Entrance Pressure Research Articles

Rheology of automotive adhesives during dispensing: A direct comparison of epoxy and rubber based systems via drag and pressure driven flows

Construction of vehicles requires adhesive dispensing for body-in-white assembly, hemming of closure panels, decking of windshields and the manufacture of battery packs. Knowledge of the rheological properties of adhesives applied using common dispensing systems is important for optimization of dispensing and application conditions. However, flow behavior of adhesives at shear rates used in dispensing is not well understood. Therefore, this study combines parallel plate and capillary rheology techniques to directly compare the rheological properties of an epoxy structural adhesive used in hemming applications and a rubber ‘topical sealer’ used to seal water leak paths across the range of shear rates observed in dispensing. Shear viscosity (η) and complex viscosity (η*) master curves were created from time-temperature-superposition (TTS) of steady shear and dynamic oscillatory data. Both adhesives did not follow the Cox-Merz rule. It was found that the Carreau-Yasuda model fit the steady shear viscosity master curve of the epoxy structural adhesive, while a simpler power law model fit the steady shear viscosity master curve of the rubber topical sealer. An inexpensive capillary rheometer was developed to simulate the adhesive dispensing process. Viscosity data was corrected for entrance pressure losses and a non-Newtonian flow front using Bagley and Weissenberg-Rabinowitsch corrections, respectively. It was observed that complex viscosity master curves better predicted viscosity during dispensing, as compared to steady shear viscosity master curves. Linear stress ramp measurements showed that the adhesives have widely different yield stresses, while the capillary rheometry measurements showed they have similar viscosities during dispensing. Furthermore, the capillary rheometer ‘shot meter’ pressures were related to the apparent and doubly corrected viscosity values through power law functions. A new quality control method based on the capillary rheology data is proposed.

Correction to: Evaluation of membrane quality and entrance pressure of oil-based mud at elevated temperatures

Correction to: Evaluation of membrane quality and entrance pressure of oil-based mud at elevated temperatures

On Characterization of Shear Viscosity and Wall Slip for Concentrated Suspension Flows in Abrasive Flow Machining.

In the realm of abrasive flow machining (AFM), precise finishing and maintaining dimensional accuracy have remained challenging due to non-uniformities in the AFM process and complexities associated with the abrasive media's shear viscosity and wall slip behavior. By addressing these challenges, this study introduces a comprehensive framework, combining theoretical foundations, measurement techniques, and experimental setups. Utilizing capillary flow, a novel compensation strategy is incorporated within the Mooney method to counter entrance pressure drop effects. This enhanced capillary flow method emerges as a promising alternative to the conventional Cox-Merz empirical rule, enabling precise characterization of wall slip behavior and shear viscosity, particularly at elevated shear rates. The abrasive media exhibit a Navier nonlinear wall slip, as highlighted by the Mooney method. Rigorous verification of the proposed methodologies and models against supplemental experiments showcases a high degree of congruence between predicted and observed results, emphasizing their accuracy and broad application potential in AFM. This research illuminates the intricacies of the abrasive media's behavior, accentuating the need for meticulous characterization, and provides a robust foundation for genuine modeling and predictions in material removal within AFM.

Argon Gas Flow Through Micro- and Nano-pipettes

Glass micropipettes and nanopipettes are widely used for injection to or aspiration from living cells, and nanopipettes can be also used for nano-fabrication by deposition. Here, we show a non-destructive and contamination-free method of examining the inside of glass micropipettes and nanopipettes by argon gas flow through the pipettes from the tip-top to the tube-end. The exit pressure for each pipette was measured at the entrance pressure of 50 kPa, and the semi-log plot of the vacuum conductance versus pipette inner diameter is compared with the calculation using tapered tube approximation assuming molecular flow. The experimental results were consistent in trend with the calculation, and the difference between the experimental results and the calculation was due to the intermediate gas flow as the pipette inner diameter increases. Therefore, the formula of the calculation was transformed using the Gompertz function to fit the experimental results well. By utilizing the plot of the inner diameter dependence of the exit pressure, the inner diameter of glass pipettes can be estimated from our developed gas flow method.

Evaluation of membrane quality and entrance pressure of oil-based mud at elevated temperatures

AbstractThis study fully explored the impact of temperature on the membrane quality of oil-based mud (OBM) using static gravimetric measurements, membrane efficiency and entrance pressure tests. More than 30 shale samples were used to assess the membrane behavior of several OBMs under elevated temperatures. Results suggested that OBM acted as a semi-permeable membrane at low temperatures (25–55˚C) since ion flow out of OBM and into shale was restricted despite the existence of a large ionic concentration gradient, while water flowed freely out of shale and into OBM because of the existence of a chemical potential difference. For temperatures higher than 55˚C, relatively higher ion flux into shale and slightly lower water flow out of shale was observed. Excessive heat may have possibly destabilized or even destroyed the emulsifier's structure that serves as a mechanism through which OBM performs as a semi-permeable membrane. The instability of OBM's emulsifier was further confirmed through entrance pressure testing where an appreciable reduction in entrance pressure of OBM was measured at high temperatures.

Experimental and Numerical Analysis of Single Screw Extrusion Process for Thermoplastic PBX Based on PVT Properties

Much of surplus ammunition stockpile inevitably requires demilitarized processing technology in the explosives industry. For the safe waste treatment and recycle, the thermoplastic polymer bonded explosive (PBX) can effectively reduce the military cost and non-conforming products. In addition, the thermoplastic PBX has excellent application prospect as the future explosive due to the good mechanical properties and insensitivity. However, for high solid content, most of thermoplastic PBXs still maintain a considerable viscosity even in high-temperature melting state, rendering traditional casting process unsuitable. In this study, a measuring method was adopted to accurately obtain the correlation of Pressure-Volume-Temperature (PVT) for the simulative materials of thermoplastic PBX at first. The equations of state for PVT and viscosity model were then created, which are of great significance in single screw extrusion. An experiment system of single screw extrusion was designed to implement the molding process considering the poor liquidity problem of the thermoplastic materials. Excellent molding stability (ρ<0.5 % variation) was achieved for the extrusion system. Moreover, a numerical investigation was also performed. Good agreements were yielded by comparing the simulation data and experimental results. The effects of operational parameters, i. e., the entrance pressure, barrel temperature and rotation speed on molding process of the thermoplastic materials were investigated in detail. The wall shear stress decreases with the feed inlet well sealed whereas the maximum temperature rise increases a little due to limited thermal diffusion. Either increasing temperature or decreasing rotation speed is beneficial to overall process safety. However, production cycle and attainable molding density also need to be considered at the same time. Furthermore, the process parameters should be optimized on the basis of the PVT and viscosity properties of material in practice. The investigations above can be a better guidance for the development and implementation of thermoplastic PBXs molding process.

Facile preparation of PVDF-HFP/GE tubular nanofiber membranes with 3D surface structure for high efficient continuous oil/water emulsion separation

Polymeric membranes show great potential for treating wastewater containing oil/water emulsions, which can cause serious environmental pollution. In this paper, novel polyvinylidene fluoride-co-hexafluoropropyle/graphene (PVDF-HFP/GE) tubular nanofiber membranes (TNMs) were fabricated by electrospinning and thermal treatment. The prepared TNMs were post-treated under different thermal treatment conditions to obtain 3-dimensional (3D) structures. The effects of thermal treatment time and temperature on membrane structure and performance were investigated by field-emission scanning electron microscopy, hydrophobicity, pore size and distribution, porosity, and liquid entrance pressure. After thermal treatment, more graphene was exposed to the membrane surface, which provided excellent oil/water selective wettability and anti-fouling performance. In addition, the thermally treated TNMs possessed an optimal pore structure and could separate surfactant-stabilized water-in-oil emulsions at high filtration rates (497.5 ±13.3 L·m −2 ·h −1 ) and separation efficiency (&gt;99%). Moreover, the filtration rate and separation efficiency remained constant over 10 filtration cycles, showing that these membranes have great potential for application to practical oil/water separation processes.

The Lomakin effect at laminar flow in journal bearings – Modeling and simulation

Superimposed axial flow causes an entrance pressure loss due to fluid inertia: the Lomakin effect. The present study aims to investigate its influence on stationary bearing performance. A new method applied to simulation data reveals that the Lomakin effect plays an important role and that the corresponding loss coefficient shows a pronounced circumferential distribution. Furthermore, a new model is derived which accounts for fluid inertia and includes Reynolds’ equation as limiting case for negligible inertia. The loss coefficient distribution is supplied to both the new model and Reynolds’ equation. The results show that correct treatment of the Lomakin effect is essential for prediction accuracy. The new model is nearly as accurate as the simulations while Reynolds’ equation shows significant discrepancies.

THERMAL-HYDRAULIC PERFORMANCE OF Al2O3 NANOFLUIDS UNDER LAMINAR FLOW IN A MINITUBE

The improvement of performance and applications that include the convection heat transfer process is extremely related to the thermophysical properties of the fluids. However, it was found that adding nanoparticles to the conventional fluids (known as nanofluids) is an advanced way to enhance their thermophysical properties leading to an enhanced heat transfer process. This study presents a numerical approach to investigate the laminar flow-based convective heat transfer of Al2O3 nanofluids in a mini-tube under constant heat flux boundary conditions (15 kW/m2) and at an inlet temperature of 25°C. For this study, the nanofluid samples are prepared for several concentrations of Al2O3 nanoparticles and ethylene glycol/water mixture as a base fluid. Also, the thermal properties of nanofluids and base fluid are characterized. Computational fluid dynamics tools are used to develop a numerical model and validate it in comparison to experimental data. The results are discussed based on the heat transfer coefficient, considering the entrance area, pressure drop, and friction factor to determine the performance of nanofluids in comparison to the base fluid. A considerable enhancement in the heat transfer, especially in the entrance area up to 17.8%, with a corresponding increase in the pressures drop, friction factor, and the required pumping power of the nanofluids was observed.

Entrance flow of unfoamed and foamed Herschel–Bulkley fluids

The present study investigates extrusion processing of unfoamed and foamed cocoa butter (CB) crystal-melt suspensions (CMSs) with varying crystal volume fraction ΦSFC. Capillary rheometry derived flow curves were fitted with the Herschel–Bulkley–Papanastasiou (HBP) model, and the derived yield stress to wall shear stress ratio τ0/τw of CB CMSs was compared for the various ΦSFC. Foamed CB CMSs behaved fluidlike for ΦSFC≤11.9% and according to a brittle porous solid for ΦSFC>11.9%. The dimensionless entrance pressure loss nen/α as a function of dimensionless shear stress τ∗ was higher for foamed compared to unfoamed CB CMSs at ΦSFC≤11.9% and lower for foamed compared to unfoamed CB CMSs at ΦSFC>11.9%. The ΦSFC dependent difference in nen/α was attributed to the crystal confinement in the die entrance flow, which is increased in the case of elastic gas bubble deformation and decreased in the case of plastic gas pore collapse. The computational fluid dynamics simulated flow of unfoamed and foamed CB CMSs through an abrupt circular 20:1 contraction with the HBP model was compared with the experimental results from quantitative entrance flow visualization (QEFV). Furthermore, the QEFV derived half center incidence angle θ as well as the entrance flow shear and elongational rates γ˙ef and ϵ˙ef were derived and used to establish a model predicting the Bagley entrance pressure loss ΔPBag and calculate an entrance flow characteristic shear and elongational viscosities ηefs and ηefe.

Basic Study of Extensional Flow Mixing for the Dispersion of Carbon Nanotubes in Polypropylene by Using Capillary Extrusion

Abstract This study evaluated the mixing effect of simple uniaxial extensional flow for the dispersion of multiwalled carbon nanotubes (MWCNTs) into polypropylene (PP) as a nonpolar matrix. An only converging flow allowed for a high strain rate and was suitable for the compounding process. The extensional flow was characterized from the entrance pressure drop (ΔP0) at the converging section. Thus, in this study, capillary extrusion was employed to generate uniaxial extensional flow. Based on the hypothesis that the dispersion of nanofillers depends on the magnitude of flow-induced stress, ΔP0, which related to extensional stress, was measured directly during capillary extrusion by using an orifice die. The influences of the mass flow rate and the hole diameter in the orifice die, which affected ΔP0, on the extrusion of PP nanocomposites with an MWCNT loading of 1.0 wt.% were studied. The extruded samples were collected, and the dispersion state was evaluated based on the melt viscoelastic properties, volume resistivity, and morphological observations by optical microscopy (OM) and transmission electron microscopy (TEM). The agglomeration area of the MWCNTs decreased with higher ΔP0 (higher mass flow rate and smaller hole diameter), which increased the uniformity of the dispersion. Moreover, the influence of the length-to-diameter (L/D) ratio of the hole in the capillary die on the dispersion state of the MWCNTs was investigated. A higher L/D ratio of the capillary die did not improve the dispersion state, although shear and extensional stresses were provided.

A one-dimensional flow model enhanced by machine learning for simulation of vocal fold vibration.

A one-dimensional (1D) unsteady and viscous flow model that is derived from the momentum and mass conservation equations is described, and to enhance this physics-based model, a machine learning approach is used to determine the unknown modeling parameters. Specifically, an idealized larynx model is constructed and ten cases of three-dimensional (3D) fluid-structure interaction (FSI) simulations are performed. The flow data are then extracted to train the 1D flow model using a sparse identification approach for nonlinear dynamical systems. As a result of training, we obtain the analytical expressions for the entrance effect and pressure loss in the glottis, which are then incorporated in the flow model to conveniently handle different glottal shapes due to vocal fold vibration. We apply the enhanced 1D flow model in the FSI simulation of both idealized vocal fold geometries and subject-specific anatomical geometries reconstructed from the magnetic resonance imaging images of rabbits' larynges. The 1D flow model is evaluated in both of these setups and shown to have robust performance. Therefore, it provides a fast simulation tool that is superior to the previous 1D models.

Three-layered hollow fiber (HF) membrane and its modification to enhance wetting resistance for membrane distillation (MD)

A three-layered hollow fiber (HF) membrane exhibiting enhanced permeability and wet-resistance was fabricated using polyvinylidene fluoride (PVDF) and poly(vinylidene fluoride–co-chlorotrifluoroethylene) (PVDF–CTFE) simultaneously for membrane distillation (MD). The inner, outer, and middle layers of the membrane were prepared using a macrovoid structure of PVDF–CTFE, the finger-like structure of PVDF, and thin sponge-like structure, respectively. The size of the macrovoid in the inner layer was enlarged and the permeability was enhanced using the polytetrafluoroethylenes (PTFE) as additive. However, the PTFE did not significantly change the liquid entrance pressure (LEP) of the membrane. The LEP and hydrophobicity of the inner layer of HF was increased by grafting pentafluorostyrene (PFS). The prepared membranes were characterized via several analytical tools, and the performance was evaluated using the vacuum MD (VMD) process. With 10% of PTFE, the size of the internal macrovoid increased, thus improving the flux to 137%. When PFS was grafted on the inner layer, the contact angle (CA) and liquid entry pressure (LEP) values increased to 117 and 154%, respectively, that showed an improvement in the wetting resistance. This study showed that the three-layered structure designed using the PTFE and PFS as an additive and grafting, respectively, were successfully fabricated to improve the wetting resistance and permeability.

Network model of porous media – Review of old ideas with new methods

The paper takes up the old ideas of describing porous media with several tube and network models. The well-known models received from literature gave a good concept of dewatering equilibria resulting in capillary pressure curves and pore size distributions (PoSD). However, numerical methods and measurement techniques were not sophisticated allowing to evaluate the models appropriately.In this work, a numerical method based on statistics is introduced to validate the network model of FATT from 1956: The porous filter cake structure is implemented as a matrix, which elements represent the pore size correlating with the capillary entrance pressure for each pore. The input for the calculations can be any mathematical approximation of a PoSD, which can be derived from capillary pressure tests or micro computer tomography (µCT) analysis of the filter cake.A procedure based on the concept of FATT is presented to generate dewatering equilibria for different applied pressures. Therefore, the elements of the matrix are checked to be ‘dewatered’ regarding to their size, position, the applied pressure level and the progress of dewatering. The network model known from literature is improved by implementing additional conditions for the description of physical phenomena, such as the formation of residual bridge liquid or hydrodynamic isolated areas.X-ray microscopy, mercury intrusion tests and laboratory desaturation experiments by using semipermeable membranes for capillary pressure tests are used to validate the pore size distribution. The different results are integrated into the matrix model as starting parameters. For the laboratory experiments, the PoSD is calculated from the measured capillary pressure curve, using the distributed tube model and the YOUNG-LAPLACE-equation on an equal basis to the established mercury intrusion analysis. However, with the tomography measurements, it is possible to determine PoSD using different defined geometry elements fitting inside the pore space. The force balance is evaluated at the pore entrance by using the wetting line of the pore throat. The direct measurement of the void geometry allows the calculation of the pressure distribution without the LAPLACIAN assumptions.In this way, the difference between experimental, measured and modelled PoSDs is emphasised to validate the old (and improved) ideas of network models describing porous media.

Influence of molecular weight, temperature, and extensional rheology on melt blowing process stability for linear isotactic polypropylene

In this work, three linear isotactic polypropylenes with different weight-average molecular weights, Mw, and comparable polydispersities were used to produce nonwovens by melt blowing technology at two different temperatures, T. The air/polymer flow rate was changed to maintain the same average fiber diameter, resulting in a different broadness of fiber diameter distribution, which was quantified by the coefficient of variation, CV. The elasticity of the material was evaluated by the reptation-mode relaxation time, λ1, and the Rouse-mode reorientation time, λ2, determined from the deformation rate dependent shear viscosity data. Extensional rheology was evaluated using uniaxial extensional viscosity measured over a very wide range of strain rates (2 × 104 s−1–2 × 106 s−1) using entrance pressure drop and Gibson methods. An obtained plateau value of uniaxial extensional viscosity at the highest extensional strain rates, ηE,∞ (normalized by the three times zero-shear rate viscosity, η0), and the minimum uniaxial extensional viscosity, ηE,min, were related to Mw and T using simple equations. It has been found that the stability of fiber production captured by CV depends exclusively on the extensional properties of the polypropylene melts, namely, ηE,U,∞3η0 and ηE,U,min. These findings are important especially with regard to the stable production of polymeric nanofibers by melt blowing technology.

Continuous rheological description of highly filled polymer melts for material extrusion

In additive manufacturing based on the material extrusion of filled polymer melts, a correct description of the rheological behaviour of the processed material is an important requirement. In case of highly filled feedstocks, complexities connected with a proper flow description are not only caused by the high packaging of powder particles (more than 50 vol.%) but also by the notable participation of polymer binder components in the quantification of shear viscosity. In this study, analytical expressions (master curves) of a true shear viscosity are developed to follow and continuously optimize the rheological dependence of the bulk feedstock on particular variables. A nickel-chromium-based compound (Inconel 718, content 59 vol.%) with thermoplastic binders of different molecular weight of polyethylene glycol was selected for the case study. The proposed master curves comprise simultaneously hitherto separately applied two corrections of an apparent shear viscosity: regarding the different capillary geometries with respect to entrance pressure and outlet extension, and determining an actual velocity profile based on shear rate distribution inside a feedstock. This approach eliminates the hitherto used non-Newtonian index, by means of which the logarithmic derivative was approximated. As the master curves depend exclusively on the shear rate and molecular weight of polyethylene glycol and do not involve any adjustable parameter, their application is straightforward. Their accuracy does not exceed experimental errors.

Power and Efficiency Optimization for Open Combined Regenerative Brayton and Inverse Brayton Cycles with Regeneration before the Inverse Cycle.

A theoretical model of an open combined cycle is researched in this paper. In this combined cycle, an inverse Brayton cycle is introduced into regenerative Brayton cycle by resorting to finite-time thermodynamics. The constraints of flow pressure drop and plant size are taken into account. Thirteen kinds of flow resistances in the cycle are calculated. On the one hand, four isentropic efficiencies are used to evaluate the friction losses in the blades and vanes. On the other hand, nine kinds of flow resistances are caused by the cross-section variances of flowing channels, which exist at the entrance of top cycle compressor (TCC), the entrance and exit of regenerator, the entrance and exit of combustion chamber, the exit of top cycle turbine, the exit of bottom cycle turbine, the entrance of heat exchanger, as well as the entrance of bottom cycle compressor (BCC). To analyze the thermodynamic indexes of power output, efficiency along with other coefficients, the analytical formulae of these indexes related to thirteen kinds of pressure drop losses are yielded. The thermodynamic performances are optimized by varying the cycle parameters. The numerical results reveal that the power output presents a maximal value when the air flow rate and entrance pressure of BCC change. In addition, the power output gets its double maximal value when the pressure ratio of TCC further changes. In the premise of constant flow rate of working fuel and invariant power plant size, the thermodynamic indexes can be optimized further when the flow areas of the components change. The effect of regenerator on thermal efficiency is further analyzed in detail. It is reported that better thermal efficiency can be procured by introducing the regenerator into the combined cycle in contrast with the counterpart without the regenerator as the cycle parameters change in the critical ranges.

Insight into filter cake structures using micro tomography: The dewatering equilibrium

In recent years, non-destructive X-ray microscopy (XRM) has become a common method to characterize particle systems in various scientific fields: Besides the size and shape of particles in bulk powders, the insight into filter cake structures provides additional information about micro processes during filtration and dewatering. Distributed particle properties mainly influence the porous network build-up with possible local deviation in vertical and horizontal alignment. This article focusses on the model-based correlation between the distributed particle properties and characteristic network parameters like tortuosity, pore radii and preferred capillaries for dewatering, using tomography data as model input. Therefore, cake-forming filtration experiments were carried out with a down-scaled, self-constructed in-situ pressure nutsch. The entire tomographic dataset consists of seven individual scans at certain desaturation steps at different pressure levels.For the experiments, a lognormal distributed particle system (crushed Al2O3) in the range of 55 to 200 µm inside an aqueous suspension was used, containing additives for contrast enhancement. Image data processing based on reconstructed 360° projections allows the identification of the background, solid particles and liquid phase by a two-step segmentation.The subsequent modelling uses experimentally verified particle size distributions from laser diffraction measurements (integral value), 2D- (limited number of particles) as well as tomographic analysis, based on calculated single-particle volumes given by the voxel-dataset (all particles within the scanned volume). To characterize the porous network, a developed tetrahedron model is first applied to follow the shortest way through the porous matrix, then again to calculate the widest capillary related to the pore entrance. Furthermore, with information about the pore throat distribution and the wetting line from the tetrahedron side faces, the force balance is evaluated. This results in an entrance pressure distribution, the capillary pressure curve. Experimental data according to VDI 2762 built filter cakes and mercury intrusion tests are taken as reference for validation.

Shear and extensional viscosity of thermally aggregated thermoplastic protein

AbstractNovatein is a thermoplastic produced from blood meal and is used in different agricultural applications. Novatein has some unique processing challenges and its rheology was studied using screw‐driven capillary rheometry, with a particular focus on sheet extrusion using ethylene glycol, glycerol, propylene glycol (PG), or triethylene glycol (TEG) as plasticizers. The entrance pressure drop contributed up to 44% of the total pressure drop (entrance and capillary pressure drop), but this was significantly reduced by plasticization or increased temperature. Polyol addition led to higher shear viscosities in comparison to no polyol plasticization, most likely due to improved chain mobility resulting in orientation effects. Elongational flow was dominated by primary plasticization of the protein‐rich phase and changes in secondary structure, whereas secondary plasticization (phase separation into a polyol‐rich phase) played a significant role in the reduction of the shear viscosity. Of the selected plasticizers, PG showed the most efficient plasticization in both shear and elongational flow. When combined with the beneficial secondary structural changes brought about by TEG, the sheet forming ability of Novatein was drastically improved.

Calculation of transition processes in stabilized power sources on the basis of a single-phase serial current inverter

In article on the basis of an operational method the design procedure of transients duple key of converters of constant pressure in constant pressure with adjustable size of target pressure is offered. Are recived recurrent parities for required currents and pressure which allow to make calculation of transitional process at change of entrance pressure, change of loading and also at their simultaneous change to settle an invoice transients at change of loading. Also results calculation of transitional process in the form of time diagram’s are presented.