Semnan University PressJournal of Heat and Mass Transfer Research2345-508X13320260901Numerical Investigation of Thermohydraulic Performance in Laminar Flow through Microchannels Equipped with Longitudinal Vortex Generators261272978510.22075/jhmtr.2025.36208.1655ENZoubirBelkacemiDepartement of Physics, Faculty of Matter Sciences, Applied Energetic Physics Laboratory (LPEA), University of Batna 1, 05000 Batna, AlgeriaZakariaBoumahratDepartment of Mechanical Engineering, Faculty of Technology Sciences, Constantine 1, Frères Mentouri University, Constantine 25000, AlgeriaAhmed DhiyaeddineFoulDepartment of Mechanical Engineering, Faculty of Technology Sciences, Constantine 1, Frères Mentouri University, Constantine 25000, AlgeriaJournal Article20241210Vortex generators (VGs) are widely employed to enhance heat transfer in channel flows by inducing vortices, with their performance strongly influenced by geometric parameters and flow conditions. This study numerically investigates the thermohydraulic performance of laminar flow (Re = 200–1200) in a rectangular microchannel (H = 0.26 mm) equipped with longitudinal vortex generators (LVGs) of reduced height (0.75H). The objective is to assess the impact of reduced LVG height on pressure loss and heat transfer enhancement, using water as the working fluid. Numerical simulations were validated against existing data, with deviations remaining below 10%, and were subsequently conducted for three LVG orientation angles (30°, 135°, and 150°). The results indicate that at Re = 1200, the LVGs increased the friction factor by up to 6% for 30° and 150° and 8% for 135°, while increasing the Nusselt number by up to 18% for 30° and 150° and 24% for 135°. The highest thermal performance factor of 1.21 was achieved at the 135° orientation for Re=1200, identifying it as the optimal configuration among those tested.https://jhmtr.semnan.ac.ir/article_9785_170347629f54ca28e66c895c1d9abdf7.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X13320260901Design and Performance Evaluation of a Multi-Stepped Absorber Plate Fin in a Flat Plate Solar Collector273284982810.22075/jhmtr.2025.36908.1682ENGulshan BaharuddinAhmedDurgapur Institute of Advanced Technology and Management Durgapur, West Bengal 713212, IndiaMd NaimHossainDepartment of Mechanical Engineering, Jalpaiguri Government Engineering College West Bengal 735102, IndiaArijitKunduDepartment of Mechanical Engineering, Jalpaiguri Government Engineering College West Bengal 735102, IndiaAshwaniKumarDepartment of Mechanical Engineering, Technical Education Department Uttar Pradesh Kanpur 202480 India & Department of Mechanical Engineering, Graphic Era Deemed to be University Dehradun 248002 IndiaJournal Article20250215This research investigates the thermal performance and optimization of a new absorber plate fin design with a double step change in thickness (rectangular profile with double step changes in local thickness, RPDSLT). It compares the thermal performance of RPDSLT to fins with simpler geometries (rectangular, trapezoidal, and rectangular with a single step change) across a wide range of geometrical parameters. The main objective of researchers in this field is to determine the maximum fin efficiency with minimal fin material usage. Therefore, the focus is on understanding the impact of the additional step change in RPDSLT on heat transfer efficiency and examining whether the fin efficiency is enhanced or not. The study aims to identify the optimal values of the geometrical parameters (plate fin thickness ratios and dimensionless step lengths) that maximize efficiency. The absorber plate fin thickness plays a crucial role in solar collector efficiency. The research explores how the double step change in RPDSLT thickness affects collector efficiency compared to simpler fin designs. Detailed schematics of each fin profile and a solar collector demonstration are presented. The result show that the RPDSLT fin exhibits a maximum fin efficiency roughly 5% greater than the rectangular profile with step changes in local thickness (RPSLT) fin when their geometries is optimized. Compared to rectangular and trapezoidal fins, the RPDSLT offers a smaller efficiency improvement of 1-2%. Nevertheless, the superior thermal performance of the RPDSLT design could make it a preferred choice for flat plate solar collectors despite its more intricate fabrication. The study indicates that optimal efficiency is achieved with the minimum tested step-length ratios of 0.1 and the maximum tested thickness ratios of 0.9. Therefore, for efficient material utilization in the plate fin, it is recommended to use minimal step-length ratios and maximal thickness ratios.https://jhmtr.semnan.ac.ir/article_9828_55664a5dc5ed2f36206b1c73678efa75.pdfSemnan University PressJournal of Heat and Mass Transfer Research2345-508X13320260901Influence Examine of Visnaga Oil Biodiesel on the Performance and Emission Characteristics of CI Engines285293982510.22075/jhmtr.2025.37420.1721ENAbdulrahman ShakirMahmoodCollege of Mechanical Engineering, University of Technology-Iraq, Baghdad, IraqMohammed KadhimAllawiDepartment of Mechanical Power Engineering, Baghdad-Technical Engineering College, Middle Technical University, Baghdad, IraqGhanim MohammedHachimKerbala University, College of Engineering, Mechanical Engineering Department, Baghdad, IraqFouad AlwanSalehMustansiriyah University, College of Engineering, Mechanical Engineering Department, Baghdad, IraqJournal Article20250416The main reason for global warming and respiratory problems in humans is the influence of emissions from fossil fuel combustion. Levels of these pollutants have increased significantly due to the expansion of vehicle numbers, especially in Iraq, exacerbating the environmental and health impacts. Procedures to mitigate these emissions include modifying engine-part design or utilizing environmentally friendly fuel sources. The aim of this research is to perform an experimental investigation examining the use of a new type of visnaga oil biodiesel on the performance and emissions of a single-cylinder, air cooled, and 4 strokes CI engines. The visnaga oil biodiesel was added to diesel fuel in volumetric ratios of 10%, 20%, 30%, and 40%. The results of the tests show that this type of biodiesel lowers the engine's thermal efficiency while raising the EGT and BSFC. The highest decrease in BTE was 7.63% and the highest increase in BSFC was 15.28%, for biodiesel at 40% in the blend (BF40). Additionally, for the visnaga oil biodiesel, the emissions of carbon monoxide (CO) and unburned hydrocarbons (HC) were decreased, but the emissions of nitrogen oxides (NOx) and carbon dioxide (CO<sub>2</sub>) were increased. The greatest reduction in CO and HC emissions was achieved with the use of the BF40 blend, where reductions of 24.7% and 39.5% were recorded respectively, while the NOX and CO<sub>2</sub> emissions increased by 36% and 38.2%, respectively.https://jhmtr.semnan.ac.ir/article_9825_f37d7df68d057dc36e068d67dccd4e82.pdf