of Heat and Mass Transfer in Combustion

Introduction to the Feature Articles: Contact Points between Aerosol Science and Measurement of Heat and Mass Transfer in Combustion

激光全息干涉测定微通道内气液传质

激光全息干涉测定微通道内气液传质