• 농업과학연구
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• 제45권4호
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• pp.847-857
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• 2018

Recently, customers' demand and attention to dried agricultural products or foods have increased due to their convenience and nutritional values. Conventional drying methods such as solar drying and hot air drying have been most widely used for producing a large amount of dried agricultural products; however, those methods require quite a long time and high energy consumption. To compensate for these issues associated with conventional methods, dielectric heating such as microwave and radio frequency heating has been used as a supplemental method in the drying procedure. This study investigated the microwave drying characteristics of squash slices with different thicknesses under different microwave power intensities and determined the best drying model that could precisely describe the experimental drying curves of the squash slices. The squash was cut into slices with two different thicknesses (5 and 10 mm), and then, they were dried under different microwave power intensity ranges between 90 and 900 W with an increase interval of 90 W. Six drying models were tested to evaluate the fit to the experimental drying data, and the effective moisture diffusivity ($D_{eff}$) values of the squash slices under microwave drying were determined. The results clearly show that as the microwave power was increased, the drying time of both squash slices was significantly decreased, and the slope of the drying rate increased. The effective moisture diffusivity was also significantly related with the microwave power intensities and thicknesses of the slices. In addition, the Page model was most suitable to delineate the drying curves of both squash slices under different microwave power intensities.

• 한국식품영양과학회지
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• 제27권3호
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• pp.386-392
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• 1998

Experiments were carried out to establish an effective artificial drying method of Pacific saury (Cololabis seira) to kwamaegi. Raw fish containing 67% moisture were dried up to containing less than 40% moisture by drying for 15 days. The fish lost moisture more rapidly during first 3 days of natural drying than artificial drying. Total lipid content increased from 16.1% to 30.3 and 29.8% by 15 days of natural and artificial drying, respectively. Neutral lipid occupying 91.63% of total lipid increased to 92~94% during 15 days of drying, while content of phospholipid and glycolipid decreased slightly. The values of peroxide and thiobarbituric acid increased up to 6 days of drying and then did not change. Peroxide levels were lower in artifically dried fish than in naturally dried ones.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.242-247
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• 2009

The present study has been conducted to reduce the cold air drying rate. According to the cold air drying method, the quality-excellent product could be made and there would be little change of color, taste and smell. As compared with the hot air drying, the cold air drying equipment has the superior dehumidification in a constant drying zone. However, in a falling drying zone that equipment is not energy-efficient because the drying period could be longer by the dehumidificated.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 하계학술발표대회 논문집
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• pp.1128-1133
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• 2008

Drying process in the thin film layer of sludge with the thickness less than a few millimeters has been investigated using the simple one-dimensional model. Thin film drying is usually used to dry the viscous materials like sewage sludge. The thin film layer of sludge is dried on the metallic surface through which thermal energy is supplied to the layer during drying. In order to solve the equations, the mass transfer rate on the drying surface should be determined. The mass flux of evaporated water vapor on the surface is estimated with the formulation given in the literature. The effect of heating temperature, film thickness, and air velocity on drying has been examined to figure out the drying characteristics of the sludge layer.

• Journal of the Korean Wood Science and Technology
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• 제26권4호
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• pp.34-42
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• 1998

Three hardwood (ash, alder and black locust) and three softwood (Japanese red pine, radiata pine and Western hemlock) specimens were dried in microwave(MlW) oven and their drying rates were obtained. Their specific permeabilities were also measured by using a modified liquid permeability measuring device. The correlation between the M/W drying rates and permeabilities of six species were statistically analyzed. It was revealed that within a species there is a logarithmic relationship between the M/W drying rates and average moisture contents and that among species there is a linear relationship between the M/W maximum drying rates and the average specific permeabilities. A exception was Western hemlock, which was of low permeability and of high drying rate. A Me-time equation, which showed a good agreement with the actual data, was derived. Thus using this equation the moisture contents of wood and the drying end points of M/W drying could be predicted. Infrared images of the thermal distribution in wood were illustrated.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.1191-1196
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• 2006

Analysis of drying characteristics has been carried out with one-dimensional model in the dryer using the principle of the refraction of radiation. The dryer is composed of hot water tank, a plastic film conveyer belt, drying material, etc. The model considers the conduction and radiation within the plastic film and drying material. The film is semitransparent to radiation and the drying material is assumed to be semitransparent or opaque to radiation. The results shows that the effect of radiative transfer on the drying rate is relatively large when the thickness of drying material is small and the water temperature is high. When the material is thin, the drying rate by only conduction is also enhanced so that drying time can considerably be reduced.

• 한국농공학회지
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• 제17권4호
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• pp.3980-3990
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• 1975

This study was carried out to develop a method of grain drying ststem that can be done by forcing the heated-air directly into the grains within the sack. The air duct was pushed into the central position of the grain-deposited sack and the heated-air was forced to flow in the radial direction. The system is referred here as the unit sack drying system. At a first step of this study, an air flow resistance tester was constructed to measure the resistance of air flow to grains in cooperated with some different sack materials, the sack materials, the tested were rice-straw bag, sack of polyethylene film, and jute sack In addition, unit sack drying system was constructed to investigate the drying characteristics of the dryer. on this dryer, two kind of terminal air ducts were attached and tested to examine its effects on uniform drying, and also, aseries of drying test was performed to trace the effect of increasing air flow rate on uniform drying. The results are as follows: 1) Resistance of air flow for each sack material was increased almost proportional to the increasing rate of air flow. Experimental data showed little significant differences of the air flow resistance among the materials. 2) From the comparison with air flow resistance of sack material and that of roughrice, it was indicated that airflow resistance of sack material was much higher than that of rice rough Therefore, in the unit sack drying sysle in which air flow is destined to face the sach material after leaving the grain, it was suggested that air flow would be inuniform to each part of grain within sack because of much higher air flow resistance of sack material than that of grain, and the fact would results inuniform grain drying. 3) Drying test on the unit sack drying system in cooperated with different type of terminal air ducts showed that high speed air is better for uniform drying than in high pressure. with the drying system which was assembled with the air ducts delivering higher speed air, there also involved a problem of significant inuniform drying. Therefore, any means to improve the inuniform drying should be undertaken for practical use. 4) A series of drying test with in creasing air flow rate resulted that increasing air flow rate in the unitsack drying system gave little effect on uniform drying, therefore, it is recommened to change its drying system for drying grain uniformly.

• 한국식품영양과학회지
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• 제29권4호
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• pp.561-567
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• 2000

참나물을 원적외선 건조기와 원적외선-진공건조기를 사용하여 건조할 때 건조조건에 따른 건조속도, 색도, 미생물 변화, 갈변도, 수화복원성 및 관능검사 등 건조참나물의 품질변화에 미치는 영향을 조사하였다. 참나물의 건조속도는 건 조온도를 5$0^{\circ}C$, 6$0^{\circ}C$ 및 7$0^{\circ}C$로 하여 원적외선-진공건조를 하였을 때는 원적외선 건조한 경 우보다 건조시간이 약 17%이상 단축되었다. 색도변화는 건조온도가 높을수록 증가되었으며 원적외선진공건조가 원적외선보다 그 변화율이 작았다. 건조시간에 따른 참나물의 미생물변 화는 건조온도가 높을수록 그리고 건조시간이 길어질수록 감소하였으나 건조방법에는 큰 영 향을 받지 않았다. 건조방법과 건조온도에 따른 참나물의 수화복원성은 원적외선-진공건조 시료가 원적외선 건조시료보다 재수화 특성값이 높았으며, 특히 건조온도가 높을수록 복원 률이 우수하였다. 재수화 후의 관능적 품질은 낮은 온도에서 그리고 원적외선 건조 참나물 보다 원적외선-진공건조 참나물이 높은 점수를 얻었으며, 특히 관능적 색도면에서는 원적외 선 건조보다 원적외선-진공건조를 행한 경우에 훨씬 좋은 점수를 나타내었다. 따라서 원적 외선-진공건조를 사용할 경우 원적외선 단독보다는 건조 효율이 증대되며, 복원성과 색도의 안전성을 증진시킴으로써 참나물의 품질저하를 최소화할 수 있었다.

• 한국식품과학회지
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• 제30권5호
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• pp.1107-1113
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• 1998

품질이 우수한 효소식품으로의 활용가능성 검토를 위해 현미를 발아시킨 후 마이크로파 진공건조로 건조하고 그 건조특성과 품질특성을 열풍건조, 진공건조, 그리고 동결건조의 경우와 비교해 보았다. 마이크로파 진공건조 1 및 2의 경우 열전달속도가 빨라 건조 개시후 5분 경과후 $60^{\circ}C$에 도달하였고 건조시간 내내 $60{\pm}2^{\circ}C$를 유지하였으나 열풍건조의 경우는 건조개시 60분 경과 후, 진공건조의 경우는 2시간 경과 후에야 $60^{\circ}C$에 도달하였다. 마이크로파 진공건조 1의 경우 건조 3시간 후 수분함량 0.08 kg water/kg solid까지 감소하였으나, 마이크로파 진공건조 2의 경우 총건조시간 2시간만에 수분함량 0.O6 kg water/kg solid까지 감소하였다. 열풍건조의 경우 건조시간 4시간만에 수분함량 0.14 kg water/kg solid까지 감소하였으나 최소한 2시간은 더 건조시켜야 할 것으로 예상되었다. 마이크로파 진공건조 1 및 2의 초기 건조속도는 0.05 kg water/kg solid/min이었으며 처음부터 건조속도가 계속 감소하는 감률건조를 보였다. 열풍건조의 경우는 초기 건조속도가 0.0057 kg water/kg solid/min으로서 마이크로파 진공건조 1 및 2의 1/10 수준이었으며 건조개시 30분까지 항률건조를 보이다가 임계수분함량 0.81 kg water/kg solid 부근부터 감률건조가 시작되었다. 건조시료의 ${\alpha}-amylase$ 활성 및 protease 활성은 마이크로파 진공건조, 동결건조, 진공건조 및 열풍건조의 순서를 보였고, diastatic activity의 경우 동결건조와 마이크로파 진공전조가 거의 대등한 품질보존효과를 보여 주었다. 이로부터 마이크로파 진공건조를 이용하여 건조할 경우 최소한 동결건조와 대등한 품질의 건조제품을 제조할 수 있으리라 예상되었다.

• Journal of Biosystems Engineering
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• 제41권1호
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• pp.34-42
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• 2016

Purpose: This study was performed to improve the drying quality and drying rate of ginseng slices by combining microwave and far-infrared drying techniques. Methods: Based on single-factor experiments and analyses, a quadratic regression orthogonal rotation combination design was adopted to study the effects of the moisture content at the conversion point between the microwave and far-infrared techniques, the ginseng slice thickness and the far-infrared drying temperature on the chip drying time, the surface color difference value, the nutritional composition and the surface shrinkage rate index. Results: Compared to the far-infrared drying alone, the combined microwave and far-infrared drying resulted in an increase in the saponin content of the ginseng slices and reductions in the drying time, surface color difference, and shrinkage rate. Conclusions: We established a mathematical model of the relationships between the surface shrinkage rate index and the experimental factors using the multi-objective nonlinear optimization method to determine the optimal parameter combination, which was confirmed to be the following: microwave and far-infrared moisture contents of 65%, a ginseng slice thickness of 1 mm, and a far-infrared drying temperature of $54^{\circ}C$.