In this study, the overall energy status of Turkey in the early stage of the COVID-19 pandemic was analyzed. The situation in the energy market and electricity demand in the pandemic period as global issues were investigated in Turkey as a developing country. In addition to this general overview using limited data for the early period of the pandemic, energy demand and energy generation values were modeled utilizing machine learning approaches. Daily energy demand values were modeled and forecasted by utilizing Nonlinear Autoregression Neural Network (NARNN), Auto-Regressive Integrated Moving Average (ARIMA), and Long-Short Term Memory (LSTM) techniques. According to the results of the first stage of the modeling process, the LSTM approach was found as the most accurate model. In the second step of the modeling and forecasting analysis, monthly electricity generation values from natural gas and coal were predicted. In the energy generation forecasting analysis for April-December 2020 period, contraction in energy generation by natural gas and coal were obtained as 6.27% and 7.19%, respectively in comparison to 2019. Finally, the energy market during and after the pandemic was evaluated and the strategies to be implemented in the post-pandemic process were discussed.

Heat pipes are one of the most preferred equipment because they have a variety of superior specifications. In this paper, the improvement of heat transfer properties of a thermosyphon heat pipe that was filled with bauxite nanofluid was experimentally investigated for different nanoparticle concentrations (1%, 2%, and 4%) and surfactant types (Triton X-100 and Sodium Dodecyl Benzene Sulfonate). Bauxite nanoparticles at different concentrations were utilized for the preparation of nanofluid suspensions. Different kinds of surfactants were also doped into the prepared nanofluid suspensions to show off how a surfactant affects the thermophysical properties of the nanofluid. The experiments were done under several heating powers and various mass flow rates of the cooling water circulating on the evaporator section. Temperature distributions both upon the evaporator and the condenser sections were recorded via 8 different K type thermocouples. Cooling water inlet and exit temperatures were also recorded and utilized for theoretical calculations. For doing an experimental comparison, thermal efficiency and resistance of the thermosyphon heat pipe were determined both for distilled water and prepared nanofluid suspensions. Moreover, contact angle-wettability analysis was carried out to determine how nanoparticles affect the surface tension. The encountered problems during the tests were addressed and discussed. The obtained experimental data illustrated that the thermosyphon heat pipe efficiency was increased by up to 20.9% with the usage of a 2% (mass) concentration of bauxite nanofluid and an anionic surfactant. The maximum enhancement in heat pipe’s thermal resistance was found as 24.3%, through bauxite nanofluid usage.

In this paper, the effect of various zinc oxide aluminate spinel (ZnOAl₂O₃) and titanium oxide (TiO₂) nanoparticle concentrations on the thermal performance of the Diffusion Absorption Refrigeration (DAR) system is investigated. The main aim of the study is to increase the efficiency of DAR systems operating with low thermal performance. The first part of the study is experimentally tested on the system under the same ambient conditions in order to develop passive heat transfer using different nanofluids as working liquids, including ammonia/water solution containing different amounts (1 wt.% and 2 wt.%) of ZnOAl₂O₃ and TiO₂ particles. In the next part of the study, the tested system is designed in MATLAB/Simulink toolbox environment to compare experimental and numerical results. The use of nanofluids can increase the surface area expansion and the heat capacity of the fluid, resulting in a significant positive increase in heat transfer. The results clarify that the use of nanofluid as working fluid in the DAR system helps quicker evaporation, which reduces operating time and increases heat transfer in the generator. Compared to a base DAR system, the nanofluid solution with a 2 wt.% ZnOAl_2O3 nanoparticle concentration among other nanofluid and proportions causes a 57% increase in the coefficient of performance (COP) of DAR system.

Nanofluids have often been utilized lately for enhancing the thermal performance of heat transfer devices operating with a working fluid. In this study, using iron aluminate spinel nanoparticles, deionized water-based nanofluids at various mass concentrations (0.5%, 1.0%, and 2.0%) of nanoparticles were prepared and tested as the test fluid inside the heat pipes of the air-to-air heat exchanger operating between hot and cold air passages. The efficiency, as well as thermal resistance of the heat pipes, were investigated under varying Reynolds number combinations of hot and cold air passages. An increase up to 87.2% in efficiency and a decrease up to 71.6% in thermal resistance of the heat pipes were obtained with the utilization of magnetic nanofluid. Furthermore, the effect of nanoparticle concentration on performance was discussed.