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

불순물을 포함한 이산화탄소의 증발 열전달계수 압력강하 상관식 비교 Comparison of the Correlations Between the Heat Transfer Coefficient and the Pressure Drop of CO2 with Non-Condensable Gas

Ju Hee Jeong ; Rin Yun

The evaporating heat transfer characteristics and the pressure drop of carbon dioxide, including impurities, were experimentally measured and compared with the predictions from existing models. The experimental setup consisted of a test section, a condenser, and a heating part. The test section used double-tube type, and the copper tube of 1/2 inch was located inside the PVC pipe. Total length of the test section was 4 meters. The temperature of carbon dioxide was measured by attaching the thermocouple to the test part using soldering. In addition, the temperature of the brine was measured by inserting the T-type thermocouple through the hole in the outer tube in order to measure the brine temperature in the PVC tube. The CO2 mixture after the test section was condensed by using two plate-type heat exchangers. The impurity of nitrogen concentration was transformed by 1.0~5.0 wt.% under 400~500 kg?m-2s-1 conditions. The heat transfer coefficients of pure CO2 and CO2+N2 were compared by using the Shrock and Grossman model, the Gungor and Winterton model, and the Yoon et al.’s model. The pressure drops were compared using the Muller-Steinhagen model, the Heck and Chislom models, and the Yoon et al.’s model. The Yoon et al.’s model and the Chislom model showed the best performance when predicting the boiling heat transfer coefficient and pressure drop for the CO2+N2 mixture, respectively.

데이터센터 냉각시스템 열복도 및 냉복도 차폐에 따른 공조성능 비교의 실험적 연구 An Experimental Comparison Study on the Thermal Performance of Hot- and Cold-Aisle Containment Systems for Data Center Cooling

Jinkyun Cho ; Woosin Choi ; Seungmin Jang ; Jaehyung Lee ; Chihyeon Park ; Seunghwan Lee

With the increased awareness of data center cooling and its energy cost impact, the hot aisle containment (HAC) system and the cold aisle containment (CAC) system are considered to be two of the most prominent techniques for IT environment control. This study investigated the thermal performance of the two systems in an experimental test, analyzing the thermal environment based on the inlet and outlet air temperature distribution according to the type of IT equipment. The filed measurements show that the HAC is more effective at cooling the IT equipment. The supply air temperature of the HAC system can be raised by 2.0℃, but the IT operation environment will be similar to that of the CAC system. The distributions of SHI and RHI of the HAC system were higher than those of the CAC system by 17.4% and 14.8%, respectively. Moreover, RTI was improved by 26.1%. This paper analyzes both systems and highlights the reasons why HAC is often the preferred solution. Even though the HAC could maintain a more stable IT environment than the CAC, the air distribution efficiency still operated imperfectly with losses in the distribution path and a mixing of hot and cold air. The development of a prototype of a fully air containment system could be a possible future development, as it could improve the two systems we tested and result in a lower risk of air recirculation and bypass.

1/4 공진기 기반 음향 메타물질의 광대역 차음성능 평탄화를 위한 내부 구조 설계 Parametric Design for the Broadband Flatness of Acoustic Metamaterial Based on a 1/4 Resonator

Seoung Ho Baek ; Sang Hu Park

For low-frequency sounds, within the audible region (20~20000 Hz), an insulation plate is traditionally used in order to control for the sounds’ resonance. This method has some disadvantages however, due to its narrow operating frequency zone, and the thickness of an insulation plate’s volume, which varies according to the operating sound wavelength. Recently, acoustic metamaterials have been developed in order to overcome such limitations. In this work, we have studied the design parameters of a 1/4 resonator in order to design a modified 1/4 resonator which flattens transmission loss by shaping its inside structures. The resonator consists of continuous resonance arrangements around a central sound flow path, with this resonator having been originally designed in a previous study. Five design parameters for internal structure application were selected, and then parameter analyses were performed via two steps. As a result, through the formation of the internal structure, we can achieve a new acoustic metamaterial structure which has smaller standard deviation and a smaller difference between the maximum and minimum transmission loss compared to those of the previous one. Through this work, we optimized the 1/4 resonator to be the higher broadband flatness of transmission loss.

소형 쇼케이스용 증기압축사이클에서의 액인젝션을 이용한 포화압축 사이클 가능성 검토 Potential Benefits of Saturation Compression Cycle with Liquid Injection in Showcase Vapor Compression Cycle

Jeong Choe ; Jongmin Jung ; Yongseok Jeon

The objective of this study is to decrease the refrigerant temperature at the compressor outlet under high thermal load conditions with low-GWP refrigerants in the showcase vapor compression cycle. When the outside temperature increases, the showcase cycle suffers a reliability problem due to the high discharge temperature. Liquid injection is a good method for decreasing the discharge temperature of the refrigeration cycle. This study presents the development of a simplified simulation model for predicting the performance of a liquid injection showcase cycle. The optimum injection pressures of the showcase cycle with R410A and R32 were presented. In addition, after the quasi-saturation compression cycle was reached through the multi-stage liquid injection control, the effect of reducing the discharge temperature was analyzed. Finally, the optimal number of injections for each of the refrigerant and operating conditions was presented.

열회수형 환기장치 적용 시 다중이용시설의 환기횟수에 따른 냉·난방부하와 감염률 Thermal Load and the Probability of Infection according to the Ventilation Rate of Multi-Use Facilities Applying ERV

Somi Jang ; Yujin Ko ; Bokyung Park ; Hiki Hong

Recently, confirmed patients of COVID-19 continue to occur in multi-use facilities, and cases of aerosol infection increase in non-ventilated spaces. As ventilation rate increases, the virus infection rate decreases exponentially, but forced ventilation for reducing the infection rate leads to energy loss. In this paper, a cafe was selected the same as the previous paper. TRNSYS18 was used to calculate the heating and cooling loads according to ventilation rates and methods. Based on this, the correlation with the infection rate was analyzed. During heating operation, the heating loads increased as ventilation rate increased, and the heating sensible loads were particularly affected. Ventilating with 3 ACH, the heating loads increased by 14 times for forced ventilation, compared to non-ventilated. Applying ERV, the heating loads increased by 3.5 and 3.3 times for the plate and rotary respectively. The cooling latent loads increased significantly as ventilation rate increased, compared to non-ventilated during cooling operation. Ventilating with 3 ACH, the cooling loads increased by 2 times for forced ventilation, 1.6 and 1.2 times for the plate and rotary respectively. When infected and non-infected people stay in the same space for 5 hours without wearing a mask, it is possible to keep the infection rate below 2% with 3 ACH. As a way to prevent the spread of COVID-19, ventilation is very effective, and considering energy savings, ERV introduction is essential.