Reverse Flow Research Articles

Demonstration of heat switch function of loop heat pipe controlled by electrohydrodynamic conduction pump

Loop heat pipes (LHPs) are attractive devices to cool electronic devices in spacecraft. The LHP operation must be shut down in some cases to avoid considerable reductions in the temperature of such electric devices. A new active technology capable of heat switching is developed for LHPs using an electrohydrodynamic (EHD) conduction pump that operates to facilitate liquid flow in the reverse direction against the normal LHP flow. To demonstrate our proposed approach, an EHD conduction pump with rod–ring electrodes was developed and evaluated to obtain generated pressure with varying applied voltages. The LHP with R134a as a working fluid was shut down successfully when a sufficiently high voltage was applied. The LHP shutdown continued until the EHD conduction pump was turned off. A comparison with a test in which a manually controlled mechanical valve caused the capillary limit showed that the EHD pump worked differently from the valve: the shutdown by the EHD pump involved a reverse flow. The consumed electric power for the EHD pump was 10–30 mW for 6–8 kV of applied voltage during the LHP shutdown. Furthermore, pressure loss through the EHD pump during normal LHP operation was approximately 0.5 % of the capillary pressure.

Numerical modeling of air ejectors covering supersonic, subsonic and closed-port operations

The physics and modeling of air ejectors in on- and off-design conditions have been extensively addressed in the past, reaching a good level of maturity. However, to achieve a robust model at system scale integrating an ejector, there is a need for developing 0D models suitable to tackle abnormal functioning modes, such as cases where the ejector works in subsonic conditions, reverse flows, or closed ports. Based on state-of-the-art models, a new 0D model has been built in the current work, where proper subroutine implementations allow covering normal and abnormal operations of convergent nozzle ejectors. The current research also focuses on understanding the physical behavior of air ejectors for aeronautical applications. In this regard, CFD-RANS simulations are used to perform model verification and calibration as well as to gain knowledge of the whole operational envelope. The regimes reproduced by the 0D model, and validated by CFD, cover the normal operating mode with different choking regimes, the occurrence of a subsonic primary flow, and the closed secondary port case. Additional cases are run to assess other features of the ejector behavior, such as the influence of geometrical properties on the choking mechanism and the impact of thermal effects.

Multiscale study of reactive transport and multiphase heat transfer processes in catalyst layers of proton exchange membrane fuel cells

Improving the performance of proton exchange membrane fuel cells (PEMFCs) requires deep understanding of the reactive transport processes inside the catalyst layers (CLs). In this study, a particle-overlapping model is developed for accurately describing the hierarchical structures and oxygen reactive transport processes in CLs. The analytical solutions derived from this model indicate that carbon particle overlap increases ionomer thickness, reduces specific surface areas of ionomer and carbon, and further intensifies the local oxygen transport resistance (Rother). The relationship between Rother and roughness factor predicted by the model in the range of 800-1600 s m-1 agrees well with the experiments. Then, a multiscale model is developed by coupling the particle-overlapping model with cell-scale models, which is validated by comparing with the polarization curves and local current density distribution obtained in experiments. The relative error of local current density distribution is below 15% in the ohmic polarization region. Finally, the multiscale model is employed to explore effects of CL structural parameters including Pt loading, I/C, ionomer coverage and carbon particle radius on the cell performance as well as the phase-change-induced (PCI) flow and capillary-driven (CD) flow in CL. The result demonstrates that the CL structural parameters have significant effects on the cell performance as well as the PCI and CD flows. Optimizing the CL structure can increase the current density and further enhance the heat-pipe effect within the CL, leading to overall higher PCI and CD rates. The maximum increase of PCI and CD rates can exceed 145%. Besides, the enhanced heat-pipe effect causes the reverse flow regions of PCI and CD near the CL/PEM interface, which can occupy about 30% of the CL. The multiscale model significantly contributes to a deep understanding of reactive transport and multiphase heat transfer processes inside PEMFCs.

Flow reversal and multiple states in turbulent Rayleigh–Bénard convection with partially isothermal plates

This paper examines turbulent Rayleigh–Bénard convection in a two-dimensional square cavity with partially isothermal conducting plates on the horizontal walls. The study reveals that controlling the relative locations of the partially isothermal plates can accelerate or completely suppress the reversals of large-scale circulation. The heat transfer efficiency, which is characterised by the time-averaged Nusselt number, is generally higher than that of the traditional Rayleigh–Bénard convection, and can be further enhanced when the reversal is fully suppressed. The reversal in our cases is mainly caused by the competition between the two alternately growing ‘corner’ vortices, fed by the detaching plumes from the hot/cold plates. This differs from those reported in traditional Rayleigh–Bénard convection. Fourier mode decomposition of the kinetic energy, reflecting the diverse contributors, in the reversing cases further emphasises the distinction between the current system and traditional Rayleigh–Bénard convection. In addition, multiple states were observed where the conducting plates were positioned at specific relative locations and had different initial conditions. It has been observed that the difference in Nusselt numbers between the anticlockwise and clockwise states increases linearly with the distance between the upper cold and lower hot plates. Moreover, the analysis of the buoyancy moment and the stability of the primary roll structure suggests that the higher heat transfer efficiency between the two states is strongly linked to a more stable primary roll structure. This study presents a new approach for controlling flow reversal and improving heat transfer efficiency by modifying the non-global conducting boundary and initial conditions.

Machine Learning Quantification of Pulmonary Regurgitation Fraction from Echocardiography.

Assessment of pulmonary regurgitation (PR) guides treatment for patients with congenital heart disease. Quantitative assessment of PR fraction (PRF) by echocardiography is limited. Cardiac MRI (cMRI) is the reference-standard for PRF quantification. We created an algorithm to predict cMRI-quantified PRF from echocardiography using machine learning (ML). We retrospectively performed echocardiographic measurements paired to cMRI within 3months in patients with ≥ mild PR from 2009 to 2022. Model inputs were vena contracta ratio, PR index, PR pressure half-time, main and branch pulmonary artery diastolic flow reversal (BPAFR), and transannular patch repair. A gradient boosted trees ML algorithm was trained using k-fold cross-validation to predict cMRI PRF by phase contrast imaging as a continuous number and at > mild (PRF ≥ 20%) and severe (PRF ≥ 40%) thresholds. Regression performance was evaluated with mean absolute error (MAE), and at clinical thresholds with area-under-the-receiver-operating-characteristic curve (AUROC). Prediction accuracy was compared to historical clinician accuracy. We externally validated prior reported studies for comparison. We included 243 subjects (median age 21years, 58% repaired tetralogy of Fallot). The regression MAE = 7.0%. For prediction of > mild PR, AUROC = 0.96, but BPAFR alone outperformed the ML model (sensitivity 94%, specificity 97%). The ML model detection of severe PR had AUROC = 0.86, but in the subgroup with BPAFR, performance dropped (AUROC = 0.73). Accuracy between clinicians and the ML model was similar (70% vs. 69%). There was decrement in performance of prior reported algorithms on external validation in our dataset. A novel ML model for echocardiographic quantification of PRF outperforms prior studies and has comparable overall accuracy to clinicians. BPAFR is an excellent marker for > mild PRF, and has moderate capacity to detect severe PR, but more work is required to distinguish moderate from severe PR. Poor external validation of prior works highlights reproducibility challenges.

Optimal dispatch of integrated electricity and heating systems considering the quality-quantity regulation of heating systems to promote renewable energy consumption

The integrated electricity and heating system (IEHS) can improve energy efficiency and promote renewable energy consumption. When quality-quantity regulation (QQR) is adopted, namely adjusting hydraulic and thermal conditions of heating system, the increase in operation flexibility is more remarkable. However, present IEHS dispatch models considering QQR overlook hydraulic characteristics of valves and variable frequency pumps resulting in inexecutable dispatch results easily and hindering IEHS's flexibility potential. Furthermore, loop networks and the access of multiple heat sources in heating systems may lead to flow reversal, but current research adopts a fixed flow direction which suppresses the potential of flow reversal to improve flexibility. In this paper, we propose an IEHS dispatch model considering QQR to promote renewable energy consumption, which considers hydraulic characteristics of valves and variable frequency pumps, and flow reversal. Specifically, we introduce two binary flow direction labels for every branch in heating system model and then the IEHS dispatch model which can deal with flow reversal is established. A sequential solution process combining linear and nonlinear optimization is formulated to overcome the non-convex feature of IEHS dispatch model. Specifically, piecewise linearization and piecewise McCormick relaxation are combined to handle complex nonlinear terms in the dispatch model. Therefore, a mixed integer linear programming model is obtained and solved, of which results are used as initial values for nonlinear optimization. Results in the case study show that operation cost is decreased by 0.97 % and renewable power consumption rate is increased from 83.31 % to 84.42 % after considering valve adjustment. Operation cost is further decreased by 6.06 % and renewable power consumption rate is increased to 94.04 % after considering flow reversal.

Starch-mediated colloidal chemistry for highly reversible zinc-based polyiodide redox flow batteries

Aqueous Zn-I flow batteries utilizing low-cost porous membranes are promising candidates for high-power-density large-scale energy storage. However, capacity loss and low Coulombic efficiency resulting from polyiodide cross-over hinder the grid-level battery performance. Here, we develop colloidal chemistry for iodine-starch catholytes, endowing enlarged-sized active materials by strong chemisorption-induced colloidal aggregation. The size-sieving effect effectively suppresses polyiodide cross-over, enabling the utilization of porous membranes with high ionic conductivity. The developed flow battery achieves a high-power density of 42 mW cm−2 at 37.5 mA cm−2 with a Coulombic efficiency of over 98% and prolonged cycling for 200 cycles at 32.4 Ah L−1posolyte (50% state of charge), even at 50 °C. Furthermore, the scaled-up flow battery module integrating with photovoltaic packs demonstrates practical renewable energy storage capabilities. Cost analysis reveals a 14.3 times reduction in the installed cost due to the applicability of cheap porous membranes, indicating its potential competitiveness for grid energy storage.

Experimental investigation on frosting performance of a microchannel heat exchanger in heat pump system for electric vehicles

Frosting of outdoor heat exchangers deteriorates the heat transfer performance of the electric vehicle (EV) heat pump system. The frosting performance of the outdoor heat exchanger in an EV heat pump air-conditioning system was investigated experimentally, considering different flow configurations, tube arrangements, and frontal air volume. The purpose of the study was to establish the optimal tube arrangements and flow configurations for minimizing frost formation and maximizing system performance. The results indicate that a three-flow configuration outperforms a two-flow setup under frosting conditions. Specifically, a flow sequence of 14-21-35 increases the heat capacity by 15.05 %–20.64 % compared to that of the reverse flow of 35-21-14. Additionally, the coefficient of performance (COP) increases by 1.19 %–3.55 %. Higher airflow reduces frost formation. A significant correlation exists between the refrigerant distribution within the heat exchanger and the corresponding frost distribution on the surface of the microchannel heat exchanger. The frost formation rate was slower for the flat tube vertical arrangement. Furthermore, horizontal tube arrangements were more conductive than vertical ones, providing a more uniform temperature distribution and higher heat transfer rates (an increase of 2.7% in heat transfer and 3.4% in heat capacity). The COP of the vertical arrangement system was consistently higher than that of the horizontal arrangement by 1.4 %–3 %.

Investigation of a rotating stall in a supercritical CO2 centrifugal compressor

Due to the nonlinear behavior of carbon dioxide properties at its critical point and the size effect of the supercritical carbon dioxide (S-CO2) centrifugal compressor, the stall causation mechanism differs between the S-CO2 centrifugal compressor and a conventional air compressor. The comprehension of the induced principle of the S-CO2 compressor rotating stall holds immense significance in enhancing stall margin and efficiency. This paper employs unsteady simulations to investigate the causes of the impeller rotating stall in the S-CO2 centrifugal compressor. The results show that the leading edge breakdown vortex (LEBV) formed by the tip leakage vortex (TLV) breakdown and the reverse flow in the passage are the reasons for blocking the passage and ultimately causing the rotating stall of the impeller. The migration motion of the LEBV not only induces the leading edge spillage phenomenon but also influences the intensity of the tip leakage flow (TLF) in adjacent passages, causing the propagation of the TLV breakdown phenomenon in the opposite direction to that of impeller rotation. The TLV undergoes intermittent breakdown in flow field, which is influenced by variations in TLF intensity. Additionally, there is a preceding process of breakdown-induced vortex formation and disappearance prior to TLV fragmentation.

Experimental investigation and modeling of onset of condensation induced water hammer in equal-height-difference natural circulation system

Condensation induced water hammer (CIWH) in equal-height-difference natural circulation systems (EHDNCS) can lead to significant damage to associated equipment. To investigate the mechanism and the prediction of the onset of CIWH in EHDNCS, a small-scale experiment of EHDNCS was conducted under different water temperatures, heat transfer powers, and resistance coefficients of the water-side inlet. This study analyzed the thermal hydraulics, flow regimes, and the onset mechanism of CIWH through temperature and pressure measurement, U-Net image segmentation, and analytical modeling. Four distinct flow regimes were observed in the horizontal pipe: single-phase flow, non-periodic bubble, periodic bubble, and CIWH. Flow regime maps based on water temperature and heat transfer power were obtained under different inlet resistance coefficients. When the steam bubble length is smaller than the pipe length, no CIWH occurs. When the steam bubble length reaches the pipe outlet to form stratified flow, CIWH occurs at a high steam channel height. The occurrence of stratified flow and reverse flow of subcooled water in the steam channel causes the onset of CIWH in EHDNCS. A dimensionless criterion has been developed to predict the onset of CIWH when the saturated steam-water mixture is discharged through a horizontal pipe in EHDNCS. This criterion effectively predicted the transition from periodic bubble to CIWH in the experiment.

Multi-center experience with intravascular lithotripsy for treatment of severe calcification during transcarotid artery revascularization for high-risk patients

ObjectiveTranscarotid artery revascularization (TCAR) offers a safe alternative to carotid endarterectomy (CEA), but severe calcification is currently considered a contraindication in carotid artery stenting. This study aims to describe the safety and effectiveness of TCAR with intravascular lithotripsy (IVL) in patients with traditionally prohibitive calcific disease. MethodsAll consecutive patients who underwent TCAR+IVL from 2018-2022 at nine institutions were identified. IVL was combined with pre-dilatation angioplasty to treat calcified vessels before stent deployment. The primary outcome was a new ipsilateral stroke within 30 days. Secondary outcomes included any new ipsilateral neurologic event (stroke/transient ischemic attack [TIA]) at 30 days, technical success, and <30% residual stenosis. ResultsFifty-eight patients (62% male; mean age, 78 ± 6.6 years) underwent TCAR+IVL, with 22 (38%) for symptomatic disease. Fifty-seven patients (98%) met high-risk anatomical or physiologic criteria for CEA. Forty-seven patients had severely calcific lesions. Fourteen patients (30%) had isolated eccentric plaque, 20 patients (43%) had isolated circumferential plaque, and 13 (27%) had eccentric and circumferential calcification. Mean procedure and flow reversal times were 87 ± 27 minutes and 25 ± 14 minutes. The median number of lithotripsy pulses per case was 90 (range, 30-330), and mean contrast usage was 29 mL. No patients had electroencephalogram changes or new deficits observed intraoperatively. Technical success was achieved in 100% of cases, with 98% having <30% residual stenosis on completion angiography. One patient had an in-hospital post-procedural stroke (1.72%). Four patients total had any new ipsilateral neurologic event (stroke/TIA) within 30 days for an overall rate of 6.8%. One TIA and one stroke occurred during the index hospitalization, and two TIAs occurred after discharge. Preoperative mean stenosis in patients with any postoperative neurologic event was 93% (vs 86% in non-stroke/TIA patients; P = .32), and chronic renal insufficiency was higher in patients who had a new neurologic event (75% vs 17%; P = .005). No differences were observed in calcium, procedural, or patient characteristics between the two groups. The mean follow-up was 132 days (range, 19-520 days). Three stents developed recurrent stenosis (5%) on follow-up duplex; the remainder were patent without issue. There were no reported interventions for recurrent stenosis during the study period. ConclusionsIVL sufficiently remodels calcified carotid arteries to facilitate TCAR effectively in patients with traditionally prohibitive calcific disease. One patient (1.7%) suffered a stroke within 30 days, although four patients (6.8%) sustained any new neurological event (stroke/TIA). These results raise concerns about the risks of TCAR+IVL and whether it is an appropriate strategy for patients who could potentially undergo CEA.

Height-modulating horizontal transport of dust particles in a dusty plasma ratchet

Dust particles are often electrostatically trapped and levitated within the non-electroneutral region of a sheath. The fascinating transport phenomena of dust particles strongly depend on the plasma parameters surrounding them within the sheath, whereas, that are quite difficult to obtain, leading to an unclear understanding of particle transport mechanisms. Here, we demonstrate a tunable horizontal transport of micron-sized dust particles by precisely manipulating their vertically suspended heights in an asymmetric ratchet sheath by designing dusty plasma ratchet. A collection of dust particles serves as micro-probes to detect the height-dependent transport properties and the feature of the sheath. Two methods are employed to lift or reduce the suspended heights of dust particles while maintaining the sheath unchanged. As the suspended heights of dust particles vary, their directional transport changes accordingly, including a flow reversal. A two-dimensional model of the ratchet sheath depicts the nonlinear distributions of plasma parameters and reveals that these unexpected transport phenomena can be attributed to the dependence of the electric ratchet potential and the resulting non-equilibrium net ion drag force on the suspended heights of dust particles. Our combined experimental and theoretical study provides insights into the fundamental transport properties of dust particles in an asymmetrical sheath.

Thermal Performance Analysis of Thermosyphon Solar Water Heating System Using Overlapped and Reverse Flow

Thermal Performance Analysis of Thermosyphon Solar Water Heating System Using Overlapped and Reverse Flow

Multi-scale investigation of heat and momentum transfer in packed-bed TES systems up to 800 K

With the rising cost of energy and the advancement of corporate social responsibility, there is a growing interest in addressing the challenge of recovering and storing high-temperature waste heat. Sensible heat storage in packed beds stands out as a cost-effective and seemingly straightforward solution for high-temperature Thermal Energy Storage (TES). Engineering models developed to design low-temperature TES systems were tentatively used to design this new generation of high-temperature systems. Delving into the physics of coupled heat and mass transfer reveals a lack of validation of this approach. This study seeks to establish a comprehensive bottom-up methodology - from the particle scale up to the system level - to provide informed and validated engineering models for the design of high-temperature TES systems. To achieve this goal, we developed a multi-scale numerical model to explore the physics of heat and momentum transfer in packed-bed TES systems. At the microscopic scale (pore/particle), we consider the flow of a compressible high-temperature gas between the particles, coupled to transient heat conduction within the particles, with particular attention given to incorporating accurate temperature-dependent viscosity for the gas phase and thermal conductivity and density for both solid and gas phases. At the macroscopic scale (engineering), we propose a high-temperature extension of state-of-the-art two-equation TES models. The governing equations considered are the volume-average conservation laws for gas-mass, gas-momentum and energy of both phases. The multi-scale strategy is applied to a randomly packed bed of spherical particles generated with the discrete element method (DEM) software LIGGGHTS. Numerical models for both scales were implemented in the Porous material Analysis Toolbox based on OpenFoam (PATO), which is made available in Open Source by NASA. Microscopic scale simulations were used to infer the effective parameters needed to inform the macroscopic model, namely, permeability, Forchheimer coefficient, effective thermal conductivities, and the heat transfer coefficient. The informed macroscopic model reproduces with excellent accuracy the average temperature fields of the physics-based microscopic model. Pore-scale analysis shows highly three-dimensional flow characterized by reverse flow and strong cross-flow in the packed bed system. Moreover, it indicates the coupling between temperature and velocity fields, where a nonuniform velocity field results in uneven temperature distributions across the fluid and the solid spheres within the packed bed, subsequently affecting the macroscopic heat transfer coefficient. The overall strategy is validated by comparison to available experimental data. This bottom-up methodology contributes to the understanding and opens new perspectives for a more precise design and monitoring of high-temperature TES systems.

Confinement-induced drift in Marangoni-driven transport of surfactant: a Lagrangian perspective

Successive drops of coloured ink mixed with surfactant are deposited onto a thin film of water to create marbling patterns in the Japanese art technique of Suminagashi. To understand the physics behind this and other applications where surfactant transports adsorbed passive matter at gas–liquid interfaces, we investigate the Lagrangian trajectories of material particles on the surface of a thin film of a confined viscous liquid under Marangoni-driven spreading by an insoluble surfactant. We study a model problem in which several deposits of exogenous surfactant simultaneously spread on a bounded rectangular surface containing a pre-existing endogenous surfactant. We derive Eulerian and Lagrangian formulations of the equations governing the Marangoni-driven surface flow. Both descriptions show how confinement can induce drift and flow reversal during spreading. The Lagrangian formulation captures trajectories without the need to calculate surfactant concentrations; however, concentrations can still be inferred from the Jacobian of the map from initial to current particle position. We explore a link between thin-film surfactant dynamics and optimal transport theory to find the approximate equilibrium locations of material particles for any given initial condition by solving a Monge–Ampère equation. We find that as the endogenous surfactant concentration $\delta$ vanishes, the equilibrium shapes of deposits using the Monge–Ampère approximation approach polygons with corners curving in a self-similar manner over lengths scaling as $\delta ^{1/2}$ . We explore how Suminagashi patterns may be produced by using computationally efficient successive solutions of the Monge–Ampère equation.

ЗАСОБИ РОЗРАХУНКУ ТА ВИБОРУ УСТАВОК ДИФЕРЕНЦІЙНО-ФАЗНОГО ЗАХИСТУ ПОВІТРЯНИХ ЛІНІЙ МІКРОПРОЦЕСОРНИХ ЗАХИСТІВ L60 В СКЛАДНИХ ЕЛЕКТРИЧНИХ МЕРЕЖАХ ДО 10 000 ВУЗЛІВ

The means for calculation and selection of phase-differential protection settings of overhead lines of L60 microprocessor protections of the General Electric company in complex electrical networks up to 10,000 nodes was developed. This software allows to select settings according to the possible types of mixed signals: forward-sequenced and reverse-sequenced, as well as additional criteria. The program makes it possible to check the sensitivity of the starting and disconnecting devices in the case of symmetrical and asymmetrical short circuits, in the case of maximum reverse power flows in various mixed starts. Ref. 3 fig. 5.

Physical modeling of ice-sheet-induced salt movements using the example of northern Germany

Abstract. Salt structures and their surroundings can play an important role in the energy transition related to a number of storage and energy applications. Thus, it is important to assess the current and future stability of salt bodies in their specific geological settings. We investigate the influence of ice sheet loading and unloading on subsurface salt structures using physical models based on the geological setting of northern Germany, which was repeatedly glaciated by the Scandinavian Ice Sheet during the Pleistocene. Apparent spatial correlations between subsurface salt structures in northern Germany and Weichselian ice marginal positions have been observed before, and the topic is a matter of ongoing debate. Recently described geomorphological features – termed surface cracks – have been interpreted as a direct result of ice-sheet-induced salt movement resulting in surface expansion. The spatial clustering and orientation of these surface cracks has not been well understood so far, owing to only a limited number of available studies dealing with the related salt tectonic processes. Thus, we use four increasingly complex physical models to test the basic loading and unloading principle, to analyze flow patterns within the salt source layer and within salt structures, and to examine the influence of the shape and orientation of the salt structures with respect to a lobate ice margin in a three-dimensional laboratory environment. Three salt structures of the northern German basin were selected as examples that were replicated in the laboratory. Salt structures were initially grown by differential loading and buried before loading. The ice load was simulated by a weight that was temporarily placed on a portion of the surface of the models. The replicated salt structures were either completely covered by the load, partly covered by the load, or situated outside the load extent. In all scenarios, a dynamic response of the system to the load could be observed; while the load was applied, the structures outside the load margin started to rise, with a decreasing tendency with distance from the load margin, and, at the same time, the structures under the load subsided. After the load was removed, a flow reversal set in, and previously loaded structures started to rise, whereas the structures outside the former load margin began to subside. The vertical displacements during the unloading stage were not as strong as during the load stage, and thus the system did not return to its pre-glaciation status. Modeled salt domes that were located at distance from the load margin showed a comparably weak reaction. A more extreme response was shown by modeled salt pillows whose margins varied from sub-parallel to sub-perpendicular to the load margin and were partly covered by the load. Under these conditions, the structures showed a strong reaction in terms of strain and vertical displacement. The observed strain patterns at the surface were influenced by the shape of the load margin and the shape of the salt structure at depth, resulting in complex deformation patterns. These physical modeling results provide more evidence for a possible interplay between ice sheets and subsurface salt structures, highlighting the significance of three-dimensional effects in dynamic geological settings. Our results lead to a better understanding of spatial patterns of the surface cracks that were mapped at the surface above salt structures and offer further room for interpretation of the influence of salt movements on the present-day landscape.

Capital flow reversals and currency crises: Do capital flow types matter?

AbstractWe analyze how reversals of several types of capital flows impact currency crises in emerging market and developing economies. Estimates of logit models show that reversals of (equity and debt) portfolio flows significantly increase the likelihood of currency crises in emerging market economies. In developing economies, reversals of portfolio debt flows and banking flows have a significant positive impact on currency crises. Finally, our results suggest that countries with mature financial systems and fixed exchange rate regimes are less likely to experience a currency crisis after a capital flow shock. The mediating role of capital account liberalization varies by country type.

Numerical Investigation of Butterfly Valve Performance in Variable Valve Sizes, Positions and Flow Regimes

Reliability and efficiency of valves are necessary for precise control and sufficient heat-flow to heat application plants for the integrated energy systems of nuclear power plants (NPPs). Strategic Management Analysis Requirement and Technology (SMART) valves’ ability to control flow and assess environmental parameters stands out for these requirements. Their ability to sustain the downstream flow rate, prevent reverse flow, and maintain pressure in the heat transport loop is much more efficient with the integration of sensors and intelligent algorithms. For assessing valve performance and monitoring, mechanical design and operating conditions are two important parameters. In this study, the butterfly valves of three different sizes are simulated with water and steam using STAR-CCM+ in various flow regimes and positions to analyze performance parameters to strategize an automated control system for efficiently balancing the heat–transport network. Also, flow behavior is studied using velocity and pressure fields for valve–body geometry optimization. It can be observed, through performance parameters, that the valves are suitable for operation between 30° and 90° positions with significantly low loss coefficients and high flow coefficients, and the performance parameters follow a certain pattern in both water and steam flow in each scenario.

‘Best Known Example of Relativity in Literature’: Personal Supertext of L.N. Tolstoy in V.V. Nabokov’s Novel “Pnin”

This article addresses the issue of interpreting the work and biographical myth of L.N. Tolstoy in V.V. Nabokov’s novel “Pnin.” The aim of the study is to examine how through the reconstruction of Tolstoy’s personal supertext, Nabokov conveys his philosophy of time. This question is relevant in the context of studying Nabokov’s historiosophy and the writer’s reflection on his own literary genealogy. The analysis reveals that in Nabokov’s reception, Tolstoy is a national genius who was able to recreate the effect of natural time flow. Explicit references to Tolstoy and his biography allow for correlating the characters’ reading experience and their perception of time: from frozen time during reading-performance to the reverse flow of time during co-creative reading. The motifs of Tolstoy’s works actualize the key problem of the relativity of time for Nabokov. Although the unreliable narrator emphasizes the power of time and fate over the lonely hero, in reality, Pnin has access to multiple temporal dimensions. Just like in “Anna Karenina,” the technique of temporal synchronization highlights the interconnectedness of characters’ fates. Tolstoy’s personal supertext enables Nabokov to understand the theme of family as a timeless connection between people that defines the characters’ place in the world.