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11 – 20 of 417Muhammed Turan Aslan, Bahattin Kanber, Hasan Demirtas and Bilal Sungur
The purpose of this study is analysis of deformation and vibrations of turbine blades produced by high electrolyte pressure during electrochemical machining.
Abstract
Purpose
The purpose of this study is analysis of deformation and vibrations of turbine blades produced by high electrolyte pressure during electrochemical machining.
Design/methodology/approach
An experimental setup was designed, experiments were conducted and the obtained results were compared with the finite element results. The deformations were measured according to various flow rates of electrolyte. In finite element calculations, the pressure distribution created by the electrolyte on the blade surface was obtained in the ANSYS® (A finite element analysis software) Fluent software and transferred to the static structural where the deformation analysis was carried out. Three different parameters were examined, namely blade thickness, blade material and electrolyte pressure on blade disk caused by mass flow rate. The deformation results were compared with the gap distances between cathode and anode.
Findings
Large deformations were obtained at the free end of the blade and the most curved part of it. The appropriate pressure values for the electrolyte to be used in the production of blisk blades were proposed numerically. It has been determined that high pressure applications are not suitable for gap distance lower than 0.5 mm.
Originality/value
When the literature is examined, it is required that the high speed flow of the electrolyte is desired in order to remove the parts that are separated from the anode from the machining area during electrochemical machining. However, the electrolyte flowing at high speeds causes high pressure in the blisk blades, excessive deformation and vibration of the machined part, and as a result, contact of the anode with the cathode. This study provides important findings for smooth electro chemical machining at high electrolyte flows.
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The purpose of this paper is to develop a numerical model to simulate the flow field as well as the conjugate heat transfer during unsteady cooling of a flat plate with a single…
Abstract
Purpose
The purpose of this paper is to develop a numerical model to simulate the flow field as well as the conjugate heat transfer during unsteady cooling of a flat plate with a single submerged water jet. At wall temperatures above the liquid boiling point, the vapor formation process and the interaction of the vapor phase with the developing jet-flow field are included.
Design/methodology/approach
The time-dependent flow and temperature distribution during all occurring boiling phases as well as the local and temporal distribution of the heat transfer coefficient on a flat plate can be simulated.
Findings
The influence of the liquid jet flow rate (10,800=Re_d=32,400) and the nozzle distance to the plate (4=H/d=20) on the transient cooling process are analyzed. This includes the time-dependant positions of the transition regions between the boiling phases on the plate as well as the temperatures at these transition regions. Additionally, the local heat transfer rates are a direct result of the unsteady cooling simulation.
Originality/value
A single model approach is developed and utilized to simulate the unsteady cooling process of a flat plate with an impinging water jet including all occurring boiling phases.
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José Pablo Montégu, Julio A. Pertuze and Carolina Calvo
The authors analyzed the effects of importing activities on both technological and non-technological innovation in Chile. They contribute to the literature by hypothesizing and…
Abstract
Purpose
The authors analyzed the effects of importing activities on both technological and non-technological innovation in Chile. They contribute to the literature by hypothesizing and testing the idea that importing activities can foster the introduction of product, process, marketing and organizational innovations in emerging market firms.
Design/methodology/approach
The authors used a combination of two economic surveys that included 1,347 Chilean companies. To test their hypotheses, they applied a variant of the Crépon-Duguet-Mairesse (CDM) model (Crépon et al., 1998) accounting for technological and non-technological innovation outputs. Specifically, four alternative innovation output indicators were used to measure the introduction of product, process, marketing and organizational innovations.
Findings
The results revealed that importing activities had positive effects on technological and non-technological innovation. Importers showed a significant advantage in the introduction of product, marketing and organizational innovations. Firms that both import and export (i.e. two-way traders) had an even greater advantage in the introduction of new or significantly improved products.
Originality/value
The authors demonstrated a relationship between importing activities and both technological and non-technological innovation that is novel and relevant, particularly at a historical moment when COVID-19 poses huge economic challenges to emerging market firms. As trade disruptions caused by the pandemic have predisposed some governments to favor protectionist policies, the authors warn that erecting barriers against imports can hamper the innovative success of local businesses.
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Zhiguo Tang, Hai Li, Feng Zhang, Xiaoteng Min and Jianping Cheng
The purpose of this paper is to explore the flow and heat transfer characteristics of the jet impingement onto a conical heat sink and evaluate the ability of heat transfer…
Abstract
Purpose
The purpose of this paper is to explore the flow and heat transfer characteristics of the jet impingement onto a conical heat sink and evaluate the ability of heat transfer enhancement.
Design/methodology/approach
A numerical study of the flow and heat transfer of liquid impingement on cone heat sinks was conducted, and transition SST turbulence model was validated and adopted. The flow and thermal performances were investigated with the Reynolds number that ranges from 5,000 to 23,000 and cone angle that ranges from 0° to 70° in four regions.
Findings
Local Nusselt numbers are large, and pressure coefficients drop rapidly near the stagnation point. In the conical bottom edge, a secondary inclined jet was observed, thereby introducing a horseshoe vortex that causes drastic fluctuations in the curves of the flow and heat transfer. The average Nusselt numbers are higher in a conical protuberance than in flat plates in most cases, thus indicating that the heat transfer performance of jet impingement can be improved by a cone heat sink. The maximum increase is 13.6 per cent when the cone angle is 60°, and the Reynolds number is 23,000.
Originality/value
The flow and heat transfer behavior at the bottom edge of the cone heat sink is supplemented. The average heat transfer capacity of different heat transfer radii was evaluated, which provided a basis for the study of cone arrays.
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Ubyrajara Dal Bello, Carla Susana Marques, Octávio Sacramento and Anderson Rei Galvão
The purpose of this paper is to study the role of neo-rural entrepreneurs in developing the entrepreneurial ecosystem and in the sustainability of the local economy, especially in…
Abstract
Purpose
The purpose of this paper is to study the role of neo-rural entrepreneurs in developing the entrepreneurial ecosystem and in the sustainability of the local economy, especially in low-density territories.
Design/methodology/approach
The entrepreneurial ecosystem theory, human capital theory, network theory, and the triple helix model are the theoretical underpinnings of this study. The study has a qualitative, multiple-case methodological approach using semi-structured interviews. The collected reports were submitted for content analysis with the help of the computer application for qualitative data analysis NVivo, version 11.0.
Findings
As main results, the following were found: the conviction that entrepreneurship is a vector of territorial development, the existence of elements of attractiveness to entrepreneurial activity in each territory of the study, the existence of obstacles to entrepreneurship, but also a set of institutional support coming from municipalities and polytechnic institutes and, finally, the type of entrepreneurship therefrom preponderant of necessity.
Originality/value
The study contributes to the extent that it completes gaps in the literature by focussing its analysis on a specific type of entrepreneurship: neo-rural and micro-sized entrepreneurship. It also offers contributions to local government to think of mechanisms that can attract more neo-rural entrepreneurs.
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Fabian Krause, Sven Schüttenberg and Udo Fritsching
The purpose of this paper is to describe the development and application of a numerical model for analysis of flow boiling phenomena and heat transfer.
Abstract
Purpose
The purpose of this paper is to describe the development and application of a numerical model for analysis of flow boiling phenomena and heat transfer.
Design/methodology/approach
For flow boiling processes, the fluid and vapour flow regimes in connection with the conjugate heat and mass transfer problem for specimen quenching through the entire boiling curve is modelled. Vaporisation and recondensation, the vapour fraction distribution and vapour movement with respect to the liquid are considered in the calculation of the two‐phase flow and heat transfer process. The derived flow boiling model is based on a mixture model and bubble crowding model approach for two‐phase flow. In addition to the conventional mixture model formulation, here special model implementations have been incorporated that describe: the vapour formation at the superheated solid‐liquid interface, the recondensation process of vapour at the subcooled vapour‐liquid interface, the mass transfer rate in the different boiling phases and the microconvection effect in the nucleate boiling phase resulting from bubble growth and detachment.
Findings
The model prediction results are compared with experimental data for quenching of a circular cylinder, showing good agreement in boiling state and heat transfer coefficient distribution. Simulation and experiments lead to a better understanding of the interaction of incident flow in the boiling state and the resulting heat transfer.
Research limitations/implications
Fluid temperatures in the range of 300‐353 K and specimen wall temperatures up to 1,000 K are considered.
Practical implications
Flow boiling is an efficient heat transfer process occurring in several technical applications. Application background of the model development is in quenching of complex metallic specimen geometries in liquids subject to fast changing heat fluxes.
Originality/value
A general model for the complex two‐phase boiling heat transfer at high wall temperatures and fast flow conditions that can be used in engineering applications does not yet exist. The results provide detailed information describing the non‐uniform phase change during the complete quenching process from film boiling to pure convection.
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Bernardí Cabrer-Borrás, Paz Rico Belda and Dolores Botella Carrubi
The purpose of this paper is to analyse the determinants of the survival of Spanish companies.
Abstract
Purpose
The purpose of this paper is to analyse the determinants of the survival of Spanish companies.
Design/methodology/approach
Two approaches are used and they are complementary. The first approach analyses the determinants of survival probability. For this purpose, a binary choice model is built and estimated using a sample of companies from the main economic sectors taken from the SABI database. Likewise, the Blinder–Oaxaca decomposition is applied to quantify the difference between companies with employees and without employees and the proportion of this difference that owes to observed factors or unobserved factors. Finally, the second approach is a survival analysis carried out through the Cox proportional hazard model that identifies the determinants of the duration of business activity.
Findings
The results of the empirical analysis show that companies without employees present less favourable conditions for survival at all stages of their evolution than companies with employees.
Originality/value
The contribution of this study to the empirical literature consists in analysing the difference between companies with and without employees. Due to the structure of Spanish companies, this aspect and the determinants of such difference are essential for policymakers to increase the survival for companies.
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Guang-Zhi Zeng, Zhi-Wei Li, Sha Huang and Zheng-Wei Chen
Based on the aerodynamic loads and dynamic performances of trains, this study aims to investigate the effect of crosswinds and raindrops on intercity trains operating on viaducts…
Abstract
Purpose
Based on the aerodynamic loads and dynamic performances of trains, this study aims to investigate the effect of crosswinds and raindrops on intercity trains operating on viaducts to ensure the safe operation of intercity railways in metropolitan areas.
Design/methodology/approach
An approach coupled with the Euler multiphase model as well as the standard k-ɛ turbulence model is used to investigate the coupled flow feature surrounding trains and viaducts, including airflow and raindrops, and the numerical results are validated with those of the wind tunnel test. Additionally, the train’s dynamic response and the operating safety region in different crosswind speeds and rainfall is investigated based on train’s aerodynamic loads and the train wheel–rail dynamics simulation.
Findings
The aerodynamic loads of trains at varying running speeds exhibit an increasing trend as the increase of wind speed and rainfall intensity. The motion of raindrop particles demonstrates a significant similarity with the airflow in wind and rain environments, as a result of the dominance of airflow and the supplementary impacts of droplets. As the train’s operating speed ranged between 120 and 200 km/h and within a rainfall range of 20–100 mm/h, the safe operating region of trains decreased by 0.56%–7.03%, compared with the no-rain condition (0 mm/h).
Originality/value
The impact of crosswind speeds and rainfall on the train’s aerodynamic safety is studied, including the flow feature of crosswind and different particle-sized raindrops around the train and viaduct, aerodynamic loads coefficients suffered by the intercity train as well as the operating safety region of intercity trains on the viaduct.
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Van Luc Nguyen, Tomohiro Degawa and Tomomi Uchiyama
This paper aims to provide discussions of a numerical method for bubbly flows and the interaction between a vortex ring and a bubble plume.
Abstract
Purpose
This paper aims to provide discussions of a numerical method for bubbly flows and the interaction between a vortex ring and a bubble plume.
Design/methodology/approach
Small bubbles are released into quiescent water from a cylinder tip. They rise under the buoyant force, forming a plume. A vortex ring is launched vertically upward into the bubble plume. The interactions between the vortex ring and the bubble plume are numerically simulated using a semi-Lagrangian–Lagrangian approach composed of a vortex-in-cell method for the fluid phase and a Lagrangian description of the gas phase.
Findings
A vortex ring can transport the bubbles surrounding it over a distance significantly depending on the correlative initial position between the bubbles and the core center. The motion of some bubbles is nearly periodic and gradually extinguishes with time. These bubble trajectories are similar to two-dimensional-helix shapes. The vortex is fragmented into multiple regions with high values of Q, the second invariant of velocity gradient tensor, settling at these regional centers. The entrained bubbles excite a growth rate of the vortex ring's azimuthal instability with a formation of the second- and third-harmonic oscillations of modes of 16 and 24, respectively.
Originality/value
A semi-Lagrangian–Lagrangian approach is applied to simulate the interactions between a vortex ring and a bubble plume. The simulations provide the detail features of the interactions.
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Van Luc Nguyen, Tomohiro Degawa and Tomomi Uchiyama
This study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume.
Abstract
Purpose
This study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume.
Design/methodology/approach
The bubbles, released from the annulus located at the bottom of the domain, rise owing to buoyant force. These released bubbles have diameters of 0.15–0.25 mm and satisfy the bubble flow rate of 4.1 mm3/s. The evolution of the three-dimensional annular bubble plume is numerically simulated using the semi-Lagrangian–Lagrangian (semi-L–L) approach. The approach is composed of a vortex-in-cell method for the liquid phase and a Lagrangian description of the gas phase.
Findings
First, a new phenomenon of fluid dynamics was discovered. The bubbly flow enters a transition state with the meandering motion of the bubble plume after the early stable stage. A vortex structure in the form of vortex rings is formed because of the inhomogeneous bubble distribution and the fluid-surface effects. The vortex structure of the flow deforms as three-dimensionality appears in the flow before the flow fully develops. Second, the superior abilities of the semi-L–L approach to analyze the vortex structure of the flow and supply physical details of bubble dynamics were demonstrated in this investigation.
Originality/value
The semi-L–L approach is applied to the simulation of the gas–liquid two-phase flows.
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