Okara Drying by Pneumatically Swirling Two-Phase Flow in Entrained Bed Riser with Enlarged Zone

Abstract

A simple and effective drying technology of okara is a possible way for long-term preservation and recycling in tofu manufacture. A continuous entrained bed dryer was proposed to enhance the heat and mass transfer between wet okara and hot air by a pneumatically swirling upward flow. The effect of the dryer's structures on drying performance was evaluated. The swirl of pneumatic flow was maintained up to the top of the riser by setting a sufficiently long shaft as a swirl guide on the centerline in the riser. An enlarged head on the riser caused a complex flow pattern in the dryer. This behavior was confirmed by hydrodynamic analysis of a single-phase flow based on a cold model that does not take into account heat and moisture transfer. The energy efficiency of the present dryer was 36–46% in the present experimental conditions, but it was corresponding almost to the limit determined theoretically by saturation of drying air humidity flowing in cocurrent with wet okara. The average drying rate could be empirically correlated by an exponential function of the residence time in the riser.

Keywords:

• Entrained bed dryer
• Foodstuff
• Okara treatment
• Pneumatic flow
• Soybean residue

Notes

Unit of each size is given in millimeters (mm).