Search Results (82)

Recent advancements in rice breeding have significantly increased production in China. However, high-yielding varieties require strong airflow for effective cleaning. Longitudinal-flow rice combine harvesters equipped with a centrifugal fan with four blades are widely used in China; however, these fans exhibit fluctuating cleaning performance and airflow maldistribution. To address these limitations, this study developed an innovative multi-blade cleaning fan design by incorporating the blade clocking effect, a concept not previously applied in centrifugal fans. To support the design process, the required airflow rates and reduction in static pressure were first analyzed. Based on these findings and fundamental fan design theory, three fan models were designed with blade clocking angles of 0°, 5.5°, and 10.5°, respectively. Three fan models were evaluated through computational fluid dynamics (CFD) simulations using a design of experiments approach based on Box–Behnken design response surface methodology to identify the optimal fan. The fan features a 10.5° clocking angle, meeting the airflow requirements for effective cleaning. In the test bench measurements, the setup with guide plate angles No. 1 and No. 2 at 32° and a fan speed of 1200 rpm was identified as optimal. The newly designed multi-blade cleaning fan overcomes the limitations of conventional four-blade designs, significantly enhancing airflow uniformity. Full article

The distribution of the health workforce affects the availability of health service delivery to the public. In practice, the demographic and geographic maldistribution of the health workforce is a long-standing national crisis. In this study, we present an approach based on Functional Principal Component Analysis (FPCA) of data to identify patterns in the availability of health workers across different regions of Kazakhstan in order to forecast their needs up to 2033. FPCA was applied to the data to reduce dimensionality and capture common patterns across regions. To evaluate the forecasting performance of the model, we employed rolling origin cross-validation with an expanding window. The resulting scores were forecasted one year ahead using Autoregressive Integrated Moving Average (ARIMA) and Long Short-Term Memory (LSTM) methods. LSTM showed higher accuracy compared to ARIMA. The use of the FPCA method allowed us to identify national and regional trends in the dynamics of the number of doctors. We identified regions with different growth rates, highlighting where the most and least intensive growth is taking place. Based on the FPSA, we have predicted the need for doctors in each region in the period up to 2033. Our results show that the FPCA can serve as a significant tool for analyzing the situation relating to human resources in healthcare and be used for an approximate assessment of future needs for medical personnel. Full article

While extensive research has focused on improving the efficiency and performance of heat exchangers (HXs), identifying the underlying causes of performance degradation remains equally important. Flow and temperature non-uniformities are among the most critical factors affecting performance, often reducing thermo-hydraulic efficiency by approximately 5–10%. These non-uniformities commonly manifest as thermal inconsistencies, airflow maldistribution, and uneven refrigerant distribution. Researchers have observed a notable performance degradation—up to 27%—due to flow maldistribution. Therefore, a clear understanding of their causes and effects is essential for developing effective mitigation strategies to enhance system performance. Despite the notable progress in this area, few studies have systematically classified the dominant non-uniformities associated with specific HX types. This article presents a two-decade review of the causes, impacts, and mitigation approaches related to non-uniformities across different HX configurations. The primary objective is to identify the most critical form of non-uniformity affecting performance in each category. This review specifically examines plate heat exchangers (PHXs), finned and tube heat exchangers (FTHXs), microchannel heat exchangers (MCHXs), and printed circuit heat exchangers (PCHXs). It also discusses mathematical models designed to account for non-uniformities in HXs. This article concludes by identifying key research gaps and outlining future directions to support the development of more reliable and energy-efficient HXs. Full article

Vascular steal refers to the diversion of blood flow between collateral vessels that share a common inflow restricted by arterial stenosis. Blood is diverted from the high-pressure to the low-pressure, low-resistance system. Vascular steal is associated with anatomical bypass or vasodilation in the collateral network and is called “the arterial steal”. However, we have demonstrated that in the presence of an outflow gradient (e.g., intra-extracranial), blood is shunted to a lower pressure system, a phenomenon we term “venous steal”. Using Thevenin’s equivalent, we generalized the concept of venous steal to apply it to any region of the vascular system with increased outflow pressure. Both arterial steal, caused by increased collateral network conductivity, and venous steal, resulting from lower collateral outflow pressure, reduce compartment perfusion. This occurs indirectly by increasing flow and the pressure gradient across the arterial stenosis, lowering the segmental compartment perfusion pressure—the difference between post-stenotic (inflow) and compartmental (outflow) pressures. Venous steal diverts blood flow from compartments with elevated pressure, such as intracranial, subendocardial, the ischemic core, and regions of focal edema due to inflammation, trauma, or external compression. In shock and low-flow states, it contributes to regional blood flow maldistribution. Treatment of venous steal addresses inflow stenosis, increased compartmental pressure and systemic loading conditions (arterial and venous pressure) to reverse venous steal malperfusion in the ischemic regions. Full article

Volume kinetics is a pharmacokinetic method for analysis of the distribution and elimination of infusion fluids. The approach has primarily been used to improve the planning of fluid therapy during surgery but is also useful for answering physiological questions. The kinetics is based on 15–35 serial measurements of the blood hemoglobin concentration during and after the fluid is administered intravenously. Crystalloid fluid, such as isotonic saline and Ringer’s lactate, distributes between three compartments that are filled in succession depending on how much fluid is administered. The equilibration of fluid between these three compartments is governed by five rate constants. The compartments are the plasma (V_c), and a fast-exchange (V_t1) and a slow-exchange interstitial compartment (V_t2). The last compartment operates like an overflow reservoir and, if filled, markedly, prolongs the half-life of the fluid. By contrast, the volume of a colloid fluid distributes in a single compartment (V_c) from where the expansion is reduced by capillary leakage and urinary excretion. This review gives 15 examples of physiological or medical questions where volume kinetics has provided answers. These include why urine flow is low during general anesthesia, the inhibitory effects of anesthetics on lymphatic pumping, the influence of dopamine and phenylephrine on urine output, fluid maldistribution in pre-eclampsia, plasma volume oscillations, and issues related to the endothelial glycocalyx layer. Full article

Poorly designed devices can cause flow maldistribution, leading to subpar performance during macromolecule separation. Analyzing the fluid flow in intricate membrane channel structures is challenging. In this study, computational fluid dynamics (CFD) was employed to investigate the effects of the channel tortuosity, size, and connectivity on flow distribution and chromatography performance. Sodium chloride (NaCl) and bovine serum albumin (BSA) were used as tracers. The results showed that the peaks from the NaCl and BSA were sharper as the tortuosity and size heterogeneity decreased to 0, revealing that both the tortuosity and size heterogeneity are critical factors that affect the flow distribution uniformity and thereby the membrane performance during biomacromolecule separation. These findings underscore the importance of optimizing the channel tortuosity and size to enhance membrane performance, offering practical insights for the design of next-generation purification systems. These insights pave the way for optimizing membrane design in future biopharmaceutical applications. Full article

This study proposes a vertically stacked thermoelectric generator (TEG) design to enhance output power per unit volume. While the proposed TEG achieved improved conversion efficiency, the high inertia of the exhaust gas leads to significant flow maldistribution across the channels, causing uneven thermal conditions on the TEM surfaces and reducing overall efficiency. To enhance waste heat recovery by improving flow uniformity in the exhaust gas channels, a perforated plate with porosity ranging from 0.15 to 0.75 was inserted. A multi-physics numerical model was developed to simulate the thermoelectric energy conversion phenomena, enabling for the accurate evaluation of both module- and system-wise performance. The insertion of the perforated plate with 0.45 porosity provided the most uniform flow distribution with only a 5% flow rate difference between the exhaust gas channels. This resulted in a system-level output power of 167.1 W, which is ~7% higher than the case without the perforated plate, along with electrical efficiency of 91.1% and conversion efficiency of 3.41%. Moreover, enhanced flow uniformity led to an improved volumetric power density of 20.8 kW/m³. When accounting for pumping losses, the perforated plate with 0.6 porosity maximized net output power, demonstrating how optimized flow distribution significantly enhances energy harvesting performance. Full article

There are calls for the democratisation of higher education in line with the principles of social justice. Collaboration with students offers the potential for creating a more inclusive higher education environment, and open textbook development initiatives can be a vehicle for change. This paper focuses on the experiences of students as co-creators in open textbook initiatives at the University of Cape Town, South Africa. Drawing on interviews with 11 open textbook collaborators, this paper utilises Nancy Fraser’s social justice framework to explore students’ perspectives on injustices, challenges of collaboration and co-creation, and power dynamics in student–staff partnerships. The study shows that students experience and navigate various injustices in their classroom contexts related to economic maldistribution, cultural misrecognition and political misrepresentation. It reveals a complex interrelationship between student voice, power dynamics in the classroom, and the power of student–staff partnerships to build confidence and flatten hierarchies in open textbook co-creation. The student views presented here provide powerful evidence of a range of benefits they experience when the traditional hierarchies between student and lecturer are levelled through collaborative open textbook development processes. Results indicate that co-creation activities enabled them to have a voice through the power of publication and own their academic journeys. Full article

Urea-based selective catalytic reduction (SCR) is highly efficient for NOx abatement within a diesel aftertreatment system. However, abnormally high NOx emissions in the aftertreatment system tailpipe during WHSC (World Harmonized Steady-State Cycle) evaluation have been observed due to insufficient urea decomposition or mixing, which cannot be predicted by the current uniform 1D (one-dimensional) modelling approach with different urea dosing ratios. As a result, a multi-channel model has been developed to investigate the effect of urea maldistribution on aftertreatment system performance, where the uniformity index (UI) is used as a characteristic parameter to describe urea mixing efficiency. It was found that NOx emissions at the tailpipe can be successfully described with the multi-channel model even with a relatively high UI (UI = 0.95). Additionally, an improved segment UI factor as a function of mass flow rate has also been applied for maldistribution description, wherein better correlation with the measured NOx emission can be obtained. Full article

In this study, a numerical model of a modified air-drying process of apple slices that considers the conjugate heat and mass transfer in the drying chamber is developed. Inside the apple slice sample, the continuum model is incorporated to describe the non-isothermal two-phase transport. The intra- and extra-sample heat, mass, and momentum transfer are coupled to simulate the transportation phenomena inside the drying chamber using the finite volume method implemented in computational fluid dynamic software (COMSOL Multiphysics 6.0). In this manner, temperature, velocity, moisture content of the drying agent inside the chamber, sample temperature, and moisture content distributions can be predicted. The validity of the proposed model is confirmed by a good agreement between the numerical and experimental data in terms of the overall evaporation rate and temperature. The simulation results indicate that the maldistribution of the convective heat and mass transfer resistance on the sample surface is significant. This can be explained by the nonuniform velocity distribution inside the drying chamber. Additionally, both experimental and numerical observations show that the drying process can be divided into two periods: the quasi-constant drying rate and falling drying rate periods. The impact of dryer operational conditions on the drying process is numerically investigated. Full article

Community genetic services were introduced in South Africa almost seven decades ago, with medical geneticists and genetic counsellors being formally recognized for the past 30 years. Initial training platforms were established at academic centres countrywide, and posts for relevant healthcare professionals, including medical geneticists and genetic counsellors were created in the public sector. Despite these early advances, the number of these specialists required to address the rising burden of congenital disorders in the country remains far below required targets established by the National Department of Health. The aim of this study was to analyse the retrospective, current and projected number of medical geneticists and genetic counsellors in South Africa. The results indicate the number of practicing medical geneticists (n = 13) and genetic counsellors (n = 28) are currently at 10% and 5% of capacity targets, respectively. There is unequal distribution of these specialists between the public and private healthcare sectors, and geographical maldistribution. An alarming trend of emigration is particularly prevalent among newly qualified genetic counsellors. With the proportion of congenital disorders expected to continue to rise in coming years, together with the increasing proportion of ageing South Africans, it is imperative that health workforce planning addresses the ever-widening gap between the supply, demand and unmet need for these crucial specialists in South Africa. Full article

Over the past two decades, double-layered microchannel heat sinks (DL-MCHs) have become increasingly popular as they provide effective performance for electronic cooling, particularly in the counterflow configuration. The cross-flow configuration, which requires much simpler headers, has seldom been considered in the scientific literature, probably due to the possible formation of a hotspot near the outlet port. The aim of this study is to show that cross-flow DL-MCHs can provide performance levels that are comparable to those attained by counterflow DL-MCHs by exploiting the nonuniform flow distribution produced by properly designed headers. Numerical simulations are performed using in-house finite element procedures to solve the parabolized Navier–Stokes equations in the microchannels and the energy equation in the entire computational domain. The analysis is carried out both for ideal linear microchannel velocity distributions and for the realistic velocity distributions induced by headers with or without baffles, as proposed by the authors in previous papers. The optimal degree of velocity nonuniformity in the microchannels yielding the best thermal performance was found to depend on the flow rate. For instance, in the case of optimal linear variations of the microchannel velocity distribution, the thermal resistance was reduced by 11.8%, 7.1%, and 4.4% compared to the case with uniform inlet velocities, and it was only 3.4%, 1.8%, and 0.3% higher than that of the counterflow configuration for average microchannel velocities equal to 0.5, 1, and 2 m/s, respectively. The main conclusion is that the cross-flow configuration, with its simple headers and piping, can achieve thermal resistance and temperature uniformity on the heated surface that are very similar to that of the counter-flow configuration through proper header design that ensures a suitable microchannel velocity distribution. Full article

The so-called internally channeled tube (ICT) is an innovative heat exchanger design proposed in our recent publications based on a channels-in-tube principle. A general, three-dimensional numerical model was suggested to describe fluid dynamics and heat transfer in the ICT. This model has already been validated for turbulent flow. The current paper presents an experimental investigation of the ICT and the model validation under laminar flow conditions. The experimental set-up and measurement procedure are given in detail and the maldistribution issue is addressed. The deviation between simulated and measured values is below 11% for the pressure drop and below 8% for the wall and bulk temperatures. Furthermore, the ICT performance was evaluated using performance evaluation criterion (PEC) including both heat transfer rate and pressure drop. Enhanced heat transfer in the ICT surpasses the associated pressure drop increase, yielding a PEC greater than one. Full article

In the pursuit of enhancing thermal management for miniaturized electronic devices, our study delves into the impact of entry effects on Ledinegg instability and flow maldistribution within parallel microchannels. Utilizing a coupled model that incorporates phase change and pressure drop dynamics in boiling flow, we examine microchannels characterized by a 50 length-to-diameter ratio and a 200 μm hydraulic diameter. Our findings unveil a significant influence of entry effects, which narrow the total flow excursion interval, thereby bolstering system stability. Specifically, as the heat flux escalates from 5 W/cm² to 120 W/cm², the entry effects increasingly mitigate flow instability and maldistribution in parallel channels, diminishing the total flow rate range susceptible to flow instability by 4.73% and 47.52%, while narrowing the total flow rate range corresponding to uneven flow distribution by 4.70% and 46.75%, respectively. Furthermore, entry effects expand the inlet subcooling range necessary for stabilizing the parallel channel system by 38.89% and 1000%. This research not only underscores the importance of considering entry effects in microchannel design but also opens avenues for further exploration into enhancing thermal management solutions. Full article

This study examined bubbling fluidized beds as an alternative to fixed-bed dry scrubbers on ships for reducing pollutants from marine fuels. It focused on overcoming the challenges of gas maldistribution/slug formation, especially under rough sea conditions. This research departed from traditional methods by introducing mobile internal elements into the bed emulsion phase and investigating their effectiveness in various settings, such as vertical, inclined, and rolling beds. A specialized hexapod-driven bubbling fluidized bed was developed to mimic marine operating conditions and to study the behavior of shipboard fluidized beds. Techniques such as digital image analysis (DIA) and particle image velocimetry (PIV) were used to observe bubble dynamics and granular phases, measuring local void fractions and particle velocities. A key finding is the effectiveness of moving internals in preventing bubble coalescence, which is critical for avoiding wall slugs, at different inclinations. Three types of packing were used as mobile internals: Super Raschig, Pall, and square rings. Super Raschig rings, which are characterized by high porosity, were the most efficient in reducing bubble coalescence, making them a preferred choice for offshore fluidized bed applications. This research contributes to the advancement of fluidized bed technology in marine applications and provides insight for future improvements. Full article