National Exhibition and Seminar (Title : Climate Change Mitigation : Role of Renewables) on Renewable Energy . Dhaka, Bangladesh,  24-25 March, 2008

 

Focus on Climate Change Mitigation: Role of Renewable

 

DEVELOPMENT OF A POLLUTION FREE SOLAR DRIER FOR TOMATO

M. A. Hossain and M. A. Hoque
Machinery Repair and Maintenance Division Bangladesh Agricultural Research Institute Gazipur-1701, Bangladesh

 

 

Introduction

 

Bangladesh

                        Tropical environment

 

       Crops

                         Fruits and vegetables

 

       Post-harvest losses

Nearly 20-30%

 

       Dried products

                    Popular food

            Potential employment sector

       80% of tomatoes consume in the form of processed products

 

        A large quantity of tomato perishes during the harvesting season

 

        Loss can be minimised by drying

 

 

 

 

 

 

Half cut tomato

 

 

 

Tomato drying

 

 

 

Dried tomato

 

       CO is a toxic air pollutant

 

 

       Fossil and biomass fuels contributes 44% of the total global CO emission

 

       Solar drying is a promising alternative for drying of crops in Bangladesh

 

       Bangladesh receives abundant solar radiation, and distribution of global solar radiation is found nearly uniform all over the country

 

       Global radiation is maximum exceeding 19.68 MJ/ m2/day in March-April and minimum is observed to be about 12.56 MJ/m2/day in December-January

       Solar energy CO free, environmentally friendly and economically viable

 

       Solar drying of foods is hygienic and dust free

 

 

 

 

 

 

 

 

 

Schematic View of the Hybrid Solar Dryer

 

 

Schematic View of the Hybrid Solar Dryer

 

 

 

Methodology

 

       Variety : Roma

 

       Origin : The Netherland

 

       Diameter (D): 57.2 £ D(58.72mm) £ 64.3 mm

 

       Weight(W): 99.4£W(124.59 g) £ 256 g

 

       Slice : half fruit tomato

 

 

 

 

 

 

Photograph of the solar drier

 

 

Photograph of the Multi Stack Solar Drier

 

 

 

 

Test modes

Day time heating with solar radiation and

 

•         Mode-1: Night time drying with ambient air

 

•         Mode-2: Night time drying with recirculating hot water from water tank

 

 

 

Results :

 

Collector temp for mode-1

 

 

 

 

 

  

Collector temp for mode-2

 

 

 

 

 

Day time collector thermal efiiciency

 

 

 

 

Drier Temp and RH of mode-1

 

 

 

 

Moisture reduction from different trays

 

 

Moisture reduction and drying rate for mode-1

 

 

 

 

 

 

Drier Temp and RH of mode-2

 

 

 

 

 

Moisture reduction and drying rate for mode-2

 

 

 

Summary of drying performance of solar and sun dryings at different drying conditions

Drying condi-tions	Moisture content  (kgkg-1 (db)		Average drying rate, (kgkg-1 (db)h-1)		Drying time (h)(day + night)		Time saving (%)	Drier system effici-ency  (%)
	Initial	Final	Solar	Sun	Solar	Sun
Mode-1	27.73	0.17	0.218	0.096	126	288	56.25	17.92
Mode-2	18.86	0.18	0.195	0.077	96	240	60.00	22.48

 

 

 

 

 

 

 

 

 

 

 

Sun dried infected tomato

 

 

 

Sun dried infected tomato

 

 

 

Dried tomato in the solar drier

 

 

Carbon monoxide emissions by conventional fuels

 

Conclusions

       Outlet temperature 30°C higher than the ambient

       Solar reflector increased 10% collector efficiency

       18 kg of half-cut fresh tomato dried to 2 kg of dried product per batch

       The average drying system efficiency varied from 17 to 29%

       CO emission highest for charcoal and lowest for natural gas

       Solar drier completely free from CO emission