NUST Institutions Library Catalogue Search for 'an:"126970"'

Maximizing Micro-Channel Heat Transfer Efficiency with Longitudinal Vortex Generators and Advanced Tri-Hybrid Nano-Fluids /

By Ahzam ,Syed Muhammad . . 65p. ; 30cm..

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Enhanced Heat Transfer in Annular Passages with Tri-Hybrid Nanofluids and Longitudinal Vortex Generators / Asher Abdullah

By Abdullah, Asher . . 82p. , Heat transfer enhancement has always been an issue that has plagued the scientific corridors for decades. Various techniques have been adopted using both active and passage techniques to reduce the thermal resistance and supplement the heat efficiency. Annular passages are one of the most commonly used in various industries and engineering systems due to their simplistic geometry and compact size. Efficiency of such systems have always been a keen point of interests for researchers and have resulted in advancements that have resulted in superior heat transfer as compared to primitive methods. One such advancement has been the introduction of nanofluids in limited concentrations with a base fluid to circumvent the limitations of the usual fluids used in the annular passages. A research gap exists in usage of Trihybrid Nanofluids in the annular passages which greatly enhances the heat transfer while providing greater thermal conductivity, improved flow and minimal thermal resistance. My research aims to study the effects of Tri hybrid nanofluids in two different types of annular passage ways (Circular and Diamond Shape) with inner and outer heating for 4 different Tri hybrid Nano fluids which are Al2O3, CuO and Fe3O4, Al2O3, TiO2, and SiO2, SWCNT, MWCNT, and TiO2, SiO2, TiO2, and ZnO, Gr, Ag, and TiO2 , CuO, MgO, and MWCNTs, all of which had a volumetric concentration of 3 percent and were suspended in water. The effectiveness of these tri hybrid Nano fluids was gauged by several factors which include calculation of Nusselt Number, hydraulic performance quantified by pressure drop whilst the heat transfer from the surface is calibrated by the heat transfer coefficient. An increase of 19.92 % for Nusselt number was observed for TiO2, SiO2, TiO2, and ZnO but the pressure drop was way too high. In order to study the confluence of these factors a performance coefficient index was computed through which a tri hybrid Nano fluid (Al2O3, TiO2, and SiO2) was selected to be coupled with longitudinal vortex generators. The vortex generators are to be applied at various pitch angles mainly at 20,30 and 40 degrees and tested for all the performance parameters. 30cm.

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Microplastic Behavior in Idealistic Exhalation Dynamics: Exploring Shape, Density, and Diameter Effects Using CFD /

By Siddiqui, Hadia Alam . . 60p. , Microplastics are now ubiquitous contaminants in the atmosphere which have raised substantial public health issues. While extensive research has focused on particle deposition during inhalation, the exhalation phase, a critical component of the complete respiratory cycle, remains comparatively less explored. The study aims at addressing this research gap by conducting a comprehensive computational investigation into the deposition dynamics of microplastic particles during exhalation within an idealized human tracheobronchial airway model from generations G3–G6. A three-dimensional airway geometry was constructed via Weibel's morphometric data, adjusted for a 50-year-old adult. Computational Fluid Dynamics (CFD) simulations are performed using the Reynolds-Averaged Navier-Stokes (RANS) approach with the (SST) 𝑘-𝜔 turbulence model. The Discrete Phase Model (DPM) was employed to track trajectories of spherical microplastic particles 2-22 µm under four exhalation flow rates 125, 300, 500, and 1000 ml/s, representing varying breathing intensities from resting to heavy exercise. The results demonstrate an inverse relationship between exhalation flow rate and overall deposition efficiency (DE). Lower flow rates resulted in the highest DE, as particles had greater residence time for gravitational sedimentation and were less influenced by turbulent dispersion. In contrast, higher flow rates generated significant turbulent kinetic energy, which enhanced particle mixing and reduced net deposition. Furthermore, deposition was strongly governed by inertial impaction, as evidenced by a positive correlation with the Stokes number. Spatial analysis revealed that while high flow rates created intense deposition hotspots at major bifurcations, the cumulative particle deposition isXIV significantly lower than at gentler flow rates, where deposition is more widespread. This study concludes that gentle exhalation poses a greater risk for microplastic retention in the lower bronchial airways. The findings challenge the assumption that higher airflow invariably leads to increased deposition and provide crucial insights into the mechanisms of particle exposure during the exhalation phase. 30cm.

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