Pure Conduction Research Articles

Conduction transition and electronic conductivity enhancement of cesium azide by pressure-directed grain boundary engineering

Pressure induces a transition from mixed ionic–electronic conduction to pure electronic conduction in CsN3. The grain boundary effect improves the conductivity of CsN3 by more than two orders of magnitude after one pressure cycle.

Encapsulating NH4Br in a metal organic framework: achieving remarkable proton conduction in a wide relative humidity range.

Proton-conducting materials are key components for constructing high-energy-density electronic devices. In this work, by accumulating NH4Br into the nanospace of the classical metal organic framework MIL-101-Cr, a proton conductivity as high as 1.53 × 10-1 S cm-1 was achieved at 363 K and 100% RH. The proton conduction of NH4Br@MIL-101-Cr was also high even at lower relative humidity; for instance, it was ∼10-2 S cm-1 at 75% RH. The activation energy was calculated to be 0.11 eV for NH4Br@MIL-101-Cr, indicative of tight H-bond networks and a low barrier to proton transfer, and confirming the occurrence of pure proton conduction as well.

Transient thermal characteristics of infrared window coupled radiative transfer subjected to high heat flux

<abstract> <p>In infrared detection system on aircrafts, the infrared window, as an essential part, always faces heating condition generated by aerodynamic effects. The accurate thermal analysis can ensure the safety and reliability of internal detection system. In this work, the transient thermal characteristics of infrared window-based encapsulation structure are investigated under a high heat flux loading. The physical model of coupled radiative-conductive heat transfer in the window is established while the spectral selectivity of the window to thermal radiation is considered. The transient temperature response is used to evaluate the thermal characteristics. The effect of the radiative heat transfer is firstly analyzed and compared with the pure heat conduction model. There is a temperature deviation (74.1 K) when the radiative heat transfer is ignored. Subsequently, the transient temperature response is simulated under three different kinds of heat flux respectively. It is found that the effect of external heat flux loading is significant. The highest temperature difference reaches 32.9% (299 K) when the heat flux is reduced by 0.5 times and achieves 86.3% (794 K) when the heat flux is increased by 2.5 times. Moreover, the geometric dimensions of window (shape of a truncated cone) generate an effect on its heat transfer characteristics. The temperature decreases significantly (37.8%) when the thickness rises from 10 mm to 20 mm (<italic>r</italic> = 25 mm) while the temperature decreases relatively small (8.1%) when the radius increases from 15 mm to 45 mm (<italic>d</italic> = 15 mm). The results reveal that the radiative heat transfer in the window should be carefully considered, especially under the high heat flux loading. Additionally, reducing heat flux or thickening window can improve insulation effectiveness so as to ensure the stable working of the internal equipment.</p> </abstract>

Evaluation of Microwave Vacuum Drying as an Alternative to Freeze-Drying of Biologics and Vaccines: the Power of Simple Modeling to Identify a Mechanism for Faster Drying Times Achieved with Microwave

Vial-based lyophilization for biopharmaceuticals has been an indispensable cornerstone process for over 50 years. However, the process is not without significant challenges. Capital costs to realize a lyophilized drug product facility, for example, are very high. Similarly, heat and mass transfer limitations inherent in lyophilization result in drying cycle on the order of several days while putting practical constraints on available formulation space, such as solute mass percentage or fill volume in a vial. Through collaboration with an external partner, we are exploring microwave vacuum drying (MVD) as a faster drying process to vial lyophilization wherein the heat transfer process occurs by microwave radiation instead of pure conduction from the vial. Drying using this radiative process demonstrates greater than 80% reduction in drying time over traditional freeze-drying times while maintaining product activity and stability. Such reduction in freeze-drying process times from days to several hours is a welcome change as it enables flexible manufacturing by being able to better react to changes either in terms of product volume for on-demand manufacturing scenarios or facilities for production (e.g., scale-out over scale-up). Additionally, by utilizing first-principle modeling coupled with experimental verification, a mechanism for faster drying times associated with MVD is proposed in this article. This research, to the best of our knowledge, forms the very first report of utilizing microwave vacuum drying for vaccines while utilizing the power of simplified models to understand drying principles associated with MVD.

A fundamental investigation of thermo-capillarity in laser powder bed fusion of metals and alloys

Several different interfacial forces affect the free surface of liquid metals during metal additive manufacturing processes. One of these is thermo-capillarity or the so-called Marangoni effect. In this work, a novel framework is introduced for unraveling the effects of thermo-capillarity on the melt pool morphology/size and its thermo-fluid conditions during the Laser Powder Bed Fusion (L-PBF) process. In this respect, a multi-physics numerical model is developed based on the commercial software package Flow-3D. The model is verified and validated via mesh-independency analysis and by comparison of the predicted melt pool profile with those from lab-scale single-track experiments. Two sets of parametric studies are carried out to find the role of both positive and inverse thermo-capillarity on the melt pool shape and its thermal and fluid dynamics conditions. The thermo-fluid conditions of the melt pool are further investigated using appropriate dimensionless numbers. The results show that for the higher Marangoni number cases, the melt pool temperature drops, and at the same time, the temperature field becomes more uniform. Also, it is shown that at higher Marangoni numbers, temperature gradients decrease, thus reducing the role of conduction in the heat transfer from the melt pool. Furthermore, for the first time, a novel methodology is introduced for the calculation of the melt pool's average Nusselt number. The average Nusselt numbers calculated for the positive and inverse thermo-capillarity are then used for finding the effective liquid conductivity required for a computationally cheaper pure heat conduction simulation. The results show that the deviation between the average melt pool temperature, using the pure conduction model with effective conductivity, and the one obtained from the advanced fluid dynamics model is less than 2%.

Transient heat exchanges under fast Reactivity-Initiated Accident

Heat exchanges during fast transient are very complex phenomena. Many studies have been led in this field, trying to quantify the heat exchanges between a heating wall, under fast increasing power, and a coolant. This kind of situation is encountered for instance during RIA (Reactivity-Initiated Accidents) in nuclear reactors, whose characteristics times of wall heat flux excursion can be as low as orders of 1 ms. The CABRI reactor, an experimental pulse reactor funded by the french Institute for Radiological protection and Nuclear Safety (IRSN) and operated by CEA at the Cadarache nuclear center (France), was build in order to study and thus to better understand RIA effects on nuclear fuels. Heat exchanges characterization is definitely one of major points to tackle in the understanding and modeling of such transients, involving single and two phase flows.This paper broaches the question of single phase heat exchanges coefficients during fast transient power excursions in the CABRI reactor.The single phase pure convection is the overlap of two main mechanisms: the advection (wall axial supply in upstream cold water) and the turbulent mixing inside the boundary layer. This latter phenomenon is due to vortices in boundary layers inducing radial mixing through the velocity boundary layer. In most cases involving turbulent flows, the turbulent mixing phenomenon is preponderant. To these mechanisms is added a pure conduction heat exchange mechanism through the thermal boundary layer. Convection and conduction overlap defining a conducto-convective heat transfer coefficient, improperly only called “convection” coefficient. This paper suggests a way to model this coefficient during a CABRI-RIA transient by a non-linear superposition of transient pure conduction and convection mechanisms. Two distinct transient phases are considered; the first one presenting a wall heat flux of exponential shape followed by the second one during which the wall heat flux remains constant. The potency of this analytical model, which is implementable into computational system tools, is demonstrated.

Effect of geometric parameter and nanoparticles on PCM melting in a vertical shell-tube system

In this study, the charging process of vertical shell-tube latent heat storage (LHS) system with two heat transfer fluid (HTF) injection orientations was investigated. A two-dimensional numerical model based on the finite volume method (FVM) was developed and verified with the experimental data. The PCM melting with pure conduction mode is regarded as a reference for analyzing the heat transfer characteristics. Results show that heat transfer is stronger for top injected HTF during the convection dominant stage, and the bottom injected HTF offers better heat transfer during the last conduction stage. The effects of PCM thickness to height ratio (R) and nanoparticles concentration (ϕ) were investigated. It is found that the melting time for the bottom injected HTF is shorter compared to the top injected HTF when R less than 0.050, and longer when R > 0.050. The nanoparticles provides better enhancement on PCM melting with bottom injection HTF. It is also found the enhancement potential of nanoparticles is weakened with the increase of R. Furthermore, R = 0.05 is recommended for maximizing thermal performance.

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

Summary Production of high-purity hydrogen by thermal-electrochemical decomposition of ammonia at an intermediate temperature of 250°C is demonstrated. The process is enabled by use of a solid-acid-based electrochemical cell (SAEC) in combination with a bilayered anode, comprising a thermal-cracking catalyst layer and a hydrogen electrooxidation catalyst layer. Cs-promoted Ru on carbon nanotubes (Ru/CNT) serves as the thermal decomposition catalyst, and Pt on carbon black mixed with CsH2PO4 is used to catalyze hydrogen electrooxidation. Cells were operated at 250°C with humidified dilute ammonia supplied to the anode and humidified hydrogen supplied to the counter electrode. A current density of 435 mA/cm2 was achieved at a potential of 0.4 V and ammonia flow rate of 30 sccm. With a demonstrated faradic efficiency for hydrogen production of 100%, the process yields hydrogen at a rate of 1.48 m o l H 2 / g c a t h .

Unraveling the limitations of solid oxide electrolytes for all-solid-state electrodes through 3D digital twin structural analysis

Abstract Solid oxides are attractive electrolyte materials for all-solid-state lithium batteries (ASSLBs) owing to their high stability and pure Li-ion conductivity. Nevertheless, the electrochemical performance of ASSLBs employing solid oxide-based electrolytes cannot compete with ASSLBs with sulfide or polymeric electrolytes due to poor interfacial contact and high boundary resistance between the active materials and solid oxide electrolytes. To overcome this hurdle, elaborate microstructural analysis of the interface of the active material/solid oxide electrolyte in ASSLBs is essentially required since the interfacial contact area dominantly acts as the ion pathway and the electrochemical reaction site in the electrode. Although recent attempts on interfacial structure analysis of ASSLBs have provided simple 2D or semi-3D microstructural features, the results have not yielded deep insights. Herein, we investigated the interfacial defects in an all-solid-state electrode with a solid oxide electrolyte via a 3D digital twin technology combining 3D structural quantification and physico-electrochemical simulations to unravel the intrinsic limitations of solid oxide electrolytes. The in-depth results can be used to design materials and optimize electrode design parameters for ASSLBs.

"Mushroom" Autologous Partial Ossicular Replacement Prosthesis: Long-term Results.

Evaluate a new autologous mushroom-shaped cortical bone partial ossicular replacement prosthesis (MPORP) for cost-effective and sustainable hearing results. Prospective study. Tertiary care center. Forty-two patients suffering from chronic otitis media with intact superstructure of the stapes and partially or completely eroded incus. Group-1 (n = 24) underwent only tympanoplasty with MPORP; group-2 (n = 18) underwent intact canal wall mastoidectomy (ICW) with MPORP. Hearing results were evaluated using a four frequency average (measured at 0.5, 1, 2, 3 kHz) pure tone air conduction (PTA), air-bone gap (ABG), and word recognition scores (WRS) after 3, 6, and 12 months and compared with preoperative results. Overall, successful rehabilitation of ABG to 20 dB or less was achieved in 92% of patients. Mean postoperative ABG was 15.35 ± 4.18 dB showing mean improvement of 23.89 ± 5.95 dB. In group-1, mean postoperative ABG was 18.47 ± 3.65 dB, showing an improvement of 25.92 ± 5.3 dB. In group-2, mean postoperative ABG was 18.47 ± 3.65 dB showing an improvement of 20.14 ± 4.96 dB. Hearing improvement in all the cases together and both the groups checked separately was statistically significant (paired t test, p < 0.001). Group 1 had, on average, 5 dB better hearing than group 2 (unpaired t test, p > 0.05). The MPORP is obtainable from the local site, easily constructed, bio-compatible, cost-effective, less bulky, adequately rigid for sound transmission, magnetic resonance imaging (MRI) compatible, and provides sustainable hearing gain because it has better chances of integration with the head of stapes.

Influence of wavy enclosure and nanoparticles on heat release rate of PCM considering numerical study

The main goal of this attempt is achieving higher rate of solidification with employing two passive techniques. Mixing the based PCM with nanoparticles and considering the wavy shape for walls were two techniques were incorporated. Copper oxide nanomaterial was dispersed in to water with concentration of 0.04 which let us employing homogeneous model. Based on this fact, empirical formulations were utilized for predicting features of NEPCM and various shapes of nano sized particles were considered in thermal conductivity formula. Due to inherent of solidification phenomena, buoyancy can be ignored and pure conduction mechanism with involving the transient source term of solid faction was solved by means of FEM. During the process, the configurations of grids change and the regions around the solid front have finer grid. This opportunity offers outputs with greater accuracy. As shape factor rises, the greater conduction mode can be obtained and similar behavior can be achieved with considering greater amplitude of wavy walls. The best case in term of discharging time is that of m = 5.7 and A = 0.5 in which 156.17 s required to finish the process. Greater amount of shape factor can decrease the time about 5.91% and 5.89% when A = 0.5 and 0.1, respectively. Also, with growth of A, time reduces about 22.66% which indicate better solidification rate. Inclusion of nanoparticles can improve the discharging rate about 17.9%.

Analytical Transport Network Theory for Onsager, Coupled Flows: Part 2—Network-Scale Modeling of Linear, Electrokinetic Flow

Abstract The analytical transport network (ATN) model was developed to study transport through heterogeneous and hierarchical microstructural networks. Here, ATN is extended to electrokinetic flow, a linear, coupled flow that satisfies Onsager’s reciprocity relations. In Part 1, a channel-scale model was developed to describe electrokinetic flow through a channel of arbitrary morphology. In Part 2, we exploit the computational economy of the channel-scale model to develop an efficient network-scale model of electrokinetic flow in large, geometrically complex material structures. The corresponding algorithm for applying the theory to voxel-based, three-dimensional (3D) images is automated and computationally efficient. In addition, it provides a means for rapidly obtaining a structure’s tortuosity factor from a 3D image. We outline the manner in which morphology and topology exerts an additional influence on electrokinetic flow relative to pure conduction and viscous fluid flow. The effort represents an important initial step in extending the ATN approach to a broader range of linear and eventually nonlinear coupled flow phenomena. The extension is relevant to a number of technological fields, including emerging energy conversion and storage technologies.

Numerical study of heat transfer in Rayleigh-Bénard convection under rarefied gas conditions.

The focus of this research is to delineate the thermal behavior of a rarefied monatomic gas confined between horizontal hot and cold walls, physically known as rarefied Rayleigh-Bénard (RB) convection. Convection in a rarefied gas appears only for high temperature differences between the horizontal boundaries, where nonlinear distributions of temperature and density make it different from the classical RB problem. Numerical simulations adopting the direct simulation Monte Carlo approach are performed to study the rarefied RB problem for a cold to hot wall temperature ratio equal to r=0.1 and different rarefaction conditions. Rarefaction is quantified by the Knudsen number, Kn. To investigate the long-time thermal behavior of the system two ways are followed to measure the heat transfer: (i) measurements of macroscopic hydrodynamic variables in the bulk of the flow and (ii) measurements at the microscopic scale based on the molecular evaluation of the energy exchange between the isothermal wall and the fluid. The measurements based on the bulk and molecular scales agreed well. Hence, both approaches are considered in evaluations of the heat transfer in terms of the Nusselt number, Nu. To characterize the flow properly, a modified Rayleigh number (Ra_{m}) is defined to take into account the nonlinear temperature and density distributions at the pure conduction state. Then the limits of instability, indicating the transition of the conduction state into a convection state, at the low and large Froude asymptotes are determined based on Ra_{m}. At the large Froude asymptote, simulations following the onset of convection showed a relatively small range for the critical Rayleigh (Ra_{m}=1770±15) that flow instability occurs at each investigated rarefaction degree. Moreover, we measured the maximum Nusselt values Nu_{max} at each investigated Kn. It was observed that for Kn≥0.02,Nu_{max} decreases linearly until the transition to conduction at Kn≈0.03, known as the rarefaction limit for r=0.1, occurs. At the low Froude (parametric) asymptote, the emergence of a highly stratified flow is the prime suspect of the transition to conduction. The critical Ra_{m} in which this transition occurs is then determined at each Kn. The comparison of this critical Rayleigh versus Kn also shows a linear decrease from Ra_{m}≈7400 at Kn=0.02 to Ra_{m}≈1770 at Kn≈0.03.

Detection of groundwater flux changes in response to two large earthquakes using long-term bedrock temperature time series

Heat as a groundwater tracer has potential application in identifying earthquake-induced changes in fluid flow. Since convective heat transport modifies the phase and amplitude of periodic oscillations under pure heat conduction condition, temporal variation of groundwater flux can thus be derived from multi-depth periodic temperature signals. Here we present groundwater flux changes after two large earthquakes nearby, determined from in situ bedrock temperature measurements in the Xianshuihe fault zone, at the eastern margin of the Tibetan Plateau. Five-year temperature time series at six different locations are recorded by high sensitivity temperature sensors (10−4 K) installed at various depths ranging from 0 to 20 m. Groundwater fluxes are estimated through time-varying amplitudes and phases of the annual oscillations, extracted from the Dynamic Harmonic Regression technique. Results show different hydrological responses to these two earthquakes. After the 2013 Ms 7.0 Lushan earthquake, sustained rise in upward flux was revealed at all locations in the intermediate-field, contradicting to the modeled coseismic static dilatational strains. However, groundwater flux patterns after the 2014 Ms 6.3 Kangding earthquake are consistent with the coseismic volumetric strain distribution of a quadrantal pattern of this event. We propose that enhanced hydraulic permeability by dynamic stress might cause the increased upward fluid flux after the Lushan earthquake in the intermediate-field, while coseismic static volumetric strain may account for the hydrological changes after the Kangding earthquake in the near-field. This is the first time that temperature–time series are used to quantify continuous earthquake-related changes in groundwater fluxes. In situ temperature monitoring can provide insights into earthquake-driven hydrologic responses, and also offer additional information to identify temporal changes in crustal strain or hydraulic properties.

Early Stages of Plastic Deformation in Low and High SFE Pure Metals

Severe plastic deformation (SPD) techniques are known to promote exceptional mechanical properties due to their ability to induce significant grain and cell size refinement. Cell and grain refinement are driven by continuous newly introduced dislocations and their evolution can be followed at the earliest stages of plastic deformation. Pure metals are the most appropriate to study the early deformation processes as they can only strengthen by dislocation rearrangement and cell-to-grain evolution. However, pure metals harden also depend on texture evolution and on the metal stacking fault energy (SFE). Low SFE metals (i.e., copper) strengthen by plastic deformation not only by dislocation rearrangements but also by twinning formation within the grains. While, high SFE metals, (i.e., aluminium) strengthen predominantly by dislocation accumulation and rearrangement with plastic strain. Thence, in the present study, the early stages of plastic deformation were characterized by transmission electron microscopy on pure low SFE Oxygen-Free High Conductivity (OFHC) 99.99% pure Cu and on a high SFE 6N-Al. To induce an almost continuous rise from very-low to low plastic deformation, the two pure metals were subjected to high-pressure torsion (HPT). The resulting strengthening mechanisms were modelled by microstructure quantitative analyses carried out on TEM and then validated through nanoindentation measurements.

Buoyant flow and instability in a vertical cylindrical porous slab with permeable boundaries

The basic stationary buoyant flow in a vertical annular porous passage induced by a boundary temperature difference is investigated. The vertical cylindrical boundaries are considered both isothermal and permeable to external fluid reservoirs. There exists a stationary parallel velocity field with a zero flow rate and pure conduction heat transfer. Its linear stability is analysed with normal mode perturbations of the pressure and temperature fields. The transition to convective instability is caused by the basic horizontal temperature gradient. Hence, its nature differs from that of the usual Rayleigh–Bénard instability. The linear dynamics of the perturbed flow is formulated as an eigenvalue problem, solved numerically. Its solution provides the neutral stability curve at each fixed aspect ratio between the external radius and the internal radius. The critical Rayleigh number triggering the instability is evaluated for different aspect ratios. It is shown that the system becomes more an more unstable as the aspect ratio increases, with the critical Rayleigh number dropping to zero when the aspect ratio tends to infinity.

Resolving the effects of local convective heat transfer via adjustment of thermo-physical properties in pure heat conduction simulation of Laser Powder Bed Fusion (L-PBF)

Numerical models, especially when validated against experimental findings, are valuable tools that can be used as a cheap and reliable alternative to the expensive and time-consuming experimental investigations. In the current work, a multiphysics model of laser powder bed fusion (L-PBF) has been developed for stainless steel SS 316-L and validated against experimental findings. By configuring the model, the effects of the inverse Marangoni flow on the melt pool morphology and the heat and fluid flow conditions were analysed. It was shown that for high surface tension sensitivities, the total heat flux through the melt pool boundaries increases. The enhanced cooling will lead to a smaller melt pool size with larger depth to width ratio and causes a relatively uniform temperature field, which reduces the role of the conduction heat transfer. Furthermore, a Nusselt number was derived to quantify the role of the Marangoni effect on the convection heat transfer from the melt pool. This expression was used to calculate an effective thermal conductivity required for a modified pure conduction heat transfer calculation. It was shown that, via using a combination of the derived Nusselt number and the concept of the effective thermal conductivity, the average melt pool temperature determined from the modified pure conduction model gets very close to that of the more advanced CFD model.

Convective Transport through Porous Layers

Convective motions are a multi-physics phenomenon, in which flow and transport processes interact in a two-way coupling. The density of the fluid depends on the value of transport variable and this back-coupling leads to non-linear behaviour. For the classical constellation of a closed fluid container heated from below convective motions appear, when a critical threshold for the Rayleigh number is exceeded. The heat transfer due to convection is much higher than in the case of pure conduction. Here systems of three layers are examined in detail. Using numerical CFD modelling it is shown that in layered systems different convective flow patterns appear than in the single layer case. The number and constellation of convection cells characterize steady flow patterns. Using a parametric sweep over the relevant parameter range of layer Rayleigh numbers and layer thicknesses we determine diagrams that show the excess heat or mass transfer of the dominant convection patterns, measured by the Nusselt- or Sherwood numbers.

High oxide ion and proton conductivity in a disordered hexagonal perovskite.

Oxide ion and proton conductors, which exhibit high conductivity at intermediate temperature, are necessary to improve the performance of ceramic fuel cells. The crystal structure plays a pivotal role in defining the ionic conduction properties, and the discovery of new materials is a challenging research focus. Here, we show that the undoped hexagonal perovskite Ba7Nb4MoO20 supports pure ionic conduction with high proton and oxide ion conductivity at 510 °C (the bulk conductivity is 4.0 mS cm-1), and hence is an exceptional candidate for application as a dual-ion solid electrolyte in a ceramic fuel cell that will combine the advantages of both oxide ion and proton-conducting electrolytes. Ba7Nb4MoO20 also showcases excellent chemical and electrical stability. Hexagonal perovskites form an important new family of materials for obtaining novel ionic conductors with potential applications in a range of energy-related technologies.

Effects of aquifers on soil temperature distribution around deep buried heat exchanger

Deep buried heat exchanger has been increasingly applied into the building heat source through the utilization of geothermal energy. During the geothermal system design process, the aquifer is an important factor that affects the overall performance prediction. The flow of underground water at different positions changes the temperature distribution of the soils around the buried pipe and then influences the heat exchange at different depths. Consequently, the variation of the temperature field causes the thermal radius of the heat exchanger no longer regularly distributed, which affects the determination of the well spacing. With the aims of improving the accuracy of performance estimation, the aquifer effect is carried out by this study. The solution to the moving line source theory is used to acquire the temperature response at different positions. The overall effect of the underground water with different velocities on the performance is evaluated. The soil temperature distribution in the heat exchange zone with aquifers at different depths is studied in detail. The predicted thermal influence radius at different depths with various groundwater velocities and soil thermal properties showed that the temperature distribution around the buried heat exchanger is largely influenced by the groundwater movement. Under the simulation condition, the thermal radius increases from less than 10 m for pure conduction condition to a maximum value of 25.3 m with groundwater flow. The aquifer enhances the heat absorption of the heat exchanger, but the high flow rate also leads to a large thermal radius. The obtained thermal influence radius under different conditions can provide guidance for the design of the geothermal system.