U. Heck, U. Fritsching and K. Bauckhage
Heat treatment by quenching of individual metallic parts with multiple impinging gas jets is an environmentally friendly alternative to conventional surface hardening and…
Abstract
Heat treatment by quenching of individual metallic parts with multiple impinging gas jets is an environmentally friendly alternative to conventional surface hardening and quenching in liquids. In the present investigation the gas flow field and simultaneous heat transfer process in gas quenching is studied by numerical simulation for surface treatment of a cylindrical sample geometry. Aim of the investigation is the evaluation of optimized flow conditions and nozzle arrangements to achieve: a maximum overall heat release (high integral heat transfer rates) to maximize the quenching efficiency; a local smooth distribution of the cooling process (spatially homogeneous heat transfer) for avoidance of spatial hardness variations. These aims are achieved by derivation of an optimized nozzle arrangement and appropriate operation conditions of the gas jet array with respect to the three dimensional sample geometry of a cylinder to be quenched.
Details
Keywords
E. Vishnuvardhanarao and Manab Kumar Das
The purpose of this paper is to consider the conjugate heat transfer from a flat plate involving a turbulent plane wall jet. The bottom wall of the solid block is heated by a…
Abstract
Purpose
The purpose of this paper is to consider the conjugate heat transfer from a flat plate involving a turbulent plane wall jet. The bottom wall of the solid block is heated by a constant heat flux.
Design/methodology/approach
High Reynolds number two‐equation model (κ‐ϵ) has been used for turbulence modeling. The parameters considered are the conductivity ratio of solid and fluid, the solid slab thickness and the Prandtl number. The Reynolds number considered is 15,000 because the flow becomes fully turbulent and then is independent of the Reynolds number. The range of parameters considered are: conductivity ratio = 1‐1,000, solid slab thickness = 1‐10 and Prandtl number = 0.01‐100.
Findings
The non‐dimensional bottom surface temperature is high for high‐Prandtl number fluid and vice versa. As conductivity ratio increases, it decreases whereas it increases with the increase in slab thickness. Similar trend is observed for the distribution of the interface temperature. The Nusselt number computed based on the interface temperature increases with Prandtl number. It is observed that for the range of parameters considered, local Nusselt number distribution superimposes with each other. The average heat flux at the interface has been computed and found to be equal with average heat flux at the bottom which ensures the overall heat balance.
Originality/value
The study of conjugate heat transfer with a turbulent wall jet will be useful for cooling of heated body.
Details
Keywords
Stefan Schneck and Eva May-Strobl
This chapter utilizes German tax data to present evidence about the direct and indirect effects of new firm formation. Cohort analysis is applied to investigate survival, sales…
Abstract
This chapter utilizes German tax data to present evidence about the direct and indirect effects of new firm formation. Cohort analysis is applied to investigate survival, sales, inputs, and value added of start-up firms. Most dropouts occur in the early years. We show that start-up microenterprises increase economic vitality directly. Sales and value added are in an approximate proportion of 3:1. With respect to the indirect effects of new firms, we find that one Euro of sales induces considerable indirect effects because 66 Cents are used to buy products and services from incumbents. For this reason, new firms substantially promote economic prosperity of incumbents. Sectoral differences are also indicated, with the manufacturing industry generating highest sales and relying most heavily on inputs in the early periods.
Details
Keywords
The paper's aim is to provide information on heat transfer and flow characteristics for a jet emerging from a conical nozzle and impinging onto the cylindrical, which resembles…
Abstract
Purpose
The paper's aim is to provide information on heat transfer and flow characteristics for a jet emerging from a conical nozzle and impinging onto the cylindrical, which resembles the laser heating process, for researchers and graduate students working in the laser processing area, which can help them to improve the understanding of the laser machining process.
Design/methodology/approach
A numerical scheme employing the control volume approach is introduced to model the flow and heating situations. The effect of jet velocity on the heat transfer rates and skin friction around the cylindrical cavity subjected to the jet impingement was investigated.
Findings
Increasing jet velocity at nozzle exit enhances the heat transfer rates from the cavity wall and modifies the skin friction at cavity wall, which is more pronounced as the cavity depth increases to 1 mm.
Research limitations/implications
The effects of nozzle cone angle on the flow structure and heat transfer characteristics were not examined, which perhaps limits the general usefulness of the findings.
Practical implications
Very useful information are provided for the laser gas assisted processing, which has a practical importance in machining industry.
Originality/value
This paper provides original information for the effects of the gas jet velocity on the cooling rates of the laser produced cavity.
Details
Keywords
Ubyrajara Brasil Dal Bello, Carla Marques, Octávio Sacramento and Anderson Galvão
This study sought to fill a gap in the literature by examining the dynamics of neo-rural small entrepreneurs’ business activities as little research has been done on these…
Abstract
Purpose
This study sought to fill a gap in the literature by examining the dynamics of neo-rural small entrepreneurs’ business activities as little research has been done on these individuals. The research was conducted in three of Portugal’s low density territories (i.e. Miranda do Douro, Penamacor and Aljezur), focusing on understanding these outsider entrepreneurs’ main motivations and challenges after they decide to leave the city to settle in rural areas and become small business owners.
Design/methodology/approach
Data were collected in semi-structured interviews with 26 neo-rural entrepreneurs. The multiple-case study method was applied to assess the differences and similarities between the interviewees and their respective contexts. NVivo 11.0 software was used to conduct content analysis.
Findings
The results reveal that rural environments appear to attract these new entrepreneurs for various reasons, such as taking advantage of business opportunities, searching for a better quality of life and responding to family needs. The multiple motives contributing to the need for change and entrepreneurship fit well within social cognitive theory. However, these individuals subsequently experience difficulties related mainly to a lack of infrastructure, little preexisting knowledge, a need for financial capital and the absence of the right workforce.
Originality/value
The findings on the experiences, difficulties and challenges of neo-rural entrepreneurs constitute new contributions because few existing studies have concentrated on migration and/or immigration entrepreneurship in rural contexts. The results can serve as a starting point for other similar studies.
Details
Keywords
Hadiseh Karimaei, Seyed Mostafa Hosseinalipour and Ramin Ghorbani
To estimate mean droplet diameter (MDD) of a spray, three different numerical models were used in this paper. One of them is investigation of the surface instability of the liquid…
Abstract
Purpose
To estimate mean droplet diameter (MDD) of a spray, three different numerical models were used in this paper. One of them is investigation of the surface instability of the liquid sheet producing from an injector.
Design/methodology/approach
First, the linear instability (LI) analysis introduced by Ibrahim (2006) is implemented. Second, the improved (ILI) analysis already introduced by the present authors is used. ILI analysis is different from the prior analysis, so that the instability of hollow-cone liquid sheet with different cone angles is investigated rather than a cylindrical liquid sheet. It means that besides the tangential and axial movements, radial movements of the liquid sheet and gas streams have been considered in the governing equations. Beside LI theory as a momentum-based approach, a new model as a theoretical energy-based (TEB) model based on the energy conservation law is proposed in this paper.
Findings
Based on the energy-based approach, atomization occurs because of kinetic energy loss. The resulting formulation reveals that the MDD is inversely proportional to the atomization efficiency and liquid Weber number.
Research limitations/implications
The results of these three models are compared with the available experimental data. Prediction obtained by the proposed TEB model is in reasonable agreement with the result of experiment.
Practical implications
The results of these three models are compared with the available experimental data. Prediction of the proposed energy-based theoretical model is in very good agreement with experimental data.
Originality/value
Comparison between the results of new model, experimental data, other previous methods show that it can be used as a new simple and fast model to achieve good estimation of spray MDD.
Details
Keywords
Jinyao Nan, Pingfa Feng, Jie Xu and Feng Feng
The purpose of this study is to advance the computational modeling of liquid splashing dynamics, while balancing simulation accuracy and computational efficiency, a duality often…
Abstract
Purpose
The purpose of this study is to advance the computational modeling of liquid splashing dynamics, while balancing simulation accuracy and computational efficiency, a duality often compromised in high-fidelity fluid dynamics simulations.
Design/methodology/approach
This study introduces the fluid efficient graph neural network simulator (FEGNS), an innovative framework that integrates an adaptive filtering layer and aggregator fusion strategy within a graph neural network architecture. FEGNS is designed to directly learn from extensive liquid splash data sets, capturing the intricate dynamics and intrinsically complex interactions.
Findings
FEGNS achieves a remarkable 30.3% improvement in simulation accuracy over traditional methods, coupled with a 51.6% enhancement in computational speed. It exhibits robust generalization capabilities across diverse materials, enabling realistic simulations of droplet effects. Comparative analyses and empirical validations demonstrate FEGNS’s superior performance against existing benchmark models.
Originality/value
The originality of FEGNS lies in its adaptive filtering layer, which independently adjusts filtering weights per node, and a novel aggregator fusion strategy that enriches the network’s expressive power by combining multiple aggregation functions. To facilitate further research and practical deployment, the FEGNS model has been made accessible on GitHub (https://github.com/nanjinyao/FEGNS/tree/main).
Details
Keywords
This paper aims to provide a brief review of the work on startup survival and a conceptual framework of factors influencing a startup firm’s survival. In addition, it lists…
Abstract
Purpose
This paper aims to provide a brief review of the work on startup survival and a conceptual framework of factors influencing a startup firm’s survival. In addition, it lists significant gaps and recommends avenues for future research.
Design/methodology/approach
This paper conducted a systematic literature review of peer-reviewed journal articles indexed in Scopus, Web of Science and EBSCO databases using Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A total of 140 articles published in 72 journals between 1993 and 2021 were considered for the review.
Findings
The comprehensive review revealed that most of the studies have applied a single theoretical lens and have taken place in advanced economies, with a narrow focus on emerging economies. Empirical research has prominently applied regression-based models to analyse the relationship between the antecedents and the outcomes. Internal resources such as human capital, financial capital and physical capital and non-financial performance measures such as survival, growth and employment are the studies’ prominently used antecedents and outcome variables. However, a limited number of studies have used mechanisms of mediation and moderation.
Originality/value
Despite the substantial scientific and practical discussion on startup survival, to the best of the authors’ knowledge, no comprehensive review has been undertaken to date, which provides a systematic and comprehensive compilation of the knowledge on the topic. This study aims to develop a unique landscape of scientific advancement by methodically reviewing, categorising and synthesising the current body of knowledge on the topic.
Details
Keywords
Michael Fritsch and Pamela Mueller
We investigate regional differences in the level and the development of regional new business formation activity. There is a pronounced variance of start-up rates across the…
Abstract
We investigate regional differences in the level and the development of regional new business formation activity. There is a pronounced variance of start-up rates across the regions. The level of regional new firm formation is rather path-dependent resulting in relatively small changes. The main factors determining the level of regional start-ups are innovative activity and entrepreneurship. These factors are also responsible for changes in the level of regional new business formation. The growth of regional demand and regional unemployment do not play a significant role for the change of regional start-up activity. Steering innovation and creating an entrepreneurial atmosphere could be an appropriate starting point for policy measures that try to promote start-ups. Our empirical evidence strongly suggests that such measures may have significant effect only in the long run.
Martin Andersson, Pontus Braunerhjelm and Per Thulin
Schumpeter claimed the entrepreneur to be instrumental for creative destruction and industrial dynamics. Entrepreneurial entry serves to transform and revitalize industries…
Abstract
Purpose
Schumpeter claimed the entrepreneur to be instrumental for creative destruction and industrial dynamics. Entrepreneurial entry serves to transform and revitalize industries, thereby enhancing their competitiveness. The purpose of this paper is to investigate if entry of new firms influences productivity amongst incumbent firms, and the extent to which altered productivity can be attributed sector and time specific effects.
Design/methodology/approach
Implementing a unique dataset the paper estimates a firm‐level production function in which the productivity of incumbent firms is modeled as a function of firm attributes and regional entrepreneurship activity.
Findings
The analysis finds support for positive productivity effects of entrepreneurship on incumbent firms, albeit the effect varies over time, what the authors refer to as a “delayed entry effect”. An immediate negative influence on productivity is followed by a positive effect several years after the initial entry. Moreover, the productivity of incumbent firms in services sectors appears to be more responsive to regional entrepreneurship, as compared to the productivity of manufacturing firms.
Originality/value
The paper employs a firm‐level production function approach allowing for time lags of the effect of entrepreneurship. The unique data implemented allow the authors to identify genuinely new ventures as compared to those associated with reorganizations of existing businesses, thereby overcoming much of data deficiencies in previous studies. In addition, data are distributed on Swedish functional labor market regions.