4.8. Proposal for an international network of research on small scale sundriers

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- M.D. Griffon

INTRODUCTION

Sundrying techniques have to go beyond the experimental stage before they can effectively contribute to a reduction in post-harvest losses and before they can be disseminated on a large scale.

In fact, sundrying techniques are not sufficiently disseminated. Numerous projects, quite well dispersed, exist and there are many prototypes, but they remain on the experimental level.

These projects are certainly interesting, but they are mostly too meticulous and we would like to go beyond that stage.

If sundrying is to be taken seriously to improve the post-harvest system, the following would be indispensable:

1. Setting up of interdisciplinary teams;
2. Establishment of an international network of groups, either using sundrying techniques or experimenting with them;
3. Co-ordination of experience gained by each group and adjustment of the sundrying techniques to this experience.

MULTIDISCIPLINARY GROUP

In order to promote the use of solar energy in an effective way, we feel that specialists of various disciplines have to collaborate:

A multidisciplinary group

Research work is already based on a multidisciplinary collaboration in France:

The French team has come up with two types of small capacity sundriers but with reliable and acceptable results:

1. a SERESOL sundrier "family type" which is particularly suited for the mediterranean zones which are located above 30 degrees latitude. It is compact and combines a heat collector and drier;
2. a SERESOL sundrier "tropical type" with a separate heat collector, heat storage element and dryer. It is suitable for all latitudes and particularly well suited for tropical areas.

The two driers have the following characteristics in common:

1. The drying takes place without the products being directly exposed to the sun. This avoids the photo-oxydation of photo-sensitive vitamins and of phenolic compounds;
2. a greenhouse effect resulting from a transparent plastic material and an absorber made of black porous material;
3. a total energy autonomy the natural ventilation is insured by a solar chimney;
4. the total volume of the moist products that can be dried amounts to 6-9 kg/m² per 3 days and 10-15 kg/m² in case of drying on trays.

AN INTERNATIONAL NETWORK

The objective is to establish an informal network of teams that are engaged in solar energy for the drying of agricultural products.

However, if one wants to pass the stage of prototypes, it seems necessary to use a standard methodology and standardized material in order to enable collaborating teams to profit from the work of partners and to use the results obtained by others.

Only with the use of standardized material could the teams compare their results and enhance their knowledge.

This standardized material exist and has already been tested by our French multidisciplinary teams

It is proposed to use the "tropical" SERESOL drier as a common tool to the various teams in the network. Ten collaborating stations among 20 laboratories (foreign institutions) have already been selected which were interested in this approach and had met with criteria of selection:

• scientific and technical knowledge;
• adequate testing equipment;
• financial contribution to the shipment of the drier.

Three distinct regions have been identified:

Six stations have already received the SERESOL "Tropical" sundrier and the other four will receive the sundrier before the end of 1983. The experiments, based on a common procedure, could start in January 1984.

ADAPTATION OF THE TECHNOLOGY

After the first experimental phase has been completed - according to a common procedure - by the various teams in the networks during which data could be transferred and compared each team will improve their own material according to the local constraints encountered.

This adaptation will require thorough research of the locally available materials and a full mastery of the technology by the users.

There are already various ideas of adaptation:

1. The partner in Mali (ISFRA) works currently on the production of a porous absorber with recyclable products (very small rubber particles from used tyres in water suspension);
2. Our partner in the Cameroon (ENSP Yaoundé) studies the optimal slope of the collector and found a correlation between the functioning of the collector and the constraints imposed by the products to be dried;
3. Our partner in Montpellier is undertaking a comparative study of the functioning of sundriers by combining natural and forced air circulation.

The collection of the improvements suggested by each team will be handled by the organized and disseminated to all teams, who, will catalyze action undertaken by local development organization or national officials in charge of these matters (planners, bankers, etc.) and {he rural users.

This development phase has to take into consideration the human potential and the local resources available in the relevant countries.

FURTHER DEVELOPMENT PROSPECTS

The results expected of the development of these efforts and their subsequent expansion are twofold:

i) On the technical level

On the basis of the results obtained under various climatic conditions, to bring to light the functioning, the advantages and inconveniences of different techniques - such as natural drying, sundrying in natural and in forced air circulation which are applied to small drying units meeting the needs of small village communities.

ii) ON THE SOCIO-ECONOMIC LEVEL

To make an economic estimate of the preceding technical criteria in relation to constraints of various production system, this will eventually lead to a combination of different techniques (predrying - final drying) and/or promote the utilization of various production units as a common tool, thereby taking into consideration the impact of the technical/economic constraints inherent to these techniques.

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