DESIGN AND DEVELOPMENT OF DESICCANT ASSISTED SOLAR DRYER FOR VEGETABLE SEED
Loading...
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
DIVISION OF AGRICULTURAL ENGINEERING ICAR-INDIAN AGRICULTURAL RESEARCH INSTITUTE NEW DELHI
Abstract
Seed is one of the vital inputs in crop production system. Quality seed enhance
productivity by 20-25 percent. The quality of the harvested seed can be improved by
seed processing. The seed process involved drying, cleaning, washing, grading and
storage. Drying is the foremost unit operation among the others. Generally the method
which is used for drying of seed is sun drying. Under high temperature and high
humidity combination causes rapid deterioration of seed quality. Vegetable seed are
more sensitive toward high temperature. In tropical regions where temperature and
humidity is high, drying time increased the leads to mould growth in seed. The solar
dryer is of simple design and very effecting drying of grain but in high humidity
condition, its thermal efficiency reduces drastically. Desiccant material has high
affinity towards water. Using desiccant material in dryer provides continuous drying
even during off-sunshine hours, increased drying rate due to hot and dry air, uniform
drying, and improved product quality especially for heat-sensitive products. Desiccant
materials can be liquid or solid type but handling of solid desiccant in dryer is easier
than liquid. Composites desiccants of three desiccants i.e. Silica gel, Bentonite clay
and activated Carbon were evaluated. The desiccant performance indices were
developed assigning different weightage factor to adsorption rate, regeneration rate
and unit cost of composite desiccant. The performance efficacy of silica gel was
observed to be highest of 91.7% among other selected desiccants. A desiccant assisted
solar dryer was designed with capacity 3kg/batch. The dryer had two sections, one for
drying the air and other for regeneration of desiccant. The collector area of the dryer
was calculated as 1.3sq.m. The overall dimensions (length, width & height) of the
drying chamber were determined as 0.65 m, 0.35 m and 0.75 m, respectively. The
dryer was equipped with temperature control unit to maintain the temperature at
preset (≤40°C). The temperature controlling unit consisted of thermoelectric cooler
peltier, microcontroller, 2- axial fans, fan speed regulator. The developed dryer was
evaluated at three air flow rates (0.038 m3/s, 0.064 m3/s, and 0.093m3/s) and three
levels of desiccant to seed ratio 0.25:1, 0.5:1 and 0.75:1 in terms of drying rate, drying
time, thermal efficiency and germination percentage. It was observed that drying rate
increased significantly from 0.074kg/h to 0.1004kg/h when air flow rate and desiccant
to seed ratio were increased from 0.038m3/s to 0.064m3
/s and 0.25:1 to 0.5:1,
respectively. The highest germination percentage and thermal efficiency were
observed as 72% and 36.24%, respectively at air flow rate 0.064m3/s and desiccant to
seed ratio 0.5:1. The drying time of the dryer with desiccant and without desiccant
was determined. It was found that drying time can be reduced up to 1.36 h by using
desiccant in the dryer for bringing down the moisture condition from 20% to 6%. Use
of desiccants had shown a marked difference in the performance parameters like
drying rate (0.0967 kg/h), thermal efficiency (34.31%) and germination percentage
(70.22%) as compared to the dryers without desiccants (0.066 kg/h, 25.16% and
67%). Based on these performance parameters, air flow rate 0.064m3/s and desiccant
to seed ratio 0.5:1 was found to be suitable for drying of onion seeds in the developed
desiccant based solar dryer. Therefore developed desiccant assisted solar dryer was
found better in terms of drying and quality characteristics of dried seed as compared
to solar dryer without desiccant.
Keywords:
Description
T-10122
Keywords
null