This study proposes a numerical investigation of enhanced thermal performance in a circular tube equipped with periodically arranged, inclined delta wings (DWs) mounted directly on the inner tube walls. The turbulent airflow is evaluated for Reynolds numbers (Re) between 3000 and 21,000 utilizing the finite volume approach along with the Realizable k–ε turbulent model. The analysis is performed in two different phases: solid delta wings (DW) and punched delta wings (PDW). In the solid DW phase, the angle of attack (α) is kept constant at 45°, and geometric parameters include a set of four base/chord ratios (BR = 0.4 to 0.7) and four pitch ratios (PR = 0.5 to 1.5). The forward delta wing (F-DW) constantly outperforms the backward delta wing (B-DW) in terms of heat transmission enhancement, as indicated by comparative analysis of the DWs. In contrast to a smooth tube, the F-DW generates streamwise vortices that greatly boost fluid interaction and heat transmission, but at the sacrifice of rising pressure loss. The greatest Nusselt number (Nu) and friction factor (f) are realized with the F-DW at the narrowest pitch ratio (PR = 0.5) and its highest base ratio (BR = 0.7). Under baseline operating parameters of PR = 0.75 and Re = 3,000, the largest thermal enhancement factor (TEF) values of 2.79, 2.82, and 2.76 are achieved, with corresponding Nu ratios of 7.69, 8.79, and 10.34 for BR = 0.4, 0.5, and 0.6, respectively. In the second phase, a novel perforation approach is employed on the optimal F-DW (BR = 0.5, PR = 0.75) to establish a forward punched delta wing (F-PDW). This cutting-edge F-PDW attains a maximum TEF of 3.01 alongside a Nu ratio of 9.24. The findings show that, as contrasted to solid DWs and smooth tubes, the F-PDW greatly increases overall TEF, indicating its great potential for efficient, smaller heat exchanger applications.
This study investigates the occurrence of gap resonance in side-by-side structures with sharp corner from the perspective of vortex dynamics. Potential flow analysis is first employed to determine the resonant and non-resonant frequency. A RANS–VOF frame based CFD model is applied to investigate the vortex dynamics during the gap resonance phenomenon. Vortex Energy Conversion (VEC) mechanism is newly discovered during the whole process of gap resonance. The VEC process consists of two consecutive stages. In the first stage, the sharp corner accumulate vorticity and turn the horizontal flow into vertical flow toward the gap region. Large amount of flow energy is captured by the newly formed vortex and transported into the gap region. In the very early second stage, the vortex shedding occurs and further accumulate field energy. Then the vortex size grows and keeps the energy in the region. In the late period of second stage, the vortex dissipates and the energy is transformed into flow kinetic energy, generating large velocity in the vertical direction and bringing in the well-known gap resonance phenomenon.
The article conducts an experimental study into heat transfer and exergy characteristics of a tube-type heat exchanger contained with delta-baffle vortex generators to enhance convection heat transmission. There are two phases to the investigation: solid delta baffles (DB) and perforated delta baffles (PDB). In the first DB phase, the specific DB parameters of four relative pitches (PR = 0.75–1.5) and three blockage ratios (BR = 0.4–0.6) are explored for a broad variety of Reynolds numbers (Re) from 4760 to 29,260. The studies are performed at a consistent attack angle (α) of 45° utilizing a forward-inclined DB configuration (F-DB), which exhibits superior thermal performance relative to the backward-inclined DB configuration (B-DB). The F-DB markedly improves thermal performance in contrast to a plain tube, achieving peak friction factor (f) and Nusselt number (Nu) values up to 27.51 and 5.9 times above those of the plain tube, respectively. The optimal thermal enhancement factor (TEF) and exergy efficiency for the F-DB are 2.57 and 0.9933, respectively, attained at BR = 0.5 and PR = 0.75. In the second phase, forward perforated delta baffles (F-PDB) with an adjustable louver-flap angle (θ = 20°, 30°, 45°, and 60°) are generated by employing a novel perforation technique on the optimal F-DB cases. The F-PDB reaches a peak TEF of 2.68 at θ = 45°, outperforming values recorded in prior studies. Lastly, the experimental correlations for f and Nu have been formulated for both F-DB and F-PDB designs.
Eu3+-doped alkali calcium alumino phosphate oxide (OD) and oxyfluoride (OF) glasses were successfully fabricated using the conventional melt-quenching route. Comparative analyses were performed between the two systems to evaluate their physical, optical, photoluminescence and X-ray induced luminescence properties. The OD glass exhibited higher density and refractive index compared to the OF glass, indicating a more compact glass network. However, the molar volume of the OD was lower than that of the OF due to the larger free volume generated by fluoride incorporation. Based on the absorption spectra, both glass systems exhibited almost identical spectral profiles with minor variations in absorbance intensity. In the photoluminescence study, both glass systems exhibited strong red emission at around 612 nm (5D0→7F2 transition) under 394 nm excitation. The OF glass exhibited a higher emission intensity than the OD glass, primarily due to the lower concentration of hydroxyl groups that act as non-radiative quenching centers. Both glass systems exhibited a reddish-orange emission, in good agreement with the CIE 1931 chromaticity coordinates. The X-ray–induced luminescence exhibited a spectral pattern comparable to that of photoluminescence, while differing in excitation source and luminescence mechanism. The integrated scintillation efficiencies of both glass systems were derived from the peak areas of their X-ray–induced luminescence spectra and compared with that of a Bi4Ge3O12 (BGO) crystal to evaluate their relative scintillation performance. The glasses were successfully imaged under X-ray excitation, confirming their strong potential as optical probes for medical imaging applications.
Material extrusion additive manufacturing (MEX) provides a cost-effective pathway for fabricating metallic components; however, its industrial use remains limited by surface defects and high roughness. This study evaluates nanosecond laser polishing (LP) as a post-processing method to improve the surface characteristics of 316L stainless steel produced by Bound Metal Deposition (BMD). The objective is to understand how laser beam diameter, scan speed, and processing atmosphere (air vs. argon) influence surface integrity. Polishing experiments were performed using 50 W and 100 W laser power with beam diameters of 200 and 400 mu m at scanning speeds of 100-400 mm/s. Areal roughness (Sa), surface waviness (Wa), surface chemistry, subsurface microstructure, and electrochemical response were systematically characterized. Laser polishing reduced Sa from 2.003 mu m to 0.371 mu m (81 % reduction) and Wa by up to 43 %. Polishing in argon produced cleaner melt tracks with minimal oxidation, a refined remelted layer, and enhanced passive film formation, leading to improved corrosion resistance (Ecorr improved from-0.466 V to-0.062 V). These findings demonstrate that LP effectively mitigates the surface limitations of BMD-fabricated stainless steel and provide process guidelines for achieving high-quality functional surfaces in MEX metal components.
