In the design of shell and tube heat exchangers encompassing a condensing zone, meticulous attention is required due to the complexities surrounding forced convection in multiphase systems. Despite extensive research, the intricacies within these multiphase systems have remained elusive, rendering the heat transfer coefficient unresolved. In this study, a novel methodology is introduced to elucidate the thermal characteristics of forced convection within the condensing region of shell and tube condensers. An amalgamation of theoretical methods, specifically the Logarithmic Mean Temperature Difference (LMTD), and empirical data sourced from industrial operations forms the foundation of this approach. Upon rigorous analysis employing both Power Law Analysis and Logarithmic Linear Regression, a correlation in terms of ${N_u}=C \cdot {Re}^m \cdot {Pr}^{\mathrm{n}}$ within the condensing region was discerned using Buckingham Pi Theorem. Findings revealed coefficients of C=1.15, m=0.893, and n=13.442. For optimization purposes, the Particle Swarm Optimization (PSO) Algorithm was employed. A focused examination of parameters such as tube length, tube outside diameter, baffle spacing, shell diameter, number of tube passings, and tube wall thickness revealed that by attenuating their values by 30%, 46%, 80.3%, 8%, 50%, and 61.9% respectively, a substantial increase in condenser effectiveness was observed, elevating the value from 0.9473 to 4.299.

This study explores the durability of plasticized polyvinyl chloride (PVC-P) geomembranes in hydraulic engineering anti-seepage structures, particularly under varying operational temperature conditions. Employing accelerated thermal air aging tests on three distinct PVC-P geomembrane variants, the study assesses their mechanical properties, specifically axial tensile strength, using an electronic universal testing machine. A comprehensive thermal air aging model, based on the Arrhenius equation, has been developed, offering insights into the lifespan prediction of these geomembranes. Results demonstrate that factors such as annual average temperature, plasticizer content, and membrane thickness significantly influence the geomembranes' service life. Post-aging observations include a notable yellowing and increased brittleness of the geomembranes, coupled with a decline in tensile strength and elongation. Elongations exhibit a decreasing trend, aligning with a first-order degradation kinetics equation. Under conditions of 50℃ over a period of 120 days, the elongation of polyvinyl chloride (PVC)-HX, PVC2.0-JT, and PVC2.5-JT geomembranes was reduced to 255.88%, 430.11%, and 434.58%, respectively. Predictions indicate that at an operational temperature of 20℃, the expected lifespans for these geomembranes are 19, 45, and 48 years, with material failure correlating to plasticizer loss rates of 58.2%, 32.5%, and 24.8%, respectively. These findings offer valuable guidance for the selection of geomembrane materials in hydraulic engineering projects, considering various designed service durations.

In the domain of compact flat plate heat exchangers, enhancing efficiency remains a pivotal challenge, primarily due to the low thermal conductivity characteristic of the gas phase. This investigation explores efficiency improvements in such exchangers by the integration of modified delta-wing longitudinal vortex generators (LVGs). The focus is centered on geometric modifications and alterations in the size ratios of the traditional delta-wing design as documented in pertinent literature. The geometric modifications include partial surface removal and elevation from the attachment surface, as well as a combination of these approaches. Concurrently, size ratio alterations involve a systematic reduction in the overall dimensions of the modified LVGs to 75%, 50%, and 25% of their initial size. Employing ANSYS Fluent, the study conducts numerical simulations to evaluate air flow at various Reynolds numbers ($Re$ = 2,000 – 10,000). Analyses include examining temperature progression along the axial distance, mapping temperature contours, and applying the Q-criterion for in-depth understanding. Performance evaluation of each modification was undertaken by calculating the thermal enhancement factor (TEF) in relation to a baseline scenario of two unmodified flat plates, utilizing the Nusselt number and the friction factor for comprehensive comparison. To ensure reliability, the study demonstrates mesh independence in results and validates the computational model through comparative analysis with established correlations and experimental data from existing literature on delta-wing LVG designs. Findings indicate that geometric modifications of vortex generators, as explored in this research, do not markedly decrease head loss nor significantly enhance system performance. In contrast, size ratio modifications, particularly the reduction of vortex generator dimensions to 75% and 50% of the original size, show an increase in TEF ranging from 3% to 9% compared to the conventional delta-wing design. This underscores the potential of incorporating an array of such modified LVGs on each plate of a flat plate heat exchanger to boost its efficiency significantly.

This investigation examines the effects of varied nanoparticle concentrations, such as zinc oxide (ZnO), copper oxide (CuO), and aluminum oxide (Al₂O₃), on the mass fraction and melting characteristics within nano-enhanced phase change materials (NEPCMs). Employing numerical simulations via ANSYS-FLUENT, the study explores these dynamics within a square enclosure subjected to distinct thermal gradients. The enclosure, measuring 10cm×10cm, incorporates a heat-supplying wall, partitioned into quarters, each exhibiting a unique temperature gradient. This setup provides a comprehensive understanding of boundary conditions relevant to NEPCM behavior. The focus lies on a comparative analysis of NEPCM’s thermal properties under varying nanoparticle concentrations: 0.1, 0.3, and 0.5 weight percent. A low-temperature wall, lined with paraffin wax and integrated with these nanomaterials, facilitates the assessment of their impact on the phase change materials (PCMs). Remarkably, an inverse relationship is observed between nanoparticle concentration and mass fraction, ranging from 0.86 to 0.08. This finding underscores the significant role of nanoparticle integration in modulating NEPCM properties. Among the nanoparticles studied, CuO emerges as the most efficacious in enhancing melting due to its low density and high thermal conductivity. The temperature distribution profile within the paraffin wax shifts from a dispersed state to a more uniform and curved pattern upon nanoparticle incorporation. Such a transformation indicates an improved thermal response of the NEPCM system. The implications of this study are manifold, extending to the design and optimization of thermal energy storage systems. These insights are particularly valuable for applications in energy conservation within buildings, solar energy equipment, transportation, and storage solutions. The research elucidates the criticality of selecting appropriate nanoparticle concentrations for achieving desired phase change properties in NEPCM-based systems. Furthermore, it contributes to a deeper understanding of how nanoparticle characteristics influence the thermal behavior of PCMs, thus offering a guide for future innovations in this field.