Adisak Nathakaranakule

A Superheated-Steam Fluidized-Bed Dryer for Parboiled Rice: Testing of a Pilot-Scale and Mathematical Model Development

This article describes the testing of a pilot-scale superheated-steam fluidized-bed dryer for parboiled rice along with development of a mathematical model for predicting the changes in temperature of steam and moisture content of parboiled rice during drying. Based on the obtained results, it was found that the superficial velocity of steam from 1.3 to 1.5 times of the minimum fluidization velocity had no significant effect on the drying rates of rice. The energy consumption for reducing the moisture content of paddy from 0.43 to 0.22 kg/kg dry basis was approximately 7.2 MJ/kg water evaporated. Drying temperature caused the appreciable change of parboiled rice qualities as characterized by water adsorption, whiteness and pasting viscosities, white belly, and hardness. Soaking paddy at a temperature of 70°C for 7–8 h before drying was sufficiently enough for producing parboiled rice, with no white belly. The gelatinization of starch during drying resulted in higher head rice yield of the product as compared to that of raw paddy.

Single-Stage Electronic Ballast Using Class-DE Low-

A single-stage high-power-factor electronic ballast with a Class-DE low-dv/dt rectifier as a power-factor corrector is proposed in this paper. The power-factor corrector is achieved by using a bridge rectifier that acts as the Class-DE low-dv/dt rectifier. The Class-DE low-dv/dt rectifier is driven by a high-frequency current source, which is obtained from the square-wave output voltage of the Class-D parallel resonant inverter through an LC -series circuit. By using this topology, the conduction angle of the bridge rectifier diode current is increased, and a low line-current harmonic is obtained. A prototype ballast is implemented to drive a 36-W fluorescent lamp. The switching frequency is fixed at about 84 kHz. Experimental results verify the theoretical analysis. The designed electronic ballast has a power factor of 0.99, a total harmonic distortion of 1.3%, a lamp current crest factor of 1.42, and 90% efficiency at full power.

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Quality of agricultural product can be degraded easily by heat. Heatless drying using an adsorption method may be a possible alternative to grain drying. The experiments of paddy drying using rice husk adsorbent were performed with single and multi-stages. In single stage, where high-moisture paddy were intimately mixed with rice husk in closed containers, high water concentration in the air within the container limits the moisture transfer rate and the resulting moisture content of the sample could not be decreased to the safe level for storage in spite of using low initial moisture content of the adsorbent or increasing the volumetric mixing ratio. However, the moisture content of paddy was reduced to the desire level as the multi-stage, where the adsorbent was physically separated in each stage and then replaced with the new one. The mathematical description of desorption-adsorption processes for a single kernel associated with the mass balance equation on the humidity ratio of the air surrounding the particles was formulated. The predictions of relative humidity and moisture contents of paddy and rice husk were shown to be in agreement with the experiments. The quality parameters, i.e., head-rice yield and rice whiteness obtained from multi-stage drying, were similar to those obtained by shade drying.

Current-Source-Driven Rectifier for Power-Factor Correction

Oil-free snacks have been increasingly demanded by health-conscious consumers. Bananas, which are among the worlds leading fruit crops, can be served as a snack. Because a porous structure is an important requirement for crispy banana, a high-temperature short-time treatment were chosen in this study. The effect of operating parameters—that is, intermediate moisture content, puffing temperature, and puffing time—on the volumetric shrinkage and quality attributes of banana were studied. The experimental results showed that the puffing temperature, puffing time, and intermediate moisture content significantly affected the shrinkage, hardness, and crispiness properties as well as color. The intermediate moisture content provided higher or lower shrinkage depending on its level and this factor subsequently affected the textural properties. The higher puffing temperature and longer puffing time resulted in less shrinkage, better texture, and a browner color. A second-order polynomial equation explained the quality parameters reasonably well. All quality parameters, except for volumetric shrinkage, were optimized by means of response surface methodology and the results showed that anintermediate moisture content of 26% db, puffing temperature of 163°C, and puffing time of 1 min should be established for puffed banana using a fluidized bed technique. Another experiment was conducted under the optimum condition to validate the quality parameters with predictions and the differences between experimental data and predictions were insignificantly different at p < 0.05.

Paddy Drying Using Adsorption Technique: Experiments and Simulation

Reducing moisture content as fast as possible, together with minimizing loss of quality, is important to food processing. To reach these objectives, experimental investigations were conducted to examine the effects of both peeled and unpeeled garlic cloves as well as operating parameters such as temperature and superficial velocity on the drying rate and quality of dried product. Peel resistance to moisture diffusion is considerably dominated and yields the longer drying time. Drying at high temperature shows the shrinkage of garlic clove to be lower than that at low temperature, whereas the product color is browner and the sizes of produced pores as revealed by scanning electron microscope are larger. The loss of volatile oil is insignificantly different among low- and high-temperature drying. The peel effect exhibits negative results on the product color, giving lower luminosity than the peeled sample, in particular at low temperature, because of longer drying time.

Optimum Conditions of Fluidized Bed Puffing for Producing Crispy Banana

The applied strategy of far-infrared radiation in paddy drying is divided into two main processes with some overlapping, namely, series and combined drying processes. The first comprises fluidized-bed drying, far-infrared radiation, tempering and ambient air ventilation as well as transport of paddy, and the latter is the combination of far-infrared radiation and hot-air convection in fluidization technique. The changes of average moisture content, grain temperature and milling quality in each paddy drying process are presented together with mathematical models. The experiments showed that series drying process was more effective to apply in the aspects of paddy drying and milling qualities than combined drying process. Due to less effectiveness in combined drying process, heat and mass transfer models, only series drying process were developed. The simulation results indicated that the models were capable of satisfactorily predicting the simultaneous average moisture contents and grain temperatures of a paddy grain as compared with the experimental results.

Effects of Peeled and Unpeeled Garlic Cloves on the Changes of Drying Rate and Quality

ABSTRACT The purpose of this research was to investigate strategies for papaya glace drying in tunnel. To evaluate the optimum conditions of drying, corresponding mathematical models were also considered. The criteria set for this study included low drying time, low specific energy consumption and acceptable qualities of papaya glace. The results obtained from the model of batch tunnel drying were in good agreement with the experimental ones. From the mathematical models, it was found that the optimum conditions of the first stage of drying of papaya glace (3.1×7.8×1.4 cm) were drying temperature of 70°C, specific air flow rate of 12 kg/h-kg dry papaya glace (velocity of 1.25 m/s) and air recycle ratio of 70%. In the second stage of drying papaya glace (0.98×0.98×0.98 cm), it was found that the optimum drying conditions were: drying air temperature of 55°C, specific air flow rate of 10 kg/h-kg dry papaya glace (velocity of 0.6 m/s) and air recycle ratio of 80%. Ambient air temperature and relative humidit...

Different Strategies of Far-Infrared Radiation Application in Paddy Drying

Healthy snacks have received more attention because of their low fat content. Color and texture are important to snack quality. Effects of chemical pretreatment, thickness, blanching, and puffing temperature on quality of banana slices were therefore investigated. Banana slices (2.5 and 3.5 mm thickness) were chemically treated by citric acid and sodium metabisulfite, blanched, and dried at a temperature of 90°C to an intermediate moisture content of 25% db. They were then puffed in a fluidized bed dryer at 160 and 180°C for 2 min and dried again at the same drying temperature as the first drying step. Blanching, puffing temperature, and thickness strongly affected the degree of shrinkage, effective moisture diffusivity, morphology, textural properties such as hardness and crispiness, and color, but the chemical treatment did not affect those qualities. Blanching can improve the product appearance; the color was uniform and shiny throughout the surface and golden yellow. However, the textural attributes of the blanched sample had higher hardness and less crispiness than those of unblanched sample.

Strategies for Papaya Glacé Drying in Tunnel

A single-stage high-power-factor (HPF) electronic ballast with a class-DE low dv/dt rectifier as a PFC has been proposed in this paper. The proposed is archived by using a bridge rectifier which acts as the class-DE rectifier. By using this topology the conduction angle of the bridge rectifier diode current can be increased then the low line current harmonic was obtained. The class-DE low dv/dt rectifier is driven by a high frequency sinusoidal current source, which an electronic ballast prototype operating 84 kHz has been implemented to drive 36-W fluorescent lamp. Experimental results verify the theoretical analysis. It is shown that the designed electronic ballast has 0.99 power factor, 1.3% total harmonic distortion, 1.32 lamp current crest factor and 90% efficiency at full power.

Influences of Pretreatments and Drying Process Including Fluidized Bed Puffing on Quality Attributes and Microstructural Changes of Banana Slices

Abstract The aim of this study is to find a better drying method to replace conventional hot air drying (HAD) in terms of faster, energy efficient and better product quality. Two alternative drying techniques, microwave combined with hot air drying (MHD) and microwave vacuum drying (MVD), are compared in this study to dry peeled and destoned longan fruit. Both MHD and MVD reduced the drying time up to 48 % and energy consumption as compared to HAD. These techniques provided lower product redness, yellowness and shrinkage but higher lightness and porous structure as compared to HAD. MVD reduced hardness and toughness of the dried product. MHD provided the highest preference score in terms of colour and shape and was as acceptable as the commercial product dried by HAD. MHD is the most suitable method for longan drying.