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Turbulent fluid flow and heat transfer characteristics are analyzed numerically for fluids flowing through a rotating periodical two‐pass square channel. The smooth walls of this two‐pass channel are subject to a constant heat flux. A two‐equation k‐ε turbulence model with modified terms for Coriolis and rotational buoyancy is employed to resolve this elliptic problem. The duct through‐flow rate and rotating speed are fixed constantly; while the wall heat flux into the fluid is varied to examine the rotating buoyancy effect on the heat transfer and fluid flow characteristics. It is disclosed that the changes in local heat transfer due to the rotational buoyancy in the radially outward flow are more significant than those in the radially inward flow. However, the channel averaged heat transfer is altered slightly due to the rotational buoyancy in the both ducts. Whenever the buoyancy effects are sufficiently strong, the flow reversal appears over the leading face of the radially outward‐flow channel, and the radial distance for initiation of flow separation decreases with increasing the buoyancy parameter. A comparison of the present numerical results with the available experimental data by taking buoyancy into consideration is also presented.

The purpose of this study is to study the simultaneous effect of embedded reverting microchannels on the cooling performance and mechanical strength of the electronic pieces.

In this study, a new configuration of the microchannel heat sink was proposed based on the constructal theory to examine mechanical and thermal aspects. Initially, the thermal-mechanical behavior in the radial arrangement was analyzed, and then, by designing the first reverting channel, maximum temperature and maximum stress on the disk were decreased. After that, by creating second reverting channels, it has been shown that the piece is improved in terms of heat and mechanical strength.

Having placed the second reverting channel on the optimum location, the effect of creating the third reverting channel has been investigated. The study has shown that there is a close relationship between the maximum temperature and maximum stress in the disk as maximum temperature and maximum stress decrease in pieces with more uniform distribution channels.

The proposed structure has decreased the maximum temperature and maximum thermal stresses close to 35 and 50%, respectively, and also improved the mechanical strength, with and without thermal stresses, about 40 and 24%, respectively.

The purpose of this paper is to develop a leakage model of metallic static seals, which can be used to accurately predict the leakage rate and study the corresponding seal characteristics. The metallic static seal is effectively applied to severe rugged environments where conventional seals cannot meet the needs. More research efforts for deepening the understanding of its seal characteristics are important for its effective and safe applications, of which the study about its leak is one key component.

In the microscopic observations of the turning surface that is general in the processing of flange surfaces, it is found that the spiral morphology is dominant, which had been also obtained by other researches. There are two potential leakage paths for the flange surface of spiral morphology, one is the radial direction perpendicular to the spiral ridges and the other is the circumferential direction along the spiral groove. Based on the microgeometry characteristics of spiral morphology, the micromorphology of turning flange surface is simplified for the calculation of leakage rate, and the simplified methods of the radial and circumferential leakage paths are presented separately. The topography of flange surface studied in this paper is actually measured, and the Abbott bearing surface curve is adopted to represent the micro-profiles parameters. The radial and circumferential leakage models are further developed based on the assumption of laminar flow of the viscous compressible gas.

The experiments used to verify the leakage models were carried out, and the experimental values are well agreed with the calculated values. As the contact pressure increases, the change rules of both radial and circumferential leakage rates are obtained and the obvious transition from radial leak to circumferential leak can be found. Using the proposed leakage models, the effects of the key micro-profiles parameters on the leakage rates are studied, and some specific conclusions are given simultaneously, which are favorable for the theoretical study and practical application of the metallic static seal.

By the interpretations of the micromorphology characteristics of turning flange surface, the leakage mechanism of the metallic static seal is further made clear. The proposed leakage model reveals the relationships between the key micro-profiles parameters and some sealing performances about the leakage and can predict the leakage rates of the metallic static seal used in various working conditions.

For the metallic static seal, the simplification of the radial leakage path and the radial leakage model are put forward for the first time, so the total leakage model can be systematically reported based on the micromorphology characteristics of turning flange surface. The effects of the key micro-profiles parameters on the seal behaviors including of the leak rate, critical contact pressure and transition from radial leak to circumferential leak etc are also clarified firstly.

A numerical study is performed to investigate flow instability phenomena in a square channel with steady, laminar throughflow. The channel rotates around an axis perpendicular to the channel longitudinal axis. The flow field extends from the channel entrance to a distance of 120 to 600Dh. The range of Reynolds number is Re = 300−2000. The inlet flow velocity is assumed uniform. Surface vorticity intensity is introduced to indicate the variation of vortices. It is revealed that at intermediate Reynolds numbers (680 > Re > 300), the flow is characterized by three vortex patterns: at slow rotation there is one vortex pair; at intermediate rotation a secondary vortex, in addition to the original vortex, emerges near the trailing wall and then breaks down downstream; and at rapid rotation the secondary vortex does not exist with the flow being restabilized to form a single‐pair vortex pattern. At low Reynolds numbers (Re ≤ 300), the flow exhibits a single‐pair vortex pattern, while at high Reynolds numbers (Re ≥ 680), the flow experiences the emergence and breakdown of a secondary vortex, but no restabilization is found with an increase in the rotational speed. It is also disclosed that the variation of the vortices is related to the distance from the inlet.

The purpose of this paper is to investigate the design dimensions in pressure or metering region of a single‐screw extruder by determining viscous power loss. The paper is the second part of a series.

Viscous power loss formed in the extruder screw channel and the radial clearance is determined and evaluated in terms of non‐dimensional parameters in order to obtain a theoretical model.

The theoretical model developed is capable of estimating the viscous power loss in the extruder metering region. With the model developed, extruder geometry and viscous power loss under different operating conditions can be predicted.

This paper offers a quick and easy opportunity to examine the viscous power loss in the extruder.

The purpose of this paper is to investigate the hydrodynamic performance of a single‐screw extruder with special reference to metering region.

The hydrodynamic analysis of a single screw extruder is carried out by dimensional and non‐dimensional parameters defining the polymer flow behaviour. The flow types formed in the extruder channel are defined and the relationship between the flow with the extruder geometry is examined.

The theoretical model developed is capable of estimating the hydrodynamic behaviour of extruder metering region. With the model developed, extruder geometry and polymer flow rate under different operating conditions can be predicted.

This paper offers a quick and easy opportunity to examine the hydrodynamic behaviour of extruder metering region. With the theoretical model developed, the behaviour of the flow in extruder can be modelled and estimated.

The purpose of this paper is to investigate the impact of mechanical vibration on the heat transfer and pressure drop characteristics of semicircular channel printed circuit heat exchangers (PCHEs), while also establishing correlations between vibration parameters and thermal performance.

By combining experimental and numerical simulation methods, the heat transfer coefficient and pressure drop characteristics of supercritical carbon dioxide (S-CO₂) in a semicircular channel with a diameter of 2 mm under vibration conditions were studied. Reinforce the research by conducting computational fluid dynamics studies using ANSYS Fluent 22.0, the experimental results were compared with the numerical simulation results to verify the accuracy of the numerical method.

The use of vibration has the potential to attenuate the degradation of wall heat transfer caused by buoyancy-induced PCHEs on the upward-facing surface. The heat transfer enhancement (HTE) was maximized by an increase of 18.2%, while the pressure drop enhancement (PDE) was elevated by over 25-fold. The capacity to enhance the heat exchange between S-CO₂ and channel walls through increasing vibration intensity is limited, indicating maximum effectiveness in improving thermal performance.

Conducting heat transfer experiments on PCHEs with mechanical vibration enhancement and verifying the accuracy of the vibration numerical model. The relation based on the dimensionless factor is derived. To provide theoretical support for using vibration to enhance the heat transfer capability of PCHEs.

Improved indigenous chicken is considered a sustainable agricultural practice with social, economic and environmental indicators. Therefore, the analysis of the choice of market channels is of considerable importance to farmers with reference to improved livelihoods and poverty alleviation in developing countries. The purpose of this study is to investigate the factors that influence market channel choices among improved indigenous chicken farmers in Baringo County and to rank the determinants according to their level of importance in influencing farmer's choice of marketing channels.

A multistage sampling technique was employed to collect data from 209 households for the study conducted between April and July 2019, out of which, 198 useful responses were obtained. Multinomial logit regression and neural network models were used to analyze the factors influencing market channel choice based on socioeconomic, demographic and farm characteristics.

It was established that group membership, education, market distance, transport costs, farm size, cost of information and bargain costs were statistically significant in the choice of market channels (wholesaler, brokers, processors and supermarkets). With the direct consumer as the base market choice. The cost of transport had the highest normalized importance in the prediction of a farmer's selection of market channels for both radial basis function (RBF) and multilayer perceptron (MLP) neural networks. However, flock attributes and age of household head had the least normalized importance in MLP and RBF, respectively.

Due to the insufficiency of resources and time, this study only focused on a small part of the country (Baringo County). However, improved indigenous chicken farming is widely practiced in Kenya. Further studies can be carried out in other counties to validate the results of this study.

The outcome can be used in policy implementation involving improved indigenous chicken production in Kenya.

This study suggests the methods aimed at enhancing poultry sector in other counties in Kenya as well as other developing countries.

Subcooled flow boiling phenomenon is characterized by coolant phase change in the vicinity of the heated wall. Although coolant phase change from liquid to vapour phase significantly enhances the heat transfer coefficient due to latent heat of vaporization, eventually the formed vapor bubbles may coalesce and deteriorate the heat transfer from the heated wall to the liquid phase. Due to the poor heat transfer characteristics of the vapour phase, the heat transfer rate drastically reduces when it reaches a specific value of wall heat flux. Such a threshold value is identified as critical heat flux (CHF), and the phenomenon is known as departure from nucleate boiling (DNB). An accurate prediction of CHF and its location is critical to the safe operation of nuclear reactors. Therefore, the present study aims at the prediction of DNB type CHF in a hexagonal sub-assembly.

Computational fluid dynamics (CFD) simulations are performed to predict DNB in a hexagonal sub-assembly. The methodology uses an Eulerian–Eulerian multiphase flow (EEMF) model in conjunction with multiple size group (MuSiG) model. The breakup and coalescence of vapour bubbles are accounted using a population balance approach.

Bubble departure diameter parameters in EEMF framework are recalibrated to simulate the near atmospheric pressure conditions. The predictions from the modified correlation for bubble departure diameter are found to be in good agreement against the experimental data. The simulations are further extended to investigate the influence of blockage (b) on DNB type CHF at low operating pressure conditions. Larger size vapour bubbles are observed to move away from the corner sub-channel region due to the presence of blockage. Corner sub-channels were found to be more prone to experience DNB type CHF compared to the interior and edge sub-channels.

An accurate prediction of CHF and its location is critical to the safe operation of nuclear reactors. Moreover, a wide spectrum of heat transfer equipment of engineering interest will be benefited by an accurate prediction of wall characteristics using breakup and coalescence-based models as described in the present study.

Simulations are performed to predict DNB type CHF. The EEMF and wall heat flux partition model framework coupled with the MuSiG model is novel, and a detailed variation of the coolant velocity, temperature and vapour volume fraction in a hexagonal sub-assembly was obtained. The present CFD model framework was observed to predict the onset of vapour volume fraction and DNB type CHF. Simulations are further extended to predict CHF in a hexagonal sub-assembly under the influence of blockage. For all the values of blockage, the vapour volume fraction is found to be higher in the corner region, and thus the corner sub-channel experiences CHF. Although DNB type CHF is observed in corner sub-channel, it is noticed that the presence of blockage in the interior sub-channel promotes the coolant mixing and results in higher values of CHF in the corner sub-channel.

The purpose of this paper is to adopt rapid prototyping (RP) technology to fabricate self‐hardening calcium phosphate composite (CPC) scaffolds with a controlled internal channel network to facilitate nutrient supplying and cell growth using RP technique and investigate their in vitro performance.

Porous scaffolds should possess branched channels to ensure uniform cell feeding and even flow of culture medium to promote uniform cell attachment and growth. A new three dimensional (3D) flow channel structure has been designed based on conversation of energy and flow. The CPC scaffold possessing such a channel network was made by indirect solid free form fabrication. Negative model of scaffold was designed by Pro/E software and its epoxy resin mold was fabricated on a sterolithography apparatus and the CPC slurry was filled in these molds. After CPC was self hardened, the mold was baked. The mold was removed by pyrolysis and then the designed scaffold was obtained.

The sizes of the fabricated scaffolds were consistent with the designed. The average compressive strength of the scaffold is approximately 6.0 MPa. Computational fluid dynamics and perfusion culture results showed that such a 3D flow channel arrangement would lead to a more uniform distribution of flow and cells and good transportation of nutrients.

The size errors of fabricated scaffolds could not escape and perfusion methods were difficult to control.

The basic design concept presented showed great promise for use in bone tissue engineering and fabrication method enhanced the versatility of scaffold fabrication. The designed scaffold structure made it possible to keep integrality of the scaffold when direct observation cells inside the channel by scanning electron microscopy (SEM).