Evaporative cooling of micron-sized droplets in a low-pressure aerosol reactor

The results of experimental and computational investigation of evaporative cooling of micron-sized droplets in a low-pressure aerosol reactor (LPAR) are reported. The cooling rate of the aerosol was found to be about . A constant low pressure, the flow rates of the carrier gas and solution are major factors that affect droplet cooling. A higher total pressure accelerated the change in droplet radius. For some regimes it was predicted that an aerosol undergoes freezing and then melting. The characteristic time required for evaporative cooling is about 1 ms. The agreement between experimental results and calculated values, based on the free molecular approximation of heat and mass transfer processes, is reasonably good.     

Hydroxypropyl Methylcellulose Reduces Particle Adhesion and Improves Recovery of Herbal Extracts During Spray Drying of Chinese Herbal Medicines

The effectiveness of hydroxypropyl methylcellulose (HPMC) as an anti-adherent during spray drying of traditional Chinese herbal extracts was explored. A small amount of HPMC (minimum concentration 8%) was sufficient to overcome problematic particle adhesion, whereas a large amount of maltodextrin (50%) was required for the same effect. HPMC exerted a strong anti-adhesive effect that was independent of the type of HPMC, raw materials used, and the process used to synthesize HPMC. The anti-adhesion mechanism was studied through an analysis of the surface tension of the prepared solutions before spray drying, the glass transition temperature (T _g ), and X-ray photoelectron spectroscopy (XPS) of spray-dried powders. The T _g of powders containing more than 8% HPMC was approximately 40°C and did not increase linearly with the HPMC concentration. The surface tension of Crataegi fructus extract was 54.1 ± 0.2 mN/m and further decreased to 46.6 ± 0.2 mN/m upon addition of HPMC to 24%. When the concentration of HPMC increased to 8%, potassium could not be detected on the surface of dried powders by XPS. These results suggest that modification of the surface properties of sprayed droplets/particles by HPMC increased the HPMC surface coverage of the particles and reduced adhesion during spray drying.     

Influence of processing conditions on flavour compounds of custard apple (Annona squamosa L.)

Changes in volatile compounds of fruit pulp of Annona squamosa, as influenced by the conditions of processing, were studied. Sweet and pleasant flavored pulp from mature ripe fruits was subjected to treatments such as frozen and stored (for 12 months), heated to 55 °C (critical temperature) and 85 °C (pasteurization temperature) for 20 min each, and spray dried with skim and whole milk powders. Volatiles from these samples were extracted into dichloromethane and n-pentane (1:1), and were subjected to gas chromatograph (GC) and gas chromatograph-mass spectrometer (GC-MS) analysis for identification and quantification of chemical constituents. Terpenes such as α-pinene, β-pinene, linalool, germacrene-d and spathulenol, esters like sec-butylbutanoate, and methyllinolenate, along with benzyl alcohol and two oxygenated sesquiterpenes were found to be the major volatiles of the fresh pulp. The 12-month-stored frozen pulp did not differ from the fresh pulp in the flavour spectrum. Heating fresh pulp at 55 and 85 °C, tended to produce increased flavour spectrum, the compounds relatively being more at 85 °C. At 55 °C, significant increase in the quantities of α-pinene, β-pinene, linalool, germacrene and spathulenol were observed; higher quantities of cineole, limonene, α-cubebene and α-copaene, caryophyllene, α-farnecene and δ-cadenene were formed, while these were totally absent in fresh pulp. Significant increase in quantities of α-pinene, β-pinene, 1,8-cineole, limonene, aromadendrene, α-farnecene, γ-cadenene, δ-cadenene and spathulenol were found by heating pulp at 85 °C. Spray-dried samples, showed increased flavor note with the use of whole milk powder as compared to the skim milk powder.     

低压环境下喷雾特征实验研究

对蒸馏水分别通过压力雾化喷嘴和直流喷嘴喷射到低压环境的喷雾过程进行了实验研究,分析了环境压力、工质温度、工质流量对压力雾化喷嘴喷雾锥角和直流喷嘴喷雾瞬态特征的影响。实验结果显示,当采用压力雾化喷嘴时,环境压力越低,工质初始温度越高,喷雾锥角越大;工质流量越大,工质冲转旋转叶片速度越快,喷雾锥角也越大。当采用直流喷嘴时,环境压力越低,工质温度越高,工质流量越大,液柱出现破碎所用的时间越短。直流喷嘴的喷雾现象表现为随时间生长的过程,喷雾形态经历了液柱—液柱破碎—液柱完全雾化的过程。工质温度、环境压力直接影响工质的过热度,来影响闪蒸的剧烈程度,从而改变喷雾形态。     

低压环境下闪蒸喷雾冷却不同润湿性表面的实验研究

对低压环境下闪蒸喷雾冷却不同润湿性表面的实验现象和换热特性开展研究,结果显示:喷雾至亲水表面和光滑铜表面的汽化过程分为四个阶段,即液膜形成阶段、液膜剧烈汽化阶段、固定液膜接触线的汽化阶段和液膜界面收缩阶段。进而研究了表面润湿性、环境压力、工质温度对两种表面温度变化的影响。结果表明,表面温度随时间都呈下降的趋势;亲水表面润湿性较好,喷雾阶段表面温度下降较快;环境压力越低,液体汽化越剧烈,表面的最终平衡温度也越低,但在喷雾阶段存在最佳环境压力使冷却效果最好,本文实验条件下,最佳环境压力为1.9 kPa;工质初始温度对表面最终温度影响很小。     

Sustainable porous hollow carbon spheres with high specific surface area derived from Kraft lignin

Hollow carbon spheres (HCSs) have attracted tremendous interest in recent years due to their intriguing structure-induced physicochemical properties and significant potential for numerous applications. However, the preparation of HCSs with precise structural control using a simple and scalable strategy remains challenging. In this work, hollow carbon particles having a well-defined spherical morphology were successfully produced using a green, economical, and facile spray drying method together with a carbonization process. Kraft lignin was employed as the carbon precursor in place of lignosulfonate with potassium hydroxide (KOH) as an activation agent. The high specific surface area (1536.5–2424.8 m² g^?1) with micro-mesoporous structure of HCSs can be easily tuned by controlling the mass ratio of KOH to carbon precursor. The KOH-to-lignin mass ratios were utilized below 1.5, lower than those in previous studies typically used higher than 3, which was in accordance with green chemistry principles. In addition, these HCSs have applications as electrode materials in supercapacitors for energy storage devices. With the great achievements and continuous efforts in this important field, these results suggest that our approach will open a new path for the development of advanced carbon materials and high value-added utilization of Kraft lignin as a promising material for potential applications.     

Lipid composition optimization in spray congealing technique and testing with curcumin-loaded microparticles

Spray-congealing, a technique based on the fast solidification of sprayed molten lipids, is considered a novel strategy to encapsulate natural products. Among others, it is a safe, low cost, fast and reproducible technique, with rising interest for several applications (e.g. food applications). One of the key parameters for the application of this technique is the lipid solidification temperature, which can be modulated by optimizing the lipid composition. In this work, three lipid components (beeswax, carnauba wax, and medium-chain triglycerides (Miglyol 812)) were selected, and the mixture composition modelled using a simplex-centroid experimental design. Three different lipid compositions were chosen to validate the proposed model, then tested in the preparation of curcumin-loaded microparticles (1.5%, w/w). The produced microparticles were analysed in terms of colour, morphology, particle size, encapsulation efficiency and load, physicochemical, crystalline, and thermal properties. Results evidenced that microparticle’s properties, including encapsulation efficiency, vary according to the used lipid mixture, supporting their tailoring role. This fact brings advantages in the design of microencapsulation systems based on spray congealing processes, broadening their applicability. Moreover, lipid composition optimisation was proved to be an important tool to precede the development of spray-congealing applications.     

雾化热解法制备活性氧化性

以锌焙砂为原料,经氨水、碳酸氢铵浸出,浸出液经雾化热解、煅烧,制得活性氧化锌。研究表明,锌焙砂在NH3/NH4+=2.5∶1、总氨浓度为8 mol/L、液固比=8∶1、时间1 h、温度35℃条件下,一段浸出液锌含量为54.34 g/L,浸出率为82.56%,经过两段逆流浸出,锌含量可达到97.62 g/L,氨浸锌平均浸出率达97%以上。浸出液经锌粉置换除杂,净化后液进行雾化分解,在雾化器进口温度为340℃,出口温度≥180℃的条件下,制得白色前躯体,在400℃条件下用马弗炉煅烧1 h,得到长度不大于2μm的针状活性氧化锌。     

高速雾化分解法制取活性氧化锌的研究

研究了用高速雾化分解法由锌焙砂制备活性氧化锌的工艺。结果表明,锌焙砂经碳酸氢铵、氨水与水浸取液浸取,浸取率为98.48%。浸取液中的氧化锌含量可达25.3%(质量分数),用锌粉除杂净化,过滤除去杂质。滤液在喷雾干燥塔430℃的入口温度下喷雾热分解,可得到高活性的氧化锌。其吸碘值为42.445 mg/g,活性显著高于蒸氨煅烧法所得的氧化锌。     

基于现场数据和PSO算法的机组主汽温系统辨识

建立精确的热工对象动态模型是提升系统控制性能的重要基础.针对某1000MW超超临界火电机组减温喷水量扰动下主汽温对象的动态特性,利用现场运行数据和混合粒子群优化算法对主汽温系统进行辨识,建立了过热器喷水量扰动下主汽温的动态数学模型.对所建立的模型进行验证,结果表明模型能够有效地反映主汽温系统的实际运行状况.