• Journal of Biosystems Engineering
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• v.34 no.5
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• pp.351-357
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• 2009

This study was conducted to verify the simulation model through the drying test, and investigate effect of factors, such as temperature of drying air, airflow rate, and velocity of the airflow, on the drying. The low temperature drying simulation model was developed based on the circulation dry simulation model presented by Keum et al. (1987), and by modifying low temperature thin layer drying model, equilibrium moisture content model, latent heat of vaporization model, and crack ratio prediction model. The heat pump and experimental dryer with a capacity of 150kg were used for the test. The RMSE between the predicted and measured value was 0.27% (drying temperature), 0.15% (crack ratio), and 2.08% (relative humidity), so the relevance of the model was verified. In addition, the effect of drying temperature, airflow rate, and velocity of the airflow on the drying was examined. The experimental results showed that the crack ratio at drying temperature of $25{\sim}40^{\circ}C$ was allowable. Moreover, at below $30^{\circ}C$, variation of the crack ratio was slight, but drying time was delayed. Given these results, the drying temperature of over $30^{\circ}C$ was effective. As the airflow rate increased, required energy dramatically increased. Whereas drying rate slowly increased, so loss of drying efficiency was caused. Considering these results, the dryer needed to be designed and adjusted to lower than $30\;m^3/min{\cdot}ton$. As velocity of the airflow increased, required drying energy increased when the velocity of the airflow was over $5\;m^3$/hr, while crack ratio and drying rate showed little variation.

• Journal of Biosystems Engineering
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• v.3 no.1
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• pp.64-76
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• 1978

A dimensional supply of petroleum fuels and increased competition for petroleum products has made the conservation of energy in grain drying an important cost and management factor. Research on solar grain drying is directed toward utilization of a renewable energy source as an alternative to petroleum fuels for drying. There are many technical and economic problems in accepting and adopting solor energy as a new energy source for grain drying. The purpose of this study are to assess the state of the art of solar grain drying and to find out the problems by reviewing literatures available. The results obtained may be summarized as follows; 1.It may be considered that the weather conditions in October of Korea was satisfactory for the forced natural air and solar heated air drying. 2. Solar energy is considered more applicable to low-temperature, In-storage drying systems than to high-temperature, high-speed drying systems. In-storage drying systems require low levels of heat input. The costs of collector systems to provide low temperature are considerably cheaper than for high-temperature systems. 3. Tubular type collector made of polyvinyle film seems to be the most practical at this stage of development and black-painted bare-plate collectors mounted on the outside of a typical, round, low-temperature drying bin can supply an appreciable amount of the energy efficiently needed for low-temperature grain drying at a lower cost. 4. All of the grains in solar drying tests was successfully dried up to safe storaged moisture levels without significant spoilage. Drying rates with solar system were faster than natural air drying systems, and usually a little slower than similar low-temperature electric drying systems. 5. Final grain moisture levels were lower in solar tests than in natural air tests, and generally higher than in tests with continuous heated air. 6. Savings of energy by use of solar collectors ranged from 23% to 55%, compared to the natural and electric ileated air drying systems. However, total drying cost effectiteness tvas not significant. Therefore, it is desirable that solar grain dry-ing sIFstems tvhich could be suitable for multiple heating purposes on farms shouldbe developed. 7. Supplemental heat with solar radiation did little to reduce air flow requirementsbut refuced drying time and increased the p\ulcornerobability of successful drying duringdrying poriod.

• Journal of the Korean Wood Science and Technology
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• v.22 no.1
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• pp.66-71
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• 1994

To increase drying rate and reduce drying degradation, pretreatments such as prefreezing and presteaming have been widely used in wood industries. Presteaming lumbers prior to kiln drying is known positively to improve its permeability, to increase diffusion coefficient and to reduce discoloration, but negatively to increase collapse. Prefreezing lumbers prior to kiln drying is also known to reduce significantly its drying defects and its shrinkages. Thus it is no doubt that the pretreated lumbers shrink diversely from the untreated. In this study the shrinkage behaviors of the pretreated specimens are investigated by drying two tropical hardwoods (Apitong and Taun) in three different dying conditions: high temperature and slow drying rate (drying in a closed cylinder), high temperature and rapid drying rate (drying in an oven) and low temperature and slow drying rate(drying at room temperature). The prefrozen specimens show the least volumetric shrinkages in most drying conditions. The specimens dried in cylinders shrink most among all drying conditions. In general the pretreated specimens reached the 30 % moisture content faster than the untreated by about 30 %.

• Journal of Biosystems Engineering
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• v.41 no.4
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• pp.342-356
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• 2016

Purpose: The drying of a thin layer of native cassava starch in a tray dryer was modeled to establish an equation for predicting the drying behavior under given conditions. Methods: Drying tests were performed using samples of native cassava starch over a temperature range of $40-60^{\circ}C$. We investigated the variation in the drying time, dynamic equilibrium moisture content, drying rate period, critical moisture content, and effective diffusivity of the starch with temperature. The starch diffusion coefficient and drying activation energy were determined. A modification of the model developed by Hii et al. was devised and tested alongside fourteen other models. Results: For starch with an initial moisture content of 82% (db), the drying time and dynamic equilibrium moisture content decreased as the temperature increased. The constant drying rate phase preceded the falling rate phase between $40-55^{\circ}C$. Drying at $60^{\circ}C$ occurred only in the falling rate phase. The critical moisture content was observed in the $40-55^{\circ}C$ range and increased with the temperature. The effective diffusivity of the starch increased as the drying temperature increased from 40 to $60^{\circ}C$. The modified Hii et al. model produced randomized residual plots, the highest $R^2$, and the lowest standard error of estimates. Conclusions: Drying time decreased linearly with an increase in the temperature, while the decrease in the moisture content was linear between $40-55^{\circ}C$. The constant drying rate phase occurred without any period of induction over a temperature range of $40-55^{\circ}C$ prior to the falling rate period, while drying at $60^{\circ}C$ took place only in the falling rate phase. The effective diffusivity had an Arrhenius relationship with the temperature. The modified Hii et al. model proved to be optimum for predicting the drying behavior of the starch in the tray dryer.

• Journal of Power System Engineering
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• v.5 no.1
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• pp.44-49
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• 2001

Low temperature vacuum drying technique shows very excellent energy efficiency and prominent drying performances compared with the conventional hot air drying technique. This study was focused on the thermal characteristics of the low temperature vacuum drying technique. From the results of this study, it was confirmed that the time consumption for drying with the new drying technique could be shortened to about 1/3 of the time consumption with the conventional hot air drying technique under the same drying conditions for wet products. Also, the maximum drying rate with the new drying technique reached to about $0.35kg/m^2h$ at about 400% of moisture content.

• Solar Energy
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• v.7 no.1
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• pp.14-22
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• 1987

This paper presents an experimental study of a solar drying system designed and installed by KIER. Experiments have been performed using the KIER system for the drying of marine products, such as squid. Presented in detail are the experimental observations of collector air temperature, solar intensity, absorber plate temperature, drying chamber temperature, humidity and other measures of drying chamber performance with variation of air mass flow rate. As a result, average temperature attained in the drying chamber during autumn weather has been adequated for drying of squids.

• Food Science of Animal Resources
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• v.18 no.2
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• pp.164-175
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• 1998

The objective of this study was to investigate the effects of freezing rate on ice crystal size and freeze-drying rate. Our experiments were carried out with self-manufactured freeze-dryer. Gelatin gels (2% w / w, 80$\times$20mm) were frozen unidirectionally (Neumann's model) from the bottom at -45, -30, -20, and -15$^{\circ}C$ and followed with freeze-drying. Under the upper conditions we measured freezing rate and the change of temperature and pressure during freeze drying. Freeze-dried gelatins were cut horizontally into 5 mm thickness from the bottom and measured their pore sizes. Also freeze-drying rate(primary drying) is estimated by measuring the temperature of sample and pressure of vacuum chamber. During freeze-drying, profiles of pressure and temperature were shown constant tendency regardless of freezing temperature and we could expect the end-point of freeze drying by considering pressure and temperature together. In temperature profiles, the point which temperature increased significantly was observed during freeze-drying. There is no relationship between freeze temperature and drying rate of primary drying in our model system. As freezing temperature increased, ice crystal size(X*) which correspond to 63.2% of cumulative frequency was increased and at the same freezing temperature ice crystal size(X*) was decreased with distance from the bottom of the sample. Freezing conditions have a strong influence on the quality of the final freeze-dried products in freeze-drying system.

• Journal of Power System Engineering
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• v.15 no.3
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• pp.46-51
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• 2011

Low temperature vacuum drying technique, whose drying time and quantity of exhausting energy is about 25~30% of hot air drying, is very excellent in the drying efficiency. This paper is made out in the aspects of heat engineering with the object of developing Korean drying machine which can dry once a large quantity of objects to be dried in the state of low temperature and vacuum. As the results, it took about 17 hours(3~4 days in case of hot air drying) for material to reach about 18% of the final moisture content in order to store products for a long time, from about 78~80% of the early moisture content at the beginning of drying, and maximum drying rate comes to about 0.35 kg/m2hr at about 400% of the moisture content.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11b
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• pp.413-422
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• 2000

Samples of banana were dried in a two-stage heat pump dryer capable of producing stepwise control of the inlet drying air temperature while keeping absolute humidity constant. Two stepwise air temperature profiles were tested. The incremental temperature step change in temperature of the drying air about the mean air temperature of 30 $^{\circ}C$ was 5 $^{\circ}C$. The total drying time for each temperature-time profile was about 300 minutes. The drying kinetics and color change of the products dried under these stepwise variation of the inlet air temperature were measured and compared with constant air temperature drying. The stepwise air temperature variation was found to yield better quality product in terms of color of the dried product. Further, it was found that by employing a step-down temperature profile, it was possible to reduce the drying time to reach the desired moisture content.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.636-641
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• 2008

Heat pump drying has a great potential for energy saving due to its high energy efficiency in comparison to conventional air drying. The heat pump dryer is usually operated at the temperature less than $50^{\circ}C$ and the drying temperature is limited to the operating temperature of the heat pump system. In order to increase the drying temperature, the special box-type heat pump dryer has been developed. The dryer uses the two-cycle heat pump system which has the two heat pump cycles for high and low temperature heating. The high temperature cycle uses the refrigerant 124 to get the temperature greater than $80^{\circ}C$ and the low temperature cycle uses the refrigerant 134a. The drying experiment has been carried out to figure out the performance of the dryer with the selected drying material.