Hot Air Drying Characteristics of Yunnan Small Seed Coffee and Its Mathematical Model

doi:10.3969/j.issn.1000-2561.2022.03.022

Abstract

Abstract:

Yunnan small seed coffee was used to explore the characteristics and optimal mathematical model of hot air drying. The hot air drying characteristics of the coffee beans under different circumstances were studied by an orthogonal experiment with wind speed, pavement thickness and stirring speed, and the applicability of 10 mathematical models in hot air drying characteristics was compared. The results showed hot air velocity could promote the heat and mass transfer in the drying process. The mixing process not only could accelerate heat transfer, but also improve heat efficiency and reduce drying time. Coffee bean pavement thickness mainly affected the drying time. The pavement thickness was inversely proportional to the change of drying rate. Data analysis revealed the drying was mainly characterized by decreasing drying speed, and there was no obvious constant speed drying stage, and the hot air temperature had the greatest influence on the drying characteristics of hot air drying. According to the range and variance analysis of the orthogonal experiment, the optimal hot air drying scheme was temperature 40℃, wind speed 1 m/s and stirring speed 2 r/min. The optimal mathematical model was an logarithmic equation. The range values of the influence of hot air temperature, hot air speed and stirring speed on the total hot air drying time was 19, 6.67, 5.5, respectively. P value of the three factors under 95% confidence interval was 0.011, 0.082 and 0.391 respectively. The primary and secondary order was hot air temperature A> hot air speed B> stirring speed C. Logarithmic model was analyzed by the nonlinear regression fitting of evaluation index R², SSE, mean square of residual and comparison experimental data with commonly used drying model. According to the date analysis, the results showed that the best-fitting degree of Logarithmic model, R² is 0.986444, SSE is 0.021734, mean square of residual is 0.002075. Taking all the factors into conclusion the mathematical model not only can predict the hot air drying characteristic curve of Yunnan arabica wet beans, but also provide a theoretical basis and reference for the actual production and processing of small seed coffee.

Key words: small seed coffee, hot air drying, drying characteristics, mathematical mode

CLC Number:

TS273

LI Yanan, WU Jian, CHEN Zhihua, JIANG Kuaile, HAN Zhengtong, WANG Xiang, CHEN Jiahao. Hot Air Drying Characteristics of Yunnan Small Seed Coffee and Its Mathematical Model[J]. Chinese Journal of Tropical Crops, 2022, 43(3): 622-633.

Figures/Tables 17

References 29

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模型 Model	模型方程 Model equation	参考文献 References
Henderson and Pabis	MR=a·exp(-kt)	[18]
Page	MR= exp(-ktⁿ)	[18]
Single exponential	MR=exp(-kt)	[19]
Logarithmic	MR=a·exp(-kt)+c	[19]
Two-term exponential	MR=a·exp(-k₀t)+b·exp(-k₁t)	[19]
Wang and Singh	MR=1+at+bt²	[19]
Lewis	MR=exp(-kt)	[20]
Verma et al.	MR=a·exp(-kt)+(1-a)exp(-gt)	[20]
Midilli et al.	MR=a·exp(-ktⁿ)+bt	[20]
Modified page	MR=exp[-(-kt)ⁿ]	[21]

模型 Model	模型方程 Model equation	参考文献 References
Henderson and Pabis	MR=a·exp(-kt)	[18]
Page	MR= exp(-ktⁿ)	[18]
Single exponential	MR=exp(-kt)	[19]
Logarithmic	MR=a·exp(-kt)+c	[19]
Two-term exponential	MR=a·exp(-k₀t)+b·exp(-k₁t)	[19]
Wang and Singh	MR=1+at+bt²	[19]
Lewis	MR=exp(-kt)	[20]
Verma et al.	MR=a·exp(-kt)+(1-a)exp(-gt)	[20]
Midilli et al.	MR=a·exp(-ktⁿ)+bt	[20]
Modified page	MR=exp[-(-kt)ⁿ]	[21]

水平 Level	热风温度 Hot-air temperature/℃	风速 Wind speed/(m·s^-1)	搅拌转速 Stirring speed/(r·min^-1)
1	30	1.0	0.5
2	40	1.3	2.0
3	50	2.0	4.0

水平 Level	热风温度 Hot-air temperature/℃	风速 Wind speed/(m·s^-1)	搅拌转速 Stirring speed/(r·min^-1)
1	30	1.0	0.5
2	40	1.3	2.0
3	50	2.0	4.0

因素 Element	水平 Level	平均水分扩散系数 Mean water diffusivity
温度	35	2.26077E-10
	45	2.85584E-10
	55	4.12895E-10
风速	0.8	1.9076E-10
	1.6	2.85584E-10
	2.5	3.34842E-10
搅拌转速	1	3.9495E-10
	3	2.68627E-10
	5	1.94519E-10
铺装厚度	1	3.38824E-10
	3	1.94519E-10
	5	1.31505E-10