Mass Exchange Processes Research Articles

A design procedure to size thermodynamically-balanced humidification-dehumidification desalination systems

Humidification-dehumidification desalination systems are best suited for small-scale and off-grid applications. The primary drawback of humidification-dehumidification systems is their low thermal performance. Thermodynamic balancing of the heat and mass exchange processes between the humidifier and dehumidifier can substantially improve their performance. The optimal thermal design is still needed; thus, the present study mostly focuses on the design of a thermodynamically-balanced system both with and without extractions. This study starts with the implementation of the temperature-enthalpy diagram model to investigate the effect of system enthalpy pinch and minimum and maximum saltwater temperatures on the performance of zero-, single-, and double-extraction systems. After that, design details are investigated to determine the size of the humidifier and dehumidifier under various conditions and power requirements. It is found that the system performance increases as a function of the heat and mass transfer areas (energy effectiveness) of the humidifier and dehumidifier. The systems’ performance is represented by the gained output ratio, recovery ratio, energy effectiveness, and enthalpy pinch. The gained output ratio of the single- and double-extraction systems is better than that of the zero-extraction system by a factor of 91% and 112%, respectively. The areas of the single- and double-extraction systems are larger than that of the zero extraction system by a factor of about 51% and 80%, respectively.

Determination the capacity of low volume mixers for processing liquid environment

The current state of science and technology requires an increase in the productivity of chemical and oil refining enterprises without increasing the overall dimensions of the main technological equipment, as well as the development of fundamentally new devices capable of intensifying the main heat and mass exchange processes. At the same time, new technological equipment in order to ensure energy-saving operating modes needs to determine dependence of design parameters of the apparatus and properties of the processed medium on power consumption.

Modelling the water phase diffusion experiment at Onkalo (Finland): Insights into the effect of channeling on radionuclide transport and retention

In fractured crystalline rocks, contaminants are transported through open fractures by fluid flow and can access the connected pore space of the adjacent rock matrix by diffusion. The mass exchange term between the fracture and the matrix depends on in-plane groundwater flow patterns. Thus, channeling and preferential flow, due to heterogeneity in fracture aperture, have an impact on the overall rock retention capacity. Here, we have used experimental data from the recent Water Phase Diffusion Experiment, carried out at ONKALO (Finland), to assess the influence of channeling on contaminant transport and retention at increasingly larger scales. The upscaling is performed by extracting non-parametric Retention Time Distribution functions from the experimental data and using them to carry out transport simulations along a segmented pathway. The analysis shows that channeling leads to anomalous early breakthroughs at short scales, whereas at increasingly larger distances this effect is smeared out and the nuclide breakthrough curves become mostly controlled by mass exchange processes between the fracture and the matrix. This homogenisation occurs at shorter scales for sorbing nuclides. The influence of channelling on radionuclide retention is shown to be modest due to compensating effects between the shorter groundwater travel times and the larger specific fracture surface area made available through in-plane diffusion into stagnant water. Also, we have shown that the late-time behaviour of the experimental breakthrough curves can be used to infer equivalent parameters that, combined with existing homogeneous-based solutions, provide a good description of contaminant breakthrough curves at larger downstream distances.

Development of Hierarchical Ensemble Model and Estimates of Soil Water Retention With Global Coverage

AbstractCorrect quantification of mass and energy exchange processes between land surface and atmosphere requires an accurate description of unsaturated soil hydraulic properties. Soil pedotransfer functions (PTFs) have been widely used to predict soil hydraulic parameters. Here, 13 PTFs were grouped according to input data requirements and evaluated against a well‐documented database (National Cooperative Soil Survey Characterization [NCSS]) covering the continental United States (87.7% of data) and other regions of the globe (12.3% of data). Weighted ensembles were shown to have improved performance over individual PTFs in terms of evaluation criteria. Validation of moisture content estimated from the ensemble models against observations showed promising results. Global maps of soil water retention data from the ensemble models as well as their uncertainty were provided. Our full 13‐member ensemble model provides more accurate estimates than PTFs that are currently being used in Earth system models, which may, therefore, provide improved water fluxes and reduce uncertainty of the estimations.

Methodology of mass-exchange processes calculation in steel SA-20A alloying by nitrogen during blow through bottom tuyeres

To alloy steel by nitrogen, any material containing nitrogen in necessary amount and being capable to dissolve in the liquid metal, can be used. Methods of alloying by nitrogen, based on melt blowing through by gaseous nitrogen are known. However to carry out this process it is necessary to have a qualitative estimation of nitrogen behavior at various stages of steelmaking process. It is also necessary to have reliable data on the nitrogen assimilation speed and conditions of its interaction with other melt components. Therefore, elaboration of a methodology of estimation of nitrogen assimilability under conditions of blowing through with stirring and thermo-dynamic conditions of vanadium nitrides formation in the steel SA-20A is rather actual. In the course of methodology elaboration, equilibrium nitrogen concentration was determined accounting parameters of interaction, calculation of stirring power and nitrogen assimilability under set conditions of blowing through were accomplished. Besides, calculations were accomplished on average effective “bubble” coefficient of mass-transfer of nitrogen to liquid steel; duration of blow through by nitrogen under conditions of stirring and thermo-dynamic conditions of VN nitrides formation under equilibrium and industry conditions. The effect of mass-transfer speed on the nitrogen assimilability by steel was shown. It was determined, that blow through parameters and first of all, gaseous nitrogen consumption are determined by a number of bubbles and the area of their surface. Results of the elaborated methodology testing presented. The necessity of specifying the methodology of estimation of gas bubbles evolution in the process of their moving during the bottom blow through justified. Comparison of the obtained data with the industrial data were confirmed by the sufficiency of nitrogen concentration in steel SA-20A for realization of the nitride hardening process.

Solar absorption air conditioning systems based on low temperature evaporative air coolers

The purpose of the study is to develop circuit solutions for alternative air conditioning systems based on the use of low-temperature air coolers. The authors developed circuit diagrams of such air coolers with a reduced limit of evaporative cooling of media from the temperature of the wet thermometer supplied to the cooling of the air flow to the dew point temperature. Air coolers are designed in separate and combined layout options. In this case, heat - mass transfer apparatus with a movable fluidized bed "gas - liquid - solid" were used as a promising direction for the development of heat and mass transfer equipment (HMT). This ensures stable operation in extreme conditions, when there is a risk of contamination and deposits on the working surfaces of HMT, as well as the intensification of heat and mass exchange processes and high uniformity of distribution of contacting gas and liquid flows in the HMT volume, especially for implementing processes in evaporative air coolers with direct placement of the heat exchanger in the apparatus. An experimental study made it possible to establish the optimal range of effective density of the packed elements for the implementation of heat and mass transfer processes in a movable nozzle, characterized by stability and homogeneity, a wide working area in terms of gas flow rate with a relatively small dynamic layer height. Based on the obtained experimental data, a comparative analysis of air conditioning systems based on a low-temperature evaporative air cooler - chiller is carried out. The developed solutions allow expanding the field of practical use of evaporative cooling methods, for example, providing air comfort parameters in the air conditioning system without involving traditional refrigeration equipment, as well as improving the basic environmental and energy characteristics of the developed systems.

Mathematical principles of modeling processes of heat and mass exchange in multiphase media

The paper presents a method for studying the process of heat and mass transfer in multiphase media by the example of constructing mathematical models.

Conceptual issues of the cold filter trap development for the sodium coolant purification in fast-neutron reactors

The paper presents the results of studying the peculiarities of heat and mass exchange in cold traps for the sodium purification of impurities in fast reactor circuits both in dedicated test areas simulating various trap components (isothermal sump, nonisothermal sump, filters, final cooling area) and in trap prototype models. As a result, a scientific rationale has been formed for developing traps of a unique design for various reactors. The impurity capacity of the traps is three to four times as high as that of the best foreign counterparts. Tests have shown these to be highly efficient in purifying sodium of oxygen and hydrogen and much less efficient in sodium purification of corrosion products and carbon. Taking into account the leakage of radioactive sodium during operation of the BN-600 reactor primary circuit traps, a decision was made to install the purification system in the reactor tank to improve the safety of the large fast reactor. It was resolved to exclude the accumulation of hydrogen in the primary circuit traps in nominal conditions. Two trap designs, with argon and sodium cooling, are discussed. It has been shown that operation of the reactor purification system with argon cooling will require 20 trap replacements during the reactor operating life and seven replacements if the deposition of hydrogen into the primary circuit cold traps is excluded. The sodium-cooled version of the trap built in the reactor tank has the same overall dimensions as the argon-cooled trap. The cooling sodium circulates in two trains: outside the jacketed working space body (up to 30% of the flow rate) and in the coil inside of the working space (up to 70% of the flow rate). Updates have been proposed to the trap design based on the calculations using the codes simulating the in-trap processes of heat and mass exchange.

Исследование природы примесей в циркулирующем растворе гликоля на установке очистки газа от кислых компонентов

Natural gas contains a large amount of moisture, which causes a lot of problems in its transportation and processing. In order to extract this moisture, natural gas gets subjected to the dewatering process, thereby reducing the moisture content and preventing further formation of hydrates. This is achieved by cleaning the gas from hydrogen sulfide and mercaptans and cooling in heat exchangers with the participation of a solution of monoethylene glycol. Together with gas, impurities come in the form of hydrocarbons, brine water, mechanical impurities, corrosion inhibitors, various SASs, resinous substances, etc. As a result of deposition of unwanted impurities on the internal surfaces of devices, the efficiency of mass exchange and heat exchange processes is reduced, equipment wear is increased, so is the laborious process of cleaning equipment during planned repairs, the temperature of the glycol block is disrupted and, as a result, the reagent consumption increases in order to maintain the necessary dewatering temperature of natural gas, and the waste of the glycol from the regeneration apparatus increases. The object of the study was the regeneration block of the saturated solution of monoethylene glycol. During the planned repairs of the plant, there was revealed significant contamination of the devices and heat exchange equipment of the glycol regeneration unit with a large number of unwanted impurities and sediments, as well as significant corrosion of pipe beams of heat exchangers and internal cavity of devices. We found that the most effective ways to prevent sediment formation in the monoethylene glycol regeneration unit are to better control the level of amine in the 374 B09 devices, to control the consumption of the amount of monoethylene glycol injected into heat exchangers, and to reduce the amount of impurities in the circulating solution of monoethylene glycol. Also, to reduce sediments in the heat exchange apparatus of the gas dewatering section, we recommend increasing the separation rate by installing jack elements in the 374 B09 separator and installing an additional filter in accordance with the proposed scheme, with a cartridge of polyphenylsulfide or fiberglass.

The Study of Heat and Mass-Exchange Processes during the Drying of Granulate of Hydrophobic Polymers

In this article, the drying characteristics were studied for granules of hydrophobic polymers, in particular, poly (ethylene terephthalate). To analyze the data, the modified quasi-stationary method was used. A modified quasi-stationary method has been proposed to describe drying kinetics of particulate materials dried in convective dryers with active hydrodynamic regimes. Parameters of reduced time and hydrodynamic intensity index were obtained for the generalized drying curve. Equations with refined parameters can be used to calculate the drying time and determine the temporal change in moisture content and material temperature.

ДОСЛІДЖЕННЯ ВПЛИВУ ПОВІТРЯНО-РІДИННОГО СТРУМІНЕВОГО ЗМІШУВАЧА НА РОБОТУ КІЛЬЦЕВОГО БІОРЕАКТОРА

In the production of biological preparations for agriculture there are promising jet bioreactors with an external circulation ring, providing intense mixing of the medium along with a high degree of aeration. However, application of these bioreactors is limited by large shear loads on the microorganisms (microorganism cells) arising in the circulation pump. The article deals with one of the ways for solving this problem by using a low-capacity pump for the circulation of the fermentation medium according to a non-standard scheme of medium jet aeration in order to intensify the mass exchange processes. There are presented results of physical simulation of the mixing parameters of flows in an aerator-jet mixer and their impact upon the intensity of metabolic processes in the circulation ring of a bioreactor.

Quantification of Mineralizable Pool of Organic Matter in Tundra Cryosols of Kolyma Lowland

The cryogenic mass-exchange processes affect the content and distribution of organic matter in Cryosol profiles enriching the mineral horizons with organic matter. It has been shown that the mineralization capacity of organic materials in Cryosols is low even under optimum conditions of temperature and moisture. Despite the significant variation in the microbial biomass content, the general pattern of its distribution in the profile with a maximum in organic horizons and a minimum in mineral horizons is preserved in all studied profiles. The fraction of the microbial biomass carbon (Cₘb) in the total organic carbon is less than 1%. The microbial respiration quotient (Qᵣ) varies from <0.1 to 0.3. The most significant influence on the microbial biomass and changes in its respiration activity in the profiles of Cryosols is recorded for the contents of total organic carbon (TOC) and total nitrogen (TN) and for the soil porosity.

Design of an intelligent controller for a grain dryer: A support vector machines for regression inverse model proportional-integral-derivative controller.

Grain drying control is a challenging task owing to the complex heat and mass exchange process. To precisely control the outlet grain moisture content (MC) of a continuous mixed‐flow grain dryer, in this paper, we proposed a genetically optimized inverse model proportional–integral–derivative (PID) controller based on support vector machines for regression algorithm which is named the GO‐SVR‐IMCPID controller. The structure of the GO‐SVR‐IMCPID controller consists of a genetic optimization algorithm, an indirect inverse model predictive controller, and a PID controller. In addition, to verify the control performances of the proposed controller in the simulation study, we have established a nonlinear mathematical model for the mixed‐flow grain dryer to represent the nonlinear grain drying process. Finally, the control performance and the robustness of the GO‐SVR‐IMCPID controller were simulated and compared with the other controllers. By the simulation results, it is shown that this proposed algorithm can track the target value precisely and has fewer steady errors and strong ability of anti‐interference. Furthermore, it has further confirmed the superiority of the proposed grain drying controller by comparing it with the other controllers.

Mathematical simulation of heat and mass exchange processes during dissociation of gas hydrates in a porous medium

Mathematical simulation of heat and mass exchange processes during dissociation of gas hydrates in a porous medium

INFLUENCE OF VARIOUS FACTORS ON RADIANT AND CONVECTION HEATING OF GREENHOUSE

The traditional heating of greenhouses (based on liquid or air) lacks efficiency, when it concerns energy-saving or economic expenditures. The agricultural industry is therefore inter-ested in the innovative approach to the power supply of greenhouses. The use of geothermal sources, biofuel, heating pumps and other conventional greenhouse heating methods is not al-ways reasonable, as their application depends on location of an object, ecological factors and others. This research investigates a complex heating, when convection heating of the green-house territory is maintained by temperature using ceiling infrared radiators. The aim of the paper is to study the influence of the outdoor air temperature, thermal prop-erties of the perimeter walls and soil surface absorbing capacity on the heating power of a greenhouse within the proposed method of radiant and convection heating. A system of complex heatand material-balance equations is used to calculate the greenhouse perimeter walls and the soil surface. The research results show the dependency of the total heating power when calculated with regard to the outdoor temperature, heat resistance properties of the perimeter walls and the soil surface absorbing capacity. The results obtained can be used to justify the efficiency of the radiant and convection heat-ing of the greenhouse in specific climatic conditions. The scientific novelty of the paper is the proposed method of calculating which accounts of multiple heater reflection, the influence of the mass-exchange process inside the greenhouse as well as the absorbing soil properties.

Optimization of energy costs for drying ferrocene-containing wastes of winemaking

The paper is devoted to the study of the processes of heat and mass exchange, when drying ferrocene containing wastes of winemaking (FWW), and to the preparation of those wastes to be fed to dairy cattle. The goals of the article are: to determine the amount of energy costs for drying FWW that are necessary for calculating the net cost of feed additives, and to estimate the economic efficiency of the suggested technological and technical solutions; and also to justify and develop the methods for estimating quantitative parameters when removing liquid from the wastes of wine production. Moisture and heat exchange are studied in the “heat agent - drying object” system for convective and infrared drying. A combined method is proposed for drying winemaking waste, to substantiate the sequence of stages and parameters of the process, a graph-analytic model, that is dwelled on the basic principles of convective and infrared drying, is designed. Numerical calculations helped to obtain graphical dependences of the energy costs of the drying process on the air velocity in the drying chamber at different temperatures of the air (for convective and infrared). The model of drying in the form of comparative graphical dependences of the reduced value of the drying speed to the heat flux on the moisture content of the mass subjected to drying is presented. Given the above data, it is recommended to use combined two-phase drying: in the first phase, use infrared radiation, when in the second phase - convective way, in order to reduce the humidity of ferrocene containing winemaking wastes from initial moisture content of 80% to the required value of 18-20% with the further use as neutralizing additives in the feed of dairy cattle. It is also suggested to use the renewable energy sources for heating in order to cut the expenses in the phase of convective drying.

Non-linear Equations of Mechanics of Swelling and Metamorphic Processes

Processes of mass transfer (primarily swelling and hydration/dehydration metamorphic processes) between underground fluid and solid phase in porous media in various kinds of rocks (primarily, sedimentary rocks) is examined. Penetration of water in swelling porous media and coupled process of consolidation and physical-chemical interaction between fluid and solid phase are analyzed. It is shown that government equation in this case is non-linear equation of “diffusion—reaction” type. The equation describes the influence of mass exchange processes (for example swelling and metamorphic dehydration) on distribution of pressure in pores, stresses and deformations in rocks.

Fluorescence imaging for mm-scale observation of macropore-matrix mass transfer: Calibration experiments

Macropores are important for gas, water, and heat movement in soils. Still, the transfer of water and solutes through the interface between macropore and matrix like the walls of biopores is less understood. For mass-exchange processes and water storage in soil aggregates, relatively small sizes and volumes limit the analysis of distributed interface properties including the permeability for water or air. Photo-based imaging techniques could perhaps be used to trace the movement of sorbing chemicals at such smaller scale similarly as for larger soil profiles. The objective was to test the suitability of Na-Fluorescein (i.e., fluorescein di sodium salt) for marking small-scaled flow and transport processes through surfaces of biopore walls and coated soil aggregates and for determining water and reactive solute mass exchange.Fluorescence imaging was carried out using fluorescence spectrometer (for aqueous solutions) and a uv/vis photo-based imaging technique for soil and intact biopore and aggregate surfaces of soil samples from the Bt-horizon of a haplic Luvisol. For calibration, a linear relation between fluorescence intensity and initial Na-Fluorescein concentrations could be used for aqueous solutions up to a concentration of 100 mg L−1 Na-Fluorescein. The fluorescence intensities of homogenized soil samples were used to determine the amount of sorbed dye at equilibrium.After calibration, the photo-based imaging technique allows determining mm-scale maps of dye concentrations at intact soil surfaces in both, the dissolved and sorbed fraction of the dye. Uncertainties are caused mainly by effects of fluorescent soil organic carbon that is heterogeneously distributed at biopore wall surfaces. The results suggest that sorption of the dye mostly occurs in the soil region next to the macropore surface. A few high concentration spots at greater distances could be an indication for rapid tracer movement along root channels suggesting occurrence of non-uniform flow and transport even at the scale of soil clods and aggregates.The method seems promising for a small-scale analysis of macropore-matrix exchange of reactive solutes.

Nuclear-Magnetic-Resonance Monitoring of Mass Exchange in a Low-Permeability Matrix/Fracture Model During CO2 Cyclic Injection: A Mechanistic Study

SummaryRecent reports have demonstrated that carbon dioxide (CO2) injection can further raise the oil recovery of fractured tight reservoirs after natural depletion, with major projects in progress worldwide. There is, however, a lack of understanding of the mass-exchange process between the matrix and fracture at pore scale. In this study, a matrix (0.8 md)/fracture model was designed to experimentally simulate a CO2-cyclic-injection process at 80°C and 35 MPa (Lucaogou tight formation). The oil (dead-oil) concentration in the matrix and fracture was continuously monitored online using a low-field nuclear-magnetic-resonance (NMR) technique aiming to quantify the oil recovery in situ and clarify the mass-exchange behaviors. The results showed that CO2 cyclic injection was promising in improving the oil recovery of fractured tight reservoirs. Nevertheless, the oil-recovery rates rapidly declined with the cycle of CO2 injection and the incremental oil was primarily produced by large pores with 100 ms &amp;gt; T2 &amp;gt; 3.0 ms. The NMR T2 profiles of the model evidenced the drainage of the matrix oil by CO2 toward the fracture. Because of the light-hydrocarbon extraction, the produced oils became lighter than the original oil. We noted that the main driving forces of the incremental oil recovery were CO2 displacement, CO2/oil interactions (mainly extraction and solubility), and pressure gradient (depressurization). In the first cycle, the CO2/oil interactions driven by CO2 diffusion during soaking enhanced the mass exchange between the matrix and the fracture. However, from the second cycle, CO2/oil interactions and CO2 displacement became insignificant. The results of this study supplement earlier findings and can provide insights into the CO2-enhanced-oil- recovery (EOR) mechanisms in fractured tight reservoirs.NOTE: Supporting information available.

Optimization and analysis of pressure swing adsorption process for oxygen production from air under uncertainty

Pressure swing adsorption (PSA) units are widely used for atmospheric air separation and oxygen concentration. However, the efficiency of such installations is reduced due to accidental changes in the characteristics of the atmospheric air to be separated. The article formulates and solves the problem of optimizing the regimes of operation of PSA units with zeolite adsorbent 13X, according to the criterion of oxygen recovery rate in the conditions of interval uncertainty of composition, temperature and pressure of atmospheric air. The optimization problem also takes into account the fulfillment of the requirements on purity of oxygen, productivity of the unit and resource saving of granulated adsorbent from granule abrasion. It is proposed to provide adsorbent saving by limiting the speed of incoming flow in the frontal layer of the adsorbent by means of "soft" stepwise change of the degree of opening of control inlet and outlet valves of the unit. The problem (including the search for time change programs for the degree of opening of control valves) was solved with the use of the developed mathematical model of cyclic heat- and mass exchange processes of adsorption-desorption in a PSA unit and a heuristic iterative algorithm. The comparative analysis of the results of the optimization problem solution, with and without taking into account the constraint on the gas flow velocity in the frontal layer of the adsorbent, is carried out. The influence of the specified requirements for the performance of the PSA unit and the purity of oxygen on the degree of its recovery has been studied.