The use of dimensionless groups to analyse the mixing of streams with large density differences in sub- and supercritical water

Continuous Hydrothermal Synthesis of Inorganic Nanoparticles: Applications and Future Directions

“…Computational or image analysis , techniques can be used to better understand the different mixers in continuous hydrothermal reactors for NP synthesis. Computational fluid dynamics modeling has been used in this regard; in many cases, it has been carried out retrospectively to explain problems or indeed good mixing behaviors. − Other computational studies include the report by Wang et al, who investigated population balance (PB) modeling as a tool to study the effects of solution concentration and reactor residence time on the particle size distribution .…”

“…Poliakoff et al have also surveyed many mixing designs. 143 As continuous hydrothermal processes are trying to mix ambient temperature metal salts with supercritical water, it is important to understand that the key aim is to allow rapid mixing of the two feeds (which are at very different temperatures and densities 144 ), while avoiding preheating of the ambient temperature metal salts or blockage of the pipe/reactor with products. Furthermore, different mixers affect the thermal "history" (time/ temperature) that the metal salt (and subsequently the nanoparticles) experience during nucleation and growth.…”

“…Often, a mixer will only work well or as needed within a range of flow rate conditions before it is better to scaleup or scale out a process (i.e., at higher flow rates) or indeed use a different mixer! Computational or image analysis 144,146 techniques can be used to better understand the different mixers in continuous hydrothermal reactors for NP synthesis. Computational fluid dynamics modeling has been used in this regard; in many cases, 147 it has been carried out retrospectively to explain problems or indeed good mixing behaviors.…”

Selective aerobic oxidation of para-xylene in sub- and supercritical water. Part 3: effects of geometry and mixing in laboratory scale continuous reactors

“…This means that the gap between the ends of the feed pipes, l 6 , decreases from 7 cm (TB-1) to 1 cm (TB-3). Modelling experiments to be described in a subsequent report 29 conrm that a reduced value of l 6 gives improved mixing because of the higher velocities of the uids emerging from the narrow bore feed pipes (the velocity of the catalyst stream in the 1/16 00 pipe is 0.26 m s À1 whereas in the larger diameter arms of the cross, it is only 0.0037 m s À1 , the velocity of the water stream is 0.035 m s À1 ). In a fourth variation, pmTB, premixed pX and catalyst solutions were fed as a biphasic mixture into the reaction via a single pipe while the unused fourth arm of the crosspiece was blanked off.…”

CFD–Aspen Plus interconnection method. Improving thermodynamic modeling in computational fluid dynamic simulations

“…In both cases, simulations are limited by the calculation of the physical properties. Since an accurate modelling of the physical properties requires creating and implementing in the CFD simulator complex user defined subroutines, the most common approach adopted has been to consider that the values of the physical properties remain constant (Housley et al, 2016;Kazemzadeh et al, 2016;Kim et al, 2016;Klenov et al, 2015;Luo et al, 2016;Nguyen et al, 2012;Troshko and Zdravistch, 2009). This is an acceptable approach in the case of single components and almost isothermal processes.…”