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In response to the century-long demand for heat energy, efficient use, conservation, and recovery of heat have become critical issues. Heat exchanger manufacturing, with its substantial capital and operational costs, now necessitates an efficient and energy-saving approach. Various methods have been developed over the years to enhance heat transfer within these systems to improve performance and reduce fuel consumption. One such approach is passive heat transfer enhancement, which involves introducing geometric alterations in the flow medium, such as using inserts or modifying the tube surface. This study aims to examine flow and heat transfer behavior within a horizontal tube, employing hexagonal perforated tube (HPT) inserts with varying diameter ratios (DR). To achieve this, a 3D model of the HPT inserts was developed and analyzed using finite volume based ANSYS Fluent software. The investigation considered Reynolds numbers (Re) within laminar flow regions, ranging from 1118 to 1676 while exploring HPT inserts with DR of 0.167, 0.238, 0.357, and 0.476, respectively. Results reveal that the Nusselt number (Nu) is notably influenced by both Re and DR of the HPT inserts. The enhancement in Nu achieved through the use of HPT inserts can reach up to an impressive 60.4% compared to the plain pipe's performance, offering substantial benefits in terms of energy conservation and system performance. [ABSTRACT FROM AUTHOR]

Microplastics, defined as plastic particles less than 5 mm in size, have become a pervasive environmental contaminant detected across a wide range of ecosystems. While the presence of microplastics in marine life and humans has been extensively documented, there remains a significant gap in understanding their full health impacts. Moreover, the effects of microplastics on animals, particularly those in close proximity to human activities, remain underexplored, representing a key area for future research. In this study, we found high levels of microplastic accumulation in animal tissues, particularly in the lungs, intestines, and reproductive organs. Our results also indicate that ingestion of microplastics occurs through multiple environmental sources, including contaminated food, water, and air, reflecting their widespread distribution. Evidence of microplastics crossing biological barriers and accumulating in critical organ systems suggests potential long-term health risks for animals that may also have implications for humans through environmental and food-chain exposure. Given the interconnectedness of ecosystems and the potential for these contaminants to enter the food chain, the presence of microplastics in animals raises serious concerns for broader ecological and human health. The findings underscore the urgent need for further research to clarify the long-term effects and to develop effective strategies for mitigating this emerging global threat. [ABSTRACT FROM AUTHOR]

The application of nanofluids has exploded in recent decades to improve the local number, mean Nusselt number, and rate of heat transfer. However, boundary layer equations of nanofluid across a flat plate with radiation have not been studied, and therefore this paper studies them mathematically for the first time. For water-based copper and aluminum oxide nanofluids, a similarity solution is presented in this study, and the subsequent system of the ordinary differential equation (ODE) is numerically solved by the Runge–Kutta method in MATLAB. Two different hydraulic boundary conditions are used in the simulations. In the first, the flow across a moving plate and the direction of the flow are analyzed, while in the second, the flow over a nonlinearly moving plate in a still fluid is investigated. The nanoparticle's boundary layer thickness is found less than the thermal and hydraulics boundary layers. The local Nusselt number and friction factor of both the nanofluids are calculated and compared with the base fluid. The results demonstrate that the friction coefficient is high and the Nusselt number is low for nanoparticles with a high volume fraction. It also revealed that the friction factor for water–aluminum oxide is 16% greater than that for the water–CuO whereas the local Nusselt number for water–aluminum oxide is only 5% more than that for the water–CuO. [ABSTRACT FROM AUTHOR]

While forced-air convective systems remain the predominant method for heating and cooling worldwide, radiant cooling and heating systems are emerging as a more efficient alternative. Current radiant cooling systems primarily rely on hydronic chilled water systems. This study introduces direct-expansion radiant cooling as a novel technique that could enhance the efficiency of radiant cooling and reduce its environmental impact. Water (R-718) has been tested as a refrigerant due to its favorable thermodynamic properties and environmental advantages; however, to the author's knowledge, it has yet to be tested in direct-expansion radiant cooling. This research investigated several refrigerants, including water (R-718), ammonia (R-717), R-410a, R-32, R-134a, and R-1234yf, for this application. The findings indicate that water demonstrates efficiency comparable to other non-natural refrigerants, making it a promising candidate, given its favorable thermodynamic properties and substantial environmental benefits. Despite challenges such as a high compression ratio necessitating multi-stage compression, a high compressor discharge temperature exceeding 300 °C and requiring specialized blade materials, and a high suction volume flow rate, direct-expansion radiant cooling operates within a different temperature range. Consequently, the compressor discharge temperature can be reduced to 176 °C, and the compression ratio can be lowered to approximately 3.5, making water a more viable refrigerant option for this application. [ABSTRACT FROM AUTHOR]