Takemi Abe

THIN LAYER SOLAR DRYING CHARACTERISTICS OF ROUGH RICE UNDER NATURAL CONVECTION

Abstract Thin-layer solar drying experiments were conducted at Matsuyama, Japan, with medium grain rough rice. The range of average drying air temperature was 22.3–34.9°C, and the relative humidities were between 34.5% and 57.9%. The initial moisture contents were in the range of 37.07–37.69% dry-basis. A mixed-mode natural convection solar grain dryer was used for this experiment. The data of sample weight and dry- and wet-bulb temperatures of the drying air were recorded continuously from morning to evening for each test. The drying data were then fitted to the Page model, based on the ratios of the differences between the initial and final moisture contents and the equilibrium moisture content (EMC). The model gave a good fit for the moisture content with an average standard error of 0.00387 dry-basis. Both the drying parameters N and K are linear functions of temperature and relative humidity. This single-layer drying equation can be used for the simulation of deep bed drying of rough rice in mixed-mode type natural convection solar dryers.

Accelerated drying of welsh onion by far infrared radiation under vacuum conditions

Abstract Far infrared radiation has excellent radiation characteristics and high energy conversion rates can be achieved using ceramic coated radiators. Using such a radiator, the dehydrating synergy, generated by far infrared radiation heating under vacuum condition, the drying of welsh onion was studied. The radiation intensity levels influenced dramatically the drying rate and the product qualities: the a ∗ for rehydrated onions, and the L ∗ and ΔE ∗ ab for dehydrated onions. A rising-rate period, a constant-rate period, and a falling-rate period were ascribed to the drying behaviour. The radiation also had significant effects on chlorophyll content. The long time in drying and the high temperature may have contributed to a decrease in rehydration properties.

THIN-LAYER DRYING CHARACTERISTICS OF ROUGH RICE AT LOW AND HIGH TEMPERATURES

Abstract Thin-layer drying characteristics of rough rice were determined at temperature ranging from 11.8 to 51 °C and for relative humidities ranging from 37.1% to 91.3%, with initial moisture contents in the range of 24.7 to 41.6% dry basis. An oven, a self contain air conditioning unit, recently developed in Japan, was used for this experiments. With this apparatus, very smooth drying curves were obtained. The data of sample weight, and dry and wet bulb temperatures of the drying air were recorded continuously throughout the drying period for each test. The drying process was terminated when the moisture content change in 24 h was less than 0.2 % d.b. (weight change was less than 0.05 g). The final points were recorded as the dynamic equilibrium moisture contents. The drying data were than fitted to the Page model. The model gave a very good fit for the moisture content with an average standard error of 0.294 % d.b Both the drying parameters, K and N, are function of drying air temperature and relativ...

FAR INFRARED–VACUUM AND –CONVECTION DRYING OF WELSH ONION

The drying of welsh onion by a far–infrared (FIR) heater under reduced pressure and convective conditions were studied to understand the drying characteristics. The effects of radiant power input and vacuum levels on the drying phenomenon were investigated. In addition, drying rate as a function of moisture content was studied vis–a–vis drying qualities such as rehydration potential, shrinkage, and color change. When onion samples were dried from about 10.1 to 0.05 w/w dry basis moisture content, the three characteristic periods, namely, rising, constant, and falling rate periods, were obtained. The drying rate increased with increasing radiant power input and was higher in a reduced–pressure environment than under a convective condition. With 0.17 W/cm2 radiant power input, the drying rate was 50% higher in the vacuum operation than under the convective condition. There was a higher shrinkage with a concomitant higher rehydration potential and superior quality of onion at lower radiant power input with the FIR–vacuum system than with the FIR–convection system.

Moisture adsorption isotherms of rough rice

Abstract Moisture adsorption isotherms of medium-grain rough rice were determined using a constant environment chamber for various combinations of air relative humidity (56–89.3%) and temperature (17.8–45°C). A thin-layer technique was employed to achieve uniform re-wetting. An oven as a self contained air conditioning unit, recently developed in Japan, was used for this experiment. Four commonly cited EMC/ERH equations, i.e. modified Henderson, modified Chung–Pfost, modified Oswin and modified Halsey equations were compared for their ability to fit the experimental data. The comparison shows that the modified Chung–Pfost equation is the best equation for describing the EMC/ERH adsorption isotherms of rough rice. Temperature dependent functions of the modified Henderson, modified Chung–Pfost and modified Oswin equations were empirically modified to fit with the multiple linear regression techniques. The adsorption EMC data obtained in this work agree with the previous data. These fitted equations are based on a wide range of temperatures and relative humidities and therefore provide a useful basis for future work on drying and storage of rough rice.

Kinematic Model for a Far Infrared Vacuum Dryer

Abstract Energy analyses in drying of welsh onion from one source of far infrared radiation at an absolute pressure of 2.6 and 5 kPa were carried out to determine the energy input at which the highest level of efficiency would be attained. The experimental results were used not only to formulate an advanced mathematical model for the prediction of moisture content of onion as a function of drying time but also to study the dryer efficiencies. Less than half of energy input was utilized for evaporating water from the onion. Approximately 73–99% of operating efficiency, which was dependent on the dryer configuration, was converted into radiant energy. The highest radiant efficiency was obtained at 40 W initial power supply, which was equivalent to the source temperature of about 100°C. An 80 W initial electrical power supply at a 10 cm distance of heater from the onion surface showed the highest drying efficiencies. At 80 W power, efficiency decreased with increasing distance from the heater source but at the expense of quality. For optimum drying efficiency without compromising quality, distance of heater from onion surface was proposed to be 10 cm.

Heat and Mass Transfer Characteristics of Barley During Fir Drying

Abstract Higher moisture removal rate and higher temperature of grain were observed with the increase in intensity level. Contrary to convective grain drying, an increase in air velocity caused a negative effect while relative humidity resulted in increase of drying rate. Initial moisture content of grain does have influence on the drying rate but less significant than radiation intensity and inlet air velocity. The drying data were fitted to the modified exponential model using NLIN regression technique. The coefficients obtained were then correlated against independent variables using stepwise multiple linear regression. The proposed model gave adequate prediction of the experimental data.

THIN–LAYER MOISTURE ADSORPTION STUDIES OF BARLEY

Thin–layer moisture adsorption data were measured for barley at temperature ranging from 5.7³C to 46.3³C and for relative humidities ranging from 48.2% to 88.6%. Thirty–three tests were conducted, and each test lasted for about a week. The re–wetting data were fitted to the Page model, based on the ratios of the differences between the initial and final moisture contents and the equilibrium moisture content. The Page model was chosen because it is both effective and relatively simple, and when incorporated into a deep–bed simulation model requires less computing time than the theoretical diffusion moisture transfer model. The model gave a very good fit for the moisture content with an average standard error of 0.176% dry–basis. The model parameter K is a function of re–wetting air temperature, relative humidity, and re–wetting time. The parameter N can be simply represented as a product–dependent constant without any considerable error in simulating the re–wetting rate of barely. It is not necessary to relate the re–wetting parameters with the initial moisture content of the sample. The results presented here are useful in calculating the moisture transfer process occurring during low–temperature drying and ventilated storage.

Far Infrared Radiation Drying of Welsh Onion under Reduced Pressure and Convection

A comparative study of the effects of initial power supply on the drying of the leafy part of welsh onion by a far infrared heater under reduced pressure and convection were studied to understand the drying phenomenon. The drying rate as a function of moisture content was studied vis-a-vis drying qualities such as rehydration potential, shrinkage, and color change. The three characteristic preheating, constant, and falling rate periods were obtained in both drying techniques. Drying rate increased with increasing radiative energy input and was higher under the reduced pressure environment than in the convective condition as was shrinkage and rehydration ratio. For optimum drying speed and product quality vis-a-vis energy savings in the drying of welsh onion, it was recommended that FIR- vacuum operation at 70-watt initial power supply be used.

DIFFUSION COEFFICIENTS FOR PREDICTING ROUGH RICE RE-WETTING BEHAVIOR

ABSTRACT Thin-layer re-wetting experiments were conducted with medium grain rough rice in the temperature range of 17.8 to 45°C and for relative humidities between 56 and 89.3%, with initial moisture contents in the range of 10.26 to 12.71% dry-basis to determine the diffusion coefficient of rough rice. Recent efforts to characterize the re-wetting characteristics of rough rice are summarized. New equation for temperature dependent liquid diffusion coefficients for medium grain rough rice are presented. The diffusion coefficient in re-wetting was lower than the drying. The results presented here, over typically five day re-wetting, will be useful in studying the longer term moisture transfer process occurring during ventilated storage.