ANNUAL JOURNAL OF TECHNICAL UNIVERSITY OF VARNA, BULGARIA

Investigationof tribological characteristics of 40Xgradesteel after hardfacedMMA welding method

Tatyana Mitkova Mechkarova — 2024-09-30

The article discusses the selection of an appropriate technology for the repair of forged structural steel through the use of hardfacing MMA welding method. Investigated, additionally, is the wear resistance of the hardfacing layers. The method used to determine the wear resistance is "block on ring". The macrostructure, microstructure and Vickers microhardness (HV0.05) were also analyzed.

Steel X65 acc. API 5L behaviour, under the influence of CO2 and H2

Georgi Stefanov Antonov — 2024-10-18

Abstract.

The paper focuses exclusively on the study of the gas pipeline steel X65 (acc. API 5L) behavior when subjected to the influence of CO₂ (carbon dioxide) and H₂ (hydrogen). Research and development of this type of document is necessary due to the needs of minimizing the CO₂ in the atmosphere produced by cement manufacturing during the process of decarbonization of limestone and clay in the cement kiln. With the expensive carbon emissions costing about 63 EUR/ton for the first quarter of 2024, it is reasonable CO₂ to be utilized. Additionally, coal-fired power plants must be transformed due to the high price of their electricity. Along with the cost for mining coal, the EU adds additional costs for emissions. Тhe market cannot afford to provide unprofitable energy to customers. The power sector somehow must take necessary action to comply with the latest government and environmental requirements.

One possible approach to address the transformation needs is to switch to green H₂ fuel or a mixture with H₂, or implement Carbon Capture and Storage (CCS) processes. Both gases have their specific problems that need to be overcome. The behavior of the already laid pipelines made by low carbon steel material exposed to these gases has not been fully assessed. Future experiments and tests will determine how these gases will affect the life cycle or design life of pipeline transportation systems.

Analysis of some flow parameters around a Magnus wind turbines models

Anastas Todorov Yangyozov — 2024-12-31

The present work presents the results of an experimental study of models of air turbines operating with the Magnus effect with a horizontal and a vertical axis of rotation. Pressure and velocity were measured with wireless data transfer equipment. Model air turbines are described and their main geometrical dimensions are presented. The experiments were done in a wind tunnel, and the working models were tested with different numbers of rotating cylinders. The problems in creating the small turbines and the limitations in their operation are discussed.

Scaling in Quantitative Survey in Management Science Research: The Perspective of Likert Scale

Olajide Idowu Okunbanjo — 2024-12-31

The research process entails the collection of data through questionnaire providing a ranking scale platform for measuring the respondents’ responses. Thus, this paper explores the topic of scaling in quantitative survey research in the field of management science, with a focus on Likert scaling. The paper delves into the types of scaling discussed in the literature, incorporating classical test theory as well as item response theory as guiding frameworks for its objectives. Employing a qualitative research approach, the paper allows for the use of contextual analysis through Qualitative Data Analysis (QDA). Presented is an overview of the various types of Likert scaling including 2-point, 3-point, 4-point, 5- point, 6-point, 7-point, 9-point, and beyond. The paper also argues that the 6-point Likert scale is the most appropriate scaling method for management science research as it divides the neutral option (mid-point) issue into parts of agreement and disagreement. The study recommends that management science researchers should familiarize themselves with the different types of Likert scale in order to determine the most appropriate for their studies. The paper suggests that the 6-point Likert scale is particularly relevant for studies within the management sciences field.