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ARS Home » Pacific West Area » Albany, California » Western Regional Research Center » Healthy Processed Foods Research » Research » Publications at this Location » Publication #206526
Title: Moisture Diffusivity Characteristics of Rough Rice Under Infrared Radiation Heating

Author
item KHIR, RAGAB - UC DAVIS, DAVIS, CA
item Pan, Zhongli
item SALIM, ADEL - SUEZ CANAL UNIV., EGYPT

Submitted to: Proceedings for CIGR World Congress Meetings
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2007
Publication Date: 9/24/2007
Citation: Khir, R., Pan, Z., Salim, A. 2007. Moisture Diffusivity Characteristics of Rough Rice Under Infrared Radiation Heating. Proceedings of 3rd CIGR World Congress Meetings Section VI Int'l Symposium on Food and Agricultural Products, 1-15.

Interpretive Summary: This study investigated the moisture diffusivity of rough rice under infrared radiation heating, which provide important information for the design and operation of an infrared rice dryer.

Technical Abstract: To design an efficient infrared (IR) dryer for rough rice, it is important to understand the drying behavior of rice grains under infrared heating. The objective of this study was to determine the moisture diffusivity and moisture diffusivity coefficient of rough rice under IR heating and cooling. The effects of initial moisture content, rice temperature, drying bed thickness, tempering, and cooling methods on moisture diffusivity and moisture diffusivity coefficient were investigated. The samples of freshly harvested medium grain rice (M202 variety) with 20.5%, 23.8%, and 25.3% (wb) moisture contents were used. They were dried with IR radiation intensity of 5348 W/m2, for six exposure times, 15, 30, 40, 60, 90, and 120 s. The tested drying bed thicknesses were single-layer, 5 mm and 10 mm. After IR heating, the effects of tempering and non-tempering followed by slow and forced air cooling treatments on moisture diffusivity and moisture diffusivity coefficient were also determined. The unsteady diffusion equation based on Flick’s law and slope methods were used to describe moisture diffusivity of rough rice under infrared heating. The results indicated that rough rice moisture diffusivities under IR heating and cooling were significantly affected by rice temperature, and tempering, respectively. High heating rate and moisture diffusivity were achieved with IR heating. It took only 60, 90 and 120 s to achieved about 60°C rice temperature and moisture diffusivities of 4.7 x 10 -9, 3.3 x 10 -9 and 3.2 x 10 -9 m2/s during heating for drying bed thicknesses of single-layer, 5 mm and 10 mm, respectively. The moisture diffusivity coefficients during heating and cooling of IR dried rice with tempering was much higher than that of convective drying, which reflected the high drying rate of IR drying method. The initial moisture content of rough rice did not show a significant effect on moisture diffusivity. It has been concluded that IR heating followed by tempering treatment could be used to achieve a high drying rate for rough rice drying.