Mobile QR Code QR CODE : Korean Journal of Air-Conditioning and Refrigeration Engineering
Korean Journal of Air-Conditioning and Refrigeration Engineering

Korean Journal of Air-Conditioning and Refrigeration Engineering

ISO Journal TitleKorean J. Air-Cond. Refrig. Eng.
  • Open Access, Monthly
Open Access Monthly
  • ISSN : 1229-6422 (Print)
  • ISSN : 2465-7611 (Online)

Korean Journal of Air-Conditioning
and Refrigeration Engineering

A journal devoted to investigations of HVAC and building technologies in various climatic conditions

• Editors-in-Chief: Doosam Song

바닥복사난방시스템에서 PCM 융해온도별 챔버 실험 Chamber Experiment by PCM Melting Temperature of Underfloor Radiant Heating System

https://doi.org/10.6110/KJACR.2022.34.8.353

Yong Ki Jung ; Seong Eun Kim ; Min Sang Yoo ; Yong Woo Song ; Jin Chul Park

This study conducted a comparative experiment of PCM melting temperature using a chamber for the purpose of providing basic data, to apply PCM to an underfloor radiant heating system. The underfloor radiant heating system in the chamber applied the standard floor structure of the apartment building, and the changes in indoor temperature and floor surface temperature were compared when none-PCM, 44℃, 35℃, and 28℃ PCM were applied to the lower part of the heating pipe. As a result of the experiment, the time required to reach the maximum temperature after operating the boiler at the indoor air temperature, was the fastest when PCM was not applied. And in the case of the floor surface temperature, the time to reach the maximum temperature was the fastest at 28℃ PCM. However, the time to reach the minimum temperature after the boiler stop, that is, the time to maintain heat, was the longest for indoor as well as floor surface temperatures, when 35℃ PCM was applied.

작동조건이 고체산화물 연료전지의 분극 특성에 미치는 영향 Numerical Analysis of the Impact of Operating Parameters on the Polarization Characteristics of Solid-oxide Fuel Cells

https://doi.org/10.6110/KJACR.2022.34.8.359

Namin Son ; Yuseung Won ; Kyungtae Park ; Woosung Park ; Jeeyoung Shin

Since the signing of the Paris Agreement in 2015, as a result, almost all countries have been tightening their environmental regulations to achieve the net zero goal by 2050. Accordingly, hydrogen energy is in the spotlight to replace carbon-based energy sources. Solid oxide fuel cell (SOFC) is considered an alternative resource for internal-combustion engines or fossil fuels, due to its high energy efficiency and zero pollutant emission. In this paper, a simulation of a single SOFC stack was developed using Aspen Plus. Performance data including output voltage at a different temperature, pressure, and porosity conditions are provided and analyzed. The results show that the output voltage is proportional to the operating temperature, pressure, and porosity. As operating conditions affect ohmic loss, activation loss, and concentration loss, performance optimizations are necessary for the economic operation of the fuel cell plant.

하이브리드 유하액막 증발기 성능에 관한 수치적 연구 Numerical Study on the Performance of Hybrid Falling Film Evaporator

https://doi.org/10.6110/KJACR.2022.34.8.371

Hak Soo Kim ; Wookyoung Kim ; Kong Hoon Lee ; Dong Ho Kim

The purpose of this study was to develop steady-state model of hybrid falling film evaporator, and to analyze performance of the heat exchanger. R1233zd(E) which is one of the low GWP refrigerants was selected as a working fluid. The steady state model was developed, based on the heat transfer correlations from previous studies for falling film evaporation and pool boiling using R1233zd(E). Based on the analysis results according to the number of nodes, the number os axial nodes was selected as 24. Performance analysis was conducted with respect to evaporator pressure, axial direction liquid refrigerant supply ratio from tray, rows of pipe for pool boiling region, and maximum heat transfer coefficient of falling film region. For the same heat capacity of the evaporator, the length of the pipe should extend approximately 3.6 times, when evaporator operation pressure increases from 49.2 to 58.4 kPa. The length of the pipe can be reduced approximately 18% as the number of rows for pool boiling region increases from one to three. The axial direction liquid refrigerant supply ratio from the tray also affects the performance of the evaporator. Compared to the equal supply ratio case, the pipe length must increase approximately 9%, when the axial direction liquid refrigerant supply ratio is 9:1 for the same cooling capacity. As the maximum heat transfer coefficient at falling film region increases from 5000 to 11000 W/m2K, the length of the pipe can be reduced approximately 27%.

열수송관의 음향 방출 및 진동 특징에 의한 누수 및 감육 탐지에 대한 실험적 연구 Experimental Study on Leak and Wall-thinning Detection by Acoustic Emission and Vibration Features of District Heating Pipe

https://doi.org/10.6110/KJACR.2022.34.8.380

Hyon Wook Ji ; Heela Jang ; Inju Hwang ; Hongcheol Lee

This study applied acoustic emission sensors and accelerometers to monitor and evaluate the conditions in pre-insulated pipes, the district heating pipes. These measurement techniques yield high accuracy in the monitoring of the pipes. The purpose was to detect leaks, which have been relatively well studied, as well as wall-thinning in the pipes. Measurement data were acquired from the acoustic emission sensors and accelerometers in a test facility with a 60-m long pipe. Filters determined through the spectral analysis of signals, considering the state of the pipes, were then applied. The results showed that leaks were detected in the low-frequency domain, whereas wall-thinning was detected in the high-frequency domain. Fifteen features were applied to the raw data and two types of filtered data, and three features that yielded the best detection performance were identified. The results were plotted in 3D coordinates, which enabled distinguishing the normal state, leak, and wall-thinning by visual observation.

심층신경망 기반 태양광열-공기열원 히트펌프 융복합 시스템의 성능예측모델 개발 Development of Performance Prediction Model for Integrated System Combining Photovoltaic-thermal and Air Source Heat Pump based on Deep Neural Network

https://doi.org/10.6110/KJACR.2022.34.8.390

Sangmu Bae ; Hobyung Chae ; Jinhwan Oh ; Soowon Chae ; Jin Woo Moon ; Yujin Nam

The purpose of this study was to develop the performance prediction model for integrated system combining photovoltaic-thermal and air source heat pump, based on a deep neural network (DNN) model. This paper describes the overall procedure of constructing the DNN model, to predict the performance of the integrated system such as data collection method, data set configuration, and the DNN model structure. To verify the reliability of the performance prediction model based on DNN model, the coefficient of variation root mean square error (CV(RMSE)) proposed by American Society of Heating, Refrigerating and Air-conditioning Engineers Guideline 14 was used. The CV(RMSE) between the predicted results of the DNN model, and the output variables was calculated as 5%. Thus, the reliability of the performance prediction model based on the DNN model was verified, and the performance prediction accuracy was similar to the energy simulation model.