https://doi.org/10.6110/KJACR.2026.38.3.119

Chae Hyung Ryu ; Hyoin Lee ; Ji Hwan Jung

This study examines the prediction accuracy of heat transfer performance in air-cooled heat sinks using various dimensional analysis methods. We developed 0D, 1D, and 3D analytical approaches and conducted both experimental and numerical analyses under different airflow conditions. The comparison of experimental and analytical results showed that the 3D CFD analysis achieved the highest prediction accuracy, with a maximum relative error of 8.42% across all airflow rates. However, it required approximately 37 hours and 24 minutes of computation time, making it the most computationally intensive option. In contrast, the 0D and 1D analyses only needed about 0.001 seconds, demonstrating superior computational efficiency but exhibiting larger deviations, with relative errors ranging from -6.17% to 46.58%. These findings highlight the importance of carefully considering flow characteristics and operating conditions when conducting dimensional analysis of air-cooled heat sinks, and they underscore the need to select the appropriate dimensional approach based on the analysis's purpose and required accuracy.This study examines the prediction accuracy of heat transfer performance in air-cooled heat sinks using various dimensional analysis methods. We developed 0D, 1D, and 3D analytical approaches and conducted both experimental and numerical analyses under different airflow conditions. The comparison of experimental and analytical results showed that the 3D CFD analysis achieved the highest prediction accuracy, with a maximum relative error of 8.42% across all airflow rates. However, it required approximately 37 hours and 24 minutes of computation time, making it the most computationally intensive option. In contrast, the 0D and 1D analyses only needed about 0.001 seconds, demonstrating superior computational efficiency but exhibiting larger deviations, with relative errors ranging from -6.17% to 46.58%. These findings highlight the importance of carefully considering flow characteristics and operating conditions when conducting dimensional analysis of air-cooled heat sinks, and they underscore the need to select the appropriate dimensional approach based on the analysis's purpose and required accuracy.

https://doi.org/10.6110/KJACR.2026.38.3.130

Youngbok Lee ; Kibong Kim ; Bong Seong Oh ; Junhyun Cho ; Gil-bong Lee ; Hee-Hwan Ko ; Bongsu Choi

This study examines the reduction of refrigerant charge for R1336mzz(Z) through heat transfer analysis in a falling film evaporator designed for industrial high-temperature heat pumps. A lab-scale test facility was established to evaluate two types of heat transfer tubes?bare tubes and E-tubes?under film Reynolds numbers ranging from 100 to 550 and heat fluxes between 5 and 25 kW/m². The results indicate that the falling film heat transfer coefficient for the bare tube increased with heat flux, demonstrating a strong dependence on surface nucleation boiling dynamics. In contrast, the E-tube showed nearly constant values regardless of heat flux, suggesting that the surface enhancement resulted in fully developed nucleation boiling. To further explore the potential for minimizing refrigerant charge, a hybrid evaporator configuration combining flooded and falling film operation was compared to a conventional flooded evaporator using E-tube conditions. The hybrid system achieved a 48% reduction in refrigerant charge per unit of evaporation capacity while maintaining comparable evaporation performance. These findings underscore the benefits of using falling film evaporators with advanced tube designs, which provide improved thermal performance and a significant reduction in the use of costly, low-GWP refrigerants like R1336mzz(Z). This work lays the groundwork for the practical design of high-temperature heat pumps aimed at industrial steam production.

https://doi.org/10.6110/KJACR.2026.38.3.141

Dong Ho Kim ; Yu Jun Jung

This study presents a control strategy for utilizing an industrial heat pump in the paper drying process, which has been experimentally validated. To address the challenge of intermittent waste heat disconnection, we stabilized the heat source temperature by redirecting heat through a plate heat exchanger, thereby reducing the need for large storage tanks. We modeled the dynamics of the heat exchanger using system identification and optimized a PI controller for the control valve through a state-space model in Simulink. In nine experimental trials, we successfully maintained the heat pump inlet temperature within ±0.5 K of the target, achieving stable responses without excessive oscillation. These findings demonstrate that the proposed strategy enables continuous and reliable operation of MW-scale heat pumps in environments with intermittent waste heat, while also reducing equipment stress and minimizing the required size of storage tanks.

https://doi.org/10.6110/KJACR.2026.38.3.149

Ho-Sung Choi

This study investigates the dynamic response characteristics of a cooling water piping system (CWS) by comparing the response spectrum recorded during the 2017 Pohang earthquake with the design response spectrum outlined in the Korean Design Standard. Due to its large diameters and significant mass, the CWS is heavily influenced by inertial forces during seismic events, making it an effective benchmark for evaluating the applicability of design response spectra. Response spectrum analyses were performed using Bentley's AutoPIPE to evaluate pipe stress ratios, resultant displacements, and anchor forces under various load combinations. The findings reveal that the stress and displacement responses derived from the Pohang earthquake spectrum show spatial distributions and relative magnitudes similar to those obtained from the Korean Design Standard spectrum. Additionally, consistent response patterns were identified across different load combinations for both spectral inputs. Regarding anchor forces, thermal expansion loads dominated the response at certain locations. However, for specific load combinations, seismic loads generated anchor forces that were comparable to or even greater than those caused by thermal effects. These results suggest that, in the absence of site-specific earthquake records, the Korean Design Standard response spectrum serves as a reliable and practical foundation for assessing the seismic performance of CWS.

https://doi.org/10.6110/KJACR.2026.38.3.159

Hyun Seok Dong ; Jae Beom Jeon ; Hye Rin Han ; Sang Hyun Jeon ; Brian Baewon Koh ; Sean Hay Kim

Determining occupancy status is crucial for effective facility control, particularly for optimizing thermal comfort and energy efficiency. However, occupancy detection based solely on baseline electrical energy values tends to be less accurate in residential buildings that do not rely on electrical heating during winter. This study aims to assess occupancy status and extract occupant schedules by analyzing energy consumption data from high-rise residential buildings. We collected energy data from actual apartments during the winter season and employed Fast Fourier Transform for correlation analysis with electricity usage. The results revealed that heating energy had the strongest correlation with electrical energy, yielding a correlation coefficient of 0.72. For data exhibiting low occupancy probabilities, we applied unsupervised learning models, specifically the Gaussian Mixture Model and Hidden Markov Model, to adjust existing occupancy probabilities using available heating energy data, ultimately calculating refined final occupancy probabilities.

https://doi.org/10.6110/KJACR.2026.38.3.167

Chang Jae Lee ; Ja Kang Yang ; Su In Chae ; Sang Ki Jin

Nuclear power generation facilities are among the most stable and reliable sources of electricity for modern society. However, the inherent risks associated with radioactive materials have heightened the emphasis on effective management and decommissioning strategies. This study examines critical issues related to the safe dismantling of nuclear power facilities, which is vital for the sustainable and secure use of nuclear energy. The research focuses on developing sound estimation and allocation methods for decommissioning costs. The analysis indicates that actual dismantling costs may exceed previous estimates by approximately 20?30%, highlighting the need for adequate financial and technical preparation. Additionally, the study underscores the importance of clearly defined roles and close collaboration among government bodies, industry, and the private sector to ensure safety and efficiency during the dismantling process. It also stresses the need for regional and international cooperation, as potential accidents related to decommissioning could have transboundary effects. The findings conclude that transparent information sharing, openness in the dismantling process, and mutual cooperation are essential for achieving safe and sustainable decommissioning of nuclear power plants.