• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집B
• /
• pp.309-313
• /
• 2000

An experimental study was conducted to analyze the characteristics of the showcase refrigeration system during frosting and defrosting process. Test showcase was constructed with a cooling capacity of 3RT including 3 evaporators. The dynamic characteristics of the system under frosting and defrosting conditions were investigated. Refrigerant temperature and pressure of the system, dry bulb and wet bulb temperature of air passing through the evaporator, air flow rate and compressor power were measured.

• 설비공학논문집
• /
• 제11권4호
• /
• pp.440-447
• /
• 1999

The frosting characteristics on the vertical parallel plates with three cooling plates were experimentally investigated. The experimental parameters were the cooling plate temperature, the air humidity, the air temperature, the air Reynolds number, and the location. The frosting conditions were limited to air temperatures from 10 to $15^{\circ}C$ , air Reynolds numbers from 1600 to 2270, air humidity ratios from 0.00275 to 0.0037kgw/kga and cooling plate temperatures from -10 to $-20^{\circ}C$. Frost growth and density toward the front of the plate were more thick and dense than toward the rear. Frost growth increased with decreasing plate temperature and increasing humidity. In the conditions of the laminar flow, dew point below $0^{\circ}C$and non-cyclic frosting period, frost thickness increased with increasing air temperature. The reason of increasing frost thickness with increasing air temperature was sublimation-ablimation process. The average growth thickness along the locations showed little dependence on the Reynolds numbers.

• 설비공학논문집
• /
• 제14권6호
• /
• pp.493-502
• /
• 2002

During the defrosting process, the temperature in the cabinet of a showcase becomes high as compared to the setting point, which is not desirable for stored foods or materials. It is necessary to develop a more efficient defrosting method to prevent large temperature fluctuation. In this study, the performance of a showcase refrigeration system with three evaporators is investigated by employing a hot-gas bypass defrosting technology in the system under frosting and defrosting conditions. The operating characteristics are compared with those for the on-off defrosting method that has been widely used in current products. As a result, the hot-gas bypass defrosting method shows higher refrigerating capacity and less temperature fluctuation than the on-off method under frosting/defrosting conditions, while the power input is relatively high for the hot-gas bypass method.

• 설비공학논문집
• /
• 제7권1호
• /
• pp.161-170
• /
• 1995

This study is concerned with the numerical analysis of performance on fin-tube heat exchanger under frosting condition. In this work, tube-by-tube method using LMED is employed. The present results are compared with O'Neal's experimental and numerical results. A standard evaporator model with 2rows-2columns is selected to investigate the effects of the various parameters such as fin pitch, air flow velocity, and humidity. The results show that frost thickness and the amount of frost per unit area decrease as fin-pitch becomes narrower. In the meantime, frost thickness and accumulation rate increase with higher inlet air humidity. It is shown that heat transfer rate increases during 30minutes and then it decreases. Heat transfer rate and the amount of frost increase with air velocity, however frost thickness does not increase over a certain velocity.

• 설비공학논문집
• /
• 제8권2호
• /
• pp.299-306
• /
• 1996

This work presents an analytical model, so called modified LMTD method, to predict the thermal performance of finned-tube heat exchanger under frosting conditions. In this model, the total heat transfer coefficient and effective thermal conductivity of the frost layer were defined as a function of frost surface temperature. The surface temperature of the frost layer formed on the heat exchanger was calculated through the analysis of the heat and mass transfer process in the air and frost layer. To examine the validity of this analytical model, the computed results from the present model, such as heat transfer rate, frost mass and thickness of frost, were compared with the ones of the expermental work and LMED method.

• 한국식품과학회지
• /
• 제34권3호
• /
• pp.413-418
• /
• 2002

제빵에 이용 할 반죽을 발효하거나 발효하지 않은 상태로 다섯 가지의 다른 냉동 및 저장 환경에서 냉동하고 일주일간 저장하여 해동 한 후 제조된 빵의 품질을 비교하였다. 냉동속도가 빠르더라도 발효한 후 냉동된 반죽은 빵의 부피가 감소하였으며 이러한 문제점은 침지식 냉동 방식에서도 해결되지 않았다. $-70^{\circ}C$의 초저온 냉동은 $-20^{\circ}C$ 침지식 냉동고에 비하여 냉동 온도가 매우 낮으나, 냉동 속도도 느리고 해동 후 재 발효하여도 빵의 부피가 작아서 효과적인 냉동 방법이 되지 못하였다. 반면 냉동 속도는 느리지만 $-20^{\circ}C$ 공기 송풍식 냉동고가 $-70^{\circ}C$ 공시 송풍식 냉동고보다 냉동에 따른 장해가 적어서 반죽의 발효가 잘되었다. 동일한 온도일 때는 침지식 냉동이 더욱 효과적이었으며 침지식 가운데도 온도가 더 높은 $-10^{\circ}C$ 냉동이 가장 효과적이어서 발효하지 않고 냉동하여 재 발효 할 경우 대조구보다도 오히려 반죽의 발효가 잘되어 빵의 부피가 더 컸다. 따라서 본 연구에 이용한 방법 가운데 $-70^{\circ}C$ 공기 송풍식 냉동고에서 냉동, 저장하는 것이 가장 비효율적이며 침지식 냉동방법들이 냉동 온도가 높더라도 오히려 해동 후 발효 장해가 적어서 효율적이었다. 위의 실험 결과를 종합하였을 때, 냉동 전에 반죽을 발효하지 않고 $-10^{\circ}C$ 침지식 냉동고에서 냉동하여 저장하거나, $-20^{\circ}C$ 침지식 냉동고에서 초기에 냉동을 하고, $-20^{\circ}C$ air freezer에 저장하는 방법이 가장 효과적이었다.