3D Cavity Research Articles

Structural Tuning of Polymers of Intrinsic Microporosity via the Copolymerization with Macrocyclic 4‐tert‐butylcalix[4]arene for Enhanced Gas Separation Performance

Abstract4‐tert‐butylcalix[4]arene (CA) is chemically incorporated into polymers of intrinsic microporosity (PIM‐1) via a one‐step nucleophilic copolymerization reaction to study the unprecedented synergistic effects of polymer structural tuning and the unique 3D cavity of CA on gas separation performance. From the wide‐angle X‐ray diffraction (XRD) and positron annihilation spectroscopy (PALS), two opposing structural effects of CA incorporation on polymer chains are found, with one being expansive for fractional free volume (FFV) and the other contractive. The bulky cup‐shape CA cavity reduces the chain packing efficiency, which increases FFV and the gas permeability, but the smaller dihedral angle of CA shrinks FFV, leading to the enhanced gas selectivity. More interestingly, CA's unique 3D open cavities also favor selective passage of gas molecules. These combinative effects impart PIM‐CA copolymer membranes with attractive and tunable gas transport properties. The gas permeability improves dominantly at small CA loadings while the selectivity is enhanced significantly at higher loadings, allowing PIM‐CA membranes with ≥1% CA loadings to perform beyond 2008 Robeson upper bounds for H2/N2, H2/CH4, CO2/N2, and CO2/CH4 separations. As a cheap commercial product with high chemical versatility, CA can expand the spectrum of PIM‐based membrane designs for more efficient hydrogen and natural gas purification processes.

A numerical methodology for efficient simulations of non-Oberbeck-Boussinesq flows

The Oberbeck-Boussinesq (OB) form of the Navier-Stokes equations can provide reliable solutions only for problems where the density differences are relatively small and all other material properties can be considered constant. For heat transfer problems at large temperature differences, the dependence of the material properties on temperature is the main source of non-Oberbeck-Boussinesq (NOB) effects. When a numerical solution is attempted for this category of problems, due to the density variations of the heated medium, a variable coefficient Poisson equation for the pressure emerges which is difficult to solve in a computationally efficient manner.In the present study, an efficient methodology to treat incompressible flows with variable properties outside the range of validity of the OB approximation is proposed. In the context of this methodology, the variable coefficient Poisson equation for the pressure is transformed into a constant coefficient Poisson equation using a pressure-correction scheme. In addition, all thermophysical properties are considered to be temperature dependent for all terms of the conservation equations. The proposed methodology is validated against results provided by previous studies on the natural convection flow of air, water and glycerol. Moreover, the potential of this methodology is demonstrated with the direct numerical simulation (DNS) of the NOB Rayleigh-Bénard convection of water inside a three-dimensional (3D) cavity. The comparison between two-dimensional (2D) and 3D results reveals significant differences, highlighting the need for efficient methodologies capable to accurately simulate NOB problems in 3D.

Compact 3D quantum memory

Superconducting 3D microwave cavities offer state-of-the-art coherence times and a well-controlled environment for superconducting qubits. In order to realize at the same time fast readout and long-lived quantum information storage, one can couple the qubit to both a low-quality readout and a high-quality storage cavity. However, such systems are bulky compared to their less coherent 2D counterparts. A more compact and scalable approach is achieved by making use of the multimode structure of a 3D cavity. In our work, we investigate such a device where a transmon qubit is capacitively coupled to two modes of a single 3D cavity. External coupling is engineered so that the memory mode has an about 100 times larger quality factor than the readout mode. Using an all-microwave second-order protocol, we realize a lifetime enhancement of the stored state over the qubit lifetime by a factor of 6 with a fidelity of approximately 80% determined via quantum process tomography. We also find that this enhancement is not limited by fundamental constraints.

3D thickness distributions of plano lenses as a means of cavity pressure characterization in microinjection molding.

This work presents a novel nondestructive cavity pressure characterization approach in microinjection molding (μIM) through measuring 3D part thickness distributions. For this purpose, a plano lens was designed and experiments based on Taguchi method were conducted. Both overall and local lens thickness distributions under various process conditions were analyzed in terms of their relevance with the cavity pressure during molding. Unexpectedly, a reliable linear regression model was developed fulfilling nondestructive multi-point or even continuous cavity pressure characterization with the overall lens thickness distribution. Furthermore, the topography of the constructed 3D thickness surface was found to depend on both process condition and measuring position. Finally, the process conditions were optimized for obtaining uniform distributions of both 3D thickness and cavity pressure.

Numerical study on combined buoyancy–Marangoni convection heat and mass transfer of power-law nanofluids in a cubic cavity filled with a heterogeneous porous medium

In this paper, the combined buoyancy–Marangoni convection of non-Newtonian power-law nanofluids in a 3D heterogeneous porous cubic cavity is investigated in detail with the compact high order finite volume method. Special attentions are given to detect the effects of heterogeneity level, Marangoni number, thermal Rayleigh number, buoyancy ratio and nanoparticle volume fraction on the fluid flow as well as on rates of heat and mass transfer. It is observed that as a result of the exponential distribution of the permeability, the heat and mass transfer rates reduce as the level of heterogeneity enhances. The effect of the surface tension on the heat and mass transfer intensity becomes insignificant when the buoyancy force is strengthened. Further, the average Nusselt and Sherwood numbers increase as the Marangoni number and thermal Rayleigh number increase due to the combined effects of buoyancy and surface tension. The augmentation of the buoyancy ratio causes convection heat and mass transfer to increase for the thermal dominated flow while decrease in buoyancy ratio also augments it for the solutal dominated flow. The heat transfer (mass transfer) rate is found to increase (decrease) with increasing the nanoparticle volume fraction. Moreover, for all above studied parameters, an intensification of the flow and an increase in average Nusselt and Sherwood numbers occur with the decrease in power-law index.

Development and validation of a stabilized immersed boundary CFD model for freezing and melting with natural convection

Numerous processes in the automotive, additive manufacturing or energy storage industries require an accurate prediction of the solidification (freezing) and melting (thawing) dynamics of substances. The numerical modeling of these phase changes is highly complex because it includes sharp moving interfaces and strong discontinuities in the material properties. This complexity is often exacerbated by the occurrence of natural convection, which induces a strong coupling between the motion of the liquid and the position of the solid–liquid interface. This leads to strongly coupled non-linear thermo-fluid problems which have to be solved in complex geometries.In this work, we introduce two novel stabilized finite element models to predict the phase change with natural convection. The first model uses a more classical viscosity approach to impose stasis in the solid region whereas the second one is based on an immersed boundary formulation to accurately describe the solid–fluid interface.The efficiency of the stabilization is first demonstrated by studying the Stefan problem. The two approaches to impose stasis are then compared using 2D test cases before they are both used to study melting in a rectangular (2D) and prismatic (3D) cavity. Significant differences are observed in the flow profiles and the solid–liquid interface position between the 2D and the 3D simulations.

Modeling and design guidelines for direct steam generation solar receivers

Concentrated solar energy is an ideal energy source for high-temperature energy conversion processes such as concentrated solar power generation, solar thermochemical fuel production, and solar driven high-temperature electrolysis. Indirectly irradiated solar receiver designs utilizing tubular absorbers enclosed by a cavity are possible candidates for direct steam generation, allowing for design flexibility and high efficiency. We developed a coupled heat and mass transfer model of cavity receivers with tubular absorbers to guide the design of solar-driven direct steam generation. The numerical model consisted of a detailed 1D two-phase flow model of the absorber tubes coupled to a 3D heat transfer model of the cavity receiver. The absorber tube model simulated the flow boiling phenomena inside the tubes by solving 1D continuity, momentum, and energy conservation equations based on a control volume formulation. The Thome-El Hajal flow pattern maps were used to predict liquid-gas distributions in the tubular cross-sections, and heat transfer coefficients and pressure drop along the tubes. The heat transfer coefficient and fluid temperature of the absorber tubes’ inner surfaces were then extrapolated to the circumferential of the tube and used in the 3D cavity receiver model. The 3D steady state model of the cavity receiver coupled radiative, convective, and conductive heat transfer. The complete model was validated with experimental data and used to analyze different receiver types and designs made of different materials and exposed to various operational conditions. The proposed numerical model and the obtained results provide an engineering design tool for cavity receivers with tubular absorbers (in terms of tube shapes, tube diameter, and water-cooled front), support the choice of best-performant operation (in terms of radiative flux, mass flow rate, and pressure), and aid in the choice of the component materials. The model allows for an in-depth understanding of the coupled heat and mass transfer in the solar receiver for direct steam generation and can be exploited to quantify the optimization potential of such solar receivers.

Mixed Convection Enhancement in a 3D Lid-Driven Cavity Containing a Rotating Cylinder by Applying an Artificial Roughness

Mixed Convection Enhancement in a 3D Lid-Driven Cavity Containing a Rotating Cylinder by Applying an Artificial Roughness

Fabrication of 3D nano-hemispherical cavity array plasmonic substrate for SERS applications

Surface-enhanced Raman scattering (SERS) have numerous applications in areas such as analytical chemistry, biochemistry, and environmental science. However to manufacture SERS active substrates with good reproducibility and low cost is not easy, which hinder the SERS technology from being widespread in various applications. In this study, we developed a batch producible hot embossing 3D nanostructured SERS substrate technology for SERS applications. This study utilized the anodic aluminum oxide (AAO) self-assembled uniform nano-hemispherical array barrier layer as a template to create a durable nanostructured nickel mold. With the hot embossing technique and the durable nanostructured nickel mold, we were able to batch produce the 3D Nanostructured SERS chip with consistent quality and low cost. In addition, according to the SERS experiments, the 3D nano-hemispherical cavity array combined with sub-10-nm-gaps Au NPs showed distinct SERS signals in both Rhodamine 6G and Chlorpyrifos measurements. Therefore, the developed method is good to be used extensively in rapid chemical and biomolecular detection applications.

A two-phase lattice Boltzmann study on injection filling of cavities with arbitrary shapes

In this paper, a multi-relaxation time (MRT) pseudo-potential based lattice Boltzmann model is implemented to investigate the isothermal injection filling of 2D cavities with arbitrary shapes. The model is capable of handling relatively large density ratios and low viscosities. First, the model is validated by a comparison of the numerical results with those of the experiments reported in the literature for a broken dam problem where a good agreement is observed. Next, the filling process of a rectangular cavity is simulated and effects of the Reynolds and Froude numbers as well as the cavity aspect ratio are investigated. Two filling regimes namely steady and splashing are identified. The formation of gas bubbles are observed in the splashing regime while in the case of steady filling, no bubbles are trapped and the liquid jet fills the cavity smoothly. Furthermore, the threshold Re number for the onset of splashing is evaluated by changing the effective variables. It was found that this threshold Re is increased by a reduction of the cavity aspect ratio (H/L) less than 0.5. Decreasing the Fr number and increasing the ratio D/L also increase the threshold Re for the onset of splashing. In the next case, filling a circular cavity with a solid core is also simulated at relatively low and high Re numbers and results at a Re of 81 are compared with those of the SPH method reported in the literature. Finally, a multi-branch header discharging into eight uniform cavities is studied. It was found that the filling sequence of the branches is different for low and relatively high Re numbers.

Entropy Conditions Involved in the Nonlinear Coupled Constitutive Method for Solving Continuum and Rarefied Gas Flows

The numerical study of continuum-rarefied gas flows is of considerable interest because it can provide fundamental knowledge regarding flow physics. Recently, the nonlinear coupled constitutive method (NCCM) has been derived from the Boltzmann equation and implemented to investigate continuum-rarefied gas flows. In this study, we first report the important and detailed issues in the use of the H theorem and positive entropy generation in the NCCM. Importantly, the unified nonlinear dissipation model and its relationships to the Rayleigh–Onsager function were demonstrated in the treatment of the collision term of the Boltzmann equation. In addition, we compare the Grad moment method, the Burnett equation, and the NCCM. Next, differences between the NCCM equations and the Navier–Stokes equations are explained in detail. For validation, numerical studies of rarefied and continuum gas flows were conducted. These studies include rarefied and/or continuum gas flows around a two-dimensional (2D) cavity, a 2D airfoil, a 2D cylinder, and a three-dimensional space shuttle. It was observed that the present results of the NCCM are in good agreement with those of the Direct Simulation Monte Carlo (DSMC) method in rarefied cases and are in good agreement with those of the Navier–Stokes equations in continuum cases. Finally, this study can be regarded as a theoretical basis of the NCCM for the development of a unified framework for solving continuum-rarefied gas flows.

Characterization of hidden modes in networks of superconducting qubits

We present a method for detecting electromagnetic (EM) modes that couple to a superconducting qubit in a circuit quantum electrodynamics architecture. Based on measurement-induced dephasing, this technique allows the measurement of modes that have a high quality factor (Q) and may be difficult to detect through standard transmission and reflection measurements at the device ports. In this scheme, the qubit itself acts as a sensitive phase meter, revealing modes that couple to it through measurements of its coherence time. Such modes are indistinguishable from EM modes that do not couple to the qubit using a vector network analyzer. Moreover, this technique provides useful characterization parameters including the quality factor and the coupling strength of the unwanted resonances. We demonstrate the method for detecting both high-Q coupling resonators in planar devices as well as spurious modes produced by a 3D cavity.

Analysis of entropy generation in combined buoyancy-Marangoni convection of power-law nanofluids in 3D heterogeneous porous media

In this paper, entropy generation due to the combined buoyancy-Marangoni convection of non-Newtonian power-law nanofluids in a 3D heterogeneous porous cubic cavity is investigated in detail with the compact high order finite volume method. The fluid in the cavity is a CMC-based nanofluids containing CuO nanoparticles, and the numerical study is conducted for a wide range of heterogeneity level ranging from 0 to 1.5, Marangoni number from 0 to 1000, thermal Rayleigh number from 104 to 106, buoyancy ratio from −2.0 to −0.1, nanoparticle volume fraction from 0 to 0.1 and power-law index from 0.76 to 1.0 to identify the irreversibility characteristics. The results show that the total entropy generation is considerably affected by the heterogeneity in permeability; it increases when the level of heterogeneity increases. Marangoni number becomes a more effective parameter on total entropy generation for lower values of thermal Rayleigh numbers. For thermal dominated flow, the increase in the buoyancy ratio provokes various irreversibilities to enhance; on the other hand, for solutal dominated flow, the rise of the buoyancy ratio declines the entropy generation. Moreover, it is also shown that the enhancement of the nanoparticle volume fraction reduces the total entropy generation. Apart from that, our numerical tests show the flow field and entropy generation are influenced appreciably by the presence of the power-law index.

Lagrangian transport in a class of three-dimensional buoyancy-driven flows

The present study concerns the Lagrangian dynamics of three-dimensional (3D) buoyancy-driven cavity flows under steady and laminar conditions due to a global temperature gradient imposed via an opposite hot and cold sidewall. This serves as the archetypal configuration for natural-convection flows in which (contrary to the well-known Rayleigh–Bénard flow) gravity is perpendicular (instead of parallel) to the global temperature gradient. Limited insight into the Lagrangian properties of this class of flows, despite its relevance to observed flow phenomena as well as scalar transport, motivates this study. The 3D Lagrangian dynamics are investigated in terms of the generic structure and associated transport properties of the global streamline pattern (‘Lagrangian flow topology’) by both theoretical and computational analyses. The Grashof number$Gr$is the principal control parameter for the flow topology: limit$Gr=0$yields a trivial state of closed streamlines;$Gr>0$induces symmetry breaking by fluid inertia and buoyancy and thus causes formation of toroidal coherent structures (‘primary tori’) embedded in chaotic streamlines governed by Hamiltonian mechanisms. Fluid inertia prevails for ‘smaller’$Gr$and gives behaviour that is dynamically entirely analogous to 3D lid-driven cavity flows. Buoyancy-induced bifurcation of the flow topology occurs for ‘larger’$Gr$and underlies the emergence of ‘secondary rolls’ observed in the literature and to date unreported secondary tori for ‘larger’ Prandtl numbers$Pr$. Key to these dynamics are stagnation points and corresponding heteroclinic manifold interactions.

Tuning a 3D microwave cavity via superfluid helium at millikelvin temperatures

Frequency tunability of three dimensional (3D) microwave cavities opens up numerous possibilities for their use in hybrid quantum systems and related technologies. For many applications, it is desirable to tune the resonance at cryogenic temperatures without mechanical actuation. We show that a superconducting 3D microwave cavity can be tuned at the percent level by taking advantage of the dielectric properties of superfluid 4He at millikelvin temperatures, without affecting its intrinsic quality factor—reaching 3 × 105 in the present experiment.

A three-dimensional thermal model for viscoelastic polymer melt packing process in injection molding

In this study, a 3D weakly compressible viscoelastic flow model with the thermal effect is developed for simulations of the non-isothermal XPP melt packing process. The 3D multi-field coupled model is solved by the collocated finite volume CLEAR algorithm with the AVLSMART scheme. The numerical model is validated against the benchmark problem. The XPP melt packing process in a rectangular cavity is simulated, and the predicted flow-induced birefringence is in agreement with the experimental and numerical results reported in the literature. For a case with a rather complex cavity, the XPP melt packing process in a 3D hemispherical shell cavity is further simulated. The distributions of melt temperatures, flow-induced stresses as well as the corresponding rheological characteristics of XPP melt in 3D cavity are vividly presented, which are difficult to be captured by previous simulations and experiments. Especially, the present model allows the effects of melt temperature and holding pressure on the first normal stress difference and density to be studied. It is shown that with an increase in melt temperature, the absolute values of the first normal stress difference increases slightly and the density decreases gradually, while the high holding pressure improves significantly the first normal stress difference and density. Numerical results demonstrate that the present 3D thermal model is an effective tool for simulating real-world viscoelastic polymer melt packing processes.

Improvements on microwave-to-optics conversion device for quantum information networks

A new design for an electro-optomechanical device uses a microwave 3D cavity and wireless coupling to improve performance.

Artificial gravity effect on spin-polarized exciton-polaritons

The pseudospin dynamics of long-living exciton-polaritons in a wedged 2D cavity has been studied theoretically accounting for the external magnetic field effect. The cavity width variation plays the role of the artificial gravitational force acting on a massive particle: exciton-polariton. A semi-classical model of the spin-polarization dynamics of ballistically propagating exciton-polaritons has been developed. It has been shown that for the specific choice of the magnetic field magnitude and the initial polariton wave vector the polariton polarization vector tends to an attractor on the Poincaré sphere. Based on this effect, the switching of the polariton polarization in the ballistic regime has been demonstrated. The self-interference of the polariton field emitted by a point-like source has been shown to induce the formation of interference patterns.

Analysis of mixed convection of nanofluid in a 3D lid-driven trapezoidal cavity with flexible side surfaces and inner cylinder

Numerical study of mixed convection in a lid-driven 3D flexible walled trapezoidal cavity with nanofluids was performed by using Galerkin weighted residual finite element method. Effects of various pertinent parameters such as Richardson number (between 0.05 and 50), elastic modulus of the side surfaces (between 1000 and 105), side wall inclination angle (between 0° and 20°) and solid particle volume fraction (between 0 and 0.04) on the fluid flow and heat transfer characteristics in a 3D lid-driven-trapezoidal cavity were numerically examined. It was observed that these characteristics are influenced when the pertinent parameters change. Flexible side surface can be used as control element for heat transfer rate. Increment and reduction in the space which are provided by the flexible side walls result in heat transfer enhancement and deterioration for side wall inclination angle of 0° and 10°. Average Nusselt number enhances by about 9.80% when the value of the elastic modulus is increased from 1000 to 105 for side wall inclination angles of θ=0°. Adding nanoparticles to the base fluid results in linear increment of heat transfer and at the highest volume fraction, 25.30% of heat transfer enhancement is obtained. A polynomial type correlation for the average Nusselt number along the hot wall was proposed and it has a fourth order polynomial dependence upon the Richardson number and first order dependence upon the solid particle volume fraction.

Active structural-acoustic control of interior noise in a vibro-acoustic cavity incorporating system identification

Linear quadratic Gaussian optimal control is one of the techniques used for active noise control. In practical implementation of this technique, one of the key difficulties faced is the estimation of the states of the plant. A state observer that accurately estimates these states can be used in this regard. Studies reported make use of analytically or experimentally derived models to build observers. This paper proposes a method for active noise control in the framework of active structural-acoustic control incorporating system identification for the development of the linear quadratic Gaussian controller. Kalman filter is used as a stochastic state observer of the plant states. System identification is carried out using modal testing and finite element model updating to obtain an accurate model of the plant for building up the Kalman filter. The objective of the proposed method is to actively reduce the noise inside the cavity due to disturbances acting on the cavity structure. The active control is achieved by controlling the structural vibrations by taking into account the degree of coupling between the various structural and the acoustic modes. The effectiveness of the proposed method is evaluated experimentally on a 3D rectangular box cavity with a flexible plate.