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원형 및 사각타원 전열관을 이용한 냉장고 증발기용 핀-튜브 열교환기의 공기측 열유동 비교평가
강준우,김진훈,이효인,정지환 대한설비공학회 2022 설비공학 논문집 Vol.34 No.10
The objective of this study was to improve performance of heat exchanger for household refrigerator by modifying the shape of heat transfer tube used in the existing evaporator. In the case of a fin-tube heat exchanger, the thermal resistance accounts for 60 to 80%. It occurs in the air-side heat exchange area, which has a great influence on performance. Existing round tube was replaced with a round rectangle tube to reduce air thermal resistance and improve thermal conduction performance. When a heat exchanger with a round tube was changed to a heat exchanger with a round rectangle tube, the f-factor decreased and the j-factor increased. The pressure loss of the air side inlet was also reduced in the round rectangle tube. Thus, changing the shape of a round tube fin-tube heat exchanger to a round rectangle tube can increase the efficiency of an energy system. 본 연구에서는, 냉장고용 증발기 튜브의 형상이 열교환기 성능개선에 미치는 영향을 수치해석과 실험을 통해 조사하였다. 수치해석과 실험 모두 열교환기의 성능이 개선되었으며, 그 결과는 다음과 같다. (1)해석결과 사각타원 튜브로 변경한 경우, friction-factor는 9.8%에서 최대 17.7%까지 감소하였으며, j-factor는 1.6%에서 최대 3.7% 증가하였다. (2) Area goodness factor 비교 결과, 사각타원 튜브를 적용할 경우, 성능은 최대 23.6% 개선되었다. 또한, Volume goodness factor 비교 결과, 사각타원 튜브를 적용할 경우, 성능은 최대 8.5% 개선되었다. (3) 실험결과 사각타원 튜브를 이용한 경우, 압력손실이 12% 감소하였으며, UA 비교 결과, 사각타원 튜브로 변경하였을 때, 5.3% 개선되었다. 또한, 에너지 비율로 비교한 결과, 사각타원 튜브 이용한 경우가 약 9%의 성능 향상을 보였다. 수치해석 및 실험결과 모두, 사각타원 튜브 열교환기의 성능이 향상되었다. 이를 통해 냉장고 증발기의 튜브를 사각타원 튜브로 변경할 경우 냉각성능 향상을 통한 에너지 효율 개선이 기대된다.
강준우 ( Jun-woo Kang ),장준복 ( Jun-pok Chang ),유지현 ( Ji-hyun Yoo ),도은수 ( Eun-soo Doh ),길기정 ( Ki-jung Kil ) 대한본초학회 2016 大韓本草學會誌 Vol.31 No.6
Objectives : This study was performed to investigate the antioxidant activity of water and ethanol extracts from Sasa borealis leaves, stems and roots. Methods : Sasa borealis leaves, stems and roots extract were prepared using water and ethanol. The total polyphenol and total flavonoid contents were analyzed. 2,2-diphenyl-1-picrylhydrazyl(DPPH) radical scavenging activity, SOD like activity, 2,2`-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)(ABTS), hydroxyl radical scavenging activity, and Nitrite scavenging activity assays were carried out to determine the antioxidant activities. Results : The antioxidant activities of the Sasa borealis appeared higher in ethanol extract than water extracts. Total polyphenol and total flavonoids contents in ethanol extracts of leaves were 24.6 ㎎/㎖ and 14.3 ㎎/㎖, respectively, which were much higher than those of any other parts. SOD like activity was 70% ethanol extract of the leaves was highest with 15.68%. Electron donating ability was 70% ethanol extract of the leaves had the highest 59.07%. It exhibited high electron donating ability than BHT(45.68%). Nitrite scavenging activity of 70% ethanol extract was higher than the water extract at pH 2.5 and pH 4.2. Nitrite scavenging activity was 70% ethanol extract of the leaves was the highest 75.2%. Hydroxyl radical scavenging activity was 70% ethanol extract of the leaves was highest with 16.16%, showed very low activity than BHT(61.56%). Conclusions : These results suggest that 70% ethanol extracts from Sasa borealis leaves, exhibited higher antioxidant activities than those of root and stem, and can be potentially used as proper natural antioxidants.