In order to accurately model the impact of a fluid droplet onto a solid surface using the volume of fluid method, an accurate method for the interpolation of viscosity is required because the free surface of a fluid changes significantly during droplet impact. There exist several conventional methods for interpolation including the arithmetic and harmonic means of the viscosities, the harmonic mean of the kinematic viscosities, and the blended arithmetic and harmonic means of the viscosities. In this study, a new method is proposed that combines the arithmetic and harmonic means of the kinematic viscosities. To evaluate the accuracy of these methods, the shape of the liquid films resulting from droplet impacts were evaluated through numerical simulation against previous experimental results, finding that the proposed method resulted in the most accurate behavior. The effect of the droplet impact angle on the shape and extent of the resulting liquid film was then examined by numerical simulation under various impact angles using the proposed interpolation method, finding that the horizontal component of the velocity had little effect on the initial spread of the liquid film, but did indeed affect the geometry and extent of spread after a period of time.
Low-thermal-conductive reaction-bonded silicon nitride (RBSN), with a thermal conductivity of 8.08 W/(m·K), was developed by the addition of mullite micro-powder as a rare-earth-free oxide sintering agent to silicon nitride. This addition was expected to generate a glassy grain boundary as well as a solid solution of oxygen across the microstructure of the RBSN, which leads to low thermal conductivity. During the fabrication of a heat-insulating component with a hollow structure made of the RBSN via slip casting and subsequent reaction sintering, it was found that the viscosity of aqueous silicon-mullite slurries decreased evidently by the addition of the mullite micro-powder with ammonium polycarboxylate as a dispersant. The viscosity decreased even though the pH (7–8) of the slurries were maintained, and the particle size distributions did not vary significantly. At the effective mullite content when the viscosity decrease was attained, the ratio of the number of particles of mullite to silicon was approximately 1. Therefore, the viscosity decrease in Si slurry (50 vol%) was primarily caused by the steric hindrance due to the adsorption of dispersant by the mullite particles, preventing the direct contact among the silicon particles, rather than by electrostatic repulsions among the silicon particles. This was also explained through the modality of bimodal dispersion. Thus, it was found that the mullite not only acts as a sintering agent but also facilitates viscosity decrease of highly concentrated aqueous Si slurry, which successfully enables the integration of the slip casting and reaction sintering processes.
A techno-economic assessment for biogas power generation projects with solid oxide fuel cells (SOFCs) in northern Japan has identified the required scale, required technological improvements and other key factors for making sufficient profit. Dairy cattle manure was assumed as the organic waste for treatment in biogas plants. It was found that, for a 10,000-cattle scale project, if the only income is from the sale of electricity, the installation and maintenance cost of the biogas plant was the greatest contributor (33%), followed by the labor cost of the truck crew (20%) and the installation and maintenance cost of the SOFC (9.8%) on a present value basis calculated with a discount rate of 2% for a 20 year project period. Focused analyses on SOFC suggested that, under the current domestic situation (ca. FIT 40 JPY/kWh), further research and development to improve the durability of the system to at least ca. 12,000 h is recommended. It was also found that profitability is affected by the high treatment cost of liquid fertilizer when more is generated than can be sold. R&D to reduce surplus liquid fertilizer by controlling the digestion process is thus important. Besides the abovementioned technology improvements, to reach the break-even to make sufficient profit, it is also necessary to reduce the other dominant costs (biogas plant cost, waste collection cost) and increase the income (sale of by-products). For example, it is effective to shorten the waste collection distance by increasing the farm size, and to increase the income by selling the by-products. With the developed model, it is now possible to synthesize a profitable business plan for a biogas plant with SOFC, that takes these factors into account in advance, and to direct research efforts towards a wider possibility for use in this application.
Segmented flow crystallization has attracted the attention of engineers in the development of drug substance processes, because the crystallization behavior is different from that observed in conventional stirred tanks. Under segmented flow conditions, the crystal size distribution is narrower, and the crystallization rate is higher than that of batch crystallization. However, the phenomenological theory of segmented flow crystallization has not been clarified. The purpose of this study was to gain more insights into segmented flow crystallization phenomena. We focused on the influence of fluid behavior on crystallization. First, we analyzed the motion of crystals in a segmented flow using computational fluid dynamics. Under the assumption that the mass transfer is the rate-determining step of crystal growth, we evaluated how particle and flow conditions contribute to the mass transfer. The shear rate under segmented flow was found to be approximately 16 times greater than that in a stirred tank. The high shear rate induced a high mass transfer rate, which is often observed under segmented flow conditions.
For material and process design support of porous polymeric membranes synthesized by phase separation and drying process in polymer/solvent/non-solvent systems, a simulation based on phase-field model was performed on the formation of the porous structure in this paper. Although this fabrication process has complicated phenomena including phase separation and drying operation, it was described as the material transfer of each component in a series of operations by simulation using the phase field model with semi-empirical and effective parameters. The simulation results for the formation of skin layer on the membrane surface, which is a problem in preparing separation membranes, has been obtained by analyzing the drying path of the surface. The drying path deeply through the separation concentration region was needed for the porous membrane without the surface skin. This result was in good agreement with the experimental result.
A process for levulinic acid (LA) production from glucose with AlCl3 catalyst in choline chloride aqueous solution has been designed and numerically simulated. Energy and process economics were evaluated. This process minimized waste materials by recovering catalysts and the coproduct formic acid (FA), and utilizing humins as a heat source. Furfural was applied for the LA purification, and octanol and toluene were used as extracting agents for the FA purification process based on the solubility with water, distribution coefficient between water and LA or FA, and green chemistry perspective. The required energy for this process was determined in the case of the glucose feed rate of 100 kg/h and the reaction time of 90, 120, and 180 min based on the literature data. Minimum selling prices (MSPs) of products were calculated based on the capital and operation costs of the production of LA and FA with an internal rate of return of 6.1% in 20 years. It was found that the energy required in this process was 40.6–44.5 MJ/kg-LA (much less than that in conventional methods), and the MSP was 6.47–8.80 USD/kg (lower than the market price of LA). Part of the required energy (12.2–24.7%) can be supplied with a furnace, which combusts humins and accounts for 21% of the total capital cost. It is found that the installing of a humin furnace only affected 0.74–1.09% of the MSP, which should be economically feasible in a practical process. Overall, the reaction time in 90 min was the most preferable process in both energy requirements and economics.