Energy aAnalysis and Kinetics of Mint Leaves Dehydration Using Vibro-Fluidized Bed Heat Pump Dryer

ماشین های کشاورزی

Article 16, Volume 5, Issue 1 - Serial Number 9, 2015, Pages 154-162   

Document Type: Research Article

DOI: 10.22067/jam.v5i1.23444

Authors

S. M. Ataei Ardestani¹; B. Beheshti¹; M. Sadeghi^{* 2}; S. Minaei³

¹Islamic Azad University Science and Research Branch

²Isfahan University of Technology

³Tarbiat Modares University

Abstract

Fluidized bed dryers have not yet been used for drying products such as mint leaves. This could be due to high porosity and low mechanical resistance resulting in poor quality of fluidization. Applying vibration has been recommended to overcome problems such as channeling and defluidization, and hence improving the fluidization quality. In this research, a laboratory scale vibro-fluidized bed heat pump dryer was designed and constructed for drying mint leaves. The experiments were conducted at vibration frequency of 80 Hz and amplitude of 3 mm. The velocity and temperature of the inlet air was controlled by an automatic control system. Experiments were carried out at 40, 50 and 60 °C, and two methods: heat pump drying (HPD) and non-heat pump drying (NHPD). The results revealed that drying process primarily occurred in the falling rate period. Effective moisture diffusivity of the samples increased with increase in drying air temperature and varied from 4.26656×10-11 to 2.95872×10-10 m2 s-1 for the HPD method, and 3.71918×10-11 to 1.29196×10-10 m2 s-1 for the NHPD method and was within the reported range of 10-9 to 10-11 m2 s-1 for drying of food materials. The activation energy was determined to be 84 kJ mol-1 for the HPD and 54.34 kJ mol-1 for the NHPD, both have very good agreement with the results of other investigators. The coefficient of performance and specific moisture evaporation rate showed the acceptable performance of the heat pump system. Moreover, the energy consumption of the dryer for the NHPD method was more than the HPD method.

Keywords

Activation energy; Coefficient of performance; Effective moisture diffusivity; Fluidized bed drying; Pharmaceutical plants

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