Yasin Varol, Hakan F. Oztop and Ioan Pop
The purpose of this paper is to study the conjugate heat transfer via natural convection and conduction in a triangular enclosure filled with a porous medium.
Abstract
Purpose
The purpose of this paper is to study the conjugate heat transfer via natural convection and conduction in a triangular enclosure filled with a porous medium.
Design/methodology/approach
Darcy flow model was used to write governing equations with Boussinesq approximation. The transformed governing equations are solved numerically using a finite difference technique. It is assumed that the enclosure consists of a conducting bottom wall of finite thickness, an adiabatic (insulated) vertical wall and a cooled inclined wall.
Findings
Flow patterns, temperature and heat transfer were presented at different dimensionless thickness of the bottom wall, h, from 0.05 to 0.3, different thermal conductivity ratio between solid material and fluid, k, from 0.44 to 283 and Rayleigh numbers, Ra, from 100 to 1000. It is found that both thermal conductivity ratio and thickness of the bottom wall can be used as control parameters for heat transport and flow field.
Originality/value
It is believed that this is the first paper on conduction‐natural convection in porous media filled triangular enclosures with thick wall. In the last years, most of the researchers focused on regular geometries such as rectangular or square cavity bounded by thick wall.
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Keywords
Hakan F. Oztop, Khaled Al‐Salem, Yasin Varol, Ioan Pop and Mujdat Fırat
The purpose of this numerical study is to investigate the effects of inclination angle and non‐isothermal wall boundary conditions in a partially open cavity filled with a porous…
Abstract
Purpose
The purpose of this numerical study is to investigate the effects of inclination angle and non‐isothermal wall boundary conditions in a partially open cavity filled with a porous medium.
Design/methodology/approach
In this study, the governing dimensionless equations were written using Brinkman‐Forchheimer model. They are numerically solved by using finite volume method with SIMPLE solution algorithm by applying open boundary conditions in one side. The opposed side of the open cavity is under non‐isothermal boundary conditions.
Findings
Results are presented by streamlines, isotherms, velocity and temperature profiles as well as the local and mean Nusselt numbers for different values of the governing parameters such as Grashof numbers, porosity, amplitude of sinusoidal function and inclination angle of the cavity. It is found that inclination angle is the most important parameter on the temperature and flow field.
Originality/value
The originality of this study is the open sided enclosure filled with porous media and non‐isothermal wall.
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Beybala Timur, Yasin Emre Oğuz and Veysel Yilmaz
Mobile food ordering apps (MFOAs) became more popular, thanks to social distancing regulations during the COVID-19 outbreak. People started to order food using these apps more…
Abstract
Purpose
Mobile food ordering apps (MFOAs) became more popular, thanks to social distancing regulations during the COVID-19 outbreak. People started to order food using these apps more than usual. As customers seem happy to use these apps, there is always a risk of spreading infection. These facts inevitably shape customer intentions. Therefore, this study aims to empirically assess the MFOA user dining attitudes (DA), e-satisfaction (ES) and continuance intention (CI) regarding the perceived risk (PR) during the COVID-19 pandemic in Türkiye.
Design/methodology/approach
This study used structural equation modelling (SEM) in the expectation confirmation theory and technology acceptance model. Data collection instruments were derived from existing literature, and 625 questionnaires were collected via online surveys. The data collection instrument consisted of eight parts that aimed to gather information about participants’ demographics, expectation confirmation, perceived ease of use, perceived usefulness, ES, PR and CI.
Findings
Results showed significant relationships between ES, DA, PR and CI. The most remarkable finding is that while ES influences customers to reuse MFOAs, PR causes a decrease in CI.
Originality/value
This study model broadened the existing MFOA study models by adding risk factors. Also, it made a valuable contribution to emerging MFOA literature both in Türkiye and the world.
研究目的
由于 Covid-19 爆发期间的社交距离规定, 移动订餐应用程序 (MFOA) 变得更受欢迎。 人们开始比平时更多地使用这些应用程序点餐。由于客户似乎很乐意使用这些应用程序, 因此始终存在传播感染的风险。这些事实不可避免地会影响客户的使用意愿。因此, 本研究旨在实证评估 MFOA 用户在 Turkiye Covid-19 大流行期间对感知风险的用餐态度、电子满意度和持续意图。
研究设计/方法/途径
该研究在预期确认理论和技术接受模型中使用了 SEM。 数据收集工具来自现有文献, 通过在线调查收集了 625 份问卷。 数据收集工具由 8 个部分组成, 旨在收集有关参与者的人口统计信息、期望确认、感知易用性、感知有用性、电子满意度、感知风险和持续意图的信息。
研究发现
结果显示电子满意度、用餐态度、感知风险和持续意愿之间存在显着关系。 最显着的发现是, 虽然电子满意度会影响客户重复使用 MFOA, 但感知到的风险会导致持续意愿下降。
研究原创性/价值
该研究模型通过添加风险因素拓宽了现有的 MFOA 研究模型。 此外, 它还为土耳其和世界新兴的 MFOA 文献做出了宝贵贡献。
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Yasin Ozgurluk, Kadir Mert Doleker and Abdullah Cahit Karaoglanli
Thermal barrier coatings (TBCs), which are used in high temperature applications of gas turbines, are damaged due to fuels and airborne minerals under working conditions. Stable…
Abstract
Purpose
Thermal barrier coatings (TBCs), which are used in high temperature applications of gas turbines, are damaged due to fuels and airborne minerals under working conditions. Stable zirconia coatings, which are usually used as topcoat materials in TBCs, are damaged by interacting at high temperatures with elements such as vanadium and sulfur from low quality fuels. The purpose of this paper is to see the failure mechanism of TBC systems after hot corrosion damages.
Design/methodology/approach
CoNiCrAlY metallic bond coatings of TBC samples were produced by cold gas dynamic spray method which is a new trend production method and stabilized zirconia ceramic top coating was produced by atmospheric plasma spray method. In total, 50% by weight of V2O5 and 50% Na2SO4 salt mixtures were placed on TBC samples and subjected to hot corrosion test at 1000°C.
Findings
Hot corrosion behaviors of TBC samples were examined by scanning electron microscopy, elemental mapping analysis, energy dispersive X-ray spectrometry analysis and X-ray diffraction analysis. TBC samples were damaged at the end of 12-h cycles.
Originality/value
The paper provides to understand the mechanism of hot corrosion of TBCs with cold sprayed metallic bond coat.