|Bolder, D - NC STATE UNIVERSITY|
|Swartzel, Kr - NC STATE UNIVERSITY|
|Farkas, Be - NC STATE UNIVERSITY|
Submitted to: Journal of Food Process Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 18, 2004
Publication Date: February 15, 2005
Citation: Bolder, D., Sanders, T.H., Swartzel, K., Farkas, B. 2005. A model for temperature and moisture distribution during continuous microwave drying. Journal of Food Process Engineering. Vol. 28(1), 68-87. Interpretive Summary: Moisture content reduction in harvested peanuts is necessary for safe warehouse storage and after field drying to reduce initial moisture, the process is generally completed artificially with gas-fire-heated air in drying wagons or bins and peanut temperature maximum is critical to quality maintenance. In order to use microwave energy in the process, an understanding of the influence of moisture, temperature and energy input was necessary. This study focused on the development and validation of a mathematical model for temperature and moisture distribution during drying of farmer stock peanuts (20 to 25% mc dry basis) in a continuous traveling wave applicator using microwaves at 915 MHz. The results confirmed that the temperature profiles in peanuts was a result of the power level for peanuts at the same moisture content. A very good correlation was determined between the peanut pod surface temperatures measured using infrared technology and the internal peanut pod temperatures measured using fiber optic probes. These results establish that internal pod temperatures may be determined from surface temperature measurement using infrared technology. The study confirms the strong potential use of microwave technology in a continuous flow peanut drying system with internal pod temperature controlled by variable microwave power input.
Technical Abstract: A heat and mass transfer model of continuous drying of farmer stock (in-shell, uncured) peanuts (Arachis hypogaea L.) in a planar microwave applicator was developed and investigated. Transport phenomena equations previously developed for batch-type microwave drying were successfully adapted to account for the spatial variation of the electric field inside the applicator. The theoretical equations developed, together with experimental methods, were used to determine the effect of microwave power level and dielectric properties on the temperature profiles and the reduction in moisture content of peanuts. The temperature profiles obtained from solution of these equations matched the experimental profiles determined using fiber optic temperature probes inserted into drying peanut pods. An exact theoretical determination of moisture content reduction during microwave drying was not possible due to the dependence of dielectric properties on the moisture content. The surface temperature distribution of the peanut bed measured using infrared pyrometry was well correlated with internal temperature profiles.