Armansyah H. Tambunan

Freeze Drying Characteristics Of Medicinal Herbs

The demand on traditional herb medicine shows a tremendous increase. Conventionally, medicinal herbs are dried at high temperatures, causing quality deterioration. The freeze-drying characteristics of medicinal herbs were studied, and the quality of the freeze-dried products assessed. The herbs studied were medicinal ginger and Javanese pepper. It was found that drying time, was more influenced by chamber pressure and freezing rate than by the surface temperature of the product. Higher chamber pressures and faster freezing rates tended to shorten the initial (primary) drying time but lengthen the secondary drying time. Quality of the freeze-dried product was assessed as slightly lower than the quality of the raw material, but higher than when oven dried at 35–40°C, and met the MMI standard.

Exergy Analysis on Simultaneous Charging and Discharging of Solar Thermal Storage for Drying Application

Exergy analysis is considered as an effective tool and has been widely used for assessing energy status of a thermal process from thermodynamic point of view. In this article, the exergy analysis is applied to the assessment of sensible thermal storage for a solar drying system. The objective of this study is to evaluate the role of the heat transfer process to the simultaneous exergy charging and discharging of the storage system in relation to the solar drying system. The results show that exergy loss ratio, which was regarded as the fraction of transferred exergy to the drying chamber, varied with the charging time and reached a minimum value at a certain charging time. The minimum exergy loss ratio and the time to reach the value are strongly dependent on the number of transfer units (NTU). The ratio of exergy loss at NTU ≅ 0 was 86%, greater than the value of practical interest. Accordingly, the application of sensible heat storage for a solar drying system will exert only a small effect to the temperature of the drying air entering the drying chamber.

Transport Properties Of Cellular Food Materials Undergoing Freeze-Drying

The samples of sliced and mashed apples were freeze-dried by controlling their surface temperatures over the usual pressure range of commercial operations. The surface of sliced samples could not be maintained at above 10°C in order to prevent the frozen layer from melting, while that of mashed samples was allowed to heat up to 70°C. Thermal conductivities and permeabilities were determined by applying the uniformly-retreating-ice front model to the dried layer of the samples undergoing freeze-drying. The values of permeability for the mashed samples were found to depend on the ice-crystallization time during freezing. The results indicated that the drying rate of sliced samples was limited by the transfer rate of water vapor flowing through the dried layer. A cellular structural model is proposed for predicting the permeability of the dried layer, based on the resistance of the cell membrane to molecular transfer of water vapor.

Measurement of Evaporation Coefficient of Water During Vacuum Cooling of Lettuce

Experimental investigations had been carried out to measure the evaporation coefficient of water from lettuce undergoing vacuum cooling, applying an evaporation boundary-layer model developed for the free surface of pure liquids. The value of evaporation coefficient for lettuce was found to be dependent on mass flux from the leaf surface, and about 4 times lower than that for the free surface of water. The effects of operating pressure to the coefficient were not appeared definitely under the experimental conditions.

Characterization of biodiesel fuel and its blend after electromagnetic exposure

Abstract It has been known that magnetic exposure of fuel prior to combustion can improve effectiveness of combustion process. However, the main reason of the phenomenon is still unclear. In this paper, characteristics of fuel as exposed to electromagnetic field was measured experimentally and inter-related appropriately in order to have preliminary insight to the clarification of the phenomenon. Fuel characteristics being investigated were viscosity, vibration of the fuel molecules, dipole moment, and refractive index. These experiments were performed using various blend compositions between fossil diesel (petrodiesel) and biodiesel fuel i.e. B0, B10, B40, B70 and B100. The electromagnetic field was generated by a galvanum tube wounded with 9,000 wire coil. The fuel characteristics of both prior and post electromagnetic exposures were then measured with time variation of 0–1,800 s. The experimental results revealed that electromagnetic exposure of the fuel increased vibrational frequency of its molecules significantly, which in turn weakened the attracting energy and caused uniform arrangement of dipole moment of the molecules. The experimental data also revealed that the fuel characteristics did not alter significantly after it was exposed to the electromagnetic field for more than 1,200 s. This information is considered to be useful for further research in order to resolutely clarify the phenomenon of efficient combustion process of fuel after exposure to magnetic field.

Experimental study on the effect of freezing medium temperature on exergy efficiency

This paper evaluates the effect of variable temperatures of a freezing medium on exergy efficiency, based on experimental data. The experiments were conducted with variable temperatures at the first, second, and third stages of the freezing course. The results show that the third stage was the most reversible stage. Irreversibility of the first stage was affected by freezing temperature of both the first and second stage. The study implies that scheduling of the freezing temperature is important for reducing the total irreversibility of the process, and the temperature has to be determined consecutively from the third to the first stage.