analysis of the axial pressing of bulk jatropha curcas l. seeds using reciprocal slope...
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Research Paper
Analysis of the axial pressing of bulk Jatrophacurcas L. seeds using reciprocal slopetransformation
David Herak a,*, Ji�rı Blahovec b, Abraham Kabutey a
aDepartment of Mechanical Engineering, Faculty of Engineering, Czech University of Life Sciences Prague,
Kamycka 129, Prague, Czech RepublicbDepartment of Physics, Faculty of Engineering, Czech University of Life Sciences Prague, Kamycka 129,
Prague, Czech Republic
a r t i c l e i n f o
Article history:
Received 9 October 2013
Received in revised form
14 January 2014
Accepted 19 February 2014
Published online 13 March 2014
* Corresponding author.E-mail address: [email protected] (D. Hera
http://dx.doi.org/10.1016/j.biosystemseng.201537-5110/ª 2014 IAgrE. Published by Elsevie
A reciprocal slope transformation (RST) with the least squares method (LSM) was used to
develop mathematical equations to describe dependency between compressive force and
deformation characteristic curves of Jatropha bulk seeds of varying initial pressing height
from 30 mm, 40 mm, 50 mm, 60 mm, 70 mm and 80 mm in linear compression. The
experimental data derived from a compression test was done using compression device
(ZDM, model 50, Germany) and pressing vessel diameter, 60 mm at compression speed of
1 mm s�1 and compressive force between 0 kN and 100 kN. Statistical analysis of both
experimental and fitted data coefficients of third order polynomial function was significant
(p > 0.05) with high coefficient of determination (R2). The RST method provides the
fundamental step for the development of generalised model in future research where
varying effect of compression factors such as moisture content, friction, compression
speed and pressing temperature would be considered.
ª 2014 IAgrE. Published by Elsevier Ltd. All rights reserved.
1. Introduction
The behaviour of Jatropha curcas L. bulk seeds in linear
compression, where the characteristic behaviour of the de-
pendency between compressive force and deformation curves
is examined, requires detailed research to understand the
compression process (Herak, Gurdil, Sedlacek, Dajbych, &
Simanjuntak, 2010; Kabutey, Herak, & Sedlacek, 2011). This
knowledge can be transformed to understand the non-linear
oil expression process involving mechanical screw presses
k).14.02.009r Ltd. All rights reserved
or expellers for the optimisation of oil recovery efficiency and
energy requirement. In the linear compression process, the
boundary conditions are that zero force relates to zero
deformation and when the compressive force approaches
infinity, the deformation characteristic curve of the bulk ma-
terial also increases with respect to the initial pressing height
until maximum deformation is reached (Herak, Kabutey,
Sedlacek, & Gurdil, 2011). Similarly, densification of biomass
material properties relates to the axial and non-linear linear
compression processes (Adapa, Tabil, & Schoenau, 2009;
Tumuluru, Wright, Kenny, & Hess, 2010) which need in-
.
Nomenclature
a coefficients of the polynomial function
(N�1 mm�2)
b coefficients of the polynomial function
(N�1 mm�1)
c coefficients of the polynomial function (N�1)
CV coefficient of variation (%)
d coefficients of the polynomial function
(N�1 mm)
D inner diameter of pressing vessel (mm)
F compressive force (N)
Fcrit critical value that compares a pair of models (e)
Frat value of the F test (e)
H initial pressing height of bulk Jatropha seeds
(mm)
Mc moisture content (% d.b.)
ms mass of bulk seeds (g)
Pf porosity (%)
Pvalue hypothesis of the study outcomes significant
level (e)
R2 coefficient of determination (e)
T amount of reciprocal slope transformation
(mm N�1)
Tmax maximal value of reciprocal slope
transformation (mm N�1)
V initial volume of pressing vessel (m3)
x deformation of bulk seeds (mm)
xm deformation in local maximum of reciprocal
slop transformation function (mm)
rb bulk density (kg m�3)
rt true density (kg m�3)
3m strain in local maximum of reciprocal slope (e)
b i o s y s t em s e n g i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 668
depth knowledge for optimisation. In the literature, densifi-
cation theories have been applied on soil consolidation
(Taylor, 1966) powdermetallurgy and ceramics (Balshin, 1972).
Compression densification can also be described by models
focused on the simplified analysis of processes that follow the
pressing of particles inside the compressed materials. These
models, based on Balshin’s Laws (Balshin, 1972), are repre-
sented by functions expressing the relation between external
pressure and density or other parameters describing the ma-
terial porosity (Adapa et al., 2009; Talebi, Tabil, Opoku, &
Shaw, 2011). Mathematically, the Balshin’s first law, which is
also known as Walker model (Walker, 1923), is expressed by
exponential relationship between pressure and density. Bal-
shin’s second law is expressed by a power relation between
the same parameters, usually used for description of the
compression of straw and is similar to Skalweit’s Law
(Blahovec & Kubat, 1987; Matthies & Busse, 1966). Generally,
the mathematical description of densification process is use-
ful for understanding the inner processes connected with oil
and fibre separation from oilseeds such as in plant extruders
(Herak, Gurdil, et al., 2010). There has been some published
information describing the mechanical behaviour and defor-
mation characteristic curves of bulk Jatropha and other oil-
seeds (Kabutey et al., 2011). In such studies the behaviour of
the force and deformation function and the border conditions
of the compression process lack mathematical understanding
since using the standard least squares method (Herak,
Kabutey, Divisova, & Simanjuntak, 2013; Kabutey, Herak,
et al., 2013) it is difficult to describe the process. To solve
this problem the tangent curve function (Herak et al., 2011,
2013), a finite element method (Petru, Novak, Herak, &
Simanjuntak, 2012), using MarquardteLevenberg process
(Lourakis, 2005; Marquardt, 1963), rheological models
(Ocenasek & Voldrich, 2009) and non-linear equations
(Blahovec & Yanniotis, 2009) have been used, but further
research is necessary to develop suitable mathematical
models do describe the compression process. In this respect,
the reciprocal slope transformation (RST) theory involving two
separate variables (Blahovec, 2011; Blahovec & Yanniotis,
2009; Błaszak & Sergyeyev, 2009) is utilised. The theory sim-
ply identifies two distinct variables, the independent and
dependent. The application of the theory on the linear
compression process can be described as the deformation of
bulk seeds, x (mm) being the independent variable whiles
compressive force F (N) as the dependent variable. But the
transformation of the dependent variable can produce a new
dependent [F], which is defined by equation (Eq. (1)) (Blahovec,
2011).
½F� ¼ xF
(1)
Based on Eq. (1) the description of the relationship between
compressive force and deformation by the reciprocal slope
transformation can be used in the form given by Eq. (2).
F ¼ x½F� (2)
It has been reported that the relationship of the new
dependent of the RST and appropriate independent can sim-
ply be fitted by using the least square method for process
simplification (Blahovec, 2011; Blahovec & Yanniotis, 2009).
Therefore the aim of this study was to investigate the use of
RST method to describe the mechanical behaviour of J. curcas
L. bulk seeds in axial pressing.
2. Materials and methods
2.1. Sample
Bulk samples of J. curcas L. seeds, variety IPB2, obtained from
North Sumatra, Indonesia were used for the experiment. The
general physical properties of the oilseed crop are given in
Table 1. The moisture content Mc (% d.b.) of the samples was
determined using standard moisture measurement equip-
ment (Farm Pro, model G, Czech Republic) which was cali-
brated by the ASAE method (ASAE S410.1 DEC97) (ASAE, 1998;
Sirisomboon, Kitchaiya, Pholpho, & Mahuttanyavanitch,
2007). Samples of 100 g mass from a batch of Jatropha seeds
were randomly selected for the moisture content determina-
tion. Themass of each samplems (g) was determined using an
electronic balance (Kern 440-35, Kern & Sohn GmbH, Balingen,
Germany). The porosity Pf (%) was calculated from the rela-
tionship between the bulk and true densities (Blahovec, 2008).
Fig. 1 e Schematic diagram of the pressing vessel.
Table 1 e Physical properties of Jatropha bulk seeds; datain the table are means ± SD.
H (mm) V (mm3) ms (g) Mc (% d.b.) Pf (%)
30 84,834 � 5650 30.04 � 0.90 8.5 � 0.2 63.49 � 3.22
40 113,112 � 4600 45.20 � 0.29 8.5 � 0.2 58.80 � 2.86
50 141,390 � 3800 54.83 � 0.74 8.5 � 0.2 60.02 � 2.99
60 169,668 � 6200 66.56 � 1.03 8.5 � 0.2 59.56 � 3.42
70 197,946 � 4800 75.16 � 1.62 8.5 � 0.2 60.86 � 3.12
80 226,224 � 6340 88.04 � 1.55 8.5 � 0.2 59.88 � 3.61
H e initial pressing height, V e volume, ms e mass, Mc e moisture
content, Pf e porosity.
b i o s y s t em s e ng i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 6 69
However, it is important to note that the bulk density rb
(kg m�3) was determined from themass of the sample divided
by initial pressing volume V (m3) which was calculated as the
area of pressing vessel multiplied by initial pressing height
(Table 1). The true seed density rt ¼ (980 � 12) kg m�3 was
determined gravimetrically (Blahovec, 2008). This means that
the mass of individual samples (10 seeds from a batch of
Jatropha, randomly selected and measured using an elec-
tronic balance (Kern 440-35, Kern & Sohn GmbH, Balingen,
Germany)), was divided by the volume of sample. However the
volume of the individual sample was determined by weighing
the sample in toluene and applying the principle of buoyancy
(Sirisomboon et al., 2007). The results obtained were
expressed as mean of three replicates.
2.2. Compression test
To determine the relationship between compressive force and
deformation characteristic curves, a compression device
(ZDM, model 50, Germany) was used to record the course of
deformation function. A single pressing vessel diameter,
60 mm with plunger (Fig. 1) was used whereby six different
initial pressing heights from 30, 40, 50, 60, 70 and 80 mm of
Jatropha bulk seeds were tested with a compression speed of
1 mm s�1 under temperature of 20 �C. The compressive force
was between 0 and 100 kN. The experiment was repeated
three times where deformationwas expressed by strain as the
ratio of deformation to that of initial height of the compressed
Jatropha bulk seeds.
2.3. Reciprocal slope transformation (RST)
The dependency between compressive force, F (N) and corre-
sponding deformation, x (mm) was transformed using recip-
rocal slope transformation (Eq. (1)) into the form given by Eq.
(3):
T ¼ x
F(3)
where T (mm N�1) is the transformed compressive force. The
obtained relation T(x) was approximated by a third order
polynomial function (Eq. (4)):
TðxÞ ¼ ax3 þ bx2 þ cxþ d (4)
The coefficients of the polynomial function, a (N�1mm�2), b
(N�1mm�1), c (N�1) and d (N�1mm),were calculatedby the least
squares method (LSM) using MathCAD software (MathCAD 14,
PTCSoftware,Needham,MA,USA).Thecompressive force,F (N)
Eq. (5) was then expressed from the product of Eqs. (3) and (4):
FðxÞ ¼ xax3 þ bx2 þ cxþ d
(5)
In Eq. (5), the compressive, F (N) and deformation, x (mm)
can also be substituted using stress and strain as reported by
Blahovec (2008) where the stress is determined as compres-
sive force divided by area of pressing vessel and strain is
determined as deformation divided by initial height of
pressing.
3. Results and discussion
In this study, the physical properties namely porosity,
Pf¼ (59.98 � 1.26)% and moisture content, Mf¼ (8.5 � 0.2)% in
dry basis (d.b.) of the Jatropha bulk seeds were constant (Table
1) therefore these parameters did not influence the results
obtained from the experiment. The dependence between the
compressive force and deformation characteristic curve and
the initial seed pressing heights are illustrated in Figs. 2e7. It
was observed that these dependencies were consistent with
the results previously published by Herak et al. (2013) and
Kabutey, Herak, et al. (2013). The above experimental datawas
transformed using Eq. (3) where their theoretical de-
pendencies were described using reciprocal slope trans-
formation (RST) of force and deformation data (Figs. 2e7).
These data were fitted by Eq. (4) using the least squares
method. The coefficients obtained from Eq. (3) for fitting the
above dependencies are presented in Table 2 which indicated
very high correlation. An analysis of variance (ANOVA) sta-
tistical analysis using MathCAD software (MathCAD 14, PTC
Software, Needham, MA, USA) of both experimental and fitted
or theoretical predicted data obtained fromEq. (5) showed that
-1)
Compressive force
Fitted compressiveforce
RST
Polynomial (RST)
T max
Fig. 2 e Dependency between compressive force and deformation at initial height, 30 mm. (The bars denote coefficient of
variation and Tmax is RST maximal value.)
b i o s y s t em s e n g i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 670
the dependency between compressive force and deformation
can experimentally and theoretically be described. The sig-
nificance of the ANOVA analysis results was based on values
of Fcrit higher than Frat values. In addition, values of Pvalue were
greater than 0.05 (Table 3). Clearly, the predicted data using
Eq. (5) were obtained within the range of experimental data
coefficients of variations (Table 2). The values of coefficients of
the polynomial function (Eqs. (4) and (5)) of the reciprocal
slope transformation for each initial bulk seed pressing height
are shown in (Table 2). These amounts show that the devel-
oped mathematical equations take into account the experi-
mental boundary conditions of the linear compression of
T max
Fig. 3 e Dependency between compressive force and deformati
variation and Tmax is RST maximal value.)
Jatropha bulk seeds for themechanical behaviour description.
The boundary conditions means that the origin of the defor-
mation curve starts from zero force and zero deformation and
is followed by an increasing function within the whole range
of pressing.When compressive force approaches infinity then
deformation reaches a maximum limit (Herak et al., 2011,
2013; Kabutey, Herak, et al., 2013). Deformation values in the
local maximum of the reciprocal slope transformation func-
tion (Eq. (4)) were transformed into strain values. The local
maximum for the initial pressing height of Jatropha bulk seeds
was observed at a strain value 3m ¼ 0.25 � 0.02 as shown in
Table 3 and Fig. 8. There was similarity in the mechanical
-1)
Compressive force
Fitted compressiveforceRST
Polynomial (RST)
on at initial height, 40 mm. (The bars denote coefficient of
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
100000
0 5 10 15 20 25 30 35 40
Deformation (mm)
Com
pres
sive
forc
e (N
)
0
0.001
0.002
0.003
0.004
0.005
0.006
Am
ount
of t
he r
ecip
roca
l slo
pe tr
ansf
orm
atio
n (m
m N
-1)
Compressive force
Fitted compressiveforceRST
Polynomial (RST)
T ma x
Fig. 4 e Dependency between compressive force and deformation at initial height, 50 mm. (The bars denote coefficient of
variation and Tmax is RST maximal value.)
b i o s y s t em s e ng i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 6 71
behaviour of the initial pressing height implying the accuracy
of the RST method to describe the mechanical behaviour of
Jatropha bulk seeds of varying initial pressing height. The
relationship between fitted values of the reciprocal slope
transformation and initial pressing height for strain values of
0.1, 0.25, and 0.5 is also presented in Fig. 9. The values of RST
for the corresponding initial pressing height in relation to
strain showed a linear function in describing the mechanical
behaviour of Jatropha bulk seeds. In Fig. 10 is shown the
maximum RST value corresponding to the minimum slope
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
100000
0 5 10 15 20 25
Deformatio
Com
pres
sive
forc
e (N
)
T max
Fig. 5 e Dependency between compressive force and deformati
coefficient of variation and Tmax is RST maximal value.)
value of the secant line connecting the point 0 of the force
deformation curve increasing to point 1 with high coefficient
of determination. It was seen that the dependencies of RST
and strain (Fig. 8) showed similarity with the theoretical de-
pendency presented in Fig. 10 based on the RST reciprocal
slope transformation distribution function (Blahovec, 2011).
The RST coefficients (Eq. (4)) values determined also implied
the inverse value of the rigidity of bulk seeds (Blahovec, 2008;
Neckar & Das, 2012) where the individual coefficients can be
described.
30 35 40 45 50
n (mm)
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01
Am
ount
of t
he r
ecip
roca
l slo
pe tr
ansf
orm
atio
n (m
m N
-1)
Compressive force
Fitted compressiveforceRST
Polynomial (RST)
on at initial pressing height, 60 mm. (The bars denote
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
100000
0 10 20 30 40 50
Deformation (mm)
Com
pres
sive
forc
e (N
)
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
Am
ount
of t
he r
ecip
roca
l slo
pe tr
ansf
orm
atio
n (m
m N
-1)
Compressive force
Fitted compressiveforceRST
Polynomial (RST)
T max
Fig. 6 e Dependency between compressive force and deformation at initial pressing height, 70 mm. (The bars denote
coefficient of variation and Tmax is RST maximal value.)
b i o s y s t em s e n g i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 672
In addition, the coefficients of the third order polynomial
function (Eq. (4)), based on RST, also influence the description
of the mechanical behaviour. Furthermore, the amount of
reciprocal transformation (Eq. (4)) is, in essence, the inverse of
bulk seed rigidity which is described by the compliance of the
system (Blahovec, 2008; Neckar & Das, 2012). The coefficients,
d denotes the initial compliance; cx as the linear compliance;
bx2 a real compliance and ax3 is the volume compliance ac-
cording to the theory published by Neckar and Das (2012) for
the structure and mechanics of fibrous materials. However,
0
10000
20000
30000
40000
50000
60000
70000
80000
90000
100000
0 10 20 30
Deformatio
Com
pres
sive
forc
e (N
)
T max
Fig. 7 e Dependency between compressive force and deformati
coefficient of variation and Tmax is RST maximal value.)
based on the experimental results which were verified by Eqs.
(4) and (5), the mechanical behaviour of Jatropha bulk seeds
can be described as by small deformations at both the initial
and linear compliances; and at moderate deformations can be
described by initial, linear and real compliances. The combi-
nation of all the above compliances constitutes themaximum
deformation (Figs. 2e8 and 10). The RST method thus can
more accurately describe the deformation characteristic
curves of Jatropha bulk seeds than other methods previously
published by Herak et al. (2013). Most importantly, the
40 50 60
n (mm)
0
0.002
0.004
0.006
0.008
0.01
0.012
Am
ount
of t
he r
ecip
roca
l slo
pe tr
ansf
orm
atio
n (m
m N
-1)
Compressive force
Fitted compressiveforceRST
Polynomial (RST)
on at initial pressing height, 80 mm. (The bars denote
Table 2 e Coefficients of Eq. (4) for different initial pressing heights of Jatropha bulk seeds.
H (mm) a (10�7 N�1 mm�2) b (10�5 N�1 mm�1) c (10�3 N�1) d (10�5 N�1 mm) R2 (e) CV (%)
30 21.76 �9.95 1.14 8.07 0.995 5.0
40 10.98 �6.34 0.89 55.84 0.992 4.5
50 5.61 �4.37 0.84 4.00 0.992 5.2
60 5.60 �4.97 1.11 �5.29 0.991 5.3
70 3.04 �3.28 0.87 44.02 0.994 5.0
80 2.14 �2.85 0.93 16.34 0.993 5.0
H e initial pressing height, a, b, c, d e coefficient of polynomial function of RST, R2 e coefficient of determination, CV e coefficient of variation of
measured characteristics.
Table 3 e Statistical analysis of general deformation curve for different initial pressing heights of Jatropha bulk seeds.
H (mm) Frat (e) Fcrit (e) Pvalue (e) R2 (e) xm (mm) 3m (e) Tmax (mm N�1)
30 0.032 3.936 0.859 0.982 8.48 0.28 0.003919
40 0.086 3.938 0.77 0.969 8.51 0.21 0.004218
50 0.391 3.926 0.533 0.934 12.64 0.25 0.004809
60 0.008 3.916 0.93 0.999 14.95 0.25 0.007409
70 0.008 3.92 0.93 0.991 18.12 0.26 0.007247
80 0.062 3.919 0.803 0.984 20.59 0.26 0.009098
He initial pressing height, Frat value of the F test, Fcrit test statistic for test rejection, Pvalue, hypothesis of the study outcomes significant level (e),
R2 e coefficient of determination, xm e RST deformation in local maximum, 3m e RST strain in local maximum, Tmax e RST maximal value.
b i o s y s t em s e ng i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 6 73
relationship between compressive force and deformation is
also dependent on moisture content and pressing tempera-
ture (Herak, Gurdil, et al., 2010; Kabutey et al., 2011). Thus,
these compression factors can also influence the individual
coefficients of the RST (Eq. (4)). The effect of friction among
seeds, as well as friction between the seeds and walls of the
pressing vessel, could also affect the coefficients of third order
polynomial function (RST) (Eq. (4)). Clearly, this model (Eq. (5))
can be used as background information for further research
which will focus on the determination of a generalised
mathematical model for the description of mechanical
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01
0 0.1 0.2 0.3
The
fitt
ed a
mou
nt o
f rec
ipro
cal t
rans
form
atio
n (m
m N
-1)
Fig. 8 e Dependency between fitted RST and st
behaviour of bulk seeds. In such follow up study, it will be
important to determine mathematical equations which will
describe the relationship between amounts of individual co-
efficients of RST function (Eq. (4)) andmoisture content aswell
as friction. For the development of ideal mathematical
models, the friction between seeds and also friction between
seeds and wall of pressing vessel needs to be considered. For
instance, the results published by Herak, Gurdil, et al. (2010),
Kabutey et al. (2011) and Herak, Sedlacek, and Kabutey (2010)
showed that the change of moisture content, pressing tem-
perature and stage of maturity of bulk oilseeds of Jatropha
0.4 0.5 0.6 0.7Strain (-)
H = 30 mmH = 40 mmH = 50 mmH = 60 mmH = 70 mmH = 80 mmTmaxMean strain Tmax
rain as function of initial pressing height.
R² = 0.9169
R² = 0.9021
R² = 0.8492
0
0.001
0.002
0.003
0.004
0.005
0.006
0.007
0.008
0.009
0.01
20 30 40 50 60 70 80 90
Initial pressing height (mm)
The
fitt
ed a
mou
nt o
f rec
ipro
cal t
rans
form
atio
n (m
m N
-1)
T0.25T0.1T0.5
Fig. 9 e Dependency between fitted RST and initial pressing height for strain values 0.1, 0.25, and 0.5.
b i o s y s t em s e n g i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 674
influenced the shape and position of the deformation curve as
well the energy demand for obtaining the oil. Nevertheless,
the oil leakage during compression process has also been re-
ported as having no influence on the dependency between the
force and deformation characteristic curves in relation to
varying pressing vessel diameters and bulk seed pressing
heights Herak et al. (2013) and Kabutey, Herak, et al. (2013).
Generally, the results of the present study were in agreement
with the results published by Braga, Couto, Hara, and Neto
(1999), Guner, Dursun, and Dursun (2003), Faborode and
Favier (1996) and Kabutey, Divisova, et al. (2013) for the
0
1
2
3
4
5
6
7
8
0 0.1 0.2 0.3 0.4
Strain (-)
Com
pres
sive
forc
e (k
N)
T
1
Fig. 10 e Dependency of compressi
description of mechanical behaviour of Jatropha bulk seeds
and other bulk oilseeds such as rapeseed in linear compres-
sion. However, it is important to highlight that the RST
method (i.e. Eqs. (4) and (5)) has the advantage of using LSM for
fitting experimental data compared methods used in earlier
published studies. It is evident that using transformation
processes as previously described by Herak, Sedlacek, et al.
(2010), the results from the present mathematical model can
be transformed into a non-linear mechanical behaviour such
as screw extruders and other processing technologies. A
combination of these models with additional information
0.5 0.6 0.7 0.8 0.90
0.1
0.2
0.3
0.4
0.5
0.6
Am
ount
of r
ecip
roca
l slo
pe tr
ansf
orm
atio
n (m
m k
N-1
)
FT
ve force and RST versus strain.
b i o s y s t em s e ng i n e e r i n g 1 2 1 ( 2 0 1 4 ) 6 7e7 6 75
such as oil point, juice point or compressibility which requires
processing technology with maximal energy efficiency, could
also be designed.
4. Conclusion
An experimental study of the dependency between the
compressive force and deformation characteristic curves of
Jatropha bulk seeds with varying initial pressing heights in
axial or linear compression loading was carried out. The re-
sults were fitted using the RST and LSM methods where the
dependency between RST and deformation was also
described. Statistical analysis of experimental and RST fitted
data using a third order polynomial function were significant
(p > 0.05) with a high coefficient of determination (R2). The
validity of RST equation was limited from zero to the
maximum deformation of the bulk Jatropha seeds with vary-
ing initial pressing height. The RST method provides a
fundamental step forward for the development of more
generalised mathematical models where parameters
including varying pressing vessel diameter, moisture content,
maturity stage and variety of bulk oilseeds, friction, oil point
pressure, pressing temperature could be considered. This in-
formation could be transformed to investigate the non-linear
pressing involving mechanical screw presses or expellers for
the optimisation of oil recovery efficiency and energy
requirements.
Acknowledgement
The research has been supported by Grant Agency of CULS
Prague e CIGA 31130/1313/313127.
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