Evaporation Rate Constant Research Articles

Characteristics of Spray Atomization for Liquid Droplets Formed Using a Rotary Bell Atomizer

In automotive engineering, paint evaporation is considered one of the major sources of volatile organic compound emission. The rotary bell atomizer (RBA) is a special atomizer used for improved automotive painting. A model to predict the droplet size was developed by combining two already-reported models. Further, the calculated values of evaporation rate constant, K, and the RBA nozzle parameter, K1, for water and clearcoat at room temperature (24 °C) are presented here. K1 was dependent on the flow rate and bell speed, but its variance for clearcoat was less than the measurement uncertainty. The Sauter mean diameter of the particle leaving the RBA at different flow rates and bell speeds can be predicted using K1. The values of K were 1.3 × 10−5 to 2.0 × 10−5 cm2/s for clearcoat and 8.6 × 10−6 to 1.53 × 10 −5 cm2/s for water. A generic model which can anticipate the evaporation rate of droplets with time length was also introduced.

Can formaldehyde contribute to atmospheric new particle formation from sulfuric acid and water?

Though sulfuric acid and ammonia/alkyl amines are recognized as main contributors to new particle formation (NPF), models and observations have indicated that other organic species may be involved. In this study we introduced a suitable flow tube system to investigate the effect of formaldehyde (CH2O) on NPF from sulfuric acid and water at 297 K. Our results showed that nucleation rates are slightly enhanced when adding CH2O of 0.31–2.40 ppbv (in the range of atmospheric CH2O peak concentration) to stable sulfuric acid and water system at relative humidity (RH) of 30%, i.e., a rise of the particle number only by a factor of about 2, which is small in comparison to the millionfold increase caused by methylamine in similar conditions. And the promoting effect was weak under different RH. Cluster growth flux at experimental conditions, obtained from quantum chemistry-based cluster evaporation rate constants applied in a cluster population dynamics model, showed H2SO4-CH2O-based clusters are hard to grow. Therefore, the effect of CH2O on NPF via directly involving in the nucleation can be eliminated. In addition, the derived information may provide new insight into the impact of aldehydes on NPF.

Fixed- and Variable-Temperature Kinetic Models to Predict Evaporation of Petroleum Distillates for Fire Debris Applications

Forensic fire debris analysis focuses on the identification of a foreign ignitable liquid in debris collected from the scene of a suspected intentional fire. Chromatograms of the extracted debris are compared to a suitable reference collection containing chromatograms of unevaporated and evaporated ignitable liquids. However, there is no standardized method for the evaporation of ignitable liquids and the process itself can be time consuming, which limits the number of chromatograms of evaporated liquids included in the reference collection. This work describes the development and application of a variable-temperature kinetic model to predict evaporation rate constants and mathematically predict chromatograms corresponding to evaporated ignitable liquids. First-order evaporation rate constants were calculated for 78 selected compounds in diesel, which were used to develop predictive models of evaporation rates. Fixed-temperature models were developed to predict the rate constants at five temperatures (5, 10, 20, 30, 35 °C), yielding a mean absolute percent error (MAPE) of 10.0%. The variable-temperature model was then created from these data by multiple linear regression, yielding a MAPE of 16.4%. The model was applied to generate a reference collection of predicted chromatograms of diesel and kerosene corresponding to a range of evaporation levels. Using the modeled reference collection, successful identification of the liquid and level of evaporation in a test set of chromatograms was demonstrated.

Effects of temperature and solution composition on evaporation of iodine as a part of estimating volatility of iodine under gamma irradiation

Abstract As a part of evaluating the volatility of iodide ions subjected to gamma irradiation, I2 evaporation experiments were performed with I2 and I– mixed solutions in the temperature range 26–80°C in an open, well-ventilated space. The evaporation of I2 was observed to follow primarily first order kinetics, depending on the I2 concentration. The evaporation rate constant increased rapidly with increase in temperature. The presence of I– slightly reduced the evaporation rate of I2 by forming relatively stable I 3 − . The effect of Cl– at

New particle formation from sulfuric acid and amines: Comparison of monomethylamine, dimethylamine, and trimethylamine

AbstractAmines are bases that originate from both anthropogenic and natural sources, and they are recognized as candidates to participate in atmospheric aerosol particle formation together with sulfuric acid. Monomethylamine, dimethylamine, and trimethylamine (MMA, DMA, and TMA, respectively) have been shown to enhance sulfuric acid‐driven particle formation more efficiently than ammonia, but both theory and laboratory experiments suggest that there are differences in their enhancing potentials. However, as quantitative concentrations and thermochemical properties of different amines remain relatively uncertain, and also for computational reasons, the compounds have been treated as a single surrogate amine species in large‐scale modeling studies. In this work, the differences and similarities of MMA, DMA, and TMA are studied by simulations of molecular cluster formation from sulfuric acid, water, and each of the three amines. Quantum chemistry‐based cluster evaporation rate constants are applied in a cluster population dynamics model to yield cluster concentrations and formation rates at boundary layer conditions. While there are differences, for instance, in the clustering mechanisms and cluster hygroscopicity for the three amines, DMA and TMA can be approximated as a lumped species. Formation of nanometer‐sized particles and its dependence on ambient conditions is roughly similar for these two: both efficiently form clusters with sulfuric acid, and cluster formation is rather insensitive to changes in temperature and relative humidity. Particle formation from sulfuric acid and MMA is weaker and significantly more sensitive to ambient conditions. Therefore, merging MMA together with DMA and TMA introduces inaccuracies in sulfuric acid‐amine particle formation schemes.

Modelling of intermittent microwave convective drying: parameter sensitivity

Abstract The reliability of the predictions of a mathematical model is a prerequisite to its utilization. A multiphase porous media model of intermittent microwave convective drying is developed based on the literature. The model considers the liquid water, gas and solid matrix inside of food. The model is simulated by COMSOL software. Its sensitivity parameter is analysed by changing the parameter values by ±20%, with the exception of several parameters. The sensitivity analysis of the process of the microwave power level shows that each parameter: ambient temperature, effective gas diffusivity, and evaporation rate constant, has significant effects on the process. However, the surface mass, heat transfer coefficient, relative and intrinsic permeability of the gas, and capillary diffusivity of water do not have a considerable effect. The evaporation rate constant has minimal parameter sensitivity with a ±20% value change, until it is changed 10-fold. In all results, the temperature and vapour pressure curves show the same trends as the moisture content curve. However, the water saturation at the medium surface and in the centre show different results. Vapour transfer is the major mass transfer phenomenon that affects the drying process.

Evaporation and decomposition of eutectics of cupric chloride and sodium chloride

The kinetics and mechanisms involved in evaporation and decomposition of CuCl2(s) from the eutectics of CuCl2(s)–NaCl(s) were investigated in this work. Based on DTA/TG, it was found that anhydrous CuCl2(s) was decomposed into CuCl(s) at 455.5 °C; then, the CuCl(s) thus obtained melt at the same temperature. After that small part of the CuCl(l) evaporated at 488.5 °C and most of CuCl(l) aggregated to form Cu3Cl3(l) in the temperature range of 488.5–667.3 °C. The boiling point of Cu3Cl3(l) was 667.3 °C. CuCl2(s) was completely decomposed into CuCl(s) in 20–40 min at 500–650 °C in Ar atmosphere. The evaporation rate constants (k) of CuCl2(s) in the time range of 20–120 min were 0.0018, 0.0072 and 0.0158 mg min−1 at the temperatures of 500, 600 and 650 °C, respectively, which were very close to the corresponding values of CuCl(s). Anhydrous CuCl2(s) reacted with NaCl to form some eutectics with a eutectic point of 374 °C. The k values of the eutectics were about one-tenth and half of those of pure CuCl2 at 600 and 500 °C, respectively. The evaporation of eutectic was inhibited more at a higher temperature of 600 °C. The addition of NaCl significantly inhibited both evaporation and decomposition of CuCl2(s) from the eutectics.

Hydration of the sulfate dianion in size-selected water clusters: From SO42−(H2O)9 to SO42−(H2O)13

Infrared photodissociation (IRPD) spectra of SO42−(H2O)n, n=9–13, recorded in the cooled cell of a Fourier-transform ion cyclotron resonance mass spectrometer, between 2900 and 3800cm−1, are reported. The structures, energetics and infrared spectra of n=9 and 11–13 were investigated by a combination of classical polarizable molecular dynamics and static quantum chemical calculations. Low-energy structures are mainly determined by the strong structuring effect of the sulfate ion, however, the highest cohesion is achieved when strong water–water interactions are present as well. As a result, the sulfate ion in the most stable structures for n=9, 11 and 12 is on the surface of the water cluster. While SO42−(H2O)9 involves a mixture of isomers, the other sizes are found to be described by a single structural family, with the most stable structures of SO42−(H2O)11 and SO42−(H2O)13 deriving from that of SO42−(H2O)12 by removal and addition of a water molecule, respectively, without substantial reorganization. An important feature of these structures is that the number of water molecules in the second solvation sphere increases with cluster size, up to 3 for n=12 and 4 for n=13. This is directly reflected in the IRPD spectra. All spectra display two main features in the 3150–3350 and 3350–3650cm−1 range, plus a small band near 3100cm−1. The 3350–3650cm−1 massif, which includes most bands arising from second sphere molecules, acquires larger intensity relative to that at 3150–3350cm−1 which is mainly composed of stretches in first sphere molecules. Whereas most water molecules have ADD coordination (where A stands for acceptor and D stands for donor of a hydrogen bond), special cases, including DD and AADD account for bands at the red and blue ends of the spectra. Computed IR spectra are able to account for most experimental features, especially when anharmonicities are taken into account for the largest red shifts. Finally, the higher abundance of n=12 relative to other sizes is related to a lower water evaporation rate constant, in good agreement with the water binding energy which is computed to be larger for n=12 than for 13.

Dissolution kinetics of volatile organic compound vapors in water: An integrated experimental and computational study

In this study we performed batch experiments to investigate the dissolution kinetics of trichloroethylene (TCE) and toluene vapors in water at room temperature and atmospheric pressure. The batch systems consisted of a water reservoir and a connected headspace, the latter containing a small glass cylinder filled with pure volatile organic compound (VOC). Results showed that air phase concentrations of both TCE and toluene increased relatively quickly to their maximum values and then became constant. We considered subsequent dissolution into both stirred and unstirred water reservoirs. Results of the stirred experiments showed a quick increase in the VOC concentrations with time up to their solubility limit in water. VOC vapor dissolution was found to be independent of pH. In contrast, salinity had a significant effect on the solubility of TCE and toluene vapors. VOC evaporation and vapor dissolution in the stirred water reservoirs followed first-order rate processes. Observed data could be described well using both simplified analytical solutions, which decoupled the VOC dynamics in the air and water phases, as well as using more complete coupled solutions. However, the estimated evaporation (ke) and dissolution (kd) rate constants differed by up to 70% between the coupled and uncoupled formulations. We also numerically investigated the effects of fluid withdrawal from the small water reservoir due to sampling. While decoupling the VOC air and water phase mass transfer processes produced unreliable estimates of kd, the effects of fluid withdrawal on the estimated rate constants were found to be less important. The unstirred experiments showed a much slower increase in the dissolved VOC concentrations versus time. Molecular diffusion of the VOCs within the aqueous phase became then the limiting factor for mass transfer from air to water. Fluid withdrawal during sampling likely caused some minor convection within the reservoir, which was simulated by increasing the apparent liquid diffusion coefficient.

Key environmental processes affecting the fate of the insecticide chloropyrifos applied to leaves

Chlorpyrifos (CP) is still a commonly employed organophosphorus insecticide worldwide. In semi-arid and Mediterranean climates, applied CP is expected to remain on leaves surfaces for relatively long time due to the lack of summer rains and common use of drip irrigation. The present work examines the loss rate of CP from leaves via different surface processes: evaporation, direct photolysis and reactions with ozone and OH radicals. Laboratory experiments showed that evaporation rate constant of CP increased from 0.109 to 0.492 h−1 with the increase in wind speed up to 4 m/s. First-order rate constant of direct photolysis, measured using a solar simulator, was k’UV = 1.15 (±0.01) x 10−20 cm2 photon−1. Second-order rate constants for the reaction of CP with ozone and OH were measured as 6 × 10−20 and 6 × 10−12 cm3 molecule−1 s−1, respectively. The above rate constants were applied successfully in an outdoor experiment to predict the disappearance of chloropyrifos under specific environmental conditions. Further modeling showed that the insecticide half-life time on exposed surfaces under typical Mediterranean environment will be in the range of 0.9–6.9 h. Evaporation is expected to be the dominant removal path under most environmental conditions, followed by direct photolysis and reaction with OH.

Microgravity experiments of fuel droplet evaporation in sub- and supercritical environments

Droplet evaporation in sub- and supercritical environments has been studied experimentally under microgravity conditions. A single suspended droplet of n-hexadecane was employed for the experiments. The initial droplet diameter was 0.4mm. A pair of alumina/silica fibers of 7µm in diameter was applied to suspend a droplet. The ambient pressure was varied in the range of 1.0–3.0MPa, and the ambient temperature was set at 773K. Sequential backlit images of an evaporating droplet were recorded using a high-speed digital video camera. Temporal variations in the droplet diameter were measured using a self-made computer-aided image analyzer. Microgravity conditions were produced by a 50-m drop tower. Temporal variations in the droplet diameter were successfully obtained for droplet evaporations in the supercritical environments. The normalized droplet lifetime increased with the ambient pressure. The evaporation rate constant increased with the ambient pressure, reached the maximum value at an ambient pressure slightly above the critical pressure of the fuel, and then decreased. The initial heat-up period linearly increased with the ambient pressure, reached the maximum value at an ambient pressure of 2.0MPa, and then decreased. The ratio of the initial heat-up period to droplet lifetime increased with the ambient pressure, reached the maximum value of about 0.6 at an ambient pressure of 2.0MPa, and then decreased. The droplet evaporation lifetime increased with the ambient pressure at subcritical ambient pressures even though the evaporation rate constant increased because the increase in the initial heat-up period overtook the decrease in the quasi-steady evaporation period. It was found that, in the case of fuels with a high critical temperature, the initial heat-up period determines the ambient pressure dependence of the droplet evaporation lifetime in the environments around the critical point of the fuel.

Effect of initial temperature on actual elemental evaporation rate in Al-Si-Cu mixture during free cooling in near-vacuum conditions

Freezing aluminum alloys in vacuum conditions could be an effective method to improve its chemical composition. Aluminum has a lower vapour pressure than most unwanted elements while values for major alloying elements are significantly below the corresponding aluminum vapour pressure curve. Here we formalize and calculate parameters for the elemental evaporation rate constants in the freezing Al-Si-Cu system. The highest evaporations were measured for Hg, Zn and Pb while no elemental losses for Si, Cu or Ni were recorded for temperatures below 760 °C. Notwithstanding the known positive effect on mechanical properties, freezing aluminum based mixtures from 760 °C in near-vacuum conditions can significantly reduce concentrations of most unwanted elements without affecting established procedures and capacities.

One-dimensional comparison of numerical approaches on two-phase flow in the membrane electrode assembly of PEMFC

Numerical simulation of two-phase flow is important for the performance evaluation of proton exchange membrane fuel cell (PEMFC). Exchange of water between vapor and liquid phases in the gas diffusion layer (GDL) was considered by Nguyen and co-workers (2000) using the evaporation and condensation rate constants. Hsuen and Yin (2011), in which a pseudo-phase-equilibrium function approximates the vapor/liquid phase equilibrium, proposed another two-phase flow approach. Both methods are capable of predicting the cell performance and the species concentration profiles in the membrane electrode assembly (MEA) without the need to track liquid water front in the GDL explicitly. The present study compares the numerical results of these two approaches in detail. In addition, one-dimensional simplified semi-analytical solution based on the instantaneous phase equilibrium assumption is used to validate the numerical calculations. The evaporation/condensation approach allows the existence of super-saturated vapor near the interface of cathode GDL and membrane. Thus, membrane can be better hydrated near the interface once liquid water emerges in the GDL as compared to the pseudo-phase equilibrium method. Consequently, smaller ohmic resistance and hence better cell performance are observed with Nguyen's prediction once liquid water appears in the GDL.

INVESTIGATION OF THE EVAPORATION PROCESSES OF COMPONENTS OF CHROMIUM-CONTAINING MELTS BY LOW TEMPERATURE PLASMA TREATMENT

The article describes the studies the evaporation of components in molten iron and Fe – Cr, Fe – Ni, Fe – Cr – Ni systems in plasma spot area during processing of low-temperature argon plasma treatment. A series of experiments was carried out with different weights of the treated metal. changing the arc power of the plasma torch determine the conditions under which stability of treated metal surface is achieved. The results showed that for the experimental conditions under which the plasma flow completely washes the surface of the metal droplets are most suitable: arc power is not less than 2.0 kW and metal sample mass is in the range of 5 to 10 grams. The dependence between evaporation process and chemical composition of melts was studied. Also, evaporation rate constants were determined. It was found that the greatest rate of evaporation in a neutral atmosphere of a laboratory plasma furnace have Fe – Cr – Ni. It was determined the temperature of the melt surface by the indirect method – the evaporation rate. The surface temperature of the melt which was treated by plasma torch varied in the range from 1950 to 2100 K for changing the arc power in the range of 1.6 to 2.4 kW.

The fate of pesticide on tea plant and the prediction of pesticide residue in fresh leaves of tea plant

The degradative kinetics of pesticides on tea plant surface are characterized by an initial rapid degradation which follows a first-order kinetics, then transferred to a more slower degradative rate. The degradative process mainly consists of photodegradation, evaporation, rainfall elution and growth dilution. The influencing parameters of these processes were investigated on tea plant. The predictive model of the initial concentration, photodegradation rate constant, evaporation rate constant, rainfall elution rate, growth dilution rate and the total degradative rate was discussed and verified in four locations situated in the range of 25°-30°N latitude, and acceptable results were obtained.

Drop evaporation on superhydrophobic PTFE surfaces driven by contact line dynamics

In the present study, we experimentally study the evaporation modes and kinetics of sessile drops of water on highly hydrophobic surfaces (contact angle ∼160°), heated to temperatures ranging between 40° and 70°C. These surfaces were initially constructed by means of controlled tailoring of polytetrafluoroethylene (PTFE) substrates. The evaporation of droplets was observed to occur in three distinct phases, which were the same for the different substrate temperatures. The drops started to evaporate in the constant contact radius (CCR) mode, then switched to a more complex mode characterized by a set of stick–slip events accompanied by a decrease in contact angle, and finally shifted to a mixed mode in which the contact radius and contact angle decreased simultaneously until the drops had completely evaporated. It is shown that in the case of superhydrophobic surfaces, the energy barriers (per unit length) associated with the stick–slip motion of a drop ranges in the nJm−1 scale. Furthermore, analysis of the evaporation rates, determined from experimental data show that, even in the CCR mode, a linear relationship between V2/3 and the evaporation time is verified. The values of the evaporation rate constants are found to be higher in the pinned contact line regime (the CCR mode) than in the moving contact line regime. This behavior is attributed to the drop’s higher surface to volume ratio in the CCR mode.

Heat and mass transport during microwave heating of mashed potato in domestic oven--model development, validation, and sensitivity analysis.

A 3-dimensional finite-element model coupling electromagnetics and heat and mass transfer was developed to understand the interactions between the microwaves and fresh mashed potato in a 500 mL tray. The model was validated by performing heating of mashed potato from 25 °C on a rotating turntable in a microwave oven, rated at 1200 W, for 3 min. The simulated spatial temperature profiles on the top and bottom layer of the mashed potato showed similar hot and cold spots when compared to the thermal images acquired by an infrared camera. Transient temperature profiles at 6 locations collected by fiber-optic sensors showed good agreement with predicted results, with the root mean square error ranging from 1.6 to 11.7 °C. The predicted total moisture loss matched well with the observed result. Several input parameters, such as the evaporation rate constant, the intrinsic permeability of water and gas, and the diffusion coefficient of water and gas, are not readily available for mashed potato, and they cannot be easily measured experimentally. Reported values for raw potato were used as baseline values. A sensitivity analysis of these input parameters on the temperature profiles and the total moisture loss was evaluated by changing the baseline values to their 10% and 1000%. The sensitivity analysis showed that the gas diffusion coefficient, intrinsic water permeability, and the evaporation rate constant greatly influenced the predicted temperature and total moisture loss, while the intrinsic gas permeability and the water diffusion coefficient had little influence. This model can be used by the food product developers to understand microwave heating of food products spatially and temporally. This tool will allow food product developers to design food package systems that would heat more uniformly in various microwave ovens. The sensitivity analysis of this study will help us determine the most significant parameters that need to be measured accurately for reliable model prediction.

Evaporation Mechanism of Sn and SnS from Liquid Fe: Part II: Residual Site and Evaporation Kinetics via Sn(g) and SnS(g)

Evaporation of Sn from molten steel was experimentally investigated for Fe-Sn-S alloy with low initial S (0.0007 < [pct S]0 < 0.05) or with high initial S (0.55 < [pct S]0 < 0.894) at 1873 K (1600 °C) using an electromagnetic levitation melting technique, in order to clarify the role of S on the evaporation mechanism of Sn. It was found that increasing initial S concentration, [pct S]0, decreased the second-order evaporation rate constant of Sn (k SnS), but there was a residual rate for the evaporation even at high [pct S]0. The obtained residual rate constant, $$ k_{\text{SnS}}^{\text{r}} $$ , was 1.4 × 10−9 m4 mol−1 s−1 at 1873 K (1600 °C). Evaporation of Sn under virtually no S condition ([pct S]0 = 0.0007) was also measured and corresponding first-order rate constant was determined to be 3.49 × 10−7 m s−1 at 1873 K (1600 °C). A comprehensive model for the Sn evaporation from molten Fe-Sn-S alloy was developed in the present study, under the condition where mass transfer in gas and liquid phases were fast and interfacial chemical reaction controlled the evaporation of Sn. The model equation is able to represent the evaporation of Sn in the forms of Sn(g) and SnS(g) simultaneously, from very low S melt (when there is no S) to very high S melt investigated in the present study up to ~0.9 mass pct. Gradual transition of major evaporation species from SnS(g) to Sn(g) was well accounted for by the developed model.

Gas chromatographic retention index as a basis for predicting evaporation rates of complex mixtures

Models that predict the fate of petroleum fuels in the environment are often required for effective remediation of fuel-contaminated sites. In this research, an environmental fuel spill was simulated by means of a diesel/water microcosm, in which the temporal changes in composition were assessed during evaporation by gas chromatography–mass spectrometry (GC–MS). First-order kinetic rate constants were calculated for 51 selected compounds and utilized to develop predictive models for evaporation rate constants, using GC retention indices on a nonpolar stationary phase. Models were initially developed to predict rates of evaporation of compounds from individual classes (normal alkane, branched alkane, alkyl benzene, and polycyclic hydrocarbon) and then expanded to include all compounds (comprehensive model). Using the comprehensive model, the rate constants were predicted with a mean absolute percent error (MAPE) of 10%, whereas the class-specific models resulted in less error (4–8%). These models were employed to predict the fraction remaining of the total fuel (6% error) as well as the fraction remaining of individual compounds (13% MAPE). Accurate models such as these will facilitate remediation of environmental releases of petroleum products.

A comparison of numerical methods on the two-phase flow in PEMFCs

Numerical simulation of two-phase flow is important for the performance evaluation of proton exchange membrane fuel cells (PEMFCs). Exchange of water between vapor and liquid phases in the gas diffusion layer (GDL) was considered by Nguyen and co-workers using the evaporation and condensation rate constants. Such an approach has been widely employed by many followers on the two-phase modeling of PEMFCs. However, the effect of water exchange rate parameters on the modeling results has never been evaluated. Another two-phase flow approach was proposed by Hsuen and Yin, in which a pseudo-phase-equilibrium function is used to approximate the vapor/liquid phase equilibrium. This method gives reasonable species profiles in the GDL and the expected polarization curves at various degrees of inlet humidification. The present study compares the numerical results of these two approaches in detail. Both 1-D and 2-D results reveal that these two methods provide accurate predictions of the overall cathode performance as long as the rate constants for water evaporation/condensation in the Nguyen's method are large enough. It was shown that profiles of liquid water saturation, water evaporation rate, water vapor flux and liquid water flux evaluated by these two methods exhibit quite different characteristics particularly in the region nearby the water front. However, the effects of such variations are averaged out within the GDL such that the polarization curves calculated using these two methods are almost identical. Although 2-D numerical results cannot be validated by any analytical means, a simplified 1-D exact solution is feasible to justify the accuracy of the proposed numerical approaches.