Exchange Model Research Articles

Comparative Analysis of Heat Exchanger Models for Phase Change Material Melting Process: Experimental and Numerical Investigation

ABSTRACTThermal energy storage systems using PCM offer promising solutions for efficient thermal applications. This study aims to provide valuable insights into the PCM melting process and compare the thermal performance of different heat exchanger models. The experimental rig is carefully designed to simulate a shell and tube heat exchanger with five longitudinal copper fins at specific conditions. Three distinct models of the heat exchanger, labeled Models A, B, and C, were examined for their heat transfer efficiency during the melting process. Numerical simulations were conducted for the three models and compared with experimental results. Model A represented the benchmark model. It had uniform fin length, location, and angle. Model B was the modified design aimed at enhancing melting progress. These modifications included a longer lower fin, a shorter side fin compared to the reference, and a lower fin angle to optimize heat transfer performance. Model C incorporates further design modifications, with a longer lower fin, a shorter top fin, and different lower fin location. Numerical simulations and experimental observations revealed significant differences in heat transfer performance among the three models. The average heat transfer rates, measured up to the critical decline point, are crucial parameters for practical applications. A comparison among the three models showed that Model B surpassed the average heat transfer rate up to the critical point of Models A and C by 10% and 4%, respectively, demonstrating its superior practical applicability.

From interacting agents to Boltzmann-Gibbs distribution of money

Abstract We investigate the unbiased model for money exchanges: agents give at random time a dollar to one another (if they have one). Surprisingly, this dynamics eventually leads to a geometric distribution of wealth (shown empirically by Dragulescu and Yakovenko, and rigorously by several follow-up papers). We prove a uniform-in-time propagation of chaos result as the number of agents goes to infinity, which links the stochastic dynamics to a deterministic infinite system of ordinary differential equations. This deterministic description is then analyzed by taking advantage of several entropy–entropy dissipation inequalities and we provide a quantitative almost-exponential rate of convergence toward the equilibrium (geometric distribution) in relative entropy.

Employing binary/ternary organic blends in integrated HP-assisted HDH desalination systems

The global demand for potable water is rising, prompting the development of various energy systems for distilled water production. However, the significance of utilizing multicomponent working fluids in these systems has been largely overlooked. This study presents three HDH-based distillation units powered by two conventional heat pump cycles, namely, the simple and vapor injection heat pumps (first and second models) and an innovative heat pump cycle with an ejector expander (third model). The significance of the research lies in its pioneering investigation of utilizing two- and three-component mixtures in heat pump-based desalination units, which has not been previously explored. The study's primary aim is to determine whether using multicomponent working fluids instead of pure fluids or introducing structural modifications can more effectively enhance the performance of heat pump-based distillation units. The proposed models are simulated using EES and MATLAB software, with the study focusing on energetic, exergetic, exergoeconomic, and heat exchanger modeling to evaluate the feasibility of the configurations. The findings revealed that the structural modifications in the third scenario using R134a resulted in the highest GOR, with improvements of 44 % and 26.03 %, respectively, compared to the other scenarios. However, utilizing binary blend R22/R142b with different compositions improved the GOR of the first to three scenarios by 41.26 %, 29.06 %, and 11.87 %, respectively. Furthermore, in this case, the unit cost of distilled water for the first, second, and third scenarios increased by 12.87 %, 14.32 %, and 12.70 %, respectively. Finally, the first scenario has the highest NPV of 4.40 M$ and the shortest PP of 8.13 years. Therefore, utilizing the blend in a simple heat pump proves to be more efficient and cost-effective than implementing structural modifications.

A Closed-Form Expression for Analysis of Dark State Exchange Saturation Transfer (DEST) NMR Experiments.

Closed-form expressions for the analysis of Dark state Exchange Saturation Transfer (DEST) NMR experiments, a powerful experimental tool for characterizing exchange processes involving the interaction of NMR visible species with very high molecular weight partners, is presented. Essentially identical exchange and relaxation parameters are derived from the analytical and numerical best fits of the DEST profiles obtained for a protein construct derived from huntingtin exon-1, comprising the N-terminal amphiphilic sequence followed by a seven-residue glutamine repeat, httNTQ7, in the presence of small (SUV) and large (LUV) unilamellar lipid vesicles. The use of analytical expressions significantly speeds up the fitting of experimental DEST profiles to a two-state exchange model and simplifies the analysis of the DEST effects.

A Hierarchical-Dealer-Centric Model of FX Swap Valuation

This paper constructs a model of foreign exchange (FX) swap valuation based on dealers’ behavior and the hierarchy of the global dollar funding system. International investors use these currency derivatives to synthetically fill their US-dollar funding gaps. In this model, three attributes of market structure drive the valuation of FX swaps: market-making costs (measured by dealers’ bid-ask spreads), dollar funding liquidity risk (measured by CIP deviation and market imperfections), and FX swap market liquidity (measured by dealer competition). The goal is to understand how market design influences the cost of US dollar funding and its spillover effects. FX dealers are vital institutions in this ecosystem, as their balance sheets connect national monetary systems to the global dollar funding markets. For currencies with low FX turnover, central banks act as market makers, while private banks serve as dealers for currencies with the highest FX turnover. Studying the “dollar funding gap” through the lens of FX swap dealers is a crucial aspect often overlooked in international finance scholarship.

Structural Plasticity as a Driver of the Maturation of Pro-Interleukin-18.

Dynamics are often critical for biomolecular function. Herein we explore the role of motion in driving the maturation process of pro-IL-18, a potent pro-inflammatory cytokine that is cleaved by caspases-1 and -4 to generate the mature form of the protein. An NMR dynamics study of pro-IL-18, probing time scales over 12 orders of magnitude and focusing on 1H, 13C, and 15N spin probes along the protein backbone and amino-acid side chains, reveals a plastic structure, with millisecond time scale dynamics occurring in a pair of β-strands, β1 and β*, that show large structural variations in a comparison of caspase-free and bound pro-IL-18 states. Fits of the relaxation data to a three-site model of exchange showed that the ground state secondary structure is maintained in the excited conformers, with the side chain of I48 that undergoes a buried-to-exposed conformational change in the caspase-free to -bound transition of pro-IL-18, sampling a more extensive range of torsion angles in one of the excited states characterized, suggesting partial unpacking in this region. Hydrogen exchange measurements establish the occurrence of an additional process, whereby strands β1 and β* locally unfold. Our data are consistent with a hierarchy of dynamic events that likely prime pro-IL-18 for facile caspase binding.

Analysis of DD* and D¯(*)Ξcc(*) molecule by one boson exchange model based on heavy quark symmetry

Numerous exotic hadrons with heavy quarks have been reported in the experiments. In such states, symmetries of heavy quarks are considered to play a significant role. In particular, the superflavor symmetry, or also called the heavy quark antidiquark symmetry is one of the interesting symmetries, which links a quark Q to an antidiquark Q¯Q¯ having the same color representation as Q. In this paper, we study a D¯Ξcc molecular state as a superflavor partner of the doubly charmed tetraquark Tcc reported by LHCb recently. Tcc locating slightly below the DD* threshold is a candidate of the hadronic molecule. Thus by replacing the singly charmed meson D(*) with the doubly charmed baryon Ξcc(*), superflavor symmetry predicts the existence of the D¯(*)Ξcc(*) bound state. We employ the one boson exchange model respecting with the heavy quark spin symmetry where the parameter is obtained to reproduce the Tcc binding energy. We apply this model with superflavor symmetry to the D¯(*)Ξcc(*) molecule and predict a bound state with I(JP)=0(12−). If the pentaquark state corresponding to D¯(*)Ξcc(*) molecular state is observed in future experiments as predicted in this work, it is more likely that Tcc is a DD* molecular state. Published by the American Physical Society 2024

Toward quantitative CEST imaging of glutamate in the mouse brain using a multi-pool exchange model calibrated by 1H-MRS.

To develop a CEST quantification model to map glutamate concentration in the mouse brain at 11.7 T, overcoming the limitations of conventional glutamate-weighted CEST (gluCEST) contrast (magnetization transfer ratio with asymmetric analysis). 1H-MRS was used as a gold standard for glutamate quantification to calibrate a CEST-based quantitative pipeline. Joint localized measurements of Z-spectra at B1 = 5 μT and quantitative 1H-MRS were carried out in two voxels of interest in the mouse brain. A six-pool Bloch-McConnell model was found appropriate to fit experimental data. Glutamate exchange rate was estimated in both regions with this dedicated multi-pool fitting model and using glutamate concentration determined by 1H-MRS. Glutamate exchange rate was estimated to be ˜1300 Hz in the mouse brain. Using this calibrated value, maps of glutamate concentration in the mouse brain were obtained by pixel-by-pixel fitting of Z-spectra at B1 = 5 μT. A complementary study of simulations, however, showed that the quantitative model has high sensitivity to noise, and therefore, requires high-SNR acquisitions. Interestingly, fitted [Glu] seemed to be overestimated compared to 1H-MRS measurements, although it was estimated with simulations that the model has no intrinsic fitting bias with our experimental level of noise. The hypothesis of an unknown proton-exchanging pool contributing to gluCEST signal is discussed. High-resolution mapping of glutamate in the brain was made possible using the proposed calibrated quantification model of gluCEST data. Further studying of the in vivo molecular contributions to gluCEST signal could improve modeling.

Exploration of lead free half-metallic double perovskites Li2Mo(Cl/Br)6 for spintronic device: DFT-calculations

The intrinsic spin of electrons has revolutionized the various aspects in the field of electronics, like data storage and quantum computing. Magnetic, structural, mechanical, transport and thermoelectric aspects of the Li2Mo(Cl/Br)6 double perovskites have been examined using the Wein2k and BoltzTraP code. These compounds having cubic structure with negative enthalpy of formation confirms their thermodynamic stability. The energy versus volume optimization for both ferromagnetic (FM) and antiferromagnetic phases (AFM) indicate AFM state due to greater release of energy in this configuration. Double exchange model p-d hybridization for partial density of states (PDOS) is investigated in band structures and half-metallicity feature is reported. The spin–orbit interaction with hybridization in d states of Mo and integral magnetic moment reveals strong spin polarization. The thermoelectric features (Seebeck coefficient, power factor, and figure of merit, electrical and thermal conductivities) have also been evaluated for utilization of these compounds in spintronics appliances.

The moderating role of emotional intelligence and HR digitalization on the relationship between compensation and employee job performance in Johor manufacturing sector

This research examines the moderating role of emotional intelligence and HR digitalization on the relationship between compensation and employee job performance in Johor manufacturing sector. The manufacturing sector, which has contributed significantly to the Malaysian national GDP, was among the most affected sectors during the remote work movement caused by several Covid-19. One of the most critical aspects was managing human resources (HR) in remote work and the challenges faced by the employees working online. Drawing upon the Theory of Social Exchange and Ability model of Emotional Intelligence, this practical study investigated the influence of compensation (COM) on employee job performance (EJP) with the moderation of human resource digitalization (HRDi) and emotional intelligence (EI). A quantitative methodology based on online and hard-copy questionnaires was adopted. The population of this study consisted of management employees, such as directors, managers, executives, and administrators working in Johor manufacturing companies. A total of 318 responses was used in this study. Utilising SPSS and Smart PLS, the researcher analysed preliminary and pilot studies, data screening and cleaning procedures, exploratory factor analysis, as well as partial least squares structural equation modeling to assess the relationships among variables and test the hypotheses. The research findings demonstrated that compensation directly affects employee job performance. Meanwhile, human resource digitalization moderates the relationships between compensation and job performance of employees. In addition, emotional intelligence moderates the relationships between compensation and employee job performance. Policymakers are urged to encourage HR digitalization implementation and training on enhancing emotional intelligence. Besides, organizations should have plans on how to enhance their implementation of HR digitalization and improve emotional intelligence.

Kinodynamic Model-Based UAV Trajectory Optimization for Wireless Communication Support of Internet of Vehicles in Smart Cities

Unmanned aerial vehicles (UAVs) are utilized for wireless communication support of Internet of Intelligent Vehicles (IoVs). Intelligent vehicles (IVs) need vehicle-to-vehicle (V2V) and vehicle-to-everything (V2X) wireless communication for real-time perception knowledge exchange and dynamic environment modeling for safe autonomous driving and mission accomplishment. UAVs autonomously navigate through dense urban areas to provide aerial line-of-sight (LoS) communication links for IoVs. Real-time UAV trajectory design is required for minimum energy consumption and maximum channel performance. However, this is multidisciplinary research including (1) dynamic-aware kinematic (kinodynamic) planning by considering UAVs’ motion and nonholonomic constraints; (2) channel modeling and channel performance improvement in future wireless networks (i.e., beyond 5G and 6G) that are limited to beamforming to LoS links with the aid of reconfigurable intelligent surfaces (RISs); and (3) real-time obstacle-free crash avoidance 3D trajectory optimization in dense urban areas by modeling obstacles and LoS paths in convex programming. Modeling and solving this multilateral problem in real-time are computationally prohibitive unless extensive computational and overhead processing costs are imposed. To pave the path for computationally efficient yet feasible real-time trajectory optimization, this paper presents UAV kinodynamic modeling. Then, it proposes a convex trajectory optimization problem with the developed linear kinodynamic models. The optimality and smoothness of the trajectory optimization problem are improved by utilizing model predictive control and quadratic state feedback control. Simulation results are provided to validate the methodology.

Diffusion and Exchange Kinetics of Microparticle Formulations by Spatial Fourier Transform Fluorescence Recovery after Photobleaching with Patterned Illumination.

The mechanism of active pharmaceutical ingredient (API) mobility during release in microparticle formulation was investigated using periodically structured illumination combined with spatial Fourier transform fluorescence recovery after photobleaching (FT-FRAP). FT-FRAP applies structured photobleaching across a given field of view, allowing for the monitoring of molecular mobility through the analysis of recovery patterns in the FT domain. Encoding molecular mobility in the FT domain offers several advantages, including improved signal-to-noise ratio, simplified mathematical calculations, reduced sampling requirements, compatibility with multiphoton microscopy for imaging API molecules within the formulations, and the ability to distinguish between exchange and diffusion processes. To prepare microparticles for FT-FRAP analysis, a homogeneous mixture of dipyridamole and pH-independent methyl methacrylate polymer (Eudragit RS and RL) was processed using laminar jet breakup induced by vibration in a frequency-driven encapsulator. The encapsulated microparticles were characterized based on particle size distribution, encapsulation efficiency, batch size, and morphology. Utilizing FT-FRAP, the internal diffusion and exchange molecular mobility within RL and RS microparticles were discriminated and quantified. Theoretical modeling of exchange- and diffusion-controlled release revealed that both RL and RS microparticles exhibited similar exchange decay rates, but RL displayed a significantly higher diffusion coefficient. This difference in diffusion within RL and RS microparticles was correlated with their macroscopic dissolution performance.

Investigation on the bottom analogs Tbb− of Tcc+

We investigate the doubly bottom state Tbb− composed of two bottom mesons with JP=1+. The potentials are obtained using the one-boson exchange model. With the heavy quark flavor symmetry, all the parameters in the model are determined by fitting the experimental data of doubly charmed state Tcc+ from our previous work. Our analysis indicates that the isospin symmetry is well preserved. We identify a deeply bound Tbb− state with quantum numbers I(JP)=0(1+), in contrast to the loosely bound Tcc+. Additionally, we discover a resonant Tbb− state with I(JP)=1(1+). Furthermore, our investigation into the B¯B¯*−B¯*B¯* coupled channel effect reveals its important impact. The binding energy of the bound I(JP)=0(1+) states becomes deeper, while the resonant Tbb− state with I(JP)=1(1+) remains nearly unchanged. Published by the American Physical Society 2024

Simple and Accurate Representation of Cumulative Nighttime Leaf Respiratory CO2 Efflux.

Leaf respiratory carbon loss decreases independent of temperature as the night progresses. Detailed nighttime measurements needed to quantify cumulative respiratory carbon loss at night are challenging under both lab and field conditions. We provide a simple yet accurate approach to represent variation in nighttime temperature-independent leaf respiratory CO2 efflux in environments with both stable and fluctuating temperatures, which requires no detailed measurements throughout the night. We demonstrate that the inter- and intraspecific variation in the cumulative leaf respiratory CO2 efflux at constant temperature, at any length of night, scales linearly with the inter- and intraspecific variation in initial measurement of leaf respiratory CO2 efflux at the same temperature at the beginning of the night. This approach informs large-scale predictions of cumulative leaf respiratory CO2 efflux, which is needed to understand plant carbon economy in global change studies as well as in global modeling and eddy covariance monitoring of the land-atmosphere exchange of CO2.

Rapid aerodynamic characterization of surface heat exchangers for turbofan aeroengines through optical techniques and additive manufacturing

Surface heat exchangers that use the bypass flow as heat sink are becoming a widely used solution to alleviate the high thermal load of modern aeroengines. Experimental characterization of such heat exchangers in full-scale engine tests is extremely expensive and time-consuming, so carrying out experiments in scaled wind tunnels that can replicate their very challenging flow conditions is highly desirable. However, intrusive instrumentation can affect the actual aerodynamics of the component due to the reduced size of the section and the typical high air velocities of turbofan engines. For this reason, a methodology to characterize a surface heat exchanger designed to work in the turbofan bypass using optical techniques is presented in this work. Additionally, the possibility of replicating the experimental conditions using additively manufactured models of exchangers would allow rapid preliminary characterization of these components. In this investigation, different non-intrusive techniques such as PIV, LDA, Schlieren, or LDV have been applied to determine the heat exchanger aerodynamic performance and vibration response, and a detailed characterization of the flow field has been carried out. Data have been cross-validated using different measurement techniques. A 3D-printed model has also been built to compare with the aluminum heat exchanger, showing almost an identical behavior in terms of velocity distribution downstream of the heat exchanger and pressure drop induced by its fins, as well as corrected frequencies, confirming thus the suitability of additive manufacturing for the aerodynamic characterization of these devices in preliminary stages.

Study on the chloride removal performance of porous anion exchange resin models constructed via 3D printing technology

Industrial production produces a large amount of wastewater containing chloride (Cl-) ions, and elevated concentrations of Cl- pose substantial environmental hazards. This study presents a novel approach using ion exchange resin for the removal of chloride, combined with the advantages of controllable and rapid model design afforded by 3D printing technology, to prepare a porous ion exchange model (PIEM). The optimal conditions for pretreatment, chloride removal, and alkaline regeneration of PIEM were systematically explored. Under these optimal conditions, the chloride removal efficiency of a single PIEM in simulated wastewater with a 1000 mg/L Cl- concentration was 67.4 %. Following five cycles, the chloride removal efficiency stabilized at 40 %. When thirty PIEMs assembled into a quartz tube device were used and subjected to six cycles, the total chloride removal efficiencies reached 85.2 % for 2 L of simulated wastewater with a Cl- concentration of 1000 mg/L and 52.6 % for 1 L of actual wastewater with a Cl- concentration of 2915 mg/L. The mechanism of chloride removal by PIEM involves ion exchange and hydrogen bonding adsorption between the ion exchange resin and Cl- in the surrounding wastewater. This study develops a new method of removing chloride by immobilizing ion exchange resin through 3D printing, which prevents the significant loss of ion exchange resin during the chloride removal process and ensures high efficiency in removing chloride, providing new insights for the development of chloride removal technology.

Does greater filial piety bring more gender income advantages? Exploring the influence of traditional Chinese filial piety on the gender wage gap

PurposeBased on traditional Chinese filial piety, this article examines the impacts and mechanisms of the two-dimensional filial piety concept “Qinqin – Zunzun” on gender wages in China via China Family Panel Studies (CFPS) conducted in 2014 and 2018.Design/methodology/approachThis article construct regression models to examine the relationship between filial piety concepts and wages. Also, it uses unconditional quantile regression and decomposition to explore the impact of filial piety concepts on the wage gap.FindingsIt is found that: (1) The effects of two-dimensional filial piety are heterogeneous in terms of gender. Specifically, authoritarian filial piety significantly suppresses individual wages and has a stronger suppressive effect on women’s wages, whereas affinity filial piety significantly enhances individual wages without gender heterogeneity; (2) Parents' time support in the intergenerational exchange model is a crucial mechanism by which filial piety affects wages, exhibiting significant gender heterogeneity; (3) Regarding wage distribution, authoritarian filial piety mainly widens the gender income gap in the low and middle income-groups, while affinity filial piety narrows the gender wage gap by “raising the floor”, with its converging effect being most significant in the middle and high-income groups. This article deepens the understanding of the gender wage gap and intergenerational income mobility, providing policy references for better utilizing the social governance function of culture.Originality/valueThe article deepens the understanding and mechanisms of the gender wage gap and inter-generational income mobility, providing policy reference for better utilizing the social governance function of culture.

Determining the efficiency of local heat recycling wastewater based on a heat exchanger

RELEVANCE. The authors research the potential energy, economic and environmental effects of using local heat recovery from wastewater generated in showers. At the moment in Russia, almost all household wastewater is disposed of in sewer networks without the beneficial use of the heat that they possess. It is important to determine the effect of implementing this method of heat recovery, to identify and analyze the problems that prevent this from being done.THE PURPOSE. The purpose of the work is to determine the potential effect of using local heat recovery from wastewater generated in showers.METHODS. Based on a verified mathematical model of the heat exchanger, the energy effect from the individual use of the shower room is determined. A number of assumptions are applied to the heat consumption structure of an individual building and, based on available data on the average annual heat consumption of residential buildings in Moscow, the economic and environmental effect of energy-saving measures is calculated.RESULTS. Relative savings within the annual heat consumption of a building with a decentralized and centralized hot water supply system were 5,3% and 3,1%, respectively (64 and 37 GCal). Fuel economy amounted to: 9145 toe and 5227 toe for a building with a decentralized and centralized hot water supply system, respectively (14,5 and 8,5 thousand tons of CO2-eq). The payback period for energy-saving measures for the case of a decentralized hot water system based on an instantaneous electric water heater was 1,5 years.CONCLUSION. Local waste heat recovery makes it possible to obtain a significant energy and environmental effect within any locality, but at the moment there are no measures to support consumers implementing energy-saving measures. Currently, this method of heat recovery is of interest only to those consumers whose source of thermal energy for the needs of hot water supply is electricity.

Ab Initio Calculation of Coupling-Constant Averaged Exchange-Correlation Holes for Spherically Symmetric Atoms.

Accurate approximation of the exchange-correlation (XC) energy in density functional theory (DFT) calculations is essential for reliably modeling electronic systems. Many such approximations are developed from models of the XC hole; accurate reference XC holes for real electronic systems are crucial for evaluating the accuracy of these models however the availability of reliable reference data is limited to a few systems. In this study, we employ the Lieb optimization with a coupled cluster singles and doubles (CCSD) reference to construct accurate coupling-constant averaged XC holes, resolved into individual exchange and correlation components, for five spherically symmetric atoms: He, Li, Be, N, and Ne. Alongside providing a new set of reference data for the construction and evaluation of model XC holes, we compare our data against the exchange and correlation hole models of the established local density approximation (LDA) and Perdew-Burke-Ernzerhof (PBE) density functional approximations. Our analysis confirms the established rationalization for the limitations of LDA and the improvement observed with PBE in terms of the hole depth and its long-range decay, which is demonstrated in real-space for this series of spherically symmetric atoms.

Heat transfer mechanism of superabsorbent polymers phase change energy storage cold-formed steel wall under fire

The superabsorbent polymer phase change materials (SAP materials) exhibit exceptional water absorption and retention properties, offering substantial potential for fire protection in steel structures, thereby reducing the need for sheathing boards and fire-retardant coatings, while minimizing energy consumption. Understanding the heat-mass exchange theory of SAP materials is crucial for enhancing their application in the building industry. This study develops a comprehensive theoretical model for heat-mass exchange in cold-formed steel (CFS) walls incorporating SAP materials. An equilibrium phase change model and a simplified thermal radiation model were developed to capture the water loss and dynamic heat exchange processes in SAP materials. These models were integrated into a transient fluid-solid-thermal coupling model using Ansys Fluent and User Defined Functions. In the case study, the newly developed numerical models can accurately predict temperature field changes in CFS walls with SAP materials, demonstrating the heat transfer mechanisms of hot and cold flanges at different temperature rise stages. The developed numerical model was used to investigate the effects of factors such as the moisture content of the SAP material, web depth, and flange width on the fire resistance of the CFS wall. Results indicated that increasing the wall stud height improves fire resistance, while increasing flange width has little effect on hot flange temperature. These findings provide a theoretical foundation and practical guidelines for the application of SAP phase change insulation materials in the building industry, promoting energy reduction and supporting sustainable construction practices.