The mixing process in a 0.42-m diameter transparent stirred tank with improved double Intermig impellers was experimentally studied using the decolorization method with four different tracer injection points. The time dependence of the tracer concentration distribution was recorded using a high-speed camera. The turbulent flow and tracer dispersion were calculated by a large eddy simulation (LES) combined with the dynamic Smagorinsky–Lilly model. The tracer diffusion process, tracer concentration response, and mixing time in the tank stirred with the improved double Intermig impellers were investigated. The results showed that the mixing process predicted by LES was consistent with that by the decolorization method experiment. The predicted mixing time was 14% longer than the experimental time. The mixing time was the shortest when the injection point was in the middle of two impellers. The mixing time increased when the injection point moved to the top or bottom of the tank. The mixing times at the monitoring points near the injection point were shorter than those at distant points. The bottom of the tank with the improved double Intermig impellers was the crucial region that was difficult to mix. The mixing times at the monitoring points at the bottom were the longest for all the injection points. Increasing the mixing speed could promote the mixing process of the medium in the stirred tank and reduce the mixing time without changing the flow field structure. Therefore, the results could serve as a guide for the design and engineering application of such a stirred tank.
In this work, forced convection heat transfer from a heated rotating cylinder in a stream of a Bingham plastic fluid has been investigated numerically over wide ranges of Reynolds number (0.1≤Re≤40), Prandtl number (10≤Pr≤100), Bingham number (0≤Bn≤103) and dimensionless rotational velocity (0≤α≤5). The results are presented in terms of the isotherm contours and Nusselt number (local and average). Also, the effects of the cylinder rotation and fluid yield stress are examined on the relative increase or decrease in the rate of heat transfer relative to a stationary cylinder (α=0) and in a Newtonian fluid (Bn=0). At high Bingham numbers, heat transfer increases more than 100% with respect to the value in Newtonian fluids and approximately by 70% over and above its value for a stationary cylinder. Finally, the Nusselt number results have been consolidated as a function of Re, Pr, Bn and α via a simple expression.
In this paper, the transient behavior of a super low specific speed centrifugal pump, with the specific speed of 25, during startup period under shut-off condition and rapid depressurization process at the pump inlet is experimentally studied. The pump performance and vibration are tested under given transient operating conditions. The experimental results show that the motor speed linearly increases when the pump started up with different accelerated speeds under shut-off condition, and reaches its highest value at the end of the startup. Meanwhile, an obvious impact head at the end of the acceleration process is found, and then declines as the startup becomes steady. The main fluctuation frequencies of the vibration acceleration in the X, Y, and Z directions at the outlet are shaft frequency or integer times of shaft frequency during the startup period with shut-off condition. The vibration acceleration amplitude had the largest component in the X direction, while the smallest component was in the Z direction. As the acceleration of startup increased, the vibration acceleration amplitude also increased with the main frequency. Compared with the instantaneous depressurization process and the stable non-cavitation condition, there is a broadband vibration ranging from 4000 Hz to 6000 Hz. The abrupt reduction of the inlet pressure of the super low specific speed centrifugal pump will accelerate the cavitation. The results provide references for further study of the transient characteristics of the super low specific speed centrifugal pump.
The importance of eco-friendly energy sources such as natural gas is increasing globally. This study comprehensively evaluated the economic feasibility of three alternative regasification systems for new entrants in the floating storage regasification unit (FSRU) business. Life cycle cost analysis with risk expenditure was selected to compare the regasification unit `options. Further, the regasification characteristics were categorized by heating methods. Failure and accident risk expenditure concepts were also used to optimize the choice of regasification unit. This study revealed that the regasification unit with seawater-based direct heating exhibited the highest production availability with simple schematics. On the other hand, the regasification unit with propane-based indirect heating presented the largest accident risk expenditure because of the usage of propane as an intermediate heating medium. Overall, the regasification unit using glycol/water-based indirect heating provided the optimum choice for application to an FSRU, with reasonable capital, operational, and risk expenditures.
Eight organic solvents were examined for use during biocrude extraction from native microalgae cultivated at Minamisoma City, Fukushima prefecture, which is located in the cool temperature zone of Japan. Differences in biocrude yields attained by using the different organic solvents were found to correlate well with the Hildebrand solubility parameter. Biocrude yields comparable to those obtained with high-temperature extraction were attained during solvent extraction at ambient temperature for 24 h without cell disruption by sonication, which suggests that the solvent process could be easy to scale-up. Furthermore, upon fractionation with a silica gel column, chloroform : methanol (2 : 1, v/v), methanol : hexane (2 : 1, v/v), and methanol extracts exhibited similar lipid distribution profiles. The results indicated that differences in extraction yield were related to the cell wall penetration capabilities of the solvents. Hexane extract was found to be more selective for neutral lipids. Furthermore, the obtained biocrude products were characterized based on their thermogravimetric profiles. Biocrude extracted with methanol attained the highest yield (11.4%) and exhibited better thermogravimetric properties than the biocrude prepared with the other solvents. The results with native microalgae cultivated in the cool temperate zone of Japan not only exhibited reasonable yields (1.5–11.4%, dry ash-free basis), but also showed good thermogravimetric properties.
Process safety of hazardous phosgenation reactions during industrial chemical production is a critical issue. We herein have designed a compact flow reaction process for phosgenation reactions and successfully installed the system at a commercial plant. The hold-up of phosgene was significantly reduced and a leakage detecting system was incorporated in the commercial process. A scale-up method for determining the mixing condition of the commercial-scale flow reactor was the most important task in this study. The Villermaux–Dushman reaction was employed to evaluate the mixing performance of the T-shaped mixers with the mixer outlet diameter, Dm ranging from 0.5×10−3 to 15.0×10−3 m. The scale-up condition was determined by the absorbance of the Villermaux–Dushman reaction solution. Utilizing the experimental results, a diagram of the mixing performance in terms of Dm and the flow rate was obtained. It was found that the fluid segment size Wc (=Dm/20.5) in a T-shaped mixer, and the Reynolds number of the mixer flow Re are important parameters for mixing in the T-shaped mixers. We derived the correlation between the mixing performance and Wc/Ren. It was found that all of the mixers utilized in this study had the same correlation with an n value of 1.19. We also confirmed that the derived equation is applicable for scaling up the T-shaped mixers.
To obtain calcium phosphates—a phosphate rock equivalent—from the incineration ash of chicken manure, which is obtained from power generation systems that use the manure as fuel, the incineration ash was treated with an aqueous solution of nitric acid to elute phosphorus. By using 0.3 M HNO3, most of the phosphorus could be eluted from 1.0 g of ash within 0.1 h. Unlike in the case of composted chicken manure which was previously examined in our laboratory, the concentration of HNO3 was increased for elution from the incineration ash. The use of incineration ash of chicken manure enabled the removal of inorganic species at a lower boiling or sublimation temperature, and organic species by calcination in the power generation system. The phosphorus contents of the incineration ash and nitric acid extract were higher than that of composted chicken manure. XRD analysis showed that the treatment of the obtained nitric acid extract with aqueous NH3 yielded a precipitate of poorly-crystallized calcium hydroxyapatite (Ca10(PO4)6(OH)2), which is one of the main components of phosphate rock. To confirm the formation and purity of calcium phosphate species, precipitation calcination was conducted at 1,078 K for 5 h. XRD analysis revealed that the calcined solid was tricalcium phosphate, and no contamination was evident. These results reveal that a phosphate rock equivalent could be easily obtained from the incineration ash of chicken manure, which implies that approximately 14% of the phosphate rock that is currently being imported into Japan could be replaced by this product.