SOLAR DRYER

Hello connection hope you are all well, this weekend i have discussed about Solar dryer. It is installed in the National Institute of solar Energy, Gurgaon. There it is tested & developed under Bikrant sir, i am really glad & thankful to him for his guidance and allow me in the test-bed.

Introduction – Drying is an important part of food preservation especially with highly perishable crops, at peak harvest time when local markets are saturated. Also drying vegetables, fruits and meat with thermal energy enables storage times and easier transportation. Although solar dryer has many useful application other than agriculture sector. Here we briefly discuss about overall the basic technology and its operation.

Solar dryer require a certain investment for the set up but no expenditures for the fuel. The basic function of a solar dryer is to flow heat air with a constant temperature by the solar energy. It facilitates extraction of humidity from crops inside a drying chamber.

Application - Solar Dryers or Solar Air Heating systems are used in various applications such as drying of different types of crops, fruits and vegetables such as onions, tomatoes, potatoes, mango, seeds also drying of handmade paper, herbs, mushrooms, tea leaves etc. These are processed heat by providing hot air generated by Solar.

Two type of solar dryer are available, those are 

	Solar dryer system placed at NISE campus, Gurugram, Haryana

 

1. Direct solar dryer - Dried storage product by create a green house effect of sun. 

2. Indirect Solar dryer - Dried storage product by the hot air effect. 

Here we are discussed about the Hot air drier or indirect solar drier.  In the solar drier system, it is combined with some parts. These are

Evacuated tube collector - it is used to heat up the air. In this system air flows continuously into the tubes and solar irradiation can concentrated to heat up the air blow which are directly coming from outside. One part of the system is completely open and another side is connected with the storage place. In between them a pump or blower (air) is installed. In some solar dryer system, collectors are used at the place of evacuated tube.

Storage place/Dryer - It is used to dry up the products by reducing the moisture content, use of hot air flow. In the storage chamber there is total two parts, one is hot air inlet part & another is moisture, hot air outlet part. 

                                

                                           Figure 2:  Single snap of a Dryer chamber

Air pump/Blower - It is used to exhaust the hot air from evacuated tube to the storage chamber. It is connected with solar panel directly.  

PV panel – It is used to power the blower and heater pad (if use).

MPPT Charge controller – It is used to track and extract more power from the solar panel. Mainly it is used to reduce the power loss by solar panel.

Pipes & others – Mostly Silicon pipes are used here which is easily bended in any place and high temperature resistive (more than 100⁰ C). Sometimes PVC pipes are also used for some low budget project, it has some disadvantages like low temperature capacity. Diameter of the pipe is 6-7 cm.

Alternate heating sources

1. Electric heater or pad is used for external heat storage. Mainly applied at night time or in cloudy weather where natural thermal air heating can’t work. An external power source is required here to run this heater.

2. Sometimes heat storage materials are used as a backup in the solar dryer. It only gives 15-18 hours backup. For example – heat storage salt, PCM are used as a heat storing material. None of the electric power supply can used here.

PCM is phase changing material – it absorbs heat at day time and discharges it at night time. It has 10 years degradation rate, after that it decreases it’s heat storing capacity.  

Steps of the procedure –

1. Sample products are placed on the trays in a proper way where the hot air can flow easily all over the place in between them hence it covers a total area of the drier

2. Trays are placed into the dryer and locked the dryer in a proper manner. Leakage doesn’t consider here.

3. At first normal air can be flown from outside to evacuated tube collector. There it is transformed into hot air then it can be transferred to the dryer by an air pump.

4.  Hot air can inletting from side lower part and it can flow total two times into the chamber, firstly when Firstly it flows from bottom to the top part of the dryer then again it flows repeatedly by another blower.

5. After repeat some cycle the moistened air can flow outside to the dryer.

 6. At last, It takes total 1-2 days to dry up the sample. It depends on many factors like solar irradiation, moisture rate of sample, weather condition, etc.

Result

Finally it takes 20-24 hrs (depends on place, weather, dried product & many other factors) to dried up completely.

Now i refer some other type of solar dryers, recently it is installed at NISE by a company- "AAGUN". In this system the drying technology is based on PCM - Phase changing material.

** Today's blog content doesn't advertise any company's product or Institute.

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