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IV. 연구개발결과
1. 냉동유닛 설계 조건 설정 및 시스템별 pilot 제작 및 시험 운전
○ 유도에너지 회로장치 개발을 위하여 교류 전압과 직류 전압을 이용한 정전기장 유도장치 설계 방식을 검토하고자 하였으며, 이에 교류(0~1,500V), 직류(-900~0V)변환 가능한 제어부 설계, AC-DC 변환기 전압조절 회로도를 검토하고, 전압조절용 가변 변압기, 승압트랜스, 전류제한저항장치, 전압조절가변저항, AC/DC변환기, 열교환기, 송풍팬, 스텐레스용기, 절연지지대 등으로 설정·검토하였음

○ 냉동물성을 증

IV. 연구개발결과
1. 냉동유닛 설계 조건 설정 및 시스템별 pilot 제작 및 시험 운전
○ 유도에너지 회로장치 개발을 위하여 교류 전압과 직류 전압을 이용한 정전기장 유도장치 설계 방식을 검토하고자 하였으며, 이에 교류(0~1,500V), 직류(-900~0V)변환 가능한 제어부 설계, AC-DC 변환기 전압조절 회로도를 검토하고, 전압조절용 가변 변압기, 승압트랜스, 전류제한저항장치, 전압조절가변저항, AC/DC변환기, 열교환기, 송풍팬, 스텐레스용기, 절연지지대 등으로 설정·검토하였음

○ 냉동물성을 증진시키기 위한 방안으로 냉동유닛에 적용할 전자기장에너지발생장치를 구상하기 위하여 발생장치의 controller는 입력전압, 출력전압 제어, 전압안정 및 주파수 안정화 등을 검토하였고, 발생기는 최대 3,500 G 발생 및 입력단자 제어가 가능하도록 하여 실험용제원으로 사용 가능하도록 제작하였음

○ 냉동물성을 증진시키기 위한 방안으로 냉동유닛에 적용할 초음파에너지발생장치는 발진기의 출력이 10W~250W (220 V, 40kHz)로 조절이 가능하도록 하였으며, 진동부는 40kHz 고정형 소자와 Transduce 및 출력 크넷터 등을 적용하여 실험용 제원으로 사용 가능하도록 제작하였음

2. 저온용 컨테이너 및 용기의 단열재 선정 및 부하용량 산출
○ 냉동 및 저온용 컨테이너/용기에 사용될 수 있는 단열재 종류별 단열특성을 조사·검토하였고 이를 활용하여 냉동 및 냉장 시스템에 적합한 단열재 소재의 최소 사양을 우레탄폼형, 35kg/m³ 이상, 0.02 kcal/m·℃·hr 이하로 설정하였음. 또한 냉동장치의 제작을 위한 부하용량 산출식을 고려하여 벽면 침입열량, 냉각열량, 피대상물 냉동소요열량, 호흡열, 포장재의 냉동부하 등을 냉동장치 제작 요소로 설정하였고, 이에 따라 온도범위(0~ -20℃), 온도편차 (±0.5℃), 유효면적 (590×450×600 : L×W×H mm), 재질 SUS, 냉매 R503으로 구성하였음.

3. 냉동유닛의 적용을 위한 대상 시료의 냉동 품질 비교
○ 냉동장치별 동결속도에 따른 열물성치 측정을 위하여 냉동 유닛의 구상 및 검토를 통한 실험용 유닛은 부착용 전자기장에너지 발생장치 및 초음파에너지 발생장치를 실험용으로 구현하여 사용하였음. 냉동유닛별 냉동특성을 조사하여 냉동유닛의 적용방안과 시제품에 대한 요소 데이터를 확보하고자 냉동장치별 동결속도에 따른 열물성치를 측정한 결과, 전자기장에너지를 적용한 냉동유닛은 최대 -8.9℃까지 과냉각현상이 발생하였고 최대 유지시간이 10,170 sec로 나타내었으며, 냉동압력은 최대 45% 감소하였고, 해동압력은 27%(약 1.8 psig) 감소하는 것으로 나타남. 전자기장에너지를 적용한 냉동유닛은 위치 및 강도에 따라 결과값이 달리 나타났고, 빙결정온도대 유지기간은 증가했으나 3,200 G의 전자기장에너지 발생 조건에서는 빙결정대 이하로 시료가 냉각되지 않은 것으로 나타내었음. 초음파에너지 적용 냉동유닛에서 출력 변화에 따른 특성을 조사한 결과 10 W의 출력조건에서 시료 온도가 빙결점이하의 온도로 내려가지 않았으며 온도 상승효과를 나타내었음.

○ 냉동유닛의 적용시험은 돼지고기, 당근, 양파, 사과를 대상 시료로 하여 냉동곡선, 냉동압력, 해동곡선, 해동압력 및 drip loss 등을 비교 분석하였음. 정전기장에너지를 활용한 냉동고의 시료가 대조구에 비하여 냉동내압은 2.9~25%가 감소하였고, 냉동속도는 0~6.1% 증가하였으며, drip loss는 14~73% 감소하는 것으로 나타내었음. 그러나 온도별(-10℃ 및 -15℃) 및 시료별 품질 향상 효과의 차이는 발생하였으나 증류수와는 달리 과냉각 현상을 발생하지 않았음.

4. 시스템의 성능평가를 위한 내부 온도분포 및 공기 유동장 해석
○ 냉장고의 온도 흐름에 대한 변화 추세 및 해석을 위하여 벽면을 통한 열플럭스에 대한 전달식을 검토하고 냉동고의 온도분포를 측정한 후 이를 적용하여 온도분포 및 유동속도를 해석화하고자 하였음. 온도분포 및 유동흐름은 윗부분에 비하여 아랫부분에서 열손실이 가장 낮은 것으로 나타남. 또한, 냉장고 냉각온도와 시료간의 열적조건 변화에 따른 수치해석 및 온도분포도 해석을 위하여 대류현상에 의한 냉각특성을 수치해석 조건을 도입하여 열유동장 해석을 실시하여 냉동실의 위부분에 비하여 아랫부분에서 열흐름이 안정하다는 것을 알 수 있었으며, 또한 열화상카메라를 이용한 냉각온도의 변화 및 분포도 측정에서도 유사한 결과를 보였음.

5. 고전압 정전기 유도 냉동고의 시스템 설정, 표준설계도면 작성 및 시제품 제작
○ 시제품에 대한 상세 설계 및 표준도면을 작성하고자 하였음. 시스템은 회로장치, AC/DC 변환기, 전압조절 회로도, 냉동기용 전기회로도로 구성하였으며, 회로장치는 교류(0~7,000 V) 변환 가능한 제어부로 설계하였음. 주요 장치로서는 유도전압조절용 가변변압기, 승압트랜스, 전류 제한 저항장치, 냉동실 내로의 유도 전기장 발생 전극, 냉동실 내로의 연결 장치, 전기 차단 안전장치 등으로 구성하였음.

○ 실험용 시스템 제작은 시판용 냉동고에 고전압 유도 냉동 시스템을 부착 및 개조하여 시스템을 구성하였으며, 고전압발생 전압 범위는 0~7,000V, 온도분포는 0℃~ -20℃ 범위, 온도편차는 ±0.5 ℃의 성능을 가지는 냉동고를 시제품으로 설계 제작하였음.

6. 고전압 정전기 유도 장치를 적용한 냉동기의 픔질 특성 분석
○ 기본 물질 및 대상 시료에 대하여 동결 방식에 따른 품질 비교를 실시하고자 하였음. 동결방식은 고전압 정전기 유도 방식의 냉동고 (7,000V)와 일반 냉동고로 구분하였으며, 시료는 증류수를 기본 시료로 하고 감자, 쇠고기, 사과를 사용하였고, 처리 온도는 -20℃로 냉동하였음. 세포손상도는 전도도, TDS, Ion leakage 및 BIA 분석으로 실시하였으며, 조직학적 분석은 H&D 염색법과 SEM 분석을 실시하였음. 고전압 정전기 유도 방식의 냉동고는 일반냉동고에 비하여 전도도가 감자는 25%, 소고기는 30%, 사과는 32%가 감소하는 것으로 나타났으며, TDS에서는 감자는 23%, 소고기는 10%, 사과는 23% 감소하는 것으로 나타났음. 또한, Ion leakage 측정에서는 감자는 5~12%, 소고기는 3%, 사과는 18~20% 감소하는 것으로 나타났으며, BIA 분석은 감자, 소고기, 돼지고기 정전기 유도 방식을 적용한 냉동시료에서 resistance value가 증가하여 세포손상도가 낮아지는 것을 나타내었음. 조직학적 분석에서도 세포손상도와 유사한 결과값을 나타내어 H&E 염색 분석에서 정전기장 유도 방식을 적용한 냉동시료에서 빙결정 생성으로 인한 세포외벽 부분의 두께 감소가 뚜렷이 나타나며, 세포의 형태에서도 생시료에 더 가까운 형태로 관찰되었음. SEM 분석에서도 감자, 소고기, 대구 시료의 정전기장 유도방식을 적용한 동결시료의 미세구조가 상대적으로 규칙적인 것으로 나타내었음.

○ 냉동처리조건 및 온도별 품질변화 측정을 위하여 고전압 정전기장 유도에너지를 적용한 냉동고에서 -20℃와 -10℃ 냉동온도와 정전기 유도 에너지 발생 전압 변화(0V, 3,000V 및 7,000V)에 따른 품질 특성을 비교하였음. 드립량에서는 대구 시료가 최대 36.25%, 소고기는 최대 45.02%, 감자는 최대 29.09% 감소하였으며, VBN은 대구 시료에서 최대 8.1%, 소고기는 최대 20% 감소하였음. 또한 정전기장의 강도가 강할수로 드립령이 감소되었고, 비타민C 함량은 증가되는 것으로 나타났음.

7. 마이너스 해동에 따른 효과 분석

○ 마이너스 해동 조건에 따른 효과 분석을 위하여 고전압 정전기장 유도에너지를 적용한 해동장치를 해동 조건에 적용하였음. 해동 평균 온도는 -1.5℃로 설정하였음. 고전압 정전기장 유도에너지 적용 마이너스 해동 효과의 평가를 위하여 시료의 냉동조건은 -20℃ 일반 냉동을 실시하였고, 해동조건은 정전기 유도 적용 해동기(-1.5℃), 일반해동기(-1.5℃), 2℃ 및 실온(25℃)으로 비교 실시하였음. 정전기장 처리구에 있어 드립율은 감자 시료가 25℃의 해동 조건에 비하여 41.38%, 2℃에 비하여 37.49%, -1.5℃ 일반해동기에 비하여 27.39%의 감소 효과를 나타내었고 소고기에서도 25℃에 비하여 57.41%, 2℃에 비하여 47.33%, -1.5℃에 비하여 17.59%의 감소 효과를 나타내었음. 방울토마토에서도 25℃ 대비 80.24%, 2℃ 대비 68.91%, -1.5℃ 대비 42.15%의 감소 효과를 나타내었음.

○ 고전압 정전기장 유도에너지 적용 냉동시료의 일반해동 중 변화를 관찰하기 위하여 감자를 시료로 하여 측정한 결과 일반 냉동시료에 비하여 총페놀함량은 5.6% 증가, 항산화활성은 2.8% 증가, 갈변도는 36.5% 감소, 색도는 최대 L값이 57% 감소하였고, △E값은 41% 감소하는 것으로 나타났음. 또한, 정전기장 유도에너지를 적용한 냉동 및 해동 방식의 시스템 적용에 대한 냉동 시료의 품질 비교를 위하여 냉동조건으 정전기 유도 방식 적용 냉동(7,000V, -25℃)과 -20℃ 일반 냉동으로 구분하고, 해동조건은 정전기 유도 적용 해동기(-1.5℃)와 일반해동기 (-1.5℃, 2℃, 10℃)로 구분하여 실험을 실시하였음. 실험 결과, -10℃ 해동에서는 고전압 정전기장 처리 냉동시료의 드립율 감소 효과가 나타나 감자 시료가 39%, 소고기 시료가 35% 감소효과를 나타내었음. 정전기장 -1.5℃ 해동에서 고전압 정전기장 처리 냉동 시스템의 냉동시료에서 감자 시료가 40.9%, 소고기가 23%의 드립율 감소를 나타내었음. 총균수에 있어서도 정전기장 냉동 및 해동 시료가 해동시 미생물 증식이 억제되는 것으로 나타났으며 온도분표도 측정에서도 해동 속도가 증가되는 것을 나타내었음.

8. 현행 냉동조건과의 품질 비교 시험
○ 저장온도별 및 방법 등에 따른 비교를 위하여 감자, 소고기, 대구에 대하여 고전압 정전기 유도 에너지를 적용 후 2개월간의 단기 저장 중의 효과를 비교 분석하였음. 정전기 유도 에너지 적용 냉동 조건은 고전압 7,000V 조건에서 -20℃ 및 -10℃에서 냉동하였으며, 일반냉동고도 -20℃ 및 -10에서 처리하였음. 냉동 후 저장온도는 -20℃와 -40℃의 온도에서 저장하면서 2개월간의 드립률, TBA, VBN, Vit C, pH, 미생물 및 색도의 변화를 관찰하였음. 실험결과, 대구의 경우 고전압 정전기 유도 에너지를 적용한 시료에서 드립률은 15.0~27.5%, TBA는 7.0~47.8%, VBN은 32.63~47.9%가 감소하였으며, 쇠고기에서는 드립률은 5.5~22.13%, TBA는 8.3~23.07%, VBN은 7.15~26.34%의 감소를 나타내었음. 감자에서도 드립률이 4.4~19.73% 감소하였고, Vit C 함량은 0~23.4% 증가하는 것으로 나타났음. 반면 pH, 미생물 함량 및 색도에서는 시료간의 차이는 저장 중 발생하지 않았음.

9. 단위 시스템 적용에 따른 냉·해동 품질평가
○ 냉동 및 해동 조건을 달리한 쇠고기 및 감자에 대한 품질을 평가함. 처리조건은 일반냉동 후 일반 해동 (GF-GT), 전기장 냉동 후 일반 해동 (EF-GT), 일반 냉동 후 전기장 해동(GF-ET) 및 전기장 냉동 후 전기장 해동(EF-ET) 처리를 하였으며 24시간 냉동 후 15시간 해동하여 분석하였음. 처리구들의 pH는 소고기는 5.49~5.55 수준, 감자는 6.04~6.11 수준으로 처리구들 간에 차이를 나타내지 않았음. 드립률은 해동시간동안 증가하는 경향을 나타내었으며 전자기장 해동처리구인 GF-ET와 EF-ET 처리구가 낮게 나타났음. 감자의 색도변화는 GF-GT처리구의 △E값은 27.15로 가장 높게 나타났으며 EF-ET(16.82)와 차이를 보였음. 소고기의 TBA 값과 VBN 값의 경우 전기장에서의 해동 처리구가 낮은 값을 나타내었음.

10. 정전기 유도에너지의 에너지 강도에 따른 품질 변화
○ 정전기 유도에너지의 에너지 강도에 따른 품질 변화를 측정하기 위하여 감자 시료를 이용하여 냉동 처리조건 1,500, 3,000, 5,000, 7,000V로 설정하여 냉동한 후 일반냉장고와 정전기장 냉장고에서 해동 후 품질을 비교하였음. 냉동시 감자의 최초 빙결정 형성 온도는 대조구가 -5.8℃였으며 정전기장 처리시 -6.4~-6.0℃로 빙결온도가 떨어지는 것을 확인할 수 있었으며, 해동곡선에서는 해동시 일반해동에 비해 정전기장 해동시 해동시간이 길게 나타났음. 드립율은 냉동방법에 관계없이 정전기장 해동법이 일반 해동법에 비해 낮게 나타났으며, 3,000V 및 5,000V 냉동처리 조건에서 7.22%로 일반 해동법에 비하여 약 28% 이상 감소하는 것을 나타내었음.

11. 최적 시스템 조건 설정을 위한 냉동 조건에 따른 품질 변화
○ 냉동 처리 조건에 따른 소고기의 품질 변화를 조사하기 위하여 냉동 처리를 위한 에너지 강도에 따른 냉동 효과를 측정하였음. 에너지강도는 0, 3,000V 7,000V로 달리하여 저장한 소고기의 품질을 평가하였음. 실험 결과 pH는 시료간에 큰 변화를 보이지 않았으며 저장기간 동안 증가하는 경향을 나타내었음. 드립률은 냉동 처리 직후 2.93~3.56% 수준이었으며 저장기간동안 증가하여 저장 6개월째 대조구 7.23%, 7000V 처리구 5.05%로 나타났음. 수분함량은 저장 기간별 처리구별 차이를 보이지 않았으며 보수력은 저장기간 동안 감소하여 경향을 나타내었음. 처리구별 보수력 결과는 저장 6개월째 대조구는 53.32% 수준을 보인 반면 7,000V 처리구는 63.26% 수준을 정전기장 처리구의 보수력이 높게 나타내었음. VBN 및 TBA 함량은 저장기간이 경과할수록 증가하는 경향을 보였으며 저장기간 동안 대조구의 VBN 및 TBA 함량은 처리구에 비해 높은 증가를 나타내었음. 처리구들의 빙결정 크기는 초기 대조구 50.61㎛와 처리구 47.15~47.38㎛로 측정되었으며 저장 6개월째 처리구는 초기에 비해 1.6~1.8배 증가한 반면 대조구는 2배 이상의 증가를 보였음. 색도는 처리구들 간에 큰 차이를 나타내지 않았으며 저장기간 동안 a값은 감소하고 b값은 증가하는 경향을 보여주었음.

○ 냉동 처리 조건에 따른 감자의 품질 변화를 조사하기 위하여 냉동 처리를 위한 에너지 강도에 따른 냉동 효과를 측정하였음. 에너지 강도는 0, 3,000V, 7,000V로 달리하여 저장한 감자의 품질을 평가하였음. 또한 열처리하여 갈변 억제 효과를 동시에 관찰하였음. 실험결과 pH는 시료간에 큰 변화를 보이지 않았으며 저장기간 동안 감소하는 경향을 나타내었음. 드립률 특정결과, 냉동 처리 직후 6.66~13.16% 수준이었으며 열처리 한 그룹이 열처리 하지 않은 그룹에 비해 높은 수준을 나타내었음. 갈변도는 초기 0.034~0.072 수준으로 냉동 에너지 강도에 관계없이 열처리 그룹이 낮은 경향을 나타내었음. 갈변도는 저장기간 동안 증가하였으며 저장 6개월째 비열처리구의 대조구는 초기에 비해 갈변도가 2배 이상 증가하였으며 정전기 유도에너지의 처리구는 큰 변화를 보이지 않아 비열처리시 정전기 유도 에너지의 적용이 갈변에 효과가 있는 것으로 나타남. 또한 PPO 활성도 대조구에 비해 처리구의 변화가 적었으며 열처리구에 비해 비열처리구가 높은 수준을 보였음. 색도 결과 초기에 비해 냉동처리 후 a값과 b값은 증가하는 경향을 나타내었음.

12. 정전기 유도 에너지 냉동 시스템의 장기저장 중 소고기의 품질변화
○ 정전기 유도 에너지를 적용한 냉동 시스템에서 냉동 및 저장 효과를 분석하기 위하여 소고기를 7,000V, -20℃의 조건에서 냉동 한 후 동일 조건하에서 6개월간 저장하면서 품질 변화를 조사하였음. 대조구로서는 일반냉동고에서 -20℃의 온도에서 품질비교를 위하여 냉동 및 저장을 실시하였음. 수분함량은 초기에 69.21~71.16%이었으며 저장기간동안 큰 변화를 나타내지 않았음. 보수력은 초기의 일반냉동고의 처리구는 65.93%, 정전기장의 67.74%로 정전기장 냉동고의 처리구가 다소 높은 수준을 보였으며 저장 6개월째 대조구는 53.32%로 큰 수준으로 감소한 반면 정전기장 저장 처리구는 67.07% 수준을 나타내었음. 드립률은 초기에는 2.93~3.07% 수준이었으나, 저장기간이 경과할수록 일반냉동고 저장 처리구의 드립 손실률이 7% 이상으로 높아진 반면 정전기장 유도 에너지 냉동고에 저장한 처리구는 4%를 넘지 않은 것으로 나타나 정전기장 처리가 드립률의 발생을 억제하는 것으로 나타남. 이러한 결과는 SEM에 의한 미세구조 분석에서 정전기장 처리 및 저장구가 일반냉동고의 냉동 및 저장구에 비하여 균일한 미세구조와 ice crystal size가 작은 것으로 나타난 것과 상관성이 있는 것으로 판단됨. 또한, VBN 및 TBA 함량이 일반 냉동 처리구에 비해 정전기장 냉동 처리구에 낮게 나타나 정전기장 냉동 처리구의 품질이 일반 냉동 처리구에 비하여 우수한 것으로 나타났음.

Abstract ▼

IV. Result of research and development
1. Setup of thc design condition of thc refrigeration unit and pilot systems development and test operation per system

A. Development of electrostatic field induction energy generator and circuit devices that can induce energy generation reliably
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IV. Result of research and development
1. Setup of thc design condition of thc refrigeration unit and pilot systems development and test operation per system

A. Development of electrostatic field induction energy generator and circuit devices that can induce energy generation reliably

○ We have reviewed electrostatic field induction device design method using alternating (AC) and direct (DC) voltages for induction energy circuit device development as well as AC (0~1,500V) and DC (-900~0V) switched controller design and AC/DC transducer voltage regulation circuit diagrams and analyzed by setting up variable voltage regulating transformers, step-up transformers, current limiting resistors, voltage controlled variable resistance, AC/DC transducers, heat exchangers, air blowing fans, stainless steel vessels, and insulation support.

○ As a measure to enhance frozen properties, input and output voltage control, voltage and frequency stability of the controller in the generator were reviewed to design the electromagnetic field energy generator that can be applied to the refrigeration unit and conditions of the generator were set to generate up to 3,500G and allow input terminal control so that the specification can be sufficient for the experimental use.

o As a measure to enhance frozen properties, output control (10W~250W), 220V, and 40kHz can be adjusted as the condition of the oscillator in order to design the ultrasonic energy generator that can be applied to the refrigeration unit and a lumped type element with 40kHz vibration, transducer, and output connector were applied to the vibration unit so that the specification can be sufficient for the experimental use.

2. Selection of insulation materials of container and vessel and calculation of load capacity
○ The insulation characteristics by insulation material type that can be used in refrigeration and low temperature containers and vessels were studied and reviewed and utilizing the result, minimum required specification of insulation materials that are appropriate for freeze and refrigeration systems were set as urethane foam type, 35 kg/m³ and more, and 0.02 kcal/m·℃·hr and less. In addition, infiltration calories through walls, cooling calorics, freeze required calories for objects to be freeze, heat of respiration, and freeze load of package materials were set as manufacturing factors of the freeze device in consideration of the calculation equation of load capacity to manufacture of thc freeze device. Accordingly, temperature range (0~-20℃), temperature deviation (±0.5℃), effective area (590×450×600 :L×W×H mm), material SUS, and refrigerant R503 were configured.

3. Comparison on freeze quality of the tested specimens to apply the refrigeration unit
○ The experimental unit through conception and review on the refrigeration unit to measure heat properties according to freeze rate per freeze device consists of attachable electrostatic field energy generator, electromagnetic field energy generator, and ultrasound energy generator, which were used as experimental components. In order to secure data of the prototype components and application plans for thc refrigeration unit by studying the frozen characteristic by refrigeration unit, heat properties according to freeze rate per refrigeration unit were measured and thc result showed that an electrostatic field energy-applied refrigeration unit experienced supercooling-cooling up to -8.9℃ and its maximum maintaining time was 10,170 sec and freeze pressure wasreduced up to 45% and thaw pressure was reduced up to 27% (approximately 1.8 psig). An electromagnetic field energy-applied refrigeration unit had varied results according to location and strength. Its maintaining period of ice crystal temperature zone was increased but under the 3,200G electromagnetic energy generation condition, specimens were not freeze below thc ice crystal zone. The changes in frozen characteristics according to changes in output in ultrasound energy-applied refrigeration unit were studied and the result showed that under the 10W output condition, specimen temperature did not go down below the freezing point while showing a temperature increase effect.

○ Analysis of comparison between refrigeration units with different application was
conducted with meat type (Category I) vegetable type (Category II), and fruit type (Category I) for the application test of the refrigeration unit for target specimens. Frozen curves, frozen pressures, thaw curve, thaw pressure, and drip loss of pork, carrot, onion, and apple were compared. A refrigerating internal pressure of the specimens in the freezer utilizing electrostatic field energy was reduced by 2.9~25% while afreeze rate was increased by 0~6.1% and drip loss was reduced by 14~73% compared to those of control group. However, there were difference in quality enhancement effects depending on temperature and specimen and the specimen did not experience supercooling unlike distilled water.

4. Analysis on indoor temperature distribution and air flow field for performance evaluation of the system
○ We aimed to conduct system modeling through transformation of the governing equations and numerical simulations according to changes in system structures and thermal conditions using numerical analysis to perform temperature distribution and flow rate analysis. We aimed to review transfer equation of heat flux through walls and measure temperature distribution of the freezer followed by analyzing the temperature distribution and flow rate to measure and analyze aspects of changes with respect to temperature flow in the refrigerator. The temperature distribution and fluid flow showed that heat loss occurred the most in the lower area rather than the upper area. The cooling characteristics due to convection phenomenon were analyzed by introducing numerical analysis conditions to perform numerical analysis and temperature distribution according to changes in thermal conditions between specimens and cooling temperature in the refrigerator thereby conducting heat flow analysis. The analysis result showed that heat flow was more stable in the lower area than the upper area of the freezer compartment and changes in cooling temperature and temperature distribution were measured using thermal imaging cameras.

5. Setup of the high-voltage electrostatic induction freezer system, creation of the standard design drawings, and prototype manufacturing
○ We aimed to conduct detailed design of the prototype and create the standard drawings. The system consists of circuit devices, AC/DC transducer, voltage control circuit diagrams, and electric circuit diagrams for freezers. The circuit device was designed as AC (0~7,000V) convertible controller. The system consists of the following main devices - induced voltage adjustment variable transformer, step-up transformer, current limiting resistor, electrode generating an electric field induced into the freezer, device connecting the freezer inside, and electrically cut off safety device.

○ To manufacture the experimental system for the prototype, a commercial high-voltage induced freeze system was attached and modified. A freezer that has a range of the high voltage between 0~7,000V, a temperature range between 0℃ ~ -20℃, and a temperature deviation between ±0.5℃ was designed and manufactured as a prototype.

6. Analysis on quality characteristics of high-voltage electrostatic induction device-applied freezer
○ We aimed to compare qualities according to freezing method of basic material and target specimens. A freezing method was divided into high-voltage electrostatic induction method applied freezer (7,000V) and general freezer. The basic material was water and potato, beef, and apple were used as specimens. The freezing processing temperature was -℃. The cell damage was determined via conductivity, TDS, ion leakage, and BIA analysis while histological analysis was done by H&E dyeing method and SEM analysis. The high-voltage electrostatic induction method applied freezer reduced conductivity of potato, beef, and apply by 25%, 30%, and 32% while TDS was reduced by 23% in potato, 10% in beef, and 23% in apple compared to those in general freezer. In addition, ion leakage was reduced by 5~12% in potato, 3% in beef, and 18-20% in apple while BIA analysis showed that resistance value increased in frozen samples of potato, beef, and port in which electrostatic induction method was applied, indicating reduction incell damage. The histological analysis also showed a similar results with that of cell damage, which indicated clear reduction in thickness of cell outer wall due to ice crystal creation in electrostatic induction method-applied frozen samples in the H&Edyeing analysis and a cell type was observed to be more closer to that of raw samples. The SEM analysis also showed that electrostatic induction method applied frozen samples of potato, beef, and cod samples had relatively regular micro-structures.

○ To measure changes in quality according to cooling processing condition and temperature, quality characteristics were compared according to freeze temperature of - 20℃ and -10℃ and changes in electrostatic induction energy generation voltage (0V, 3,000V, and 7,000V) in the High voltage electric field-applied freezer. A drip amount was reduced by up to 36.25% in cod sample, up to 45.02% in beef, and up to 29.09% in potato while VBN was reduced by up to 8.1 % in cod sample and up to 20% in beef. A drip amount was reduced more as strength of electrostatic field became stronger during freeze of samples when electrostatic induction system was applied whereas vitamin C contents were increased.

7. Analysis on the effect of minus temperature thaw
○ To analysis the effect of the minus temperature thaw, a High voltage electric field-applied thaw device was applied with respect to the thaw condition. The mean temperature of thaw was set at -1.5℃. To assess the High voltage electric field-applied minus temperature thaw effect, a freeze condition of samples was set at -20℃ general freeze while thaw condition was set at electrostatic induction-applied defroster (-1.5℃) and general defroster (-1.5℃), 2℃, and 25℃ respectively. A drip rate showed that potato samples had a reduction effect by 41.38% compared to 25℃ thaw condition, 37.49% compared to 2℃, and 27.39% compared to -1.5℃ general defroster. A drip rate showed that beef samples also had a reduction effect by 57.41% compared to 25℃ thaw condition, 47.33% compared to 2℃, and 17.59% compared to -1.5℃. Cherry tomato samples also had a reduction effect by 80.24% compared to 25℃, 68.91% compared to 2℃, and 42.15% compared to -1.5℃.

○ To observe changes while general thaw of High voltage electric field-applied frozen samples, potato samples were selected to be measured. The total phenolic content increased by 5.6℃, antioxidant activity increased by 2.8%, browning degree decreased by 36.5%, and surface color showed that the maximum △L value decreased by 57% while △E value decreased by 41% compared to general frozen samples. In addition, experiments were conducted that freeze condition was divided into electrostatic induction method applied freeze (7,000V, -20℃) and -20℃ general freeze while thaw condition was divided into electrostatic induction applied defroster (-1.5℃) and general defroster (-1.5℃, 2℃, and 1℃) to compare qualities of frozen samples with respect to high-voltage electrostatic field induction energy-applied freeze and thaw method systems. The experiment results showed that a drip rate reduction effect was found in high-voltage electrostatic field processed frozen samples under -10℃ thaw. For example, potato samples had 39% and beef samples had 35% reduction effect Under the electrostatic field -1.5℃ thaw, high-voltage electrostatic field processed freeze system showed that potato and beef samples had a drip rate reduction by 40.9% and 23%. The total bacterial count showed that microbial growth was inhibited during thaw of electrostatic field freeze and thaw samples and temperature distribution measurement also showed increase in a frost rate.

8. Test of quality comparison with the current freeze condition
○ To make a comparison according to storage temperature and methods, High voltage electric field was applied to potatoes, beef, and cod and the effect was analyzed during a short period of storage within two months. The electrostatic induction energy applied freeze condition was -℃ and -10℃ under the high voltage 7,000V condition while the general freezer condition was -20℃ and -10℃ to make a comparison. A storage temperature after freeze was -20℃ and -40℃ and changes in a drip rate, TBA, VBN, Vit C, pH, microorganisms, and surface color were observed for two months. The experiment result showed that cod samples to which High voltage electric field was applied had a reduction in drip rate by 15.0 ~ 27.5%, TBA by 7.0 - 47.8%, andVBN by 32.63 ~ 47.9% while beef samples had a reduction in drip rate by 5.5- 22.13%, TBA by 8.3 ~ 23.07%, and VBN by 7.15 ~ 26.34%. In the case of potato, a drip rate was decreased by 7.15 ~ 26.34% and Vit C content was increased by 0~23.4%. On the other hand, there were no difference between samples in pH, microorganism contents, and chromaticity.

9. Evaluation of freeze and thaw quality according to the application of the unit system
○ Qualities of beef and potato by differentiating freeze and thaw conditions were assessed. The processing conditions were: general freeze followed by general thawing (GF -GT), electric field freeze followed by general thawing (EF-GT), general freeze followed by electric field thawing (GF-ET), and electric field freeze followed by electric field thawing (EF-ET). The analysis was done by freezing for 24 hours followed by thawing lor 15 hour. There was no difference 1n pH between samples in treatment group. For example, pH of beef was in a range of 5.49~5.55 and pH of potato was 6.04-6.11. A drip rate tended to increase during thawing and GF-ET and EF-ET treatment groups, to which electrostatic field thawing was applied, were lower than others. The surface color result of potato showed that △E of GF -GT treatment group was the lowest as 27.15, which had a large difference with that of EF-ET (16.82). TBA values and VBN values of beef in the thawing treatment group in the electric field were low.

10. Changes in quality according to energy strength of electrostatic induction energy
○ To measure changes in quality according to energy strength of electrostatic induction energy, potato samples were used and a freeze processing condition was set to 0, 1,500, 3,000, 5,000 and 7,000V thereby comparing qualities of samples between general and electrostatic field refrigerators after thawing. The first ice crystal forming temperature during freezing of control group was -5.8℃ and after electrostatic field processed, it became -6.4 ~ -6.0℃, verifying that freezing temperature was decreased while thawing curve showed that electrostatic thawing took longer than general thawing. A drip rate using an electrostatic thawing method was lower than that of a general thawing method regardless of freeze method and it was 7.22% w1der 3,000V and 5,000V freeze processing condition, which was reduced by about 28% compared to that of general thawing method.

11. Changes in qualities according to freeze conditions to set up thc optimum system condition
○ To study changes girl qualities of beef according to freeze processing condition, a freeze effect according to energy strength for freeze processing was measured. The energy strength varied within a range of 0, 3,000V and 7,000V to evaluate qualities of stored beef. The experiment result showed that there was no significant change in pH between samples while showing a tendency of increase during the storage period. A drip rate was in a level of 2.93~3.56% immediately after freeze processing and continued to increase during storage period, resulting in 7.23% in control group and 5.05% in 7000V treatment group after 6 months of storage. The water contents had no difference between treatment groups by storage period while the water holding capacity tended to decrease during the storage period. The water holding capacity shown by the treatment group showed that control group had a level of 53.32% after 6 months storage whereas 7,000V treatment group had a level of 63.20%, showing that electrostatic treatment group had higher water holding capacity. The contents of VBN and TBN tended to increase as the storage period increased and the contents of VBN and TBA in control group showed higher increase them those of treatment group. The ice crystal size of treatment group showed that initial control group had 50.61㎛ and treatment group had 47.15 ~ 47.38 ㎛. After six month of storage, treatment group increased the ice crystal size by 1.6~1.8 times than the initial one whereas control group increased it by more than two times. The surface color did not have a significant difference between treatment groups. During the storage period, the following tendency was shown that a value decreased whereas b value increased.

○ To study changes in qualities of potato according to freeze processing condition, a freeze effect according to energy strength for freeze processing was measured. The energy strength varied within a range of 0, 3,000V and 7,000V to evaluate qualities of stored potato. Tn addition, a browning suppression effect due to heat treatment was also observed at the same time. The experiment result showed that there was no significant change in pH between samples while showing a tendency of decrease during the storage period. The drip rate measurement result showed that immediately after the freeze processing, it was within a range of 6.66 ~ 13.16% and that of heat-treated group had a higher level than that of non-heat-treated group. A browning degree was In a rangeof 0.034~0.072 and heat-treated group had a lower tendency of browning degree regardless of freeze energy strength. A browning degree increased during the storage period and control group with respect to non-heat treatment increased a browning degree by more than two times than initial degree while electrostatic induction energy treatment group had no significant change, which indicated electrostatic induction energy application had a positive effect on brow[li[lg effect during non-heat treatment. The PPO activity result also showed that changes in treatment group were fewer than that of control group and non-heat treatment group had a higher level than that of heat treatment group. The surface color result showed that a and b values tended to increase alter freeze processing compared th their initial values.

12. Changes in beef quality during long-term storage In the electrostatic induction energy freeze system.
○ To analyze the freeze and storage effect in electrostatic induction energy-applied freeze system, beef was frozen under the condition of 7000V and -20℃ and stored under the same condition for six months thereby inspecting changes in qualities. For control group, they were frozen and stored in general freezer under -20℃ temperature condition to compare the quality. The water content, whose initial value was in a range of 69.21 ~ 71.16%, did not have a significant change during the storage period. The water holding capacity showed that treatment group in general freezer was 65.93% while electrostatic field freezer was 67.74%, which was slighter higher than treatment group in general freezer. Control group alter six month storage had 53.32%, which was reduced significantly whereas electrostatic field storage treatment group had 67.07%. drip rate was initially a range of 2.93 ~ 3.07% but as storage period was elapsed, a drip rate of general freezer storage treatment group increased to 7% or more whereas treatment group stored in the electrostatic induction energy freezer did not exceed 4%, which indicated that electrostatic field treatment suppressed an occurrence of a drip rate. These results are considered as being related with more uniform microstructure and smaller ice crystal size of electrostatic field treatment and storage groups than freeze and storage groups in the general freezer as found in the microstructure analysis via SEM. In addition, VBN and TBA contents showed that electrostatic field freeze treatment group had lower results than general freeze treatment group, which indicated that qualities of electrostatic field freeze treatment group were better than those of general freeze treatment group.