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Optimization of Solar Tunnel Drier for Drying of Chilli

M. A. Hossain
MR&M Division, BARI, Gazi pur.

J. L. Woods
School of Agriculturc, Food and Rural development, University of Newcastle upon Tyne, UK.

B. K. Bala
Dept. of Farm Power and Machinery, BAU, Mymensingh.

Abstract/ Executive Summary:

A technique has been developed to optimize the design of a PV operated forced convection solar tunnel drier for drying of chilli in Bangladesh. The lenglh of both the collector and the drying unit is found to be the same for basic mode and optimum mode designs. Two types of optimum designs are obtained. One is l4-0 m long and 1.9 m wide and another is 13.0 m long and 2.0 m wide collector or drying unit. The basic mode drier was 10.0 m long and 1.8 m wide collector or drying unit. There is no significant difference of performance between basic mode and optimum mode driers except capacity. From the economic point of view, the capacity of optimum mode driers are higher than the basic mode drier and hence achieves a cost saving of l5.9%. The pay back period of the basic mode drier is 4 years and optimum mode driers about 3 years.Sensitivity analysis showed that the design geometry is sensitive to costs of major construction materials of the collector and air temperature in the drier. An objective function of the optimisation programme based on the cost of major construction material for the collector is proposed for design of the optimum drier geometry.

Keywords: Chilli, Solar tunnel, Drying

Location: Bangladesh Agricultural Research Institute, Gazipur.

Start Date:

End Date:

Program Area: Farm Mechanization

Commodity: Drier

Objectives:

To optimize the physical component of the solar tunnel drier for the drying of chilli efficiently and economically.

Methodology:

Simulation Model Analysis of Collector In the forced convection solar tunnel drier, the airflow is driven by a fan operated by a solar module and air passes through the single cover collector between the cover and the absorber. The heated air passes over and under the products spread in the drying chamber and thus moisture is evaporated and carried away from the products.Economic Model: For calculation of the cost of drying, a simple annual cost model was used as described. The total cost of the solar drier consists of the cost of the collector, drying tunnel, fan and PV module. The materials used in collector and drier were GI sheet, timber, glass wool, MS rod, angle bar, polyethylene cover, rubber rope, aluminium U-channel, DC fan, PV module, GI pipe, plastic net and miscellaneous materials.Taking an interest rate of 12%, inflation rate of 15%, life of drier 10 years, number of working day per year 120 days and number of working hours per day E hours, the drying cost per unit moisture removal for chilli was calculated. The annual net income was computed based on the number of drying batches per year, unit cost of fresh chilli and the selling price of chilli per kilogram. The price of chilli in the year 2000 and production of dried chilli using solar tunnel drier .Constrains and Optimisation Procedure In carrying out the simulations, the system was assumed to be operated from 9:00 am to 4:00 pm daily. The weather data and solar data used in the simulation model for optimisation are presented in Table 3. The economic optimisation was combined with the physical simulation model. For different combinations of drier geometry (length and width) under constraint conditions, the cost of drying was estimaled. Then the minimum objective function was determined by search technique. The optimisation programme was written in BASIC programme. For different combinations of length and width a total of 392 drier geometries were considered.

Source of Information: Agricultural Engineering Division, Pag:233-243, Nov- 2002

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The main feature of the optimum &sign is a relatively long collector. Two types of optimum designs arc obtained. One is 14.0 m long and 1.9 m wide and another is 13.0 m long and 2.0 m wide. There is no significant difference of efficiency between the basic mode and optimum mode driers. From the economic point of view, the capacity of optimum mode driers is higher than the basic mode drier and hence cost saving by 15.89%. Pay back period of basic mode drier is 4 years and optimum mode & driers are about 3 years. No significant differences were found between two optimum mode driers in terms of performance and economics.Sensitivity analysis showed that the design geometry was not very sensitive to minor material costs, fixed cost and operating cost. Drying unit has also no influence on the design geometry of the drier. The design geometry is sensitive to costs of major construction materials of the collector, solar radiation and air velocity in the drier. This optimization technique may be applied for design and construction of solar tunnel drier for drying of other crop as well as chilli.

Knowledge Management: Journal