- The document describes the design and performance testing of a triple pass solar dryer for drying agricultural products. - An experimental setup was developed with a 2m^2 flat plate collector, drying chamber, blower, and circulation fan. Various sensors measured temperature, humidity, and solar intensity during testing. - Experiments were conducted drying mint leaves, bitter gourd, potato, and other crops. Results found the solar dryer significantly reduced drying time compared to natural drying, with up to 90% moisture removal achieved in 5-6 hours. - Thermal efficiencies of the collector ranged from 8-29% depending on solar intensity. The triple pass design improved heat transfer over single pass designs.

1. COIMBATORE INSTITUTE OF ENGINEERING AND TECHNOLOGY
PERFORMANCE STUDY ON TRIPLE PASS SOLAR
DRYER FOR AGRICULTURAL PRODUCTS
Presented by
Subhash.S 710511114044
Vinothkumar.P 710511114052
Sadham Hussain.S 71051114312
Sanjeev Kumar.B 710511114313
Guided by
Mr. S.Vijayan M.E.,
Project Viva-Voce Date:- 10.04.2015

2. CONTENTS
• Overview
• Problem identified
• Objective
• Methodology
• Experimental setup
• Experimental study
• Results and discussion
• Conclusion
• references

3. OVERVIEW
• Solar energy is radiant light and heat from the sun harnessed using a range of ever-
evolving technologies and it is an important source of renewable energy which is
one of the cleanest energy source available in the earth.
• Solar drying uses the sun as direct source of energy to dry the crops thermally.
• In direct solar drying the agricultural products are dried by placing in products
under the glass plate which is directly exposed to sunlight but it has several
disadvantages.
• The disadvantages of this type is overcome by the indirect type forced convection
solar drying.

4. PROBLEM IDENTIFICATION
• Solar dryers with flat plate collector have a disadvantage that it
has a less heat transfer rate of air.
• The availability of the system for operation i.e. solar radiation
available only in the day time.
• The intermittent property of sun’s radiation may lead to
improper drying or detoriation of quality of the product.
• Direct exposure of the product to the sun radiation results in
colour loss, change in the nutritional values etc.,

5. OBJECTIVE
• Improving the heat transfer rate of air by introducing porous
medium in the path of air.
• The products to be dried in a constant drying rate by
incorporating a thermal stabilizing medium like sand.
• Excessive thermal energy can be stored in the thermal storage
medium for later use.
• The drying of the agricultural products quality can be
improved by drying it inside the chamber.

6. METHODOLOGY
• Design of an experimental setup
– Selection of heat transfer improvement method
– Selection of thermal storage medium
• Development of a triple pass solar dryer with 2 m2 aperture area.
• Selection of the drying products
• Study the performance
• Results and discussions.

7. EXPERIMENTAL SETUP
• The schematic of the solar dryer consisting of a flat plate collector, drying
chamber, blower and a circulation fan.
• An aluminum sheet painted matte black is used as an absorber plate to
absorb incident solar radiation.
• A plain window glass is used as transparent cover to avoid heat losses at
the top.
• The collector air channel depth is 20 mm and the space between the
absorber to the transparent glass cover is 25 mm.
• The space between the bottom glass cover and the desiccant bed is 50 mm.

8. COMPLETE SETUP

9. DESIGN AND FABRICATION OF DRYING
SYSTEM
• The collector consists of three passes
with the turbulent flow this increase the
efficiency of the collector.

10. SECTIONAL VIEW OF COLLECTOR

11. TOP VIEW OF THE FLAT PLATE COLLECTOR

12. DRYING CHAMBER

13. SIDE VIEW OF THE SOLAR CHAMBER

14. EXPERIMENTAL SETUP IN 3D

15. INSTRUMENTS USED
• Solarimeter (0-2000 w/m2 )
• Blower (1hp)
• Anemometer
• Hygrometer (0-100 % RH)
• Weighing machine (0-10 kg)
• 12 point digital meter
• K-Type thermocouple (0-12600C)

16. THERMOCOUPLE POSITIONS

17. PROCESS OVERVIEW
 Pretreatment of the product
 Loading the product
 Measuring the various factors such as temperature, relative humidity and
solar intensity for a regular interval of time.
 Drying is continued until the product attaining equilibrium moisture
content.
 Unloading the product.
 Measure the amount of moisture removed.

18. EXPERIMENTAL STUDY
• Experiments were conducted on drying of mint leaves, to study the effect of drying as
well as the climatic and operational parameters on the dryer performance.
• The hot air from the solar flat plate collector was forced through the grain bed and left
through the exit.
• To estimate the system performance temperature, relative humidity, weight loss of
drying product and solar intensity were recorded at 1 hour interval time.
• The drying process was continued until the product achieved its equilibrium moisture
content.
• The initial and final moisture content of the drying products were determined by the
oven method.

19. FORMULAE USED

20. FORMULAE USED

21. PRODUCTS DRIED
• THIN LEAVES
- Mint
• VEGETABLES
- Bitter Guard
- Carrot
- Potato
- Garlic

22. EXPERIMENTS CONDUCTED
• PRODUCT : BITTER GUARD
• PRETREATMENT : The bitter guards are washed in the water and it is
sliced up to 2mm thickness and loaded on the trays.
• By changing the thickness is from 2mm – 5mm the performance of the
system is studied.
• Each tray is loaded with 950 gms of bitter guard and the experiment is
carried out.

23. OBSERVATIONS OF BITTER GUARD
Tim
e
SI T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12
RH
(atm)
RH
(dry
)
RH
(exit
)
Useful
collector
gain
Thermal
efficiency
(%)
10.3
0
AM
765 40 40 46 44 44 44 38 35 34 32 34 42 49 48 52 122.49 8.13
11.3
0
AM
810 37 36 48 46 45 45 39 36 35 34 36 45 37 37 40 275.60 17.27
12.3
0
PM
925 37 36 52 49 49 49 44 40 38 37 39 48 31 32 34 398.09 21.84
1.30
PM
975 35 34 52 49 49 48 43 42 40 39 41 48 24 23 24 459.34 23.91
2.30
PM
845 36 34 52 49 48 48 43 41 40 40 42 47 25 23 24 428.71 25.75
3.30
PM
630 35 34 19 47 46 45 42 42 41 41 42 45 20 22 23 367.47 29.61
4.30
PM
562 35 36 45 42 42 42 39 39 38 39 39 41 18 19 18 183.73 16.59

24. MOISTURE CONTENT REMOVAL
Trays Tray 1 Tray 2 Tray 3 Tray 4
Time Initial wt Final wt Initial wt Final wt Initial wt Final wt Initial wt Finalwt
10.30
AM –
11.30
AM
950 540 950 636 950 700 950 734
11.30 –
12.30
PM
540 343 636 469 700 437 734 700
12.30
PM -1.30
PM
343 190 469 300 437 400 700 505
1.30 PM-
2.30 PM
190 108 300 163 400 213 515 234
2.30 PM-
3.30 PM
108 97 163 147 213 164 234 170
3.30 PM-
4.30 PM
97 88 147 89 164 125 170 125

25. RESULT AND DISSCUSSION
GRAPH
0.00
5.00
10.00
15.00
20.00
25.00
30.00
35.00
40.00
0
200
400
600
800
1000
1200
10.30 AM 11:30 AM 12:30 PM 1:30 PM 2:30 PM 3:30 PM 4:30 PM
Solarintensity(w/m2)
Time (Hr)
Solar intensity (I) vs Thermal efficiency
solar intensity(I)
thermal eff of coll %

26. GRAPH
0
200
400
600
800
1000
1200
1400
1600
1 2 3 4 5 6 7 8
SolarIntensity(I)
Drying time (Hr)
Usefull collector gain vs Solar Intensity (I)
useful coll gain
solar intensity(I)

27. GRAPH
0
200
400
600
800
1000
1200
10.30 AM 11:30 AM 12:30 PM 1:30 PM 2:30 PM 3:30 PM 4:30 PM
solarintensity(i)w/m2
Drying time (Hr)
Solar intensity(I) vs Time (t)
solar intensity(I)

28. CALCULATIONS
• Mass flow rate = Area of air inlet x Density of air x Velocity of air
= π/4 *(0.16)2x1.225x33
= 0.812 (kg/s)
• Useful collector gain = Qu = Ma×Cp (T5-T2)
= 0.812×1005×(44-40)
= 122.49 (J/kg K)
• Thermal efficiency = ɳ =
𝐐 𝐮
𝐀 𝐱 𝐈
×100
= (122.49/ (2×765))×100
= 8.13%
• Percentage of moisture content =
𝐈𝐧𝐭𝐢𝐚𝐥 𝐰𝐞𝐢𝐠𝐡𝐭−𝐅𝐢𝐧𝐚𝐥 𝐜𝐨𝐧𝐭𝐞𝐧𝐭
𝐈𝐧𝐭𝐢𝐚𝐥 𝐰𝐞𝐢𝐠𝐡𝐭
𝒙 𝟏𝟎𝟎
= (950-88/950) ×100
= 90.73 %

29. PERFORMANCE MEASURE
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
1 2 3 4 5 6 7
MoistureContent(%)
Drying Time (Hr)
Opun sun drying
Solar Drying

30. PERFORMANCE EVALUATION
• The above graph shows the moisture content removal between the natural
drying and the indirect type forced convection solar drying.
• The heat transfer rate of the solar drying system is higher than the natural
drying.
• The amount of moisture content removal rate in triple pass indirect type
solar drying is comparatively higher than the direct solar drying.
• The time taken for drying the product inside the system is 5 hours while
the natural drying requires 7 hours.
• 85% of moisture content is removed efficiently with the help of the system.

31. ADVANTAGES
• This Solar Air Dryer reduces the cost compare to other conventional
process.
• It is simple in design and fabrication.
• The agricultural products can be preserved long time.
• The drying period is less.
• We can minimise the human power.
• Economically it is suitable for all agricultural commercial uses.

32. CONCLUSION
In this project work a triple pass indirect forced convection solar
dryer was designed and developed with low cost material and various
agricultural products such as mint leaves, potato, and bitter guard are dried.
The initial moisture content of 92.8%, 85% and 90.7% of the products
mint, potato and bitter guard has been reduced to 7.1%, 15% and 9.3%
respectively with the drying period of 4 hours, 5 hours and 6 hours. The
maximum thermal efficiency of the collector is noted as 58.48% with a long
time energy storage.

33. APPENDIX

39. THANK YOU