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Low Cost Rural Chiller.

Problem Statement :

Low cost option for freezing Sitaphal (Custard Apple) pulp—low cost rural chiller.

As always this Sristi Summer School problem statement is also related to upliftment of community. The community in focus are the tribal people living in Devla District of Rajasthan. These people remain isolated and live a life full of hardships. There are about 45,000 households of tribal people adding up to a population of over 3 lakhs. Thus, any small effort made for improving their life will have a huge impact.

Mind Map : On the basis we prior art search we have developed a Mind Map which is presented below.

As it can be seen in the branch 1 we have mentioned the process that is carried out and the elements involved in this. As we came to know that there are four main steps involved that are collection, pulp extraction, storage, transportation and selling in the market.

Branch 2 highlight the uses and values of Sitaphal in which there are money, nutritional and medicinal values for it. It is an extra source of incomes for tribal communities during the season.

Branch 3 focuses on the areas in which Sitaphal are found. Main states are Rajasthan, Andhra Pradesh, Uttar Pradesh, Madhya Pradesh and Maharashtra.

Next comes Branch 4 which highlights the existing problem in these regions, that are mainly of getting low product value due to loss while processing of Sitaphal and other major problems are unavailability of electricity and no continuous employment.

In last Branch 5, we have mentioned about the potential solutions, that are freezing using mitticool, ground pit method, etc. We also came to know about availability of energy resources like Solar, Wind and Biomass which is abundantly available.

Updated Mind Map :

(Click on link for zoomed in image)

Field Visit :

Understanding the dexterity of these people in identifying and collecting the forest produce, forest department of Rajasthan has started various projects to create employment opportunities by setting up local processing centres for forest produce. These processing centres makes soaps, shampoo, incense sticks, flavours for ice cream etc. The products are now even traded on E- Commerce platforms under the brand name of VANRAJ (king of forest).

To get a more details about the problem and interact with the stakeholders the team went for a Field visit from Grambharti ( Gandhinagar) to Devla district of Rajasthan. The team was greeted there by District Forest officer Mr.O P Sharma, who explained about the problem statement of refrigerating sitaphal. Team then proceeded to the Devla district which is about 80km from Udaipur city. Forest Ranger Bhupendra Singh accompanied the team for field visit.

Site: Range Karyalaya Devla (Udaipur)

Sitaphal Processing centre

Observation: Most of the people team met were woman, reason being men migrate to cities to work as labourers, drivers while they depend on cattle and farming. Sitaphal processing is an opportunity which will result in providing employment locally to both genders.

Sitaphal is a seasonal fruit which grows in abundance in this region. Before winter it provides 2 months of stable employment to tribal people. They collect and bring the fruit to the processing centre, here women segregate the good quality fruit and extract pulp from inside. A machine separates seed from pulp. Sitaphal seeds have huge demand because of their medicinal values. The pulp is sealed in airtight packets and stored in a conventional freezer until a collection van arrives. Women are able to earn 200-300 per day during the season of sitaphal, which is way better than the condition before opening of the plant. The plan is to replicate the success of a sitaphal processing centre of Devla Range karyalaya to other zones also but challenge is non availability of electricity to run the compressor of freezer. If this bottleneck could be removed then processing can be done at more centres, thus positively impacting more number of lives.

Conversations: The team interacted with some of the local people with the help of translation by forest guards.

  • Rashmi Bai: She is a tribal woman trained by Forest Department for Incense stick making process.She told that her husband works in city and the VFPMC helps her earn some stable income. Her earnings are in range of 200-300Rs/Day. According to her, the financial condition has become stable after this project (about 3 years).

  • Megi(22): She works in sitaphal processing centre during the season and earns 150Rs/day. During off-season she earns by farming and depends on her cattle.

  • Kishan (36): He works as a labourer and shared deeply about the problems faced by him, ranging from non-availability of electricity to faraway market place. His children walk 6 kms daily for going to school.

Problems Identified :

Not all villages can afford the freezer used for chilling the pulp

  • The main problem is no electricity. Because of this they are unable to do many basic things like processing wheat, keeping vegetables etc. The people are unaware of the economic potential of the products they collect. Another basic problem is unemployment.

  • Medical facilities are far away

  • Ignorance of valuable products of forests

  • Forest fires are common

Proposed Solutions:

  • Because of distributed house connection to grid is a problem. Thus solar power can be used for basic needs like light and fan. A small solar powered mill can also be setup to make flour from wheat.

  • A low cost refrigeration system can be made to operate on solar energy or biomass.

  • The biomass and dry leaves from forest can be used to produce electricity and cooling. This would also increase employment and simultaneously reduce incidents of forest fires.

These problems and potential solutions will be discussed in details with the mentors and next plan of action will be constructed.


A variety of solutions can be used for refrigeration like natural evaporative cooling, forced convection cooling, refrigeration systems like vapour compression refrigeration system or vapour absorption refrigeration system. A few unconventional methods were also studied like using vacuum to freeze water at low temperature. Using zeolite to adsorb water to cause cooling.

The main ideas and their advantages and disadvantages are discussed :The main ideas and their advantages and disadvantages are discussed :

Evaporative cooling: All of us are familiar with earthen pots. It is the most basic type of refrigerator used in almost all homes in rural India to cool drinking water. Water evaporates taking away heat and thus remaining water is cooled.The design prepared for cooling the sitaphal can be seen in the figure.It’s a hut like structure with walls of mud covered with jute bags. The bags and mud wall help in better evaporation, resulting in increased cooling. A small pump powered by solar energy is used to sprinkle water from the top. The water drips down from the walls and collects in the tank below the ground to be used again. A fan can also be added to get better cooling.

The advantages of this design are

  • Cost is low, simple design and construction from locally available materials.

  • Negligible maintenance and operating cost.

The Disadvantages are:

  • Very low temperature drop.

  • Difficult to maintain a constant temperature.

  • Not good for areas with high humidity.

Because of the constraint of reaching 10 degree Celsius this method could not be used as the maximum temperature attainable by evaporation is about 27 degree Celsius.

Prototype 1

On the basis of above principle we made a simple prototype, in which air(at ambient temperature) is blown in a pipe using fan and the pipe is passed through wet honey comb pad and was grounded in drain to cool the pipe. The cold air was then collected in a closed ice box in which a hole was made at top for exit of warm air. This prototype was not so successful as it could attain a temperature drop of only 5oC.

Absorption based Refrigeration : Zeolites are microporous, aluminosilicate minerals which readily adsorbs water. They can be dehydrated and rehydrated again and again. This property makes them useful in cooling anything. The design can be understood from the figure. During cooling cycle , a vacuum pump is used to decrease the pressure first in zeolite chamber and then in evaporator container. This causes the water/methanol to evaporate , absorbing heat from the container, making it cold. In the regenerative cycle, heat is supplied to regenerative chamber for separating methanol/water vapour, which are then collected again in evaporator after condensation in heat exchanger.

The advantages of this system are:

  • Desired temperature can be reached easily.

  • Waste heat/ Solar heat/ Biomass etc can be utilised.

  • The system is non hazardous and environment friendly.

The disadvantages are:

  • New technology thus limited experience.

  • The system is little bit complex.

  • The system cycle is intermittent.

  • Increased cost.

Prototype 2:

Icy ball method: It is an example of gas absorption refrigerator. It consists of two metal ball: a hot ball, which is fully charged absorber and a cold ball containing liquid ammonia. These are joined by the pipe.The pipe allows ammonia gas to move in either direction. When the cold ball fully charged with liquid ammonia the device turned around, placing the hot ball in the cold water. As the hot ball cools ,the pressure in the system falls,eventually dropping o the point where the liquid ammonia in the cold ball begins to evaporate and the cold ball begins to cool.

Based on the above principle there exists a refrigerator which contains ammonia as refrigerant and it works by heating the coil and causing the ammonia to evaporate.

Prototype 3

The third prototype which we made is for cooling using Phase Change Material(PCM). PCMs have property of releasing heat when transforming from liquid to solid form and absorb heat when transform from solid to liquid phase. Most commonly used PCMs are Glycol and Salt water. These once freezed remains cool for 24hrs and are used in refrigerators used by ice-cream vendors.

We made 2 chambers in which the inner chamber is to store the fruit and after that is the bigger container which acts as a cooling jacket and it contains mixture of glycol and water which has melting temperature between -12 to 0 degree Centigrade. We can freeze the mixture using electricity or using liquid Nitrogen. Doing this we can maintain temperature of the inside chamber for 24 hrs.

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