Issue 3 (203)/2025

ALSE and ACS Style
Abeye, T.A.; Nurgie, T.L.; Anawte, D.A. Optimisation of the performance of a cleaning-type teff thresher using response surface methodology. Journal of Applied Life Sciences and Environment 2025, 58 (3), 469-480.
https://doi.org/10.46909/alse-583186

AMA Style
Abeye TA, Nurgie TL, Anawte DA. Optimisation of the performance of a cleaning-type teff thresher using response surface methodology. Journal of Applied Life Sciences and Environment. 2025; 58 (3): 469-480.
https://doi.org/10.46909/alse-583186

Chicago/Turabian Style
Aseffa, Tasfaye Abeye, Tamirat Nurgie Lema, and Dereje Anawte Alemu. 2025. “Optimisation of the performance of a cleaning-type teff thresher using response surface methodology.” Journal of Applied Life Sciences and Environment 58, no. 3: 469-480.
https://doi.org/10.46909/alse-583186

Optimisation of the performance of a cleaning-type teff thresher using response surface methodology

Tasfaye Abeye ASEFFA*, Tamirat Nurgie LEMA  and Dereje Anawte ALEMU

Department of Agricultural Engineering Research, Ethiopian Institution of Agricultural Research, Melkassa, Ethıopıa; email: miracot21@gmail.com; drjalemu@gmail.com

*Correspondence: asst4907@gmail.com 

Received: Aug. 26, 2025. Revised: Oct. 03, 2025. Accepted: Oct. 07, 2025. Published online: Oct. 31, 2025

ABSTRACT. Traditional teff threshing methods are labour intensive, inefficient and prone to considerable post-harvest losses. To address these limitations, a mechanical teff thresher was designed and developed. However, the initial prototype demonstrated suboptimal threshing performance and cleaning efficiency. This study aimed to optimise the performance of the developed teff thresher through the application of empirical modelling and response surface methodology. The optimisation focused on the threshing unit, particularly the drum length and diameter. The machine was fabricated from mild steel, angle iron, aluminium and round bar materials. Based on structural analysis, the total stress was 0.6776 MPa, the maximum shear stress was 0.00013242 MPa and the equivalent (Von Mises) stress was 16.126 kPa. Performance was evaluated at three drum speeds (1000, 1100, and 1200 rpm) and three feed rates (620, 660, and 700 kg/h), under a concave clearance of 0.03 m and a grain moisture content of 14%. A split-plot experimental design was employed, generating 27 observations that were analysed using the Design-Expert software. The results indicated that both drum speed and feed rate significantly influenced threshing performance. The maximum threshing capacity of 287.3 kg/h was achieved at a drum speed of 1200 rpm and a feed rate of 700 kg/h, representing an improvement from the baseline capacity of 187.5 kg/h. Increasing both drum speed and the feed rate within the studied range markedly enhanced the threshing efficiency and throughput of the machine. The optimised operating conditions are recommended to maximise the performance of the teff thresher.

Keywords: optimisation; response surface methodology; thresher.

 

INTRODUCTION

Tef (Eragrostis tef) is a native Ethiopian annual crop that is grown primarily in lowland and highland areas. It is used for different purposes, mostly as staple foods, especially to make injera. There are 350 tef varieties available and it is a significant source of both farm income and food and nutrition security (Gebru and Sbhatu, 2020). Tef is one of the major Ethiopian crops cultivated throughout the nation, next to maize, wheat, and barley (Barretto et al., 2021). In the main production season, tef was cultivated on 2,760,803.73 hectares in 2020/21 and 2,932,670.03 hectares, in 2021/22. The total in these years was 52,339,955.69 and 56,143,388.01 quintals, respectively. In the case of production for tef, in 2020/21 and 2021/22, yield production per hectare was 18.96 and 19.14 quintals, respectively (World Bank, 2023).

During the tef production, the methods of planting, harvesting, and threshing are challenges for farmers. Notably, the threshing process involves a high loss of operation, and it needs higher drudgery and low quality and quantity during threshing (Gidelew et al., 2022). The farmer practices that are threshed by animals represented a major problem of post-harvest loss, especially for tef, resulting in low quality, high drudgery, and time consumption. As a result, the threshed tef had lost quality of crop yield, and that reduced the value chain of the tef crop in food and the market system (Gebrehiwot and Ndinda, 2024). A post-harvest loss is the operation that reduced yield tef production and tackled the food insecurity problem as a whole. Also, Reduced returns for tef growers are the result of incorrect distribution, bad handling, and poor storage (Teferra, 2022). Post-harvest losses remain a major challenge to cereal production in Ethiopia. National estimates indicate that cereal losses range between 4.65% and 5.99%, with on-farm operational losses accounting for 3.90%-4.78% and storage losses for 0.75%-1.21% (Hengsdijk and de Boer, 2017). The main causes of these losses include delayed harvesting, inefficient threshing and winnowing practices, and inadequate storage conditions.

To mitigate these losses and to enhance the level of agricultural mechanisation, Ethiopian agricultural mechanisation research programmes have made significant contributions through the development of various technologies, such as teff planters, teff harvesters, multi-crop threshers and cleaning-type teff threshers (Ahmad et al., 2013). It is necessary to continuously modify these technologies to improve their threshing performance by optimising key design parameters such as the feed rate, the moisture content, and drum dimensions. Previous studies have demonstrated that factors including peg number and arrangement and the drum diameter and length have a substantial impact on threshing capacity, performance, grain damage and losses in longitudinal-flow threshing systems (Tadesse, 2020).

The performance of a cleaning-type teff thresher has been evaluated under varying operational parameters. The feed rate and drum speed, particularly at an optimal moisture content, are the most influential factors that affect threshing performance (Abich et al., 2018). Similarly, grain cleaning efficiency is primarily governed by drum speed, the feed rate, and the moisture content (Abeye, 2024). Dula (2016) recommended an operating drum speed of 1000-1200 rpm at an average moisture content of 14% to achieve optimal threshing performance.

The Melkassa Agricultural Engineering Research Center has developed a teff thresher based on the advancements reported in the literature. Although it is superior to traditional methods, it still exhibits low threshing capacity, efficiency, and cleaning performance, and requires substantial labour input. The thresher’s initial capacity of 187.5 kg/h is inadequate given Ethiopia’s high teff production and user feedback during field demonstrations.

Therefore, this study focuses on improving and optimising the performance of the Melkassa-developed teff thresher by examining key design and operational parameters, including crop characteristics, machine design factors and operational conditions. The primary aim was to enhance teff production efficiency and to minimise post-harvest losses while reducing operator drudgery. The findings from this study should contribute to the advancement of teff mechanisation and thereby improve national crop productivity and post-harvest management.

 

MATERIALS AND METHODS

The study was conducted in the towns of Awash Melkassa and Bushoftu in the East Showa Zone of the Oromia Region, Ethiopia.

Materials

The engineering properties of the teff crop were measured using a tap, a digital balance, and a Vernier calliper with a precision of 0.01 mm. The recorded parameters included plant height (L, mm), the spike height, and the biomass weight (W). Agronomic data were also collected during the evaluation. The equipment used for the performance tests included a tachometer for measuring drum speed, a stopwatch for timing operations, and a graduated cylinder for recording fuel consumption. These instruments were employed to obtain the data required for the experimental analysis.

Methods

The design and subsequent improvement of the teff thresher were based on the crop moisture content, concave clearance, the feed rate and drum speed. Numerical formulas were employed to determine the dimensions and performance characteristics of the main components, followed by simulation to validate the results. The Melkassa teff thresher was redesigned using the actual working dimensions of the prototype to optimise performance. The length of the belt between pulleys was determined using the standard formula (Istifanus et al., 2022):

where L is the effective length, C is the centre distance between the pulleys, and D and d are the diameters of the driven and driving pulleys, respectively.

The grain-to-straw ratio (δ) was calculated using the following empirical relationship (Sharma, 2010):

where qs is the straw output (kg/h) and qg is the grain output (kg/h).

The feed rate (Fr, kg/h) used for the optimisation and simulation is directly related to thresher performance and depends on drum diameter, drum length, the number and arrangement of pegs, and the inlet and outlet sizes. It was determined as the sum of the straw and grain outputs:

Drum speed is one of the main parameters that affects threshing efficiency. It was determined using the following empirical equation (Sharma, 2010):

where N is the drive speed (rpm), V is the peripheral drum speed (m/s), and d is the cylinder diameter (m).

Drum length was estimated as follows (Sharma, 2010):

where q is the thresher’s feed rate (kg/s), Rb is the number of rasp bars, N is the drum speed (rpm), Ld is the drum length (m), k is a constant (0.17-0.32 kg/m), and ψ is equal to 1/δ.

The total force required to thresh teff (Fr, N) was calculated as (Sharma, 2010):

where Ff is the friction force (N) and Fi is the impact force of the cylinder (N). The impact force (Fi), can calculated as:

where qr is the feed rate (kg/s), V1 is the entry velocity (i.e. the speed of teff as it enters the cylinder; m/s), and V2 is the exit velocity (i.e. the speed of teff as it leaves the cylinder; m/s). Note that V2 is linearly proportional to the cylindrical speed (V):

where R is the drum radius (m) and N is the cylinder speed (rpm).

The total threshing force is expressed as:

where f is the coefficient of friction for spike-tooth threshers (0.7-0.8).

The threshing power (Pt, W) was estimated using the following equation (Belay and Woldemichael, 2021):

where q is the feed rate (kg/s), V is the linear drum speed (m/s), and V1 and V2 are the entry and exit velocity, respectively. The linear drum speed typically ranges from 15 to 37 m/s at a moisture content of 14%-16%.

The power required to overcome air resistance and bearing friction (pf) was calculated as:

where k and z are constants for the coefficients of friction and (5-5.5 N) and air resistance (0.045 Ns2/m²), respectively, for spike-tooth threshers. Then, the total power (PT) required to operate the drum was calculated as:

The number of pegs on the drum (Nb) was calculated as:

For the Melkassa thresher, assuming a grain-to-straw ratio of 1:2 and a grain output of 300 kg/h, the straw output (qs) is 600 kg/h, resulting in a total feed rate of 900 kg/h (0.25 kg/s). With a recommended peripheral speed of 20 m/s, the corresponding drum speed is approximately 1200 rpm. Using these parameters, the total power requirement was found to be approximately 0.53 kW.

A 3D model of the improved thresher was developed in SolidWorks 2021 and exported as an IGES (*.igs) file for structural analysis in ANSYS Student 2025 R1 (Figure 1 and Figure 2). The threshing drum, made of mild steel, exhibited a total deformation of 0.6776 MPa, a maximum shear stress of 0.00013242 MPa, and an equivalent (Von Mises) stress of 16.126 kPa. These stress levels are within the safe limits for the material, indicating sufficient mechanical strength under operational loading from the crop and machine weight.

Evaluation of the teff thresher performance

A performance evaluation of the improved thresher was carried out to assess its cleaning efficiency, threshing efficiency and grain loss. The quantities of threshed, unthreshed and damaged grains and the proportion of blown grains were recorded (Kidanemariam, 2020). The threshing efficiency and threshing capacity were calculated as follows:

The performance of a thresher is primarily influenced by three groups of factors: machine parameters, crop properties, and operational conditions (Abich et al., 2018). Among these, drum speed and feed the rate were identified as the dominant factors affecting threshing performance. Figure 3 shows images of the teff thresher as well as pictures from the field test. A split-plot experimental design was employed for the experimental trials at three feed rates (620, 660 and 700 kg/h) and three drum speeds (1000, 1100 and 1200 rpm) using a split-plot design. Each combination was replicated three times, resulting in 27 total observations. For optimisation purposes, the Design Expert 11 software was used to analyse the effects of independent variables – drum speed, the feed rate, plant height, spike height, the grain-straw ratio, and concave clearance – on the dependent variable, threshing capacity.

 

 

 

 

The data are presented as the mean ± standard deviation and were analysed using the R statistical software, employing analysis of variance to determine the significance of differences among treatments. The least significant difference test was applied to separate treatment means to determine significant differences (P ≤ 0.05). The following variables were analysed: the effective threshing capacity, threshing efficiency, the feed rate, fuel consumption, moisture content and drum speed.

 

RESULTS AND DISCUSSION

Table 1 presents the average engineering properties of the Boset teff variety, including the maximum and minimum plant height, spike height and moisture content under threshing conditions. The maximum and minimum plant height were 62.45 and 42.32 cm, respectively, while the spike height ranged from 25.12 to 35.42 cm. The moisture ranged from 11.35% to 15%.

Table 2 indicates that both the feed rate and drum speed have a significant effect on threshing capacity (p < 0.05). The threshing capacity ranged from 215.03 kg/h (recorded at a feed rate of 620 kg/h with a drum speed of 1000 rpm) to 287.3 kg/h (recorded at a feed rate of 700 kg/h and a drum speed of 1200 rpm) when operated for 1 h. These findings align with a previous study (Ahmad et al., 2024), confirming that increasing drum speed and feed rate significantly enhance threshing capacity. Moreover, as drum speed and the feed rate increase, threshing performance improves, accompanied by a corresponding rise in fuel consumption. The data demonstrate a clear positive correlation between drum speed, the feed rate and both threshing capacity and fuel usage.

Table 3 shows that thresher capacity is directly related to both the feed rate and drum speed. Although the maximum threshing capacity of 287.3 kg/h occurred at a feed rate of 700 kg/h and a drum speed of 1200 rpm, the optimisation results suggest that the maximum achievable threshing capacity could reach approximately 300 kg/h (Figure 4).

 

Table 1
Engineering properties of the Boset teff variety

Variable	Average minimum	Average maximum
Plant height (cm)	42.32 ± 0.23	62.45 ± 0.12
Spike height (cm)	25.12 ± 0.3	35.42 ± 0.27
Moisture content (%)	11.35	15

 

Table 2
Analysis of variance for threshing capacity of the Boset teff variety

Sources	DF	SS	MS	F	P
Feed rate	2	0.02794	0.01397	0.0147	0.014**
Drum speed	2	0.01620	0.0178	0.1752	0.000142***
Feed rate × drum speed interaction	4	0.02285	0.00571	0.0475	0.0124**
Moisture	2	0.00049	0.00025	0.56	0.5821
Fuel consumption	2	0.00049	0.00025	0.56	0.5102

DF, degrees of freedom; MS, mean square; SS, sum of squares

 

Table 3
Performance evaluation of the teff thresher

Feed rate (kg/h)	Drum speed (rpm)	Capacity (kg/h)	Fuel consumption (L/h)
700	1200	287.30 ± 11.6a	2.045 ±12a
700	1100	285.57 ± 11ab	2.011 ± 0.3ab
700	1000	283.37 ± 11bc	2.021 ± 0.8ab
660	1200	280.40 ± 11bc	2.015 ± 13ab
620	1200	263.97 ± 11bc	2.072 ± 0.1ab
660	1100	257.33 ± 11cd	2.07 ± 0.3b
660	1000	250.37 ± 11de	2.03 ± 0.8b
620	1100	228.03 ± 12e	2.003 ± 0.4b
620	1000	215.03 ± 11bc	2.0011 ± 0.8ab

 

 

The optimal design parameters for achieving this performance include a drum length of 0.98 m, a drum diameter of 0.80 m, a drum speed of 1200 rpm, and a feed rate of 700 kg/h.

Figure 5 shows optimisation of thresher performance. According to the regression analysis, threshing capacity increases by 0.3884 kg/h for every 1 kg/h increase in feed rate, with a coefficient of determination (R²) of 0.6766, indicating that 67.66% of the variation in threshing capacity is explained by the feed rate.

Similarly, the threshing capacity increases by 0.02329 kg/h for every 1 rpm increase in drum speed, with an R² of 0.8637, meaning that 86.37% of the variation in threshing capacity is explained by drum speed.

 

 

These findings are consistent with previous research on chickpea threshing optimisation, where cylinder speed, the feed rate, concave clearance and the moisture content significantly influenced seed germination, grain damage, threshing capacity and threshing efficiency (Salari et al., 2013). Likewise, Khayer et al. (2019) reported that threshing performance is strongly affected by operational parameters such as drum speed, the feed rate, the moisture content and fuel consumption.

 

CONCLUSIONS

This study provides valuable insights into the performance of a threshing machine that was designed to efficiently thresh teff. The machine exhibited optimal threshing efficiency at 1200 rpm with a feed rate ranging from 660 to 700 kg/h, although the differences were not statistically significant. The maximum threshing capacity and efficiency recorded were 287.03 kg/h at a feed rate of 700 kg/h and a drum speed of 1200 rpm, with a moisture content of the threshed biomass of 11.35%-15%. Of note, a higher moisture content during operation causes engine stalling, so the moisture content significantly affects threshing capacity and efficiency. The ideal moisture content for teff threshing is 12%-14%, which enhances performance when combined with the recommended drum speed.

So far, farmers in Ethiopia have responded positively to this technological advancement, recognising its potential to improve their livelihoods. With rising labour and animal costs, a shift towards mechanical threshing is expected to accelerate, impacting smallholder teff producers in local communities. Continued support for the adoption and training in the use of these machines is essential to maximise their benefits.

Utilising established custom hiring services allows farmers to access this technology while mitigating the financial burden associated with traditional threshing methods. This suggests a promising future for teff threshing driven by technological innovation and efficiency improvements.

 

RECOMMENDATIONS

Smallholder households stand to benefit significantly from the adoption of mechanisation technologies for teff, wheat and barley through reduced grain losses and increased income due to improved handling and better market prices.

Policymakers, local manufacturers, researchers and agricultural extension workers will also benefit across various value chains by supporting the development and use of teff threshers, which can further drive research and machine improvement. Researchers and university students are encouraged to apply response surface methodology to optimise post-harvest technologies to enhance design and to improve performance.

 

Author contributions: Conceptualization: TAA, TLN, DAA; Proposal writing: TLN; Methodology: TAA, TLN; Technical advice: TAA, TLN; Data pre- and post-processing: TAA, TLN, DAA; Statistical analysis: TAA, TLN, DAA; Draft writing and reviewing; TAA; Draft editing and finalizing: DAA. All authors declare that they have read and approved the publication of the manuscript in this present form.

Data availability statement: The data presented in this study are available on request from the corresponding authors.

Conflicts of interest: The authors declare no conflict of interest.

 

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