https://hdl.handle.net/20.500.12809/183 Sat, 04 Apr 2026 05:41:47 GMT 2026-04-04T05:41:47Z https://hdl.handle.net/20.500.12809/11036 Assessing the current and future effects of Covid-19 on energy related-CO2 emissions in the United States using seasonal fractional grey model Utkucan Şahin; Yan,Chen Accurate CO2 forecasting plays an important role in energy planning. However, in the annual forecasting studies on CO2 emissions, the seasonal effects cannot be predicted. To overcome this problem, this study proposed a novel prediction model based on the seasonally optimised fractional nonlinear grey Bernoulli model (SOFANGBM(1,1)), combining the seasonal fluctuation technique with optimisation of the background, power index, and fractional order values. The proposed novel model offers two important improvements in prediction performance: (1) This model combined optimised fractional nonlinear grey Bernoulli model (OFANGBM(1,1)) with the seasonal fluctuation technique to enable monthly and quarterly predictions (2) The seasonally optimised fractional nonlinear grey Bernoulli model (SFANGBM(1,1)) was improved by optimising the background value. CO2 emissions had the largest share in global GHG emissions, and the United States was the second largest CO2 emission emitter worldwide after China in 2019. However, cases and deaths from Covid-19 continue in the United States, and important questions arise: How has Covid-19 affected CO2 emissions by fossil fuel type in the past, and how will it reshape them in the future? This study aimed to analyse how Covid-19 affects CO2 emissions from fossil fuels in the U.S., how it will reshape its future, and also contribute to Sustainable Development Goals (SDGs). Quarterly CO2 emissions from coal, natural gas, petroleum, and total CO2 emissions in the U.S. were forecasted using a novel grey prediction model under pandemic and pandemic-free scenarios. The pandemic-free scenario determined the CO2 emissions gap due to Covid-19, and the pandemic scenario presented forecasted results of quarterly and annual CO2 emissions by 2025. The prediction performance was tested from 2022-Q1 to 2022-Q4 by simulated from 2015-Q1 to 2021-Q4. Using the SOFANGBM(1,1), Covid-19 caused 2 %, 2 %, 16 %, and 12 % reductions in CO2 emissions from coal, natural gas, petroleum, and total CO2 emissions, respectively, in 2020. SOFANGBM(1,1) also forecasts that total CO2 emissions will reach 4520.6 Mt by 2025. Sun, 01 Jan 2023 00:00:00 GMT https://hdl.handle.net/20.500.12809/11036 2023-01-01T00:00:00Z https://hdl.handle.net/20.500.12809/11034 Thermo-hydraulic efficiency of lung-inspired compact plate heat exchangers made using additive manufacturing techniques with steel, aluminum and titanium powders Güler, Onur Vahip; Gürel, Barış; Aryanfar, Yashar; Castellanos, Humberto Garcia; Göltaş, Merve; Keçebaş, Ali; Akkaya, Volkan Ramazan The selection of material for compact plate heat exchangers (CPHEs) is of increasing importance due to global economic and supply constraints. Additionally, the influence of material selection on the thermo-hydraulic characteristics of CPHEs is an area of ongoing research. This study aims to address these issues by analyzing the thermo-hydraulic performance of CPHEs made from steel, aluminum, and titanium materials with small, complex channels. Using an additive manufacturing method (specifically Direct Metal Laser Sintering), lung-inspired CPHEs of identical geometry and roughness were manufactured from steel, aluminum and titanium powders. The thermo-hydraulic characteristics of CPHEs as well as that of a traditional one with Chevron-type, were investigated using both experimental and numerical techniques under specific operating conditions to determine the optimum between maximum heat transfer and minimum pressure drop. The findings of this study reveal that as the temperature difference between the inlet on the hot and cold sides, as well as the flow rate, were increased, there was a corresponding increase in both amount of heat transferred and loss of pressure across all investigated CPHEs. Compared to the chevron type brazed plate heat exchanger, the CPHE made from aluminum showed a 75.2 % and 11.2 % increase in heat transfer and a 31.8 % and 10.9 % reduction in pressure drop at 3 and 6 L/min, respectively, for a temperature difference of 90–40 °C. This study suggests that the use of materials with different thermal conductivities in CPHEs may offer a promising solution to achieve elevated heat transfer rates while minimizing pressure drop. Mon, 01 Jan 2024 00:00:00 GMT https://hdl.handle.net/20.500.12809/11034 2024-01-01T00:00:00Z https://hdl.handle.net/20.500.12809/10925 Design and experimental analysis of a parallel-flow photovoltaic-thermal air collector with finned latent heat thermal energy storage unit Yağız Gürbüz, Emine; Şahinkesen, İstemihan; Tuncer, Azim Doğuş; Keçebaş, Ali In this work, it is aimed to improve the performance of a photovoltaic-thermal (PVT) air collector using finned latent heat thermal energy storage unit. In this regard, four different types of parallel-flow PVT (PPVT) systems have been designed, manufactured and tested including a conventional PPVT, a PPVT with paraffin-based thermal energy storage unit, a PPVT with 3-finned storage unit and a PPVT with 6-finned storage unit. A parallel-flow collector geometry has been designed to convey excess heat from both surfaces of the photovoltaic panel in the systems. Moreover, the effect of increasing the number of fins in the storage system in the PPVT on the performance has been analyzed within the scope of this work and the developed systems have been tested simultaneously. According to the experimentally obtained findings, overall efficiency value of the PPVT was improved from 55.83% to 76.79% using thermal energy storage with 6-fins. The performance ratio and sustainability index values were obtained between 0.64-0.76 and 1.0277–1.0474, respectively. Enviro-economic analysis has been performed and payback periods of the systems were attained between 0.991 and 1.146 years. Also, employing 6-finned storage unit in the PPVT upgraded the annual carbon dioxide savings as 33.71% in comparison to the unmodified PPVT. Sun, 01 Jan 2023 00:00:00 GMT https://hdl.handle.net/20.500.12809/10925 2023-01-01T00:00:00Z https://hdl.handle.net/20.500.12809/10863 Optimal insulation of underground spherical tanks for seasonal thermal energy storage applications Karaca Dolgun, Gülşah; Keçebaş, Ali; Ertürk, Mustafa; Daşdemir, Ali The literature deals specifically with compressed gas characteristics, solar radiation, storage volume and heat load fluctuation in aboveground storage and thermal energy storage (TES) applications. To prevent their negative effects, the use of underground insulated spherical tanks in the storage process has been overlooked. This study details the physical and economic aspects of using insulation in underground spherical tanks for seasonal TES systems. In determining the storage heat load, the degree-time method is recommended for the heat transfer mechanism between soil and storage temperature degrees. Using life cycle cost analysis, the insulation thickness, energy saving and payback period in the underground spherical tank are discussed in detail for hot and cold storage capacities. The results of the study indicated that the degree-hour method can be used in the design of hot and cold TES systems despite the temperature fluctuation. Insulation can be taken care of in hot fluid storage instead of cold alternative. With insulation in the underground spherical tank, it is observed than about 200 % energy savings is possible with approximately 50 % shorter payback period. For the hot fluid storage with insulation, as the storage fluid temperature, soil thermal conductivity and tank diameter rise and the depth falls, but the optimum insulation thickness value increases. As a result, this study is expected to be a guide for further seasonal TES applications using insulation in underground spherical tanks. Sun, 01 Jan 2023 00:00:00 GMT https://hdl.handle.net/20.500.12809/10863 2023-01-01T00:00:00Z