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AbstractThe present study examines the development of a push-pull ventilation system with localized extraction located for use in wastewater treatment. The proposed approach aims to minimize the concentration of H2S in the settling stage of a wastewater treatment plant located in Santiago de Chile. Computational fluid dynamic simulations were implemented, and these were contrasted with actual measurements of H2S emission to assess and to improve the existing forced crossed ventilation system in place. Along with the measurement of H2S emissions, other important operating parameters of the existing ventilation system, including air velocity and NH3concentration were measured. The measurements at different positions of the settling stage of the wastewater treatment process showed H2S concentrations as high as 21 mg/m3at the center over the water surface when utilizing the existing crossed ventilation system. In general, the measured H2S concentrations agree with those predicted by computational simulations, with discrepancies between 8.1% and 28.4%. An assessment of the improved ventilation system with localized extraction systems (push-pull) was carried out to determine the level of effectiveness of decreasing the concentration of H2S in the settling plant. According to the obtained results, the concentration of H2S in the corridors of the plant does not surpass 7.5 ppm, which meets the required Chilean regulation.

The demand for air conditioning and heating in the construction sector has increased in about two decades, mainly because of demographic and economic growth. The result of this increase in energy consumption has been more greenhouse gas emissions (GHGs). This paper proposes a multi-objective optimization design that helps reduce heating, ventilation, and air-conditioning (HVAC) energy consumption and increases the thermal comfort levels in low-income housing. Achieving these objectives required choosing a dwelling unit that is representative of the Chilean housing stock, which was identified with the help of the National Housing Monitoring Network (ReNaM). The selected optimization variables correspond to the type of windows, type and thickness of ceiling insulation, and type of PCM-impregnated Pinus radiatawood panel, with PCM melting points between 8 and 27 °C. Subsequently, we minimized the hours of thermal discomfort and the dwelling typology's electrical consumption of heating and cooling by using the algorithm the Non-dominated Sorting Genetic Algorithm-II (NSGA-II). The main results include a reduction of up to 21.5 % in the thermal discomfort hours and a decrease of up to 80.5 % in energy consumption associated with the optimal housing typology compared to the base case. Additionally, the economic analysis indicated the payback period is 12.9 years for the Pareto solution, which presents a lower distance to the utopic point (UP).

The encapsulation of phase change materials (PCMs) is a convenient alternative for latent heat thermal energy storage systems (LHTESSs) because of the excellent relationship between their storage volume and the heat transfer surface. The goal is to establish a unified heat transfer behavior of encapsulated PCM. Computational fluid dynamics (CFD) numerical simulations are performed with ANSYS/Fluent of the melting and solidification processes of the commercial organic PCMs RT5HC and RT10HC. The numerical study involve a parametric study of the sphere diameter (40, 60, and 80 mm), thermal gradient (difference between wall temperature and phase change temperature) for melting (1–5 °C), and thermal gradient for solidification (1–3 °C). The numerical simulations implemented the experimentally obtained and temperature-dependent thermophysical properties of thermal conductivity (k), phase change enthalpy (L), specific heat (cp), and viscosity (μ) of the PCMs. The computational simulations allowed us to determine the behavior of the heat transfer coefficient (h) as a function of the liquid fraction (φ) and solid fraction (φso) of the PCM. Furthermore, nonlinear regression adjustments to the Nusselt number (Nu) curves allowed the fitting of power-law curves with suitable correlation parameters. Finally, the coefficients (a, b, and c) of the proposed fitting power-law curves were plotted and adjusted via linear regression through the origin as a function of the dimensionless numbers of Archimedes (Ar), Stefan (Ste), Grashof (Gr), Prandtl (Pr), and dimensionless thermal conductivity (κ), unifying the behavior of the melting and solidification processes through two correlations of the Nu number. These correlations will be helpful in the design of LHTESS tanks for their application in heat-pump-type air-conditioning systems in buildings.

Water-based nanofluids prepared with ZnO nanoparticles (⩽17 nm) were characterized. The thermal conductivity and viscosity were measured as a function of temperature (278–303 K), for two ZnO concentration (1wt% and 3wt%) establishing that, whereas the nanofluid prepared with a concentration of 1wt% registered an average improvement of the thermal conductivity of 10.31% at a concentration of 3wt%, the viscosity decreased an average of 5.03% respect to the base fluid. An analysis of the stability of these nanofluids was carried out via UV–vis, finding that for a concentration of 3wt% the stability is better, since it requires 168 h to decrease its absorbance in the same amount as the sample of 1wt%. Additionally, the laminar three-dimensional flow of these nanofluids has been numerically studied considering symmetric microchannels (200 ⩽Re⩽ 1200) of fixed-width rectangular cross-section (283 μm) and three different heights (200 μm, 600 μm, and 400 μm), subjected to a constant heat flux in the lower wall (50 W/cm2). The microchannels have been simulated considering the properties of the nanofluid variable with respect to temperature through experimentally determined models (for 1wt% and 3wt%), finding that thermal conductivity improves mostly for a concentration of 1wt%, registering an increase in average 10.31% in the studied temperature range.The numerical results showed that the use of nanofluids favors heat transfer at low Reynolds numbers with the maximum improvement in the coefficient of heat transfer by convection (42.33%). A decrease in temperature of the base of the microchannel is also observed, which is more significant at low Reynolds numbers for a concentration of 1wt%. In the case of MCH-1 with Re=200, the decrease in the mean temperature of the lower wall is 5.65% (20.45 K), a value that decreases to 0.90% (2.94 K) for Re=1200. This configuration also offers the highest net heat gain, considering the increase in the coefficient of friction produced by the incorporation of ZnO nanoparticles. Finally considering the experimental studies of the thermal properties and stability of nanofluids, and the numerical results associated with the thermal and fluid-dynamic performance of the microchannels, a methodology is proposed to carry out a comprehensive approach to the application of nanofluids in microchannels.