Heat and Mass Transfer during Microwave Steam Treatment of Contaminated Soils

A time-dependent mechanistic model has been developed to describe the coupled heat and mass transfer during microwave steam treatment of contaminated soils. The model consists of multiphase mass and energy conservation equations, along with various temperature-dependent parameterizations of important physical state properties. The coupled nonlinear equations were solved numerically by applying a macroscopic control volume method with the appropriate boundary and initial conditions and using a finite-difference scheme. Microwave heating experiments of soil samples were performed. The effects of microwave power, soil sample depth, and soil type on water evaporation rate and temperature were measured with time. The modeled results are in good agreement with the experimental data. The results revealed that microwave power density and soil sample depth significantly affect the microwave evaporation process of water from soils. Water evaporation rate and temperature variation are complex and associated with the dielectric properties of liquid water distributed within the soil. The deeper the soil sample, the more nonuniform the evaporation process, although nonuniformities diminish as the evaporation process approaches completion. Finally it was verified that soil types and their thermal properties play a minor role, provided that the soil minerals are microwave transparent.     

面向船舶多种余热梯级利用的TEG-ORC联合循环性能

传统的温差发电（TEG）和有机朗肯循环（ORC）等技术难以兼顾船舶多种性质余热的不同特点,且利用率较低。本文提出了一种TEG-ORC联合循环船舶余热梯级利用系统,研究了ORC底循环蒸发压力变化对系统输出功率、热效率、多级余热利用量和成本等重要性能的影响。结果表明,TEG-ORC联合循环实现了发电成本和热效率的优化,在TEG/ORC底循环比为0.615的工况下,主机烟气余热利用率随ORC蒸发压力的增加在小区间波动,系统的余热利用功率、输出功率和热效率均随ORC蒸发压力的增加而增大,系统单位发电成本随ORC蒸发压力的增加而降低。在ORC蒸发压力达到0.9 MPa时,主机烟气余热利用率为62.15%,余热利用功率为1919.68 W,输出功率为139.22 W,热效率为7.25%,单位发电成本为3.09 ￥·(kW·h)–1。      

Vacuum Evaporation of Pure Metals

Theories on the evaporation of pure substances are reviewed and applied to study vacuum evaporation of pure metals. It is shown that there is good agreement between different theories for weak evaporation, whereas there are differences under intensive evaporation conditions. For weak evaporation, the evaporation coefficient in Hertz-Knudsen equation is 1.66. Vapor velocity as a function of the pressure is calculated applying several theories. If a condensing surface is less than one collision length from the evaporating surface, the Hertz-Knudsen equation applies. For a case where the condensing surface is not close to the evaporating surface, a pressure criterion for intensive evaporation is introduced, called the effective vacuum pressure, p _eff. It is a fraction of the vapor pressure of the pure metal. The vacuum evaporation rate should not be affected by pressure changes below p _eff, so that in lower pressures below p _eff, the evaporation flux is constant and equal to a fraction of the maximum evaporation flux given by Hertz-Knudsen equation as 0.844 $ \dot{n}_{\hbox{Max} } $ . Experimental data on the evaporation of liquid and solid metals are included.     

Estimating Evaporation Using ANFIS

Water resources engineering assessment requires simple but effective evaporation estimation procedures, especially from readily measurable meteorological factors. Unfortunately, such approaches are rather scarce in the literature. In this paper, an adaptive neural-based fuzzy inference system (ANFIS) was applied to daily meteorology data from the Lake E?irdir region in the southwestern part of Turkey. Daily evaporation, solar radiation, air and water temperatures, and relative humidity measurements were used to develop the ANFIS method, which helps to assess possible contributions that each input variable has on the evaporation estimates. Such an assessment is not possible by any conventional procedure including the Penman method. However, the Penman method daily evaporation estimations were used as output data for the verification of the ANFIS approach. Classical evaporation estimation models treat the data individually. However, ANFIS models process past data collectively and then adaptively provide estimates as new sets of data become available. In the ANFIS architecture as developed in this paper, there are four measured input variables and one output variable to estimate evaporation. The estimation results from the ANFIS model had a high coefficient of determination of 0.98 when compared with the Penman method results and a low average performance error of 4.6% among other alternatives. The average performance error is less than the practically acceptable limit of 10%.     

Evaporation of reaction-zone components in the low-temperature plasma treatment of chromium-bearing melts

The evaporation of iron, Fe–Cr, Fe–Ni, and Fe–Cr–Ni melts at the plasma spot in treatment by low-temperature argon plasma is studied. Experiments with different masses of metal and with variation in arc power of the plasmatron are conducted so as to determine the conditions corresponding to stable surface temperature of the metal. The results show that, for experiments in which the plasma flux completely exposes the surface of the metal droplet, arc power no less than 2.0 kW is optimal; the mass of the metal should be 5?10 g. The evaporation process is studied as function of the melt composition, and the evaporation rates are determined. Of the alloys considered, Fe–Cr–Ni melt is characterized by the highest evaporation rate in the neutral atmosphere of a laboratory plasma furnace. The surface temperature of the melt is determined indirectly, on the basis of the evaporation rate. The surface temperature of the plasma-treated melt is found to vary in the range 1950–2100 K with variation in arc power from 1.6 to 2.4 kW.     

Diffusion models for evaporation losses during electron-beam melting of alpha/beta-titanium alloys

An analysis of the evaporation of aluminum during electron-beam melting (EBM) of alpha/beta-titanium alloys was performed. The analysis was based on the solution of the one-dimensional diffusion equation for the solute-concentration gradient in the melt pool subject to the flux boundary condition for the evaporation rate at the melt surface quantified using the Langmuir equation. The effect of process parameters and material coefficients (e.g., the diffusivity and solute activity in the melt) on predicted concentration gradients and melt losses under steady-state melting conditions was established for both the finite-domain and the semi-infinite-domain diffusion problems. The accuracy of the modeling approach was validated by comparison to previous measurements for the EBM of alloys with a nominal Ti-6Al-4V composition.     

Performance Study of SPAW Model with Temperature-Derived ET0 as Input in Place of Pan Evaporation under Wheat Crop in a Semiarid Subtropical Climate

In this study, we have attempted to enhance the utility of soil–plant–atmosphere–water (SPAW) model that has been used successfully by various workers in different countries for soil moisture prediction under different cropping conditions. One of the major climatic inputs for SPAW model is pan evaporation, which in many places is not readily available. To address the above, and to get the benefit of this model in regions characterized by limited weather data availability, this study was undertaken using computed ET0 from air temperature by the 1985 Hargreaves equation, as one of the inputs in place of pan evaporation. For the purpose, actual air temperature collected from experimental farm area, as well as forecast air temperature collected from National Centre for Medium Range Weather Forecasting, Government of India, were used. First, the SPAW model was calibrated and its performance was evaluated under wheat, taking layerwise and profile soil moisture as the variables for comparison between the predicted and observed values. The results showed that the root-mean-square error (RMSE) varied from 0.30?to?0.58?cm for measured values ranging between 2.24 and 4.25?cm. The index of agreement (d) varied from 0.81 to 0.92 and coefficient of determination (r2) from 0.46 to 0.73 for 0–15, 15–30, 30–45, and 45–60?cm soil depths. For the whole 60?cm profile, the RMSE was 1.07?cm with d and r2 values of 0.94 and 0.85 respectively. The RMSE and d varied from 0.36?to?0.63?cm and 0.77 to 0.89 respectively when ET0 computed from actual air temperature was used in place of pan evaporation, where as when ET0 computed from forecast air temperature data was used, the corresponding values were 0.35–0.64?cm and 0.68–0.85 respectively for the four soil layers. There was a tendency of the models to underestimate when the computed ET0 was used as input in place of pan evaporation. In general, performance of the models were better at lower depths.     

Application of Artificial Intelligence to Estimate Daily Pan Evaporation Using Available and Estimated Climatic Data in the Khozestan Province (South Western Iran)

Estimation of evaporation, a major component of the hydrologic cycle, is required for a variety of purposes in water resources development and management. This paper investigates the abilities of genetic programming (GP) to improve the accuracy of daily evaporation estimation. In the first part of the study, different GP models, comprising various combinations of daily climatic variables, namely, air temperature, sunshine hours, wind speed, and relative humidity, were developed to evaluate the degree of the effect of each variable on daily pan evaporation. A dynamic modeling of evaporation was also performed, with the current climatic variables and one of the previous variables, to evaluate the effect of their time series on evaporation. In the second part of the study, the estimated solar radiation data were used as input vectors instead of recorded sunshine values. Statistics such as correlation coefficient (R), root mean square error (RMSE), coefficient of residual mass (CRM) and scatter index (SI) were used to measure the performance of models. Tthe dynamic model approach was shown to give the best results with relatively fewer errors and higher correlations. To assess the ability of GP relative to the neuro-fuzzy (NF) and artificial neural networks (ANN), several NF and ANN models were developed by using the same data set. The obtained results showed the superiority of GP to the NF and ANN approaches. The Stephen-Stewart and Christiansen methods were also considered for comparison. The results indicated that the proposed GP model performed quite well in modeling evaporation processes from the available climatic data. The results also showed that the estimated solar radiation data can be applied successfully instead of the recorded sunshine data.     

Vacuum evaporation of KCl-NaCl salts: Part II. vaporization-rate model and experimental results

A model based on the Hertz-Langmuir relation is used to describe how evaporation rates of the binary KCl-NaCl system change with time. The effective evaporation coefficient (α), which is a ratio of the actual evaporation rate to the theoretical maximum, was obtained for the KCl-NaCl system using this model. In the temperature range of 640 °C to 760 °C, the effective evaporation coefficient ranges from ～0.4 to 0.1 for evaporation experiments conducted at 0.13 Pa. At temperatures below the melting point, the lower evaporation coefficients are suggested to result from the more complex path that a molecule needs to follow before escaping to the gas phase. At the higher liquid temperatures, the decreasing evaporation coefficients result from a combination of the increasing vaporflow resistances and the heat-transfer effects at the evaporation surface and the condensate layer. The microanalysis of the condensate verified that composition of the condensate changes with time, consistent with the model calculation. The microstructural examination revealed that the vaporate may have condensed as a single solution phase, which upon cooling forms fine lamellar structures of the equilibrium KCl and NaCl phases. In conclusion, the optimum design of the evaporation process and equipment must take the mass and heat transfer factors and equipment materials issues into consideration.     

Nanomaterials of SHS technology for tribological applications: A review

A review of results of applying the powder technology of self-propagating high-temperature synthesis (SHS) for obtaining various nanomaterials that can be used according to the tribotechnical indentation is given. First, these are low-cost nanopowders of sulfides, oxides, nitrides, carbides, borides, and metals which are suitable as solid lubricants and friction modifiers for liquid and plastic lubricating materials. Second, these are solid compact nanostructured ceramic and composite materials for the fabrication of tribotechnical construction. This type of nanomaterial can be fabricated both ex situ from SHS nanopowders by sintering or introduction into the melt both in situ in one stage from initial powders reagents by gasostatic SHS technology, forced SHS compaction, SHS casting, and SHS in the melt, which considerably simplifies and cheapens the production of such materials. Third, these are SHS materials for the deposition of nanostructured coatings of various thicknesses with a high wear resistance and low friction coefficients, such as nanostructured materials for surfacing and spraying, electrospark alloying electrodes, multicomponent targets for magnetron sputtering, cathodes for vacuum-arc evaporation, and nanodispersed fillers of electrochemical and chemical coatings.     

Investigating the surface of particles of ultradispersed copper powders obtained by gas-phase condensation

Ultradispersed powders of metal copper obtained by evaporation-condensation technology are investigated. It is shown that, depending on the evaporation rate, various dispersities and degrees of agglomeration of copper powders are attained with the conservation of the weight fraction of copper in them no lower than 99.0%. It is established using the XPES method that a 5- to 6-nm-thick CuO layer (on the surface of which there is a Cu₂O layer up to 1 nm thick) is always present on the surface of Cu particles of all powders under consideration. It is assumed that, because of a low residual air pressure in industrial installations, the surface layer of copper oxidizes to the lower oxide Cu₂O during the evaporation of metal, while oxide CuO is formed as a result of the decomposition of Cu₂O during the condensation of copper particles. The smaller the particle size of the powder is, the higher the content of oxides is.     

Experimental Study of Evaporation from Saline Tailings

Many of the mining operations in Western Australia are located in arid and semiarid regions where there is a severe scarcity of freshwater. Most of the processing is carried out using ground water from paleochannels. Much of this ground water is very saline, with concentrations approaching saturation in many cases. The potential rates of evaporation in the region can be very high (over 3 m∕year). With careful management, tailings deposited subaereally in this region can achieve high strengths and densities due to evaporation. However, high salinity results in a severe reduction in the rate of evaporation from the tailings, thereby inhibiting consolidation due to evaporation. This paper presents the results of laboratory evaporation tests carried out to examine the mechanisms by which this reduction occurs. In these tests, all tailings samples with saline water formed salt crusts on the surfaces during evaporation, resulting in evaporation rates that were markedly low compared with those from equivalent freshwater tailings samples. This was the case even if the salinity was low. From measurements made on these samples, it is concluded that the most important mechanisms for reduction due to the salt crust are the increase in surface reflectivity and the increase in the surface resistance to moisture transfer. The vapor pressure reduction in the air due to the salinity of the tailings water is also a factor.     

Thermodynamic Consideration of the Removal of Iron from Titanium Ore by Selective Chlorination

Thermodynamic study of the chlorination reactions of oxides such as titanium oxides and iron oxides at elevated temperatures was carried out in order to consider the removal of iron from titanium ore using selective chlorination method. In particular, various chlorination reactions were analyzed by utilizing chemical potential diagrams, and the applicability and usefulness of this thermodynamic study for analyzing the selective chlorination of titanium ore were demonstrated. Furthermore, chlorination reactions using various types of chlorinating agents were discussed from different viewpoints. It was shown that the selective chlorination of iron from titanium ore by HCl gas is thermodynamically feasible and efficient for upgrading titanium ore. Further, thermodynamic analysis showed that under certain conditions, TiCl₄ can be used as a chlorinating agent for the iron in the ore, and iron can be removed by evaporation directly from the ore as chloride gas. The results presented in this study provide useful information for developing a process for upgrading low-grade titanium ore for use as a titanium smelting feed through a dry method.     

Thermal Treatment for Incinerator Ash: Evaporation and Leaching Rates of Metals

The disposal of different residues containing high concentrations of heavy metals causes environmental problems. To understand the effects of various properties of the residues on the evaporation and leaching rates of heavy metals (Cd, Pb, Zn, Cr, and Cu) by thermal treatment, three types of residues (including bottom ash, spray dryer ash, and baghouse ash) generated from various incineration conditions including spray dryer additives (SiO2, CaCl2, and NaHCO3), and feedstock additives [polyvinyl chloride (PVC), and NaCl] were investigated in the present study. The results indicated that the evaporation rate of Cd and Pb in the spray dryer ash and in the baghouse ash was higher than that in the bottom ash. The leaching rate of heavy metals in the spray dryer ash was less than 20% before the thermal treatment when Ca(OH)2 was used in the spray dryer. The addition of PVC could increase the evaporation rate of Zn in the spray dryer ash, whereas the addition of NaCl could decrease the leaching rate of Zn and Cu in the baghouse ash after the thermal treatment.     

Elimination of inclusions and evaporation control during melting of Ti-48Al-2Cr-2Nb-1B intermetallic alloy

Titanium aluminide intermetallic compounds have an excellent capability for use in engineering structures at high temperatures. In the present work the formation of Nb rich inclusions in microstructure and evaporation of Al during melting of γ-TiAl based alloy (Ti-48Al-2Cr-2Nb-1B (at %)) was studied. The results show that the inclusions cannot be removed even with a four-stage melting process, when elemental Nb is used as raw material. However, by replacing Nb with NbAl₃ and using a three-stage melting process, the inclusions were removed from microstructure and also evaporation of Al was reduced remarkably. Otherwise, with removing elemental Al from raw material by using TiAl compound, evaporation of Al will be very low. Increasing vessel pressure from 400 to 600 mbar will not influence evaporation of Al. The article is published in the original.     

Field Investigation of Evaporation from Freshwater Tailings

Safe and economical storage of tailings is now a major consideration in the operation of many mining operations. Tailings in slurried form, particularly if they have a significant clay content, can take a very long time to consolidate under the action of self-weight consolidation alone. However, if the operation is located in an area of high potential evaporation, this can be used to accelerate the rate of tailings densification. This paper presents a study of the evaporation behavior of a clayey tailings slurry deposited into an evaporation pond in the southwest of Western Australia. Over a six-month period, the rate of evaporation from the tailings surface was monitored using the Bowen Ratio method and the microlysimeter method. This was compared with the evaporation from a Class A pan located nearby. The tailings underwent very significant cracking as drying proceeded, and it was found that these cracks had a significant influence on the overall rate of evaporation once the top surface of the deposit started to desaturate. A large strain consolidation model was used to model the behavior, and the algorithm used in this model to include the effects of evaporation is shown to provide a reasonable prediction of the observed evaporation behavior.     

Data Mining Process for Integrated Evaporation Model

The purpose of this study is to develop an integrating evaporation estimation model using a data mining process for the Lakes District in the southern part of Turkey. Lakes E?irdir, Kovada, and Karaca?ren Dam are located in the Lakes District. The proposed data mining process is applied on these lakes for evaporation estimation. The daily pan evaporation data used in the data mining process are taken from State Hydraulic Works in southern Turkey. These data cover an 8-year period between 1998 and 2005 inclusively for daily pan evaporation of Lakes E?irdir, Kovada, and Karaca?ren Dam. It is known that a developed integrated daily pan evaporation model is necessary for these lakes, which are so important to the Lakes District. Therefore, a data mining model having two inputs and one output is developed. Input parameters used in the developed models for Lakes E?irdir, Kovada, and Karaca?ren Dam were daily pan evaporation values of Lakes Kovada + Karaca?ren Dam, Lakes E?irdir + Karaca?ren Dam, and Lakes E?irdir Kovada, respectively. As a result, in comparing the developed models with measured daily pan evaporation values, the REP tree model has better agreement with measured daily pan evaporation than other models. The results show the developed model was more accurate.     

FAO-56 Dual Crop Coefficient Method for Estimating Evaporation from Soil and Application Extensions

Crop coefficient curves provide simple, reproducible means to estimate crop evapotranspiration (ET) from weather-based reference ET values. The dual crop coefficient (Kc) method of the Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) is intended to improve daily simulation of crop ET by considering separately the contribution of evaporation from soil. The dual method utilizes “basal” crop coefficients representing ET from crops having a dry soil surface and separately predicts evaporation from bare soil based on a water balance of the soil surface layer. Three extensions to the evaporation calculation procedure are described here that are intended to improve accuracy when applications warrant the extra complexity. The first extension uses parallel water balances representing the portion of the soil surface wetted by irrigation and precipitation together and the portion wetted by precipitation alone. The second extension uses three “stages” for surface drying and provides for application to deep cracking soils. The third extension predicts the extraction of the transpiration component from the soil surface layer. Sensitivity and analyses and illustrations indicate moderate sensitivity of daily calculated ET to application of the extensions. The dual Kc procedure, although relatively simple computationally and structurally, estimates daily ET as measured by lysimeter relatively well for periods of bare soil and partial and full vegetation cover.     

Water Flow through Cover Soils Using Modeling and Experimental Methods

The vertical flow of water in cover soils is simulated using published analytical and finite-element methods. The two methods gave virtually identical pressure head and water content profiles during steady infiltration of water in a multilayer soil cover and transient infiltration in a single-layer cover. The finite-element model was then used to simulate flow in two laboratory columns packed with multilayer soils and subjected to downward drainage and conditions of evaporation and no evaporation. The model adequately predicted transient pressure heads and water contents for the first 7.5 h of drainage in a till-sand layer without evaporation. Predictions at times equal to and greater than 3 days were not as good, probably due to the formation of discontinuous water pockets in the draining sand around the residual water content, which apparently produced “locked-in” or “static” nonequilibrium pressures. These pressures are not captured by existing methods used for estimating the unsaturated hydraulic conductivity–pressure function of soils. Further modeling showed that at times greater than 8 days, the flux from the column with evaporation was all in the vapor phase.     

脱硫废水烟道喷射的数值模拟

以某电厂300 MW燃煤机组为例,对脱硫废水烟道喷射系统进行CFD数值模拟,研究了雾化粒径、烟气温度、烟气流速和喷枪布置方式对液滴蒸发的影响。结果表明:雾化粒径明显影响液滴群蒸发质量百分比和蒸发时间,在较低的烟温下(140℃),需要较小的雾化粒径(≤50μm)才能保证液滴完全蒸发;烟气温度对液滴群蒸发质量百分比和蒸发时间的影响显著,随着烟气温度升高,液滴蒸发速率加快,蒸发时间明显减少;烟气流速对液滴蒸发特性影响不大,随着烟气流速升高,烟气量增大,液滴群蒸发时间会降低,而液滴群蒸发质量百分比变化不大;在烟道同一截面处,不同喷枪布置方式对液滴蒸发影响小。