Evapocooler invention for cooling camels milk in Somalia

Or How to get your camel milk to market in 40 degree C climate.

My brother Dominic Wanjihia invented this gadget which he calls Fine Lined Evaporative Cooler, for rural application in Somalia – the cooling of camels milk for transportation . He was working on a project for VETAID, Somali Pastoral Dairy Development Program – SPDDP,in Burao, Somalia June 2008. All this content belongs to Dominic who has allowed me to post it here- please seek his permission to use this content elsewhere dwanjihia@yahoo.com

Cool-box design Fine Lined Evaporative cooler
Cool-box design Fine Lined Evaporative cooler

Evaporative cooling technology

The evaporative cooling concept has been used for centuries in countless applications. Cooling occurs when a fluid changes state from liquid to vapor. Put simply, evaporation. In order to evaporate, the liquid requires energy or heat. It acquires this heat energy from its immediate surrounding. As the surrounding gives up this heat, it lowers in temperature or cools.

The rate at which evaporation occurs depends largely on two main factors, the amount of heat available and the humidity in the air.

The cooler must also be shaded from direct sunlight otherwise the surfaces absorb UV heat and warms up, becoming ineffective as a cooler.

In short

Evaporative cooling devices work most efficiently in windy, dry and shaded conditions

Charcoal cooler

Everyone knows how to make charcoal fridges. After carrying out extensive tests on evaporative coolers in hot arid Burao, Somaliland, with day temperatures as high as 36OC in the shade, the charcoal would absorb ambient heat from the air and as opposed to cooling, would warm up the interior compartment.

Imagine wearing a wet thick winter jacket under the palms at a breezy beach. The jacket acts as a wetsuit and will insulate your body preventing heat from escaping.

Fine lined cooler

However, imagine wearing a wet skintight t-shirt in similar conditions. The water evaporates quite rapidly and cools your body.

I applied this concept to the cooler prototype pictured and achieved startling results. The cooler would drop as low as 15.5OC at night when temperatures averaged 25OC and maintain under 17OC during the day at average temps of + 32OC.



An elevated metal box is lined interior and exterior with a fabric. In this case I used locally available corrugated galvanized iron sheets for the container and sisal sacking fabric for lining. The upper ends of the fabric overhang in a water trough that rings the top of the cooler. Capillary action causes the water to slowly trickle over the inner and outer surfaces. A small vent keeps the interior air circulating and wind guides or tunnels direct air flow over the exterior surfaces. A low speed small solar powered fan can be incorporated in areas where there is not a constant breeze.

How it works

The circulating air in the interior causes evaporation on the wet surfaces. The necessary energy is acquired from the contents hence cooling them and is transfers to the iron sides.

Wind guides or tunnels direct an airflow over the external sides. The evaporation that occurs acquires energy from the sides causing further cooling of the interior.

Convection current system to increase water bath cooling
Convection current system to increase water bath cooling

Construction design

Cool-box with water-bath interior for rapid milk cooling application– Collection Point Cooler

Walk-in cold-room for vegetable storage

Vehicle mounted for long distance transporters

Features (Comparison to conventional charcoal coolers)

Very simple construction

Corrugated galvanized iron or GI sheets increase the surface area

Wind tunnels guide air flow efficiently over evaporation surfaces

Air flow coolers at tunnel entrances

Being galvanized, the sheets are long lasting

GI sheets are affordable and available in most rural areas

Secondhand sacking fabric is available in virtually every vegetable market

The simple capillary action dripping system replaces more complicated dripping apparatus

Convection current system to increase water-bath cooling efficiency

Cool box design with waterbath for rapid drop in temperature of milk
Cool box design with waterbath for rapid drop in temperature of milk
The design simplified
The design simplified

In hot arid regions, cooling the warm ambient air before it reaches the wet evaporation surfaces increase efficiency. Note. Setup for airflow from either direction

level coolers – achieved low’s of 16OC at ambient temp of 30OC +
level coolers – achieved low’s of 16OC at ambient temp of 30OC +
Rapid Temperature Drop Test 4 lts boiling water in aluminum milk churn placed in water-bath at 16OC
Rapid Temperature Drop Test 4 lts boiling water in aluminum milk churn placed in water-bath at 16OC

For further information and other rural development concepts and innovative designs, Dom can be reached on

mobile tel +254 722 700 530 dwanjihia@yahoo.com