The Effect of Variety, Size, and Moisture Content Of Sunflower Seed And Its Kernel On Their Terminal Velocity, Drag Coefficient, and Reynold's Number

Abstract

In this article, terminal velocity, Reynold's number, and drag coefficient of three varieties of Iranian sunflower seed and its kernel were evaluated as a function of size and moisture content at three moisture content levels in the range of 3 to 14% d.b. The obtained results showed that terminal velocity and Reynold's number of sunflower seed and its kernel for the studied varieties and size categories increased and drag coefficient for both seed and kernel decreased with the increase in moisture content. Investigating the effect of size revealed that terminal velocity and Reynold's number of sunflower seed and its kernel increased as size of the samples increased from small to large while the drag coefficient of sunflower seed decreased with increasing size. In contrast, drag coefficient of the sunflower kernel increased with the increase in size.

Keywords:

• Aerodynamic properties
• Sunflower seed and kernel
• Moisture content
• Variety
• Size

INTRODUCTION

Sunflower seed (Helianthus annuus L.) is one of the most productive crops in the world's oilseeds industry.[1] Sunflower kernel has 50% oil content of which 30% is essential fatty acid and linoleic acid. The monounsaturated fatty acid and oleic acid that accounts for about 10% of the total fat content make it nutritionally superior than other oilseeds.[2] The hull comprises 20–30% of the seed depending on the variety and contains mostly crude fiber and an insignificant quantity of fat.[3] According to Iranian government statistical data of 2005, over 35 varieties of sunflower are cultivated in Iran. The produce of the sunflower seed is used for oil production and fresh consumption with the ratio of 90 and 10%, respectively.[4]

In processing of agricultural produce, often air is used as a carrier for separating the produce from undesirable materials. In addition, agricultural materials are routinely conveyed using air stream in pneumatic conveyers. Therefore, the aerodynamic properties, such as terminal velocity, drag coefficient, and Reynold's number, are needed to determine the proper air speed in either air conveyor or pneumatic separator.[5] These parameters are affected by the density, shape, size, and moisture content of produce.[6] So, it is compulsory to determine the aerodynamic properties of sunflower seeds and kernels as a function of numerous factors, such as moisture content, size, and variety.

Many valuable researches have been carried out about the aerodynamic properties of agro-food materials as a function of moisture content for wheat,[7,8] rice,[8,9] cotton seeds,[10] corn,[8] barley,[8] and sunflower seed.[11] Also, many researchers reported a linear increase in terminal velocity with an increase in moisture content for various food and agricultural produce (pigeon pea,[12] soybean,[13] pumpkin seed,[14] lentil seed,[15] white lupin,[16] hazel nut,[17] almond nut and kernel,[18] cherry laurel,[19] and moth gram,[20] respectively).

Arora[9] conducted an experiment to study terminal velocity, drag coefficient, and resistance coefficient of three varieties of rough rice. It was found that all these parameters increased with increasing moisture content. Matouk et al.[8] found that increasing the grain moisture content tended to increase terminal velocity, drag coefficient, and Reynold's number of rice, corn, wheat, and barley. They stated that the relationship between terminal velocity and moisture content may be described by an exponential model while drag coefficient and Reynold's number increased linearly as the moisture content increased. Gupta et al.[11] studied some aerodynamic properties of only sunflower seed as a function of moisture content. Neither aerodynamic properties of sunflower kernel nor the effect of size were investigated.

Literature reviews showed that there is not enough published work relating to the affected aerodynamic properties of sunflower seed and its kernel by moisture content, size, and variety. Hence, the present study was carried out to investigate the effect of moisture content, size, and variety on aerodynamic properties of three major Iranian varieties of sunflower seed and its kernel. The properties, including terminal velocity, drag coefficient, and Reynold's number, were determined at various moisture contents, which ranged from 3–14% d.b. for three size categories (small, average, and large).

MATERIALS AND METHODS

Sample Preparation

The samples were selected from three major commercial Iranian varieties of sunflower seed, namely, Shahroodi, Fandoghi, and Azargol. These cultivars were obtained randomly from different regions of Khorasan Razavi province, Iran, during the autumn season in 2008 (Fig. 1). A portion of seeds equal to 20 kg was also randomly selected from each variety. The seeds were manually cleaned to remove all foreign matters, such as dust, dirt, stones, and immature and broken seeds. To get whole kernels, the seeds were manually dehulled. The initial moisture content of seeds and kernels were determined using the standard hot-air oven method with a temperature setting of 105 ± 1°C for 24 h.^{[1, 4,} 21,22] The initial moisture content of the seeds was found to be 7.9, 6.8, and 7.2% d.b. for Shahroodi, Fandoghi, and Azargol, respectively. The similar level of moisture content for kernels of Shahroodi, Fandoghi, and Azargol were obtained to be 5.9, 5.6, and 5.4% d.b., respectively. To investigate the effect of seed size on aerodynamic properties, the seeds of each variety were graded into three size categories (small, medium, and large) using 5.5-, 6.5-, and 8-mm square mesh sieves. All properties were measured for three moisture contents in the range of 3–14% (d.b.), which is the usual range since harvesting, transportation, storage, and processing operations of sunflower seed. To get the seeds and kernels with the desired moisture contents, sub-samples of seeds and kernels of each variety and size category (small, medium, and large), each weighing 0.5 kg, were drawn from the bulk samples and dried (by putting them in the oven at 75°C for 2 h) or adding a calculated amount of distilled water, through mixing and then sealing in separate polyethylene bags of 90 μm thickness. The samples were kept at 5°C in a refrigerator for 7 days to distribute the moisture uniformly throughout the sample. Before starting the tests, the required quantities of seed and kernel were taken out of the frig and allowed to warm at room temperature for approximately 2 h.^[1,4,14]

Figure 1 The illustrated view of seed and kernel of three varieties of sunflower (L: Large; M: Medium; S: Small) (color figure available online).

Aerodynamic Properties Measurement

The aerodynamic properties of both sunflower seeds and their kernels were measured in terms of terminal velocity, drag coefficient, and Reynold's number. The terminal velocity (V_t ) of a seed may be defined as the air velocity at which a particle is suspended in a vertical column. The drag coefficient of a seed and its resistance to airflow depends upon the bed thickness of the seed, shape, surface roughness, and its orientation.[11] Reynold's number is defined as the ratio of the fluid's inertial forces to its drag forces. This parameter is a critical issue in the matter of convention of agriculture produce.[8] To measure the terminal velocity of the samples, an air column was designed and fabricated (Fig. 2). It consists of a vertical transport column made of Plexiglas (so that the suspended seeds could be seen from the outside), the inverter, AC electric motor, fan, and diffuser. The latest part, the diffuser, provides equal distribution of air inside the column. For each test, a sample was dropped into the air stream from the top of the air column, in which air was blown to suspend the sample (seeds or kernels). The air velocity inside the column, which is called terminal velocity, was measured by a hot-wire anemometer with the accuracy of ±0.1 m/s.[23] The terminal velocity for each sunflower seed and kernel was measured ten times and the average terminal velocity for each sample was determined. This methodology was used by Baryeh,[24] Hauhouot-O'Hara et al.,[25] and Joshi et al.[14] Knowing V_t , the drag coefficient (C_d ) of the seed and kernel was calculated using the following formula:^[10,23]

(1)

Figure 2 Apparatus for measuring terminal velocity.

where m is the mass of the sample in kg, ρ _a is the air density in kg m⁻³, g is acceleration of gravity in m s⁻², and A is the projected area of the sample normal to the direction of motion in m². The value of the air density was assumed as 1.2 kg m⁻³ at a temperature of 25°C.^[5] The projected area (A) of the sunflower seed or kernel for the studied size category, variety, and moisture content was estimated using the following relationship:[11]

(2)

where L and W are the length and width of the seed or kernel, respectively. The values of two parameters were carefully measured using a digital vernier caliper (Diamond, China) with an accuracy of ±0.02 mm. In this study, Reynold's number (R_e ) was calculated using the terminal velocity and drag coefficient of each variety, size category, and moisture content by the following expression:[8]

(3)

where μ is the air viscosity at room temperature (1.85 × 10⁻⁵ N.sec m⁻²) and D_g is the geometric mean diameter of seeds (or kernels) that was calculated using the following equation:[26]

(4)

where L, W, and T are length, width, and thickness of the sunflower seed or kernel in mm, respectively.

Statistical Analysis

The experiments were done, at least, in ten replications for each level of moisture contents, varieties, and size categories, then the average values were reported. Statistical analysis was done on completely randomized design with factorial experiment applying the analysis of variance (ANOVA) using SPSS software, version 16. The F test was used to determine significant effects of each treatment, and Duncan's multiple ranges test was used to separate means at a 5% level of significance.

RESULTS AND DISCUSSION

Variance analysis of data indicated that the effect of variety, moisture content, and size of the seed or kernel on terminal velocity, drag coefficient, and Reynold's number were significant (P < 0.01). Also, the interaction of variables on each other was significant for different combinations. Gupta et al.[11] reported that variation in moisture content of the sunflower seed and kernel influenced terminal velocity and drag coefficient significantly. The maximum values of terminal velocity among the studied varieties of seed were found for Fandoghi (6.28–7.68 m/s), then Azargol in the range of 5.78–6.74 m/s, and the lowest values belonged to Shahroodi (5.24–6.12 m/s). The similar order was also found among kernels: Fandoghi (6.06–6.98 m/s), Azargol (5.24–6.5 m/s), and Shahroodi (5–5.68 m/s). The drag coefficient of Shahroodi, Fandoghi, and Azargol seeds ranged from 0.73–0.93, 0.55–0.81, and 0.55–0.78 m/s while this value for the corresponding kernels varied from 0.75–0.92, 0.59–0.86, and 0.34–0.66 m/s, respectively, with increasing moisture content from 3 to 14% d.b. in each size category. The Reynold's number of Shahroodi, Fandoghi, and Azargol seeds were found to vary from 2519.9–3450, 2200.5–4215.7, and 2209.8–3538.9, respectively. These values for the corresponding kernels were 1600–2108.7, 1673.7–2325.5, and 1538.5–2287.7, respectively. In the following paragraphs, the effects of each factor on the terminal velocity, drag coefficient, and Reynold's number are comprehensively discussed.

Variety

Stepwise analysis of the obtained results revealed that among studied variables, namely, variety, moisture content, and size category, the dominant factor on the terminal velocity of the seed and kernel is variety. The variation of terminal velocity of the sunflower seed and its kernel at different moisture contents for each variety and size category are shown in Table 1. The terminal velocity of sunflower seed and its kernel for each variety and size category increased as the moisture content increased from 3 to 14% d.b. The reason can be attributed to the increase in mass of the individual seed or the kernel per unit volume. The other reason is probably that the drag force can be affected by the moisture content of the sample. A similar increasing trend of terminal velocity with moisture content has been reported by Joshi et al.[14] for pumpkin seeds, Carman^[15] for lentil seeds, Tabak and Wolf[10] for cotton seeds, Gezer et al.[27] for apricot pit and kernel, Kashaninejad et al.^[6] for pistachio nut and kernel, and Gupta et al.[11] for sunflower seed. According to Table 1, it is apparent that the average terminal velocity of seeds was significantly higher (5.24–7.68 m/s) than that of kernels (5–6.98 m/s) in all studied moisture levels for each variety and size category. This may be attributed to the hull or the seed coat, which is bulkier than the kernel such that it causes a considerable increase in the total mass of the seed. This justification can be proved by Eq. (1) that V_t is directly related to the mass.

Table 1 Variation of terminal velocity (m/s) of sunflower seed and kernel with moisture content, size, and variety (± standard deviations)

		Moisture content (% d.b.)
		3		7		14
Variety	Size	Seed	Kernel	Seed	Kernel	Seed	Kernel
Azargol	Large	6.22(0.08)	6.06(0.05)	6.46(0.11)	6.28(0.08)	6.74(0.11)	6.5(0.07)
	Medium	5.92(0.13)	5.68(0.08)	6.14(0.11)	5.98(0.08)	6.46(0.05)	6.2(0.07)
	Small	5.78(0.08)	5.24(0.05)	5.9(0.1)	5.46(0.05)	5.98(0.11)	5.66(0.05)
Fandoghi	Large	6.6(0.07)	6.34(0.05)	7.2(0.07)	6.68(0.08)	7.68(0.08)	6.98(0.08)
	Medium	6.58(0.08)	6.26(0.05)	6.82(0.13)	6.46(0.05)	7.08(0.13)	6.7(0.07)
	Small	6.28(0.08)	6.02(0.05)	6.52(0.08)	6.2(0.07)	6.8(0.1)	6.4(0.07)
Shahroodi	Large	5.78(0.08)	5.24(0.05)	5.98(0.08)	5.46(0.05)	6.12(0.08)	5.68(0.08)
	Medium	5.36(0.05)	5.14(0.05)	5.56(0.05)	5.36(0.05)	5.86(0.05)	5.56(0.05)
	Small	5.24(0.05)	5.00(0.07)	5.48(0.08)	5.14(0.08)	5.82(0.08)	5.24(0.08)
All data are means of ten replications.

The variation of drag coefficient at different moisture contents and size categories for investigated varieties of sunflower seed and its kernel are shown in Tables 2 and 3. As it can be seen from these tables, the drag coefficient for Azargol, Fandoghi, and Shahroodi varieties of sunflower seed decreased from 0.78–0.56, 0.81–0.55, and 0.94–0.73, respectively, as the moisture content increased from 3 to 14% d.b. This may be due to increasing terminal velocity with moisture content that it causes a substantial decrease in drag coefficient (Eq. 1). In agreement with these results, Gupta et al.[11] reported that the drag coefficient of sunflower seed varied from 0.17 to 0.40 for decrease of moisture from 6 to 14% d.b. As it can be seen from these tables, the drag coefficient value for Shahroodi variety of sunflower seed was higher than Fandoghi and Azargol varieties. Also, the similar order was found among kernels. These differences in drag coefficient could be the result of the individual cultivars.

Table 2 Mean comparison of terminal velocity (m/s), drag coefficient, and Reynold's number of sunflower seed and kernel considering interaction effect of moisture content and variety

		Variety
		Azargol		Shahroodi		Fandoghi
		Seed	Kernel	Seed	Kernel	Seed	Kernel
Parameter	Moisture content (%)
Terminal velocity	3	5.97 a	5.66 d	6.49 g	6.22 j	5.46 m	5.13 p
	7	6.17 b	5.91 e	6.85 h	6.45 k	5.67 n	5.32 q
	14	6.39 c	6.12 f	7.19 i	6.69 l	5.87 o	5.49 r
Drag coefficient	3	0.68 a	0.55 b	0.72 c	0.73 c	0.90 d	0.85 d
	7	0.66 a	0.52 b	0.65 c	0.71 c	0.83 d	0.83 d
	14	0.64 a	0.50 b	0.60 c	0.69 c	0.80 d	0.80 d
Reynold's number	3	2772.1 a	1736.6 b	2775 a	1876.1 d	2789.3 a	1700.9 g
	7	2821.9 a	1888.5 b	3054.3 ef	2013.3 d	2978.9 e	1832.3 g
	14	3046.5 ef	2041.9 b	3424.9 c	2131.7 d	3137 f	1948.7 g
The means with the same letter is not significant at the 5% level according to Duncan's multiple ranges test.

Table 3 Mean comparison of terminal velocity (m/s), drag coefficient, and Reynold's number of sunflower seed and kernel considering interaction effect of variety and size

Variety
		Azargol		Shahroodi		Fandoghi		Full amount of variety
Parameter	Size category	Seed	Kernel	Seed	Kernel	Seed	Kernel	Seed	Kernel
Terminal velocity	Large	6.47 a	6.28 d	7.16 g	6.67 j	5.96 m	5.46 p	6.53 a	6.14 d
	Medium	6.17 b	5.95 e	6.83 h	6.47 k	5.59 n	5.35 q	6.20 b	5.93 e
	Small	5.89 c	5.45 f	6.53 i	6.22 l	5.45 o	5.13 r	5.96 c	5.60 f
Drag coefficient	Large	0.59 a	0.63 d	0.62 g	0.84 i	0.78 c	0.88 l	0.65 a	0.78 d
	Medium	0.66 b	0.58 e	0.62 g	0.68 j	0.87 k	0.83 i	0.72 b	0.70 e
	Small	0.76 c	0.35 f	0.73 h	0.61 d	0.88 k	0.77 m	0.79 c	0.58 f
Reynold's number	Large	3414.2 a	2114.6 d	2781.8 b	2223 h	3316.3 a	1962.3 l	3504.1 a	2100 a
	Medium	2850.9 b	1876 e	3005.2 g	2006.5 i	2878 b	1819.3 j	2911.4 b	1900.6 b
	Small	2375.3 c	1676.3 f	2467.2 c	1791.6 j	2710.9 k	1700.3 c	2517.8 c	1722.7 c
The means with the same letter is not significant at 5% level according to Duncan's multiple ranges test.

The Reynold's number of sunflower seed and its kernel for the investigated varieties was calculated as a function of moisture content and size. As shown in Tables 2 and 3, the values of Reynold's number for both seed and kernel of Azargol, Fandoghi, and Shahroodi varieties were increased with increasing moisture content in each size category. This may be due to increasing terminal velocity and geometric mean diameter with moisture content (Eq. 3). It is also found that the highest Reynold's number for sunflower seed was obtained for Fandoghi (4215.7), then Azargol (3538.9), and the minimum in Shahroodi (3450.2). The similar order was also found among kernels: Fandoghi (2325.5), Azargol (2287.7), and Shahroodi (2108.7). Based on Tables 2 and 3, also for all treatments (variety, size, and moisture content) the sunflower seeds exhibited a higher value of Reynold's number than the sunflower kernels. This can be related to the high values of terminal velocity and geometric mean diameter of seeds than kernels.

According to Table 2, the changes in variety influenced significantly the terminal velocity, drag coefficient, and Reynold's number of seed and kernel (P < 0.05). As it can be found from this table, the terminal velocity of Fandoghi was about 1.22-fold of Shahroodi variety of sunflower seed. In the same way, the average terminal velocity of Fandoghi variety of kernels was about 1.21-fold of that of Shahroodi variety. Also, the drag coefficient of Shahroodi was significantly more than Azargol variety of sunflower seed (around 1.27 times). This value for corresponding kernel was around 1.60. These differences in terminal velocity and drag coefficient could be the result of the individual cultivars properties and different environmental and growth conditions of cultivars. Furthermore, the average Reynold's number of Fandoghi seed was about 1.07-fold of Azargol. This value for corresponding kernel was around 1.06.

Moisture Content

Gaining moisture from 3 to 14% d.b. showed an increase in the terminal velocity and Reynold's number and a decrease in drag coefficient for both seed and kernel in the cases of variety and size category. This conclusion was consistent with the findings of Matouk et al.,[28] who reported that terminal velocity and Reynold's number of soybean and canola increased linearly with the increase of seeds moisture content while drag coefficient decreased with the increase of moisture content. The reason for increasing terminal velocity and drag coefficient by moisture content was because of increasing the mass (Eq. 1).

According to Table 2, terminal velocity of seed was 6.48 m/s at 14% moisture. This is significantly more than the terminal velocity of seed at 3% moisture (around 1.08 times). This value was the same for the corresponding kernel (around 1.08). Also, the drag coefficient of the sunflower seed at 3% moisture content was about 1.13-fold of that of the one at 14% moisture content. In the same way, the average drag coefficient of kernels was about 1.08-fold of that of the kernel at 14% moisture content. Furthermore, Reynold's number of the sunflower seed and kernel at 14% moisture was significantly more than the Reynold's number values for both seed and kernel at 3% moisture content (around 1.15 for both seed and kernel).

The interaction effect of variety and moisture content on terminal velocity, drag coefficient, and Reynold's number of the sunflower seed and its kernel are shown in Tables 2 and 3. As it can be found from these tables, the means indicate that variety and moisture content created a significant effect on terminal velocity for both seed and kernel (P < 0.05), while these factors had not a significant effect on drag coefficient for studied varieties of sunflower seed. Also, there was no significant difference for values of drag coefficient and Reynold's number of kernel in each size categories at the studied levels of moisture content. Considering the values presented in Table 2, the highest difference in terminal velocities of seed was attributable to the Shahroodi variety. Furthermore, the terminal velocity of seed was lowest for the Fandoghi variety. In the case of kernel (Table 2), the most and the least differences for terminal velocity and Reynold's number belonged to Shahroodi and Fandoghi varieties, respectively.

Size

There was a significant difference between small and large sizes for both sunflower seed and its kernel (P < 0.05) as shown in Table 3. As given in this table, the terminal velocity of sunflower seed and its kernel increased as size increased from small to large, so that the average terminal velocity of the large category was about 1.09-fold of that of small ones for both seed and kernel. These differences in results can be attributed to the increase in mass of the individual seed or kernel per unit with size category. This justification can be proved by Eq. (1) that V_t has a direct relation with mass. However, the drag coefficient of sunflower seed decreased with increasing the size. In contrast, drag coefficient of sunflower kernel increased with increase in size. These discrepancies can be related to the cell structure and the variation of physical properties in seeds and kernels when size is changed. Also, investigating the effect of size on Reynold's number showed that this parameter increased as the size increased for both seed and kernel. The reason for this trend is due to the size increase, which is because of the increase in the geometric mean diameter of the sample (seed or kernel). According to Table 3, the Reynold's number of seed was 3504.1 at large size categories. This is significantly more than the Reynold's number of seed at small size category (around 1.31 times). In the same way, the average Reynold's number of kernels at large size was about 1.22-fold of that of kernels for small sizes.

Considering the interaction effect between variety and size category, the highest difference in terminal velocity for sunflower seed and kernel belonged to Shahroodi variety. Based on Table 3, there was no significant difference (P < 0.05) between large and medium seed sizes for drag coefficient of Shahroodi variety. Also, the drag coefficient showed any significant difference among medium and small seed size (P < 0.05). But in the case of kernel, all means indicated that size category created a significant effect on terminal velocity for each variety (P < 0.05). Investigating the interaction effect of size and variety on Reynold's number for both seed and kernel showed that most differences between varieties in the case of size category belonged to Azargol variety. In addition, it is denoted from this table that the least effect of size category on Reynold's number seed and kernel belonged to Azargol variety.

Terminal velocity, drag coefficient, and Reynold's number for both seed and kernel can be strongly correlated to such variables as variety, moisture content, and size category. These relationships are shown in Table 4. These relationships had a high coefficient of determination that they can be beneficial in estimating terminal velocity, drag coefficient, and Reynold's number for goals, such as air conveyor and pneumatic separator of sunflower seed and kernel.

Table 4 Terminal velocity (V_t ), drag coefficient (C_d ), and Reynold's number (R_e ) of sunflower seed and its kernel as a function of variety (V), moisture content (M), and size category (S)

Product	Relationship	R ^2	SEE	DF
Seed	Vt  = 3.315 + 3.57V + 0.59M − 0.19S − 0.92V^2 − 0.001M^2 + 0.046S^2 − 0.093VM − 0.072VS	0.96	0.05	134
	− 0.16MS + 0.045VMS
	Cd  = 0.67 − 0.19V − 0.045M + 0.115S + 0.093V^2 + 0.011M^2 + 0.002S^2 − 0.021VM − 0.0288VS	0.90	0.11	134
	− 0.007MS + 0.003VMS
	Re  = 4060.66 + 340.68V − 68.29M − 1195.62S − 160.44V^2 + 39.09M^2 + 99.61S^2 + 64.24VM	0.83	0.16	134
	+ 154.73VS + 43.66MS − 22.96VMS
Kernel	Vt  = 3.93 + 2.81V + 0.28M − 0.28S − 0.85V^2 − 0.006M^2 − 0.059S^2 − 1.68VM − 1.04VS − 1.85MS + 1.12VMS	0.98	0.03	134
	Cd  = 0.68 + 0.19V − 0.15M − 0.14S − 0.035V^2 + 0.002M^2 − 0.017S^2 + 0.006VM + 0.051VS + 0.01MS − 0.004VMS	0.85	0.17	134
	Re  = 1707.07 + 483.39V + 190.22M − 314.55S − 148.88V^2 − 5.37M^2 + 10.74S^2 − 3.40VM + 55.04VS − 2.56MS − 5.50VMS	0.89	0.16	134
R ^2: determination coefficient; SEE: Standard Error of Estimate; DF: Degree of Freedom.

Application of Results

The obtained results of aerodynamic properties in this study could be applied to predict the range of proper air velocity during handling and processing of sunflower seed and its kernel. Typically, values of investigated properties could be used in the development of design specification for either an air conveyor or the separation equipment. Maximum terminal velocity of sunflower seed to determine the proper air speed for conveying can be considered to be about 7.68 m/s. Also, the maximum terminal velocity of sunflower kernel for this application was 6.98 m/s. Values higher than these numbers will lead to braking and wasting of seeds or their kernels and less than that probably would not give results in separating of the seeds or their kernels from each other or foreign material. The suggested applicable drag coefficient of sunflower seed and its kernel to resist to the air flow is 0.73 and 0.69, respectively. The maximum value of Reynold's number, which is important to determine the ratio of inertial forces to viscous forces in fluid mechanics and heat transfer of sunflower seed and its kernel, are obtained as 4215.7 and 2325.5, respectively.

CONCLUSION

Statistically, variation in moisture content as well as sunflower variety (seed and kernel) either individually or in combination (interaction) was significantly influenced by the terminal velocity, drag coefficient, and Reynold's number (P < 0.01). The values of terminal velocity and Reynold's number of sunflower seed and its kernel increased with increasing moisture content from 3 to 14% d.b., while drag coefficient decreased with the increase of moisture content for all studied varieties and size categories. Terminal velocity of seeds was significantly higher (5.24–7.68 m/s) than that of kernels (5–6.98 m/s) in all levels of moisture content, variety, and size category. In addition, the sunflower seeds exhibited a higher Reynold's number than the sunflower kernels for all treatments (variety, size, and moisture content). The values of terminal velocity and Reynold's number of sunflower seed and its kernel increased as size increased from small to large, while the drag coefficient of sunflower seed decreased with increasing size category. In contrast, drag coefficient of sunflower kernel increased with increasing size.

ACKNOWLEDGMENTS

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