Cylindrical Gap Research Articles

Theoretical and experimental investigation of cylindrical air gap membrane distillation system and effect of the membrane support net on its performance.

In present study a cylindrical module is studied based on air gap membrane distillation configuration and studied for desalination purpose. A complete theoretical model was developed with consideration of design and operating parameters that enabled a Cylindrical Air Gap Membrane Distillation (CAGMD) module specific performance analysis. Theoretical model was verified with the literature as well as with the experimental results carried out on a lab scale CAGMD module. The effect of support nets which supports the membrane on the air gap side is also discussed on the performance. Support nets made up of four different thermal conductivities material- copper, aluminum, brass and polypropylene (PP) are considered for this study. The effect of feed temperature and flow rate, air gap width, cold flow rate, effect of thermal conductivities of support nets and height of the module was studied on the performance of CAGMD module. Permeate flux, Specific Thermal Energy Consumption (STEC) and the Gained output ratio (GOR) was selected as the performance indicators and the results for all the resulted parameters obtained from experimental and theoretical model falls in good agreement with only 6% deviation, that suggests that the proposed model is best suitable for predicting the behavior of any cylindrical AGMD module with great effectiveness. It is suggested that for better performance of the system feed flow rate, temperature and cold flow rate should be maintained at higher level. Maximum permeate flux achieved from the CAGMD module is 9.22kg/m2h.

A lumped-parameter model of the free-flooded ring transducer array.

The free-flooded ring (FFR) transducer is an extensively used ring-type acoustic transducer in underwater environments owing to its broad operating frequency bandwidth and small size. However, achieving high sound pressure levels with a single FFR transducer is often difficult, thus necessitating the construction of vertically arranged FFR transducer arrays. This study presents a comprehensive analysis of the electrical and acoustic characteristics of an FFR transducer array by considering the mutual radiation load and the effects of gaps between adjacent piezoelectric rings. The lumped-parameter models of the piezoelectric ring, cylindrical cavity, cylindrical gap, and radiation impedance constitute an entire impedance matrix. The radiation impedance matrix for the FFR transducer array is calculated using the Helmholtz-Kirchhoff integral formula by considering the interaction of the FFR surfaces with the surrounding fluid medium. The proposed model predicts the resonance peaks in the admittance and transmitted voltage response (TVR) with a relative error of 5%, and the TVR level within a 3 dB range. Detailed analyses of a four-FFR transducer array reveal that a wider gap between each FFR leads to a decreased chance of negative conductance and broader operating bandwidth. The proposed model offers valuable insights into the design of FFR transducer arrays.

Research on Micro Gap Flow Field Characteristics of Cylindrical Gas Film Seals Based on Experimental and Numerical Simulation

Flexible support cylindrical gas film seals (CGFSs) adapt well to rotor whirling and have a good gas lubrication effect during thermal deformation. However, when a CGFS operates under the “three high” (high interface slip speed, high-pressure differential, and high ambient temperature) operating conditions, the complex deformation of the support structure is a crucial factor affecting the stability of the CGFS. A thorough and systematic analysis of the micro gap flow field characteristics of flexible support CGFSs is a fundamental problem when we study the deformation of the support structure under multiple physical field conditions. This study uses a cylindrical gas film high-speed rotor test rig to study and compare the sealing characteristics of experiments and numerical simulations and then optimizes and verifies the accuracy and effectiveness of the simulation model. A cross-scale gas film grid model is used to analyze the flow field characteristics and seal ability of different groove models and compare the mechanical characteristics and sealing performance. We also analyze the gas film pressure distribution in micro gaps and explore the impact of dynamic pressure groove microstructure on flow field characteristics. Results show that micro gaps are the primary conditions for generating hydrodynamic effects, and high rotational speed, high-pressure differential, and large eccentricity have a significant effect on improving hydrodynamic effects and enhancing gas film stability. However, an increase in these parameters can cause an increase in leakage rate. A single flow channel makes it easier to improve the hydrodynamic effect, gas film load-bearing ability, and gas film stability while reducing leakage rate. The analyses in this study supplement and improve the theory of the flow field characteristics of cylindrical annular micro gaps and provide a theoretical basis for exploring the relation between the support structural parameters of the CGFS and the mechanical characteristics of the micro gap flow field. This study provides important guidance to the establishment of a quantitative design theory of supporting structures.

FIXATION OF THE OPTICAL FIBER IN THE CONNECTOR USING HYDROGEL

A method of fastening optical fiber in a quartz connector with a sodium polysilicate hydrogel obtained in a cylindrical gap between the connector and the fiber due to the alkaline decomposition of quartz surfaces of parts was developed. The conditions of thermal decomposition of the hydrogel are determined and it is shown that the decomposition of the hydrogel with the formation of a cellular structure is possible at temperatures below the temperature of thermal decomposition of the polymer coating of the fiber. The conditions for obtaining and thermal properties of the hydrogel are determined. Conclusions are drawn about the suitability of the proposed method for fixing optical fiber in a quartz connector.

Kinetic Model of Vacuum Plasma Expansion in a Cylindrical Gap

Results of a theoretical description of collisionless kinetics of radial expansion of two-component (electron–ion) plasma in the one-dimensional cylindrical formulation of the problem are presented. The electric-field mechanism of supersonic expansion of the plasma flame due to the motion of the electron–ion ensemble and self-consistent electric field in the diode with the potential difference applied to it is demonstrated. The spatiotemporal evolution of the ion energy distribution function, electric potential, and rate of expansion of the emission boundary of the plasma flame is shown. The calculated rates of flame expansion at the copper cathode (~1.5 × 106 cm/s) well agree with the experimental data.

Kinetic Model of Vacuum Plasma Expansion in a Cylindrical Gap

Results of a theoretical description of collisionless kinetics of radial expansion of two-component (electron–ion) plasma in the one-dimensional cylindrical formulation of the problem are presented. The electric-field mechanism of supersonic expansion of the plasma flame due to the motion of the electron–ion ensemble and self-consistent electric field in the diode with the potential difference applied to it is demonstrated. The spatiotemporal evolution of the ion energy distribution function, electric potential, and rate of expansion of the emission boundary of the plasma flame is shown. The calculated rates of flame expansion at the copper cathode (~1.5 × 106 cm/s) well agree with the experimental data.

Biofilm Removal from In Vitro Narrow Geometries Using Single and Dual Pulse Er:YAG Laser Photoacoustic Irrigation.

The disinfection and removal of biofilm from titanium dental implants remains a great challenge in oral medicine. Here we present results of novel photoacoustic irrigation laser modalities for biofilm removal in model geometries mimicking the peri-implant pocket. The efficacy of single pulse (Er:YAG-SSP) and dual pulse (Er:YAG-AutoSWEEPS) photoacoustic irrigation modalities were determined for Enterococcus faecalis biofilm decontamination from titanium surfaces in narrow cylindrical and square gap geometries. The density of bacteria as well as the number of live bacteria were determined prior and after different photoacoustic treatments. Both SSP and AutoSWEEPS photoacoustic irrigation techniques removed at least 92% of biofilm bacteria during the 10 s photoacoustic treatment. The effectiveness of cleaning was better in the narrow square gap geometry compared to the cylindrical geometry. The dual pulse Er:YAG-AutoSWEEPS photoacoustic irrigation showed better results compared to SSP modality. No chemical adjuvants were needed to boost the effectiveness of the photoacoustic irrigation in the saline solution. The results imply that photoacoustic irrigation is an efficient cleaning method for debridement and decontamination in narrow geometries and should be considered as a new therapeutic option for the treatment of peri-implant diseases.

Convective heat transfer and entropy generation evaluation in the Taylor–Couette flow under the magnetic field

An applied magnetic field could effectively regulate the fluid heat transmission after adding magnetic particles, and it has a wide application perspective in various fields. In the current research, the flow behavior and heat transfer characteristics of Iron (II, III) oxide (Fe3O4) microparticle suspension in a coaxial cylindrical annular gap with a magnetic field have been performed numerically. Lorentz force and Joule heat are evaluated to elucidate the mechanism of the flow and heat transfer properties regulated by a magnetic field. The entropy generation method is applied for analyzing energy loss inside the annular gap. The results demonstrate that enhancing the Reynolds number (Re) and Hartmann number (Ha) improves the heat transfer capability of the Taylor vortex flow. The maximum improvement in heat transfer performance compared with the case at no magnetic field is 8.09%, under the Re 2663∼4009 and Ha 0∼186. The applied magnetic field causes the velocity and temperature distributions to exhibit anisotropy, and it gets more prominent with the increase of Hartmann number. Lorentz force derived from the magnetic field promotes particle motion and facilitates the base fluids and particles to exchange momentum and energy, and the Joule heat effect also regulates heat transmission. When Re =2663, the SF increase by 21.72% but ST decrease by 17.15% as Ha increases from 0 to 186. It demonstrates the changes in frictional and thermal entropy generation (SF and ST) are positive and negative correlated with the enhancement of Ha. Additionally, the effect of volume fraction on entropy production is less than that of magnetic field intensity which indicates the advantage of a magnetic field in reducing irreversibility. The analysis presented herewith provides a new means to enhance heat transfer in Taylor-Couette flow for utilizing magnetic fields.

Photothermal-induced interactions in a semiconductor solid with a cylindrical gap due to laser pulse duration using a fractional MGT heat conduction model

Photothermal-induced interactions in a semiconductor solid with a cylindrical gap due to laser pulse duration using a fractional MGT heat conduction model

Об одной из причин нарушения надежной и безопасной работы рудничной водоотливной установки

The Russian Federation is one of the world leaders in diamond mining. Currently, the predominant part (about 95 %) of all the Russian diamonds is mined at the ore (kimberlite) and alluvial deposits located on the territory of Yakutia. Practice shows that the underground development of kimberlite deposits in the territory of Western Yakutia is associated with an abundant flow of mine water into the mine workings. Without the use of a sufficient amount of pumping equipment, mine waters make the process of mining diamond-bearing ores more difficult, and most importantly, unsafe for the operating personnel. Currently, electric pump units of sectional type are used to combat the mine waterways at the kimberlite mines. In order to ensure safe mining of deposits of the solid minerals by the underground method, and to avoid flooding of the mine workings, the pumping equipment of the main drainage plant must always be in the working order, which is ensured by increasing its operational reliability. One of the probable reasons for a significant deterioration in the performance and reliability of sectional pumps is considered. As a material for analysis, practical data on the operation of the main drainage plant of the Udachny underground mine were taken. It is established that the reason for a significant deterioration in the performance of sectional pumps can be an increase in the cylindrical gap of the hydraulic heel assembly. It is shown that the increase in the gap is associated with a decrease in the outer diameter of the cylinder of the unloading disk. A significant reduction in the size of the cylinder can occur as a result of the total impact of such negative factors: an increase in the concentration of mechanical impurities in the mine water passing through the cylindrical gap of the hydraulic heel assembly; uneven distribution of pressure in the gap due to unskilled repair of the discharge cover.

A Method for Estimating the Cloud Adjacency Effect on the Ground Surface Reflectance Reconstruction from Passive Satellite Observations through Gaps in Cloud Fields

A method for estimating the cloud adjacency effect on the reflectance of ground surface areas reconstructed from passive satellite observations through gaps in cloud fields is proposed. The method allows one to estimate gaps of cloud fields in which the cloud adjacency effect can be considered small (the increment of the reflectance Δrsurf≤ 0.005). The algorithm is based on statistical simulation by the Monte Carlo method of radiation transfer in stochastic broken cloudiness with a deterministic cylindrical gap. An interpolation formula is obtained for the radius of the cloud adjacency effect that can be used for the reconstruction the ground surface reflectance in real time without calculations by the Monte Carlo method.

Shears and vortices of rotational couette flow in a cylindrical gap with radial injection and suction

We examine the shear states and vortices of rotational Couette flows with radial injection and suction. The gap of finite radius and infinite axial length lying between two concentric cylinders is assumed to be filled with incompressible Newtonian viscous fluids. To this goal, a rectilinear injected Couette flow is briefly reviewed as a preliminary to a rotational injected Couette flow. After making clear the differences among a simple shear, a pure shear, and generic shears, we formulate a single normalized shear parameter along any curve on a two-dimensional plane. By this way, the relative roles of stretch, shear, and vorticity are clarified through a suitable three-part decomposition of a velocity gradient tensor. For both rectilinear and rotating Couette flows, a certain material fluid particle spends a finite time while traveling from one boundary of injection to the other boundary of suction. We have solved material dynamics for both types of Couette flows to show how a certain fluid particle undergoes various shear states along a curved material trajectory. Such varied shear states are then compared with the shear states found from conventional spatial dynamics. In addition, the roles of enstropy and energy-density gradient are freshly examined from the viewpoints of shear states. The resulting relationships among stretch, shear, and vorticity for the injected rotational Couette flow turn out to shed light on what are going on in realistic flow configurations such as fountain flows, sink-hole flows, tokamak plasma, and tumor-cell flows, to name a few.

Decoupling tests on axial heat-transfer in highly turbulent Taylor-Couette flow using thermal waves

This study experimentally investigates the axial heat transfer of the secondary flow in the cylindrical annular gap around a flywheel within a canned reactor coolant pump, belonging to the Taylor-Couette (TC) flow. A dynamic method based on the transient temperature responses of the TC flow to the input thermal waves, where the axial heat transfer coefficient is determined by the amplitude decay and phase lag of axially propagating temperature waves, is proposed. The influences of viscous heating are distinguished using the mean temperature distribution, allowing for the performance of decoupling tests of axial heat transfer and viscous heating in TC flow. The modification of the boundary heat loss on the axial propagation of temperature waves in a rotor-fluid-stator TC system was modeled. The measured axial heat-transfer coefficient was insensitive to the oscillating periods of the input thermal waves within the maximum permitted period. The axial heat transfer coefficients with different Taylor numbers and radius ratios were measured based on the proposed method. The correlations between the axial heat-transfer coefficient and Taylor number satisfied the scaling law with an effective exponent of 0.5, but they change non-monotonically with respect to the radius ratio in highly turbulent TC flow. This study provides insight into the axial heat transfer characteristics of TC flow.

Reaction-Diffusion Modeling to Assess what Limits Effective Acetylcholine Fluctuations at High Frequency Cholinergic Electroplaques

In the weakly electric fish Eigenmannia (glass knifefish), high frequency (200-550Hz) electric organ discharge (EOD) is driven by high frequency cholinergic synaptic input onto the electrocytes at their electroplaques. Evolutionarily, this system derives from skeletal muscle endplate synapses. We are interested in what, physically, limits the rapidity with which acetylcholine (ACh) concentrations can oscillate to successfully activate post-synaptic ACh receptors (AChR) and thereby trigger EODs at the oscillating frequency. Assuming periodic release of ACh into a 50nm wide cylindrical synaptic gap, we solve numerically a one dimensional reaction-diffusion model at 200Hz and 500Hz. The model included the diffusion of ACh and its interactions with AChesterase (AChE) and AChRs. For ACh released periodically at the two frequencies, we vary the ratio of ACh input to the AChE concentration. The biochemical/biophysical characteristics of AChE/ACh and AChR/ACh are those typical of neuromuscular junctions. The AChR can be in four states: closed (AR), with one or two bound ACh molecules (AR1 and AR2) and finally open state (AR2open). At 500Hz a higher AChE/ACh ratio is needed to remove ACh from the cleft between consecutive ACh releases. Only a small fraction of the ACh molecules reaches the AChRs, and there are residual amounts of ACh molecules from the preceding release. Previous computational studies showed that the persistently present ACh should not impede high frequency electrocyte firing, provided the cholinergic current is subthreshold for triggering firing. In our simulations, the fast AChE-ACh reactions (not AChR-ACh kinetics) limit the upper frequency for triggering electrocyte action potentials. We suggest, therefore, that carry-over (persistent) activation of AChRs could account for the observed upper limit for EOD frequency in Eigenmannia individuals.

Numerical Simulations of Heat Transfer Performance of Taylor–Couette Flow in Slit Model

A partially averaged Navier–Stokes model is used to simulate the fluid field in the coaxial cylindrical gap, and the reliability of numerical simulation is verified by comparing with the particle image velocimetry experiment. Firstly, the influence of structural parameters and physical parameters on heat transfer enhancement of the slit model is investigated. In the next step, response surface method is adopted to obtain the slit parameter structure with optimal heat transfer performance. Slit width (2.5 mm < w < 15 mm), slit number (9 < N < 15), Reynolds number (2000 < Re < 4652) and Prandtl number (5.90 < Pr < 6.22) are selected as design parameters while the average Nusselt number is taken as the objective function. The results show that the increasing of Reynolds number strengthens the jet flow of vortex pairs, which enhances the heat transfer capacity of the Taylor vortex. As increasing the slit width, heat transfer performance of the model increases first and then decreases. The optimized model with slit structure parameters of N = 12 and w = 13.15 mm has the best heat transfer capacity, which increases by 12.42% when Reynolds Numbers is 4652.

Analysis and optimization of a new cylindrical air gap membrane distillation system

Abstract Membrane distillation is a rate-governed non-isothermal membrane separation technique that utilizes trans-membrane temperature difference for evaporating water and thereby separating it from brackish feed for reproducing fresh water. A novel design of a cylindrical air gap membrane distillation module is presented. The module is fabricated in a way similar to a shell and tube heat exchanger. A PTFE hydrophobic membrane is used and is formed in a cylindrical shape. Design of experiments (DOE) is used to design the experiments statistically and to identify the significant operating parameters. Experiments were performed according to the Taguchi design approach using an L16 orthogonal array. Optimization of the whole process is performed by response surface methodology. It is shown that the feed temperature and feed flow rate have a positive effect, whereas the salinity has a negative impact on flux. The maximum value of flux achieved with this system is 3.6 kg/m2 hr. A high value of flux of 2.6 kg/m2 hr was achieved under optimum conditions at a temperature of 45 °C and a flow rate of 1.5 lpm with a salinity of 5 g/litre.

Simulation Study on Gap Flow Field in EDM Micro-hole Machining Based on Gas-liquid-solid Three-phase Flow

In the process of micro-hole machining in EDM, if the debris and bubbles are not removed from the gap flow field, the concentration of debris and bubbles will increase, which will cause arcing discharge and seriously affect the processing efficiency and surface quality. In this paper, the geometric model of three-dimensional cylindrical gap flow field was established. The influence of bubble generation on the gap flow field and the debris under single pulse discharge condition was analyzed by Fluent. Then using the secondary development function of Fluent, the process of the debris and bubble on the bottom surface is continuously generated and the influence of bubble on the movement of debris under continuous discharge conditions were simulated and analyzed. Finally, by considering side flushing, the motion process of bubbles and debris under the conditions of flushing was analyzed.

Critical Conditions for Plane-to-Cylindrical Detonation Wave Transformation

The critical conditions for the transformation of a plane detonation wave into a cylindrical detonation wave are experimentally found. For mixtures of oxygen with hydrogen or methane, the geometric conditions are determined for detonation initiation in a cylindrical gap at various diameters of the orifice through which the plane detonation enters the gap. To identify features of observed explosive processes, the results of two-dimensional numerical modeling are analyzed.

The volume ratio effect on flow patterns and transition processes of thermocapillary convection

Thermocapillary convection has always been one of the most important research topics in microgravity fluid physics. A space experimental study on the thermocapillary convection in an open annular liquid pool – a typical thermocapillary flow system – has been conducted on the SJ-10 satellite of China. This space experiment has observed the spatial temperature distribution of the liquid free surface using an infrared thermal imager, obtained the flow pattern transition process, analysed the oscillation characteristics and revealed the instability mechanism of themocapillary convection. The shape effects on the flow instability are researched by changing the volume ratio, Vr, which denotes the ratio of the liquid volume to the volume of the cylindrical gap between the walls. The volume ratio effect has been focused on for the first time. For a certain volume ratio, the flow pattern would transform from the steady state to the oscillation state accompanied by directional propagating hydrothermal waves with increasing temperature difference. In addition, the significant influences of the volume ratio on the critical conditions and wavenumber selection have been analysed in detail.

Saw-tooth type piezoelectric multi-modal energy harvester

The paper presents results of numerical and experimental investigations of a new design piezoelectric energy harvester based on a saw-tooth type cantilever array. The proposed energy harvester has multi-modal operation principle and allows to harvest mechanical vibrations energy in narrow frequency range. Moreover, the multi-modal operation principle of the harvester enable summation of bending strains of several cantilevers and allows to improve efficiency of the harvester. The proposed multi-modal energy harvester consist of four cantilevers that are connected rigidly to each other at 30° angles. Cross-sections of the cantilevers were modified by cylindrical gaps in order to increase bending strain. Seismic masses were placed at each corner of the harvester in order to reduce values of natural frequencies and to create additional rotation moment. Numerical investigation revealed that the energy harvester has five resonance frequencies in the range from 20 Hz to 135 Hz. The numerical investigation of electrical characteristics showed that voltage density of 48.39mV/mm3 and energy density of 61.25μJ/mm3 was obtained. Experimental investigations confirmed the results of numerical investigation and showed that voltage and energy densities reached 55.65mV/mm3and 52.56μJ/mm3, respectively.