Performance Evaluation of a Laboratory-Scale Rotary Dryer

Author : Sicat, Raquel Co
Major Adviser : Alcanzare, Edilberto A.; Demafelis, Rex B. 
Committee Members : Movillon, Jovita A.; Manoto, Russel D.
Year : 1994
Month : April
Type : Thesis
Degree: BS
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The effects of material moisture content, air flowrate and temperature on drying rate were evaluated in the study.

Drying tests conducted at different air temperatures showed that drying rate increased from 18.7 to 28.4, 15.2 to 20.8, 12.1 to 20.8 and from 4.3 to 9.1 with an increase in air temperature from 60 to 64 °C. This is due to a decrease in air absolute humidity caused by air temperature increase.

Effects of material moisture content on drying rate were also investigated. Increase in drying rate from 20.8 to 28.4, 9.1 to 20.8, 15.2 to 18.7 and from 4.3 to 12.2 was generally observed as grain initial moisture content was increased from 17 to 21 % due to the mass transfer limitations imposed by the mechanism and rate of liquid movement within the grain.

Different air flowrates were also used in the drying tests conducted. It was observed that drying rate increased from 4.3 to 15.2, 12.1 to 18.7, 9.1 to 20.8 and from 20.8 to 28.4 as venting rate increased. Air flowrate was found to have the most prominent effect to drying rate. It prolongs grain residence time by blowing through the dryer counter-current to the flow of the grain which results to better heat and mass transfer inside the dryer, hence increase drying rate.

An empirical equation for drying rate as a function of material moisture, air temperature and flowrate was formulated using the overall results of the experiments performed. The resulting equation is :

DR = 1.797Δt + 0.0111Δf + 1.909Δm + 1.426×10⁻⁴ΔtΔf + 0.126ΔtΔm – 6.386×10⁻⁴ΔfΔm + 5.138×10⁻⁶ΔtΔfΔm + 4.081

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