Drying is an operation which removes it after evaporating the moisture of an object weight from heat. About 2500kJ/kg of fusion heat which changes water into vapor should be heat transferred to a dried matter by using a certain of heating way in any case. Various objects for drying are hedged round with restrictions in each quality, and they cannot be said to be good if thinking of only the efficient supply of the heat of vaporization. That is, the most efficient heat transfer method should be considered and the improvement of the efficiency should be studied among the drying methods suitable for requirements on the quality of dry products, among restrictions of the allowable temperature related to it.
Because the processing technology lags behind other nations relatively though our country has global-class aquiculture and fishing technology at present, processed marine products are mainly frozen foods, canned goods, salty food(fermented fish products), fish paste products(boiled fish paste), and we can see that high-value dehydrated foods by drying are very few. These problems are considered to be caused directly by the lack of drying technology.
The drying methods performed widely throughout the present industry include an hot-air drying method by convective heat transfer, a vacuum drying by conduction or radiant heat transfer and vacuum freeze drying, infrared drying or microwave drying and ultrasonic drying using mechanically vibration energy. In particular, among these drying methods, interests in the drying methods which the regulation of the moisture contents in the material is easy as compared to other devices, which the thermal deformation of the material is less because the drying temperature is relatively lower, which the corruption and deterioration of the material that may occur during the drying process can be prevented because the oxygen concentration is very low, and which the drying time is relatively short as compared to a hot-air dryer.
This paper aims at developing the localized design technology of an energy-efficient vacuum drying oven which can dry the sea cucumber with the difficult drying condition and the expected overproduction in a short time within 24 hours in a high-quality condition of more than the natural drying level.
The following results were obtained in the scope of this experiment.
1. As the result of having surveyed in Hong Kong for the objective evaluation for the international product level of the sea cucumber dried in this experiment, more excellence as compared to even Japanese products called the world's best quality in the quality was realized in the actual place.
2. As the result of having measured the required electric power and the power, they were the maximum value as 4~5kW in the first stage of drying, average power of 3kW or so was required after about 4 hours, and this was confirmed to be very energy-efficient as compared to other dryers.
3. The experiment showed that the typical constant-rate drying period and falling-rate drying period exist definitely, and the weight changes during the constant-rate drying period presented the experiment results in the linear expression for the time elapsed, the weight changes during the falling-rate drying period presented the experiment results in the exponential expression which the weight gradually decreases for the time elapsed.
4. We could see that the heat transfer per unit area of the drying board after 8 hours which the drying began, namely, during constant-rate drying period, has the heat flux of 711.75~1046.70kJ/m2hr, and that also the heat flux decreases exponentially in proportion to this because the evaporation of the moisture decreases gradually during the falling-rate drying period.
5. Through a temperature change curve, temperature rising is completed if 2 hours pass after the drying begins, most moisture is evaporated if the regular active evaporation progresses for 8~9 hours, and we can see that the drying is being completed as the temperature in the sea slugs gets similar to the superficial temperature.