Agricultural Research Management Information System

Home
Research Summary
Search
About Us
- ARMIS
- Brochure
Contact Us
Report
User Request
Data Input
Help
- Operation Manual
  - PDF
  - Video
- Program Area & Commodity
We have reached 37600 number of research entries at this moment.

- Logout

Research Detail

Home
Research
Detail

Dehydration Behavior of Summer Onion in Solar Cum Mechanical Dryer

Md. Masud Alam
Senior scientific officer
Spices Research Center, Bangladesh Agricultural Research Institute, Shibganj, Bogura

Md. Nazrul Islam
Professor
Department of Food Technology and Rural Industries, Bangladesh Agricultural University, Mymensingh

Abstract/ Executive Summary:

Experiment was carried out on dehydration behavior of most perishable summer onion in solar cum mechanical dryer with temperature variation of solar energy and electrical energy separately or combined. Dehydration was done with one kilowatt one fan (1 kW 1F), two kilowatt one fan (2 kW 1F), two kilowatt two fan (2 kW 2F) and solar dehydration with no fan/one fan/two fan (S1F/S2F) respectively. Dehydration behavior of onion slices having thickness 3, 5 and 7mm in upper and lower shelf’s of dryer were also investigated. It was observed that 3mm thick onion slices become wrinkled during dehydration. On the other hand 5 and 7mm thick onion slices were chosen as good dried product. It was also found that, for a specific moisture ratio (MR), faster dehydration was achieved for thin samples compared to thicker ones. Activation energy (E_a) for diffusion of water from onion was 4.25 kcal/g -mole and 12.02 kcal/g-mole for mechanical and solar dehydration respectively at upper shelf for 7mm thick slices indicating that the solar dried samples are more temperature dependent than those dried in mechanical mode.

Keywords: Dehydration behavior, Summer onion, Activation energy

Location: Spices Research Centre, BARI, Bogura, Bangladesh

Start Date: 01-06-2009

End Date: 01-06-2010

Program Area: Postharvest and Agro-processing

Commodity: Onion

Objectives:

To know dehydration behavior of summer onion in a combined solar cum mechanical cabinet dryer with variable temperature.

Methodology:

To analyze the experimental data, Fick’s 2^nd law of diffusion was used (Brooker et al. 1974 and Islam, 1980). Thickness dependence of dehydration rate was analyzed by plotting “log” of dehydration rate constant (m) against “log” of sample thickness (L); the relationship is derived from the solution of Fick’s 2nd law of diffusion (Islam, 1980). To determine the temperature dependence of diffusion co-efficient, (D_c) was plotted against inverse absolute temperature (T_abs^-1) as per Arrhenius equation (Brooker et al. 1974 and Islam, 1980).

Description of dryer and operational conditions:

The developed dryer can be used in 3 mode such as mechanical, solar and combined solar and mechanical mode (combined mode). In the mechanical mode, heated air at different velocities can be used for drying. For solar drying, the surrounding air comes into the air heating chamber and becomes hot as it collects heat from black collector as well as from direct sunlight. The heated air passes through the duct as a result of density variation. For the combined mode, both the solar and mechanical arrangement runs together providing heated air for air drying. As reported by Bhuiyan et al. (2011) the highest temperature (70⁰C) was achieved in the upper shelf by 2 kW -1F and was successively followed by 60⁰C by 2 kW-2F, 56.7°C by 1 kW -1F and 47°C 1 kW-2F and for lower shelf the highest temperature (50⁰C ) was given by 2 kW -1F, while the lowest temperature (42°C) was given by 1 kW -2F, and 47°C was given by either 2 kW -2F or 1 kW -1F. The velocity of air for system with 1 fan was 0.35 m/sec. and that system with 2 fan was 0.7 m/sec as recorded by an Anemometer.

Dehydration of onion

For both the solar and mechanical drying, the peeled and cleaned onion slices of different thickness (3, 5 and 7mm) were placed on each shelf in single layer and hot air passed through the shelf and the products were dried for desired periods. The weight of slices was noted at a regular interval of 1hr from the known initial. moisture content and the moisture content at any time interval was calculated. To investigate influence of temperature on dehydration rate at constant air velocity, sample with constant thickness was dried at variable temperature using various fan-heater combinations.

Source of Information: RDA Journal, 19 (1): 105-114. 2016. www.rda.gov.bd, ISSN 1019-9624

Article Link (Online Journal):

Funding Source:

1. Government

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Temperature variation was found between upper shelf and lower shelf of the drier due to dryer’s shelf location from heating sources. While this study was limited to mechanical fan assisted solar drying. Combined mechanical and solar dehydration is possible with this dryer thus eliminating the risk of weather uncertainty. To cope with this uncertainty, an alternative approach will be to have an osmotic pretreatment especially using salt solution or sugar-salt mixed solution to have breathing time and to obtain higher dryer throughput.

Knowledge Management: Journal