Exchange Performance Research Articles

Impact of inlet steam state on ejector internal flow and performance considering non-equilibrium condensation

Most of the numerical studies adopted dry gas model to predict transonic and supersonic flow in steam ejectors, but it cannot accurately reflect flow characteristics in ejectors, since the condensation and evaporation of wet steam is ignored. The current work develops and validates a CFD model describing spontaneous condensation to simulate complicated flow behaviors and phase transition inside an ejector, and illustrates the impact of initial state of primary fluid including wet, saturated and superheated state on flow characteristics, mass and heat exchange and ejector performance. It is found that the initial steam wetness obviously impacts the average liquid fraction in the ejector. Both the superheated and wet initial primary steam suppress the process of mass and heat exchange during nucleation, and the position and intensity of nucleation are influenced by the inlet steam state. Compared with the case of dry saturated inlet steam, the superheated inlet steam improves entrainment ratio by 3.7%, and decreases compression ratio by 2.5%.

Insight into ion exchange behavior of LDHs: Asynchronous chloride adsorption and intercalated ions release processes

Cl− adsorption and intercalated ions release processes during LDHs are highly intricate phenomena. In this study, ion exchange performance of LDHs with specific cation interlayers and intercalated anions (CaAl–NO3-LDHs, CaAl–NO2-LDHs, CaFeAl–NO3-LDHs and CaFeAl–NO2-LDHs) were extensively investigated. The results indicate that in the presence of low chloride concentration, the intercalated anions are prematurely released due to partial dissolution of LDHs in neutral deionized water and ion exchange with OH− in alkaline simulated concrete pore solution. Therefore, Cl− adsorption of LDHs and release process of intercalated anions in LDHs are not completely synchronized. Compared to partial LDHs dissolution, the accelerating effect of OH− exchange on intercalated anion release in simulated concrete pore solution is more pronounced. Further, higher stability of LDHs in testing solutions is mainly corresponding to higher binding energy between intercalation ions and cation interlayers, thus saturated Cl− adsorption content of NO3-LDHs with high binding energy is higher than NO2-LDHs with low binding energy, and saturated Cl− adsorption content of CaAl-LDHs with high binding energy is higher than CaFeAl-LDHs with low binding energy in testing solutions.

Theoretical model for high-altitude gas exchange process in multi-fuel poppet valves two-stroke aircraft engine

Under the demand of global aviation carbon reduction, the multi-fuel poppet valves two-stroke (MF-PV2S) aircraft engine exhibits advantages such as lower lubricant consumption and the flexibility to high-altitude valve timing adjustment, which position it to play a more significant role in general aviation aircraft and unmanned aerial vehicle propulsion systems. High-altitude gas exchange performance is a critical factor in the thermal efficiency and power characteristics of two-stroke aircraft engines. However, the applicability and accuracy of existing models in predicting the gas exchange process for PV2S engines remain insufficiently discussed. Recognizing discrepancies in the predictions of PV2S gas exchange processes by existing models, a theoretical model applicable to high-altitude gas exchange in an MF-PV2S aircraft engine is established. The modified model adjusts the exhaust composition during the second and third phases of the scavenging process, and a novel model characteristic coefficient, designated as b3, is incorporated to signify the proportion of mixed gas in the exhaust gases at a given moment. Moreover, the model characteristic coefficients b1 and b2, are determined with nonlinearity, based on appropriate relationships that account for the characteristics of the PV2S gas exchange process. The model calculates gas exchange characteristics under different operating conditions and fuels, comparing these results with simulations and tracer gas-based experiments. The findings demonstrate that the model successfully captures the characteristics of early appearance and prolonged duration of fresh charge loss during PV2S gas exchange, significantly enhancing the predictive accuracy. Through adjustments of model coefficients based on specific conditions, the model predicts and describes the variation process of PV2S gas exchange performance parameters under different conditions, including various speeds, different intake-exhaust pressure differences at different altitudes, valve overlaps, and fuel types. The maximum relative errors between model predictions and experimental trapping efficiency, delivery ratio and charging efficiency are 2.58 %, 4.33 %, and 3.89 % respectively. The model can be used for rapid and accurate prediction of gas exchange characteristics under different conditions for the MF-PV2S aircraft engine. Also, it serves as an alternative model of three-dimensional simulation models that can be coupled into the one-dimensional thermodynamic cycle simulation.

The impact of ferrofluid actuated by an external magnetic field on heat exchange performances of curved channels

The development rules of ferrofluid flow and heat exchange in curved channels under the influence of external magnetic field were thoroughly investigated using the finite element method. The comprehensive strengthening performance of elbows under magnetic fields was evaluated based on the factors including the dimensionless pressure coefficient, heat transfer coefficient, and comprehensive strengthening factor. The results demonstrate that the heat transfer coefficient can be improved by increasing the volume fraction of ferrofluid in the presence of lower or no magnetic field, while it exhibits no significant variation with the increase of the volume fraction for higher magnetic fields. For a given volume fraction, a lower magnetic field may slightly inhibit heat transport of ferrofluid. A higher magnetic field can induce a complex swirling flow of the fluid along the curved axis. As the curvature decreases, the magnetic field effect becomes stronger, leading to the coupling of the magnetic field force with the centrifugal force. This coupling results in three pairs of secondary vortices on the cross-section and the heat exchange capacity is significantly enhanced. Within the study, the heat transfer coefficient of the curved tube with a dimensionless curvature of 0.067 for the magnetic field intensity of 1800G increased by 43.51%, and the comprehensive strengthening factor is 1.326, compared to without a magnetic field.

Understanding the Moderating Role of Dollar Exchange Rate in Shaping the Linkages Between Foreign Direct Investment and Pakistan Stock Exchange Performance

The stock exchange market is a crucial component of the economy, providing investors with the opportunity to participate in the shares of different enterprises. This study investigates the influence of the United States Dollar exchange rate and foreign direct investment (FDI) on the Karachi Stock Exchange-100 index, a key component of the Pakistan Stock Exchange. Utilizing monthly data from July 2008 to March 2023, the research employs an Augmented Dickey-Fuller test for stationarity and Johnson Cointegration test for model confirmation. Results from the Granger Causality test highlight significant long-term relationships between FDI, inflation, interest rates, balance of payments, and the Karachi Stock Exchange-100 index. Conversely, the exchange rate and FDI exhibit statistical insignificance in the short term. Introducing moderation effects, the exchange rate demonstrates negligible long-term impact but reveals a negative short-term association with the Karachi Stock Exchange-100 index. Impulse response analysis indicates positive reactions to shocks for FDI, balance of payments, and the dollar exchange rate, with inflation and interest rates exhibiting negative responses. The study's novel contribution lies in uncovering the nuanced temporal dynamics between economic indicators and the stock market, offering valuable insights for policymakers crafting investment strategies to navigate market volatility and enhance stock market returns.

Impact of COVID-19 Pandemic and Russo-Ukrainian War on Tunisian Stock Exchange Performance and Volatility

The purpose of our study was to investigate the impact of COVID-19 pandemic and the Russo-Ukraine (RU) war on the return volatility and value of the Tunisian Stock Exchange proxied by TUNINDEX. We applied GARCH (1,1) to assess the impact on the index return volatility, using daily observations from January 2019 to December 2022, and a multiple linear regression to determine the effect on the index value, based on monthly observations for January 2018 to December 2022. GARCH output revealed that both exogenous shocks led to higher stock market return volatility. The regression results disclosed statistically significant though opposite impacts on the index price. The pandemic exerted a positive, though extremely mild impact on the Index value, while the war had a negative effect on its performance. As for the control variables, both inflation rate and industrial production index exhibited positive effects on the TUNINDEX values, while trade balance had a negative impact. GDP growth rate and interest rate however, showed no significant influence on the index performance during the study period. We faced some difficulty accessing data, in addition to the scarcity of data on other potentially relevant factors, along with a short study period. Incorporating new variables i.e. mortality rates, unemployment due to the lockdown, travel bans effect, trade dependence with Ukraine and Russia, and using Time-Varying Vector Auto Regressive model may add additional value to our work. The paper contributes to the literature on external shocks impacts on stock markets, specifically on the Tunisian stock exchange. In addition, it offers insights on the potential expected economic effects of unpredicted events, and may help identify appropriate strategies to mitigate their dramatic effects. Finally, this research presents the first investigation on the impact of the Russian invasion on Ukraine on the Tunisian stock exchange by probing into the impact on both volatility and performance of the market’s index.

THE EFFECT OF ECONOMIC GROWTH ON STOCK EXCHANGE

Economic growth measures growth in economic activities. Economic growth is important for countries, because it often brings better economic and social standards. Stock exchange performance is often a good indicator of the economy since it shows the performance of some of the important companies in the economy. The empirical analysis in this article aims to investigate the relationship between economic growth and stock exchange performance. Percentage change in GDP of Turkey and BIST100 are used as variables for this purpose. Two different data sets; 2003-2022 and 2013-2022 are available in the research. The analysis include error correction model, vector auto regression, Granger causality, impulse response, and variance decomposition. For the period 2013-2022, cointegration long run relationship is determined but there is no short run relationship as explained by error correction model. 30% of changes in economic growth can be explained by stock exchange performance and only 5% of changes in stock exchange performance can be explained by economic growth. BIST100 Granger causes economic growth. For the period 2003-2022, both short run and long run relationships are detected. Shocks in the long run disappear by 24%. The results indicate that the stock exchange performance can be used as an indicator of economic growth. Works in the literature also show significant relationship between stock markets and GDP both in local and international studies. The findings have important academic, policy and practical implications.

THE ROLE OF PERSONALITY AS A MEDIATOR IN THE RELATIONSHIP BETWEEN LEADER-MEMBER EXCHANGE AND JOB PERFORMANCE

Academic staffs are the main asset to Higher Education Institutions (HEIs) since education is the institution's core business. The ability of academic staff to meet the goals set by the HEIs is of utmost importance. They must possess strong competencies and excellent personality to improve their performance and achieve the desired target. Although the effect of organizational and individual factors has been verified in previous studies, it remains unclear what underlying mechanisms explain the relationship. This study examined the role of personality as a mediator in the relationship between leader-member exchange (LMX) and job performance. This research used a quantitative method with a total sample of 260 academic staff in private HEIs, which were analyzed using the SEM Amos software. The findings showed that LMX and job performance (β= -0.26) and LMX and personality (β= 0.42) were significantly related, and academic staff personality was found to have the most substantial effect on job performance (β= 1.07). The result also indicated that personality partially mediates the relationship between LMX and job performance. The study's findings propose that the management of HEIs can improve the organizational factors through the proper implementation of LMX, which will nurture individual factors' effectiveness and improve academic staff job performance.

Comprehensive Evaluation of the Performances of Heat Exchangers with Aluminum and Copper Finned Tubes

The finned-tube heat exchanger is the core part of an air conditioning system. Its heat exchange performance directly affects the energy consumption and efficiency of the air conditioner. The shortage and rising price of copper have led to increasing replacement of copper tubes with aluminum tubes in finned-tube heat exchangers. This paper studies two kinds of such heat exchangers, one consisting of copper tubes and aluminum fins and the other consisting of aluminum tubes and aluminum fins. The influences of the different base tube materials on heat transfer are compared and analyzed in terms of heat transfer strength and cost per unit heat transfer. The results show that the heat transfer and heat transfer coefficient increase with increasing inlet wind speed. Under different inlet wind speeds, the heat transfer and heat transfer coefficient of the finned-tube heat exchanger with aluminum tubes are 4%–12% and 7%%–9% lower than those of an identically structured heat exchanger with copper tubes, respectively. The aluminum-aluminum exchanger achieves 67% higher heat transfer than that of the copper-aluminum exchanger at only 8% of the cost. These results are significant for guiding the development and application of finned-tube heat exchangers.

Acclimation of the Grapevine Vitis vinifera L. cv. Assyrtiko to Water Deficit: Coordination of Structural and Functional Leaf Traits and the Dynamic of Calcium Oxalate Crystals

Grapevine leaves contain abundant CaOx crystals located either within the mesophyll in the form of raphides, or in the bundle sheaths as druses. CaOx crystals function as internal carbon pools providing CO2 for a baseline level of photosynthesis, named “alarm photosynthesis”, despite closed stomata; thus, preventing the photoinhibition and the oxidative risk due to carbon starvation under adverse conditions. Structural and functional leaf traits of acclimated grapevine plants (Vitis vinifera L. cv. Assyrtiko) were investigated in response to water availability, in order to evaluate the dynamic functionality of CaOx. Leaf water potential, leaf area, leaf mass per area, stomatal properties, gas exchange parameters and performance index (PI) were decreased in leaves of vines acclimated to water deficit in comparison to the leaves of well-irrigated vines, although the chlorophyll fluorescence parameters showed that the operational efficiency of the photosystem II (PSII) photochemistry (Fv/Fm) did not change, indicating that the photosynthetic apparatus was not subjected to water stress. During the afternoon, more than half of the morning’s existing druses disappeared in the drought-acclimated leaves. Also, the raphides’ area of the drought-acclimated leaves was reduced more than that of the well-watered leaves. The substantial decomposition of druses under water deficit conditions compared to that of the raphides may have important implications for the maintenance of their different though overlapping roles. According to the results, it seems likely that, under water deficit conditions, a mechanism of “alarm photosynthesis” provides an additional tolerance trait in the leaves of Vitis vinifera cv. Assyrtiko; hence, leaf structure relates to function.

Experimental characterization of a spiral heat exchanger for waste water heat recovery from partially filled sewage pipes

This paper focuses on the experimental characterization of horizontal, spiral heat exchangers used for heat recovery from sewage pipes. Such non-intrusive heat exchanger configurations are appealing for this application, but they often exhibit reduced heat exchange performances compared to more compact designs. To compare the performance of this configuration with that of an ideal counter-flow heat exchanger, a representative test setup was constructed. As the sewer pipes are generally not completely filled, tests were conducted using three different fillings (100%, 50%, 33%) and a filling parameter z was introduced in the heat transfer equations. Correction factors to be applied in the Logarithmic Mean Temperature Difference (LMTD) design method for this specific spiral configuration were derived from the test results. It was found that the filling of the sewer pipe has minimal impact on the correction factor, which ranges between 0.78 and 0.83. The average value of 0.81 is recommended for design purposes.

Synthesis of binder-free pelletized Y zeolite for CO2 capture

Y-type zeolites are widely used in the carbon dioxide (CO2) adsorption applications due to their exceptional ion exchange performance and high stability. However, the pelletization of Y powder by adding binders such as kaolin often results in performance drops, which has limited its industrial application. This study employs a zeolite-kaolin blend to produce cylindrical pelletized Y zeolite, in which the kaolin is then transformed to zeolites via hydrothermal crystallization, resulting in binder-free Y pellets. The Design-Expert software and the response surface method (RSM) are employed to optimize the hydrothermal crystallization conditions for binder transformation, with the objective of attaining a maximized capacity for CO2 adsorption. Results demonstrate that optimized synthesis conditions yield cylindrical Y zeolite with a notable CO2 adsorption capacity of 5.52 mmol/g at 298 K and 1 bar, surpassing that of the initial Y powder. The average crushing strength is 110 N per particle (Diameter × Height = 3 mm × 3 mm). The IAST selectivity of CO2/N2 (15/85) is 824 at 298 K and 1 bar. The reaction mechanisms of the binder transformation are also investigated via experiments and DFT simulation. This study presents a simple and reliable method for manufacturing binder free Y zeolite, which is promising for carbon capture applications.

Leader–member exchange (LMX) and work performance: an application of self-determination theory in the work context

ABSTRACT Using self-determination theory (SDT) as a guiding framework, we examined the effects of leader–member exchange (LMX) on performance through psychological need satisfaction and intrinsic motivation. Lagged data was collected from 333 dental hygienists across four time points. We examined three forms of performance: task performance, organizational citizenship behaviour (OCB), and counterproductive work behaviour (CWB). LMX was positively related to all three forms of psychological need satisfaction (competence, relatedness, autonomy), autonomy need satisfaction was positively related to intrinsic motivation, and intrinsic motivation was negatively related to CWB. Overall, there were significant indirect effects from LMX to all forms of performance; however, the mediating mechanisms varied. LMX was indirectly linked to task performance through competence need satisfaction and autonomy need satisfaction, to OCB through competence need satisfaction, and to CWB through the sequential effects of autonomy need satisfaction on intrinsic motivation. Our results highlight the complexity of the LMX-performance relationship and show that SDT can help to explain the relationship, depending on the type of performance being assessed.

Study on hydro-thermal coupling heat transfer performance of flue gas-water heat exchanger

The finned tube heat exchanger is the core component of the flue gas waste heat utilization system. In order to optimize and control the heat transfer efficiency of the heat exchanger in real time under smart heating conditions, we use the entransy dissipation thermal resistance as a kernel index to assess its heat exchange performance, and Trnsys simulation software is employed to figure out the influence of heat exchanger operating parameters (flue gas inlet velocity) and fin structure parameters (fin height, fin pitch) on heat exchanger heat transfer characteristics. The results show that in a reasonable range, increasing the flue gas inlet velocity can decrease the irreversible loss of heat transfer, obviously improving the heat transfer effect. The pitch and height of the fin also have a large impact on the performance of heat transfer. To significantly promote the performance of the heat exchanger, it is useful to reduce the pitch of the fin and increase the fin height within a reasonable range.

Exchange Rate Effects and Performance of Financial Institutions in South Sudan

Exchange Rate Effects and Performance of Financial Institutions in South Sudan

Heat extraction through conductive proppants

The absence of direct contact between the working fluid and the geothermal formation in closed-loop geothermal system (CLGS) limits its application to direct heating. Enhancing the CLGS heat extraction performance could lead to an effective utilization of CLGS for power generation purposes. Optimizing CLGS performance is still an active area of research. In this paper, we propose a fractured closed-loop geothermal system (FCLGS) with a conductive plug installed downhole and a fracture propped with conductive proppants to improve heat exchange performance of CLGS. Using an integrated numerical approach, we first explore the potential to improve the thermal conductivity of common types of proppants by applying metallic coatings. Applying a thick layer of copper coating to Aluminum Nitride proppants yields a thermal conductivity of 44.91 W/(mK), 24 times larger than that of uncoated sand. The proppant/coating with largest thermal conductivity is used for field-scale simulations. Heat extraction performance of FCLGS is evaluated at the field-scale under different parameter combinations. Numerical results show that incorporating a conductive plug into a fractured CLGS improves net power output by 30.60 %. Conductive plug shape and size play an important role in heat extraction in FCGLS. In addition, a circulation velocity of 2 m/s is observed to yield the highest increase in net power output.

Computational fluid dynamics-based design and invitro characterization of a novel pediatric pump-lung.

Although extracorporeal membrane oxygenation (ECMO) has been used to provide temporary support for pediatric patients suffering severe respiratory or cardiac failure since 1970, ECMO systems specifically designed for pediatric patients, particularly for long-term use, remain an unmet clinical need. We sought to develop a new pediatric ECMO system, that is, pediatric pump-lung (PPL), consisting of a unique cylinder oxygenator with an outside-in radial flow path and a centrifugal pump. Computational fluid dynamics was used to analyze the blood fluid field for optimized biocompatible and gas exchange performances in terms of flow characteristics, hemolysis, and gas transfer efficiency. Ovine blood was used for invitro hemolysis and gas transfer testing. Both the computational and experimental data showed that the pressure drop through the PPL's oxygenator is significantly low, even at a flow rate of more than 3.5 L/min. The PPL showed better hemolysis performance than a commercial ECMO circuit consisting of the Quadrox-iD pediatric oxygenator and the Rotaflow pump at a 3.5 L/min flow rate and 250 mm Hg afterload pressure. The oxygen transfer rate of the PPL can reach over 200 mL/min at a flow rate of 3.5 L/min. The PPL has the potential to provide adequate blood pumping and excellent respiratory support with minimal risk of hemolysis for a wide range of pediatric patients.

Examining The Impact Of Interest Rate, Inflation And Balance Of Trade On Saudi Arabia’s Financial Markets Performance

A confirmatory framework, utilizing the positivist standpoint, provides clarifications of the issue at hand. Investigating the impact of the macroeconomic factors on the profits of Saudi Arabia’s stock exchange was developed. Following thorough research, it became clear that a correlative study was required. Secondary data, gathered from to 2006 to 2021, was interpreted through regression analysis for the purpose of the study. As such, a numerical examination was conducted in order to observe the correlation of the macroeconomic variables and changes in Saudi Arabia’s stock market. The findings results indicate that the balance of trade has a consequence on Saudi Arabia’s stock exchange performance. The aim of this study is to improve the level of understanding of the stock market behavior for entrepreneur, stock market decision maker, whereas deterrent measures in contrast to the risk comprised in stock market performance can be taken by the establishments.

Effect of Leader–Member Exchange on Proactive Employee Behavior and Employee Performance: The Moderating Role of Innovative Climate

This study aims to investigate the mechanisms and regulatory processes underlying the relationship between leader–member exchange and employee performance. Social exchange theory and self-determination theory argue that proactive employee behavior has an intermediary effect on the relationship between leader–member exchange and employee performance. In addition, it is predicted that the innovative climate will regulate this indirect effect. Data were collected via questionnaire from 266 people working in organizations operating in various sectors located in Gebze and Istanbul using a survey method. Data analysis was conducted using structural equation modeling (SEM) and PROCESS macro. According to the findings, the hypothesis that leader–member exchange is positively related to employee performance and that proactive employee behavior mediates this relationship is supported. In addition, an innovative climate regulates the positive relationship between leader–member exchange and proactive employee behavior, deepening the theoretical understanding of the consequences of this interaction.

Application of a VOF Multiphase Flow Model for Issues concerning Floating Raft Aquaculture

Floating raft aquaculture has gradually become a mainstream aquaculture model in the waters of Changhai County, Dalian. To quantitatively describe the impact of floating raft aquaculture facilities on the hydrodynamic environment of nearby sea areas, in this study, we took a single floating raft aquaculture structure as the research object and built a numerical prediction model for water flows passing through the floating raft aquaculture structure using a six-degree-of-freedom VOF (volume of fluid) multiphase flow simulation method based on an overset moving mesh system. Then, we verified the numerical model by utilizing oblique hydraulic jumps and water flows passing through a submerged bar. As shown by the findings, the simulated values are in good agreement with the theoretical solutions and measured values, indicating that the model features high precision and great stability. The impact of the raft area on the hydrodynamic force was introduced into the source term of an equation for consideration. In order to further determine the hindering effect of the raft body on the water body, transport equations and the tracer method were used to simulate the impact of floating raft aquaculture facilities on the water exchange performance of nearby sea areas. This study shows that the VOF multiphase flow model can be easily and accurately applied to studies on floating raft aquaculture, which can greatly reduce the limitations of experiments that utilize pure hydraulic models, wherein the impacts of floating raft aquaculture facilities on hydrodynamic force are generally considered simply based on observations, water roughness or the secondary drag force coefficient, thereby effectively improving the scientific understanding of the physical mechanism involved in floating raft aquaculture.