Problem definition : – Less efficiency of dryer.

Objective :-

1) To increase the efficiency of microwave dryer by reducing the amount of energy required for drying, by reducing operating cost and by reducing drying period.

2) To suggest the pre – dryer.

Work-done : –

Firstly we took the all information about the microwave dryer.

The basic information about the dryer is as below :-


The name of the dryer is ‘ Electromagnetic Infrared Oven ‘

Working principle :-

The dryer has three divisions. First two are Microwave ovens, in which the outer part of the stuff gets dried. Then the last section is Infrared oven, in which the innermost part of the stuff gets dried. In first two ovens we use the electromagnetic waves for drying and in last oven we use the infrared waves for drying the stuff. All the stuff is conveyed by means of conveyor belt.

After drying the product we make the powder of it and we sell it to five star, three star hotels or we export it.


The cost is about 27 lakh and it is bought from Gujrat.

General working of dryer :-

There are three divisions of drying – firstly the stuff dried under the first microwave oven and then it is goes through the second microwave oven. In both of these ovens the outermost layer of the stuff get dried. Then the stuff goes into the third oven called as the infrared oven. In this oven the innermost part of the stuff get dried. In this way the whole stuff get dried but the drying rate and no of rotations of the stuff over the belt is depend on the moisture content of the particular stuff.

Motors and Magnetrons :-

There is one conveyor belt which is run on about 3 hp motor and there is one blower which is run on 2 hp motor. There are 2 magnetrons in first microwave oven and 1 magnetron in second oven. Each magnetron is of 1.6 kW. There are 8 heaters each of 1 kW.

Controllers :-

There are 2 timers and three temperature controllers out of which one controller indicates the temperature of whole machine. There are two current meters and one extra current meter is provided. There is three phase indicators and one door indicator which indicates the whether the door is open or close. One conveyor on/off switch and blower on/off switch is provided. Three on/off switches are provided for magnetron 1,2 and 3. Two switches are provided for heater 1 and heater 2. The magnetrons are related with the microwave oven and the heaters are related with the infrared oven.There is one belt speed controller.The belt speed ranges from 1 to 50 rpm.

Products :-

We can dry almost 30 types of stuffs on this dryer including lemon, pomegranate, mint, moringa, coriander etc.The selling brand name is ‘Anandghana Industries’.

Various solar dryers at Vigyan Ashram, Pabal :-

At Vigyan Ashram, Pabal there are three types of solar dryers. Namely – solar convection dryer, dome dryer and ARTI dryer.

Solar Convection Dryer :-

Working principle :-

The working principle of natural convection solar dryer is, once the air in the solar dryer is heated by solar energy, the air relative humidity will drop and floating up through the drying chamber.This air will take the moisture out of the product. And product gets dried.

The capacity of dryer is about 8 – 10 kg and it depends on the product to be dried.


Dome Dryer :-

The name of the dryer is dome dryer because it has a dome shape. The dryer is provided with two layers of treys. Where we can put the products to be dry. Below each tray the wholes are provided through which the air enters naturally into the dryer. The outer surface of dome is painted black to absorb more solar energy. Because of this the temperature increases inside the dryer due which the air becomes hotter and it circulates through the product and the product gets dried.

The exhaust fan is provided to remove the warmer air from the dryer. The exhaust fan run on the one controller programme set in the ardino circuit. And it controls on humidity inside the dryer.

The capacity of dryer is about 25 kg and it is also depends on the product to be dried.


ARTI Dryer :-

This dryer is first made by the Appropriate Rural Technology Institute (ARTI). This dryer is made up of Bamboo and it has three trays. The trys are covered with the black polythene sheet, due to which more solar radiations are get absorbed into the dryer.

The capacity of the dryer is about 3-4 kg and it depends on the product to be dried.


So we dried the various products in all these three dryers and took their weight before drying, weight after drying and calculated the moisture loss from the product for each dryer. From that, we compared the readings of all these dryers and from these readings, we are trying to decide which dryer is suitable as a pre-dryer. Up till now, we have tested the Bottle gourd, Beet, Tomato, Raw Mango, Fig, Sweet Potato, Coriander, Mint etc.

At the same time we took the LOD ( Loss On Drying ) of the product with initial moisture.

After drying at various solar dryers at Vigyan Ashram, Pabal we dried the same product in the ‘ microwave dryer ‘ at Nhavara. We took the initial weight then final weight and we also calculated the moisture loss from this dryer. Before loading of the product we need to fix the belt speed. It is depend on your product to be dry.

We kept the third oven off which is infrared oven. We took the samples for LOD from oven 1 and oven 2. We took the LOD for respective samples in microwave oven. We follow the same procedure for each product. And we noted the readings.

Concept of L0D :-

LOD (Loss On Drying) :-

In the loss on drying, we kept the sample in the oven. We took the weight of the sample after the fixed interval of time. We took the readings up-to we get the constant weight of the sample.

This constant weight of the sample indicates the weight of only solid matter. In LOD we remove the moisture as well as volatile matter from the product.

Below are some pics of our work-done.

Microwave dryer :-


Controllers :-


Domestic Flour Mill for making powder :-


Various products :-


Loading of various products in microwave dryer :-



Beet :-


Coriander :-


Mint :-


Sweet – potato :-


Fig :-


Raw Mango :-


Tomato :-


Loading of Beet into dome dryer :-


Loading of Beet into convection dryer :-


Loading of Tomato into Convection Dryer:-


Loading of Beet into ARTI Dryer :-


Loading of Tomato into ARTI Dryer :-


Taking LOD :-


Conclusion :-

We have decided the dome dryer is suitable as a pre-dryer.

Reasons to decide dome dryer as a pre-dryer.

1. Area and Capacity :- The area required for the installation of the convection dryer is more than the dome dryer and ARTI dryer and capacity is less as compared to dome dryer. For ARTI dryer area required is less than the dome dryer and convection dryer but the capacity also less. For dome dryer the area required is less than convection dryer and more than ARTI dryer but the capacity is higher than both the dryers.

2. Drying Period and Rate :- The drying rate of convection dryer is more than that of dome dryer and the ARTI dryer. So it requires less period to dry in convection dryer than other two dryers. For convection dryer the drying period and rate of drying depends on at what time we dry the product and intensity of the solar radiations.                                            In case of ARTI dryer, the drying period is depends on both at what time we dry the product and intensity of the solar radiations. In case of the ARTI dryer the drying period and rate of drying is less than that of solar convection dryer.                                                          In case of the dome dryer, drying period and rate of drying  is less than convection dryer but more than the ARTI dryer. The plus point of the dome dryer is that, we can dry the product at day time as well as at night time. At day time solar energy helps to dry the product and at night time the controlled exhaust fan helps to dry the product.                           So we can use the dome dryer at day and night time but we can’t use the convection and ARTI dryer at night time.

3. Product quality :-                                                                                                                                         The quality of product matters great. Dome dryer gives the better quality of product than convection dryer and ARTI dryer. The colour, smell and taste of the product is better in dome dryer than convection dryer and ARTI dryer.

4. Energy consumption :-                                                                                                                               The solar convection dryer and ARTI dryer only required the natural sun light. But the dome dryer requires the both the solar energy and the electrical energy for operating the exhaust fan.

5. Capital cost :-                                                                                                                                                   The capital cost of solar convection dryer of 8 kg to 15 kg capacity is about 1.5 lakh.  ARTI dryer of 5 to 8 kg capacity having capital cost about Rs 700/ – Rs 800/- and the capital cost of the Dome dryer of capacity 25 kg to 50 kg is about 1 lakh to 1.5 lakh. Hence according to capacity of dryer the Dome dryer is cost effective.