Initial Water Volume Research Articles

Hydrothermal co-gasification of sorghum biomass and çan lignite in mild conditions: An optimization study for high yield hydrogen production

In this study, response surface methodology (RSM) combined with a 3–factor and 3–level Box–Behnken design (BBD) was performed to obtain high yield hydrogen production from hydrothermal co–gasification of sorghum biomass and low rank Çan lignite in a batch type reactor at 500 °C. The individual and the combined effects of the process parameters of coal amount (%) of the coal/biomass mixtures, initial water volume (mL) of the reactor and amount of the coal/biomass mixtures (kg) on system pressure, total gas yield, hydrogen production and product distribution were determined. Water volume directly affected the system pressure and the reaction medium was supercritical water medium above 48.2 mL with a pressure of 22.06 MPa. The highest values of both total gas volume and hydrogen gas volume were reached by gasification of 5.0 g of feedstock. It has been observed that total gas volume and hydrogen volume were directly affected by the water volume in the reactor and the coal ratio of the coal-biomass mixtures. The highest total gas and hydrogen volumes can be achieved under the conditions where the higher levels of water volume of the reactor and lower levels of coal percentage of the coal/biomass mixture were combined. Optimum conditions for maximum hydrogen production with 5.0 g of coal/biomass mixture were determined with numerical optimization as coal percentage of 25.6% and initial water volume of 68.5 mL. By combining the impregnated K2CO3 (3%, (w/w)) and CaO catalysts an excellent hydrogen selectivity was achieved. The hydrogen selectivity was drastically increased from 32.0% to 70.8% by capturing more than 99% of CO2 with a H2/CO2 mol ratio of 88.5.

A numerical investigation of SBLOCA scenario in nuclear heating reactor

ABSTRACT Small break loss of coolant accident (SBLOCA) is one of the most important severe accidents in nuclear heating reactor. Nuclear heating reactor designed by Tsinghua University, whose primary loop is integrated layout and designed without main pump. The initial water volume in the reactor vessel is important to determine whether the reactor will be cooled or not as no safety injection system is designed for coolant makeup during the whole scenario. This paper simulates SBLOCA in nuclear heating reactor based on RELAP5. Transient behavior of relevant thermal parameters is specifically analyzed. Moreover, investigation also has been made on SBLOCA scenario based on different residual heat removal correlations and found the long-term residual heat removal capacity is decisive in determining the loss of coolant. The mathematical form of residual heat removal correlation is specifically deducted and can be widely applied to different situations. The envelope line that differentiates the region whether the core is safe or not under different maximum PRHRS capacity is also given.

Influence of fluidity on mechanical and permeation performances of recycled aggregate mortar

Abstract The use of recycled fine aggregates in making mortar is an effective measure to increase the social and ecological values these days due to the pressing issues associated with the over-exploitation of natural sand as well as disposal of construction and demolition wastes. To counteract the synergetic effects of W/C ratio, recycled fine aggregates quality and its content, fluidity was considered as parameter to formulate the recycled aggregate mortar. The experimental results of this investigation elucidate the effectiveness of fluidity on mechanical and permeation performances of recycled aggregate mortar. A comparison with the outcomes of conventional mortar is also presented. The experimental outcomes reveal that, recycled aggregate mortar requires additional amount of water to attain the same fluidity of controlled mortar due to inferior characteristics of RFA, such as high initial water absorption and volume of voids with in mortar. The setting characteristics of recycled aggregate mortar were influenced by the fluidity, recycled fine aggregates quality and its content and their setting times were earlier than that of controlled mortar. However, recycled aggregate mortar corresponding to the fluidity of 110 ± 2.5 mm and 160 ± 2.5 mm attained lower strength characteristics, lower pulse velocity value, higher permeable void content, higher water absorption by immersion and higher sorptivity than those associated to the fluidity of 135 ± 2.5 mm. Therefore, recycled aggregate mortar associated to the moderate fluidity of 135 ± 2.5 mm is feasible and exhibits better mechanical and permeation performances.

Analysis of start-up and long-term operation characteristics of passive residual heat removal system

Since the passive residual heat removal system (PRHRS) can transfer the decay heat from the core through the passive form and increase the inherent reliability of the system, it has received the attention of many researchers. The present researches mainly focus on the analysis of heat removal characteristics and design optimization, but pay less attention to the start-up and long-term operation characteristics under different conditions. In this paper, the simulation models of the reactor and PRHRS on the secondary side of steam generator are established by the RELAP5/MOD4.0 computer code. The operating characteristics of the PRHRS under the station blackout accident are studied. The results show that the operation of the system is affected significantly by the water level of the pressurizer and the initial water volume of the water tank. Based on the results, the start-up and long-term operation characteristics of the PRHRS are further analyzed. The research results show that, when the injected flow rate of the CMT is large enough, the natural circulation in the primary loop would be interrupted because a lot of residual heat is absorbed by the cool water, but this phenomenon will not threaten the safety of reactor; the different start-up time of the PRHRS has certain influences on the primary loop parameters, with little effect on the final heat derivation; the effective operation time of the PRHRS is strongly dependent on the initial volume of the water in the tank and the introduction of separate heat pipe could greatly reduce the dependence. The research results in this paper have important reference values that are critical for the design and operation of the PRHRS on the secondary side of the steam generator.

Hydrogen production by gasification of Kenaf under subcritical liquid‒vapor phase conditions

In this study, Kenaf biomass was gasified under subcritical liquid-vapor conditions and effect of initial water amount on gas composition and hydrogen production was evaluated at different temperatures. Gasification was carried out in a batch type reactor, with various initial water volumes (0, 12, 25, 50, 75 mL), at different temperatures (250, 275, 300, 325 °C) and with different catalysts (Ru/C, Pt/C, Na2CO3, Fe2O3, CaO, CaCO3 and RuCl3). The results revealed that the gasification efficiency and hydrogen selectivity are dramatically varied with initial water percentage that was fed to the reactor. The gaseous products obtained from hydrothermal gasification of kenaf were mainly H2, CO2, and in lower but varying amounts, CH4 and C2H4. Water soluble RuCl3 was found to be more effective than water insoluble Ru/C catalyst on biomass gasification. RuCl3 catalyst has a high catalytic activity for kenaf gasification with greater H2 selectivity. Maximum total gas (462.5 mL) and H2 mole fraction in the gaseous product (44.5%) were obtained at 250 °C with RuCl3 catalyst. The maximum carbon conversion (%) was also obtained with RuCl3 as 71.3%. Water behaves as both the reaction medium and the second main reactant beside biomass, during the subcritical liquid-vapor phase gasification process.

Thermal performance analysis and optimization design for LNG submerged combustion vaporizer

Submerged combustion vaporizer (SCV) is an efficient and energy-saving liquefied natural gas (LNG) heat exchange facility, which is developed by multiphase flow heat transfer combined with supercritical fluid heat transfer technology. This paper adopted the computational fluid dynamics (CFD) approach to investigate thermal performance of a real-life SCV with the designed handling capacity of 202 t/h. The numerical results and monitoring industrial data were in good agreement, indicting the feasibility of present method. Results displayed that two typical physical processes, namely, hot flue gas and water flowing across stagger tube bundle wall and supercritical LNG gasification, occurred inside the SCV system. The shell-side heat transfer capacity was mainly affected by the initial water level and volume rate of flue gas. Higher inlet LNG velocity could effectively enhance local tube-side heat transfer coefficient, and the maximum value may depend on the inlet LNG pressure. Furthermore, the Han models could be used to predict the overall thermal performance of SCV with a higher accuracy. Eventually, an optimization design method for SCV system was provided.

Modelling extreme desiccation tolerance in a marine tardigrade

It has recently been argued that the enigmatic tardigrades (water bears) will endure until the sun dies, surviving any astrophysical calamities in Earth’s oceans. Yet, our knowledge of stress tolerance among marine tardigrade species is very limited and most investigations revolve around species living in moist habitats on land. Here, we investigate desiccation tolerance in the cosmopolitan marine tidal tardigrade, Echiniscoides sigismundi, providing the first thorough analysis on recovery upon desiccation from seawater. We test the influence on survival of desiccation surface, time spent desiccated (up to 1 year) and initial water volume. We propose analysis methods for survival estimates, which can be used as a future platform for evaluating and analysing recovery rates in organisms subjected to extreme stress. Our data reveal that marine tidal tardigrades tolerate extremely rapid and extended periods of desiccation from seawater supporting the argument that these animals are among the toughest organisms on Earth.

Transient, spatially resolved desaturation of gas diffusion layers measured via synchrotron visualization

The transient 3-D visualization of the desaturation process of flooded gas diffusion layers (GDLs) is presented for the first time. Desaturation rates and pathways are reported for two commercial GDL samples, one with a PTFE treatment and the other without. On-the-fly Synchrotron X-ray CT is performed while the GDL sample is subjected to a humidified or dry air flow stream to visualize the transient desaturation. The two humidification conditions assist in separating the convective and evaporative components of the desaturation process, showing a slight contribution from the convective effect, while the majority of the desaturation is due to evaporative removal. The convective removal is found to be insufficient to fully desaturate either GDL, with water remaining trapped underneath the channel rib with the more hydrophobic GDL and within the pore space in the more hydrophilic GDL. Stop-and-shoot Synchrotron X-ray computed tomography (CT) is then used in conjunction with program-assisted segmentation to determine initial saturation water volumes. These are then combined with the desaturation times found from the on-the-fly experiments to determine desaturation rates for both GDLs. The desaturation rate using dry air flow for the more hydrophobic GDL is found to be nearly four times faster than that of the more hydrophilic GDL. Results demonstrate that an evaporative contribution is necessary for either GDL sample to reach full desaturation.

Studies on water carrying of diesel oil in upward inclined pipes with different inclination angle

The characteristics of oil-water two phase flow in the case of water initially accumulated at low position in upward inclined pipelines were researched. A large scale experiment loop was conducted to analyse the flow characteristics by using a series of 50 mm transparent acrylic bends with different inclination angle (10° ∼ 45° at the interval of 5°). Five flow patterns were identified and a corresponding flow pattern map was established. The same situation was also simulated by using computational fluid dynamics (CFD) techniques, and the results of simulation were validated by comparing with the experimental results. The impact of oil superficial velocity, inclination angle and initial water volume on flow characteristics was further investigated. The results indicate that the backflow effect in water phase is the major factor that causes water accumulation at the bottom of the pipe. The initial residual water volume has no influence on the oil-water flow pattern and the water-carrying capacity of oil. The lower flow rate and the higher inclination angle cause the decrease of water-carrying capacity of oil, resulting in the water accumulation at the low position and internal corrosion of product oil pipelines.

Optimal Stocking Density with the Provision of Self‐feeders for Striped Knifejaw, Oplegnathus fasciatus (Temminck and Schlegel 1844)

AbstractTo determine the optimal stocking density, three densities of 5 (SD5), 10 (SD10), and 15 kg/m3 (SD15) were used to culture striped knifejaw, Oplegnathus fasciatus, for 10 wk. A total of 10, 20, or 30 juveniles with mean weights of approximately 96 g were stocked into one of nine 300‐L tanks (with an initial water volume of 200 L) and fed with commercial feed via self‐feeders. The fish were sampled at 4 and 8 wk, and the stocking density was maintained by adjusting the water volume of the tanks. The final body weights in SD10 and SD15 were 183.8 and 178.9 g, respectively, which were significantly higher than 161.7 g in SD5 (P< 0.05). However, there was no significant difference between the SD10 and SD15 (P > 0.05). A similar trend was observed in the specific growth rate among the treatments. Feed efficiency and the lipid retention efficiency were both significantly higher in SD10 than that in SD5. The plasma levels of cortisol, glucose, and total protein were similar among the treatments. These results clearly suggest that densities of 10 and 15 kg/m3 can be used to improve the growth performance of striped knifejaw, O. fasciatus, when fed with a self‐feeder.

Combustion of a single emulsion fuel droplet in a rapid compression machine

The autoignition and combustion characteristics of a single water/n-decane emulsion droplet were examined using a rapid compression machine. A specific volume ratio of water was added to the n-decane, and a water-in-oil emulsion was formed by ultrasonication. The emulsion droplet was suspended at the tip of a fine thermocouple and placed at the center of the reaction chamber. The time evolutions of droplet temperature and diameter were observed. Droplet combustion was classified into four stages, and the characteristics of each stage varied little with the water volume ratio. Ignition delay increased monotonically with initial droplet diameter and water volume ratio. Increasing the water ratio boosted the intensity of micro explosions, while the rise in droplet temperature was hindered by the specific heat and latent heat of the water. The average burning rate was elevated when the initial droplet diameter increased. However, the burning rate was not affected much by the water volume ratio.

An Experimental Procedure to Estimate Lifetime of Water Drop with Graphite Inclusion under Intensive Vaporization with Explosive Breakup

We developed an experimental setup equipped with tube furnace for continuous heating of heterogeneous drops at a constant temperature and high-speed camera to study characteristics of phase transitions at interfaces of these drops. Also, an experimental procedure was proposed to estimate time characteristics of processes occurring when heated heterogeneous drops in high-temperature environment. As an example, at temperature of heating of 1373 K, lifetime of 15 μl water drop with 1 mm solid inclusion made of natural graphite in high-temperature environment equals almost to 1 s. Experimental data also enabled to reveal minimum temperature at which intensive vaporization of 5 μl, 10 μl and 15 μl drops with inclusions in size of 2×2×2 mm proceeds with explosive breakup. This temperature equals to 803 ± 10 K depending on initial water volume in heterogeneous drops.

The Numerical Modeling of Spherical Explosion in the Foam

The spherical explosion propagation process in aqueous foam with the initial water volume content α10=0.0083 corresponding to the experimental conditions is analyzed numerically. The solution method is based on the one-dimensional two-temperature spherically symmetric model for two-phase gas-liquid mixture. The numerical simulation is built by the shock capturing method and movable Lagrangian grids. The amplitude and the width of the initial pressure pulse are found from the amount of experimental explosive energy. The numerical modeling results are compared to the real experiment. It’s shown, that the foam compression in the shock wave leads to the significant decrease in velocity and in amplitude of the shock wave.

Tunable Pickering emulsions with polymer-grafted lignin nanoparticles (PGLNs)

Lignin is an abundant biopolymer that has native interfacial functions but aggregates strongly in aqueous media. Polyacrylamide was grafted onto kraft lignin nanoparticles using reversible addition–fragmentation chain transfer (RAFT) chemistry to form polymer-grafted lignin nanoparticles (PGLNs) that tune aggregation strength while retaining interfacial activities in forming Pickering emulsions. Polymer graft density on the particle surface, ionic strength, and initial water and cyclohexane volume fractions were varied and found to have profound effects on emulsion characteristics, including emulsion volume fraction, droplet size, and particle interfacial concentration that were attributed to changes in lignin aggregation and hydrophobic interactions. In particular, salt concentration was found to have a significant effect on aggregation, zeta potential, and interfacial tension, which was attributed to changes in solubility of both the kraft lignin and the polyacrylamide grafts. Dynamic light scattering, UV–vis spectroscopy, optical microscopy, and tensiometry were used to quantify emulsion properties and nanoparticle behavior. Under all conditions, the emulsions exhibited relatively fast creaming but were stable against coalescence and Ostwald ripening for a period of months. All emulsions were also oil-in-water (o/w) emulsions, as predicted by the Bancroft rule, and no catastrophic phase inversions were observed for any nanoparticle compositions. We conclude that lower grafting density of polyacrylamide on a lignin core resulted in high levels of interfacial activity, as characterized by higher concentration at the water–cyclohexane interface with a corresponding decrease in interfacial tension. These results indicate that the interfacial properties of polymer-grafted lignin nanoparticles are primarily due to the native hydrophobic interactions of the lignin core. These results suggest that the forces that drive aggregation are also correlated with interfacial activities, and polymer–nanoparticle interactions are critical for optimizing interfacial activities. Controlled radical polymerization is a powerful tool for polymer grafting that can leverage the intrinsic interfacial functions of lignin for the formation of Pickering emulsions.

Laplace pressure evolution and four instabilities in evaporating two-grain liquid bridges

Dynamic variables characterizing evolution during evaporation of capillary bridge between two spheres are analyzed. The variables include: average Laplace pressure, pressure resulting force, surface tension force and total capillary force calculated based on the previously reported geometrical variables using Young-Laplace law [1,2]. This is the first time to our knowledge that Laplace pressure is calculated from the measured bridge curvatures along the process of evaporation and compared to experimental measurement data. A comparison with the experimental data from analogous capillary bridge extension tests is also shown and discussed.The behavior of evaporating liquid bridges is seen as strongly dependent on the grain separation. Initial negative Laplace pressure at small separations is seen to significantly augment during an advanced stage of evaporation, but to turn into positive pressure, after an instability toward the end of the process, and prior to rupture. At larger separations the pressure is positive all the time, changing a little, but rupturing early. Rupture in all cases occurs at positive pressure. However, because of the evolution of the surface area of contact, the resultant total capillary forces are always tensile, and decreasing toward zero in all cases. Comparison between measured total resultant capillary forces and those calculated from the Young-Laplace law is very good, except for some discrepancies at very small separations (below 50μm). Up to four consecutive instabilities of capillary bridge are seen developing at some sphere separations. They are: re-pinning-induced suction (pressure) instability; Rayleigh nodoid/catenoid/unduloid unstable transition, associated with zero-pressure; Rayleigh unduloid/cylinder unstable transition, associated with the formation of a liquid-wire; and lastly, a pinching instability of the liquid-wire, associated with the bridge rupture. Rupture of the bridges is seen at large separations to occur quite early, at only 1/4–1/3 of the initial water volume evaporated. At smallest separations, rupture occurs in a seemingly unstable way when water evaporates from the bridge thinnest section of the neck.

Experimental study of relationship between average isotopic fractionation factor and evaporation rate

Isotopic fractionation is the basis of tracing the water cycle using hydrogen and oxygen isotopes. Isotopic fractionation factors in water evaporating from free water bodies are mainly affected by temperature and relative humidity, and vary significantly with these atmospheric factors over the course of a day. The evaporation rate (E) can reveal the effects of atmospheric factors. Therefore, there should be a certain functional relationship between isotopic fractionation factors and E. An average isotopic fractionation factor (α*) was defined to describe isotopic differences between vapor and liquid phases in evaporation with time intervals of days. The relationship between α* and E based on the isotopic mass balance was investigated through an evaporation pan experiment with no inflow. The experimental results showed that the isotopic compositions of residual water were more enriched with time; α* was affected by air temperature, relative humidity, and other atmospheric factors, and had a strong functional relation with E. The values of α* can be easily calculated with the known values of E, the initial volume of water in the pan, and isotopic compositions of residual water.

Precipitation of calcium carbonate in reverse osmosis retentate flow by means of seeded techniques — A tool to increase recovery

The present work is aimed at development of a new approach to reduce RO concentrate flow and to increase recovery. To increase recovery values, a new process is developed that use continuous crystallization of calcium carbonate at a constant supersaturation level provided by a constant raise of retentate TDS while RO is operated in circulation mode. The described techniques enable us to remove calcium carbonate from RO concentrate by means of “seed” crystallization. These proposed techniques use “open channel” spiral wound membrane modules that can directly treat water with high scaling and fouling potentials without pretreatment. The experimental procedure is described and experimental plots are presented that describe precipitation kinetics. The test membrane unit was operated in circulation mode and recovery values reach 95% or higher. RO concentrate constantly passed through the precipitation reactor where seed crystals were contained. Seed crystal formation was initiated by injecting caustic solution to RO concentrate. The concentrated solution that contains all rejected salts and impurities constitutes no more than 1% of initial feed water volume and can be withdrawn together with wet sludge as sludge moisture.

Effect of cryoprotectant on optimal cooling rate during cryopreservation

The effect of initial Me2SO concentration (cgi) inside the cell lines on the optimal cooling rate is studied using a well established water transport model. A correlation formula is proposed for the determination of optimal cooling rate of freezing biological systems which depends on the cell activation energy, reference membrane permeability, initial Me2SO concentration, and the cell geometrical parameters. Here, the optimal cooling rate is defined as the highest cooling rate for which amount of trapped water inside the cell is equal to 5% of the initial cell water content at an end temperature of −40°C. It is found that the optimal cooling rate varies linearly with the reference membrane permeability and the ratio of surface area for water transport to the initial volume of intracellular water. The developed correlation is valid for cell activation energy between 20 and 80kcal/mole and initial Me2SO concentration between 0.1 and 1.3M. It has been observed that the optimal cooling rate does not follow a single trend for the studied initial concentration of Me2SO. However, three regions are identified within which, the variation is almost similar; the three regions are: 0.1M⩽cgi⩽0.7, 0.7M⩽cgi⩽0.9, and 0.9M⩽cgi⩽1.3M. It has been shown that the predicted optimal cooling rate is in a very good agreement with the published experimental/numerical prediction.

Modernization of conventional spiral wound module—principles to design RO without pretreatment and concentrate effluents

The present work is aimed at development of a new approach to reduce RO concentrate flow and to increase recovery. The described techniques enable us to remove calcium carbonate from RO concentrate by means of “seed” crystallization. These proposed techniques use “open channel” spiral wound membrane modules that can directly treat water with high scaling and fouling potentials without pretreatment. The experimental procedure is described and experimental plots are presented that describe precipitation kinetics. The test membrane unit was operated in circulation mode and recovery values reach 95% or higher. RO concentrate constantly passed through the precipitation reactor where seed crystals were contained. Seed crystal formation was initiated by injecting caustic solution to RO concentrate. The driving force for crystal growth was constantly created by RO process due to increase in calcium and carbonate ion concentration values. Fouling control is achieved by providing sufficient cross-flow velocities, flushings and cleanings. Coagulated suspended matter after membrane flushes is collected, sedimented and finally dewatered. The concentrated solution that contains rejected salts and impurities constitutes not more than 1% of initial feed water volume and can be withdrawn together with wet sludge as sludge moisture. The described technical procedure enables us to completely utilize concentrate and produce quality product water, softened water and sludge.

Measures to Increase Recoveries and Avoid Concentrate Disposal: Principles to Control Scaling and Reduce Concentrate Disposal in Reverse Osmosis Applications

The present work is aimed at development of a new approach to reduce RO concentrate flow and to increase recovery. The described techniques enable us to remove calcium carbonate from RO concentrate by means of "seed" сrystallization. These proposed techniques use "open channel" spiral wound membrane modules that can directly treat water with high scaling and fouling potentials without pretreatment. The experimental procedure is described and experimental plots are presented that describe precipitation kinetics. The test membrane unit was operated in circulation mode and recovery values reach 95% or higher. RO concentrate constantly passed through the precipitation reactor where seed crystals were contained. Seed crystal formation was initiated by injecting caustic solution to RO concentrate. The driving force for crystal growth was constantly created by RO process due to increase of calcium and carbonate ion concentration values. Fouling control is achieved by providing sufficient cross flow velocities, flushings and cleanings. Coagulated suspended matter after membrane flushes is collected, sedimented and finally dewatered. The concentrated solution that contains rejected salts and impurities constitutes no more than 1 per cent of initial feed water volume and can be withdrawn together with wet sludge as a sludge moisture. The described technical procedure enables us to completely utilize concentrate and produce quality product water, softened water and sludge.