Mass Transfer Measurements Research Articles

Visualization and determination of local heat transfer coefficients in shell-and-tube heat exchangers for in-line tube arrangement by mass transfer measurements

The local heat transfer coefficients on the shell-side of shell-and-tube heat exchangers for in-line tube arrangement are visualized and determined from mass transfer measurements. The mass transfer experiments are carried out using a technique based on absorption, chemical and coupled colour reaction. Local mass transfer coefficients are measured for fully developed flow conditions on each tube surface. These coefficients were transformed to heat transfer coefficients by employing the analogy between heat and mass transfer. The averaged heat transfer coefficients and the pressure drop are compared with the predictions from the literature.

Convective Mass Transfer from Cylinders in a Jet Flow

A photoevaporative mass-transfer measurement technique has been used to determine the convective mass-transfer behavior of stationary and rotating cylinders which were immersed in a two-dimensional jet of air. For a stationary cylinder, the circumferential distributions of the local mass-transfer rate were determined as a function of jet Reynolds number (45000−176000) and ranges of other parameters of practical importance (relative position of cylinder in jet (L/D) and relative size of cylinder and jet nozzle (d/D)). Circumferentially averaged values of the mass-transfer coefficient were estimated by integration and the results used to produce correlations for the mean Sherwood number. For a rotating cylinder immersed in the slot jet, circumferentially averaged values of Sherwood number were directly determined for a range of conditions similar to those used in the study of the stationary cylinder but with rotational speed as an additional variable. Predictions of the mean Sherwood number for cylinders dr...

Mass transfer influences on the design of selective catalytic reduction (SCR) monolithic reactors

A selective catalytic reduction (SCR) monolithic reactor based on Ti–V–W–Sepiolite catalyst for removal of nitrogen oxides from Power Plant was simulated by using an approaching model which took into account interfacial and intraphase gradients. Different correlations for mass transfer between the solid and the fluid phase were compared, the best obtained results were the corresponding results for the experimentally determined correlations of Ullah (U. Ullah, P. Waldram, C.J. Bennet, T. Truex, Monolithic reactors: mass transfer measurements under reacting conditions, Chem. Eng. Sci. 47 (1992) 2413–2418) and Votruba (J. Votruba, J. Sinkule. V. Hlavacek, J. Skrivanek, Heat and mass transfer in honeycomb catalysts I, Chem. Eng. Sci. 30 (1975) 117–123; J. Votruba, O. Mikus, K. Nguen, V. Hlavacek, J. Skrivanek, Heat and mass trasfer in honeycomb catalysts II, Chem. Eng. Sci. 30 (1975) 201–206). For the considered reaction, internal behavior seems to be essential. A refined study of the intraparticle behavior, calculating D e from an experimental tortuosity factor previously obtained, was accomplished. It was shown that the amount of catalyst could be drastically reduced without changing the performance of the monolithic reactor.

In Situ global method for measurement of oxygen demand and mass transfer

Two aerobic microorganisms, Saccharomycopsis lipolytica and Brevibacterium lactofermentum, have been used in a study of mass transfer and oxygen uptake from a global perspective, using a closed gas system. Oxygen concentrations in the gas and liquid were followed using oxygen electrodes; the results allowed for easy calculation of in situ oxygen transport. The cell yields on oxygen for S. lipolytica and B. lactofermentum were 1.01 and 1.53 g/g, respectively. The mass transfer coefficient was estimated as 10/h at 500 rpm for both fermentations. The advantages with this method are noticeable, since the use of model systems may be avoided, and the in situ measurements of oxygen demand assure reliable data for scale-up.

Multiphase Flow-Enhanced Corrosion Mechanisms in Horizontal Pipelines

Previous work has demonstrated the mechanism of enhanced corrosion in slug flow due to entrained pulses of gas bubbles (Gopal et al., 1997). Corrosion rate measurements have been made at pressures up to 0.79 MPa and temperatures up to 90°C, and it has been shown that the effect of these pulses of bubbles increases with pressure and Froude number. This paper describes mass transfer measurements under multiphase slug and annular flows using the limiting current density technique. The experiments are carried out in a 10-cm-dia pipe using a 0.01-M potassium ferro/ferricyanide solution in 1.3 N sodium hydroxide for the liquid phase and nitrogen in the gas phase. Froude numbers of 4, 6, and 9 in slug flow have been studied, while gas velocities up to 10 m/s are investigated in annular flows. The results show instantaneous peaks in the mass transfer rates corresponding to the pulses of bubbles in slug flow. Instantaneous increases of 10–100 times the average values in multiphase flow are seen. Peaks are also seen in instantaneous mass transfer rates in some annular flows.

Evaluation of a novel self‐aerating, oscillating baffle column

AbstractWe describe the operation of a pilot scale oscillating baffle column using a self‐aeration system for oxygenation of water. The top baffle has a high constriction ratio and is sufficiently near to the surface of the water such that gas bubbles are generated. This aeration plate is coupled with a series of equally spaced low constriction orifice baffles, which lead to uniform dispersion of entrained air bubbles throughout the liquid volume. Flow visualisation experiments using video and still photography were used to identify two mechanisms for bubble generation: bubble formation under the water surface by surface vortex suction, and bubble generation from the collapse of a surface fountain and subsequent entrainment of bubbles into the bulk. Mass transfer measurements have shown that under most conditions a uniform oxygen concentration could be obtained throughout the column as a result of efficient mixing, and that the sole limitation to mass transfer performance was determined by the aeration mechanism. Initial comparison on the basis of aeration efficiency with other devices reveals a modest oxygen transfer rate, but with low specific power consumption of order 0.3 kW/m3.

Microporous hollow fibres for carbon dioxide absorption: mass transfer model fitting and the supplying of carbon dioxide to microalgal cultures

A method of supplying to photosynthetic algal cultures was devel- CO 2 oped based on mass transfer measurements of through microporous hydro- CO 2 phobic hollow -bres for various gas and liquid Now rates. A mathematical model was derived to describe the mass transfer. The designed hollow -bre module led to overall mass transfer coefficient values ranging from 1E26 ) 10~3 to 2E64 ) 10~3 cm s~1. Higher efficiencies of the transmission were obtained CO 2 at high liquid Now rates and low gas Now rates. The use of microporous hydro- phobic hollow -bres enabled an enhancement of the carbon dioxide transfer per area of membrane surface by a factor of 10, in comparison to operation with silicone tubing. The hollow -bre module was operated in an external bypass to a 1d m 3microalgae culture vessel. In this system the algal growth pattern was similar to that obtained with a control culture where was bubbled. CO 2 However, the dissolved oxygen concentration was always lower in the vessel in which was supplied by the module. 1998 SCI. CO 2 ( J. Chem. T echnol. Biotechnol. 71 ,6 1 E70 (1998)

Free Convective Mass Transfer at Down-Pointing Isosceles Triangles of Varying Inclination

Free convective mass transfer at down-pointing triangular surfaces of different length and down-facing inclination was investigated using the limiting diffusion current technique of mass transfer measurement. The mass transfer rate was observed to be higher for a down-pointing triangular inclined surface over the entire range of inclination than that for an inclined rectangular surface because of the different rleading edger condition. A mass transfer correlation for down-facing inclined triangular surfaces of different length was found to be ShL = 0.774(RaL cos θ)0.25 for the RaL cos θ range from 2 . 106 to 2 . 1011.

Effect of the leakage on pressure drop and local heat transfer in shell-and-tube heat exchangers for staggered tube arrangement

Experiments are performed to determine the response of the pressure drop and local heat transfer on the shell side of shell-and-tube heat exchangers to a change in the leakage between baffles and shell in the fully developed regime. The local mass and heat transfer coefficients are visualized and determined by means of mass transfer measurements. The shell-side flow distribution was calculated from the measurements of the pressure distribution in the baffle compartment. This leakage between baffles and shell can greatly reduce the pressure drop and the per-compartment average heat transfer coefficient.

Study of mercury deposition from chloride solutions as test reaction for mass-transfer measurements

This paper deals with a systematic study of mercury deposition from sodium chloride solutions to determine the feasibility of using this reaction for mass-transfer measurements. The study was performed with a glassy carbon rotating disc electrode and reproducible results were obtained only when the electrode was catodically pretreated. Polarization curves at different concentrations of sodium chloride and mercury (ii) are reported. Hydrogen evolution and oxygen reduction has also been considered as side reactions and the conditions where their influence may be neglected are discussed. Experimental conditions where mercury deposition can be used as test reaction are given.

Measurement and prediction of mass transfer to experimental coral reef communities

The uptake of nutrients (N and P) into coral reef communities is proposed to be limited by diffusion through concentration‐depleted boundary layers between the water and organisms, or what is termed “mass transfer limitation.” The mass transfer rate is a physical limit to the rate of nutrient uptake. Maximum uptake rates by highly rough biological surfaces have not yet been evaluated. Engineering correlations indicate that increased surface roughness should increase mass transfer, although it has been difficult to quantify roughness of living corals. In this paper, the effects of highly rough coral surfaces on mass transfer were investigated by using dissolution of gypsum (plaster‐of‐paris) from flat smooth surfaces and coral skeletons. The gypsum dissolution rates were measured as an increase in concentration of calcium ions in freshwater recirculating over experimental surfaces. Stanton numbers (Stm, a dimensionless number giving the ratio of uptake rate per unit area to the rate of advection of the substance past the uptake surface) of experimental smooth surfaces ranged from 2.6 to 3.5 × 10−5 and were the same as values in the engineering literature for smooth surfaces. Stm for coral‐shaped surfaces ranged from 70 × 10−5 at 0.03 m s−1 to 17 × 10−5 at velocities up to 0.50 m s−1 and were in general 9 ± 1 times that of smooth surfaces. The measured Stm for each coral‐shaped surface was the same as the predicted Stm (±10%) calculated from measured friction and roughness using a correlation of heat transfer. Stm for ammonia uptake on living coral reef communities show the same relationship between mass transfer, friction, and roughness as the coral‐shaped gypsum surfaces. The transport rates of nutrients to reef surfaces are controlled by large‐scale roughness, typically associated with coral heads, and not small‐scale roughness elements on the organisms, nor biological alterations of diffusive boundary layers. Nutrient uptake and possibly other metabolic exchange rates arc governed by concentration, water velocity, and friction dissipated over the reef, denoting that coral reef community metabolism is physically forced.

Quantitative spatially resolved measurements of mass transfer through laryngeal cartilage

The scanning electrochemical microscope (SECM) is a scanned probe microscope that uses the response of a mobile ultramicroelectrode (UME) tip to determine the reactivity, topography, and mass transport characteristics of interfaces with high spatial resolution. SECM strategies for measuring the rates of solute diffusion and convection through samples of cartilage, using amperometric UMEs, are outlined. The methods are used to determine the diffusion coefficients of oxygen and ruthenium(III) hexamine [Ru(NH3)6(3+)] in laryngeal cartilage. The diffusion coefficient of oxygen in cartilage is found to be approximately 50% of that in aqueous electrolyte solution, assuming a partition coefficient of unity for oxygen between cartilage and aqueous solution. In contrast, diffusion of Ru(NH3)6(3+) within the cartilage sample cannot be detected on the SECM timescale, suggesting a diffusion coefficient at least two orders of magnitude lower than that in solution, given a measured partition coefficient for Ru(NH3)6(3+) between cartilage and aqueous solution, Kp = [Ru(NH3)6(3+)]cartilage/[RU(NH3)6(3+)]solution = 3.4 +/- 0.1. Rates of Ru(NH3)6(3+) osmotically driven convective transport across cartilage samples are imaged at high spatial resolution by monitoring the current response of a scanning UME, with an osmotic pressure of approximately 0.75 atm across the slice. A model is outlined that enables the current response to be related to the local flux. By determining the topography of the sample from the current response with no applied osmotic pressure, local transport rates can be correlated with topographical features of the sample surface, at much higher spatial resolution than has previously been achieved.

Gas-liquid mass transfer in gas-liquid-liquid dispersions

Gas-liquid mass transfer measurements by dynamic absorption in a stirred autoclave have been performed successively in various single liquid phases and in liquid-liquid mixtures. Data were interpreted through a pseudo-homogeneous model based on Danckwerts surface renewal theory and on continuous liquid-liquid equilibrium due to very fast liquid mass transfer. As a major result, the volumetric mass transfer coefficient k1a is clearly increased when adding a disperesed organic phase, with a clear maximum at 3 to 4% of organic volume fraction. Higher enhancement (up to 70%) was performed at high stirring speed and with hydrogen better than with carbon monoxide as the dissolving gas.

Caprolactam production: A comparison of different layouts of the liquid‐liquid extraction section

AbstractTwo different layouts for the liquid‐liquid extraction section of an industrial caprolactam process are evaluated. Laboratory mass transfer measurements on streams obtained from an industrial and a demonstration plant with different extraction sections are interpreted by a model describing the effect of surface contaminants on mass transfer coefficients. Indications of the impact of these layouts on the complexity of the extraction section, quality of products and efficiency of the extraction processes are given.

Electrochemical mass transfer measurements in rough surface pipe flow: geometrically similar V-shaped grooves

The electrochemical technique has been used to measure mass transfer rates between nickel surfaces and the ferro-, ferricyanide electrolyte solution flowing in a 38 mm ID circular pipe. Data for one smooth and six rough surfaces are reported. The surfaces were fabricated by a novel electroplating technique. The rough surfaces had V-shaped grooves transverse to the flow direction, 76–1500 μm deep. The experiments covered the Reynolds number range of 500–350 000; Schmidt numbers varied from 550 to 4720. Friction factors were measured for 4000 < Re < 240 000. The results are correlated by the mass transfer similarity function. Transfer enhancement depends on groove size and frequency and on flow conditions. Rates higher than three times the corresponding smooth surface values were observed. A mass transfer efficiency index is proposed, relating enhancement to frictional losses.

Heat transfer and flow field in a pipe with sinusoidal wavy surface—II. Experimental investigation

In Part I of this paper the heat and mass transfer in a pipe with a wavy surface was studied numerically. To validate the predictions and to close the gap in the Reynolds number range 400 < Re dm < 2000, where a numerical simulation of the transitional flow structure was not possible, an experimental investigation was performed. Applying the naphthalene sublimation technique, the local mass transfer was studied along the axis of the pipe. Using analogy functions, the measured Sherwood numbers were transformed into Nusselt numbers. In addition to the results of the mass transfer measurements this paper also presents flow visualization experiments.

Development and Testing of a Kinetic Model for Oxygen Transport in Porous Media in the Presence of Trapped Gas

AbstractThe ability to predict the transport of dissolved gases in the presence of small amounts of trapped gas in an otherwise water‐saturated porous medium is needed for a variety of applications. However, an existing model based on equilibrium partitioning of dissolved gas between aqueous and trapped gas phases does not accurately predict the shape of experimentally observed breakthrough and elution curves in column experiments. The objective of this study was to develop and test a kinetic model for dissolved gas transport that combines the advection‐dispersion equation with diffusion controlled mass transfer of dissolved gas between the aqueous and trapped gas phases. The model assumes one‐dimensional, steady‐state ground‐water flow, a single dissolved gas component, and a stationary trapped gas phase with constant volume. The model contains three independent parameters: the Peclet number, P, retardation factor, R, and dimensionless mass transfer parameter, ω. The model accurately described the shape of breakthrough and elution curves for dissolved oxygen in column experiments performed with a poorly graded sand and varying amount and composition of trapped gas. Estimated values of P for the bromide tracer increased from 5.92 to 174, corresponding to a decrease in dispersivity from 5.02 to 0.17 cm, as the trapped gas volume increased from 0 to 30% of the pore space. It is speculated that this effect is due to a narrower pore size distribution (and hence more uniform pore scale velocity distribution) caused by trapped gas bubbles selectively occupying the largest pores. Estimated values of R increased from 1 to 13.6 as the trapped gas volume increased and confirmed earlier observations that even small amounts of trapped gas can significantly reduce rates of dissolved oxygen transport. Estimated values of ω ranged from 0.3 to 12.1. Although it was not possible to independently measure mass transfer coefficients or interfacial areas, values computed from flow rates and estimated w values are consistent with values computed by assuming (1) that interfacial area is proportional to trapped gas volume, (2) that trapped gas bubbles are spheres with diameters the same size as soil particles, and (3) that mass transfer is limited by diffusion of dissolved oxygen through water films surrounding trapped gas bubbles.

Phase holdup, liquid dispersion, and gas-to-liquid mass transfer measurements in a three-phase magnetofluidized bed

The gas holdup, ε g , liquid-phase axial dispersion coefficient, D ax, and volumetric gas-to-liquid mass transfer coefficient, k l a, have been measured for a three-phase magneto-fluidized bed (MFB) as a function of gas superficial velocity, liquid superficial velocity, and magnetic field strength. The solid phase consisted of 4 mm diameter calcium alginate spheres within which magnetite powder was entrapped. The liquid and gas phases were water and air, respectively. An axial, direct-current magnetic field having a magnitude between 0 and 300 G was applied by an external solenoid. Six different bed operating regimes were distinguished by visual inspection. Local values of ε g were measured using a fiber-optic probe, and the average values of ε g were measured using the valve technique. Average ε g values decreased by as much as 20% with increasing field strength due to bed contraction and the formation of preferred channels. Local ε g measurements correlated well with average measurements at low field strengths but became erratic at high field strengths due to bubble channeling. The liquid-phase axial dispersion coefficient was measured using a salt tracer. A fourfold decrease in D ax was observed in the channel regime. The volumetric oxygen mass transfer coefficient ( k l a) was determined from measurements of the steady-state oxygen profile across the reactor. A 30% increase in k l a was observed in the chain-channel regime. The experimental results for the MFB were compared to published correlations for conventional fluidized bed systems.

Heat (mass) transfer measurement and analysis with flows around film cooling holes and circular cylinders

The present study investigates heat/mass transfer around film cooling jets and circular cylinders to compare the characteristics of each other. Experiments are conducted to obtain the detailed heat/mass transfer coefficients of flat plate with injections through an array of holes and for flows around an array of protruding circular cylinders using the naphthalene sublimation technique. The inclination angles of cylinders are set to the same ones of jets; a, the angle between the jet and the surface is fixed at 30 deg. through the whole experiments and .betha., the angle between the projection of the jet on the surface and the direction of main stream is adjusted to 0 deg., 45 deg. and 90 deg. to investigate the effect of variation of injection angles. The influence of blowing rates of jets and those of cylinder length to diameter ratios are also investigated. The results indicate that the increase of angle .betha. influences the spanwise uniformity of heat/mass transfer remarkably for both jets and cylinders, but that variation of cylinder length to diameter ratios has weaker effects on heat/mass transfer coefficients than that of blowing rates.

Heat transfer on the base surface of threedimensional protruding elements

Five basic geometries (cylinder, cube, diamond, pyramid and hemisphere) are comparatively examined at a Reynolds number of 1.7 × 10 4 to determine the effect of a single roughness element on surface heat (mass) transfer. Local mass transfer measurements obtained using the naphthalene sublimation technique are substantiated by flow visualization. Results show that the upstream horseshoe vortex system and the inverted arch-shaped vortex immediately behind the elements are the dominating effects in elementendwall interaction. Based on information concerning the extent of spanwise influence of each element, an inter-element spacing may be proposed for array configurations to achieve optimal heat transfer performance.