I have undertaken an agricultural project in a developing country, specifically cultivating cantaloupe with a number of 'out-growers' in a poor region of the country. The initial aim of the project was to undertake trial working with a select group of small land holders. The trial was rated a success in respect to quality and yield of the cultivated cantaloupe. However, we also suffered a large post-harvest loss due to not having access to any pre-cooling technology. This year we are planning to expand and are desperately trying to locate a low-cost design for a mini-submersible hydrocooler. Can you help us? (G.R.)
The simplest and cheapest system to build uses ice to cool the water. Build an ice bunker above a perforated shelf. Cooling time will be about 30 to 45 minutes, depending on size of fruit, so size the shelf to hold the fruit produced in about one hour of packing. Pump water from a shallow reservoir below the shelf to a water distribution pan (sheet metal with 1 cm diameter holes, spaced 8 to 10 cm apart). Water is distributed over the ice, crushed to fist sized pieces, and is cooled before falling past the melons. You can assume that 50% of the cooling capacity of the ice is actually used for cooling the melons and water flow rate is 7 to 10 liters per second per square meter of shelf area. If you do not have access to ice then you will need to replace the ice bunker with a refrigeration coil.
This is kind of a brief description of a system, but gives you the basic ideas behind a very low cost system. If you need more detail send me your specific questions and I will get back to you.