EFFECTS OF STEAMING AND MICROWAVE PRETREATMENTS ON MASS TRANSFER CHARACTERISTICS OF ALEPPE OAK (QUERCUS INFECTORIA)

Hadi Dashti, Mahdi Shahverdi, Hamid Reza Taghiyari, Shoboo Salehpur, Sina Heshmati

Abstract


In this research, effects of steaming and microwave pretreatments on the mass transfer properties of never-dried Q. infectoria were investigated. Specimens at green moisture content were exposed to microwaves of frequency 2450 MHz for 10 minutes. The pre-steaming was performed at a temperature of 160°C for 1 hour under a pressure of 2 to 3 bars. Air permeability values were measured to be 4.8 and 4.9 (× 10-16 m3 m-1) in the sapwood and heartwood, respectively. Results showed a significant general increase in the air permeability and diffusion coefficients in the pretreated sapwood specimens. The presence of tyloses in the heartwood prevented the penetration of steam to the inner parts of the specimens, resulting in the diffusion coefficient remaining constant. The pressure gradient caused by the microwave heating resulted in the distortion of the tyloses structure in the heartwood, thus resulting in a significant increase in the air permeability. It may be concluded that the presence of tyloses has a significant effect on the final impact of either of the pretreatments.

Keywords


Drying; Microwave; Steaming; Diffusion; Permeability

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