alexa Performance Evaluation of the Cowpea Wet De-Hulling Machine | Open Access Journals
ISSN: 2168-9873
Journal of Applied Mechanical Engineering
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Performance Evaluation of the Cowpea Wet De-Hulling Machine

Kamaldeen OS1*, Awagu EF1, Isiaka M2 and Arowora KA3

1Nigerian Stored Products Research Institute, Kano Station, PMB 3032, Hadeija Road, Kano, Nigeria

2Department of Agricultural Engineering, Faculty of Engineering, Ahmadu Bello University, Zaria, Kaduna, Nigeria

3Department of Biochemistry, Federal University Wukari, Taraba, Nigeria

*Corresponding Author:
Kamaldeen OS
Nigerian Stored Products Research Institute, Kano Station
PMB 3032, Hadeija Road, Kano, Nigeria
Tel: +234 811 776 7204
E-mail: ksk_deen@yahoo.com

Received Date: December 19, 2016; Accepted Date: January 04, 2017; Published Date: January 08, 2017

Citation: Kamaldeen OS, Awagu EF, Isiaka M, Arowora KA (2017) Performance Evaluation of the Cowpea Wet De-Hulling Machine. J Appl Mech Eng 6:248. doi: 10.4172/2168-9873.1000248

Copyright: © 2017 Kamaldeen OS, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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Abstract

The performance evaluation of the cowpea de-hulling machine was done using a factorial experiment in a completely randomize design involving speed, soaking time and cowpea variety each at 3, 3, and 2 levels respectively. These were replicated three times. LSD was used to further analyze the significant means. The results showed that the speed, soaking time and cowpea variety had significant effect on de-hulling efficiency and output capacity for the developed de-huller while only soaking time and speed had significant effect on mechanical damage. The developed de-huller performs the best at 120 rpm speed, 11 mins soaking time, and with Dan-barere variety. Based on these variables, the performance indices obtained were 90.75%, 74.27 kg/hr. and 0.39% for de-hulling efficiency, output capacity and mechanical damage respectively.

Keywords

De-hulling; Soaking; Cowpea; Dan-barere, Dan-sokoto

Introduction

Cowpea (Vigna unguiculata or Vigna sinensis nunguiculata) is a popular leguminous crop in Africa which is known as “black-eyed peas” in America. In Nigeria, it is known as ‘beans’. Kano State is one of the largest cowpea producing areas in Nigeria, cultivating about 4,050 ha which yields above 1,000 kg/ha compared with the national average of 212 kg/ha. Common varieties include SAMPEA 10, SAMPEA 8, and Oloka [1]. Cowpea is one of the most highly proteineous African crop that feeds people, their livestock and the next crop. The nutritional value of cowpea is in the composition of its grain. Cowpea grains are rich in amino acids, lysine and tryptophan making it better than cereal and root and tuber based diets of many coastal and forest communities [2]. In Nigeria and some other West African countries, cowpea grains are eaten in various forms; as porridge along with fried or boiled yam or plantain, as bean cake called akara or kosei among Yoruba and Hausa respectively, as moin-moin which is steamed – cook of wet – milled cowpea mixed with cooking ingredients, and cowpea stew called gbegiri in Yoruba language [3].

De-hulling can be defined as the removal of seed coat (hull) from the seed, resulting in the separation of the cotyledons from the hulls [4]. In the rural sector, the wet method of de-hulling process is still part of the house wife’s manual work in food preparation. Water soaking is used to facilitate hull removal. The cowpea seeds absorb moisture and swell, thereby facilitating de-hulling process. If thoroughly soaked, the seed coats can be removed by hand. If not, the aid of a grinding stone or a mortar is needed to roughly bruise the skins with a stirring action (not pounding).

Material and Methods

Experimental procedure

The performance evaluation of the cowpea wet de-hulling machine as shown in Figure 1 was carried out, such conditions considered are the 3 levels of machine operating speeds, 3 levels of soaking time, and 2 varieties of cowpea. The effect of these conditions was investigated on the de-hulling efficiency, output capacity and mechanical damage of the machine.

applied-mechanical-engineering-de-hulling-machine

Figure 1: Evaluation of cowpea wet de-hulling machine.

Experiment to study was carried out at Nigerian Stored Products Research Institute, (NSPRI), Kano, Kano State, Nigeria, where the cowpea wet de-hulling machine was developed.

Performance indices

The performance indices that were used include; De-hulling efficiency (%) and Output capacity (kg/hr).

De-hulling efficiency - DE (%): This shows how efficiently the machine is de-hulling the sample. It was expressed as given by Olotu et al. as:

applied-mechanical-engineering (1)

Where, W1 = Weight of de-hulled cowpea seed (kg).

W2 = Weight of un-dehulled cowpea seed (kg)

Output capacity - Oc (kg/hr): This is the total quantity of cowpea seeds collected at the machine outlet per batch per unit time. It was expressed as given by Olotu et al. as:

applied-mechanical-engineering (2)

Where W = Total weight of de-hulled cowpea, unde-hulled cowpea and hulls collected at the outlet of the machine (kg).

T = Time taken to dehul the cowpea seed (hr).

Experimental index

The factors that were considered in the evaluation of the constructed de-hulling machine were Operating speed (S), Soaking time (F) and Cowpea variety (V).

Operating speed (S): The operating speed of the machine is the speed of the shaft carrying the de-hulling component. Olotu et al. reported optimum de-hulling speed for cowpea as 150 rpm. Based on this value, the constructed de-hulling machine was evaluated with following operating speeds: S1 = 120 rpm, S2 = 150 rpm and S3 = 180 rpm.

Soaking time (T): The soaking time is the time required for the cowpea seeds to absorb moisture through soaking. Babatunde and Olotu et al. [5] reported 7 and 6 mins respectively as optimum soaking time before cowpea de-hulling. Based on these values, the constructed de-hulling machine was evaluated with following soaking times: T1 = 5 mins, T2 = 8 mins, and T3 = 11 mins.

Cowpea varieties (V): Danbarere and Dansokoto varieties of cowpea which can be of smaller and bigger sizes are widely used in Kano (Dakata/Yankaba) area by most bean cake sellers. Based on this, smaller sizes of the two varieties [Danbarere (V1) and Dansokoto (V2)] were selected.

Results and Discussion

Effect of evaluated factors on de-hulling efficiency of the ecto de-hulling machine

The results of the analysis of variance are as shown in Table 1. The results show that there is no significant difference at 1% probability level between the means of the replicate, meaning that the experimental error is minimum. The results also show that the speed of operation (S), soaking time (T) and cowpea varieties (V) as well as their interactions were all significant at 1% probability level. That means all the evaluated factors and their interactions had effect on the de-hulling efficiency of the machine.

Source of Variation Degree of Freedom Sum of Squares Mean Square F (Value) 5% 1%
Rep 2 0.0022333 0.001116 0.00NS 3.29 5.31
V 1 88.283107 88.28310 58.99** 3.29 5.31
T 2 118.2420247 59.121012 39.51** 3.29 5.31
S 2 186.859668 93.429834 62.43** 4.14 7.48
V × T 2 0148224 73.007411 48.79** 3.29 5.31
V × S 2 63.5730113 31.786505 21.24** 3.29 5.31
T × S 4 344.665088 86.166272 57.58** 2.66 3.94
V × T ×S 4 154.969745 38.742436 25.89** 2.66 3.94
Error 34 50.880231 1.496477 -- -- --
Total 53 1153.489933 -- -- -- --

Table 1: Analysis of variance showing effect of variables and their interaction on de-hulling efficiency (DE).

Effect of speed of operation on the de-hulling efficiency

The effect of operating speed on the de-hulling efficiency was further analysed using Least Significant Difference (LSD) test and the results of the analysis are as shown in Table 2. The results show that the mean de-hulling efficiency for 120 rpm operating speed is higher and significantly different from those of 150 rpm and 180 rpm. The mean for 150 rpm operating speed is also different and higher than that of 180 rpm operating speed. That is, the de-hulling efficiency decreases as operating speed increases. This can be explained by the fact that the lower the operating speed, the longer the residence time for the soaked cowpea seeds to rub against one another and wall of the dehulling chamber which results to detachment of hulls before discharge. This result is in agreement with Reichert et al. [6] who reported that de-hulling of cowpea seeds at lower speed is more efficient than dehulling at higher speed. Similarly, Olotu et al. also reported that the higher the speed of operation, the lower the de-hulling efficiency. Mean de-hulling efficiencies of 90.58%, 87.46% and 86.04% were achieved for 120 rpm, 150 rpm and 180 rpm operating speed, respectively.

S(rpm) DE (%) LSD T (mins) DE (%) LSD V DE (%) LSD
120 90.58 a 5 86.77 c Dan-barere 89.25 a
150 87.46 b 8 87.11 b Dan-sokoto 86.70 b
180 86.04 c 11 90.20 a -- -- --
S.E = 1.342 -- -- S.E = 1.092 -- -- S.E. = 1.278 -- --

Table 2: LSD test for effect of speed (S), soaking time (T) and cowpea variety (V) on de-hulling efficiency. (DE).

Effect of soaking time on de-hulling efficiency

The results of further analysis of the effect of soaking time on the de-hulling efficiency using Least Significant Difference (LSD) test are as shown in Table 2. The results show that the mean de-hulling efficiency for 5 mins soaking time is lower and different from those of 8 mins and 11 mins. The mean for 8 mins is also different and lower than that of 11 mins soaking time. That is, the de-hulling efficiency increases as soaking time increases. This can be attributed to the fact that the longer the soaking, the more the water is absorbed and the weaker the adhesive force between the hulls and cotyledons of the cowpea seeds. The results are in agreement with Olowonibi [7] who reported that the longer the soaking period of cowpea, the higher the de-hulling efficiency. Mean de-hulling efficiencies of 86.77%, 87.11% and 90.20% were achieved for 5 mins, 8 mins and 11 mins soaking time respectively.

Effect of cowpea varieties on de-hulling efficiency

The results of further analysis of the effect of cowpea variety on the de-hulling efficiency using Least Significant Difference (LSD) test are as shown in Table 2. The results show that the mean de-hulling efficiency for Dan-barere is significantly different and higher than that of Dan-sokoto. That is, the de-hulling efficiency differs for different variety of cowpea. This can be attributed to the fact that cowpea seed as a biological material grouped into different varieties and each variety is known with specific characteristics. Dan-barere with higher de-hulling efficiency might have weaker adhesive force between its hulls and cotyledons than that of Dan-sokoto which makes it easily detachable. This result is in agreement with Olotu et al. who reported that variety of cowpea can be an important factor that can affect de-hulling efficiency. Mean de-hulling efficiencies of 89.25% and 86.70% were achieved for Dan-barere and Dan-sokoto cowpea variety, respectively.

The interaction effect of cowpea variety and operating speed on de-hulling efficiency

The results for the interaction effect of the cowpea variety and operating speed on de-hulling efficiency are as presented in Table 3. The results show that operating speed of the machine interacting with cowpea variety is a major factor affecting the de-hulling efficiency. The de-hulling efficiency for 120 rpm operating speed interacting with Dan-barere and Dan-sokoto cowpea variety respectively was high compared with that of 150 rpm operating speed and considerably high when compared with that of 180 rpm operating speed. It can also be seen from the table that for the same Dan-barere cowpea variety, the mean de-hulling efficiency decreases as the operating speed increases. Similarly, for the same Dan-sokoto cowpea variety, the mean dehulling efficiency also decreases as operating speed increases. Highest de-hulling efficiency was obtained from interaction of Dan-barere and 120 rpm while lowest de-hulling efficiency was obtained from interaction of Dan-sokoto and 180 rpm.

Treatment MeanDE LSD
V1S1 90.33 a
V2S1 90.83 a
V1S2 89.26 b
V2S2 88.28 c
V1S3 85.65 d
V2S3 83.24 e
S.E = 1.201 -- --

Table 3: LSD test for interaction effect of variety (v) and operating speed (s) on de-hulling efficiency (DE).

The interaction effect of cowpea variety and soaking time on de-hulling efficiency

The results for the interaction effect of the cowpea variety and soaking time on de-hulling efficiency are as presented in Table 4. In these results, no definite pattern was established. However, the mean for Dan-sokoto variety and 11 mins is the highest and different from other means. There is no significant difference in mean de-hulling efficiency for Dan-barere /8 mins and Dan-barere/11 mins. There is also no difference in Dan-barere/ 5 mins soaking time and Dan-sokoto / 5 mins. The mean de-hulling efficiency for Dan-sokoto/ 8 mins is the lowest and differs significantly from other means.

Treatment Mean DE LSD
V2T3 91.34 a
V1T2 89.60 b
V1T3 89.25 b
V1T1 88.92 bc
V2T1 85.30 c
V2T2 83.94 d
S.E = 1.153 -- --

Table 4: LSD test for interaction effect of variety (v) and soaking time (t) on dehulling efficiency (DE).

The interaction effect soaking time and operating speed on de-hulling efficiency

The results for the interaction effect of the soaking time and operating speed on de-hulling efficiency is as presented in Table 5. From the results, the effect of operating speed is more pronounced when compared with that of the soaking time. In these results, no definite pattern was established. However, on average the mean for 11 mins soaking time and 120 rpm is the highest and different from other means. There is no significant difference in mean de-hulling efficiency for 5 mins/150 rpm interaction, 8 mins/120 rpm interaction and 11 mins/180 rpm interaction. There is also no difference in 5 mins/120 rpm interaction, 11 mins/150 rpm interaction and 8 mins/180 rpm interaction. Consequently, mean de-hulling efficiency for 5 mins and 180 rpm operating speed is the lowest and significantly differs from other means.

Treatment Mean DE LSD
T3S1 92.04 a
T1S2 90.95 b
T2S1 90.37 b
T3S3 90.29 b
T1S1 89.33 c
T3S2 88.27 cd
T2S3 86.79 d
T2S2 83.15 e
T1S3 81.04 f
S.E = 1.242 -- --

Table 5: LSD test for interaction effect of operating speed (s) and soaking time (t) on de-hulling efficiency (DE).

The interaction effect of cowpea variety, soaking time and speed of operation on de-hulling efficiency

The results for the interaction effect of the cowpea variety, soaking time and operating speed on de-hulling efficiency are as presented in Table 6. In these results, no definite pattern was established. However, it can be seen from the table that there is no significant difference in mean de-hulling efficiency for Dan-sokoto /11 mins/180 rpm interaction, Dan-sokoto /11 mins/120 rpm interaction, Dan-barere/5 mins/150 rpm interaction, Dan-barere/8 mins/120 rpm interaction, Dan-barere/11 mins/120 rpm interaction, Dan-sokoto/5 mins/150 rpm interaction and Dan-barere/8 mins/180 rpm interaction. There is also no difference in mean for Dan-sokoto/8 mins/120 rpm interaction, Dan-sokoto/5 mins/120 rpm interaction, Dan-barere/11 mins/180 rpm interaction, Dan-barere/5 mins/120 rpm interaction, Dan-barere/11 mins/180 rpm interaction, Dan-barere/8 mins/150 rpm interaction, Dan-sokote/11 mins/150 rpm interaction, Dan-barere/5 mins/180 rpm interaction and Dan-sokoto/8 mins/180 rpm interaction. However, the first set listed above have significantly different and higher means for de-hulling efficiency the later set mentioned. Mean for Dansokoto/ 8 mins/120 rpm interaction is statistically at par with that of Dan-sokoto/5 mins/180 rpm interaction but lower than the second set mentioned above.

Treatment Mean DE LSD
V2T3S3 94.46 a
V2T3S1 93.27 a
V1T1S2 91.15 a
V1T2S1 91.12 a
V1T3S1 90.81 a
V2T1S2 90.75 a
V1T2S3 90.12 a
V2T2S1 89.61 b
V2T1S1 89.60 b
V1T3S2 89.08 b
V1T1S1 89.06 b
V1T3S3 88.21 b
V1T2S2 87.56 b
V2T3S2 87.46 b
V1T1S3 86.53 b
V2T2S3 83.45 b
V2T2S2 78.74 c
V2T1S3 75.54 c
S.E. = 1.115 -- --

Table 6: LSD test for interaction effect of cowpea variety, soaking time, and operating speed on de-hulling efficiency (DE).

Effect of evaluated factors on output capacity of the de-hulling machine

The results for experimental evaluation of the effect of operating speed, cowpea varieties and soaking time on output capacity of the developed machine using completely randomized design are as presented. The results of the analysis of variance are as shown in Table 7. The results show that there is no significant difference at 1% probability level between the means of the replicate, meaning that the experimental error is minimum. The results also show that the speed of operation (S), soaking time (T) and cowpea varieties (V) as well as their interactions were all significant at 1% probability level. That means all the evaluated factors and their interactions had effect on output capacity of the machine.

Source of Variation Degree of Freedom Sum of Squares Mean Square F (Value) 5% 1%
Rep 2 0.00378 0.00189 0.00NS 3.29 5.31
V 1 1192.05932 1192.0593 2237.47** 3.29 5.31
T 2 44.29943 22.14971 41.57** 3.29 5.31
S 2 35245.0505 17622.525 33077.1** 4.14 7.48
V × T 2 1254.99940 627.49970 1177.80** 3.29 5.31
V ×S 2 1220.33632 610.16816 1145.27** 3.29 5.31
T × S 4 308.81013 77.20253 144.91** 2.66 3.94
V × T × S 4 1058.87298 264.71824 496.87** 2.66 3.94
Error 34 18.11423 0.53277 -- -- --
Total 53 40342.5461 -- -- -- --

Table 7: Analysis of variance showing effect of variables and their interaction on output capacity (OC).

Effect of speed of operation on the output capacity

The effect of operating speed on the output capacity was further analysed using Least Significant Difference (LSD) test and the results of the analysis are as shown in Table 8. The results of the LSD show that the mean output capacity for 120 rpm operating speed is lower and significantly different from those of 150 and 180 rpm. The mean for 150 rpm operating speed is also different and lower than that of 180 rpm operating speed. That is, the output capacity increases as operating speed increases. This can be attributed to the fact that since the number of turns of conveying auger per unit time increases at higher speed, then the quantity of soaked cowpea being conveyed per unit time is expected to increase as well. This result is in agreement with Olotu et al. and Babatunde who reported that increase in operating speed increases the output capacity of the de-huller. Mean output capacity of 49.83 kg/ hr, 68.33 kg/hr and 110.84 kg/hr were achieved for 120 rpm, 150 rpm and 180 rpm operating speed respectively.

S(rpm) DE (%) LSD T (mins) DE (%) LSD V DE (%) LSD
120 49.83 c 5 77.08 a Dan-barere 71.81 b
150 68.33 b 8 76.53 b Dan-sokoto 81.20 a
180 110.8 a 11 75.38 c -- -- --
S.E = 18.62 -- -- S.E = 0.38 -- -- S.E. = 4.70 -- --

Table 8: LSD test for effect of speed (s), soaking time (t) and variety (v) on output capacity (OC).

Effect of soaking time on output capacity

The results of further analysis of the effect of cowpea variety on the output capacity using Least Significant Difference (LSD) test are as shown in Table 4. The results of the LSD show that the mean output capacity for 5 mins soaking time is significantly higher and different from those of 8 mins and 11 mins. The mean output capacity for 8 mins is also significantly different and higher than that of 11 mins soaking time. That is, the output capacity decreases as soaking time increases. This can be attributed to the fact that the longer the cowpea seed is soaked the more the moisture absorbed which increases its weight and size. This might reduce the quantity of soaked cowpea seeds handled by the machine per unit time. The results are in agreement with Olowonibi who reported that the longer the soaking period of cowpea, the lower the machine output capacity. Mean output capacity of 77.08 kg/hr, 76.53 kg/hr and 75.38 Kg/hr were achieved for 5 mins, 8 mins and 11 mins soaking time respectively.

Effect of cowpea varieties on output capacity

The results of further analysis of the effect of cowpea variety on the output capacity using Least Significant Difference (LSD) test are as shown in Table 4. The results of the LSD show that the mean output capacity for Dan-barere is significantly different and lower than that of Dan-sokoto. That is, the output capacity differs for different variety of cowpea. This can be attributed to the fact that cowpea seed as a biological material grouped into different varieties and each variety is known with specific characteristic part of which is the way different variety flows when it is being conveyed within a conveyor system. This result is in agreement with Olotu et al. who reported that cowpea varieties affect output capacity of de-hulling machine. Mean de-hulling efficiency of 71.81 kg/hr and 81.20 kg/hr were achieved for Dan-barere and Dan-sokoto cowpea variety respectively.

The interaction effect of cowpea variety and operating speed on output capacity

The results for the interaction effect of the cowpea variety and operating speed on output capacity are as presented in Table 9. The results show that operating speed of the machine is a major factor affecting the output capacity. The output capacity for 180 rpm operating speed interacting with Dan-barere and Dan-sokoto cowpea variety respectively was high compared with that of 150 rpm operating speed and considerably high when compared with that 120 rpm speed. It can also be seen from the table that for the same Dan-barere cowpea variety, the mean output capacity increase as the operating speed increases. Similarly, for the same Dan-sokoto cowpea variety, the mean output capacity also increases as operating speed increases.

Treatment Mean OC LSD
V2S3 124.67 a
V1S3 99.77 b
V2S2 72.67 c
V1S2 63.98 d
V2S1 51.09 e
V1S1 48.56 f
S.E = 1.201 -- --

Table 9: LSD test for interaction effect of variety (v) and speed (s) on output capacity (OC).

The interaction effect of cowpea variety and soaking time on output capacity

The results for the interaction effect of the cowpea variety and soaking time on output capacity are as presented in Table 10. In these results, no definite pattern was established. However, the mean for Dansokoto variety and 8 mins interaction is the highest and statistically at par with that of Dan-sokoto variety and 5 mins interaction. There is no significant difference in mean output capacity for Dan-barere /11 mins interaction, Dan-sokoto/11 mins interaction and Dan-barere / 5 mins interaction. Consequently, mean output capacity for Dan-barere and 8 mins interaction is the lowest and differs from other means.

Treatment MeanOC LSD
V2T2 85.10 a
V2T1 82.79 a
V1T3 78.72 b
V2T3 75.03 b
V1T1 70.27 b
V1T2 65.67 c
S.E = 1.201 -- --

Table 10: LSD test for interaction effect of variety (v) and soaking time (t) on output capacity (OC).

The interaction effect soaking time and operating speed on output capacity

The results for the interaction effect of the soaking time and operating speed on output capacity is as presented in Table 11. From the results, the effect of operating speed is more pronounced when compared with that of the soaking time. In these results, no definite pattern was established. However, the mean for 5 mins interaction and 180 rpm interaction is the highest and different from other means. The mean output capacity for 11 mins and 120 rpm operating speed is the lowest and differs from other means.

Treatment Mean OC LSD
T2S3 113.18 a
T1S3 111.10 b
T3S3 108.24 c
T3S2 73.68 d
T1S2 68.47 e
T2S2 62.84 f
T2S1 50.14 g
T1S1 50.03 g
T3S1 49.31 h
S.E = 1.242 -- --

Table 11: LSD Test for interaction effect of operating speed (s) and soaking time (t) on output capacity (OC).

Cowpea variety, soaking time and speed of operation interaction effect on output capacity

The results for the interaction effect of the cowpea variety, soaking time and operating speed on output capacity are as presented in Table 12. It can be seen from the results that the difference in mean output capacity for Dan-sokoto /11 mins/150 rpm interaction, Dan-sokoto /11 mins/120 rpm interaction, Dan-barere/8 mins/120 rpm interaction, Dan-sokoto/5 mins/150 rpm interaction and Dan-barere/5 mins/120 rpm interaction are statistically at par. Also difference in mean for Danbarere/ 11 mins/150 rpm interaction and Dan-sokoto/8 mins/150 rpm interaction, Dan-barere/5 mins/150 rpm interaction and Dan-barere/8 mins/150 rpm interaction are statistically the same. Mean values of output capacity for the first list of interactions was significantly higher than those for the later list of interactions. Mean for Dan-sokoto/5 mins/120 rpm interaction is statistically at par with Dan-sokoto/8 mins/120 rpm operating speed but lower than the previous set of interactions.

Treatment Mean OC LSD
V2T2S3 137.53 a
V2T1S3 121.11 a
V2T3S3 110.72 a
V1T3S3 107.00 a
V1T1S3 101.01 a
V1T2S3 100.82 a
V2T3S2 78.61 b
V2T3S1 74.65 b
V1T2S1 74.64 b
V2T1S2 74.27 b
V1T1S1 74.06 b
V1T3S2 68.74 c
V2T2S2 65.13 c
V1T1S2 62.66 c
V1T2S2 60.55 c
V2T1S1 52.99 d
V2T2S1 52.64 d
V1T3S1 50.98 d
S.E. = 1.115 -- --

Table 12: LSD test for interaction of effect cowpea variety, soaking time and operating speed on output capacity (OC).

Effect of evaluated factors on mechanical damage of the dehulling machine

The results for experimental evaluation of the effect of operating speed, cowpea varieties and soaking time on mechanical damage of the developed machine using completely randomized design are as presented. The results of the analysis of variance are as shown in Table 13. The results show that there is no significant difference at 1% probability level between the means of the replicate, meaning that the experimental error is minimum. The results also show that the speed of operation (S) and soaking time (T) significantly affected mechanical damage of seed 1% probability level while varieties as well as all variables interactions have no significant effect on mechanical damage of seed at 1% probability level. That means, only operating speed and soaking time had effect on the mechanical damage of the machine while varieties and interaction of all the evaluated factors had no effect on mechanical damage.

Source of Variation Degree of Freedom Sum of Squares Mean Square F (Value) 5% 1%
Rep 2 0.011 0.003 0.001NS 3.29 5.31
V 1 0.007 0.007 1.384NS 3.29 5.31
T 2 1.301 0.650 56.245** 3.29 5.31
S 2 0.018 0.009 7.869** 4.14 7.48
V ×T 2 0.015 0.007 0.586NS 3.29 5.31
V ×S 2 0.017 0.008 2.186NS 3.29 5.31
T ×S 4 0.008 0.002 0.142NS 2.66 3.94
V × T × S 4 0.022 0.022 1.449NS 2.66 3.94
Error 34 0.054 0.532 -- -- --
Total 53 1.453 -- -- -- --

Table 13: Analysis of variance showing effect of variables and their interaction on mechanical damage (Md).

Effect of soaking time on mechanical damage

The results of further analysis of the effect of soaking time on the mechanical damage using Least Significant Difference (LSD) test are as shown in Table 14. The results of the LSD show that the mean value of mechanical damage for 5 mins soaking time is significantly lower and different from those of 8 and 11 mins. The mean mechanical damage for 8 mins is also significantly different and lower than that of 11 mins soaking time. That is, the mechanical damage increases as soaking time increases. This can be attributed to the fact that the longer the cowpea seed is soaked the more the moisture absorbed and the softer the cotyledons become. This might increase the quantity cowpea seeds being deformed during the de-hulling process. The results are in agreement with Olowonibi, who reported that the longer the soaking period of cowpea, the higher the de-hulling efficiency but the more the percentage of mechanical damage. Mean mechanical damage of 0.55%, 0.69% and 0.93% were achieved for 5 mins, 8 mins and 11 mins soaking time respectively.

S(rpm) Mean
Md(%)
LSD T(mins) Mean
Md(%)
LSD
120 0.706 c 5 0.55 c
150 0.711 b 8 0.69 b
180 0.747 a 11 0.93 a
S.E. = 0.002 -- S.E. = 0.057 --

Table 14: LSD test for effect of speed (s) and soaking time (t) on mechanical damage (Md).

Effect of operating speed on mechanical damage

The results of further analysis of the effect of operating speed on the mechanical damage using Least Significant Difference (LSD) test are as shown in Table 14. The results of the LSD show that the mean mechanical damage for 120 rpm operating speed is significantly lower and different from those of 150 rpm and 180 rpm. The mean mechanical damage for 150 rpm is also significantly different and lower than that of 180 rpm soaking time. That is, the mechanical damage increases as operating speed increases. This can be attributed to the fact that the higher the speed of operation the more the impact effects on cowpea cotyledons. This might increase the quantity cowpea seeds being deformed during the de-hulling process. Mean mechanical damage of 0.706%, 0.711% and 0.747% were achieved for 120 rpm, 150 rpm and 180 rpm operating speed respectively (Table 13).

Recommendations

The de-hulling machine should also be evaluated on other legume seeds such as soybean and locust bean seeds so as to make it multi-crop de-hulling machine and increase its potential.

Conclusion

Cowpea de-hulling machine had been evaluated. From the evaluation of the machine, de-hulling efficiency, output capacity and mechanical damage were in the range of 86.04% to 90.58%, 49.31 kg/ hr to 137.53 kg/hr and 0.23% to 0.93% respectively. The best de-hulling efficiency, output capacity and mechanical damage were obtained at 120 rpm operating speed, 8 mins soaking time, and with dan-barere cowpea variety. Based on this, the average de-hulling efficiency, output capacity and mechanical damage of the machine were 90.79%, 74.27 kg/hr. and 0.39%.

References

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