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Home Case Studies

CHARCOAL COOLER IN VEGETABLE,,TOMATO AND MEET PRESERVATION

Charcoal cooler for long shelf life

jkm by jkm
October 16, 2021
in Case Studies, Did you Know, Featured, Food & Drink, General, Guide
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A Charcoal Cooler is a storage chamber constructed from locally available materials and is used to store perishable commodities under cool temperatures.
Target region(s):  Target region for distribution/implementation (listed by country if specified)

Warm regions of the world, especially the rural areas where households are not connected to electricity.

Distributors/implementing organizations Organization(s) distributing/deploying this product directly to communities/individuals?”

Cost  :  this is Open source technology, can be locally fabricated using available resources

 

Farmers who grow crops such as vegetables and fruits face challenges of keeping them fresh as they head to the market. Unfavourable temperatures and unprotected storage areas increase post-harvest losses and reduce profits.

Against this backdrop, a joint research carried out by Uganda Christian University and Makerere University has yielded a charcoal-walled evaporative cooler to help farmers curb post-harvest losses and increase shelf life for vegetables and fruits. This was in partnership with Coalition for Health Agriculture and Income Network Uganda (Chain), which is the implementing agency.

Evaporative cooler
Charcoal is used because it has a porous structure that can hold water, is affordable and easily available in many places.

The cooler is a room with charcoal-laden walls. It has a wooden frame, which supports the walls and roof. The frame is covered with wire mesh separated by about 10cm with the interior being filled with charcoal.

The charcoal is on all four sides, filled in the space and leaving a gap of 15cm to 20 cm to the roof.

This space is left open to allow air circulation. The charcoal remains moist, and as warm dry air passes through, the water on the charcoal evaporates and cools the air. This keeps the room very cool.

This cooler provides a low-cost way to preserve the produce using readily available materials.

A 100-litre tank, a pump for constant water supply, charcoal, plastic or coated net, wooden poles, ventilator and tiled shelter to keep off the heat are the materials needed to complete the charcoal cooler.

The average measurements for the room are 2.5m in width, 1.5m in length and 3m high. A room this size can store leafy vegetables for up to five days, milk for four days, and vegetables/fruits such as tomatoes for up to 14 days.

Location
The site on which the cooler is to be built should be considered carefully because air movement is very important.

Evaporative coolers rely on air movement in order to be effective, thus it should not be placed where there is little or no wind.
It also requires a lot of water in order for the cooler to be operational, thus a good source of water should be close to the site.

A shade would be ideal as it would reduce the use of water as the walls will need less water and will reduce temperatures faster.
The charcoal cooler, which was tested for storing leafy vegetables and fruits, was been found to preserve them between four to six days.

 

Advantages of the cooler

Farmers can store their produce in the cooler for up to three days so they can harvest more before going to market or wait for buyers to pick them up. With fresher and longer-lasting produce, farmers are able to get good prices for their produce, which enhances their incomes.

The availability of constant water allows the farmer to recycle it and use it in irrigation of the crops or reuse it to cool the store.
It can reduce post-harvest losses by up to 80 per cent depending on the type of vegetable, especially those that perish within hours.

It is a low cost facility easy to construct at farm level by an individual farmer or a cooperative society.

Dr Apollo Kasharu of Chain Uganda, the implementing agency, says time has come to transfer the technology from the university research to implementation stage.

“We have started with Namulonge Horticulture Farmers Association in Wakiso District with 100 members and the next beneficiaries will be the farmers of Jinja District,” he says.

CHARCOAL COOLER IN VEGETABLE PRODUCTION
A charcoal cooler uses the principal of evaporative cooling to maintain a cool interior temperature for refrigeration and food preservation. The device is constructed from an open timber frame with charcoal filled sides, which is kept continually moist. As warm, dry air flows through the moist charcoal, water is evaporated into the air and it is cooled. The basic principles of heat and mass transfer underlie the function of the charcoal cooler. The cooler is cost effective economic wise since the needed resources are not difficult to get.
Developmental Need
Evaporative cooling can be used to address two main developmental needs: space cooling (air conditioning) and refrigeration. The charcoal cooler addresses the need for refrigeration in areas where electricity is unavailable.
Refrigeration of food is a method of slowing bacteria growth and extending shelf life. Typical refrigerators are kept around 2-3 degrees Celsius and can extend the shelf life of produce by weeks.
In hot climates where electricity is unavailable, refrigeration of food is a developmental need. In Sudan, for example, tomatoes will only last 2 days in the hot sun. Preservation of crops through refrigeration can help with hunger and starvation in the developing world by keeping foods fresh longer. In areas with no electricity, refrigeration is particularly challenging, and has led to the design of a variety of heat driven refrigeration devices, including evaporative coolers. While these devices are not typically capable of maintaining temperatures of 2-3 degrees Celsius, they can be significantly cooler than ambient temperature, and even moderate drops can significantly extend the shelf life of produce. For example, when housed using a similar evaporative cooling device, the life of tomatoes can be extended from 2 to 20 days. Evaporative cooling has an added benefit of increasing the air moisture content, preventing food from drying out and further extending shelf life.
Climatic Limitations
As discussed further below in engineering principles, the potential for evaporative cooling depends on the difference in wet bulb and dry bulb temperatures of the air. Humid air has a high relative humidity, and not as much capability to evaporate moisture. As the relative humidity of the air increases, the performance of the system will decrease, limiting its application in moist climates. Evaporative cooling is most effective in climates where relative humidity is less than 30%. As humidity increases, the cooling capability declines, and the temperature difference between the outside and inside of the chamber decreases.
Additionally evaporative cooling must be used in areas where water is available. Depending on the conditions, and cooler dimensions, the device may use 20-70L of water per day when working effectively.
Scientific Principles
Evaporative cooling is based on the principle that water requires heat energy to evaporate. In hot, relatively dry climates the evaporation of water into hot, dry air can create a cooling effect, suitable for space conditioning or refrigeration.
The cooling capacity is therefore approximately proportional to the rate of evaporation of water, which depends on:
Ambient Temperature
Ambient Humidity
Surface Area
Evaporative Media
Air Movement (natural or artificial)
To maximize the cooling effects these variables must be optimized for a given application
Psychometrics
Evaporation, the process of changing water from a liquid to a gas, requires heat from the surrounding environment. Psychometric properties of moist air, as well as the principals of heat and mass transfer apply to the evaporation of water for cooling. Understanding the properties of moist air is key in understanding how evaporative cooling works.
Evaporation is the change in state between a liquid and a gas. For water and air, evaporation involves liquid water vaporizing into a moist air stream. For the purpose of the Charcoal Cooler model, two simplified mass transfer cases were considered: evaporation from a surface, and evaporation through a transfer medium.
Evaporation through a Transfer Medium
Many evaporative cooling units pass air through a porous soaked pad that is kept replenished with water .Fundamental Heat Transfer
Heat is transferred through conduction, convection and radiation. Often the effects of radiation can be ignored, as they are small when compared to other forms of heat transfer. Conduction occurs through a solid surface
Fundamental Heat Transfer
Heat is transferred through conduction, convection and radiation. Often the effects of radiation can be ignored, as they are small when compared to other forms of heat transfer. Conduction occurs through a solid surface
Device Construction
A prototype charcoal cooler was constructed. The materials used, and detailed construction instructions are below. The prototype charcoal cooler was 1ft x 2ft x 3ft but instructions should apply regardless of device size. One of the advantages of this device is that it is versatile and can be made out of many available materials, therefore substitutions are suggested.
Materials Use:
Wood
Nail
Charcoal
Jute sack
Water hose
Wire mesh and net
Procedure of manufacturing a Charcoal Cooler
Identify a suitable location for your fridge.
Determine the size of your fridge that you want to construct.
Erect a double wire mesh boundary with at least a sizable width within.
Pack large charcoal particles in between while filling the gaps with smaller charcoal particles. And avoid the use of charcoal dust because it will pollute your food.
Insert a drip hose through the open space between the wood in order to water the charcoal and moisten it.
Then rap a jute sack around the already erect charcoal system. This is to ensure that the moisture content of the charcoal is maintained.
Do not forget to put a door to keep away animals and thieves.
Advantages of Charcoal Cooler
Less expensive to construct
Easy to construct
Reliable since no fluctuation in electricity will occur
Easily adjustable
Disadvantages of Charcoal Cooler
Labor intensive since watering have to be done
It may make stored produce dirty /spoilage if not well constructed
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