Information: – At Vidyan Ashram, there is a need for a dryer with specific requirements. The dryer needs to have a capacity of 100 kilograms for drying chillies. I was assigned this project by Sir to fulfil this requirement. The unique aspect of this dryer is that it will operate using sunlight. This is all the information available about the dryer project.


How does the dryer work? I had a discussion about this with Dixit sir.

During our discussion, we talked about the factors that contribute to drying up the chillies. We considered elements such as humidity, temperature, and dryness in the air.

26/02/2023 The purpose of the discussion was to:

  1. Search for information about the dryer.
  2. Read all previous blogs and understand how the dryer works.
  3. Identify the problems that can arise while drying the chillies and what challenges need to be addressed during the drying process.

27/02/2023 Conclusion of the previous meeting:

After reading all the information, we came to the following understandings:

  1. If water molecules are present in chillies, it can lead to the growth of bacteria.
  2. When chillies get cut, the seeds can fall on the ground, which can be problematic when moving lower-level chillies to upper-level positions.
  3. Solar dryers are devices that utilize solar energy to dry chillies. They use the heat from the sun to remove moisture from the chillies. There are two main types of solar dryers: Direct and indirect dryers.

There are two types of chilli dryers:

  1. Direct chilli dryer: In these dryers, the food or clothing is exposed directly to sunlight. The sunlight removes the moisture from the substance.
  2. Indirect chilli dryer: In this type of dryer, the chamber’s temperature increases, and the water present in chillies mixes with dry air. The dry air becomes humid, and that humid air is then removed from the chamber.

In summary, there are three methods to dry chillies: using direct chilli dryers, indirect chilli dryers, or sunlight exposure.

  1. Increase the air temperature.
  2. Lower the substance temperature. When the substance temperature decreases, water molecules present in the air condense and form dew on the surface of the dryer. When the temperature is increased again, the dry air absorbs the remaining water molecules from the substance, even at lower temperatures.
  3. Hygroscopic materials have the property of absorbing water vapour from the air. Here are some examples of hygroscopic materials.
  • Table salt (sodium chloride)
  • Sodium hydroxide
  • Potassium hydroxide
  • Sulfuric acid
  • Brown sugar

In that meeting, Prasad sir, Mahesh sir, and Dixit sir were present.

Prasad Sir demonstrated how to raise the room temperature. In his project, he showed how to evenly distribute hot air throughout the chamber. They achieved this by using a Hot air duct to supply hot air to the entire chamber, making it suitable for nighttime drying purposes. Based on this idea, we also considered incorporating a radiator into the setup.

In the meeting, we brainstormed several ideas. Initially, we considered supplying hot water tubes below the tray in the dryer chamber. However, we realized that the structure would absorb heat, which was not desirable. So, we abandoned that plan.

Next, we thought about using a heater in the dryer chamber to raise the temperature. However, this option required more electricity, which could be costly. Hence, we discarded that idea as well.

Then, we came up with the concept of supplying hot air to the chamber. To achieve this, we explored the possibility of using a radiator, which is an efficient heat transfer device.

We also discussed how to increase the chamber’s temperature for drying purposes. We considered using a radiator in our dryer and utilizing the efficiency of a solar water heater.

During the meeting, we planned to supply hot water from an evacuated tube solar water heater for the radiator. This would help us achieve our drying objectives effectively.

We are gathering information about radiators and the different types available.

In a radiator, heat transfer occurs through conduction between water and air. We can supply air to the radiator, and with the help of forced air circulation, the heat is distributed.

Currently, we are gathering information about fans, blowers, and compressors. We are deciding which type of fan or blower would be suitable to use with the radiator. Additionally, we are also determining the CFM (Cubic Feet per Minute) of the fan we plan to use.

fan vs. blower vs. compressor Download

Now, we need to calculate the area requirement for drying 100 kg of chillies. Based on our calculations from the previous blog, we estimate that we will need approximately 250 square feet of space to dry 100 kg of chillies.


Objective discussion.

We need to determine how to match the energy required for drying 100 kg of chillies. The goal is to ensure that the output energy from the radiator matches the energy needed for drying 100 kg of chillies. To achieve this, we calculate the energy required for the drying process.

Conclusion of meeting.

First, we need to determine how much energy is required to convert 1 kg of water into its vapour form.

It takes 2260 kJ to change 1 kg of liquid water at the normal boiling point to steam (water vapour).

For 1 kg of chilli, the percentage of water present is 74% (1000 gm – 74% = 260 gm dry chilli & 740 gm water).

We calculate the energy required using the formula: Q = M * ΔHv, where M is the mass of water converted in kg and ΔHv is the heat of vaporization.

Q = 0.740 * 2260 (kg * kJ/kg) Q = 1672.4 kJ (energy required for 1 kg of dry chilli)

To calculate the total energy requirement for the plant: 1672.4 * 100 = 167,240 kJ (42,940 kJ of energy is required for the plant).


We discussed with Sir Dixit, Sir Mahesh, Sir Prasad, and another member of DIC about the selection of the dryer’s shape.

The topic of the meeting was the selection of the dryer’s shape. We considered different shapes like the Pentagon tunnel drive, dome dryer, and flat dryer. After studying and analyzing all the dryers in blogs, we came to the conclusion that the dome dryer offers the best surface area and maximum sun exposure compared to other shapes. It also has low air resistance and requires fewer materials to construct, making it a cost-effective and sturdy option for our purposes.

During the meeting, we also discussed using the dryer for 24 hours, including nighttime usage. The main reason for running the dryer 24/7 is to reduce drying time compared to other dryers. We plan to use a radiator to heat the dryer at night, in addition to utilizing solar heat during the daytime. This way, we can achieve efficient drying of chillies both during the day and at night.

Objective discussion

During the discussion, we focused on how to supply air inside the dome dryer. We considered the dome’s size and explored two options: natural convection and forced convection for air supply.

Next, we looked into selecting a suitable fan for the dryer. We determined the number of fans required and their CFM (Cubic Feet per Minute) value.

We also discussed the number of layers to be used in the dryer and how to supply air to each layer effectively.

Furthermore, we explored various possible shapes of trays and selected the one with the largest surface area for better efficiency.

Conclusion of discussion

We plan to create a two-layered dome for comfortable use. The tray size for each layer will be as follows:

  • For the first layer, the distance between the ground and the tray will be 1 foot.
  • The second layer will be placed at a distance of 3 feet from the first layer to ensure comfortable usage.

In the dome, we will leave a working area of 3 feet in the centre, as shown in the figures. This design will provide a practical and user-friendly setup for drying chillies efficiently.

(Front view of Dome.)

We can calculate the number of areas we get for the tray using this figure.

  1. The first layer gives us an area of 190 square feet, which we can use.
  2. The second layer provides 85.22 square feet of area, which is suitable for drying.
  3. To select a tray, we need more information on how to do it. We should understand the tray’s size with the help of a figure.
  4. For better understanding, we use Catia v5 Software.

The first layer has the following dimensions:

  • It can accommodate 15 trays.
  • The exact dimensions of the trays are shown in the figure.
  • The total area of both trays combined is 11.46 square meters.

The second layer has the following dimensions:

  • It can hold 13 trays with the same dimensions as shown in the figure.
  • The total area of both trays combined is 9.89 square meters.

Afterwards, we will create a hopper to facilitate the circulation of hot air from the top layer of the dome, pushing it down into the bottom layer, the dimensions are also shown in the figure.

After designing the hopper, we will now select the appropriate fan that can circulate the hot air for this purpose. We will calculate the required CFM (Cubic Feet per Minute) of the fan to achieve the desired air circulation.

In the Dome, how much area is covered by the sun?

We need to calculate that area.

And that is 402.12 Metro Square.

How much sunlight falls on that area? We need to calculate that. And that is 23.11 megajoules per day.

402.12*23.11*10^6…………………………(Meter Square. * Mega joules/day)

Our system efficiency is 30%. We consider flat dryers.

We need to change the temperature difference or Delta T is between 20 to 50 degrees Celsius. Then our delta T is 30


258.94/25,000=10357……………………….(Here 25,000 is time in seconds)

10357.902 kg/1.29kg=8029.38-meter cube……………………..(hear 1000 lit=1.29 kg)

To convert the given value into Feed Cube. Because we calculate fan in terms of Feet Cube. or CFM. So, we want to answer in fit Cube. And that is 283.554.87 Feet Cube.

Now we want to remove that humid air in 12 hours a day.

283554.87 / (12*60) =393.82 CFM fan we want.

I want to use 24 small fans around the perimeter of each layer.


raffle calculations of the design of the dryer photo


After completing the previous step, we will create a model to check if the actual dryer looks like the one shown in the photo. The model will compare various aspects of the dryer, ensuring that it closely resembles the design in the photo. This way, we can verify that the manufactured dryer matches the intended design accurately.

The objective of the meeting

Using Catia V5 software, we will design a 3D model of the dome dryer.


with the help of Catia software, I drew this drawing.

The circulation of hot air will happen as follows

We will use hot air generated at the top of the dome, and with the help of a fan and funnel, we will draw this hot air down to the bottom chamber where the chillies are located. The exhaust fan will remove humid air from the tray and expel it from the dome. Fresh hot and dry air will be drawn from the top to replace the removed air. The dry air will absorb moisture from the chillies, and the cycle will continue. If the humidity is detected by a sensor, the fan will turn on to remove the humid air, and if not, the fan will remain off.

BOM of the structure. It is as follows.

Copy of BOM_rahul(1).xlsx

In the review meeting, I requested a budget of 135,100 rupees for this project. However, they informed me that Vigyan Ashram does not have that amount of funds available. As a result, the project was halted, and they assigned me to work on the maintenance of the natural flow flat dryer instead.


After the previous meeting about manufacturing the dome dryer, the project was halted due to funding limitations.

One month later, a farmer from Nashik approached Vigyan Ashram with a request for a dryer with a capacity of 50 kg.

To complete the previous project, the authorities decided to take this order for the dryer.

Accordingly, the dome tray structure was redesigned to match the required capacity. The dimensions were reduced, and SolidWorks drew the new tray structure as shown in the photo.

Now, we have created a this-shaped structure as seen in this picture. It’s easy to make and it’s also stronger when holding things. That’s why we picked this design – it will also lower the cost of making it.

Based on that, we have decided on the following dimensions.

After designing the tray structure in the model, the next step is to begin the fabrication process.

22/06/2023 TO 24/06/2023

Here are the simple steps for fabricating the tray structure:

  1. Take a metal tube with dimensions 20*20*2.
  2. Cut the tube to match the desired length of the tray.
  3. Arrange the cut parts to form the shape of the tray.
  4. Use spot welding to quickly join the parts together (in case of mistakes, the structure can be easily disassembled and re-welded).
  5. Check that all tubes are in the correct positions and then perform perfect welding for a strong connection.
  6. Create a stand using a 25*25 tube to hold the tray structures at a specific height.
  7. After welding, use a grinder to remove any slag and sharp corners from the welded joints.
  8. Assemble the entire structure to ensure that all parts fit together properly, and check for any issues that need to be fixed.
  9. A video of the assembled structure can be found below.

Afterwards, we made a stand that would support the weight of all the trains and their structures on it. The design looks like the one in the picture.

The entire structure will be supported and held up by this stand.

The dimensions are as follows.

To ensure that our created structure can be assembled, we made a tray-like arrangement. We put it together in the workshop at Vigyan Ashram to see if it fits properly.

After assembling all the parts successfully, disassemble the structure.

Next, we will create a tray to place on the structure. The key consideration is that the tray should be lightweight, easy to lift, and effortlessly movable, following the design we have created. We plan to use aluminium for the tray, and the sheet specifications are as follows:

The image on the left shows the outer side tray, while the image on the right shows the inner side tray. In each compartment, two trays can be placed.

Based on this design, we will create a three-layer tray. We will cut this sheet using a laser cutter. The dimensions are as follows:

25/06/2023 TO 05/07/2023

After completing the tray fabrication, it’s time to apply paint. Before painting, it’s essential to polish the surface with sandpaper to ensure proper adhesion of the paint. This step is crucial as it prevents the paint from peeling off later.

To protect the tray from rust, apply a coat of red oxide primer, which acts as a rust inhibitor.

Next, apply a coat of black Japanese paint with a matte finish. This matte finish helps the tray absorb more light instead of reflecting it.

However, if the first coat of black Japan paint is of a matte finish, you may need to apply a second coat for better adhesion and coverage.

06/07/2023 TO 07/07/2023

After allowing the paint to dry, we proceeded to assemble the structure inside the dome. This can be a bit challenging due to the limited space. However, during the assembly, we encountered a problem where there was an air gap at the bottom of the dome due to a short black sheet. This unintended air circulation was undesirable for our purpose.

To solve this issue, we designed and created hooks at the bottom of the dome. By using these hooks and ropes, we were able to secure the loose sheet in place and eliminate the air gap. Please refer to the figure for a visual representation of the solution.

The red colour represents the rope, and the black colour represents the dome sheet. When we tie the rope, the hooks will pull the sheet towards the centre. However, there is still a gap between the two hooks.

To solve this issue, we dug a hole below the dome and inserted the dome into the pit.

You can see the process in the video.

After that, we attach the foldable duct, which is made of aluminium material. The duct is connected to the centre of the funnel-shaped face, and on the top side of the funnel, there is a fan attached to circulate the air. You can better understand this setup with the help of images.

After completing all the tasks,

Afterwards, we’ll load 25 kgs of fenugreek into the dome and spread it thinly on the tray to facilitate effective water removal. Using a thick layer would slow down the process of removing water.

we collected readings to determine if the newly created dryer was functioning efficiently or not. However, during this reading collection, various seasons were occurring. This affected the expected temperature. Nevertheless, we proceeded to record temperatures.

There are two types of temperature readings we captured. The first set was taken without the fan running, representing the stable hot air temperature. The second set of temperature readings was taken with the fan operating, representing the air circulation caused by the fan. This second set of readings was taken. Here are the recorded readings.

After gathering the readings, we made a decision to calculate the energy being generated by the Dome at present, especially during the rainy season. To do this, we assessed how much heat is transferred from the top chamber to the bottom chamber, both with and without the fan operating. We also measured the amount of heat that is being wasted if the fan is off and needs to be calculated in calories. The calculations are as follows.

During a rainy day, we receive 1185 calories from the dome over a day.

motor specification W-50, time-3600/4.18


=43.06 kcal

To distribute those 1185 calories into the chamber, we must use a fan to circulate the energy to the bottom layer. In addition, we calculated that the fan consumes only 45 calories of energy to distribute that amount of energy into the bottom chamber.

These calculations were conducted during the rainy season. If we were to use the dome in the summer season, the calorie generation would certainly increase.

The only tasks left for the dome are to make the inlet and exhaust.

To complete the task, we observed that the air circulation in the dome, both the intake and exhaust, was not meeting our expectations. To improve air circulation, we tried lifting the black paper from the bottom, but even then, we couldn’t achieve satisfactory temperature readings inside the room.

We discussed this issue with Dixit, Sir Prasad, and Mahesh sir, and various ideas were proposed during our discussion. One idea was to create an exhaust hole around the perimeter of the dome. However, we realized that this could lead to problems with moisture entering the dome at night, making this idea less viable.

So, we considered another idea based on a mechanism we saw in Vigyan Ashram’s toilet, which had a fan with a flap. When the fan was turned on, the flap opened, and when it was off, the flap closed. We thought we could apply a similar concept to our dome. By using a flap, we could remove humid air from the dome while preventing moisture from entering at night.

The next challenge was deciding where to place the fan. To address the moisture issue, we decided to install the fan on the top side of the dome, just below the funnel. This way, the fan would draw moisture from the top, expelling it outside the dome.

However, we recognized that running the fan continuously wouldn’t be efficient, as it could disrupt the natural temperature changes inside the dome during sunrise and sunset. To address this, we discussed using a timer. The timer would activate the fan if the temperature inside the dome exceeded 50 degrees Celsius. It would also periodically turn the exhaust fan on and off to maintain proper air circulation.

In conclusion, our meeting led us to the decision to use a fan with a flap mechanism to control the moisture and temperature inside the dome. This way, we can expel excess moisture while keeping the air circulation in check.

Following our earlier discussion, I began the task, and I successfully completed it.

After completing the installation of the fan assessment, we disassembled the dome, wrapped the materials and machinery, and entrusted them to some skilled students for transportation. The dome was then delivered to Nashik and reinstalled at the designated site.