Spray Flash Evaporation Research Articles

Tunable continuous production of RDX from microns to nanoscale using polymeric additives

The versatility of the Spray Flash Evaporation (SFE) has been extended within the introduction of solid and viscous polymers in solvent. Those polymers are food additives namely polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG); both additives were successfully used to control crystallization steps, thus the particle size and shape of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). The role of PVP as nucleation and growth inhibitor allowed the formation of spherical RDX particles with an average size of 160nm; we found that only 1wt% of PVP per gramme of RDX is needed to reach that size and further addition reduces only the dispersion. The PEG triggered the nucleation of RDX with a low rate and so promoted the growth of RDX particles up to 5μm. Despite a lower thermal stability, the synthesized energetic composites exhibit reduced sensitives towards electrostatic discharge, friction and impact.

Time for pairing: cocrystals as advanced energetic materials

Energetic materials that can store and rapidly release large amounts of chemical energy on demand play a vital role in both military and civilian fields. Modern energetic materials should have high density, high heat of formation and possess molecular stability that allow them to be manufactured, stored and handled safely. Recently, cocrystallization technology offers a promising platform for energetic materials to achieve a desired balance between high detonation performance and low sensitivity. This paper highlights recent developments of energetic cocrystals and details intermolecular interactions, physical parameters and detonation properties. The major part of the discussion relates to the different types of energetic cocrystals including cocrystals composed of energetic molecules and solvents, 2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20)-based cocrystals and azole-based cocrystals, et al. In addition, resonant acoustic mixing (RAM) technique, bead milling and spray flash evaporation technique are also introduced as means for large-scale production of nanosized energetic cocrystals.

Smart Energetic Nanosized Co-Crystals: Exploring Fast Structure Formation and Decomposition

The interest in co-crystals of energetic materials is explained by the fact that they can offer better thermodynamic stability and tunable sensitivity and detonation performance. In the present work, a combination of DSC, ultrafast chip calorimetry, high-resolution X-ray powder diffraction, and nanofocus X-ray diffraction was employed to investigate the thermal behavior and structure formation in nanosized co-crystals of CL-20 with HMX and TNT prepared using Spray Flash Evaporation (SFE). The CL-20/HMX co-crystal does not reveal any thermal transitions up to the thermal decomposition. In contrast, CL-20/TNT exhibits an irreversible melting transition. Upon melting, it can rapidly crystallize on heating or, at a slower pace, at room temperature to form homocrystals of γCL-20, the polymorph stable at high temperature. These observations constitute the first evidence of a CL-20 crystallization process, which occurs from the melt and not from solution. The solid–liquid phase separation occurring during heatin...

Nanostructuring of Pure and Composite‐Based K6 Formulations with Low Sensitivities

AbstractThe aim of this work was to desensitize keto‐RDX, respectively 2‐oxo‐1,3,5‐trinitro‐1,3,5‐triazacyclohexane (K6). For this purpose, two different methods were employed. First, nano‐K6 was produced by means of the Spray Flash Evaporation process. Particles with a median size of 74 nm were obtained. Sensitivity to friction and electrostatic discharge were reduced by downscaling particle size of K6. Second, due to their molecular analogy, the mixing of K6 and RDX was studied. For that reason, a physical nanometric mixture of K6 and RDX was produced by the same technique. In the latter case, an inter‐particular synergy between both compounds was noticed but without forming a cocrystal. The median particle size of the mixture is about 82 nm, and its sensitivity is between the ones of raw nano‐materials concerning friction and electrostatic discharge. Moreover, the mixture is less sensitive to impact (3.03 J) than nano‐K6 (<1.56 J) and nano‐RDX (threshold is 2.0 J).

Continuous Crystallization of ZnO Nanoparticles by Spray Flash Evaporation versus Batch Synthesis

AbstractRegarding the scaled up and accelerated processing of ZnO particles, an advanced continuous pilot plant device is used for ZnO nanoparticle production from a zinc acetate dihydrate solution. A qualitative and mechanistic study is presented to show the feasibility of the process with respect to the formation of semiconducting ZnO nanoparticles. In order to evaluate the continuous approach based on the particle characteristics, a laboratory batch synthesis approach is additionally consulted for conventional preparation. In both cases, the precursor solutions are identical, on the basis of ethanol; no alkaline precipitant is added. The main finding in this comparison is the differing surface chemistry of the particles derived from these two approaches which triggers a whole cascade of differences in particle size distribution and spectroscopic and morphological properties of the particles.

Continuous engineering of nano-cocrystals for medical and energetic applications.

Cocrystals, solid mixtures of different molecules on molecular scale, are supposed to be tailor made materials with improved employability compared to their pristine individual components in domains such as medicine and explosives. In medicine, cocrystals are obtained by crystallization of active pharmaceutical ingredients with precisely chosen coformers to design medicaments that demonstrate enhanced stability, high solubility, and therefore high bioavailability and optimized drug up-take. Nanoscaling may further advance these characteristica compared to their micronsized counterparts – because of a larger surface to volume ratio of nanoparticles. In the field of energetic materials, cocrystals offer the opportunity to design smart explosives, combining high reactivity with significantly reduced sensitivity, nowadays essential for a safe manipulation and handling. Furthermore, cocrystals are used in ferroelectrics, non-linear material response and electronic organics. However, state of the art batch processes produce low volume of cocrystals of variable quality and only have produced micronsized cocrystals so far, no nano-cocrystals. Here we demonstrate the continuous preparation of pharmaceutical and energetic micro- and nano-cocrystals using the Spray Flash Evaporation process. Our laboratory scale pilot plant continuously prepared up to 8 grams per hour of Caffeine/Oxalic acid 2:1, Caffeine/Glutaric acid 1:1, TNT/CL-20 1:1 and HMX/Cl-20 1:2 nano- and submicronsized cocrystals.

Synthesis and Desensitization of Nano‐β‐HMX

AbstractEfforts are made worldwide to desensitize explosives against accidental initiation. For several years, nanostructuring of explosives is a promising field of research aiming for this goal. In this work we describe the continuous preparation of nano‐β‐HMX and a promising approach towards the desensitization of nano‐energetic materials. By means of the Spray Flash‐Evaporation (SFE) technique, nano explosives and nano composites with reproducible properties can be prepared in a single processing step. By increasing the thermal effusivity of an energetic nanomaterial the heat created by hot‐spots can more rapidly be dissipated, reducing the risk of an unwanted reaction.

Experimental study on a spray flash desalination (influence of the direction of injection)

A comparison study of a spray flash desalination process with the direction of injection based on experimental results of upward jet flash evaporation is presented. Superheated liquid at 24.0, 30.0, and 40.0°C was injected upward into a depressurized chamber through a stainless steel cylindrical nozzle to compare with the phenomenon of a downward jet flash evaporation method. A series of experiments were carried out to analyze the effect of the direction of injection against the spray flash evaporation phenomenon. The tube-type nozzle was used with an internal diameter of 20.0 mm and a length of 81.3 mm. The range of the mean velocity of the superheated liquid inlet was from 1.74 to 3.62 m/s. The temperature descent of the superheated liquid inlet along the nozzle axis was measured by thermal resistance. Furthermore, the data and empirical equation for the downward jet method previously reported were used to compare the experimental results on the upward jet method. As a result, a tendency that the upward jet method needs a shorter distance to complete the flash evaporation than the downward jet method was observed. Therefore, the upward jet method has the possibility of making the spray flash desalination system more compact and efficient.

Transient characteristics and performance of a novel desalination system based on heat storage and spray flashing

A hybrid latent heat storage and spray flash evaporation system has been devised in an attempt to develop an energy saving desalination system that stores intermittent thermal energy such as waste heat, solar heat or heat from the surplus steam of a power station at night and utilizes the stored energy not only for the generation of process steam from seawater for industries and domestic air conditioning but also for the production of fresh water from the generated steam for industrial and domestic uses on demand. Experimental results of the transient discharge characteristics of the heat storage column packed with the phase change material and the transient spray flash evaporation characteristics are reported. It is also shown that by using the numerical results of the discharge characteristics and the empirical equation of the efficiency of spray flash evaporation, the amount of generated steam and produced water can be predicted with sufficient accuracy. The utilization of more than 95% of the amount of stored energy for the generation of process steam and the production of fresh water, substantiated experimentally, confirms the high efficiency of the hybrid system.

98/03326 Transient characteristics and performance of hybrid latent heat storage and spray flash evaporation system: Miyatake, O. et al. J. Chem. Eng. Jpn., 1997, 30, (6), 1076–1082

98/03326 Transient characteristics and performance of hybrid latent heat storage and spray flash evaporation system: Miyatake, O. et al. J. Chem. Eng. Jpn., 1997, 30, (6), 1076–1082

Transient characteristics and performance of hybrid latent heat storage and spray flash evaporation system.

A hybrid system of latent heat storage and spray flash evaporation is devised in an attempt to develop an energy saving system, which stores intermittent thermal energy such as solar heat, waste heat or heat from the surplus steam of a power station at night and utilizes the stored energy for the generation of steam for industries, power stations and domestic air conditioning. Experimental results of the transient discharge characteristics of the heat storage column packed with the phase change material and the transient flash evaporation characteristics are reported. It is also shown that by using the numerical results of the discharge characteristics and the empirical equation of the efficiency of flash evaporation, the amount of generated steam can be predicted with sufficient accuracy. The utilization of more than 97% of the amount of stored energy for the generation of steam, substantiated experimentally, confirms the high efficiency of the present system.

Efficiency of Spray Flash Evaporation

Efficiency of Spray Flash Evaporation

Simplified expression for efficiency of spray flash evaporation.

Based on the authors' previous experimental studies of spray flash evaporation occurring in a superheated water jet ejected from a simple tubular nozzle into a low-pressure vapor zone, a simplified expression for the efficiency of flash evaporation, η, was derived asη=1- {1+kΔTs (t-t0)} -1where, k is an empirical coefficient, ΔTs the superheat of liquid at the nozzle exit, t the residence time of jet in the flash chamber and t0 the time lag of the initiation of flashing.It was realized that, for those cases in which bubble nuclei were sufficiently injected by electrolyzing warm feed water, the empirical coefficient k became practically independent of the nozzle diameter, the flow rate of liquid and the superheat of liquid at the nozzle exit, and increased up to 91s-1 K-1 on average at 60°C jet inlet temperature.

Enhancement of Spray Flash Evaporation by Means of the Injection of Bubble Nuclei

Spray flash evaporators are being used or considered for power systems utilizing solar energy, ocean thermal energy, and geothermal energy. As part of an attempt to develop a compact, efficient flash evaporator, an experimental study of the effect of injection of bubble nuclei has been conducted. The bubble nuclei were generated by electrolyzing warm water, which was ejected from a simple tubular nozzle into a low-pressure vapor zone. Effects of electrolytic current level, nozzle diameter, liquid flow rate, liquid temperature, and superheat were investigated. The evaporator rates attained were superior to those in conventional multistage flash evaporators with open channels.

Enhancement of Spray Flash Evaporation and Its Attendant Reduction in Non-Equilibrium Temperature Difference

Enhancement of Spray Flash Evaporation and Its Attendant Reduction in Non-Equilibrium Temperature Difference

Effect of liquid temperature on spray flash evaporation

To complement the authors' previous experimental study of spray flash evaporation pursued at 60°C jet inlet temperature, an additional experimental study has been made of the effect of liquid temperature on the spray flash evaporation by changing jet inlet temperatures to 40 and 80°C. From the experimental results, a more general empirical equation suitable for predicting the variation of liquid temperature in the center of jet with residence time was deduced, and the recommendable operating conditions were proposed. Furthermore, an expedient method for prediction of the liquid temperature drop along the length of jet was devised for the recommendable operating conditions. It was realized that, even at lower liquid temperatures, the spray flash evaporation still has higher evaporation performance and extremely faster evaporation rate than the flash evaporation occurring in other systems.

An experimental study of spray flash evaporation

An experimental study has been conducted on spray flash evaporation occurring in a superheated water jet injected through a circular tube nozzle into a low-pressure vapor zone. The effects of superheat, flow rate and nozzle diameter on spray flashing were pursued at 60°C jet inlet temperature. From the experimental results, an empirical equation suitable for predicting the variation of liquid temperature with residence time was deduced.