Electronic Journal of Polish Agricultural Universities (EJPAU) founded by all Polish Agriculture Universities presents original papers and review articles relevant to all aspects of agricultural sciences. It is target for persons working both in science and industry,regulatory agencies or teaching in agricultural sector. Covered by IFIS Publishing (Food Science and Technology Abstracts), ELSEVIER Science - Food Science and Technology Program, CAS USA (Chemical Abstracts), CABI Publishing UK and ALPSP (Association of Learned and Professional Society Publisher - full membership). Presented in the Master List of Thomson ISI.
2011
Volume 14
Issue 3
Topic:
Food Science and Technology
ELECTRONIC
JOURNAL OF
POLISH
AGRICULTURAL
UNIVERSITIES
Shakeri M. , Khodabakhshian R. 2011. THE PHYSICAL ATTRIBUTES OF SAFFLOWER SEED AS A FUNCTION OF MOISTURE CONTENT, VARIETY AND SIZE, EJPAU 14(3), #06.
Available Online: http://www.ejpau.media.pl/volume14/issue3/art-06.html

THE PHYSICAL ATTRIBUTES OF SAFFLOWER SEED AS A FUNCTION OF MOISTURE CONTENT, VARIETY AND SIZE

Mohsen Shakeri, Rasool Khodabakhshian
Department of Agricultural Machinery Ferdowsi University of Mashhad

 

ABSTRACT

Physical attributes of two common Iranian varieties of safflower seed (namely Golshid and Afshan), such as geometric properties (size, geometric mean diameter and sphericity), gravimetric properties (thousand seed mass, bulk density, true density and porosity) frictional properties (emptying angle of repose and coefficient of static friction on four structural surfaces) and terminal velocity were determined as a function of size (large, medium, small) and moisture content in the range of 4 to 20% (d.b.). The results showed that the mean values of all geometric properties increased linearly with increasing moisture content. Among the varieties, Afshan had the highest values of geometric properties, in all moisture contents and size studied. At studied moisture contents and size categories, thousand grain mass, true density and porosity increase linearly, but the bulk density of safflower seeds linearly decrease as moisture content increase from 4 to 20 %. Among the applied surfaces, rubber (0.5–0.69) showed the highest value of friction coefficient safflower seed followed by plywood (0.45–0.63), galvanized iron (0.41–0.54) and aluminium (0.36–0.47). The obtained values of emptying angle of repose increase linearly with an increase in moisture content and size categories. The terminal velocity of Golshid variety varied from 6.1 to 6.7, 5.8 to 6.3 and 5.3 to 5.9 m/s for large, medium and small sizes, respectively. The range of terminal velocity for Afshan variety obtained 6.4–7.2, 6.3–6.9 and 6–6.6 m/s, respectively.

Key words: Frictional properties, geometric properties, gravimetric properties, safflower seed, terminal velocity .

INTRODUCTION

The safflower (Carthamus tinctorius L.), which belongs to the Compositae family, is cultivated in several parts of the world due to its adaptability to different environmental conditions. Large scale cultivation of safflower containing 35 to 45 percent oil has started about 25 years ago in Iran. Traditionally known as source of dye in ancient Iran, the safflower has attained considerable importance as an oilseed crop. Knowing physical attributes of safflower seed such as gravimetrical properties (unit mass, bulk density, true density, and porosity), geometrical properties (shape, size, geometric mean diameter and sphericity), frictional properties (angles of repose and coefficients of friction) and terminal velocity are necessary parameters for machine design and quality of processing production line and reducing the waste.

Bulk density, true density and porosity can be useful in sizing grain hoppers and storage facilities; they can affect the rate of heat and mass transfer of moisture during aeration and drying processing [6]. The porosity is the most important factor for packing and it affects on the resistance to airflow through bulk seeds. Seed densities have been of interest in breakage susceptibility and hardness studies. Therefore, it is required to determine these properties. The size and shape of seeds are important for either their electrostatic separation from undesirable materials or the development of sizing and sorting machinery. The identification of seed shape could also be important for an analytical prediction of its drying behavior. The design of hoppers, storage and handling systems for seeds requires data on friction coefficients of commonly used materials (aluminium, plywood, galvanized iron and rubber) and angles of repose. Furthermore, if the conveying or handling of the seed is required, knowledge of their coefficient of friction on common surfaces is essential for selecting material of surface for related equipment. The terminal velocity is needed to determine the proper air speed in either air conveyor or pneumatic separator.

Many valuable studies have been carried out about the physical properties of agricultural products by researchers [2, 4, 8, 13, 16, 17, 18, 19, 22, 25, 26, 34, 35, 36]. Olajide and Clarke [26] determined geometric mean diameter, volume and surface area for cashew nuts. Aviara et al. [2] reported the average of length, width, thickness and surface area for guna seeds. Erica et al. [14] investigate the effect of moisture content on some physical properties of safflower seeds typically cultivated in Argentina. They indicated that volume, weight of seed, the expansion coefficient and porosity increase lineally with the increase in seed moisture content. Also, they revealed that an increase in moisture content yielded a decrease in bulk density trend and true density varied nonlinearly. Isik and Izil [18] investigated some moisture-dependent properties of sunflower for only the Turkey sunflower seed cultivar. They showed that the thousand grain mass, true density and porosity increased while the bulk density decreased with an increase in the moisture content range of 10.06–27.06 % (d.b.). Gupta and Das [16] have reported static and dynamic friction coefficients of sunflower seed and its kernel on six different surfaces (plywood, mild steel, galvanized iron, aluminium, stainless steel and rubber) between 4 and 20% d.b.

Literature review showed that there is no enough published work relating to the affected physical attributes of safflower seed by moisture content, size and variety. Hence, the present study was carried out to investigate the effect of moisture content, size and variety on physical attributes of two major Iranian varieties of safflower seed. The properties including size, geometric mean diameter, sphericity, thousand seed mass, bulk density, true density, porosity, empting angle of repose, static coefficient of friction and terminal velocity at various moisture contents ranged 4–20% d.b for three size categories (small, medium and large).

MATERIALS AND METHODS

Sample preparation, moisture content determination and seed size grading

Two safflower varieties namely Golshid and Afshan were obtained from different regions of Khorasan Razavi province (North East of Iran) in 2011 (Fig 1). A mass of 20 kg from each variety was weighted and transported to the lab. The seeds were manually cleaned to get rid of foreign matters, broken and immature seeds. The initial moisture of seeds was determined using the standard hot air oven method with a temperature setting of 105 ± 1°C for 24 h [1, 11, 21]. The initial moisture content of the seeds was found 7.9% and 8.2% d.b for Golshid and Afshan, respectively. According to Khodabakhshian et al. [21], the seeds were sieved into three size categories (small, medium, and large) using 2, 3 and 4 mm square mesh sieves. All the physical attributes of the seeds were measured for four moisture contents in the range of 4 to 20% (d.b.) that is a usual range since harvesting, transportation, storage and processing operations of safflower seed. To get the seeds with the desired moisture contents, sub-samples of seeds of each variety and size category (small, medium and large), each weighing 0.5 kg, were drawn form the bulk sample and dried (by putting them in the oven at 75°C for 2 h) or adding the calculated quantity of water to the samples. Finally, the sub-samples were kept in double-layered low-density polyethylene bags of 90µm thickness, sealed and stored at low temperature (5°C in a refrigerator) to avoid the growth of microorganisms and allowing to uniformity of moisture distribution. Before starting the tests, the required quantities of seed was taken out of the refrigerator and allowed to warm with room temperature for approximately 2 h [19, 21].

Fig. 1. Pictorial view of Iranian safflower seed

Geometrical properties measurement

To determine the size and shape of safflower seed for revealing the interrelations of length, width and thickness, totally 100 seeds of each sub- samples were randomly selected and labeled for easy identification. This method of random sampling was similar to Baryeh [5] and Saiedirad et al. [32]. Finally, three main dimensions namely length, width and thickness of safflower seed were carefully measured using a digital caliper (Diamond, China) with an accuracy of ±0.02 mm. The geometric mean diameter, Dg, of the safflower seed was calculated by using the following relationship [24]:

(1)

Where L is the length, W is width and T is the thickness. The criterion used to describe the shape of safflower seed was sphericity. The sphericity, φ, of safflower seed was determined using the following formula [24]:

(2)

Gravimetrical properties measurement

The 'thousand seed mass' was measured by counting and weighting 100 seeds (using a precision electronic balance with an accuracy of 0.001 g) and then multiplied by 10 to give the mass of 1000 seeds of each seed size category. The true density of a seed (ρt, kg m-3) is defined as the ratio of its mass to its actual volume and hence was calculated by dividing the unit mass of each sample (seed) to its true volume [30]. The bulk density of particulate materials (ρb, kg m-3) is the ratio of the sample mass to its total volume. This was determined by filling a cylindrical container of 500ml volume with seeds to a height of 15cm at a constant rate and then weighting the contents. This method has also been employed by others 15, 21, 29]. Thompson and Isaac described the porosity (ε) as the fractions of the space in the bulk grain that is not occupied by the grain. Accordingly, Mohsenin [24] calculated the porosity as follow:

(3)

Frictional properties measurement

The static coefficient of friction, µ, for seed was measured on four structural surfaces: aluminium, plywood, galvanized iron and rubber. An open-ended galvanized iron cylinder, 100 mm diameter and 50 mm height, was filled with the sample of the desired moisture content and was placed on the adjustable tilting surface so that the cylinder dose not touch the surface. The tilting surface with the cylinder resting on it was raised gradually with a screw device until the cylinder just started to slide down. Then the angle of tilt (α) was read from a scale [15, 21, 30]. The coefficient of friction (µ) was calculated from the following relationship Mohsenin [24]:

µ=tan α

(4)

To determine the empting angle of repose, Θ, a plywood box of 300 × 300 × 300 mm with a removable front panel was used. The box was filled with the safflower seed samples at the desired moisture content, and the front panel was quickly removed, allowing the samples to flow and assume a natural slope ([5, 16]. The empting angle of repose was calculated from the measurements of the vertical depth and radius of spread of the sample [21].

Terminal velocity measurement

To measure the terminal velocity of the samples, an air column was designed and used. It consists of a vertical transport column made of Plexiglas so that the suspended seeds could be seen from the outside, the variator, AC electric motor, fan and diffuser. For each test, a sample was dropped into the air stream from the top of the air column, up which air was blown to suspend the seeds. The air velocity near the location of the seeds suspension was measured by a hot – wire anemometer having a least count of 0.1 m/s. This methodology was used by Joshi et al. [19].  

Statistical analysis

The experiments were done at least in ten replications for each moisture contents, variety, size categories and the average values were reported. Average, minimum, maximum, standard deviations, correlation coefficients of dimensions and regression equations were computed using Microsoft Excel software (2003).

RESULTS AND DISCUSSION

Dimensions and size distribution of safflower seed, geometric mean diameter and sphericity

The three axial dimensions of the safflower seed at different levels of moisture content for studied varieties and size categories are shown in Figs 2 and 3.  From these Figs it is clear that as the moisture content was increased from 4 to 20% d.b., the dimensions of the three axes increased. This indicates that during the moisture absorption process, the studied varieties of safflower seed will simultaneously expand in all dimensions. Khodabakhshian et al. [21] reported similar results for sunflower seed and its kernel. For the studied range of moisture content (4–20% d.b.) and in both studied varieties of safflower seed, the highest average expansion was along the length and the lowest along the width. Deshpande et al. [13] found that the expansion rate of soybean seeds to be the largest along their thickness in comparison with their other two principal axes. This could be as a result of the different cell arrangements, environmental and growth conditions for the seeds and their kernels. Among the studied varieties, Afshan cultivar had greater values in width and thickness than Golshid variety for all studied treatments.

Fig. 2. Variation of dimensions of Golshid variety of safflower seed with moisture content and size

Fig. 3. Variation of dimensions of Afshan variety of safflower seed with moisture content and size

The ranges of length for Golshid and Afshan safflower seed at 8 % (d.b) were 6.89–7.57 and 6.65–7.27 mm, respectively. Erica et al. [14] reported the range of 6.66–8.68 mm for the length of an modern variety of safflower seed typically cultivated in Argentina at 6.9 %(d.b). They also reported the values of 3.83 and 3.25 mm for width and thickness of this variety of safflower seed at 6.2 %(d.b) respectively. In this study, the average width and thickness of Golshid variety of safflower seed were found as 3.17 and 1.92 mm at a moisture content of 8% d.b., respectively. These values for Afshan variety were 4.20 and 2.16 mm, respectively.

Table 1 shows the variation of geometric mean diameter and sphericity as a function of moisture content for all size categories of the investigated varieties of safflower seed. The results revealed that geometric mean diameter increased linearly with increase in moisture content. It can be found that the minimum and maximum values geometric mean diameter of safflower seed among studied treatments were belonged to Golshid and Afshan varieties, respectively. Erica et al. [14] reported the equivalent diameter of safflower seed in the range 4.319 to 4.543 mm when moisture content varied from 3.7–15.6%. Also they found a linear trend with the moisture content. As it can be seen from Table 1, the sphericity index of studied varieties increased linearly with increase in size and moisture content. A similar trend has been observed between seed moisture content and sphericity by other researchers (Deshpande et al. [13] for soybean; Baryeh [5] for millet; Erica et al. [14] for safflower seed; Isik and Izli [18] for sunflower seed; Garnayak et al. [15] for jatropha seeds). According to Table 1, the sphericity for Golshid and Afshan safflower seeds ranged from 0.42–0.5 and 0.44–0.5, respectively. Erica et al.  [14] indicated a linear increase in sphericity of safflower seed (0.58 to 0.62) with increase in moisture content.

Table 1. The sphericity and geometric mean diameter for both studied varieties of safflower seed as a function of moisture content (4–20% d.b.) and size

Variety Parameter Size Moisture content (%)
4
8
14
20
Golshid
Geometric mean diameter (mm)

Large

4.93
5.18
5.41
5.82
Medium
4.69
4.86
5.02
5.51
Small
4.34
4.57
4.72
5.12
Sphericity (%)
Large
0.46
0.47
0.48
0.50
Medium
0.45
0.46
0.47
0.48
Small
0.42
0.44
0.45
0.47
Afshan
Geometric mean diameter (mm)
Large
5.35
5.57
5.73
5.93
Medium
5.08
5.24
5.40
5.71
Small
4.96
5.12
5.29
5.45
Sphericity (%)
Large
0.47
0.48
0.49
0.50
Medium
0.45
0.46
0.48
0.49
Small
0.44

0.45

0.47
0.48

One thousand seed mass, bulk density, true density and porosity

The one thousand safflower seed mass increased with increasing moisture content from 4% to 20% d.b. in all studied varieties and size categories (Fig 4). The ranges of one thousand safflower seed for Golshid and Afshan variety were 19–105 and 38–112 g, respectively. This parameter is useful in determining the equivalent diameter which can be used in the theoretical estimation of seed volume and in cleaning using aerodynamic forces. Similar to the present observations, a increase in the thousand seed mass as the seed moisture content increases was noted by Ozarslan [27] for cotton seed, Sacilik et al. [31] for hemp seed, Yalcin and Ozarslan [38] for vetch, Cagatay et al. [7] for linseed, Coskuner and Karababa [12] for flaxseed, Isik and Izli [18] for sunflower seed; Garnayak et al. [15] for jatropha seed.

Fig. 4. Effect of moisture content, size and variety on one thousand safflower seed mass (♦, large; ■, medium; ▲, small; —, Afshan variety; - - -, Golshid variety)

The experimental results of the true density and bulk density of safflower seeds for the studied varieties and size categories at various moisture contents are shown in Table 2. According to this Table, the true density of Golshid and Afshan safflower seeds varied from 615–707.5 and 632.5–712.5 kg m-3, respectively when the moisture content increased from 4 to 20% d.b. Erica et al. [14] reported the true density of safflower seed in the range of 755–775kg m-3 when moisture varied from 3.7 to 15.6%. The variation of results for the true density of different studies indicates that this parameter is highly dependant of seed variety. The results also show a linearly increasing trend of true density with moisture content for all varieties and size categories. This implies a denser seedbed structure of such particulate materials with high moisture content. This agrees with the results of Cagatay et al. [7] for linseed, Coskuner and Karababa [12] for flaxseed, Isik and Izli [18] for sunflower seed; Garnayak et al. [15] for jatropha seed. However, it is in contradiction of the results of Deshpande and Ojha [13], Joshi et al. [19], Suthar and Das [36] who found that the true density decreases with moisture content for soybeans, pumpkin seeds and karigda seeds, respectively. Therefore, it can be concluded that while, some particulate materials may dilate with increase of moisture content the others exhibit a denser bed structure.

Table 2. Effect of moisture content, size and variety on true density and bulk density of safflower seed

Variety Parameter (kg m-3) Size Moisture content (%)
4
8
14
20
Golshid
True density

Large

675
690
700
707.5
Medium
650
660
670
677.5
Small
615
625
640
650
Bulk density
Large
600
580
562
550
Medium
620
600
585
573
Small
645
620
598
582
Afshan
True density
Large
687.5
697.5
705
712.5
Medium
660
667.5
680
690
Small
632.5
640
650
660
Bulk density
Large
590
575
550
535
Medium
615
598
572
554
Small
630

614

595
578

The range of bulk density at different moisture levels for seed of Golshid and Afshan were obtained between 550–645 and 535–630 kg m-3, respectively. Erica et al. [14] reported the bulk density of safflower seeds in the range of 427–450 kg m-3. As it can be seen from Table 2, the bulk density decreased when the moisture content increased from 4 to 20% d.b. In other words, the increase in mass because of moisture gain in the seed was smaller than the accompanying volumetric expansion of the bulk. A similar decreasing trend of bulk density with moisture content has been reported by Deshpande et al. [13], Carman [8], Visvanathan et al. [37], Ogut [25] and Garnayak et al. [15] for soybean, lentil seeds, neem, white lupin and jatropha seed, respectively. It can be implied that such materials become more turgid in the presence of moisture, consequently occurring the dilation phenomenon of bed structure which is very important for silo structural analysis.  However, a direct correlation between bulk density and moisture content was found for some other agricultural particulate materials by Hsu et al. [17], Suther and Das [36] and Chandrasekar and Viswanathan [10] for pistachios, karingda seeds and coffee, respectively. Also, for all treatments the small seeds exhibited a higher bulk density than the larger seeds. This can be related to the ratio of kernel mass to the hull mass of seeds. In other words for small seeds the specific surface area of hull (with lower true density) is lower than the larger seeds.

Fig. 5 shows variations of porosity with moisture content for all varieties and size categories of safflower seed. As it can be seen, the porosity linearly increased with increase of moisture content. The porosity of safflower seeds for Golshid and Afshan ranged from 37–55 and 42–56 %, respectively. The porosity of safflower seed was found to increase linearly from 41.6% to 44.6% as the moisture content increased from 3.7% to 15.6% d.b. by Erica et al. [14]. The linearly increasing trend of porosity with increase of moisture content was also observed for some other seeds, such as Carman [8], Singh and Goswami [35], Ogut [25], Baryeh and Mangope [4] for lentil seeds, cumin seed, white lupin and pigeon pea, respectively. However, Baryeh [5] reported a nonlinearly increasing trend of porosity with increase of moisture content for millet. In contrast, Deshpande et al. [13], Joshi et al. [19], Suther and Das [36], Chandrasekar and Visvanathan [10] reported a linearly decreasing trend of porosity with increase of moisture content for soybean, pumpkin seed, karingda seed and coffee, respectively. Kashaninejad et al. [20] reported a nonlinearly decreasing trend of porosity with moisture content for pistachio. These discrepancies can be related to the cell structure and the variation of densities in different seeds and grains when moisture content is altered.

Fig. 5. Effect of moisture content, size and variety on porosity (♦, large; ■, medium; ▲, small; —, Afshan variety; - - -, Golshid variety)

Regression equations and their coefficients of determination (R2) obtained for the true density and bulk density of safflower seeds are presented as a function of variety, size category and moisture content in Table 3. These equations and coefficients confirm a linear behavior for all treatments.

Table 3. Regression models and coefficients of determination achieved for true density (ρt) and bulk density (ρb) of studied safflower varieties as a function of moisture content (4–20% d.b.) and size.

Variety
Size
True density
R2
Bulk density
R2
Golshid

Large

ρt = 1.9473Mc + 670.73
0.94
ρb = -3.0612Mc + 608.2
0.96
Medium
ρt = 1.6922Mc + 644.91
0.98
ρb = -2.8367Mc + 627.12
0.96
Small
ρt = 2.2109Mc + 607.07
0.99
ρb = -3.8469Mc + 655.49
0.97
Afshan
Large
ρt = 1.5051Mc + 683.32
0.97
ρb = -6.5034Mc + 602.79
0.99
Medium
ρt = 1.8963Mc + 652.57
0.99
ρb = -3.8537Mc + 629.07
0.99
Small
ρt = 1.7092Mc + 625.97
0.99
ρb = -3.2211Mc + 641.29
0.99

Static coefficient of friction and empting angle of repose

The static coefficients of friction for studied varieties of safflower seed in three size categories on four structural surfaces including aluminium, plywood, galvanized iron, and rubber against moisture content in the range of 4–20 % d.b are presented in Figs 6 and 7. As it can be found from these Figs, static coefficient of friction on four studied surfaces increased linearly as moisture content increased from 4 to 20% in all varieties and sizes. This may be explained by increased cohesive force of wet seeds with the structural surface, since the surface becomes stickier as moisture content increases. Similar findings were reported for millet [5], almond nut [2], pistachio nut and kernel [30] caper fruit [33] and barbunia bean [9]. The highest static coefficient of friction was obtained on the rubber surface, followed by plywood, galvanized iron, and finally aluminium surfaces. In addition, the static coefficients of friction for Golshid variety were lower than that of Afshan variety at similar moisture contents of the seeds and the same surfaces. Also, the results showed that the values of static coefficients of friction of safflower seed increased with an increase in size.

Fig. 6. The static coefficients of friction for Golshid variety of safflower seed in three size categories on four structural surfaces

Fig. 7. The static coefficients of friction for Afshan variety of safflower seed in three size categories on four structural surfaces.

The investigational results of empting angle of repose for studied varieties of safflower seed at different moisture levels and size categories are shown in Table 4. The emptying angle of repose increased with an increase in moisture content. It attributes to the higher moisture content which cause higher stickness of seeds surfaces and then lowers easiness of rolling seeds on each other [30]. Among the studied varieties of seed, Afshan had maximum value for empting angle of repose (20.58–24.45°) and the lowest values belonged to Golshid variety (19.35–23.51°). Empting angle of repose values of small sizes were higher than the values for large sizes in all varieties and moisture levels. This can be due to the higher moisture content and higher sphericity of the shape for the seeds of large size in comparison with small size of them that permits the easiness of sliding of seeds on each other and causes a higher value for radius of spread of the seed. No reported results for empting angle of repose of safflower seed were found to compare with the results obtained in this study. However, A linear increase in empting angle of repose when the seed moisture content increases has also been noted for karingda seeds, cumin seed, chick pea seeds, edible squash, fenugreek, sorghum seeds [22, 28, 35, 36],

Table 4. The emptying angle of repose (degree, °) of studied varieties of safflower seed a as a function of moisture content and size.

Variety Size Moisture content (%)
4
8
14
20
Golshid

Large

19.35
20.37
21.16
22.02
Medium
19.99
20.92
21.79
22.25
Small
20.10
21.33
22.16
23.51
Afshan
Large
20.58
21.23
22.73
23.15
Medium
20.88
21.62
23.10
23.85
Small
20.94
21.85
23.21
24.45

Terminal velocity

The variation of terminal velocity of the Afshan and Goshid variety of safflower seed at studied moisture contents for each size category are shown in Fig. 8. As it can be seen from this Fig., the terminal velocity of the Afshan and Goshid variety increased linearly from 6–7.2 and 5.3–6.7 m/s, respectively as the moisture content increased from 4 to 20% d.b for the studied size categories. This may be attributed to the increase in mass of the seeds per unit, when their frontal areas were presented to the air flow to suspend the material. The other reason is probably that the drag force is affected by the moisture content of particle. This conclusion was consistent with the findings of Matouk et al. [23], who reported terminal velocity and Reynold's Number of soybean and canola increased linearly with the increase of seeds moisture content. Also similar results reported by Joshi et al. [19] for pumpkin seeds, Carman [8] for lentil seeds, Singh and Goswami [35] for cumin seeds, Suthar and Das [36] for karingda seeds, Gezer et al. (2003) for apricot pit and kernel, and Aydin and Akar [3] for gumbo fruit. According to Figure 7, the terminal velocity of safflower seed increased as size increased from small to large.

Fig. 8. Effect of moisture content, size and variety on porosity (♦, large; ■, medium; ▲, small; —, Afshan variety; - - -, Golshid variety)

CONCLUSION

In this paper, geometrical properties, gravimetrical properties, frictional properties and terminal velocity of safflower seed were investigated as a function of moisture content, size and variety. The following are concluded:

  1. All the linear dimensions, geometric mean diameter and sphericity of safflower seeds increase linearly with increase in seed moisture content and size category.
  2. The bulk density decreased linearly with increasing moisture content for each variety and size category, whereas thousand grain mass, true density and porosity increased linearly with increasing moisture content of all safflower varieties and size categories.
  3. For all moisture contents, thousand grain mass, the true density and porosity of safflower seed increased when size increase. However, a decreasing trend was observed between bulk density and size.
  4. For all treatments, as the moisture content increased, the empting angle of repose and coefficient of static friction increased linearly. Also, the results showed that the highest value of static coefficient of friction for safflower seed was on the rubber surface, followed by plywood, galvanized iron, and finally aluminium surfaces.
  5. The terminal velocity of safflower seed for all size categories and studied varieties increased as the moisture content increased. Also, the terminal velocity of safflower seed increased as size increased from small to large.

ACKNOWLEDGMENTS

 The authors would like to thank Ferdowsi University of Mashhad for providing the laboratory facilities and financial support.

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Accepted for print: 30.09.2011


Mohsen Shakeri
Department of Agricultural Machinery
Ferdowsi University of Mashhad
P.O. Box. 91775-1163 Mashhad, Iran

Rasool Khodabakhshian
Department of Agricultural Machinery
Ferdowsi University of Mashhad
P.O. Box. 91775-1163 Mashhad, Iran
email: ra_kh544@stu-mail.um.ac.ir

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