沙漠研究 22-1, 187 -190 (2012 )"ICAL 1 / DT X"

Journal of Arid Land Studies－Refereed Paper－

Development of Solar Dryer for UV Sensitive Arid Area Medicinal Plants
Raghib JAMAL1),2), Ajay KUMAR3), Shilpa CHOUDHARY2), Sangeeta SINHA*2) and Ram Ashish SINGH2),4)
Abstract: Deserts and arid areas in India lack energy sources and specialized transportation facility. One of the main reasons issparse population and low production density. Since most of them are of perishable nature, they are consumed mostly locally and has
hardly any economic value as compared to the cost of production. Consequently, people in these areas are loosing their interest inthese medicinal plants and fruits mainly. With continued migration of people to other areas, the danger of extinction of these plant
species is also looming large. Introduction of alternative means of sustainable development is vital for deserts and arid area
development and ecosystem preservation. Solar drying has immense potential to initiate the reversal of the present situation. In thepresent paper, family size (5 kg capacity) UV sensitive FRP solar dryer is designed for drying of low thickness drying materials
including leaves. The performance is modeled theoretically and evaluated experimentally using shrinkage factor. It was found thatthe heat transfer coefficient remains constant for thickness of drying materials between 2 mm and 10 mm, while it has hardly any effecton less than 2 mm materials, especially leaf types. The heat transfer coefficient is controlled by the combination of high heat capacity
material and Phase change material to preserve the colour of the drying material.
Key Words: Arid, Medicinal plant, Solar dryer, UV protection

1. IntroductionArid areas and deserts all over the world has inherent
drawback - low population density. With globalization ofeconomy, profit making has become the keyword. Almost all
the governments are stressing on privatization. Thesedevelopments have caused considerable negligence indevelopmental efforts in arid and desert areas. In India, withInformation Technology revolution, things are slowly changing
in arid areas with private initiatives, still a long way is left
ahead. Nevertheless, in last decade, climate related disasters,
mostly attributed to green house gas emissions have decisivelyinfluenced our perception of deserts and arid areas. Materialand human loss due to these disasters all over the world hascompelled planners and researchers to find ways of remedy
and alternative methods of development. It is felt thatenvironmental degradation affects events beyond politicalboundaries. International Energy Agency under its Annexure
8 brought together scientists and researcher to investigate ‘Very
Large Scale Photo Voltaic’ (VLS plants to temperature anddirect sunrays, particularly Ultra Violet rays makes the existing
designs unsuitable. Though UV- opaque glasses are availablein cities, but these are costly and the cost itself renders it
infeasible for the present purpose. Family cabinet solar dryer(CSD) is designed, fabricated of Fibre Reinforced Plastic(FRP) and investigated. It can use diffused sunlight andindirect heating for drying. Theoretical modelling and field

investigation of the process shows that controlling the heattransfer coefficient by a combination of H PV) installation indeserts, for future energy supply. European commission, USand Japan also formed task group for assessing such options.
At the same time, another group of researchers initiatedinvestigation into carbon mitigation option by plantation indesert and arid areas. Large scale plantation remains still thebest option for creating carbon stock. Besides, it helps inreclaiming land in several areas for agriculture purpose, needed
to feed burgeoning population in coming years. These efforts
were also supplemented by peripheral investigation into otheraspects of arid areas and deserts such as, preservation of its
ecology, better livelihood for native people, desert plants andfruits etc.
Alternative methods of development andexploration of untapped medicinal properties of desert and arid
area plants attracted several researchers from various
disciplines.
Arid areas adjoining Thar Desert in North-West India isalso a rich source of medicinal plants and fruits. These wereused to be traditionally grown by local people in sustainable
manner, taking into account local requirement, production
capacity of soil and, scarce natural resources such as water
availability. These considerations have resulted into scatteredplantation pattern throughout the region. These medicinal
plants are mostly consumed locally due to perishable nature,scattered plantation, unavailability of technical expertise andmeans to preserve and transport to nearby markets. Thesearid areas are also worst hit by global climate changes.

* Corresponding Author: prof.ssinha@gmail.com (Sangeeta Sinha, e-mail)CREER, P.O. Box - 5, Muzaffarpur-842001, Bihar, India
1) Department of Computer Sc., Al- Jazan University, Saudi Arabia3) Dept. of Physics, M.S. College, Motihari, Bihar, India

2) Centre for Renewable Energy and Environmental Research, Muzaffarpur, Bihar, India

4) #25, Rd no. 5, East Patel Nagar, Patna, Bihar, India

Options of sustainable development have shrieked at a fasterpace than expected. Ecosystems are under stress and regional
disparity in economic development has tremendously
increased, causing demographic changes.
These arid areas are blessed with high solar insolation
almost throughout the year. Solar dryers can be used fordrying and preservation of these medicinal plants (Choudharyet al., 2005, 2006, 2009). However, sensitivity of these igh
Heat Capacity material and phase change material, improves
the quality of the dried product. Phase change materials forsuch uses are investigated by Sharma et al. (2004) and are also
documented by Grigoriev and Meilikhov (1995). It is very
crucial for drying object of thickness 2-10 mm.

2. Materials and Methods
2.1. Theoretical modelling
In order to derive expression for heat transfer coefficient ‘h’(W/m2 °C), the following assumptions are made to simplify themodel,(i) Evaporation occurs only at the surface of the drying mass,(ii) Within the drying mass, temperature and moisture content
remains almost uniform within the solid. This is truesince only thin materials are considered for drying. This
also emplies that there is no temperature gradient in drying
mass. This is justified since the ratio of internal toexternal resistance to heat transfer, (Bi = hL/k) (Biotnumber, Bi) remained less than 1.
(iii) The convective heat transfer remains the dominant modeof heat transfer.
The heat balance equation for the drying mass can bewritten as (following Luikov, 1968),

md (1 + M )C Pd TP= h A (T − TP ) − nw A λdt(1)

md (1 + M )C Pd TP dM = h A (T − TP ) − md λdt
 dt (3)This leads to an expression for heat transfer coefficient,m  dM dTV   ρ C P (1 + M ) P + d λAdtA  dt h=(T − TP )where, ρ is density of drying material (kg/m3), V is volume ofsample (m3).
The ratio of surface area to volume (shrinkage factor) isinvestigated for small pieces of Emblica officinalis, Aegle
marmelos for fixing the amount of high heat capacity material(HHCM) and Phase change material (PCM) in cabinet size
solar dryer. Since shrinkage depends on the moisture content
and the type of product, the ratio of Av and Avo is considered
to be important as found earlier in case of potato drying (Ratti,1994; Rahman and Kumar, 2009). They defined theshrinkage factor hsh as,h sh =

 M 
 M 
AV
 + 3.661
= 2.175 − 3.194
AVO
 MO 
 MO 

md dM
A dt

3

2.2 Construction of CSD
Three prototypes of family size cabinet solar dryer wereconstructed from (a) double layer galvanize sheet, (b) particle
wooden board and, (c) Fibre Reinforced Plastic board (FRP).
Later was found to be most efficient since the loss of thermalenergy was minimal. Figure 1 shows the family size FRP(2)Here, nw is correlated to the dried mass M. From equation (1)and (2), it follows,

2

 M 
 (5)− 1.661 MO 
Where, Avo and Av are initial and instant area per unit volume(1/m), Mo and M are initial and instant mass of the drying
object (kg).

where, md is mass of dry matter (kg), M is moisture content(kg water/kg dry matter), Tp is temperature of sample surface(C), T temperature of drying air (oC), A is surface area (m2), his heat transfer coefficient (W/m2 oC) and, λ is latent heat ofvaporization of sample (kJ/kg), Cp is specific heat capacity(kJ/kg oC), t is drying time (s).
The water mass flux, nw can be expressed in the followingform,

nw =(4)

Fig. 1. Family size FRP CSD.

250
1.5

hsh/h

40
130
20

0.5
100

Temperature of CSD (oC)

60

0
8:00

9:00

10:00

11:00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

Time (hours)
Fig. 2. Variation of temperature inside the CSD with 45 kg of HHCM and 15 kg of PCM, and corresponding variation in hsh/h.

from all the sides. In the bottom, 0.75 mm particle board isCabinet Solar Dryer (CSD). The effective area of the CSD
exposed to solar radiation is 1 m2. It has double layer of FRP
used between the two layers of FRP to provide strength forplacing up to 80 kg of HHCM and PCM. In side walls, 0.75
mm of thermocole is used between the FRP layers to improve
insulation. The whole system is properly insulated. It has
two trays with two compartments each. On these trays,drying materials up to 5 kg may be placed for drying. At thebottom a perforated pipe is placed to suck air by the PV
operated fan at the top to control temperature in a particularrange. This also helps in fast removal of high moisture fromCSD. Drying material in the upper trays are covered toprotect it from UV rays.

3. Results and Discussion
At first, temperature stabilization inside the dryer was themajor issue as it varied with insolation and even reached 90
degree C. It affected the quality of the dried product making
it sometimes brittle. Loss of nutrients was also observed.
Therefore, HHCM (blackened stones and pebbles) were used,
but it delayed initial rise in temperature and reduced thenumber of hours suitable for single day drying. A 65 kg
combination of phase change material (NaOH . H2O) andHHCM in the ratio of 1:3 was found suitable for drying of 5 kgof medicinal plants and fruits (more than 5 mm thickness).
However, two problems were detected in the course ofinvestigation,(a) the drying is not suitable for thin masses (less than ~ 5 mmthick) including leafy types.
(b) Drying by direct insolation caused blackened texture withbreaking of sugar content if present.

Table 1. Vaiation of hsh/h with HHCM and PCM.

Thickness ofMaterials
(mm)
10月8日
8月6日
6月4日
4月2日
<2PCM

HHCM

h sh /h(kg)20151050(kg)
45
50
60
7080

(W/m2 o C) -1
<1.8
<1.8
<1.8
<1.8
<1.8

Available literature showed that it is mainly due to two
reasons, uncontrolled heat transfer coefficient and UV rays.
Hence in the present investigation, a methodology is developed
to control the heat transfer coefficient. The ratio of Shrinkage
factor to heat transfer coefficient is found to be most suitablefor controlled drying of medicinal plants and thin pieces ofmedicinal fruits. The ratio of hsh/h must be kept below theabsolute value 2 for better drying results. Shrinkage factor
depends upon moisture content inside the sample and theexternal temperature. Higher water flux at high temperaturedamages the texture and also affects the quality of the product.
Figure 2 shows the variation of CSD temperature andcorresponding variation in hsh/h for drying of Emblica
officinalis, and Aegle marmelos pieces in the FRP CSD. The
ratio of HHCM and PCM affects the parameter hsh/h. It
also depends upon the thickness of the drying objects.
However, it has hardly any effect from the total mass of thedrying material.
To cut off UV radiation, three methodologies were applied,(a) Top glass cover was changed to UV opaque glass.
Though the results were excellent, it was considered
impractical to use such glasses. Their availability in arid
areas and cost was major cause of concern.

4. Conclusion

Fig. 3. Drying under direct sunlight in CSD.

Solar drying of medicinal plants and fruits from arid areas
has several benefits. It encourages economic activity in arid
areas and provides ingredients to newly sought after ‘naturalcure’. By evolving methodology for cost-effective drying
process for the illiterate masses, new and alternative
opportunities of development could be created. It would help
in stabilizing life of people in these areas and stop migration ofpeople to stressful life in search of livelihood. The FRP CSD
design developed and presented here is cost effective andoperation friendly. It can be used for drying of several
products in arid areas with minor changes in the ratio andamount of high heat capacity material and phase changematerial.

References

Fig. 4. Drying under shade in CSD.

(b) Top plane glass is changed to provide diffused light so thatinstead of direct sunlight, only diffused light could enter theCSD. This system reduced the efficiency by more than30%. Hence, it was discarded.
(c) A very simple method was evolved - using black paperover the drying object supplemented by small one watt fan
at the top and operated by power from PV panel. It wasmost effective.
Particularly in case of leafy types, it was found easy to dry
under such condition. Figure 3 shows the drying results ofleaves with medicinal characteristics drying under direct sun
light in the CSD. Figure 4 shows the result of drying undershade using the above mentioned methodology. The former
changed to brownish colour while the later maintained thegreen colour upon complete drying, i.e., less than 7% moisturecontent.

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