•The coalesced bubble flow was identified from the multi-bubble flow.•The bubble size follows a specific step-type distribution.•The wall effect has impact on the coalescence of bubbles.•The larger coalesced bubbles dominate the rise velocity of the multi-bubble flow.Hydrodynamic study was performed on the gas-liquid-solid micro-fluidized beds with 0.8 mm bed diameter and multi-bubbles through high speed camera recording system. Flow regimes including dispersed bubble flow, coalesced bubble flow and slug flow were identified from the multi-bubble flow. Wall effect at the small bed-to-particle diameter ratio led to the occurrence of bubble coalescence and flow regime transition at lower solid holdups. Obvious bed contraction appeared only at lower liquid velocities or higher gas velocities. The diameter range of the spherical micro-bubbles in the micro-fluidized beds was 200–500 μm. The bubble size in dispersed bubble flow was normally distributed and slightly increased with the solid holdup. And in coalesced bubble flow, the bubble size was decided by the overall coalescence probability and presented a special step distribution. The larger coalesced bubbles concentrated the distribution of bubble terminal velocity. And the bubble terminal velocity decreased with the solid holdup and inversely with the bubble size. In dispersed bubble flow regime, there was positive linear relationship between the apparent viscosity and the solid holdup. Three-phase micro-fluidized beds meet the further development of micro-reactors, and this study on the hydrodynamic characteristics contributes to their wider application.Download high-res image (111KB)Download full-size image

•Particle-tube collision behavior was first studied by vibration signal analysis.•The kurtosis of vibration signals is negatively related to collision frequency.•Vibration intensity increased with the growth of steam pressure and solid holdup.•Boiling coefficient was enhanced and explained according to collision behavior.It is necessary to investigate the collision behavior of fluidized solid particles on the wall of a brittle graphite heat exchange tube of a fluidized bed evaporator for a better fundamental investigation on the vibration risk assessment and heat transfer process enhancement. Vibration acceleration signals of the single graphite tube with an inner vapor-liquid-solid boiling flow at varied steam gauge pressure, solid holdup and particle size were measured with developed signal acquisition and processing system. Main results are as follows. Circulating rate of the vapor-liquid-solid flow, kurtosis and standard deviation of vibration signals were considered as measures of collision force, collision frequency and vibration intensity, respectively. The largest standard deviation occurs in axial middle position of the graphite tube, and kurtosis of vibration signals decreases from the top to the bottom. As the steam gauge pressure increases, the collision frequency of smaller solid particles (1.3, 2.4 mm) increases first and then gradually reaches to a stable value, while a fluctuating or slight decreasing tendency of kurtosis appears for the larger solid particles (3.5 mm). The collision force and the comprehensive vibration intensity factor of all three sizes of solid particles enhance with the increase of steam gauge pressure. As the solid holdup increases, the collision frequency increases obviously, while the collision force decreases. Vibration intensity is higher both with the addition of solid particles and the increase of solid holdup. The boiling coefficient shows a clear enhancement and can be explained according to the conclusions on the collision behavior of solid particles. The results effectively support the reliability of collision behavior research between fluidized solid particles and tube walls by vibration signals analysis, which lays the foundation of reasonable design and further application of the fluidized bed evaporator.Download high-res image (172KB)Download full-size image

•Chaotic dynamics of vibration signals of a graphite tube with boiling flows were studied.•No multi-value phenomenon in the original vibration acceleration signal was found.•Three-scales are obtained from correlation integral curves of reconstructed signal.•Solid particles affect greatly regularity of vibration motion of the graphite tube.The vibration signal is seldom applied to study the nonlinear characteristics of the fluidization system with boiling flows even though it is very important to understand the vibration behavior of the system. In this paper, the multi-value phenomenon of correlation dimension and its relationship with multi-scale flow behavior were investigated based on the chaotic analyses of the vibration acceleration signals as well as pressure drop signals measured from a single graphite tube in the vapor-liquid-solid fluidized bed evaporator. With wavelet decomposition and signals reconstruction techniques, the characteristics of the medium and low frequency signals are displayed. Nonlinear vibration behavior in multi-phase boiling flow system was analyzed at varied solid holdup and steam gauge pressure. The influence of solid particles on the correlation and regularity of the motion of the system is more obvious than that of the steam pressure. Three-scales were obtained, namely the macro-scale, meso-scale and the micro-scale, respectively. It is an effective method to characterize the multi-scale behavior in the multi-phase fluidized bed evaporator by measuring and analyzing the vibration acceleration signals.Download high-res image (244KB)Download full-size image

•The solubility of ciclesonide in seven pure organic solvents was determined by gravimetric method.•The solubility order was interpreted by virtue of density function theory (DFT).•The experimental solubility of ciclesonide was correlated by four thermodynamic models.•Mixing thermodynamic properties of ciclesonide were calculated and discussed.The solubility of ciclesonide in seven organic solvents (ethanol, 2-propanol, 1-propanol, 1-butanol, acetonitrile, toluene and ethyl acetate) in the temperature range from 278.15 K to 313.15 K was measured by gravimetrical method under atmospheric pressure. The results indicate that the solubility of ciclesonide increases with elevating temperature in all investigated solvents. The solubility order in different solvents was interpreted through comparing interaction force between solute and solvent molecules by virtue of density function theory (DFT). Thermodynamic equations including the modified Apelblat equation, λh equation, Wilson equation and NRTL equation are all suitable to correlate the solubility results. Based on the Wilson equation, the thermodynamic parameters from the mixing process are calculated, and the results indicate the mixing process of ciclesonide in the selected pure solvents is spontaneous and entropy-driven.

•Hybrid polysiloxane-ferroferric oxide coating was fabricated.•Corrosion resistance of coated steel was improved in simulated geothermal water.•Equivalent circuits used to describe corrosion process were proposed.•All tested polysiloxane coatings showed less than 8% weight losses under 300 °C.•Compactness and thickness are important for corrosion resistance of coatings.Corrosion from plants and pipelines made of carbon steel is a severe problem for the utilization of geothermal energy. In order to control corrosion, various polysiloxane-ferroferric oxide composite coatings were successfully fabricated on carbon steel substrates. The morphologies and chemical compositions of these composite coatings were characterized. The thermal stability was tested by thermal gravity analysis (TGA). Wettability was investigated by contact angle measurement. Equivalent thickness was measured by weight method. The corrosion behaviors of composite coatings were tested by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in 3.5 wt.% NaCl solution and simulated geothermal water of Huabei oilfield. According to potentiodynamic polarization curve and EIS, the inhibition of corrosion for each carbon steel coated with composite coating is improved, because the corrosion current density decreases by one or two orders of magnitude. Corrosion mechanism for carbon steel coated with composite coating was analyzed with EIS measurement and equivalent circuit simulation. TGA of various polysiloxane coatings shows less than 8% weight losses for all polysiloxane coatings tested at 300 °C. The composite polysiloxane coatings show good corrosion resistance and thermal stability.

•Surface hydrophilization was applied to retard deposition of oil soiling.•Flow velocity enhancement was utilized to inhibit formation of oil soiling.•Adding chemical additive was attempted for oil soiling removal.•Obvious oil soiling removal was obtained with small amount of additives.•Mechanism of oil soiling removal was explained.Crude oil fouling on heat transfer surface (HTS) is a very troublesome problem for the utilization of oilfield geothermal water in which slight crude oil exists. The deposition of crude oil on HTS will decrease heat transfer efficiency, increase the pressure drop of fluid flow, and even block flow channel. In this study, surface hydrophilization via anodization, flow velocity enhancement and chemical addition three measures were adopted to solve the problem of crude oil soiling via weakening the adhesion force between crude oil and HTS as well as intensifying the interaction between water and crude oil. Contact angle measurement and microscopic morphology study were conducted on the highly-hydrophilic surface fabricated via anodization. Oil-soiling experiments accompanied with three mentioned techniques were carried out in plate heat exchanger (PHE) apparatus, and obvious oil-fouling inhibition effects were presented. The effect was reflected by the decrease of fouling thermal resistance. For 110 °C simulated oilfield geothermal water, which contained approximate 1 vol.% crude oil soiling, with 0.24 m/s flow velocity, the fouling induction period extended to 500 min from 0 min when surface hydrophilization was applied through anodization. In anodized PHE with titanium plates, the value of fouling thermal resistance decreased by about 77.8% when the flow velocity of 110 °C hot fluid without chemical additive increased from 0.24 m/s to 0.72 m/s, and the value could be reduced by around 62.5% after the addition of 0.29 g/L chemical additive LIUXU-10 mainly composed of sodium dodecyl sulfonate (SDS), when the flow velocity of 110 °C hot fluid was 0.12 m/s. Compared with PHE with titanium plates (Ti-PHE) at 0.24 m/s hot fluid flow velocity, the fouling thermal resistance decreased by approximate 93.3% when the Ti-PHE was anodized to be highly hydrophilic, the hot fluid flow velocity increased to 0.6 m/s and 0.87 g/L chemical additive was added.

•Stainless steel meshes (SSM) with bipolar wettability were successfully fabricated.•Oil (low density)-water mixtures can be separated by highly-hydrophilic SSM.•Oil (high density)-water mixtures can be separated by hydrophobic SSM.•Modified SSM of small pore size can present effective oil-water separation.•Hydrophobic SSM can be used to collect oil from oil-contaminated water.Oil contamination from oilfield geothermal water severely restricts the efficient utilization of geothermal energy. Oil-water separation pretreatment via removing oil from water may provide a kind of possibility to mitigate the oil pollution problem. Stainless steel filtration mesh with bipolar wettability was successfully fabricated to attempt the gravity-driven separation of various oil-water mixtures. The highly hydrophilic mesh was prepared by liquid phase deposition of TiO2, and the hydrophobic mesh was realized via the subsequent modification of fluorosilane on highly hydrophilic mesh deposited by TiO2. Only with relatively small pore size, the highly hydrophilic mesh and the hydrophobic mesh were applicable for separating oil-water mixtures. Besides, microscopic morphologies, surface chemical compositions, contact angles, water wetting behaviors, water-holding capacities, abrasion test and oil collection were also investigated. In general, the modified mesh with bipolar wettability presents gravity-driven oil-water separation for various oil-water mixtures, which may have potential industry application value such as the pretreatment of oilfield geothermal water.

Two novel solvates of ciclesonide were successfully obtained and characterized by various analytical techniques (X-ray powder diffraction, X-ray single-crystal diffraction, differential scanning calorimetry, thermogravimetric analysis and hot-stage microscopy). Crystal structure analysis results indicate that the solvate of ciclesonide formed with cyclohexane (HCC) is a channel solvate and isostructural with ciclesonide, while the solvate formed with methanol (MC) isa discrete position solvate. Thermal analysis results show that HCC could desolvate without destroying the crystal lattice. However, MC would transform into an amorphous form after desolvation and the amorphous form could recrystallize into the crystalline form of ciclesonide. Moreover, the kinetics of the HCC and MC isothermal and non-isothermal desolvation processes is calculated and discussed.

•Multi-scale phenomena were detected by wavelet analysis of acceleration signal.•Vibration signal is decomposed into micro-, meso- and macro-scale components.•Power spectra of vibration signal reflect axial particle or bubble distribution.•Energy of tube vibration shows a slight increase with heating steam pressure.•Higher steam pressure is acceptable operation conditions for graphite tube.In this study, a fluidized bed evaporator mainly made of a brittle graphite heat transfer tube was developed and the vibration acceleration signals of the tube were measured by means of accelerometer sensors and datum acquisition systems at varied steam pressure, solid holdup, particle diameter and axial position to investigate the vibration characteristics of the tube induced by an internal vapor–liquid–solid boiling flow. Multi-scale characteristics of the vibration acceleration signals are identified by the power spectral density and wavelet transformation analyses. The high (3000–9000 Hz), intermediate (500–3000 Hz) and low (0–500 Hz) frequency components of the signals are motivated by the micro-scale motion of solid particles, meso-scale motion of vapor bubbles and macro-scale motion of the circulating liquid flow, respectively. The axial distributions of solid particles and vapor bubbles in the opaque graphite tube can be well reflected by the power spectral density analysis. The tube vibration energy enhances with the increase of solid holdup. Especially, the energy of the micro-scale vibration sub-signal gradually rises and then dominates the system with solid holdup. However, the energy of the micro-scale sub-signal shows a slight increase with heating steam pressure due to the uniform axial distribution of solid particles. The influence of particle diameter is mainly reflected in the enhancement of micro-scale motion. In order to balance the possible destruction caused by tube vibration and heat transfer enhancement due to the addition and fluidization of solid particles, operating conditions of lower solid holdup and higher steam pressure are recommended for the industrial application of vapor–liquid–solid fluidized bed evaporators.

•Fluorinated TiO2 nanotube surface infused by lubricant was fabricated on titanium.•Necessity for immobilizing lubricant via roughening and fluorination was revealed.•Antifouling for crude oil contamination and corrosion resistance were presented.Soiling and corrosion are severe problems in industrial process, such as fluid transportation in pipelines and heat exchange. Therefore, fluorinated TiO2 surface infused by liquid perfluoropolyether (PFPE) was successfully fabricated on titanium. The anti-soiling and corrosion resistance performance were investigated. TiO2 formation and fluorination were realized by anodization and chemical graft. PFPE was infused in fluorinated TiO2 via capillary force. The morphologies of TiO2 were characterized and liquid PFPE film equivalent thickness was measured. Corrosion resistance of the treated samples in 3.5 wt.% NaCl solution was investigated and its corrosion resistance was obviously improved. Contact angle hysteresis and sliding angle were measured. Compared with titanium, the PFPE infused fluorinated TiO2 surface presents lower contact angle hysteresis and sliding angle for various liquids. The necessity of immobilizing PFPE with surface roughening and fluorination was revealed. Soiling tests of the samples were proceeded by immersion in crude oil. Initially few crude oil soiling was adhered on the surface infused by PFPE and the good anti-soiling performance was kept about 120 min. In general, the lubricant infused fluorinated TiO2 surface displays outstanding corrosion resistance in 3.5 wt.% NaCl solution and effective anti-soiling for crude oil contamination.

•Liquid–solid fluidization in mini-fluidized beds (MFBs) was experimentally investigated.•The study was focused on wall effect in MFBs.•Influence of particle size distribution on Richardson-Zaki exponent was explored.Expanded fluidization behavior in liquid–solid mini-fluidized beds (MFBs) was experimentally investigated using visual measurements. Wall effects in the liquid–solid MFBs were identified and explained. The measured incipient/minimum fluidization liquid velocity (umf) in the MFBs was 1.67 to 5.25 times higher than that calculated using the Ergun equation when the ratio of solid particle diameter to bed diameter varied from 0.017 to 0.091. The ratio of the Richardson–Zaki (R–Z) exponent obtained by fitting with experimental data to that calculated using the R–Z correlation varied from 0.92 to 0.55. A wider solid particle size distribution resulted in a smaller R–Z exponent. The influence of the solid particle material on umf and R–Z exponent was negligible.

Surface coating is considered to be an efficient method to control the corrosion of carbon steel. Sol–gel silica coatings and hydrophobic silane–silica coatings were prepared on the substrates of polished and phosphated carbon steel and were characterized with scanning electron microscopy, energy-dispersive spectrometry, X-ray photoelectron spectroscopy and contact angle analyzer. Corrosion behaviors of these coated samples were investigated by potentiodynamic polarization tests in 3.5 wt% sodium chloride solution at 25 °C. Uniform, flat and dense silica coatings were formed on the phosphated carbon steel. The contact angle of water increased from about 70° on silica coating to 127° on hydrophobic silane–silica coating, while there was no significant change on contact angle by phosphating pretreatment. Both of the corrosion potential and polarization resistance of the coatings increased and the corrosion rate decreased with phosphating pretreatment. However, the addition of silane could reduce the corrosion resistance of the coatings to a certain degree, and most coatings had defects such as cracks, which were adverse to corrosion prevention.

Pool boiling of CaSO4 solution on prepared microscale and nanoscale hydrophobic titania–fluoroalkylsilane (TiO2–FPS) composite coatings on polished AISI304 stainless steel (SS) substrates was carried out to evaluate the antifouling behavior of these surfaces. Lower fouling resistance and looser, slender, and larger CaSO4 crystals on hydrophobic TiO2–FPS coatings were observed compared to those on the TiO2 coatings and SS surfaces. The colloidal interaction energies between crystalline particles and coated surfaces were analyzed by using the extended Dejaguin– Landau–Verwey–Overbeek (XDLVO) theories to explore the possible mechanism of inhibition of fouling. The results of the XDLVO analyses generally agree to the experimental observations. The Lewis acid–base component contributes most of the total XDLVO interaction energy. Low surface free energy and electron donor component of heat transfer surface lead to a low fouling resistance and a small initial deposition rate of CaSO4 fouling. On the basis of the XDLVO evaluations, a key strategy to reduce the CaSO4 deposition rate on heat transfer surface is suggested.

The fractal structures of flow images of gas–liquid–solid circulating fluidized beds (GLSCFBs) with low solid holdups of macroporous resin particles at different operating conditions and liquid physical properties were investigated by the fractal analysis method. The images were obtained with the high-speed image acquisition and treatment system of complementary metal oxide semiconductor (CMOS). The results show that the structure of the gas–liquid–solid circulating flow exhibits certain fractal behavior and the fractal dimension D can be used to describe the multiphase self-organization flow structure from the point of view of geometry. The fractal dimension changes with the phase holdup and the agglomeration degree of bubbles or/and particles. Generally, higher solid or gas holdup leads to larger fractal dimension and more extensive aggregation or self-organization degree results in lower entropy and thus lower fractal dimension. In order to avoid the appearance of the aggregation in the GLSCFB riser, higher superficial velocity of primary liquid flow, lower superficial velocity of auxiliary liquid flow, and lower liquid surface tension may be exerted.

Two critical problems in geothermal utilization are corrosion and fouling on the surfaces of plants and fittings, and use of surface coatings is a good method to overcome such difficulties. Silica coatings with film thickness of several hundred nanometers on copper substrates were prepared by the liquid-phase deposition technique and characterized with respect to surface morphology, composition, surface free energy, roughness, and film thickness. Examinations of both fouling in calcium carbonate solution and corrosion in corrosive geothermal water on the surfaces of SiO2-coated samples were performed. The results showed that the fouling rate on the SiO2-coated surface was obviously reduced compared with that on the polished surface. Moreover, the inhibition of corrosion on the modified surface was found even though, after a long immersion time, the corrosion resistance action decreased because of the surface peeling of SiO2-coated samples. The corrosion behavior of the SiO2 coating was further studied with electrochemical measurements by electrochemical impedance spectroscopy. This work suggests a new possibility for solving the fouling and corrosion issues encountered in the use of geothermal water.

A novel gas−liquid−solid circulating fluidized bed adsorber for the separation of natural products or traditional Chinese medicines from extracts was successfully developed in this work. The hydrodynamics, axial dispersion, and mixing characteristics of phases and the adsorption and desorption of Ginkgo flavonoids in macroporous resin particles with prepared extract were investigated. The results showed that with the increase of downer superficial gas velocity, the deviation degree of flow pattern from plug flow, and the liquid back-mixing in the downer were enhanced because the liquid Pe number of the downer became smaller while its axial dispersion coefficient got larger. Similar tends were found for the riser as the riser superficial gas velocity climbed. Compared with that of the downer, the flow in the riser was more close to plug flow. Investigations on the adsorption kinetics of macroporous resin particles showed that the adsorption separation of Ginkgo flavonoids from extract was controlled by the surface film mass transfer and intraparticle diffusion. Experimental results of adsorption separation of Ginkgo flavonoids in the three-phase circulating fluidized bed indicated that the air bubbles introduced in a liquid−solid circulating fluidized bed could enhance the adsorption and desorption processes, and smaller particles, lower superficial feed velocity, and adsorbate concentration were favorable for the three-phase circulating fluidized bed adsorption separation. The adsorption model of the downer and the desorption model of the riser were built, and they predicted the adsorption and desorption processes well.

In this paper, the clustering behavior of solid particles in a two-dimensional (2D) liquid–solid fluidized-bed was studied by using the charge coupled devices (CCD) imaging measuring and processing technique and was characterized by fractal analysis. CCD images show that the distribution of solid particles in the 2D liquid–solid fluidised-bed is not uniform and self-organization behavior of solid particles was observed under the present experimental conditions. The solid particles move up in the 2D fluidized-bed in groups or clusters whose configurations are often in the form of horizontal strands. The box fractal dimension of the cluster images in the 2D liquid–solid fluidized-bed increases with the rising of solid holdup and reduces with the increment of solid particle diameter and superficial liquid velocity. At given solid holdup and solid particle size, the lighter particles show smaller fractal dimensions.