ACOUSTIC DRYING OF GREEN RICE

The effects of acoustic drying of rice in a fluidized bed were evaluated at frequencies of 12 kHz and 19 kHz and air temperatures of 20.5° C and 40° C. The intensity levels were 132 and 128 dB respectively, intensities that are considerably lower than the 145 dB and higher usually applied in drying experiments of this type. The results confirmed that the effectiveness of acoustic drying is more pronounced at the lower temperatures, a significant fact especially in drying heat sensitive materials. The rate of water removal increased when acoustical energy at either frequency was applied with room temperature air. Increase in drying rate was not obvious when acoustic energy was applied at 40° C at the intensity levels of these experiments.     

ACOUSTIC DRYING OF ONION

ABSTRACT

Drying processes have long been used as a means of preserving foods and other biological materials. In recent years, the use of drying processes has had great impact on both the production and the processing phases of the agricultural industry. Dehydration of three thickness onion slices using sound waves was evaluated at two frequencies, two sound pressure levels and three temperatures. Compressed air served as the driving force of an aerodynamic siren ( sound source) as well as the carrier of the evaporated moisture. Experimental results showed that drying rates are increased by acoustic vibrations and the increase depended on the sound frequency. The loss of pungency in onion ( measured as the percent of remnant pyruvic acid) was not significantly different at a confidence level of 95% for all variables studied.     

ACOUSTIC DRYING OF COAL

The influence of acoustic energy in drying of high ash coal in association with thermal energy is studied. The variables used in the experiments are air temperatures 70°C and 120°C, acoustic intensities 120, 135 and 145 dB for different grain sizes ranging from 44 to 1000 microns (µm). It is established that the drying process in coal is feasible above a critical sound pressure level given by P=125+10 log f (f is the acoustic frequency in KHz). Removal of moisture in coal is enhanced with time, intensity of sound and air temperature. The drying rate is more pronounced for coal with particle size range 149 to 297 microns.     

ACOUSTIC DRYING OF COAL

The influence of acoustic energy in drying of high ash coal in association with thermal energy is studied. The variables used in the experiments are air temperatures 70°C and 120°C, acoustic intensities 120, 135 and 145 dB for different grain sizes ranging from 44 to 1000 microns (µm). It is established that the drying process in coal is feasible above a critical sound pressure level given by P=125+10 log f (f is the acoustic frequency in KHz). Removal of moisture in coal is enhanced with time, intensity of sound and air temperature. The drying rate is more pronounced for coal with particle size range 149 to 297 microns.     

INTERMITTENT DRYING OF ROUGH RICE

Abstract

This work obtains thin-layer drying data for rough rice from 108 treatments. A thin-layer drying equation is also derived using these data with drying air absolute humidity, drying air temperature, tempering time interval and drying time interval as the independent variables. In addition, an intermittent drying equation is developed to predict the drying behavior of rough rice in a re-circulating type rice dryer.     

DRYING KINETICS OF ONION AND GREEN PEPPER

ABSTRACT

Drying kinetics were examined by introducing one-parameter empirical mass aansfer model, where the characteristic parameter (drying constant), is a function of process variables. The model was tested with data produced in an experimental through dryer, using direct regression analysis. Investigation involved two vegetables (namely, green pepper and onion) and a wide range of characteristic dimensions of samples and air conditions (temperature, humidity, and velocity). The parameters of the model considered were found to be greatly affected by sample characteristic dimension and air temperature.     

DRYING KINETICS OF ONION AND GREEN PEPPER

Drying kinetics were examined by introducing one-parameter empirical mass aansfer model, where the characteristic parameter (drying constant), is a function of process variables. The model was tested with data produced in an experimental through dryer, using direct regression analysis. Investigation involved two vegetables (namely, green pepper and onion) and a wide range of characteristic dimensions of samples and air conditions (temperature, humidity, and velocity). The parameters of the model considered were found to be greatly affected by sample characteristic dimension and air temperature.     

ACOUSTIC AND ELECTROACOUSTIC METHODS OF DEWATERING AND DRYING

Interesting results have been observed in applying acoustic energy to dewatering and drying materials. However, drying by acoustic energy alone is expensive, energy intensive, and at best can be justified only in applications where rapid drying is necessary to preserve a product, the product is heat sensitive and its value justified the cost. However, synergistic effects have been observed when acoustic energy has been used with electrophoresis and electro-osmosis to dewater materials. An electroacoustic dewatering (EAD) technology has been developed in recent years that indicates good economic potential and an effectiveness that exceeds most conventional methods of dewatering. Very good results have been obtained from laboratory studies using the techniques with fine coal slurries, food products, municipal sewage sludges, and many other products.     

FINITE ELEMENT SIMULATION OF ROUGH RICE DRYING

Milled, brown and rough rice samples were dried in the laboratory with heated air and diffusivities of the endosperm, bran and husk were evaluated with a search technique using the finite element method. The endosperm had the highest diffusivity. The husk had a slightly higher diffusivity than the bran because the trapped air inside the husk was considered as an integral part of the husk. The finite element method predicted rough rice drying that was in good agreement with experimental results.     

COMPUTER SIMULATION ON INTERMITTENT DRYING OF ROUGH RICE

This study applied a partial differential equation model with newly-developed thin layer equations to simulate batch re-circulating dryers under different drying conditions, which are combinations of four parameters: drying air temperature, drying air absolute humidity, drying period duration, and tempering period duration. The moisture change and the drying rate, which were of particular concern with respect to the simulated data, were investigated. Validation drying tests were carried out in a lab scale re-circulating rice dryer. Two sets of experiment were performed involving different drying parameters to simulate re-circulating rice dryers which are extensively used in Asian countries. Comparing these two experimental data with two simulated drying curves respectively, it revealed they are quite consist with each other under the same drying conditions. Drying air temperature, drying air humidity, drying period duration and tempering period duration significantly influenced the drying rate. Under the same drying condition, the tempering period duration effect was insignificant to the drying rate in drying zone as the drying air humidity or temperature increased. And, a higher initial moisture content obtained higher time and energy efficiency for the re-circulating rice dryers.     

CONDUCTION DRYING OF RAW AND STEABED RICE BRAN

The effects of conduction heating in a steam jacketed cylindrical dryer-cum stabilizer at the drying surface temperatures ranging from 100° to 120°C on thin layer conduction drying characteristics of raw and steamed rice bran were studied. Results show that both raw and steamed rice bran at 13.7·14.2 and 14.7 ·16 ·· 3 percent (d b) initial moisture contants (imc; respectively dried uncer fillinq-rate period only, where as steamed bran at 30·3 per cent imc dried initially under constant rate period for a very short time and then dried under fall ing-rate period. The drying surface temperature of 115°C can be taken as optimumu for conduction drying of both raw. and steamed rice bran. The empirical drying equations, developed for the above drying conditions. can be used to predict the drying time with fairly good accuracy.     

DYNAMIC OPTIMAL CONTROL OF BATCH RICE DRYING PROCESS

The drying of paddy rice may result in quality degradation, expressed as a head kernel yield, leading to significant commercial depreciation of the product. A mathematical model of the drying and of the quality degradation process was combined with a dynamic optimization algorithm to determine the drying conditions (air temperature and relative humidity as functions of time) that ensured the highest possible final product quality for a specified drying time and a specified final moisture content. The robustness of the optimal drying strategy with respect to the initial state of the product, to the model parameters and to the initialization of the optimization algorithm was verified. The compromise between the highest achievable final quality and the allowed total drying time was studied. The combination of simulation and optimization yielded a new insight in the rice drying process and in the quality preservation strategies.     

CONCURRENT FLCW RICE DRYING

Long- and medium-grain rice were dried in a commercial multi-stage concurrent-flow dryer. Drying air temperatures varied fran 82°C to 177°C. Over six points of moisture were removed in one dryer pass without affecting the rice head-yield. Energy consumption of the dryers was half that of conventional rice dryers. Simulation played a major role in the design of the mUlti-stage concurrent-flow rice dryers.     

INFLUENCE OF DRYING ON THE STORAGE ABILITY OF RICE BRAN

It is known that the rate of formation of free fatty acids in rice bran is dependant on the history of temperature and moisture content experienced by the bran since its formation. A mathematical model is already available to predict the rate of formation of free fatty acids in rice bran for heat treatment conditions. This paper attempts to apply the model for storage conditions in order to predict the storage ability of rice bran which has undergone varying drying conditions. Experimental results already available were found to be in agreement with the predicted theoretical values based on the model.     

CONCURRENT FLCW RICE DRYING

ABSTRACT

Long- and medium-grain rice were dried in a commercial multi-stage concurrent-flow dryer. Drying air temperatures varied fran 82°C to 177°C. Over six points of moisture were removed in one dryer pass without affecting the rice head-yield. Energy consumption of the dryers was half that of conventional rice dryers. Simulation played a major role in the design of the mUlti-stage concurrent-flow rice dryers.     

A COMPARTMENTAL MODEL OF THIN-LAYER DRYING KINETICS OF ROUGH RICE

ABSTRACT

Rough rice at about 21% (wet basis) was dried at various conditions of temperatures and evaporating capacities of air. The influence of both parameters on drying rate has been studied. At high temperatures, high drying rates can be achieved with low evaporating capacities. In addition, desorption isotherms of rough rice were measured at 35, 60 and 85°C and the experimental isotherms data were fitted using a modified Pfost equation.

A compartmental model was developed to simulate the grain moisture content. Heat and mass transfer coefficients were optimized using a Nelder & Mead method. Internal mass transfer coefficient was written as an exponential function of the average moisture content and temperature of the grain and the external mass transfer coefficient as a function of air temperature. The compartmental approach predicts very well the average moisture content with a mean error of about 5% in static and dynamic conditions.     

A COMPARTMENTAL MODEL OF THIN-LAYER DRYING KINETICS OF ROUGH RICE

Rough rice at about 21% (wet basis) was dried at various conditions of temperatures and evaporating capacities of air. The influence of both parameters on drying rate has been studied. At high temperatures, high drying rates can be achieved with low evaporating capacities. In addition, desorption isotherms of rough rice were measured at 35, 60 and 85°C and the experimental isotherms data were fitted using a modified Pfost equation.

A compartmental model was developed to simulate the grain moisture content. Heat and mass transfer coefficients were optimized using a Nelder & Mead method. Internal mass transfer coefficient was written as an exponential function of the average moisture content and temperature of the grain and the external mass transfer coefficient as a function of air temperature. The compartmental approach predicts very well the average moisture content with a mean error of about 5% in static and dynamic conditions.     

MODELING OF ROUGH RICE DRYING IN THIN VERTICAL COLUMNS

ABSTRACT

The solution of classical diffusion equation based on the assumption of average moisture diffusion coefficient did not adequately represent natural convection drying of rough rice in thin vertical columns exposed on both sides to hot air. Instantaneous moisture diffusivity coefficients determined from experimental drying curves decreased continuously with an increase in exposure duration and were linearly related to moisture ratio. The proponionality constant which was called apparent moisture diffusion coefficient was distinctly related to air temperature, relative humidity, and initial moisture content of rough rice. The modified moisture diffusion model using the instantaneous moisture diffusion coefficient was found to best represent the moisture removal from bulk rough rice.     

EFFECT OF FLUIDIZED BED DRYING ON STABILIZATION OF RICE BRAN

ABSTRACT

Rice bran was treated in a batch fluidized bed at temperatures starting from 90°C up to 130°C in steps of 10°C for different treatment periods. Drying characteristics of rice bran so obtained were used in a mathematical model to predict the maximum possible storage period of rice bran treated under fluidizing conditions. It was observed that the fluidized bed treatment of rice bran requires much lower treatment times for stabilization of rice bran compared with packed bed processes and therefore could be very attractive in commercial applications.     

EFFECT OF FLUIDIZED BED DRYING ON STABILIZATION OF RICE BRAN

Rice bran was treated in a batch fluidized bed at temperatures starting from 90°C up to 130°C in steps of 10°C for different treatment periods. Drying characteristics of rice bran so obtained were used in a mathematical model to predict the maximum possible storage period of rice bran treated under fluidizing conditions. It was observed that the fluidized bed treatment of rice bran requires much lower treatment times for stabilization of rice bran compared with packed bed processes and therefore could be very attractive in commercial applications.