A dynamic model representing the continuous FLUIDIZED BED DRYER is presented. The model takes into account the presence of the three phases: bubble phase, cloud phase and emulsion phase. The transient analysis for step disturbances in the input variables is obtained. The influence of operating conditions on the dynamics of the DRYER is discussed and the results are compared with the experiment. The model can be used for developing a model based on other suitable control strategies.

The objective of this study was to examine the effects of the FLUIDIZED-BED drying method on the final quality of two varieties of Iranian rice, medium- and long grain. The results were compared to that of paddy drying using a traditional method. Rough rice was treated in the FLUIDIZED BED drier at 140°C for 2 minutes. Similar samples were dried for 8-10 hrs by the traditional method. Dried samples were dehusked and polished. Quality factors, including trade quality (head rice yield percent and whiteness), cooking quality (amylose content, gelatinization temperature, gel consistency, aroma and flavor) and nutritional quality (thiamine and lysine contents), were then measured for each sample. Finally, the data was analyzed. Results show that paddy drying in a FLUIDIZED BED DRYER would reduce the quality factors except for rice whiteness for which conventional drying is more acceptable. Therefore modification of FLUIDIZED-BED drying technique is recommended.

Exergy analysis is one method for studying of energy efficiency and optimization for systems and machines including DRYERs. FLUIDIZED BED DRYERs despite widespread usage have low energy efficiency. Therefore a new method has been proposed that the fluid BED drying has been combined with thick (fix) BED DRYER as outlet air from the FLUIDIZED BED section is conducted to the thick BED section for drying the other material or same kind material that existed in the first section. Experiments were performed in three temperatures, 50, 60 and 70oC and three BED depth in down, FLUIDIZED BED drying, 4, 6 and 8 cm and two BEDs depth in up, batch BED drying, 6 and 8 cm. The results show that exergy loss of top floor is lower than down floor. And also increasing in BED depth of down floor causes increasing in exergy loss of top floor. But exergy loss of down floor decreases with increasing in BED depth of top floor.

In FLUIDIZED BED DRYER, high velocity of air causes wastage of thermal energy. In order that fixed BED DRYER be combined with FLUIDIZED BED DRYER, it was mounted after FLUIDIZED BED in air way. According to the first law of thermodynamic, energy and effective parameters on energy consume were analyzed. Experiments were performed at three temperature ranges of 50, 60 and 70oC, three BED depths of 4, 6 and 8cm for the lower BED and two BED depths of 6 and 8 cm for the higher. Increasing BED depth of each BED showed clear effects on EU and EUR of the other floor. The EU value of top floor was more than that of bottom floor. Maximum energy consumption was obtained in 70oC at 8dw-8up BED depth and energy consumption ratio was obtained in 50oC at 8dw-8up.

Heat transfer phenomena in batch FLUIDIZED BED DRYER have been studied and analyzed using three phase model including solid phase, interstitial gas phase and bubble phase based on Rizzi model. New correlations of heat transfer coefficient to surrounding and convection heat transfer coefficient between solid and interstitial gas are being proposed. In addition, some modifications have been done according to the state of flow and particle properties.The model was used to study the effects of particle diameter, particle density and input gas temperature on Geldart group D particles. The numerical results of heat transfer such as solid and gas temperature distributions have been compared with the available experimental data and good agreement between them is observed.

Modeling of drying kinetics of canola was studied at 30 to 100oC in a Lab scale FLUIDIZED BED DRYER. Drying rate of the crop was assessed, using many conventional moisture ratio models employed in food science. Effective Diffusivity coefficient (Deff) and activation Energy (Ea) of kernel moisture were determined using Fick's Law of Diffusion and Arrhenius Equation. Besides, the effects of temperature changes on drying time were modeled through, regression method. Results indicated that static pressure dropped from 596 to 583 Pa when kernels starting to fluidize. In fluidizing state, canola drying time becomes reduced by 74% through an increase of temperature from 30 to 100oC. In comparison with the other models, Approximate Diffusion model and two term Exponential model are in good agreement with the experimental data respectively with high R2 and low c2 as well as RMSE. Also Newton model was of little with the other models. It bears a single coefficient, and is easy and convenient to be used for an estimation of drying rate of canola in FLUIDIZED BED DRYER. Temperature changes from 30 to 100oC cause Deff to increase from 3.759×10-11 to 8.457×10-11. In this research, Ea of canola moisture was determined as 11.03 kJ/mol. Selected exponential Regression model is in good agreement with the experimental data and suitable for an estimation of drying time in temperature range of 30 to 100oC.

One of the effective drying mechanisms is FLUIDIZED BED DRYER where particles are FLUIDIZED by hot air. Mixing and heat transfer are very rapid, therefore the drying time is short. In order to study the mechanism of drying under different conditions a two-fluid model is imposed. The model uses one-dimensional conservation of mass, heat and momentum equations for each phase of gas and solids. Numerical method is carried by finite-volume scheme. The verification of the theoretical results was done by the use of an experimental setup. The results indicate a good qualitative agreement. By eliminating the convective terms in a solid phase and drags model; packed BED condition is obtained. The result verified with the performed packed BED experimental data. Futher, with the proposed model, the performance and comparison of fluidzed and packed BED DRYER can be shown.

One of the effective drying mechanisms is FLUIDIZED BED DRYER where particles are FLUIDIZED by hot air. Mixing and heat transfer are very rapid, therefore the drying time is short. In order to study the mechanism of drying under different conditions a two-fluid model is imposed. The model uses one-dimensional con servation of mass, heat and momentum equations for each phase of gas and solids. Numerical method is carried by finite-volume scheme. The verification of the theoretical results was done by the use of an experimental setup. The results indicate a good qualitative agreement. By eliminating the convective terms in a solid phase and drags model; packed BED condition is obtained. The result verified with the performed packed BED experimental data. Further, with the proposed model, the performance and comparison of FLUIDIZED and packed BED DRYER can be shown.      

AbstractBackground and objectives: Among the various hot air drying methods, FLUIDIZED BED drying has significant advantages such as high heat and mass transfer, uniform moisture reduction of products with short time and high drying rate and uniform process at entire surface of the product due to efficient mixing with the drying air and high efficiency of process. In recent years, usage of infrared drying to dry food products has increased over conventional drying methods due to higher product quality, uniform heat distribution, high energy efficiency, high heat transfer rate and less processing time, facilitating the control of raw material temperature, reduced necessity for air flow across and the high ability to control process parameters in infrared heating. In this study, kinetics of carrot cubes drying by infrared-FLUIDIZED BED DRYER were investigated.Materials and methods: Fresh carrot were washed with tap water and peeled manually then diced by dicer. To drying carrot cubes by combined infrared- FLUIDIZED BED method a laboratory scale DRYER was designed and performed. In this study, drying of carrot cubes (0.5 and 1 cm3) was performed in factorial design experiments using air temperatures of 50, 60 and 70 °C and three levels of infrared power (200, 400 and 600 W) in three replications. To describing the infrared-FLUIDIZED BED drying behavior of carrot cubes, five mathematical models (Page, Modified Page, Henderson & Pabis, Midilli and Logarithmic) were evaluated.Results: The results demonstrated that the change in inlet air temperature, size of carrot cubes and infrared power had a significant effect (P <0.05) on water withdrawal from the sample and drying time decreased with increasing air temperature and infrared power and decreasing carrot cubes size. Therefore, the energy consumption was also reduced considerably, decreasing from 12.63 Kwh/kg in BED FLUIDIZED method (without infrared power) to 2.28 Kwh/kg using infrared -FLUIDIZED BED drying. The Page model was identified as the suitable model to describe the drying kinetics of carrot cubes by infrared-FLUIDIZED BED DRYER that showed a good agreement with experimental data.Conclusion: The statistical analysis of variance showed that air temperature, sample size and infrared power had a significant effect on water withdrawal rate of samples and therefore drying time. According to the results, using infrared-FLUIDIZED BED drying as a combined method in comparison with conventional hot air drying methods can reduce drying time and energy consumption and costs considerably.Keywords: Infrared, Combined FLUIDIZED BED, Drying, Kinetics, Carrot

Several studies have been conducted on equipping conventional FLUIDIZED BED with some technologies to increase drying efficiency and its performance. The objective of the study was to investigate the influence of high power ultrasound on FLUIDIZED BED drying of corn in terms of drying kinetics and quality characteristics of corn in three levels of ultrasound power density (11.1, 14.6 and 18.7 kW m-3), three levels of drying air temperature (30, 40, and 50oC) and four levels of frequency (20, 25, 28, and 30 kHz) in which the moisture content reduced from 32±0.5 (%d.b.) to 17±0.5 (%d.b.). Results revealed that the frequency of 25 kHz was the most efficient in terms of drying time. The frequency of 25 kHz and power density 14.6 kw m-3 was the most efficient frequency and caused reduction of the drying time by 43% in comparison with no ultrasound condition (control). The sponge effect caused by ultrasound application led to reduction of failure strength and toughness of the dried samples. According to the results, toughness compared to the failure strength was an appropriate index of the grain hardness.