Surface Renewal Research Articles

New turbulence modeling for simulation of Direct Contact Condensation in two-phase pressurized thermal shock

Injection of Emergency Core Cooling System (ECCS) water into the primary loops of the Pressurized Water Reactors (PWRs) leads to rapid cooling of Reactor Pressure Vessel (RPV) inside wall after Loss Of Coolant Accident (LOCA). This condition, known as Pressurized Thermal Shock (PTS) intensifies the propagation of the RPV structural defects and would be considered as an ageing mechanism. For structural and fracture analysis of RPV wall, thermal-hydraulic analysis of PTS should be accomplished to obtain the steam/water flow characteristics in the downcomer. For this purpose, simulation of steam/water stratified flow (due to density difference) after the injection point should be done by Computational Fluid Dynamics (CFD) methods. In this region, steam condensation over water layer is considered as the only heat source and controlled by turbulence eddy motion near the steam/water interface. Based on Surface Renewal Theory (SRT), Heat Transfer Coefficient (HTC) would be calculated by evaluation of turbulence length and velocity. Therefore, prediction of turbulence characteristics plays a significant role for estimation of interfacial mass transfer and temperature profile. High gradient of velocity and Turbulence Kinetic Energy (TKE), and interfacial mass and momentum transfer at the steam/water interface needs some modifications for application of traditional turbulence models. Implementation of damping function is one of the common solutions to overcome the overestimation of TKE at the steam/water interface. Although, this function improves flow characteristics of smooth stratified flow, investigation of conservation equations and experimental data implies that the other source function is needed when the flow regime changes to wavy flow. In this paper, a new source function of TKE based on variations of turbulence characteristics is proposed for steam/water interface leading to a special boundary condition of turbulence. To investigate the effects of this modification, simulation of air/water and steam/water stratified flow in three different test facilities is performed. The results show that the implementation of the source function of TKE improves the prediction of turbulence characteristics at the interface of isothermal stratified flow. Also condensation rate and temperature gradient of steam/water stratified flow have a better agreement with experimental data.

An electrochemical sensor based on CuO nanoparticle for simultaneous determination of hydrazine and bisphenol A

In the present research, the direct electrochemical oxidation of hydrazine in the presence of bisphenol A was investigated at a copper oxide nanoparticles/ionic liquid/carbon paste electrode (CuO NPs/IL/CPE). The combination of the good conductive 1-hexyl-3-methylimidazolium hexafluorophosphate and CuO nanoparticles resulted in an electrode with attractive properties for the determination of hydrazine in the presence of bisphenol A. The linear dynamic ranges were obtained in the ranges of 0.05–150 and 0.2–175 µM with the detection limits (3sb/m) 0.03 and 0.1 µM for HY and BPA, respectively. High stability, sensitivity, selectivity and reproducibility, fast response, the ease of preparation, and surface renewal made the sensor well suitable for the determination of hydrazine in the presence of bisphenol A, which are important pollutants in the environment. Finally, this new sensor was used for the determination of HY and BPA in some water samples such as river water and wastewater.

Estimating cotton water consumption using a time series of Sentinel-2 imagery

Crop coefficient (Kc)-based estimation of crop water consumption is one of the most commonly used methods for irrigation management. Spectral modeling of Kc is possible due to the high correlations between Kc and the crop phenologic development and spectral reflectance. In this study, cotton evapotranspiration was measured in the field using several methods, including eddy covariance, surface renewal, and heat pulse. Kc was estimated as the ratio between reference evapotranspiration and the measured cotton evapotranspiration. In addition, a time series of Sentinel-2 imagery was processed to produce 22 vegetation indices (VIs) based on the sensor’s unique spectral bands. Empirical Kc – VI models were derived and ranked according to their prediction error. In accordance with previous studies, we found a strong correlation between the normalized difference vegetation index (NDVI) and Kc (R2 = 0.94), and yet, we also identified other spectral indices that are more strongly correlated to Kc. The indices that were found to be the most suitable for Kc prediction were based on the red and red-edge bands (MTCI, REP, and S2REP). This progress in estimating cotton water consumption using satellite imagery that are available at no cost is a leap forward towards the development of crop irrigation requirements models. Consequently, this work sets the scene for near-real-time irrigation decision support systems.

A surface renewal model for unsteady-state mass transfer using the generalized Danckwerts age distribution function.

The recently derived steady-state generalized Danckwerts age distribution is extended to unsteady-state conditions. For three different wind speeds used by researchers on air–water heat exchange on the Heidelberg Aeolotron, calculations reveal that the distribution has a sharp peak during the initial moments, but flattens out and acquires a bell-shaped character with process time, with the time taken to attain a steady-state profile being a strong and inverse function of wind speed. With increasing wind speed, the age distribution narrows significantly, its skewness decreases and its peak becomes larger. The mean eddy renewal time increases linearly with process time initially but approaches a final steady-state value asymptotically, which decreases dramatically with increased wind speed. Using the distribution to analyse the transient absorption of a gas into a large body of liquid, assuming negligible gas-side mass-transfer resistance, estimates are made of the gas-absorption and dissolved-gas transfer coefficients for oxygen absorption in water at 25°C for the three different wind speeds. Under unsteady-state conditions, these two coefficients show an inverse behaviour, indicating a heightened accumulation of dissolved gas in the surface elements, especially during the initial moments of absorption. However, the two mass-transfer coefficients start merging together as the steady state is approached. Theoretical predictions of the steady-state mass-transfer coefficient or transfer velocity are in fair agreement (average absolute error of prediction = 18.1%) with some experimental measurements of the same for the nitrous oxide–water system at 20°C that were made in the Heidelberg Aeolotron.

Computational efficiency for the surface renewal method

Abstract. Measuring surface fluxes using the surface renewal (SR) method requires programmatic algorithms for tabulation, algebraic calculation, and data quality control. A number of different methods have been published describing automated calibration of SR parameters. Because the SR method utilizes high-frequency (10 Hz+) measurements, some steps in the flux calculation are computationally expensive, especially when automating SR to perform many iterations of these calculations. Several new algorithms were written that perform the required calculations more efficiently and rapidly, and that tested for sensitivity to length of flux averaging period, ability to measure over a large range of lag timescales, and overall computational efficiency. These algorithms utilize signal processing techniques and algebraic simplifications that demonstrate simple modifications that dramatically improve computational efficiency. The results here complement efforts by other authors to standardize a robust and accurate computational SR method. Increased speed of computation time grants flexibility to implementing the SR method, opening new avenues for SR to be used in research, for applied monitoring, and in novel field deployments.

Surface Renewal Application for Estimating Evapotranspiration: A Review

The estimation of evapotranspiration (ET) is essential for meteorological modeling of surface exchange processes, as well as for the agricultural practice of irrigation management. Hitherto, a number of methods for estimation of ET at different temporal scales and climatic conditions are constantly under investigation and improvement. One of these methods is surface renewal (SR). Therefore, the premise of this review is to present recent developments and applications of SR for ET measurements. The SR method is based on estimating the turbulent exchange of sensible heat flux between plant canopy and atmosphere caused by the instantaneous replacement of air parcels in contact with the surface. Additional measurements of net radiation and soil heat flux facilitate extracting ET using the shortened energy balance equation. The challenge, however, is the calibration of SR results against direct sensible heat flux measurements. For the classical SR method, only air temperature measured at high frequency is required. In addition, a new model suggests that the SR method could be exempted from calibration by measuring additional micrometeorological variables. However, further improvement of the SR method is required to provide improved results in the future.

Energy and water balance of a treatment wetland under mediterranean climatic conditions

During 2013–2014 period, the surface renewal (SR) – energy balance (EB) method combined with the water balance approach was adopted to define the energy and water budget of a treatment wetland (TW) in Eastern Sicily (Italy). The main objective was to evaluate the differences between energy and water balances and understand the underlining mechanisms of environmental control. Results shown that the seasonal variation in evapotranspiration (ET) had similar trend as the seasonal variation of leaf area index (LAI) and net radiation (Rn). During the study period, the daily rate of ET by EB ranged from −0.1 mm d−1 to 9.3 mm d−1, with a total ET of about 1837 mm in 17 months. The crop coefficient Kc (e.g. obtained using the FAO-56 mean Kc approach) for the TW ranged from 0.5 to 2.4, with a mean annual value of 1.24. On a 10-day mean basis, ET fluxes from the TW water balance were 15% higher than ET by EB.

Modeling air-water heat transfer induced by buoyant convection

The instantaneous 2D velocity field obtained at the air-water interface in previously performed direct numerical simulations (DNS) of interfacial heat transfer driven by buoyant convective instability is used to estimate the heat transfer velocity [2]. After reconstructing the three-dimensional velocity field immediately underneath the surface, a Lagrangian particle tracking method was used to assess the surface age. The surface heat transfer velocity, obtained using Danckwerts’ surface renewal model, was found to underestimate the heat transfer velocity acquired directly from the DNS data by about 16%.

An Assessment of the General Applicability of the Relationship Between Nucleation of CO Bubbles and Mass Transfer of Phosphorus in Liquid Iron Alloys

The current paper seeks to demonstrate the general applicability of the authors’ recently developed treatment of surface renewal during decarburization of Fe-C-S alloys and its effect on the mass transport of phosphorus in the metal phase. The proposed model employs a quantitative model of CO bubble nucleation in the metal to predict the rate of surface renewal, which can then in turn be used to predict the mass-transfer coefficient for phosphorus. A model of mixed transport control in the slag and metal phases was employed to investigate the dephosphorization kinetics between a liquid iron alloy and oxidizing slag. Based on previous studies of the mass-transfer coefficient of FeO in the slag, it was possible to separate the mass transfer coefficient of phosphorus in metal phase, $$ k_{m} $$ , from the overall mass-transfer coefficient $$ k_{{\text{o}}} . $$ Using this approach, $$ k_{m} $$ was investigated under a wide range of conditions and shown to be represented reasonably by the mechanism proposed. The mass-transfer model was tested against results from the literature over a wide range of conditions. The analysis showed that the FeO content in the slag, silicon in the metal and the experimental temperature have strong impact on, $$ k_{m} $$ , almost entirely because of their effect on decarburization behavior.

Estimation of liquid‐side mass transfer coefficient and liquid film thickness in a bubble column using single spherical bubble model

AbstractA macroscopic mass transfer model based on the unsteady‐state liquid film mass transfer mechanism for a single spherical bubble was formulated. Analytical solution of the model equation was obtained in Laplace transform using surface renewal rates based on Danckwerts' surface age distribution function. The mass transfer coefficient, kL, in a slurry bubble column under different operating conditions of temperature, pressure, gas flow rate, and solid concentration has been simulated using a program code “BUBBLESIM” in MATLAB®, developed by the authors. The proposed model has been validated using secondary data for a slurry system under a wide range of operating conditions. The predicted values of kL show very good agreement with the experimental data within an average deviation of ±2%. The results show that the mass transfer coefficient, kL, increased with increasing superficial gas velocity and temperature and decreased with increase in slurry concentration, while it changed slightly with pressure. Based on the present work, empirical correlations have been proposed for the prediction of δ in terms of dimensionless groups for H2–, CO–, and CO2–paraffin–quartz sand systems under elevated temperatures (298–423 K) and elevated pressures (1–3 MPa) in a slurry bubble column.

How old are lunar lobate scarps? 1. Seismic resetting of crater size-frequency distributions

Previous studies have estimated the ages of lunar lobate scarps, some of the youngest tectonic landforms on the Moon, based on the estimated life-times of their fresh morphologies and associated small graben, using crater degradation ages, or via buffered and traditional crater size-frequency distribution (CSFD) measurements. Here, we reexamine five scarps previously dated by Binder and Gunga (1985) with crater degradation ages to benchmark the evaluation of both the buffered and traditional CSFD approaches for determination of absolute model ages (AMAs) at scarps. Both CSFD methods yield similar ages for each individual scarp, indicating that fault activity not only can be measured on the scarp itself, but also in the surrounding terrain – an indication that tectonic activity causes surface renewal both adjacent to and even kilometers distant from scarps. Size-frequency variations in the regions surrounding the scarps are thus useful for studying the extent and severity of the ground motion caused by coseismic slip events during scarp formation. All age determination approaches continue to indicate that lunar lobate scarps were active in the late Copernican, with some scarps possibly experiencing activity within the last 100 Ma.

Mobility of free surface in different liquids and its influence on water striders locomotion

Dynamics of the surface layer in different liquids is examined by means of infrared thermography of the surface and simultaneous velocity fields measurements using surface and infrared Particle Image Velocimetry. This technique allows measurements and comparison of two velocity fields—at the surface and at small depth about 50–200 μm. In distilled water the velocity fields at the surface and at small depth exhibit significant dissimilarity. The flow field below the surface is essentially 3D, whereas the surface flow is characterized by vanishing 2D divergence of velocity, indicating predominantly planar motion. In contrast, in ethanol–butanol mixture two velocity fields are well correlated, both corresponding to 3D flow with continuous surface renewal. Thermal patterns, observed at the surface, and the flow field structure in different liquids are associated with different boundary conditions for velocity at the surface. Water surface is seldom renewed, which inhibits heat and mass exchange between the liquid and atmosphere. However, absence of vertical advection also enables organisms to live within the surface layer, to stand and walk on the free surface. This is illustrated by the difficulties a water strider faces on the surface of ultrapure water, which exhibits Marangoni convection.

Air-water interface transport and surface renewal under impacting droplets

Air-water interface transport and surface renewal under impacting droplets

Outer-tubes Falling Film Evaporator with Well-Mixed Surface Renewal

A falling film evaporator with a liquid flowing laminarly outside vertical cylindrical tubes was studied by a mathematical modeling in order to describe the performance of the system and the results are later used for a design of a falling film evaporator. In this study a mathematical model was developed from mass and energy as well as momentum transfer processes in an evaporation of a sugar solution. The equations were solved by using a numerical technique known as implicit method. This model yields the prediction of velocity, temperature and concentration profiles of solution as well as rate of mass evaporation and energy required in this process. Evaporation limitation was disclosed to be based on water mass transfer across the liquid thin film. Renewable surface was proposed to enhance the evaporation by adding a collector for liquid mixing before further evaporation. Adding only one collector at the half height of the evaporation tube could increase water evaporation rate by 1.3 and 2.1 % in case of the liquid perfect mixing, respectively.

Applicability of enhancement factor models for CO2 absorption into aqueous MEA solutions

In many chemical industrial processes, mass transfer across gas-liquid interfaces accompanied by chemical reaction is the governing phenomena. In case of mass transfer accompanied by a chemical reaction in the liquid phase, the reaction will enhance mass transfer and generally the mass transfer enhancement is quantified in terms of an enhancement factor. Large number of enhancement factor models have been developed in literature and used without critical analysis for analyzing pilot data for CO2 absorption into aqueous amines. In order to perform such a critical analysis, 24 models are tested using lab-scale experimental data from four independent apparatuses for CO2 absorption into MEA solutions covering a range of different conditions such as short and long contact times, with and without gas phase resistance, high and low CO2 loadings and temperatures. Of the 24 enhancement factor models tested only six models were found to satisfactorily predict the experimental CO2 fluxes. These were the models based on the simple pseudo-first order reaction assumption, Emodels 1, 2 and 3 by Hatta [2] and Dankwerts [4] respectively, Emodel 20, the deCoursey and Thring [44] model based on Danckwert’s surface renewal theory with unequal diffusivities, Emodel 24, the recently published generalized model by Gaspar and Fosbøl [51] and Emodel 21, the Tufano et al. [67] model based surface renewal theory. All these models were found to work equally well to the discretized penetration model. No significant difference was found between Emodels 1, 2 and 3, indicating that whether one uses as basis a film, penetration or surface renewal model, is of insignificant importance.The success of the simple models is attributed to the short contact times in the experiments used as basis and the accuracy of the kinetic model. Contact times of the same magnitude between mixing points is also encountered in industrial packings and it is believed that the simple enhancement factor models may work well also in these cases if an accurate kinetic model is used.

Dephosphorization Kinetics between Bloated Metal Droplets and Slag Containing FeO: The Influence of CO Bubbles on the Mass Transfer of Phosphorus in the Metal

Dephosphorization kinetics of bloated metal droplets was investigated in the temperature range from 1813 K to 1913 K (1540 °C to 1640 °C). The experimental results showed that the overall mass transfer coefficient, \( {k_{\text{o}}} \), decreased with increasing temperature because of decreasing phosphorus partition ratio, \( {L_{\text{P}}} \). It was also found that the mass transfer coefficient for phosphorus in the metal, \( {k_{\text{m}}} \), had the highest value at the lowest temperature [i.e., 1813 K (1540 °C)] because the formation of smaller CO bubbles increased the rate of surface renewal, leading to faster mass transport. Meanwhile, metal droplets without carbon were also employed to study the effect of decarburization on dephosphorization. The results show that although decarburization lowers the driving force significantly, \( {k_{\text{m}}} \) (6.2 × 10−2 cm/s) for a carbon containing droplet is two orders of magnitude higher than that for carbon free droplets (5.3 × 10−4 cm/s) because of the stirring effect provided by CO bubbles. This stirring offers a faster surface renewal rate, which surpasses the loss of driving force and then leads to a faster dephosphorization rate.

Nitrogen doped RGO–Co3O4 nanograin cookies: highly porous and robust catalyst for removing nitrophenol from waste water

The fabrication of nanograins with a uniform morphology wrapped with reduced graphene oxide (RGO) in a designed manner is critical for obtaining a large surface, high porosity and efficient catalytic ability at mild conditions. Hybrid structures of metal oxides decorated on two-dimensional (2D) RGO lacked an interface and channels between the individual grains and RGO. The present work focuses on the synthesis of RGO-wrapped Co3O4 nanograin architecture in micron-sized polyhedrons and the ability to reduce aromatic nitro compounds. Doping N in the designed microstructure polyhedrons resulted in very large surface area (1085.6 m2 g−1) and pore density (0.47 m3 g−1) microcages. Binding energies from x-ray photoelectron spectroscopy (XPS) and Raman intensities confirmed the presence of doped N and RGO-wrapped around Co3O4 nanograins. However, the morphology and microstructure was supported by FESEM and HRTEM images revealing the fabrication of high integrity RGO–Co3O4 microstructure hybrids composed of a 10 nm grain size with narrower grain size distribution. Ammonia treatment produced interconnected channels and dumbbell pores that facilitated ion exchange between the catalyst surface and the liquid medium at the grain boundary interfaces, and offered less mass transport resistance providing fast adsorption of reactants and desorption of the product causing surface renewal. Prepared N–RGO–Co3O4 shows the largest percentage reduction (96%) of p-nitrophenol (p-NP) at room temperature as compared to pure Co3O4 and RGO–Co3O4 nanograin microstructures over 10 min. Fabricated architectures can be applied effectively for fast and facile treatment of industrial waste streams with complex organic molecules.

Comparative performances of a bare graphite-polyurethane composite electrode unmodified and modified with graphene and carbon nanotubes in the electrochemical determination of escitalopram

A bare composite graphite-polyurethane electrode (EGPU) and two other modified with graphene (EGPU-GR) and functionalized multi-walled carbon nanotubes (EGPU-CNTs) were prepared and compared regarding their voltammetric response to escitalopran (EST). The modifiers were characterized by Raman spectroscopy and the resulting electrode materials by contact angle measurements with a hydrophilicity character in the ascending order for the composites: GPU > GPU-GR > GPU-CNTs and scanning electron microscopy (SEM). The electroactive areas of the EGPU, EGPU-GR, and EGPU-CNTs were 0.065, 0.080, and 0.092cm2, respectively, calculated from the chronocoulometry using K3[Fe(CN)6] as a probe and the Cottrell equation. The cyclic voltammograms obtained for EST indicated irreversible electrochemical behavior, with an anodic peak at ca. +0.80V (νs. SCE). These measurements were carried out with the three electrodes, and comparison of the analytical responses led to the EGPU-GR electrode being selected for use in the subsequent experiments. Under optimal conditions, square wave and differential pulse voltammetry at EGPU-GR presented linear dynamic ranges between 1.5 × 10−6 and 1.2 × 10−5mol L−1, with a detection limit of 2.5 × 10−7molL−1 (SWV) and 1.5 × 10−6 and 1.2 × 10−5molL−1, with a detection limit of 3.2 × 10−7molL−1 (DPV) for EST. The proposed method was applied for the quantification of EST in synthetic urine and cerebrospinal fluid samples, offering advantages including simplicity of fabrication, no requirement for analyte preconcentration and surface renewal, fast response, and selectivity.

Modeling and data analysis of multistory flat plate quasi-counter-flow membrane dehumidifier

A two-dimensional steady-state heat and mass transfer mathematical model is established to study the performances of air-to-liquid dehumidifier with PVDF ultrafiltration membrane in liquid desiccant dehumidification in this paper. Terms in this mathematical model are amended with experimental data and improved with the method of calculating enthalpy of lithium chloride solution. The mean Nusselt number in air channel and mean Sherwood number are calculated and the correlations are fitted with the relevant quantities for predicting the heat and mass transfer coefficients. Furthermore, the corresponding heat and mass transfer coefficients are obtained and substituted as initial conditions into the mathematical model. Meanwhile, according to the relationship between the moisture content difference and water vapor partial pressure difference between inlet and outlet on air side, the diffusion coefficient is modified to meet the actual situation of the experiment. Joint surface renewal rate is proposed and regarded asa comprehensive index describing the relative motion of the fluids on both sides in the membrane dehumidification process. After analyzing the influences of controlled variables on mass transfer coefficient divided by density, the conclusion is obtained that the variable solution temperature group is inferior to the variable solution concentration group. The importance of maintaining low solution temperature during the dehumidification process is emphasized.

Rate-Based Modeling of CO2 Absorption into Piperazine-Activated Aqueous N -Methyldiethanolamine Solution: Kinetic and Mass Transfer Analysis

A comprehensive two-dimensional mathematical model based on surface renewal theory has been developed to analyze the CO2 absorption into piperazine (PZ)-activated aqueous N-methyldiethanolamine (MDEA) solvent by taking into account the structured packed bed column hydraulics, mass transfer resistances, and chemical reactions. The modeling results have been validated with the experimental data reported in the literature, and they have been found to be in good agreement with the experimental results. The effects of amine concentration, liquid temperature, initial CO2 partial pressure, liquid flow rate, and CO2 loading on the mass transfer performance have been evaluated in terms of overall mass transfer coefficient (KGav). The overall mass transfer coefficient and absorption flux of CO2 into aqueous MDEA+PZ blended solution have been calculated over the CO2 partial pressure range of 4–16 kPa, temperature range of 298–333 K, and solvent concentration of 1–3 M. To evaluate the performance of different solvents on separation process, some common industrial chemical absorbents including monoethanolamine (MEA), diethanolamine (DEA), triethylamine (TEA), MDEA and PZ were compared with a MDEA+PZ blended solution. The results indicate that CO2 absorption reaction with PZ is faster than that with MDEA, but also adding small amounts of PZ as a promoter to MDEA solvents improves significantly the absorption rate. The results show that CO2 absorption reaction with the MDEA+PZ blended solution is faster than that with TEA and MDEA, also comparable with DEA, but slower than those with MEA and PZ. The modeling results illustrate that the KGav enhances with increasing the solvent concentration, liquid temperature, and liquid flow rate, but reduces with increasing the CO2 loading and initial CO2 partial pressure. In addition, the reaction kinetics in terms of enhancement factor was found to decrease as the CO2 loading enhances and increase as the operating temperature rises.