Search Results (127)

Transpiration cooling that utilizes the phase change of a liquid coolant is recognized as an effective thermal protection technique for extreme environments. However, the introduction of phase change within the porous structure brings about challenges, such as vapor blockage, pressure fluctuations, and temperature inversion, which critically influence system reliability. This study conducts numerical analyses of coupled processes of heat transfer, flow, and phase change in transpiration cooling using a Two-Phase Mixture Model. The simulation incorporates a Local Thermal Non-Equilibrium approach to capture the distinct temperature fields of the solid and fluid phases, enabling accurate prediction of the thermal response within two-phase and single-phase regions. The results reveal that under low heat flux, dominant capillary action suppresses dry-out and expands the two-phase region. Conversely, high heat flux causes vaporization to overwhelm the capillary supply, forming a superheated vapor layer and constricting the two-phase zone. The analysis also explains a paradoxical pressure drop, where an initial increase in flow rate reduces pressure loss by suppressing the high-viscosity vapor phase. Furthermore, a local temperature inversion, where the fluid becomes hotter than the solid matrix, is identified and attributed to vapor counterflow and its subsequent condensation. Full article

Isobaric vapor-liquid equilibrium (VLE) data for binary mixtures of biomass–derived ethyl levulinate and ethanol were measured using an apparatus comprising a modified Rose-Williams still and a condensation system. Measurements were taken at temperatures ranging from 329.58 K to 470.00 K and pressures of 40.0, 60.0 and 80.0 kPa. The thermodynamic consistency of the VLE data was evaluated using the Redlich-Kister area test, the Fredenslund test and the Van Ness point-to-point test. The data was correlated using three activity coefficient models: Wilson, NRTL and UNIQUAC. The Gibbs energy of mixing of the VLE data was analyzed to verify the suitability of the binary interaction parameters of these models. The activity coefficients and excess Gibbs free energy, calculated from the VLE experimental data and model correlation results, were analyzed to evaluate the models’ fit and the non–ideality of the binary system. The accuracy of the regression results was also assessed based on the root mean square deviation (RMSD) and average absolute deviation (AAD) for both temperature and the vapor phase mole fraction of ethyl levulinate. The results indicate that the NRTL model provided the best fit to the experimental data. Notably, the experimental data showed strong correlation with the predictions of all three models, suggesting their reliability for practical application. Full article

Vapor–liquid equilibrium (VLE) experimental data are reported for three binary systems: isobutanol + 1-butanol, isobutanol + 2-ethyl-1-hexanol, and 1-butanol + 2-ethyl-1-hexanol. Due to the limited and incomplete data available in the literature, we determined the p-T-x experimental VLE data for these binaries using an equilibrium apparatus, designed and built in our laboratory, which had been used extensively in various determinations. The temperature and pressure ranges for determining the VLE data are as follows: (305.15–388.15) K and (2.284–99.779) kPa for the isobutanol + 1-butanol system, (305.15–455.15) K and (2.284–99.779) kPa for the isobutanol + 2-ethyl-1-hexanol, and (320.15–455.15) K and (3.635–98.039) kPa for the 1-butanol + 2-ethyl-1-hexanol. The experimental VLE data for these binary systems were regressed using the nonrandom two-liquid (NRTL) model. The results indicate a reasonably good agreement between the model and the experimental data, with maximum deviations of 7% in the liquid-phase composition of the most volatile component from the binary and 4.5% in pressure. Full article

Zero-liquid discharge (ZLD) of desulfurization wastewater from coal-fired power plants is a critical challenge in the thermal power industry. Flash evaporation technology provides an efficient method for wastewater concentration and the recovery of high-quality freshwater resources. In this study, numerical simulations of the high-temperature and high-pressure spray flash evaporation process within a flash tank were conducted using the Discrete Phase Model (DPM) and a self-developed heat and mass transfer model for superheated droplets under depressurization conditions. The effects of feedwater temperature, pressure, nozzle spray angle, and mass flow rate on spray flash evaporation characteristics were systematically analyzed. Key findings reveal that (1) feedwater temperature is the dominant factor, with the vaporization rate significantly increasing from 19.78% to 55.88% as temperature rises from 240 °C to 360 °C; (2) higher pressure reduces equilibrium time (flash evaporation is complete within 6 ms) but shows negligible impact on final vaporization efficiency (stabilized at 33.93%); (3) increasing the spray angle provides limited improvement to water recovery efficiency (<1%); (4) an optimal mass flow rate exists (0.2 t/h), achieving a peak vaporization rate of 42.6% due to balanced evaporation space utilization. This work provides valuable insights for industrial applications in desulfurization wastewater treatment. Full article

The thermodynamic properties of di-2-ethylhexylphosphoric acid (D2EHPA) in organic solvents are critical for optimizing metal extraction processes in hydrometallurgy, necessitating precise determination of activity coefficients in binary systems such as D2EHPA–n-hexane. This study was devoted to the determination of n-hexane’s concentrations in the vapor phase over D2EHPA solutions at 293.0 K using gas chromatography (GC) and isopiestic (IP) methods. Comparison with literature data confirmed the superior reliability of GC measurements at low n-hexane concentrations. The experimentally determined activity coefficients of hexane, obtained via GC, served as the initial input parameters for UNIFAC modeling. The optimized interaction parameters were 1144 ± 25 (CH₂-HPO₄) and 228 ± 50 (HPO₄-CH₂), with the infinite dilution activity coefficient for D2EHPA ${\gamma }_{\infty }=22.1$. These results experimentally clarify the non-ideal behavior of D2EHPA–n-hexane mixtures, establishing a validated thermodynamic modeling framework for organophosphorus extractant systems. This work establishes a fundamental basis for investigating ternary systems, such as D2EHPA–aliphatic solvent–aromatic solvent and D2EHPA–metal complex–solvent systems, paving the way for enhanced liquid–liquid extraction efficiency. Full article

The diastereoselectivity of the liquid- and vapor-phase Catalytic Transfer Hydrogenation (CTH) of cyclic ketones: x-methylcyclohexanones (x = 2, 3 or 4), 4-t-butylcyclohexanone, and bicyclic ketones: 2-norbornanone, camphor, fenchone, and a tricyclic ketone (2-adamantanone) with secondary alkanols (2-propanol, 2-butanol, 2-pentanol, or 2-octanol) as hydrogen donors in the presence of ten metal oxides as the catalysts was studied. Among the oxides, only four, namely, MgO, ZrO₂·nH₂O, ZrO₂, and Al₂O₃, exhibited good or high activity. The reaction products are diastereoisomeric alcohols, the relative ratio of which depends on the structure of the ketone, mode of reaction, temperature, and, in the liquid-phase mode, reaction time. The results of vapor-phase CTH revealed that, in this mode of reaction, the diastereoselectivity to the trans isomer is lower than in the liquid phase. For the three x-methylcyclohexanones, the most pronounced difference between the experimental values and reference values was noted for x = 3. For bicyclic ketones, the implementation of heterogeneous catalysts allowed us to obtain a substantial excess of the less favorable diastereomer. In the case of 2-norbornanone, the thermodynamic equilibrium mixture contains 21% endo and 79% exo alcohols, whereas our product mixtures contained up to 79% of the endo isomer. Full article

2-Methyl-2-cyclopentenone (MCP) is the main by-product of the newly developed heterogeneous catalysis process for producing crotonaldehyde, which serves as an important intermediate for drug synthesis. However, how to recover and purify MCP from the product mixture is not known. To decipher this, a computer-aided process based on the measured phase-equilibrium data was developed. The improved Rose–Williams equilibrium kettle was used to measure the vapor–liquid equilibrium data for MCP–crotonaldehyde and MCP–water. Surprisingly, MCP and water formed a minimum azeotrope, which aided its own recovery from its dilute solution. The mole fraction of MCP in the azeotrope was 9.1%, the mole fraction of water was 90.9%, and the azeotropic temperature was 96.8 °C. Equilibrium data from the two binary systems were correlated using the Wilson and NRTL activity coefficient models. The NRTL-RK model was selected to simulate the process for recovering and purifying MCP. A two-column process was developed and optimized in this study, and the aim of effectively utilizing the by-product MCP was achieved with this process. Full article

Moisture phase change (MPC), a key process in bread baking, significantly impacts heat and mass transfer, as confirmed by experiments. However, existing models poorly characterize this phenomenon, and its quantitative impact on baking needs systematic study. This research develops a coupled multiphase model for heat and mass transfer with large deformation, employing both equilibrium and nonequilibrium approaches to describe MPC in closed and open pores, respectively. Experimentally calibrated pore-opening functions and viscosity variations revealed that pore-opening primarily occurs at 71–81 °C, whereas dough solidification occurs at 50–110 °C. Model-based analysis indicates that in closed pores, evaporation–diffusion–condensation is the primary mode of moisture transport and heat transfer with contributing approximately 60% of the total effective thermal conductivity, and when pores open, water vapor evaporates or condenses on pore walls, forming an ‘evaporation front’ and ‘condensation front’. The content of liquid water increases at the ‘condensation front’ and decreases at the ‘evaporation front’. Bread deformation is predominantly governed by pressure differentials between closed pores and the ambient environment, with the partial pressure of water vapor emerging as the principal driver because its average content exceeds 70% within closed pores. These findings demonstrate that MPC governs heat and mass transfer and deformation during bread baking. Full article

A typical head–disk interface of hard drives can feature pressures exceeding 50 atmospheres, where the non-ideal gas effects can play an important role. One possible consequence is a change in the rate of water evaporation from the disk. This report describes a semi-analytical procedure that employs the concept of fugacity to investigate the non-ideal gas effects on the saturation pressure of water at an elevated temperature and pressure. A vapor–liquid equilibrium equation is solved to derive the saturation pressure. The results show a deviation from the ideal gas law, which is further examined through saturation pressure isotherms. At areas of low temperature and high pressure, lighter gases such as helium show about a 10% deviation from the ideal gas law, whereas heavier gases such as nitrogen deviate by up to 100%. As temperature increases, the differences between the gases decrease. Full article

In this work we propose a method of geochemical feed zone (FZ) analysis based on the assumption of thermochemical equilibrium between geothermal fluids and hydrothermal minerals, for each FZ contributing to well discharge. Using our method, it is possible to calculate the mass fraction and the chemistry of each FZ fluid, namely (1) the pH and the concentrations of SiO₂, CO₂, Na, K, Ca, Mg, HCO₃, SO₄, F, and Cl of FZ liquids, and (2) the concentrations of SiO₂ and CO₂ of FZ vapors. The method can be applied to wells with two single-phase FZs and to wells with either three single-phase FZs or two FZs, one single-phase and the other two-phase, with different temperature and fluid chemistry. Full article

The vapor–liquid equilibrium (VLE) data of the ternary system methanol–methyl formate–methylal was measured at atmospheric pressure using a modified Rose equilibrium kettle with vapor–liquid double circulation method. The experiment data were correlated with the NRTL, UNIQUAC, and Wilson activity coefficient model equations. The results shown that the root mean square deviation (RMSD) between the calculated and simulated values of the three models followed the order: UNIQUAC ≈ NRTL < Wilson, and except for the RMSD (T) in the range of 0.4–0.5, the others are less than 0.01. In addition, the NRTL model was selected to link with Aspen Plus software to simulate the separation process of polyformaldehyde (POM) waste liquid. The simulation results show that the methyl formate in POM waste stream can be purified by simple distillation, while the methylal separated from the POM waste liquid, which was affected by factors like the azeotropic behavior of binary components, necessitates a complex distillation process. Under optimal operating conditions, the recovery yield of methyl formate through direct distillation can reach 99.7%, with an economic benefit of 6960.1 CNY per ton of waste liquid. Although the economic benefit of the multi-component distillation reach 7281.2 CNY, the increase in the number of equipment and the complexity of the process have negative impacts. Full article

In this study, vapor–liquid equilibrium (VLE) experimental data were measured for two binary solvents based on 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU), which can be used as a new CO₂-binding organic liquids (CO₂-BOLs) solvent. No experimental data are available in the literature and are fundamental to determine whether the considered mixtures are suitable to be possible alternatives to traditional amine solutions for CO₂ removal. The bubble point data of 1,2-propanediol+1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) and 1,4-butanediol+DBU mixtures were measured at 30 kPa. The experimental determination was carried out in an all-glass dynamic recirculation still at the Process Thermodynamics laboratory (PT lab) of Politecnico di Milano. The thermodynamic modeling of the VLE behavior of two DBU-based mixtures was performed considering the NRTL, the UNIQUAC, and the Wilson models, and binary interaction parameters of the NRTL activity coefficients model were regressed on the basis of the measured experimental data. Full article

CO₂ removal, especially the one applied to reduce the emissions of CO₂ to the atmosphere (carbon capture, utilization, and storage), is one of the main research topics nowadays because of its great contribution to the reduction in climate change and to making many industrial processes sustainable. In this regard, alternative solvents to the traditional ones are under study with the aim of employing a more sustainable solvent for the environment, health, and society, in comparison with the traditional amine aqueous solutions that are toxic and corrosive. The CO₂-binding organic liquids (CO₂-BOLs) are a class of components of interest. In this work, the vapor–liquid equilibrium (VLE) data for two newly selected binary mixtures based on CO₂-BOLs, 1,3-Propanediol+DBU and DBU+Sulfolane, have been experimentally determined at the Process Thermodynamics laboratory (PT lab) of Politecnico di Milano to evaluate the suitability of these mixtures for being a solvent for CO₂ removal. All the experiments have been carried out by using the Fischer^® Labodest^® VLLE 602 unit at a constant pressure of 30 kPa. The densities of the mixtures for all the considered compositions have been determined at atmospheric pressure with a density meter (Mettler Toledo Densito Density2Go). No data on the VLE of these mixtures can be found in the literature. This is the first work focusing on mixtures of these components that could be employed as solvents for CO₂ removal as alternative solvents to the monoethanolamine (MEA) aqueous solution in the process of chemical absorption. The collected experimental data have then been used for the definition of the thermodynamic model by considering different possible theories (NRTL, Wilson, and UNIQUAC) that could be employed for the representation of the two systems. Full article

This research deals with gas hydrates formation and dissociation within a marine quartz-based porous sediment and in batch conditions. Hydrates were formed with small-chain hydrocarbons included in natural gas mixtures: methane and also ethane and propane. The dissociation values were collected and provided both graphically and numerically. The results were then compared with the theoretical hydrate-liquid-vapor phase boundary equilibrium for the same species, defined according to the existing literature. The deviation of the experimental results from the ideal ones, associated with the porous sediment, was quantified and discussed. For the scope, the grain size distribution and chemical composition of the sediment were provided along with the text. The results proved that the different size of guest species and, consequently, the different hydrate structures formed, played a relevant role in determining the promoting, inhibiting or neutral behavior of the porous sediment during the process. Full article

Measurements taken on a historical dike in the Netherlands over one year showed that interaction with the atmosphere led to oscillation of the piezometric surface of about 0.7 m. The observation raised concerns about the long-term performance of similar dikes and promoted a deeper investigation of the response of the cover layer to increasing climatic stresses. An experimental and numerical study was undertaken, which included an investigation in the laboratory of the unsaturated behavior of a scaled replica of the field cover. A sample extracted from the top clayey layer in the dike was subjected to eight drying and wetting cycles in a HYPROP™ device. Data recorded during the test provide an indication of the delayed response with depth during evaporation and infiltration. The measurements taken during this continuous dynamic process were simulated by means of a finite element discretization of the time-dependent coupled thermohydraulic response. The results of the numerical simulations are affected by the way in which the environmental loads are translated into numerical boundary conditions. Here, it was chosen to model drying considering only the transport of water vapor after equilibrium with the room atmosphere, while water in the liquid phase was added upon wetting. The simulation was able to reproduce the water mass balance exchange observed during four complete drying–wetting cycles, although the simulated drying rate was faster than the observed one. The numerical curves describing suction, the amount of vapor and temperature are identical, confirming that vapor generation and its equilibrium is control the hydraulic response of the material. Vapor generation and diffusion depend on temperature; therefore, correct characterization of the thermal properties of the soil is of paramount importance when dealing with evaporation and related non-steady equilibrium states. Full article