Friction factor evaluation of compressible microflows using 1D Fanno flow-based numerical model

A numerical model based on the conventional Fanno flow theory for the friction factor evaluation of the gas flows inside microchannels has recently been developed by Cavazzuti et al. [1]. The current work aims to compare this numerical model with experimental results of microchannels. Pressure drop experiments are performed for a circular cross sectional microtube and a rectangular microchannel with Nitrogen gas as working fluid. The hydraulic diameters of microtube and microchannel are 100 \u3bcm and 69.4 \u3bcm respectively. Rectangular microchannel with an aspect ratio (height to width) of 0.036 is chosen for the comparison. This allows to treat the rectangular microchannel as parallel plate in the numerical Fanno model. During experiments stagnation pressure at the inlet is increased such that maximum Reynolds number is 3000 in the case of microchannel and 7600 for microtube. Results show that for the evaluation of average friction factor in both considered geometries, there exists a good match between Fanno-based 1D numerical model and experimental results in the laminar regime whereas comparison worsens as the flow approaches choking. Limitations as well as the potential reasons for the discrepancies between the developed model and experiments will be discussed

A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger

In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of 200 m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of 100 μm. Microchannels have a rectangular cross section of 200 μm x 200 μm with a wall thickness of 100 μm in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy–Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations

Experiments on measurement of heat transfer rate of gas flow through microchannel with constant wall temperature

Experimental results for the measurement of heat transfer rates in microchannel gas flow are crucial for gas to gas micro heat exchangers. A critical overview of the main factors that play an important role in the determination of heat transfer rate is presented. The experimental and numerical data obtained from authors' previous studies are used in order to highlight the characteristics of convective heat transfer of gas through microchannels with constant wall temperature. It is suggested to obtain heat transfer rates by determining the difference between the gas enthalpy at the inlet and outlet by measuring local temperature and pressure. The heat transfer rates obtained in the present study were compared with those determined by the difference in total temperatures and incompressible flow Nusselt number

Methyl 2-(but-3-en­yl)-4-hy­droxy-1,1-dioxo-2H-1λ6,2-benzothia­zine-3-carboxyl­ate

In the title compound, C14H15NO5S, the thia­zine ring adopts a sofa conformation and an intra­molecular O—H⋯O hydrogen bond forms an S(6) ring. In the crystal, molecules are linked viaC—H⋯O inter­actions

Theoretical and experimental investigation of thiourea derivatives: synthesis, crystal structure, in-silico and in-vitro biological evaluation

ABSTRACT. In this study, five different thiourea derivatives were synthesized from aryl amines according to the reported method. 1-Benzoyl-3-(4-methoxyphenyl)thiourea (2) was confirmed with single crystal XRD analysis while 1-benzoyl-3-phenylthiourea (1), 1-benzoyl-3-(4-hydroxyphenyl)thiourea (3), 1-benzoyl-3-(2-nitrophenyl) thiourea (4) and 1-benzoyl-3-p-tolylthiourea (5) were elucidated with FTIR and NMR techniques. The geometry optimization of the targeted molecules was accomplished with density functional theory applying B3LYP function. The experimental (XRD) and calculated (DFT) bond angles and bond lengths were compared. The frontier molecular orbitals and molecular electrostatic potential were computed to determine the charge density distribution and possible sites for electrophilic and nucleophilic reactions of the crystalline compound. The synthesized compounds were evaluated as an anti-radical scavenger and enzyme (esterases and protease) inhibitor using in-vitro models. The results confirmed that the synthesized molecules have good anti-oxidant property while a moderate enzyme inhibiting activity. Docking study was conducted with acetylcholine and butyrylcholine esterase which suggested that molecules under study have a potential to inhibit these esterases and protease enzymes. On the basis of in-vitro studies, it is concluded that compound 2 is most active against all tested assays.                     KEY WORDS: Thiourea, 2,2-Diphenyl-1-picrylhydrazyl, Enzyme inhibition, Density functional theory, Docking studies   Bull. Chem. Soc. Ethiop. 2021, 35(3), 587-600. DOI: https://dx.doi.org/10.4314/bcse.v35i3.1

Numerical and Experimental Study of Microchannel Performance on Flow Maldistribution

Miniaturized heat exchangers are well known for their superior heat transfer capabilities in comparison to macro-scale devices. While in standard microchannel systems the improved performance is provided by miniaturized distances and very small hydraulic diameters, another approach can also be followed, namely, the generation of local turbulences. Localized turbulence enhances the heat exchanger performance in any channel or tube, but also includes an increased pressure loss. Shifting the critical Reynolds number to a lower value by introducing perturbators controls pressure losses and improves thermal efficiency to a considerable extent. The objective of this paper is to investigate in detail collector performance based on reduced-order modelling and validate the numerical model based on experimental observations of flow maldistribution and pressure losses. Two different types of perturbators, Wire-net and S-shape, were analyzed. For the former, a metallic wire mesh was inserted in the flow passages (hot and cold gas flow) to ensure stiffness and enhance microchannel efficiency. The wire-net perturbators were replaced using an S-shaped perturbator model for a comparative study in the second case mentioned above. An optimum mass flow rate could be found when the thermal efficiency reaches a maximum. Investigation of collectors with different microchannel configurations (s-shaped, wire-net and plane channels) showed that mass flow rate deviation decreases with an increase in microchannel resistance. The recirculation zones in the cylindrical collectors also changed the maldistribution pattern. From experiments, it could be observed that microchannels with S-shaped perturbators shifted the onset of turbulent transition to lower Reynolds number values. Experimental studies on pressure losses showed that the pressure losses obtained from numerical studies were in good agreement with the experiments (<4%)

Anomaly Detection in Time Series: Current Focus and Future Challenges

Anomaly detection in time series has become an increasingly vital task, with applications such as fraud detection and intrusion monitoring. Tackling this problem requires an array of approaches, including statistical analysis, machine learning, and deep learning. Various techniques have been proposed to cater to the complexity of this problem. However, there are still numerous challenges in the field concerning how best to process high-dimensional and complex data streams in real time. This chapter offers insight into the cutting-edge models for anomaly detection in time series. Several of the models are discussed and their advantages and disadvantages are explored. We also look at new areas of research that are being explored by researchers today as their current focuses and how those new models or techniques are being implemented in them as they try to solve unique problems posed by complex data, high-volume data streams, and a need for real-time processing. These research areas will provide concrete examples of the applications of discussed models. Lastly, we identify some of the current issues and suggest future directions for research concerning anomaly detection systems. We aim to provide readers with a comprehensive picture of what is already out there so they can better understand the space – preparing them for further development within this growing field

4-(4-Methoxy­phen­yl)piperazin-1-ium chloride

In the title compound, C11H17N2O+·Cl−, the dihedral angle between the benzene ring and the basal plane of piperazine ring is 39.20 (8)°. In the crystal, intermolecular N—H⋯Cl hydrogen bonds occur. There is also a C—H⋯π inter­action between the benzene rings

The relation of ABO blood group to the severity of coronavirus disease: A cross-sectional study from a tertiary care hospital in Karachi

Background: Blood groups are considered to have an impact on the occurrence and severity of coronavirus disease. While among Chinese and Caucasian, blood group O individuals were less and group A were more likely to have severe disease and mortality, data on South Asians aren’t available. Objective: This study aimed to find out the association of disease severity with blood group among coronavirus disease 2019 (COVID-19) patients.Materials and methodology: Data were collected on a predesigned questionnaire containing details of patient demographics, medical comorbidities, clinical presentation, and laboratory parameters. Multiple logistic regression was used to determine the association of the blood group with the severity of coronavirus disease.Result: Among the study participants, blood group B has the highest distribution (39.8%), followed by O (30.0), A (21.9%), and AB (8.1%). About three-fourths (69.9%) had mild to moderate disease while 30.0% had severe disease. Age, gender, hypertension, diabetes mellitus, and hemoglobin level were all associated with disease severity among COVID-19 patients in univariate analysis on P-value for selection (Conclusion: Blood groups don’t have any role in forecasting the severity of coronavirus disease. However, the male gender and diabetics are prone to have severe disease

Revisiting the Role of Tourism and Globalization in Environmental Degradation in China: Fresh Insights from the Quantile ARDL Approach

Ascertaining sustainable development is a major issue across the globe, and the economic growth pattern achieved is a predominant reason behind this. The globalization-led economic growth achieved by the emerging economies might not be ecologically sustainable, as globalization might not have been utilized as a policy tool. Moreover, a sound policy calls for considering the entire data spectrum for the analysis, which is largely ignored in the literature. This research contributes to the literature by proffering a policy framework for the emerging economies by analyzing the impact of globalization and tourism on environmental degradation, by considering the Chinese context as a sample. Following the quantile autoregressive distributed lag model, the impact of economic growth, globalization, and tourism on greenhouse gas emissions, carbon dioxide emissions, and the ecological footprint in China over 1978Q1-2017Q4 are analyzed. The results demonstrate that economic growth stimulates environmental degradation, while the presence of Environmental Kuznets Curve is also validated. Moreover, tourism has been found to exert positive environmental externalities, while globalization exerts negative environmental externalities. Based on the outcomes of the research, a comprehensive policy framework has been suggested, following which the Chinese economy might be able to attain the objectives of Sustainable Development Goals 7, 8, and 13