Theoretical Model Computations for Different Components of a Hot Box Type Solar Cooker Fabricated using polymeric and recyclable Materials

International Journal of Civil, Mechanical and Energy Science (IJCMES) [Vol-3, Issue-2, Mar-Apr, 2017]
https://dx.doi.org/10.24001/ijcmes.3.2.5 ISSN: 2455-5304
www.ijcmes.com Page | 114
Theoretical Model Computations for Different
Components of a Hot Box Type Solar Cooker
Fabricated using polymeric and recyclable
Materials
Dr. Minal Bafna, Dr. Manjari Gupta
Department of Physics, Agrawal P.G. College, Jaipur, Rajasthan, India.
Abstract— Many countries having tremendous solar
potentials are also the victim of the power crises since the
available solar energy is not utilized efficiently. It has
been recognized that the widespread use of solar thermal
appliances (STA) for domestic work is being held back by
excessive cost, low efficiency, high weight, and
inconvenience of user and by lack of confidence in the
long term durability of the material. In the present work,
the limitations of materials used in various components of
commercial available STA have been underlined and it
has been shown that use of polymeric materials as
specific component in solar thermal appliances can solve
most of the existing limitations and may improve the
efficiency of the existing appliances. In this paper
theoretical model computations have been done for
different components of a hot-box type solar cooker viz.,
glaze, insulation and casing material for the spectral
transmittance, the solar flux absorbed and the optical
efficiency, thermal efficiency, heat loses, weight, thermal
profile and adjusted cooking power for several suitable
materials, both conventional as well as new polymeric
materials. Significant improvement in all the mentioned
characteristic properties /figures of merit of the solar
cooker can be achieved if right combination of polymeric
materials is used in making glaze, insulation and casing.
The present study offers that component improvements of
a system results into cost reduction, extended lifetime and
makes system easy to handle. This shall surely help in
popularization of the solar appliances and enhancement
of eco-friendly environment.
Keywords— Solar Cooker, recyclable Materials, solar
thermal appliances.
I. INTRODUCTION
In the current scenario of rapidly growing power crises,
environmental pollution and ecological imbalances; the
search of efficient and clean cooking fuel has become
mandatory for the energy scientists. At present, the
materials used in solar cooker are glass, metal or alloy
which make them bulky, heavy, fragile, expensive,
difficult to transport etc. Research work done during last
decade about correlation in structure and properties of
polymeric materials as well as development and study of
light weight, low cost, portable solar cookers reveals that
some polymeric materials may prove to be highly
promising candidates for improving most of the
limitations of solar thermal appliances. The selection of
efficient materials for various components of a solar
cooker is extremely important for the efficient use of the
solar power. In literature several materials have been
suggested for glaze viz. glass, acrylics, polycarbonate
(PC), coated glass reinforced polyester (GRP), poly vinyl
fluoride (PVF). In the present paper only three glaze
materials- glass, polycarbonate (PC) and poly (methyl
methacrylate) (PMMA)) have been considered. The most
important attribute to justify the suitability of these
materials for glaze option is transmittance and thus
theoretical formalism for this has been done. The
transmittance variations have been depicted for double
glaze of each selected material. Besides this certain
generally used insulation materials in the Solar Cooker
have been selected for a comparative study.
II. DESIRED PROPERTIES OF MATERIALS
OF VARIOUS COMPONENTS OF SOLAR
COOKER
A solar cooker usually consists of the following
components:-
(i) Glaze, which may be one or more sheets of glass or
some other diathermanous material.
(ii)Tubes, fines or passage for conducting or directing the
heat transfer fluid from the inlet to the outlet or containers
to keep food load on absorber tray in case of solar
cooker..
(iii)Absorber plate, which may be flat, corrugated or
grooved with tubes, fines or passages attached to it.

(iv)Insulation, which minimizes heat loss from the back
and sides of collector.
(v) Housing or casing, which surrounds the various
components and protects them from dust, moisture etc.
(vi) Concentrator, focusing or non focusing type, which
increases optical efficiency of absorber by
directing large area radiation on small absorber
area.
Materials of the transparent cover (glaze):- The work of
a glaze is to transmit maximum solar energy to the
absorber plate; to minimize upward heat losses from the
absorber plate to the environment and to shield the
absorber plate from direct exposure to weathering. In this
context the properties required for glaze material cover
are high transmittance for visible light and opacity to
infrared and long wavelength radiations; poor thermal
conductivity, high specific heat, low emissivity in the
thermal radiation region. It should also posses’ durability,
which includes resistance to degradation due to ultraviolet
radiations, moisture penetration, corrosion due to
pollutants in the atmosphere. Low coefficient of
expansion, high melting or softening temperatures, good
impact strength, good scratch resistance and light weight
are also desirable.
These considerations make glass a contender because it is
inorganic, indicating a minimum effect from aging. In
addition, glass is readily available from a very
competitive market which should result in a minimum
cost product. So far invariably glass glazes are used in
solar thermal appliances. However, glass has some
serious limitations such as relatively high brittleness and
density which worsens the solar collector’s unit weight
index high density, and potential difficulties in fabricating
very large think panels that might have to be covered or
have a complex cross section such as in the linear fresnel
lens. Presently, efforts are made to replace it by other
suitable substitute. Polymers like PC, PTFE and PMMA
are good candidates for this purpose. Of these polymeric
materials, polymethyl methacrylate (PMMA) may prove
to be very promising candidate as it has extraordinarily
resistant to oxidative photodegraduation, there being no
damaging u.v. absorption in the pure polymer down to
0.285m.In addition to its good aging and optical
characteristics, it is also adaptable to diverse processing
techniques such as casting, extrusion, modeling the
thermoforming. Therefore it is necessary to undertake
research and experimental technological works on
creating special plastics for the transparent covers of the
collectors.
The insulation materials:- These materials should posses
low thermal conductivity and must be heat resistant
briefly to 180 C and for a long time to 80 C. They must
not release volatile substances when heated, should have
low moisture absorption, should not release dust
particles, and should have good durability and rigidity,
low density, ecological clean production and the cost
effective. Materials likes Polystyrene, polyurethane,
glass wool, sawdust, rock wool, cotton wool are the
common commercially used material for insulation We
have also done a comparative study of various
polymeric insulation materials and the commercial used
ones. The study clearly establishes that polymeric
insulation materials are far more superior.
Casing:-The choice of materials for the casing of a solar
collector is determined by the requirements of structural
strength and longevity under all types of atmospheric
action over the course of the collector’s operating life and
also on technical aesthetics. Such materials can be GI
sheets, aluminum alloys with protective anode coating,
radiation – and cold-resistant plastics and a combination
of corrugated cardboard and aluminum alloys.
Surprisingly, corrugated cardboard shows very impressive
performance as done by our group in designing low cost
solar cooker.
However, for creating a collector at the modern technical
level the materials should be selected with considerations
of all of the requirements imposed, some polymeric
materials may prove to be promising candidates if cost
considerations may be relaxed.
III. PARAMETERS OF INTEREST IN SOLAR
THERMAL APPLIANCES WHICH MAY BE
IMPROVED BY USE OF POLYMERIC
MATERIALS
For the trapping of solar radiation in the collector,
proper glazing of the trap is required. The most
important property required for glaze material is high
transmittance. Through a theoretical formalism of
transmittance for glaze, a quantitative study has been
done. The theoretical formalism is as follow:
In transient state of a STA the flux S absorbed by the
collector plate can be written as:
S = Ibrb ()b +{Idrd + (Ib + Id)rr} ()d (1)
and at any time the flux incident on a surface is given by:
Is = Ibrb +Idrd + (Ib+Id)rr (2)
where Ib is the beam radiation, Id is the diffuse radiation,
rb, rd are the tilt factors for beam and diffuse radiation
respectively, and rr is the radiation shape factor for a tilted
surface with respect to the sky. For the horizontal upper

glaze the value of rb, rd and rr are found to be 1, 1 and 0,
respectively.
In equation 1,  is the transmissivity of the glaze material,
 is the absorptivity of the collector plate, ()b and ()d
are the transmissivity-absorptivity product for beam and
diffuse radiation falling on the collector, respectively.
The overall transmissivity ‘’ of a transparent cover is
given by:
 = ra (3)
where r is the transmissivity obtained by considering
only reflection and refraction, a is the transmissivity
obtained by considering absorption.
)+(
2
1
rIIrIr   (4)
I
1)-(21
-1 I
rI



M
 (5)
II
rII
1)-(21
-1



M
II

 (6)
where rI and rII are transmissvities of the two
components of polarization and M is the number of
covers, which governs effect of number of covers on r.
ρI and ρII are the reflectivities of the two components of
polarization and i and r are the angle of incidence and
refraction, respectively, at the upper glaze surface. The
direction of the incident and refracted beams are related to
each other by Snell’s law in which the refractive indices
of the two media n1, n2 are related.
The transmissivity based the on absorption is given by:
rcos/exp  ca KM (7)
where extinction coefficient K is a property of the cover
material, M is the number of covers, c is the thickness of
the cover material and r is the angle of refraction.
Further the optical efficiency of the trap of a STA is given
as:
sI
S
 (8)
where S and Is are defined in equation(1) and (2),
respectively.
In most of the solar thermal appliances good insulation is
mandatory to prevent the transmission of heat from inner
part of the trap to outside environment. A study of
different insulation materials has been done on the basis
of (i) thermal conductivity (ii) density (iii) service
temperature (iv) weather-ability and (v) cost. The heat
transfer coefficient (U) value is a most powerful
parameter for the comparison between different insulation
materials. The U (heat transfer coefficient)-value of a flat
insulation material, assuming the flow of heat transfer to
be one dimensional and steady, and neglecting the
convective resistance, can be computed by the following
expression :
L
k
U  (9)
where L and k are thickness and thermal conductivity of
the insulation material, respectively. As the thickness of
insulation differs between 40 to 60 mm in most solar
cookers, a common thickness of 50 mm the U-values of
selected insulation materials are calculated.
IV. DISCUSSION OF RESULTS
Following results can be inferred from the theoretical
model calculations done for the above mentioned
characteristic properties:-
From study it is quite evident that transmittance based on
absorption ( a)is almost independent of angle of
incidence whereas that based on reflection refraction( r)
is a sensitive for of angle of incidence. It can be clearly
seen in fig1 that the total transmittance ( ) decreases with
angle of incidence sharply beyond incident angle 50º.
This is major reason for decrease in efficiency of Solar
Thermal Appliances during winter. Thermal
characteristics of glaze material play a crucial role in
deciding the top heat losses and availability of solar
radiation into the solar appliance.
Since we generally use double glaze illustrative number
for total transmittance for different glazes are given in fig
1. It can be seen from this table that transmittance at all
angle remain higher in order for PTFE, PMMA, PC and
glass. All the polymeric materials studied here are more
transparent than glass. From fig 2 it can be found that the
total flux absorbed S for polymeric material glazes remain
10-13% higher than that for glass glaze. This aspect is
also reflected in figure whereas spectral transmittance of
PMMA and glass are shown. The comparative study of
glass and transparent polymeric materials clearly
establishes that polymeric glazes are far more superior to
glass glaze on the basis of both, weight index as well as
optical efficiency. Although conductive losses through
top are small, these can be made negligible by the use of
extruded polymer and designing glaze such that thickness
of sheet remains perpendicular to the draw direction.
Similarly from table1 it can be inferred easily that PS
expanded insulation is good enough to be used in solar
cookers. Table 2 indicates that by just replacing glass
glaze by PMMA glaze, 50% reduction in weight can be
obtained. Interestingly if plastic material is used for
casing also the thickness of insulation may be decreased
considerably for small bottom loss. In fact a major
component of cost of solar appliances is due to insulation.
Thus reduction insulation thickness would decrease cost

considerably and would make appliance economically
viable. Similarly the combination F and B, listed in table
3 and which are of polymeric materials are used for
casing and insulation, the weight as well as bottom loss
coefficients are significantly reduced. In Table 4
Comparison of total body weight of commercial available
solar cooker and novel design light weight solar cooker
has been done The study confirms that the overall body
weight of the LSC designed using polymeric materials is
significantly less than the commercially available solar
cooker. This reduction in weight will ease the small scale
and large scale transportation.
To further stress on the superiority of LSC (low weight
low cost solar cooker) designed using polymeric material
and light weight insulation, a comparison of thermal
profile of LSC and CSC is shown in Figure 4. This is a
representative temperature profile of solar cooker with
bare plate with reflector. The initial rise is higher in case
of LSC which is enough for two meal cooking. It clearly
indicates that optical efficiency with acrylic plate is much
better than CSC.An important parameter of solar cookers
is the adjusted cooking power is shown in Figure5 . The
adjusted cooking power of LSC obtained is higher than
the reported ones.[Funk P.A(2000).] In the fig 5 where
comparision of adjusted cooking power of LSC and CSC
with excess of temperature is shown, the slope of LSC
are less than CSC indicating better cooking performance
of LSC .
It can be concluded that selection of suitanble polymeric
material for each components of solar cooker would lead
to its significant improvemnt and popularity.
REFERENCE
[1] Lenel U R & Mudd P R, Sol. Energy, 32 (1984) 109.
[2] Mcqueen H J, Shapiro M M & Feldman D, J Matls
Energy Systems, 2 (1980) 65.
[3] Hommam P S, Hilleargy & Darnall K R, Solar
Heating Materials Handbook, Anachem, (1981).
[4] Sexena A, Varun, Pandey S P & Srivastav G, Renew
Sust Energ Rev, 15 (2011) 3301.
[5] Garg H P & Rani U, Sol Energy, 29 (1982) 467.
[6] Nahar N M, Energy Convers Mgmt, 23 (1983) 91.
[7] Jubran B A & Alsaad M A, Energy Convers Mgmt,
32 (1991) 223.
[8] Nahar N M, Renew Energ, 23 (2001) 167.
[9] Nandwani S S, Renew Energ, 32 (2007) 427.
[10]Kumar S, Renew Energ, 30 (2008) 1117.
[11]Harmim A, Belhamel M, Boukar M & Amar M ,
Energy, 35 (2010) 3799.
[12]Sengar N, Dashora P & Mahavar S, Indian J Sci
Technol, 3 (2010), 1038.
[13]Dashora,P., Bafna M, Bhargava A, 2007 Synthesis
of PMMA sheets from regenerated monomer and
their characterization for use as glaze in solar
appliances, in Journal of solar energy society of
india, 16(1), 33-43, (2007).
[14]Sukhatme S P, Solar Energy: Principles of Thermal
Collection and Storage, Tata McGraw-Hill Book
Co. (2007)
[15]Goswami D Y, Kreith F & Kreider J F, Principle of
solar engineering, Taylor & Francis, USA, (2000).
[16]Minal B, A Study of Thermal Properties of Potential
Polymeric Materials and their use in Solar Thermal
Appliances, Thesis , University of Rajasthan, Jaipur,
(2009)
Table.1: Comparison of the heat loss for different insulation material,, with different thickness of insulation materials and
no. of glaze = 2
Insulation
material
thermal
conductivity
( )
W/mK
heat loss in (W/m2
K) when thickness
(m) of insulation is used
0.04 0.05 0.1
Sawdust 0.08 2 1.6 0.8
Polywool 0.065 1.625 1.3 0.65
rock wool 0.045 1.125 0.9 0.45
Glass
wool
0.04 1 0.8 0.4
PS
expanded
0.03 0.75 0.6 0.3
Cotton
Wool
0.029 0.725 0.58 0.29

Table.2: Comparison of weight between different glaze material when no. of glaze = 2
Material Density
(g/cm3
)
Weight of single
glaze
(kg)
Weight of double
glaze
(kg)
Glass 2.235 1.67 3.34
PTFE 2.3 1.72 3.44
PC 1.2 0.9 1.8
PMMA 1.19 0.89 1.78
Table.3: Model calculation of weight of the combination of materials for casing and insulation
Table.4: Comparision of Overall body weight of CSC and LSC
Component Material used in
CSC
Weight of
component (kg)
Material used in
LSC
Weight of
component (kg)
Casing GI sheet
(.5mm)
1.98 Corrugated
cardboard
0.38
Glaze
(Double)
Toughened glass
(4 mm)
2.62 PMMA
(3mm)
1.16
Insulation Felt
(5 cm)
4.02 PS Expanded
(10 cm )
&
1 layer of Cor.Crd.
brd.
0.96
Reflector Plain glass
(4mm)
1.45 PMMA
(4mm)
0.77
Accessories 3 1.5
Total weight ≈ 13 ≈ 4.8
0.5250.6520.030.0125
PS
expanded
0.21
0.085
g/cm2
Corrugated
Card board
F
0.7922.30.040.0245Glass wool71.87.850.5GI sheetE
0.9972.040.0650.025
Poly
wool
0.2821.183PMMAD
0.75512.840.040.55Felt0.2821.183PMMAC
0.5121.8630.030.0125
PS
expanded
0.2821.183PMMAB
0.7692.970.040.0245Glass wool2352.72AluminiumA
(W/m2K)(kg)W/mK(gcm-3)(cm)W/mK(gcm-3)(mm)selected
combinationcombinationdensitythicknessMaterialdensitythicknessMaterial
of
materials
Bottom loss
coefficient
for
Weight
of
insulationCasingCombination
0.5250.6520.030.0125
PS
expanded
0.21
0.085
g/cm2
Corrugated
Card board
F
0.7922.30.040.0245Glass wool71.87.850.5GI sheetE
0.9972.040.0650.025
Poly
wool
0.2821.183PMMAD
0.75512.840.040.55Felt0.2821.183PMMAC
0.5121.8630.030.0125
PS
expanded
0.2821.183PMMAB
0.7692.970.040.0245Glass wool2352.72AluminiumA
(W/m2K)(kg)W/mK(gcm-3)(cm)W/mK(gcm-3)(mm)selected
combinationcombinationdensitythicknessMaterialdensitythicknessMaterial
of
materials
Bottom loss
coefficient
for
Weight
of
insulationCasingCombination

Fig.1: Curves for total transmittance of beam radiation for (
______
)PTFE,
(
_ _ _ _
) PMMA , (------) PC and (
__ _ _ __
)glass when number of glaze = 2. a is transmittance due to absorbtance, r
is transmittance due to reflection-refraction, = a  r is total transmittance
Fig.2: Comparison of total flux absorbed (S) for (
______
)PTFE,
(
_ _ _ _
) PMMA , (------) PC and (
__ _ _ __
)glass, when number of glaze = 2
Fig.3: Transmittance of the commercially available toughened glass and PMMA over the entire solar spectrum.

Fig.4: A comparison of thermal profile for CSC and LSC
Fig. 5: A comparison of cooking power curves for CSC and LSC

Theoretical Model Computations for Different Components of a Hot Box Type Solar Cooker Fabricated using polymeric and recyclable Materials

More Related Content

What's hot (20)

Similar to Theoretical Model Computations for Different Components of a Hot Box Type Solar Cooker Fabricated using polymeric and recyclable Materials (20)

Recently uploaded (20)

Theoretical Model Computations for Different Components of a Hot Box Type Solar Cooker Fabricated using polymeric and recyclable Materials