Environment-friendly surface cleaning using micro-nano bubbles

Cleaning a surface using a solution containing a large number of micro to nano scale bubbles has significant advantage regarding environmental protection. This review first briefly introduces the cleaning mechanism of micro-nano bubbles (MNBs), including physical and chemical effects. Then the applications of MNBs in cleaning of metal parts, precision parts, cultural relics or food are introduced. After that, coupled cleaning method of ultrasound and bubbles is introduced. Finally, the characterization methods for the cleaning effect are introduced, which mainly focuses on the changes of physico-chemical properties (mass or cleaning area, infiltration, colony number and light scattering intensity) of the cleaned parts or that (like conductivity) of the solvent. It is believed that MNBs technology will be applied in a broader range of surface cleaning applications.     

Requirements and system design for a robot performing selective cleaning in young forest stands

Cleaning is a silvicultural tending operation, primarily aimed at improving the growing conditions of the remaining trees in young stands (ca. 3 m of height). The cost of cleaning has increased in comparison to other forest operations, and the annually cleaned area has decreased in Sweden. Therefore, cleaning with robots might be the key to improve profitability. This paper aims at assessing some design requirements, and suggesting an architecture for a robot cleaning in young forest stands, based on reviewed literature and our own research. The results of cleaning performed by robots have to reach acceptable results and be done at a competitive cost. The robot has to find, select, and handle trees in the whole assigned area according to given instructions. Furthermore, it must be safe for humans, capable of moving safely within the forest environment, and be able to handle snow and other prevalent boreal weather conditions. The vehicle’s size and mass are of importance, and bear on its ability to manoeuvre among remaining stems. Generally, the robot must be capable of operating independently and unattended for several hours in a dynamic and non-deterministic environment. Obstacle avoidance and target identification are identified as the most difficult problems. Machine vision, radar, and laser scanners are promising techniques for both obstacle avoidance, tree identification, and tool control. The proposed architecture is based on a hybrid between the reactive and the hierarchical robot paradigms.     

Engineering and chemical factors associated with fouling and cleaning in milk processing

The problem of fouling from food fluids is very severe, leading to the need for rapid and effective cleaning. Fouling of the process plant happens as a result of complex processes that occur when a fluid is heated: protein and minerals are both deposited on the surface. This review describes research into both the engineering and the chemical factors that lead to deposition. Fouling can be modeled by using data for the thermal behavior of β-lactoglobulin, coupled with models for the flows and temperatures of the process plant. The rate of cleaning depends on both the deposit present and the type of chemical treatment used.     

Transient removal of a contaminated fluid from a cavity

A numerical and experimental study of the time-dependent hydrodynamic removal of a contaminated fluid from a cavity on the floor of a duct is presented. The duct flow has a parabolic inlet velocity profile and laminar flows are considered in a Reynolds number range between 50 and 1600 based on the duct height. The properties of the contaminated cavity fluid are assumed to be the same as for the fluid flowing in the duct. Attention is focussed on the convective transport of contaminated fluid out from the cavity and the effect of duct flow acceleration on the cleaning process. Passive markers which are convected with the flow are used in the numerical simulation for the purpose of identifying the contaminated cavity fluid. It is shown that the cleansing of the cavity is more pronounced during the unsteady start-up of the duct flow and the rate of cleaning decreases as the flow reaches a steady state. The cleaning process is enhanced as the cavity aspect ratio is increased and as the duct Reynolds number increases. A ‘volumetric’ approach based on the spread of markers is shown to be useful in determining the fraction of the cavity that remains contaminated after steady conditions have been reached. The distribution of the contaminant in a cavity during the unsteady stage and after steady conditions are reached are identified using passive markers.     

Drying of Salt Solutions from Porous Media: Effect of Surfactants

Transport in Porous Media - The evaporation of salt (NaCl) solutions from porous media is studied in the presence of surfactants, because surfactants are often used as cleaning agents for...     

Effect of duct velocity profile and buoyancy‐induced flow on efficiency of transient hydrodynamic removal of a contaminant from a cavity

This paper describes a preliminary numerical analysis of the effect of duct velocity profile and buoyancy‐induced flow generated by the heat source on hydrodynamic removal of contaminants contained in cavities. The process of fluid renewal in a cavity is modelled via a numerical solution of the Navier–Stokes equations coupled with the energy equation for transient flows. The foulant has the same density as the fluid in the duct and the duct velocity profile is considered to be Poiseuille flow and Couette flow, respectively. The results show that the change in Grashof number and duct flow velocity profile causes a dramatic difference in the observed flow patterns and cleaning efficiency. From a cleaning perspective, the results suggest that Couette flow at higher value of Grashof number becomes more effective in further purging of contaminated fluid from a cavity. Copyright © 2004 John Wiley & Sons, Ltd.     

Method for reprocessing and recycling of aqueous rinsing liquids from car painting with water-based paints in automobile industry

In the paint processes of modern car plants the paint to be applied on the car bodies change after every few numbers. In order to avoid intermixtures of different lacquers the application systems has to be cleaned before every change by means of a rinsing liquid. Water based lacquers require water based cleaning agents. For these rinsing waters a new recycling process based on an evaporation process, a fractionated condensation and an after treatment of the condensates is described. The compatibility of the recycled system for lacquers is investigated. After a test with ten recycling loops no accumulation of harmful substances occurs. In comparison to original agents the recycled rinsing liquids show comparable or better cleaning abilities. The comparison of the energy consumption and the disposal of CO₂ and of volatile organic compounds between the application of fresh rinsing liquid with disposal after usage and recycled rinsing liquid show major advantages of the recycling process.     

Reverse osmosis membrane biofouling

The development of biofouling and its effects on membrane processes are reviewed, emphasizing the microbial attack on the membrane material and its costs. Detection and monitoring techniques are compared, and different types of countermeasures are described. Discussion is also focused on the use of biocides and the cleaning strategies to be followed in practical cases.     

Removal of Particle Bridges From a Porous Material by Ultrasonic Irradiation

Particle bridge formation during the flow of a liquid with particles through a porous material is a fouling mechanism that can block the pores and, hence, decrease the permeability of the material. Ultrasonic irradiation of the material is a cleaning method that can restore the permeability. We make a numerical study of this cleaning method using the lattice-Boltzmann method. We start from a pore blocked by two spherical particles attached to the pore wall by colloidal adhesion forces, thus forming a particle bridge. Next we calculate the hydrodynamic force exerted by a high-frequency acoustic wave on the two particles. By comparing the hydrodynamic force and the adhesion force we investigate, whether the particle bridge will be removed by the ultrasonic irradiation. A sensitivity study is carried out to investigate the influence of some relevant parameters, such as the acoustic wave amplitude, the acoustic frequency, the fluid flow velocity and the ratio of particle diameter and pore diameter. An upscaling procedure is applied to translate the microscopic results for the removal of the particles at the pore level to the permeability improvement of the material at the macroscopic level. A comparison is made between numerical results and experimental data. The agreement is reasonable.     

Numerical simulation of time‐dependent hydrodynamic removal of a contaminated fluid from a cavity

The time‐dependent hydrodynamic removal of a contaminated fluid from a rectangular cavity on the floor of a duct is analysed numerically. Laminar duct flows are considered for Reynolds numbers of 50 and 1600 where the characteristic length is the duct height. Two cases are considered where: (1) the fluid density in the cavity is the same as that for the duct fluid and (2) the cavity fluid has a higher density than the duct fluid but the two fluids are miscible. The flow is solved by a numerical solution of the time‐dependent Navier–Stokes equations. Attention is focused on the convective transport of contaminated fluid out from the cavity and the effect of duct flow velocity profile on the cleaning process. Passive markers are used in the numerical simulation for the purpose of identifying the contaminated cavity fluid. The results show that the flow patterns in the cavity are influenced by the type of duct flow. From a cleaning perspective, the results suggest that it is easier for the duct flow to penetrate a cavity and to remove contaminated cavity fluid when the duct flow is of the Poiseuille type and the aspect ratio is large. Copyright © 2003 John Wiley & Sons, Ltd.     

空间飞网两种动力学模型的比较研究

空间飞网由轻质绳索编织, 通过抛撒展开形成一定构型的网, 在空间在轨服 务、飞行器回收、轨道清理、空间拦截等领域具有巨大的应用潜力. 采用非线性有限元 软件ABAQUS建立柔性模型与松弛飞网模型, 对两种飞网模型的抛撒展开进行了对比, 提出了 飞网展开效果的衡量标准, 重点讨论了不同工况下牵引质量块质量、抛射角度、抛射速度和 绳索等效阻尼的影响. 仿真表明, 松弛模型的展开效果优于柔性模型; 牵引质量块质量、抛 射速度与绳索结构阻尼主要决定飞网的展开, 抛射角度是影响飞网在预定位置展开面积的关 键因素.     

Wave field of a directed explosion

We consider an underwater gas explosion in a cylindrical tank which is open at the bottom. The pressure field in the water is a toroidal compression wave with gradually increasing pressure behind the wave front. In the linear approximation the pressure shock occurs only under the cylinder with the gas. Filling of the lower portion of the cylinder with water alters the compression wave profile.The results obtained may be used in marine seismological prospecting for developing sources for exciting elastic vibrations which are not hazardous to the fish population, in explosive cleaning of filters in water wells, etc.     

Two-dimensional simulation of a hydraulic fracture crack cleaning process with consideration of lateral inflow of a fluid from the surrounding porous saturated rock

The cleaning of a hydraulic fracture crack filled with a fluid injected through a well is studied as one of the stages of oil extraction. A crack is considered as a porous medium whose permeability is much higher than that of the surrounding rock and whose length is several times larger than its width and is many times larger than its thickness. A two-dimensional model of this process is used; in this model it is assumed that a less viscous fluid displaces a more viscous fluid in a porous medium with consideration of inflow through the lateral surface of the crack.     

热液体动力扭带清洗动力学及其工程应用

为了解决传统扭带存在自转动力矩弱和传热强化幅度低的问题,研究入口反旋斜齿扭带的动力学理论,方法是将总动力矩分解为虚拟的光滑扭带动力矩和虚拟光滑扭带下的螺旋液流对斜齿的冲推力矩之和,运用动量矩定理分析建立了动力矩计算式．以此式指导结构优化和工程应用,使自转动力矩和传热系数均比传统扭带有了成倍提高,设备总阻力仍然在工程许可范围内,成为可以广泛应用于较低流速下自动清洗防垢与高效强化传热的新元件．     

Rotating vane rheometry — a review

The use of rotating vane geometries for the measurement of the flow properties of very non-Newtonian liquids has become increasingly popular over the last 20 years. Originally, these geometries were used to measure the apparent yield stresses of inorganic dispersions, but have more recently been used to measure other rheological parameters also. These include the low-strain modulus and the steady-state flow-curves of structured liquids. The particular advantages of the vane geometry are its simplicity of fabrication, ease of cleaning and more than anything else, its elimination of serious wall-slip effects. The development of the vane technique and the theory to go with it, together with its use in various areas are described, where these areas include inorganic colloidal dispersions, foods, bioengineering fermentation broths, etc.     

A rapid chemical method for improving peel strength at Cu-epoxy interfaces

The effect of a chemical treatment of a Cu surface on the interfacial strength between a thermoset polymer and that Cu surface has been determined. Spray technology was used to apply fixed amounts of a silane surface modifier to the cleaned Cu surface using three different plain-orifice atomizer hand-pump sprayers. The amount of spray coverage was determined for each sprayer as a function of the number of sprays and the peel strength was found to increase with the spray coverage for each sprayer. Substantial improvements to 340% in peel strength were achieved compared to the as-received condition, indicating good chemical bonding between Cu and epoxy. These results compare favorably with the results from a more complicated cleaning and oxidizing treatment which produced nano-scale features which mechanically interlock with the epoxy.     

Investigation of a heat transfer augmenter as a fouling cleaner and its optimum geometry in the tube side of a condenser

A spiral wire was used to augment the heat transfer inside the tubes of surface condensers or shell-and-tube heat exchangers. A spiral wire with a reinforcing component in the direction of the spiral axis has been investigated as a fouling cleaner on the internal surface of a tube, when it is driven in a reciprocating motion with the help of reinforcing wires. When it stays in the tube, it augments the convective heat transfer. Based on the an experimental investigation, the relationships among the heat transfer, drag, cleaning effectiveness, fouling rates, and geometric variables of the cleaner-augmenter performance were found. The results of the experimental investigations on the cleaner-augmenter and the comprehensive evaluation criterion for the device as a fouling cleaner are presented along with the dimensions of tube diameter, wire diameter, and pitch.     

Observation of multibubble phenomena in an ultrasonic reactor

A cylindrical ultrasonic reactor radiated by a BLT (bolted Langevin transducer) with a large horn operated at 27.3 kHz was employed to investigate the behaviors of bubbles in the present research. The characteristics of this reactor were analyzed using experimental methods. It was found that traveling transient bubbles can eliminate the effect of standing wave on cleaning efficiency. Fresh tap water and degassed water were employed as test liquids. In tap water, a conical cavitation structure was observed as the input voltage of transducer was increased over 100 V. The detail of the conical cavitation structure was anatomized and its shape varied with the change of input voltage. In degassed water, ultrasonic fireworks were observed and special attention was paid to their subsequences, snowflake bubble clouds and water jet.     

SIMULATION OF PARTICLE COATING IN THE SUPERCRITICAL FLUIDIZED BED

Fluidized bed technology using supercritical carbon dioxide both as a fluidizing gas and as a solvent for the coating material makes possible the production of thin, uniform and solvent-free coatings. But operation at low fluidizing velocities, which is favorable to facilitate gas cleaning under the high pressure conditions, may lead to uneven distribution of the coating in the fluidized bed and to unstable operation due to agglomeration. Therefore a model has been developed which describes local fluid dynamics within the high pressure fluidized bed. Based on this model, the coating process is described and the distribution of the coating inside the fluidized bed is calculated. Furthermore a submodel for the calculation of local concentrations of liquid paraffin has been set up, which may be used as a basis for the prediction of agglomeration and thus stability of operation.     

Frequency response of a cold-wire in a flow seeded with oil particles

Experiments have been carried out to investigate the effects of aging on the frequency response of a fine cold-wire located in a flow seeded with oil particles used for laser Doppler anemometry. Transfer functions are shown to depend strongly on the running time. Photo-micrographs show that the contamination effect is due to discrete droplets, the diameter of which increases with running time. Reduction of frequency response is shown to affect at first the high-frequency range and then an intermediate range of frequencies that are larger than the inverse of the oil droplets time constant. Good agreement is found between experimental results and predictions derived from a simple model of the contaminated wire. This contamination process requires testing and cleaning the wire steadily in order to keep a significant frequency response and, if needed, to correct temperature fluctuations.