The effect of tert-butyl alcohol (TBA) as a freezing solvent on the pore structure of a porous tungsten body prepared by freeze-drying is analyzed. TBA slurries with a WO3 content of 10 vol% are prepared by mixing with a small amount of dispersant and binder at 30oC. The slurries are frozen at -25oC, and pores are formed in the frozen specimens by the sublimation of TBA during drying in air. After hydrogen reduction at 800oC and sintering at 1000oC, the green body of WO3 is completely converted to porous W with various pore structures. Directional pores from the center of the specimen to the outside are observed in the sintered bodies because of the columnar growth of TBA. A decrease in pore directionality and porosity is observed in the specimens prepared by long-duration drying and sintering. The change in pore structure is explained by the growth of the freezing solvent and densification.

The effect of sublimable vehicles on the pore structure of Cu fabricated by freeze drying is investigated. The 5 vol% CuO-dispersed slurries with camphene and various camphor-naphthalene compositions are frozen in a Teflon mold at -25oC, followed by sublimation at room temperature. After hydrogen reduction at 300oC and sintering at 600 °C, the green bodies of CuO are completely converted to Cu with various pore structures. The sintered samples prepared using CuO/camphene slurries show large pores that are aligned parallel to the sublimable vehicle growth direction. In addition, a dense microstructure is observed in the bottom section of the specimen where the solidification heat was released, owing to the difference in the solidification behavior of the camphene crystals. The porous Cu shows different pore structures, such as dendritic, rod-like, and plate shaped, depending on the composition of the camphornaphthalene system. The change in pore structure is explained by the crystal growth behavior of primary camphor and eutectic and primary naphthalene. Keywords: Porous Cu, Pore structure

Porous Cu-14 wt% Co with aligned pores is produced by a freeze drying and sintering process. Unidirectional freezing of camphene slurry with CuO-Co3O4 powders is conducted, and pores in the frozen specimens are generated by sublimation of the camphene crystals. The dried bodies are hydrogen-reduced at 500oC and sintered at 800oC for 1 h. The reduction behavior of the CuO-Co3O4 powder mixture is analyzed using a temperature-programmed reduction method in an Ar-10% H2 atmosphere. The sintered bodies show large and aligned parallel pores in the camphene growth direction. In addition, small pores are distributed around the internal walls of the large pores. The size and fraction of the pores decrease as the amount of solid powder added to the slurry increases. The change in pore characteristics according to the amount of the mixed powder is interpreted to be due to the rearrangement and accumulation behavior of the solid particles in the freezing process of the slurry.

Korean sliced rice cakes, or tteokguk, are conventionally dried and rehydrated during their preparation. In this study, the effects of the perforation process and various drying methods (e.g., hot-air drying, vacuum drying, low temperature drying, and freeze drying) on the quality characteristics of tteokguk (rice cake soup) were evaluated. In the experiment, the rehydration capacity and lightness increased as the pore number increased. The hardness, redness, and yellowness of tteokguk, in contrast, tended to decrease as perforations increased. The texture, taste, and overall acceptability scores of tteokguk increased as perforations increased. With respect to drying methods, the rehydration capacity was greatest for vacuum drying. The hardness of tteokguk was lowest for vacuum drying. The redness, yellowness, pH, and sensory characteristics did not differ significantly among tteokguk samples treated through various drying methods. These results suggest that high-quality ready-to-eat Korean sliced rice cakes could be created by perforation and vacuum drying.

The aim of this study is to investigate the effects of combined drying conditions on the quality characteristics of lotus root chips. A combined drying was conducted using the superheated steam (SHS) at 220°C for 6 min, then subsequent contact drying at 150°C for specified times (2, 4 or 6 min) and finally hot air at specified temperatures (50, 60 or 70°C) for 1 hr. Changes in appearance of lotus root chips such as surface color, shrinkage and deformed shape were resulted from the extent of time and temperature of post-drying conditions. Moisture content of lotus root chips decreased with increasing the time and temperature of post-drying process. Surface color of lotus root chips was determined mainly by the contact drying step of a combined drying process. Polyphenol content was influenced by the temperature of hot air rather than the duration of contact drying. Meanwhile hardness of lotus root chips decreased significantly with increasing the duration of contact drying. These results suggested that a combined drying process with appropriate processing conditions could be applicable successfully for the manufacturing of un-fried lotus root chips.

Physicochemical properties of cherry tomato dried using the conventional hot air (HA) and superheated steam (SHS) combined with either HA or far-infrared (FIR) were measured to evaluate the effects of combined drying process on the product quality. Conventional HA drying caused the greater extent of water removal than that of SHS combined with HA or FIR due to comparatively its longer drying time, resulting the lower water activity. Total acidity of cherry tomato produced by combined drying processes was slightly lower than that of conventional HA drying. Application of SHS combined with FIR resulted in higher retention of vitamin C and lycopene content with faster rehydration capacity than those of both conventional HA and SHS with HA drying. These results suggested that SHS combined with FIR would replace the conventional HA drying process successfully in production of dried cherry tomato with appropriate quality characteristics

Recently, semi-dried sweet potato is popular as a natural snake for children’s dessert. The drying condition was optimized to obtain high quality of sweet potato by oven drying process. The mashed yellow and chestnut sweet potato was dried using the oven drier at different temperature (50, 60, 70, and 80°C) then evaluated for the moisture content, appearance observation, texture properties, and sugar contents and sensory test in every 2, 6 and 12 hours. During the dehydration and drying process, the ending point of moisture content divided in three zone from 0-2 hour, 4-6 hour and 8-12 hour. The moisture content was dramatically decreased from 0 hour - 8 hour, but after 8 hour there is no significant decrease. Yellow sweet potato dried at 80°C for 6 hours was investigated as good product base on the sensory test, hardness value, and color appearances as compared to chestnut potato.

Garlic (Allium sativum) has been used as a medicinal plant due to its various functionalities such as reduction of cholesterol levels. The purpose of this study was to optimize conditions for the production of microencapsulated garlic powder (MGP) coated with whey protein isolate (WPI) to improve its production yield. WPI was mixed with distilled water followed by magnetic stirring at 500 rpm for 12 h to hydrate it completely. Garlic powder (GP) was added into the WPI mixture. Ratio of GP to WPI was 1:1. Subsequently, GP-WPI mixture was homogenized, and then spray-dried. To maximize the production yield of MGP, variables such as the mixing time and homogenizing condition such as rpm and time were tested. The optimum conditions for producing MGP were found to be as follows: GP and WPI mixing for 1 h and homogenizing at 8100 rpm for 10 min which improved liquid flow rate during spray drying process. The production yield of MGP under optimum conditions was 25.6 g/h. The results of this study might provide scale-up parameters on applications of GP for its commercialization.

저온진공건조 조건에 따른 곶감의 건조특성 및 품질적 변화를 분석하였다. 곶감의 건조 특성 은 전형적인 항율건조기간과 감율건조기간이 존재함을 확인 할 수 있었다. 진공압력이 높을수록 가열온 도가 높을수록 곶감의 당도, 당 함량, 경도 값은 높게 나타났으며 이에 비해 명도 값은 낮게 나타남을 알 수 있었다. 기존 천일 및 열풍건조를 대처할 수 있는 진공건조의 최적 조건은 진공압력이 40~50kPa abs., 가열온도 30℃, 건조시간은 3~4일 이었다.

Porous W with spherical and directionally aligned pores was fabricated by the combination of sacrificial fugitives and a freeze-drying process. Camphene slurries with powder mixtures of WO3 and spherical PMMA of 20 vol% were frozen at −25 oC and dried for the sublimation of the camphene. The green bodies were heat-treated at 400 oC for 2 h to decompose the PMMA; then, sintering was carried out at 1200 oC in a hydrogen atmosphere for 2 h. TGA and XRD analysis showed that the PMMA decomposed at about 400 oC, and WO3 was reduced to metallic W at 800 oC without any reaction phases. The sintered bodies with WO3-PMMA contents of 15 and 20 vol% showed large pores with aligned direction and small pores in the internal walls of the large pores. The pore formation was discussed in terms of the solidication behavior of liquid camphene with solid particles. Spherical pores, formed by decomposition of PMMA, were observed in the sintered specimens. Also, microstructural observation revealed that struts between the small pores consisted of very fine particles with size of about 300 nm.

In this paper, we investigate how the power consumption of a heat pump dryer depends on various factors in the drying process by analyzing variables that affect the power consumption. Since there are in general many variables that affect the power consumption, for a feasible analysis, we utilize the principal component analysis to reduce the number of variables (or dimensionality) to two or three. We find that the first component is correlated positively to the entrance temperature of various devices such as compressor, expander, evaporator, and the second, negatively to condenser. We then model the power consumption as a multiple regression with two and/or three transformed variables of the selected principal components. We find that fitted value from the multiple regression explains 80~90% of the observed value of the power consumption. This results can be applied to a more elaborate control of the power consumption in the heat pump dryer.

The present study demonstrates the effect of solidification condition on the pore structure in freeze drying process using the slurries of CuOlimable vehicles. Camphene and Camphor-45 wt% naphthalene based slurries with 14 vol% CuO powder were frozen into a mold at -25℃<, followed by sublimation at room temperature. The green bodies were hydrogen-reduced and sintered at 500℃ for 1 h. The porous Cu specimen, frozen the CuO/camphene slurry into the heated mold of the upper part, showed large pores with unidirectional pore channels and small pores in their internal wall. Also, it was observed that the size of large pores was decreasing near the bottom part of specimen. The change of pore structure depending on the freezing condition was explained by the nucleation behavior of camphene crystals and rearrangement of solid powders during solidification. In case of porous Cu prepared from CuO/Camphor-naphthalene system, the pore structure exhibited plate shape as a replica of the original structure of crystallized vehicles with hypereutectic composition.

This study reports a simple way of fabricating the porous Cu with unidirectional pore channels by freezedrying camphene slurry with Cu oxide coated Cu powders. The coated powders were prepared by calcination of ball-milled powder mixture of Cu and Cu-nitrate. Improved dispersion stability of camphene slurry could be achieved usingthe Cu oxide coated Cu powders instead of pure Cu powders. Pores in the frozen specimen at -25oC were generated bysublimation of the camphene during drying in air, and the green bodies were sintered at 750oC for 1 h in H2 atmo-sphere. XRD analysis revealed that the coated layer of Cu oxide was completely converted to Cu phase without anyreaction phases by hydrogen heat treatment. The porous Cu specimen prepared from pure Cu powders showed partlylarge pores with unidirectional pore channels, but most of pores were randomly distributed. In contrast, large andaligned parallel pores to the camphene growth direction were clearly observed in the sample using Cu oxide coated Cupowders. Pore formation behavior depending on the initial powders was discussed based on the degree of powder rear-rangement and dispersion stability in slurry.

In this paper, we investigate the statistical correlation of the time series for temperature measured at the heat box in the automobile drying process. We show, in terms of the sample variance, that a significant non-linear correlation exists in the time series that consist of absolute temperature changes. To investigate further the non-linear correlation, we utilize the volatility, an important concept in the financial market, and induce volatility time series from absolute temperature changes. We analyze the time series of volatilities in terms of the de-trended fluctuation analysis (DFA), a method especially suitable for testing the long-range correlation of non-stationary data, from the correlation perspective. We uncover that the volatility exhibits a long-range correlation regardless of the window size. We also analyze the cross correlation between two (inlet and outlet) volatility time series to characterize any correlation between the two, and disclose the dependence of the correlation strength on the time lag. These results can contribute as important factors to the modeling of forecasting and management of the heat box’s temperature.

곳감 생산 현장에 적용하기 위해 식초, 자몽추출물 등 총 6종의 추출물에 대한 배합비를 설정하였고, 그 결과 우수한 활성을 가지는 천연 복합 활성제의 최종적인 혼합비는 정향 18.18%, 계피 9.90%, 감초 9.09%, 천궁 4.55%, 자몽종자출물 4.55% 및 사과 식초 54.54%임을 확인하였다. 대조구 및 처리구의 수분 함량을 측정한 결과는 항갈변 실험과 항진균 실험, 항갈변/항진균 실험 모두에서 전체적으로 1주차에 비해 6주차에서 수분의 함량이 증가 하였으며 측정 주차 별로 control이 처리구에 비해 수분 함량이상대적으로 낮았다. 당도 변화에서는 건조가 진행됨에 따라 전반적 곶감의 당도는 증가하였다. 항갈변/항진균 실험에서 30∼39 °brix로 높은 당함량을 보였다. 경도를 측정한 결과에서는 control과 처리구는 거의 비슷하였으며 6주 뒤 평균적으로 0.5∼0.8정도 줄어들었다. 색도변화에서는 △값의 변화는 건조 기간 중감소하는 경향을 나타냈다. 천연 추출물은 곶감의 건조기간 중에 나타나는 품질저하를 효과적으로 억제하고 유해성 논란이 되고 있는 유황훈증법을 대체할 수 있을 것으로 사료된다.

Expanded graphite (EG) was prepared using a drying process for application as an oil-adsorbent: the morphology, expansion volume, and oil absorption capacity of the EG were investigated. The expanded volume of the EG increased with an increasing reaction time and heat treatment temperature. The oil adsorption capacity of the EG was 45 g of n-dodecane per 1 g of EG. It is noted that the drying process of EG is a useful technique for a new oil-adsorbent.

Ocean discharge of sewage sludge, which started in the year of 1993 in Korea, was stopped in the beginning of 2012, Landfill of sewage sludge was also prohibited in 2003 owing to public acceptance of the lanfill sites, and partially reopened in 2007 due to the necessity of organic component in sludge to produce methane gas. Sludge recycle ratio will increase in sewage sludge treatment by volume reduction and drying, and then recycle of the thermal energy as fuel in power plant and also material as raw material of cement. Several drying processes are compared with reasoning and an appropriate drying sequence is suggested.

Porous W with controlled pore characteristics was fabricated by a freeze-drying process. WO3 powder and camphene were used as the source materials of W and sublimable vehicles, respectively. Camphene slurries with WO3 contents of 10 and 15 vol% were prepared by milling at 50˚C with a small amount of oligomeric polyester dispersant. Freezing of a slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at -25˚C while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at 800˚C for 30 min and sintered in a furnace at 900˚C for 1 h under a hydrogen atmosphere. Microstructural observation revealed that all of the sintered samples were composed of only W phase and showed large pores which were aligned parallel to the camphene growth direction. The porosity and pore size increased with increasing camphene content. The difference in the pore characteristics depending on the slurry concentration may be explained by the degree of powder rearrangement in the slurry. The results strongly suggest that a porous metal with the required pore characteristics can be successfully fabricated by a freeze-drying process using metal oxide powders.

The synthesis behavior of nanoporous silica aerogel in the macroporous ceramic structure was observed using TEOS as a source material and glycerol as a dry control chemical additive (DCCA). Silica aerogel in the macroporous ceramic structure was synthesized via sono-gel process using hexamethyldiazane (HMDS) as a modification agent and n-hexane as a main solvent. The wet gel with a modified surface was dried at under ambient pressure. The addition of glycerol appears to give the wet gel a more homogeneous microstructure. However, glycerol also retarded the rate of surface modification and solvent exchange. Silica aerogel completely filled the macroporous ceramic structure without defect in the condition of surface modification (20% HMDS/nhexane at 36hr).