Ahmet Yüksel

The goal of this study is to numerically investigate the effects of different phase change material (PCM) types, thicknesses, and placement positions within the external wall structure on latent heat storage and, consequently, on heating and cooling energy savings in residential buildings. Three different PCM types were analyzed and compared with a phase stabilized material (PSM), which possesses identical thermal properties but does not undergo phase transition, to isolate and quantify the specific contribution of latent heat. In addition, comparisons with a conventional wall without PCM were carried out, enabling the evaluation of both latent heat contribution and the overall effect on thermal inertia. The analyses were conducted under the climatic condition of Istanbul, Turkey, which is classified as a Csa (hot-summer Mediterranean) climate according to the Koppen-Geiger classification. This study addresses not only annual and monthly analyses but also daily and hourly assessments, enabling a deeper understanding of the transient thermal behavior and thermal inertia of PCMs. The findings underline the importance of optimizing PCM type, thickness, and placement in building envelope design to maximize energy efficiency. The results reveal that placing PCM closer to the inner surface provides the most effective latent heat utilization and the highest energy savings, with 30mm RT18 reducing annual heating and cooling energy demand by up to 4% compared to the base case. While increasing PCM thickness from 1 mm to 30 mm generally reduced total annual energy demand (by 2.5% on average), the cooling load response was not consistent. For instance, when RT18 was placed near the outer surface, a 1 mm layer has same cooling demand as base case while an 18 mm layer increased it by 1% due to delayed heat release during peak cooling periods. For some cases, such as when RT21 and RT25 PCMs were positioned near the outer surface, the latent heat effect was negligible, resulting in nearly the same total annual load as the reference case. Moreover, when PCMs were placed closer to the inner surface, the latent heat contribution remained consistently positive across all thicknesses.

This study presents a numerical investigation of supersonic flows through a convergent conical rocket engine nozzle, focusing on the influence of turbulence models on shock structures and nozzle performance. Simulations were performed in ANSYS Fluent for nozzle pressure ratios (NPRs) from 1.4 to 7.0 under steady-state conditions. Four turbulence models [Realizable k–ε, Standard k–ω, Shear Stress Transport (SST) transition model, and Reynolds Stress Model (RSM)] were evaluated for their ability to predict Mach distributions, shock-cell structures, and pressure-based performance metrics. Results indicated that the SST k–ω model provided sharper, more accurate shock-cell structures and captured shock–boundary-layer interactions more effectively, especially at higher NPRs. At NPR = 5.0, the SST model predicteda maximum exit Mach number of 1.85, closely matching the experimental 1.88 ± 0.03, whereas the Realizable k–ε model underestimated it at 1.75. The k–ε model offered greater numerical stability and lower computational cost but tended to oversimplify flow features and underpredict shock intensity. RSM captured anisotropic turbulence effects but required more computational resources and exhibited higher sensitivity. Aerodynamic performance evaluation showed that the SST model predicted thrust and discharge coefficients (CV, CD) more accurately across all NPRs. At NPR = 4.0, it produced a CV of 0.92 and a CD within 3% of experimental values, compared to 0.87 and up to 7% deviation for the k–ε model. Therefore, the SST model was recommended for high-fidelity analyses requiring accurate prediction of shock behavior and nozzle performance, while the realizable k–ε model was suitable for preliminary analyses prioritizing faster, stable convergence with reduced detail.

This study investigated the effects of varying metabolic rate (MR) and occupancy levels on indoor air temperature, interior surface temperatures, and internal thermal gains within a non-ventilated building model. The goal was to evaluate how these parameters influence thermal dynamics and determine which plays a more dominant role. Ventilation was intentionally excluded to isolate the thermal effects of occupants and eliminate external influences. The relative humidity generated by occupants accumulated, causing relative humidity to reach saturation in all scenarios. Since relative humidity showed no variation between cases, it was not included in the analysis. The results demonstrated that both MR and occupancy significantly impacted indoor thermal responses. Higher values of either parameter led to increased temperatures, though their relative influence varied. MR had a stronger effect under low-occupancy conditions, while its impact diminished as occupancy increased. For instance, in scenarios with 50 occupants, the indoor air temperature difference between MR values of 50 and 200 W/person reached 6.7oC. Conversely, increasing occupancy led to more uniform total thermal gains due to expanded heat transfer surface area, especially with 200 occupants. The study concluded that both MR and occupancy need to be considered when modeling indoor thermal comfort and energy efficiency. Additionally, the results indicated that occupancy had a more significant influence on indoor temperature dynamics, particularly due to its role in heat transfer surface area expansion. These findings underscored the critical role of occupancy density in shaping indoor temperature profiles and highlighted the need to account for metabolic activity levels when designing energy-efficient and thermally comfortable building environments.

This study comprehensively analyzed the energy performance of a health care clinic (HC) building by simulating various phase change material (PCM) integration scenarios under the climatic conditions of Istanbul/Turkiye. PCM with a melting temperature of 25oC was applied to the building envelope in different orientations and combinations, and its effects on heating and cooling energy consumption were assessed. Results showed that PCM's impact on energy performance of the HC building varied based on the number and orientation of facades. During winter, phase change was often limited due to low ambient temperatures, resulting in increased natural gas consumption in scenarios with limited facade coverage. Conversely, in the cooling season, PCMs effectively reduced electricity demand, especially when applied to facades with high solar exposure. When active phase change occurred on both internal and external walls, savings increased to 1100 kWh (24%) in electricity and 71 kWh (1%) in natural gas. External wall-only applications led to a 791 kWh reduction in electricity but a 372 kWh increase in natural gas use. Among single-facade applications, the south facade was most effective in reducing cooling loads. Multi-facade configurations, particularly North+East+West and East+West+South, achieved up to 666 kWh in electricity savings. The results highlighted that optimal PCM integration strategies should consider facade orientation, surface coverage, and seasonal dynamics to enhance energy efficiency in HC buildings.

Integrating phase change materials (PCMs) into building envelopes offers a powerful method for enhancing thermal mass and reducing heating, ventilation, and air conditioning energy demand. This study provides a comprehensive analysis of combining PCMs with various roof designs (flat, gable, and domed) and shading strategies in a Mediterranean climate to optimize residential building performance. Through a 3E (energetic, environmental, and economic) assessment and computational fluid dynamics (CFD) modeling, we determined that the use of PCM23 significantly enhances occupant comfort, improving the predicted mean vote by 17% and enhancing overall thermal comfort by 14%. The most effective configuration, a gable roof with integrated PCMs, outperformed a flat roof by reducing annual energy consumption by 20% (1103 kWh). This optimal design also yielded substantial economic and environmental benefits, including a 16.2 TD/m² reduction in annual energy costs, a short investment payback period, and a 4% decrease in operational CO₂ emissions. These results highlight the significant potential of pairing PCMs with passive architectural features to create more energy-efficient, cost-effective, and comfortable living environments.

In this study, a closed-circuit heat pump food drying system was investigated by integrating a 50 W infrared lamp (IR) and a carbon fiber film heater (CFH) into the cabinet to dry 3 mm thick apple slices at 1 m/s air speed and 40℃ temperatures. The study aimed to investigate the differences in drying performance and energy consumption between a typical heat pump drying system (Scenario-I) and an IR and CFH supported heat pump drying system (Scenario-II). The results of the six-hour experiments conducted under laboratory conditions showed that the system reached a steady state 50% faster in Scenario-II and 41 g more moisture was extracted from the products. Furthermore, a 2% decrease in energy consumption and cost caused by the compressor was observed with IR and CFH support. The products that initially weighed 600 g were reduced to 200 g by 28% faster with 25% energy savings in Scenario-II. Finally, it was determined by thermal camera images that the products were dried homogeneously thanks to CFH. Therefore, it has been identified that IR and CFH supported HPD systems are preferable systems in terms of energy saving for low compressor load and fast drying processes.