Spacing Analysis of Casting Dolly Windows for Tunnel Sidewall Lining Based on the Flow Characteristics of Freshly Mixed Concrete

During the actual construction of tunnel sidewall lining, construction workers often use only one or two windows per layer for pouring in order to reduce the construction sequence, which often leads to a reduction in the quality of tunnel sidewall concrete pouring. Therefore, this study analysed the necessity of the window-by-window pouring of sidewall lining through the study of concrete flow characteristics of the tunnel sidewall lining pouring process, and the reasonable spacing of pouring windows was analysed. This study firstly verified the accuracy of the simulation parameters and the feasibility of the simulation method of the lining pouring process through indoor experiments and simulation analyses, and then it numerically simulated and analysed the flow of concrete during the lining pouring process of tunnel sidewalls. The following conclusions were made: the smaller the slump of the freshly mixed concrete, the higher the pumping flow rate; additionally, the shorter the one-time pouring distance, the smaller the spacing of the trolley feeding window should be. Furthermore, this study makes suggestions for the reasonable spacing of pouring trolleys under several working conditions.

Study on the Characteristics of Circumferential and Longitudinal Flow of Vault Concrete during Tunnel Lining Pouring Processes

With a large number of railroad and highway tunnels opening for operation, the diseases caused by hidden lining defects are increasing. The study of flow characteristics of freshly mixed concrete during tunnel lining casting is the key to revealing the formation mechanism of hidden defects. This paper revealed the location of blank lining formation by investigating the circumferential and longitudinal flow characteristics of concrete in the vault during tunnel pouring to provide suggestions for improving the quality of tunnel lining pouring for the various projects. This paper adopted the method of indoor testing, selected the suitable working conditions and flow parameters, validated the accuracy of the test with a numerical simulation, and simulated the secondary lining pouring process of the tunnel arch from the circumferential direction and longitudinal direction. This revealed the flow characteristics of the freshly mixed concrete in the process of pouring the arch lining. The flow of concrete in the arch lining was basically characterized by two major features which were similar to the flow in the pumping pipe and the layered flow. It also revealed the relationship between the concrete flow rate, flow distance, and the location of the formation of the blank lining risk zone with the slump of the concrete, the pumping pressure, and the radius of the tunnel.

Liquid Mixing on Falling Films: Marker-Free, Molecule-Sensitive 3D Mapping Using Raman Imaging

Following up on a proof of concept, this publication presents a new method for mixing mapping on falling liquid films. On falling liquid films, different surfaces, plain or structured, are common. Regarding mixing of different components, the surface has a significant effect on its capabilities and performance. The presented approach combines marker-free and molecule-sensitive measurements with cross-section mapping to emphasize the mixing capabilities of different surfaces. As an example of the mixing capabilities on falling films, the mixing of sodium sulfate with tap water is presented, followed by a comparison between a plain surface and a pillow plate. The method relies upon point-by-point Raman imaging with a custom-built high-working-distance, low-depth-of-focus probe. To compensate for the long-time measurements, the continuous plant is in its steady state, which means the local mixing state is constant, and the differences are based on the liquids' position on the falling film, not on time. Starting with two separate streams, the mixing progresses by falling down the surface. In conclusion, Raman imaging is capable of monitoring mixing without any film disturbance and provides detailed information on liquid flow in falling films.

Flow Characteristics of Heat and Mass for Nanofluid under Different Operating Temperatures over Wedge and Plate

BACKGROUND AND PURPOSE

Nanofluids are a new class of heat transfer fluids that are used for different heat transfer applications. The transport characteristics of these fluids not only depend upon flow conditions but also strongly depend on operating temperature. In respect of these facts, the properties of these fluids are modified to measure the temperature effects and used in the governing equations to see the heat and mass flow behavior. Design of Model: Consider the nanofluids which are synthesized by dispersing metallic oxides (SiO₂, Al₂O₃), carbon nanostructures (PEG-TGr, PEG-GnP), and nanoparticles in deionized water (DIW), with (0.025-0.1%) particle concentration over (30-50 °C) temperature range. The thermophysical properties of these fluids are modeled theoretically with the help of experimental data as a function of a temperature and volume fraction. These models are further used in transport equations for fluid flow over both wedge and plate. To get the solution, the equations are simplified in the shape of ordinary differential equations by applying the boundary layer and similarity transformations and then solved by the RK method.

RESULTS

The solution of the governing equation is found in the form of velocity and temperature expressions for both geometries and displayed graphically for discussion. Moreover, momentum and thermal boundary layer thicknesses, displacement, momentum thicknesses, the coefficient of skin friction, and Nusselt number are calculated numerically in tabular form.

FINDING

The maximum reduction and enhancement in velocity and temperature profile is found in the case of flow over the plate as compared to the wedge. The boundary layer parameters are increased in the case of flow over the plate than the wedge.

Design of Improved Flow-Focusing Microchannel with Constricted Continuous Phase Inlet and Study of Fluid Flow Characteristics

This paper proposed an improved flow-focusing microchannel with a constricted continuous phase inlet to increase microbubble generation frequency and reduce microbubbles' diameter. The design variables were obtained by Latin hypercube sampling, and the radial basis function (RBF) surrogate model was used to establish the relationship between the objective function (microbubble diameter and generation frequency) and the design variables. Moreover, the optimized design of the nondominated sorting genetic algorithm II (NSGA-II) algorithm was carried out. Finally, the optimization results were verified by numerical simulations and compared with those of traditional microchannels. The results showed that dripping and squeezing regimes existed in the two microchannels. The constricted continuous phase inlet enhanced the flow-focusing effect of the improved microchannel. The diameter of microbubbles obtained from the improved microchannel was reduced from 2.8141 to 1.6949 μm, and the generation frequency was increased from 64.077 to 175.438 kHz at the same capillary numbers (Ca) compared with the traditional microchannel. According to the fitted linear function, it is known that the slope of decreasing microbubble diameter with increasing Ca number and the slope of increasing generation frequency with increasing Ca number are greater in the improved microchannel compared with those in the traditional microchannel.

Effect of Fuel Preheating on Engine Characteristics of Waste Animal Fat-Oil Biodiesel in Compression Ignition Engine

The present study aims at understanding the effects of fuel preheating on engine characteristics of waste animal fat-oil (WAF-O) biodiesel in a single-cylinder CI engine, with the preheating technique proposed as an effective means for enhancing the fuel properties. To understand the effects of the preheated fuel, the WAF-O biodiesel was preheated at 60, 80, 100 and 120 °C and tested along with neat diesel and unheated WAF-O biodiesel. For this purpose, biodiesel was produced from different animal wastes by means of KOH-assisted ethanol-based transesterification, reporting its maximum yield as 96.37 ± 1.8%, with significant distribution of unsaturated oleic acid, saturated palmitic acid and stearic acid. Upon evaluating its fuel characteristics as per ASTM D6751 standards, a rise in preheating temperature by 1 °C reduced the density and kinematic viscosity of WAF-O biodiesel by 0.383 kg/m3 and 0.025 mm2/s, respectively, and was explained by the weakening of intermolecular forces between its fatty acid ester molecules. Preheated samples reported superior combustion characteristics by exhibiting increased in-cylinder pressure (2.24%, on average) and heat release rates in addition to their shortened ignition delay (1−4 °CA). Furthermore, preheating of WAF-O biodiesel reduced its specific fuel consumption and increased its brake thermal efficiency by 7.86% (on average) and 9.23% (on average), respectively. However, higher preheating temperatures (>120 °C) resulted in increased fuel consumption owing to its varied flow characteristics. In addition to the changes in combustion characteristics, preheating WAF-O bio-diesel also resulted in reduced carbon monoxide, nitrous oxide and hydrocarbon emission by 13.88%, 7.21% and 26.94%, respectively, and increased carbon dioxide emission by 7.58%. Summing up, the enhancements in overall engine characteristics of preheated samples were accounted for by their improvised fuel injection characteristics due to their reduced density and viscosity, which ensured for their effective combustion.

Marker-Free, Molecule Sensitive Mapping of Disturbed Falling Fluid Films Using Raman Imaging

Technical liquid flow films are the basic arrangement for gas fluid transitions of all kinds and are the basis of many chemical processes, such as columns, evaporators, dryers, and different other kinds of fluid/fluid separation units. This publication presents a new method for molecule sensitive, non-contact, and marker-free localized concentration mapping in vertical falling films. Using Raman spectroscopy, no label or marker is needed for the detection of the local composition in liquid mixtures. In the presented cases, the film mapping of sodium sulfate in water on a plain surface as well as an added artificial streaming disruptor with the shape of a small pyramid is scanned in three dimensions. The results show, as a prove of concept, a clear detectable spectroscopic difference between air, back plate, and sodium sulfate for every local point in all three dimensions. In conclusion, contactless Raman scanning on falling films for liquid mapping is realizable without any mechanical film interaction caused by the measuring probe. Surface gloss or optical reflections from a metallic back plate are suppressed by using only inelastic light scattering and the mathematical removal of background noise.

Prediction on Flow and Thermal Characteristics of Ultrathin Lubricant Film of Hydrodynamic Journal Bearing

This paper focuses on the flow and thermal characteristics of the lubricant film in the micro clearance of a hydrodynamic journal bearing (HJB) at high rotating speed. A thermohydrodynamic (THD) method consists of the Reynolds equation coupled with energy and viscosity-temperature equation with considering the cavitation is put forward. The 3D surface diagrams of the lubricant film thickness, pressure, temperature, liquid mass fraction, flow rate and heat dissipation distributions under different geometric, operating, slip and no-slip boundary conditions are systemically exhibited and analyzed. The results show that with the rise of eccentricity or length diameter ratio, the maximum peaks of pressure, temperature and heat dissipation are rapidly increased, the cavitation is aggravated, and the flow rate is accelerated in different extent. As the bearing speed accelerating, the maximum peak of temperature is strongly increased, whereas, the distinction between peaks of flow rate and heat dissipation is magnified and reduced, respectively. It provides a fruitful inside view of the inner flow and thermal characterizations of HJB for further understanding its flow-thermal interaction mechanisms and offers theoretical support for improving its working performance.

Morphology Development and Flow Characteristics during High Moisture Extrusion of a Plant-Based Meat Analogue

Plant-based meat analogues that mimic the characteristic structure and texture of meat are becoming increasingly popular. They can be produced by means of high moisture extrusion (HME), in which protein-rich raw materials are subjected to thermomechanical stresses in the extruder at high water content (>40%) and then forced through a cooling die. The cooling die, or generally the die section, is known to have a large influence on the products' anisotropic structures, which are determined by the morphology of the underlying multi-phase system. However, the morphology development in the process and its relationship with the flow characteristics are not yet well understood and, therefore, investigated in this work. The results show that the underlying multi-phase system is already present in the screw section of the extruder. The morphology development mainly takes place in the tapered transition zone and the non-cooled zone, while the cooled zone only has a minor influence. The cross-sectional contraction and the cooling generate elongational flows and tensile stresses in the die section, whereas the highest tensile stresses are generated in the transition zone and are assumed to be the main factor for structure formation. Cooling also has an influence on the velocity gradients and, therefore, the shear stresses; the highest shear stresses are generated towards the die exit. The results further show that morphology development in the die section is mainly governed by deformation and orientation, while the breakup of phases appears to play a minor role. The size of the dispersed phase, i.e., size of individual particles, is presumably determined in the screw section and then stays the same over the die length. Overall, this study reveals that morphology development and flow characteristics need to be understood and controlled for a successful product design in HME, which, in turn, could be achieved by a targeted design of the extruders die section.

Numerical Simulation of Swirl Flow Characteristics of CO2 Hydrate Slurry by Short Twisted Band

The development of oil and gas resources is gradually transferring to the deep sea, and the hydrate plugging of submarine pipelines at high pressures and low temperatures is becoming an important problem to ensure the safety of pipeline operations. The swirl flow is a new method to expand the boundary of hydrate safe flow. Numerical simulation of the hydrate slurry flow characteristics in a horizontal pipeline by twisted band has been carried out, and the flow of CO₂ hydrate slurry in low concentration has been simulated by the RSM and DPM models. The results show that the heat transfer efficiency is also related to Re and particle concentration. The velocity distribution has the form of symmetrical double peaks, and the peaks finally merge at the center of the pipeline. Vortexes firstly appear on both sides of the edge of the twisted band, and then move to the middle part of the twisted band. Finally, the vortex center almost coincides with the velocity center. The rotation direction of hydrate particles is the same as the twisted direction of the twisted band, twist rate (Y) is smaller, Re is larger, and the symmetric vortex lines merge farther away. The initial swirl number is mainly related to Y, but not Re. The swirl flow attenuates exponentially, and its attenuation rate is mainly related to Re, but not Y. Compared with ordinary pipelines, the swirl flow can obviously improve the transportation distance of hydrate slurry.

Time-Resolved PIV Measurements and Turbulence Characteristics of Flow Inside an Open-Cell Metal Foam

Open-cell metal foams are porous medium for thermo-fluidic systems. However, their complex geometry makes it difficult to perform time-resolved (TR) measurements inside them. In this study, a TR particle image velocimetry (PIV) method is introduced for use inside open-cell metal foam structures. Stereolithography 3D printing methods and conventional post-processing methods cannot be applied to metal foam structures; therefore, PolyJet 3D printing and post-processing methods were employed to fabricate a transparent metal foam replica. The key to obtaining acceptable transparency in this method is the complete removal of the support material from the printing surfaces. The flow characteristics inside a 10-pore-per-inch (PPI) metal foam were analyzed in which porosity is 0.92 while laminar flow condition is applied to inlet. The flow inside the foam replica is randomly divided and combined by the interconnected pore network. Robust crosswise motion occurs inside foam with approximately 23% bulk speed. Strong influence on transverse motion by metal foam is evident. In addition, span-wise vorticity evolution is similar to the integral time length scale of the stream-wise center plane. The span-wise vorticity fluctuation through the foam arrangement is presented. It is believed that this turbulent characteristic is caused by the interaction of jets that have different flow directions inside the metal foam structure. The finite-time Lyapunov exponent method is employed to visualize the vortex ridges. Fluctuating attracting and repelling material lines are expected to enhance the heat and mass transfer. The results presented in this study could be useful for understanding the flow characteristics inside metal foams.

Using aeration to probe the flow characteristics associated with long-term marine macrofouling growth and suppression

It is well-established that hydrodynamics affect the settlement of biofouling organisms. Laboratory studies have demonstrated a connection between larval attachment rates and the prevalence of time windows that satisfy certain instantaneous flow conditions. However, it is unclear whether a link exists between short-term hydrodynamics and long-term macrofouling survival and growth, or if it is applicable at an ecosystem-wide level. This study used single bubble stream aeration in field and laboratory experiments to find critical flow characteristics that correlate to long-term, multi-species fouling prevention. The research was accomplished by combining PIV-derived flow statistics with fouling severity measured over seven weeks in the field. Flows with a decreasing proportion of time windows defined by a flow speed < 15.1 mm s^-1 for longer than 0.03 s correlated to decreased biofouling growth and survival. These results provide a potential framework for studying and comparing flow fields that successfully inhibit biofouling growth.

Flow Characteristics of the Entrance Region with Roughness Effect within Rectangular Microchannels

We conducted systematic numerical investigations of the flow characteristics within the entrance region of rectangular microchannels. The effects of the geometrical aspect ratio and roughness on entrance lengths were analyzed. The incompressible laminar Navier–Stokes equations were solved using finite volume method (FVM). In the simulation, hydraulic diameters (Dh) ranging from 50 to 200 µm were studied, and aspect ratios of 1, 1.25, 1.5, 1.75, and 2 were considered as well. The working fluid was set as water, and the Reynolds number ranged from 0.5 to 100. The results showed a good agreement with the conducted experiment. Correlations are proposed to predict the entrance lengths of microchannels with respect to different aspect ratios. Compared with other correlations, these new correlations are more reliable because a more practical inlet condition was considered in our investigations. Instead of considering the influence of the width and height of the microchannels, in our investigation we proved that the critical role is played by the aspect ratio, representing the combination of the aforementioned parameters. Furthermore, the existence of rough elements obviously shortens the entrance region, and this effect became more pronounced with increasing relative roughness and Reynolds number. A similar effect could be seen by shortening the roughness spacing. An asymmetric distribution of rough elements decreased the entrance length compared with a symmetric distribution, which can be extrapolated to other irregularly distributed forms.

Improved processability of ethambutol hydrochloride by spherical agglomeration

Ethambutol hydrochloride (ETB), high dose anti-tubercular drug exhibits poor micromeritics and compressibility. The current study aimed to enhance flow, compressibility and packing characteristics, thereby improving processability of ETB by spherical agglomeration. Quasi emulsion solvent diffusion method was used for agglomeration process in which saturated aqueous ETB solution was prepared and the crystallization was carried out subsequently at different ratios of acetone and ethyl acetate which act as anti-solvent. Further the process was optimised statistically using 3² factorial design keeping 'speed of stirring' and 'ratio acetone and ethyl acetate' as independent variables and particle size as dependent variable. Optimised batch of ethambutol hydrochloride spherical agglomerates (ETB-SA) was characterised for sieve analysis, solid state characteristics and Kawakita analysis. The uniformity of ETB-SA was observed with SEM while XRPD studies revealed reduction in crystallinity for ETB-SA. DSC and FTIR indicated no polymeric or chemical alteration during crystallization process. The flow properties of ETB-SA were found superior and its Kawakita parameters indicated improved packability and flowability compared to ETB. ETB has high solubility in water therefore was no significant difference was observed in in vitro dissolution of ETB and ETB-SA. Thus spherical agglomeration, a revered particle engineering technique, continues to be a salient approach for enhancing processability of high-dose drugs like ETB.

Standard Reference Materials for Cement Paste, Part I: Suggestion of Constituent Materials Based on Rheological Analysis

The purpose of this study was to develop a standard reference material that can simulate the flow characteristics of cement paste. For this purpose, it is important to determine the constituent materials of the standard material for cement paste. Generally, cement paste is a mixture of cement and water. To determine the constituent material of cement paste, it was divided into powder that can replace cement and matrix fluid. With the concept of rheology, which can evaluate the flow properties of selected materials quantitatively under certain mixing conditions, experiments were carried out step-by-step according to material composition combination, stage of aging, and material types. As a result, limestone powder was determined to be a cement substitute, and glycerol and water were determined to be a matrix fluid substitute. After an analysis of the compatibility with the required properties of the particulate standard materials, the finally selected standard reference material was found to satisfy the required performance.

[Design of Complex Cavity Structure in Air Route System of Automated Peritoneal Dialysis Machine]

This paper introduced problems about Automated Peritoneal Dialysis machine(APD) that the lack of technical issues such as the structural design of the complex cavities. To study the flow characteristics of this special structure, the application of ANSYS CFX software is used with k-ε turbulence model as the theoretical basis of fluid mechanics. The numerical simulation of flow field simulation result in the internal model can be gotten after the complex structure model is imported into ANSYS CFX module. Then, it will present the distribution of complex cavities inside the flow field and the flow characteristics parameter, which will provide an important reference design for APD design.

Development of Metal Plate with Internal Structure Utilizing the Metal Injection Molding (MIM) Process

In this study, we focus on making a double-sided metal plate with an internal structure, such as honeycomb. The stainless steel powder was used in the metal injection molding (MIM) process. The preliminary studies were carried out for the measurement of the viscosity of the stainless steel feedstock and for the prediction of the filling behavior through Computer Aided Engineering (CAE) simulation. PE (high density polyethylene (HDPE) and low density polyethylene (LDPE)) and polypropylene (PP) resins were used to make the sacrificed insert with a honeycomb structure using a plastic injection molding process. Additionally, these sacrificed insert parts were inserted in the metal injection mold, and the metal injection molding process was carried out to build a green part with rectangular shape. Subsequently, debinding and sintering processes were adopted to remove the sacrificed polymer insert. The insert had a suitable rigidity that was able to endure the filling pressure. The core shift analysis was conducted to predict the deformation of the insert part. The 17-4PH feedstock with a low melting temperature was applied. The glass transition temperature of the sacrificed polymer insert would be of a high grade, and this insert should be maintained during the MIM process. Through these processes, a square metal plate with a honeycomb structure was made.

Micro-particle image velocimetry for velocity profile measurements of micro blood flows

Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles seeded in blood flows. The images are cross-correlated to give an accurate velocity profile. A protocol is presented for μPIV measurements of blood flows in microchannels. At the scale of the microcirculation, blood cannot be considered a homogeneous fluid, as it is a suspension of flexible particles suspended in plasma, a Newtonian fluid. Shear rate, maximum velocity, velocity profile shape, and flow rate can be derived from these measurements. Several key parameters such as focal depth, particle concentration, and system compliance, are presented in order to ensure accurate, useful data along with examples and representative results for various hematocrits and flow conditions.