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
  • ISSN : 1229-6422 (Print)
  • ISSN : 2465-7611 (Online)

교차감염 예방을 위한 전실 유무에 따른 음압병실에서의 입자 유출 해석 A Numerical Study on Particle Migration for Prevention of Cross-Infection in Negative Pressure Isolation Room According to the Presence of Anteroom

https://doi.org/10.6110/KJACR.2019.31.3.099

Minji Jung ; Jin Kwan Hong

Negative pressure isolation rooms are used to contain infected aerosols within the room for patients with airborne infections. When the door is opened, the pressure difference in the two rooms cannot be maintained and this leads to the risk of cross-infection. Anterooms plays an crucial role in minimizing the escape of infectious particles into a corridor when the door is opened. However, most of the hospitals use isolation room with no anteroom when hospitalizing patients with infectious diseases like tuberculosis. Two cases were evaluated through the performance of CFD simulations to examine the effects of a healthcare worker walking in and out of isolation rooms, and door opening/closing on the transport characteristics of cough particles from the infected patient in the isolation room. The first case was a negative pressure isolation room with an open space corridor and no negative pressure. The second case was a negative pressure isolation room with anteroom both of which were negatively pressurized by mechanical ventilation. The simulation results showed that the movement of healthcare worker has a significant influence on airflow patterns by producing distinct wave flow regions which affect suspended particles. In both cases, air and cough particles from isolation rooms moved to the corridor and anteroom when the door opened and a healthcare worker walked out from the isolation room.

표면의 미세구조물 형상이 액적의 부착력에 미치는 영향 Effect of the Micro Structured Surface on Adhesion Force of Droplet

https://doi.org/10.6110/KJACR.2019.31.3.109

Gyu Dae Lee ; Ji Hwan Jeong

Condensation occurs when steam contacts a cool surface and attains a temperature below the saturation temperature. To understand the relationship between the surface energy and the change in the condensate behavior, it is necessary to understand the adhesive force. A host of researchers have employed the line contact analysis method to predict the adherence of droplets. However, it is difficult to apply this method to surfaces possesing different surface energy. To solve this challenge, recent studies have proposed a new model to predict droplets adhesion using surface area. The new model exhibited better adhesion predictions on flat surfaces compared to the earlier models developed from previous studies. In this study, the adhesion of droplets in the micro structured surface was analyzed. Moreover, the adhesion force model using the line contact model and the contact area was compared.

친유 처리를 한 접선 방향 입구를 갖는 사이클론 방식 유분리기의 성능 특성 Performance of a Cyclone-type Oil Separator with Tangential Inlet and Oleophilic Surface

http://dx.doi.org/10.6110/KJACR.2019.31.3.118

Joon Ahn ; Seongil Jang

CFD analysis shows that if the inlet of a cyclone type oil separator is eccentric; the pressure drop can be reduced while increasing the separation efficiency. It has also been shown that the application of oleophilic surfaces can lead to higher separation efficiency but lead to increased pressure drop. In the present study, an oil separator with an eccentric inlet was fabricated and the CFD prediction results tested through performance evaluation in the actual refrigeration cycle. When the inlet of the cyclone type oil separator is eccentric, the improvement in the separation efficiency was not significant compared with the result predicted using numerical analysis, but the pressure drop was greatly reduced. In conclusion, the pressure loss is greatly reduced when the inlet is eccentric. The separation efficiency was enhanced by about 15% with a 30% reduction in pressure drop with the application of an olephilic surface treatment on the geometry.

고효율 증기 분리식 2단 팽창 냉동 사이클 성능 특성 연구 Study on the Performance Characteristics of High Energy Efficient Refrigeration Cycle with Vapor Separation Two-stage Expansion Process

http://dx.doi.org/10.6110/KJACR.2019.31.3.124

Sang Kook Yun

The objective of this study was to improve the performance of the vapor compression refrigeration cycle comprised of a compressor, condenser, expansion device, and evaporator. In an original refrigeration system, a portion of the liquid refrigerant evaporates after the expansion process. The vaporized refrigerant does not have a role in the refrigeration effect in the evaporator. This study, therefore, aims to improve the energy efficiency by introducing a vapor separation mechanism in a two-stage expansion refrigeration cycle. In other words, the vapor separation process would separate the vapor from mixture beforehand so that higher amounts of liquid refrigerant flow within the evaporator. Results indicated a significant improvement of about 30% more than the existing refrigeration cycle using the new vapor-separated cycle, when a middle expansion pressure of 5 bars is applied in a typical R134a domestic freezer cycle with high pressure conditions of 10.166 barat 40℃ and low pressure conditions of 1.064 bar at -25℃. Moreover, since the mass flow-rate of the liquid phase in the evaporator decreased by about 15%~20% more than the current cycle, evaporator size could be significantly reduced.

상태공간 모델링에 의한 오일쿨러의 Robust LQG 제어기 설계 Robust Linear Quadratic Gaussian Controller Design for Oil Coolers Based on a State Space Model

http://dx.doi.org/10.6110/KJACR.2019.31.3.130

Seok Kwon Jeong ; Tae Eun Kwon

This paper presents a robust LQG controller design method by a state space model to improve control performance of a refrigeration cycle under process and measurement noise. First, a state-space model of an oil cooler is derived as a 4th order system equation using several governed equations based on a moving boundary model. Next, the LQG controller which uses the Kalman filter is designed using linear quadratic regulator (LQR) gain and the Kalman gain to minimize an evaluation function and the individual influence of noise. We can independently determine the two gains of LQR and Kalman by the Riccati equation using the separation theorem. If the weighted matrices of the evaluation function are designed to satisfy the desired control performance and energy condition input, the designer conclusively determines LQR gain. Finally, the validity of the proposed design method is validated by computer simulations and real experiments in several cases. The results of some of the simulation and experiments showed that the proposed method can be implemented as a robust control.