Pneumatic Drying of Solid Particle: Experimental and Model Comparison

Abstract

This article presents a mathematical model approach to studying the drying phenomena of solid particle in a pneumatic (flash) dryer. The analysis is focused on the pneumatic momentum, mass, and heat balance of the solid particle when it moves inside the reactor. A fixed bed fluidization model was used to calculate the forces balance on the single solid particle. By solving mass and heat balance occurred in the particle, the water/liquid removal efficiency can be calculated. To validate the model calculations, we conducted a set of experiments and compared the simulation with the experimental data. High-moisture, natural concrete sand, the additional material for portland cement, was used and dried along a vertical cylindrical tube with length of 2 m and diameter of 6.68 cm. The drying gas was supplied by a high-capacity air blower which was connected to the burner to produce 120 m³/h of drying gas with maximum temperature of 800°C.     

Microstructure evolution of sol-gel HA films

Bioactive hydroxyapatite films were fabricated on titanium alloy by a sol-gel method. The samples were firstly precoated at a low drying temperature for many times and then calcined at a relative high temperature. The phase constitution, microstructure and composition analysis were studied by X-ray diffraction (XRD), electronic probe microanalysis (EPMA), and the microstructure evolution was explained by some schematic illustrations. When the samples were precoated only once, hexagonal structure is always observed. After the samples were precoated many times, the hexagonal structure can be preserved only when the drying temperature is 500 °C or above. When the drying temperature is below 500 °C, the dried layer easily redissolved into the next coated sol because of the existence of some water-soluble ions such as NO₃⁻, consequently the hexagonal structure disappeared and a coarse surface with some small pores formed. High calcining temperature can accelerate the atomic diffusion which may integrate the adjacent grains, but excessively high temperature such as 900 °C or above would make the whole film be incinerated completely.     

Liquid xenon study under shock and quasi-isentropic compression

Abstract

The shock adiabat for liquid xenon in the density range of 5.2–7.9 g/cm³ and pressure range of 8–70 GPa was investigated. The brightness temperature of a shock wave front from 5000 K to ?15,000 K, as well as the electrical conductivity behind the front from 4·10³ to 1.2·10⁵ 1/Ohm m, were measured. X-ray technique was used to measure quasi-isentropic compression of liquid xenon up to ～13 g/cm³.

The equations of state for liquid and solid phases of xenon were found. Anomalous behavior of xenon at p=8.37 g/cm³ was revealed, that is due to a structural transition.     

Drying of PAAm Hydrogels at Various Temperatures: A Fluorescence Study

The steady‐state fluorescence (SSF) technique was employed for studying the drying of polyacrylamide (PAAm) hydrogels. Disc‐shaped hydrogels were prepared by free‐radical crosslinking copolymerization of acrylamide (AAm) with N,N′‐methylene bisacrylamide (BIS) as crosslinker in the presence of ammonium persulfate (APS) as an initiator. Pyranine (P) was introduced as a fluorescence probe and the intensity of pyranine was monitored during in situ drying at various temperatures. It was observed that the fluorescence intensity of pyranine increased during the drying process. A supporting, gravimetrical experiment was also performed. A phenomenological equation was introduced to determine the desorption coefficient, D, of water molecules from the drying hydrogels at various temperatures. The desorption activation energy, ΔE _d, values were measured for the drying processes and found to be 91.08 and 36.82 kJ mol^–1 by fluorescence and gravimetrical methods, respectively. This difference most probably originates from the origin of the techniques; the fluorescence technique measures the parameters at a molecular level, whereas the gravimetrical technique measures a parameter in the bulk.     

Dehydration of hawthorn fruit juices using ultrasound-assisted vacuum drying

In this study, ultrasound-assisted vacuum drying (UAVD) was employed as a new approach to improve the efficiency and produce dried hawthorn fruit juice powders with acceptable quality. To achieve these goals, the effects of ultrasound intensity (at four levels of 15.29, 20.38, 22.93 and 24.46 kW/m²) were evaluated. The results showed that UAVD significantly shortened the drying time (P < 0.05), and with the increasing ultrasound intensity, the drying rate increased and the drying time decreased. Based on statistical tests, the Page model was found to fit well to the drying kinetics. After drying, a decline in quality of fresh juices was observed. As compared with vacuum drying individually, UAVD significantly reduced the colour degradation, and increased the retention of the total flavonoids content, five flavonoid compounds contents and antioxidant activity. It was shown that UAVD at the higher ultrasound intensity varied from of 20.38 to 24.46 kW/m² contributed to a better quality in the dried juice powders. Overall, this study demonstrates that UAVD is a promising technique for improving the drying efficiency and quality retention of hawthorn fruit juices.     

Study of the X-ray emission from Ta plasma obtained by ns laser ablation

In this work, the continuum spectrum of X-rays originated from the interaction of a moderate intensity ns Nd:YAG laser (1064 nm, 9 ns, 30 Hz, 900 mJ, 10¹¹ W/cm²) with Ta target producing plasma is investigated. Plasma expands unisotropically with a velocity, depending on the pressure of the residual gas in the vacuum chamber. The X-ray intensity is a function of the laser energy and of the gas pressure inside the chamber. The X-ray energy is measured with an X-ray filter positioned in front of the Si(Li) solid-state detector. A temperature of about ～1–2 keV of the hot electrons, responsible for the continuum spectrum emission from the plasma, is calculated from the fit of the X-ray spectrum, applying a Maxwellian distribution.     

Influence of 120 MeV Si9+ ion irradiation on ZnTe semiconductor thin films

ABSTRACT

ZnTe (Zinc Telluride) is a potential semiconducting material for many optoelectronic devices like solar cells and back contact material for CdTe-based solar cells. In the present study, ZnTe thin films were prepared by thermal evaporation technique and then irradiated with 120?MeV Si⁹⁺ ions at different fluences. These films are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Visible spectroscopy techniques. XRD study confirms increased crystallinity and grain growth for post-irradiated ZnTe thin films for fluences, up to 1?×?10¹¹ ions cm^?2. However, the grain size and crystallinity decreased for higher fluence-exposed samples. SEM images confirm the observed structural properties. Modification of the surface morphology of the film due to the ion irradiation with different fluences is studied. Optical band gap of film is decreased from 2.31?eV (pristine) to 2.17?eV after irradiation of Si⁹⁺ ions.     

Novel room temperature ionic liquid for fluorescence enhancement of Eu and Tb

The newly prepared ionic liquid, 1-butyl-3-methylimidazolium benzoate, ([bmim][BA]), was found to enhance the fluorescence of Eu³⁺ and Tb³⁺. The fluorescence enhancement resulted from a sensitization of the lanthanide fluorescence by the benzoate anion of the ionic liquid, [bmim][BA], and a reduction in the non-radiative channels in the non-aqueous environment provided by the ionic liquid. However, the fluorescence enhancement of the lanthanides in the ionic liquid was limited due to the operation of the inner filter effect, which resulted from the strong absorption of the benzoate. The inner filter effect was minimized by observing the Eu³⁺ fluorescence using a front face geometry and also by diluting the lanthanide-[bmim][BA] system, using another ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([bmim][Tf₂N]), as a solvent. In the case of Tb³⁺, the emission from the lanthanide was masked by the strong emission from the ionic liquid in the region 450-580 nm. The long lived Tb³⁺ emission was therefore observed using delayed gated detection, where an appropriate delay was used to discriminate against the short lived emission from the ionic liquid. The large fluorescence enhancement due to ligand sensitized fluorescence observed with [bmim][BA] diluted in [bmim][Tf₂N], leads to nanomolar detection of the lanthanides. This is, to the best of our knowledge, the first report of an ionic liquid being employed for ligand sensitized fluorescence enhancement of lanthanides.     

Submicron Li<Subscript>2</Subscript>MoO<Subscript>4</Subscript> material prepared by rheological phase method and its evaluation of lithium storage performances

In this paper, submicron Li₂MoO₄ material was synthesized via rheological phase method. The structure, composition and morphology of the obtained powders were characterized by X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS) and scanning electron microscope (SEM), respectively. The key calcination temperature was 700 ^oC. The particle sizes were about from 100 to 300 nm. As anode material of lithium ion batteries, lithium storage performances of the as-prepared Li₂MoO₄ were evaluated at different current densities. The best capacity retention was 75.7% of the initial capacity (592.13 mAh g^-1) after 50 cycles at 0.2 mA cm^-2 in 0.1-2.5 V, and the resistance was about 123.5 Ω, indicating a potential prospect in the application of lithium ions batteries.     

Isomerization and fluorescence characteristics of sterically hindered azobenzene derivatives

We report synthesis and isomerization behaviors of sterically hindered azobenzene derivatives (1 and 2) with decyloxy and hydroxy groups, respectively, and their fluorescence enhancement under UV light irradiation characterized by means of absorption and fluorescence spectroscopy measurements. Upon irradiation of as-prepared solution (1) with UV light (∼200 mJ/cm²) a cis-rich photostationary state was reached. Obviously different from 2 showing very fast thermal cis-to-trans isomerization within 2 min, slow cis-to-trans thermal back isomerization of 1 with a long alkyl chain at ambient temperature was observed on the time scale of weeks. In contrast to no striking changes in absorption and fluorescence spectra of compound 2, the azobenzene 1 showed green fluorescence upon prolonged irradiation with UV light (about 3-8 J/cm² exposure doses), although both the initial trans-rich and cis-rich states of azobenzene molecules were not fluorescent in solution. The stability of fluorescence efficiency caused by drying and redissolving processes was examined.     

Preparation of nanosized iron oxide and its application in low temperature CO oxidation

A method to prepare iron oxide material which has a higher surface area and nanosized particle was developed. It was used as a catalyst for CO oxidation at low temperature. Iron oxide materials were prepared by precipitation under constant pH value. The effects of preparation parameters, such as iron salt (FeCl₃, Fe(NO₃)₃ and FeCl₂), pH value (between 8 and 12), drying temperature (between 120°C and 300°C), and feeding rate of the aqueous solution of the iron salt, on the characteristics of iron oxide have been investigated. The materials were characterized by N₂ sorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The surface area of iron oxide was greater than 400 m²/g using FeCl₃ as the starting material with very low feeding rate of 10 ml/min, the pH value of 11, and drying at 120°C. The XRD patterns indicated that the iron oxide samples heated at a temperature below 180°C was either amorphous or of a particle size too small (<4 nm) for the samples prepared with FeCl₃. Depending on the preparation conditions, the iron oxide samples showed a phase transition from amorphous to various crystalline phases. Large amount of hydroxyl groups were preserved if the drying temperature was below 200°C. TEM images showed that the particle diameters were less than 4 nm for the samples prepared with FeCl₃ at pH value of 11 with a low feeding rate of 10 ml/min, and heated below 200°C. XPS Fe 2p_3/2 spectra showed the phase transition of iron oxide from Fe₃O₄ to FeO. The feeding rate of starting material and pH value during precipitation played the important roles to obtain iron oxide with high surface area. The nanosized iron oxide demonstrated high activity for CO oxidation even at ambient condition. The higher activity of Fe _x O _y nanoparticles in CO oxidation was attributed to a small particle size, high surface area, high concentration of hydroxyl groups, and more densely populated surface coordination unsaturated sites.This revised version was published online in August 2005 with a corrected issue number.     

Preparation of nanosized iron oxide and its application in low temperature CO oxidation

A method to prepare iron oxide material which has a higher surface area and nanosized particle was developed. It was used as a catalyst for CO oxidation at low temperature. Iron oxide materials were prepared by precipitation under constant pH value. The effects of preparation parameters, such as iron salt (FeCl₃, Fe(NO₃)₃ and FeCl₂), pH value (between 8 and 12), drying temperature (between 120°C and 300°C), and feeding rate of the aqueous solution of the iron salt, on the characteristics of iron oxide have been investigated. The materials were characterized by N₂ sorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The surface area of iron oxide was greater than 400 m²/g using FeCl₃ as the starting material with very low feeding rate of 10 ml/min, the pH value of 11, and drying at 120°C. The XRD patterns indicated that the iron oxide samples heated at a temperature below 180°C was either amorphous or of a particle size too small (<4 nm)=" for=" the=" samples=" prepared=" with=">₃. Depending on the preparation conditions, the iron oxide samples showed a phase transition from amorphous to various crystalline phases. Large amount of hydroxyl groups were preserved if the drying temperature was below 200°C. TEM images showed that the particle diameters were less than 4 nm for the samples prepared with FeCl₃ at pH value of 11 with a low feeding rate of 10 ml/min, and heated below 200°C. XPS Fe 2p_3/2 spectra showed the phase transition of iron oxide from Fe₃O₄ to FeO. The feeding rate of starting material and pH value during precipitation played the important roles to obtain iron oxide with high surface area. The nanosized iron oxide demonstrated high activity for CO oxidation even at ambient condition. The higher activity of Fe _x O _y nanoparticles in CO oxidation was attributed to a small particle size, high surface area, high concentration of hydroxyl groups, and more densely populated surface coordination unsaturated sites.     

Drying Characteristics-Property Correlationships in Gas-Fired Infrared Drying of Paper Obtained by Diffuse Reflectance FT-IR Spectroscopy

Introduction

Infrared (IR) drying of paper in a pilot scale has been investigated by several researchers in the past [1–3]. Both high-intensity electric heating and medium-intensity gas heating are now being used industrially either to preheat wet paper before conventional steam drying [1] or as a moisture-profile corrector just before paper sizing press [2]. Our own investigation [3] on the use of radiant energy from a gas-fired IR radiator have revealed that the drying efficiency of IR radiation is influenced by the nature of association of water molecules with cellulose in wet paper. Depending on the total moisture content of a paper, the free and bound moisture contents of paper will vary in wet paper sheet. Our previous study [3] has also confirmed that it is possible to remove free moisture more efficiently using gas-fired IR emitter operated at 1373 K rather than as 1223 K. It is reported that besides emitter temperature, the efficiency of drying also depends on the location of the emitter. In general, the efficiency is high if the emitter is installed near the preheating zone and the efficiency changes in the following order: falling rate < constant rate < preheating. Pikulik [4] compared the efficiency of hot gas impinging drying with conventional steam drying emphasizing the paper properties. The properties of a high-intensity hot gas-dried paper has been reported to be better than those of conventionally steam dried paper. An immediate quality improvement in terms of reduced moisture steaks and superior resistance to paper embrittleness was also observed when installing a high-intensity infrared drying system [5,6].     

Live Cell Imaging With Biocompatible Fluorescent Carbon Quantum Dots Derived From Edible Mushrooms Agaricus bisporus,Pleurotus ostreatus,and Suillus luteus

In the study, fluorescent imaging of live cells was performed using fluorescent carbon quantum dots derived from edible mushrooms species; Agaricus bisporus, Pleurotus ostreatus, and Suillus luteus as a fluorophore agent. Carbon quantum dots were synthesized through a facile and low-cost method based on microwave irradiation of dried mushroom samples in hydrogen peroxide solution under optimized conditions (microwave energy, solution type, duration of microwave treatment, amount of mushroom). Upon purification with centrifugation, microfiltration, and dialysis, the lyophilized carbon quantum dots were identified through UV–visible, fluorescence and FT-IR, X-ray photoelectron spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy, and quantum yield calculation. Cell viability assessment of the carbon quantum dots was evaluated against human epithelial cell line PNT1A using the Alamar Blue Assay. In vitro fluorescence cell imaging studies demonstrated that the carbon dots could dynamically penetrate the cell membrane and nuclear membrane and localize in both the cytoplasm and the nucleus.

     

Alumina nanotubes: preparation and textural,structural and morphological characterization

Alumina nanotube was synthesized by hydrolysis of aluminum isopropoxide followed by gelation and drying under hypercritical condition. The influence of temperature on the structural, textural, and morphological properties of the material was studied by powder X-ray diffraction, infrared spectroscopy, nitrogen adsorption, thermal analysis, scanning and transmission electronic microscopy. The as-prepared alumina (300°C) was formed by boehmite crystallites. Its structure collapsed after heating (500–1200 °C) yielding γ, δ and θ alumina nanophases. The aerogel surface area changed from 254 to 99 m² g⁻¹ in this heating range. The formation of alumina nanotubes was verified by transmission microscopy analysis at the heating range.     

喷气式Z箍缩等离子体辐射软X射线能谱的研究

研制了一台五通道ROSS-FILTER-PIN软X射线能谱仪，能谱范围为0.28—1.56keV.它由5个连续能段组成，每个能段的起止边由罗斯滤片对(ROSS-FILTERS)的L或K吸收边确定.罗斯滤片对的厚度通过优化计算得到，为了使每个通道的灵敏区外响应(即所测能段外响应)与通道总响应之比最小，在滤片对的第二滤片上镀上了一定厚度的第一滤片材料；为了缩减滤片表面积以增强低能滤片的抗冲击能力及方便滤片加工，能谱仪采用了小探测面积的PIN探测器(1mm²).借助此能谱仪，测量得到了喷气式Z箍缩(Z-pinch)等离子体辐射软X射线能谱的分布，并研究了软X射线产额随箍缩状况的变化趋势. 关键词： Z箍缩等离子体 罗斯滤片 软X射线能谱     

Molecular Forms of Coumarin-307 in Sol-Gel Glasses

Coumarin-307(C-307) impregnated sol-gel glass samples were prepared by two methods - (I) predoping using HNO₃ as catalyst, and (II) postdoping using HNO₃ as catalyst and formamide as drying control chemical additive (DCCA). The absorption/fluorescence properties including fluorescence lifetime of the dye in these sol-gel host matrices were studied and results were compared with dye in methanol (MeOH). In addition to usual non-polar form of C-307 that exists in MeOH, amino-protonated form and dimer of dye have also been found to co-exist in the dried state of samples prepared by predoping method. This behaviour of dye was uncommon to sol and gel states of materials. The fluorescence quantum yield (Q_f) of C-307 doped solid was found to be 0.77 and it was almost constant in the concentration range 5×10¹⁶ to 8.8×10¹⁷ cm⁻³. On the other hand, only non-polar form of C-307 has been observed in the samples prepared by postdoping method. The Q_f value of dye was 0.96 in the postdoped samples. To explain such behaviour of C-307 in the two types of sol-gel matrices: dye concentration, role of HNO₃, water, formamide and matrix effect have been taken into account.     

Applications of ultrasound to enhance fluidized bed drying of Ascophyllum Nodosum: Drying kinetics and product quality assessment

In this study, ultrasound either as a pretreatment technique or as an integrated technique was employed to enhance fluidized bed drying of Ascophyllum nodosum, and drying kinetics and dried product quality were assessed. In order to compare technology efficiency and dried product qualities, oven drying and fluidized bed drying (FBD) were employed. The novel drying methods included airborne ultrasound-assisted fluidized bed drying (AUA), ultrasound pre-treatment followed by FBD (USP), and hot water blanching pre-treatment followed byFBD (HWB). Six drying kinetics models were used to describe the drying curves, among which the Page model was the best in fitting USP and AUA. Model by Millidi et al. was employed to describe HWB. Airborne ultrasound in AUA did not reduce energy consumption or drying time, but retained total phenolic content (TPC) as well as colour, and exhibited the highest yield among the novel drying methods. USP and HWB showed lower energy consumption and drying time considerably, but the TPC was the lowest among the studied methods. At the same time, USP dried product exhibited the lowest a_w, followed by HWB and then AUA. This studyalso demonstrated that FBD could be a very practical drying method on Irish brown seaweed, and ultrasound-assisted drying methods may have potential developments in Irish brown seaweed drying process.     

Influence of thermal effect on the efficiency of a solar cell

The short-circuit current and open-circuit voltage of a solar cell based on the p-n junction are studied theoretically, taking into account the thermoemf originating due to the temperature difference between the front and back surfaces of the solar cell. It is shown that the consideration of the thermal motion of photogenerated carriers leads to the increase in the collection coefficient. Calculations show that at the irradiation intensity 5 × 10²⁰ photon/cm² s and at the temperature gradient ～ 30–40°C for silicon solar cells the open circuit voltage increases by ～ 6–7% and the short circuit current by ～40–50%.     

Experimental investigation of the optical signal, gain, signal-to-noise ratio and information content characteristics of X-ray phosphor screens

In this study, the quality of medical images produced by X-ray phosphor screens is described by a model based on the light generation and emission properties of the phosphor material. Combined detector gain (CDG), modulation transfer function (MTF), detective quantum efficiency (DQE) and information capacity (IC) of the screens were expressed and evaluated as functions of emitted optical fluence, incident X-ray fluence and emitted optical spectrum. Phosphor screens with coating thickness ranging from 21 mg/cm² to 137 mg/cm² were prepared in the laboratory and were irradiated by X-rays with X-ray voltages from 50 to 140 kVp. Experimental data were obtained in both transmission and reflection modes of measurement (light emission from both screen sides). Results showed that most image quality parameters (CDG, MTF, DQE) depend strongly on phosphor screen thickness. CDG and DQE also depend on X-ray tube voltage. However, the total quantity of information (IC), which depends on both the incident X-ray fluence and phosphor material type, was not found to be significantly affected by phosphor thickness. Received: 7 September 2000 / Revised version: 8 January 2001 / Published online: 27 April 2001