Guee-Won Moon

In-Situ Diagnosis of Vapor-Compressed Chiller Performance for Energy Saving

In-situ diagnosis of chiller performance is an essential step for energy saving business. The main purpose of the in-situ diagnosis is to predict the performance of a target chiller. Many models based on thermodynamics have been proposed for the purpose. However, they have to be modified from chiller to chiller and require profound knowledge of thermodynamics and heat transfer. This study focuses on developing an easy-to-use diagnostic technique that is based on adaptive neuro-fuzzy inference system (ANFIS). The effect of sample data distribution on training the ANFIS is investigated. It is found that the data sampling over 10 days during summer results in a reliable ANFIS whose performance prediction error is within measurement errors. The reliable ANFIS makes it possible to prepare an energy audit and suggest an energy saving plan based on the diagnosed chilled water supply system.

Design and Performance Test of a Closed Loop Thermal Control System for Thermal Vacuum Chamber

A closed loop thermal control system simulates space thermal environment to verify the satellites` functionality in extremely cold/hot temperature. It is composed of a cryogenic blower, thermal shroud, heater, cryogenic valves. This paper presents an overview of closed loop thermal control system`s design parameter and test results for control parameter. A capacity of blower is calculated through energy balance equation and an advantage/disadvantage for a shroud material and a type was analysed. The thermal control system is controlled by a constant density of fluid in the system. A requested performance of closed loop thermal control system was verified by measuring a homogeneity and stability of shroud through control parameter such as density and RPM of blower.

A Study on the PZT Application for Spacecraft Components under Space Environment

In the high vacuum condition of the space, outgassing from any assembly of satellite can contaminate satellites, especially second surface mirror and optical lens, it cause satellite to fail in own missions. Therefore, all unit shall be check for compatibility with vacuum using CVCM (Collected Volatile Condensable Material) and TML (Total Mass Loss) in advance. CVCM and TML of the PZT-5 piezoelectric ceramic vibrator has less than 0.1% and 1.0% respectively. Also, it has less than 500 of Thermoelectric Quartz Crystal Microbalance for vacuum bake-out test using high temperature(more than ) and high vacuum (less than Pa). Thus, piezoelectric ceramic vibrator may be employed in the vacuum environments. Finally, it can be confirmed that the characteristics change of the piezoelectric ceramic vibrator is less than 1% under vacuum environments.

Development and Validation of Cryopanel Cooling System Using Liquid Helium for a Satellite Test

A cooling system utilizing liquid helium to chill the cryopanel (800 mm × 700 mm dimensions) down to 4.2 K was designed, implemented, and tested to verify the role of the cryopanel as a heat sink for the payload of a spacecraft inside the large thermal vacuum chamber (effective dimensions : 8 m (Φ) × 10 m (L)) of KARI (Korea Aerospace Research Institute). Two LHe (Liquid Helium) Dewars, one for the main supply and the other for refilling, were used to supply liquid helium or cold helium gas into this cryopanel, and flow control for the target temperature of the cryopanel within requirements was done through fine adjustment of the pressure inside the LHe Dewars. The return helium gas from the cryopanel was reused as a thermal barrier to minimize the heat influx on the core liquid helium supply pipe. The test verified a cooling time of around three hours from the ambient temperature to 40 K (combined standard uncertainty of 194 mK), the capacity for maintaining the cryopanel at intermediate temperatures, and a 1 K uniformity over the entire cryopanel surface at around 40 K with 20 W cooling power. § 이 논문은 2009년도 열공학부문 춘계학술대회(2009. 5. 20-22, BEXCO) 발표논문임 † Corresponding Author, wittycho@kari.re.kr 조혁진 · 문귀원 · 서희준 · 이상훈 · 홍석종 · 최석원 214 Fig. 1 Schematic of cryopanel cooling system W @ 85 K)을 위해서, 방열판에서 일정거리만큼 떨어져 설치된 가로 약 800 mm, 세로 약 700 mm, 두께 약 7 mm의 극저온패널을 40 K이하로 냉각시키고, 극저온패널 전 표면에 대하여 1 K 이내의 균일한 온도 분포를 갖도록, 액체헬륨 Dewar를 이용해 액체헬륨을 직접 극저온패널에 공급한 뒤 외부로 배출하는 방식을 적용하였다. 냉각 시스템의 선정시, 상용의 G-M 냉동기의 콜드헤드를 이용해 열전도 링크로 시편을 연결하는 방법과 압축된 헬륨가스를 G-M 냉동기의 콜드헤드와 열교환시켜 순환시키는 방법, 액체헬륨 액화기를 이용한 방법 등이 고려되었으나, 열용량과 시편 표면의 온도분포도, 사용 빈도, 제작 기간 등을 고려하여 경제성과 효율성을 최우선으로 하여 최종 액체헬륨 Dewar를 사용하는 방법이 선택되었다. 액체헬륨 Dewar를 사용해 직접 액체헬륨을 시험대상에 공급하는 경우, 사용된 액체헬륨을 외부로 그대로 배기하여 소모하기 때문에 시험 요구 조건을 만족시키는 범위 내에서 공급 유량을 최소화하여 액체헬륨의 소비를 최소화는 것이 시스템 효율화의 가장 중요한 목표가 된다.