Abstract
The objective of this work is to analyse the extent to which a change in the drying air velocity may affect the drying kinetics of tomato in a forced-convective solar tunnel dryer. 2 m⋅s−1 (V1) and 3 m⋅s−1 (V2) air speeds were applied in similar drying air temperature and humidity conditions. Main drying constants calculated included the drying rate, the drying time and the effective water diffusivity based on the derivative form of the Fick’s second law of diffusion. Henderson and Pabis Model and Page Model were used to describe the drying kinetics of tomato. We found that solar drying of tomato occurred in both constant and falling-rate phases. The Page Model appeared to give a better description of tomato drying in a forced-convective solar tunnel dryer. At t = 800 min, the drying rate was approximately 0.0023 kg of water/kg dry matter when drying air velocity was at 2 m/s. At the same moment, the drying rate was higher than 0.0032 kg of water/kg dry matter when the drying air velocity was 3 m/s. As per the effective water diffusivity, its values changed from 2.918E−09 m2⋅s−1 to 3.921E−09 m2⋅s−1 when drying air velocity was at 2 and 3 m⋅s−1 respectively, which is equivalent to a 25% increase. The experimentations were conducted in Niamey, on the 1st and 5th of January 2019 for V2 and V1 respectively. For both two experiments, the starting time was 9:30 local time.
Highlights
Our results show that increasing the drying air velocity from 2 m/s to 3 m/s leads to a 25% increase of water effective diffusivity during tomato drying
The drying constants we obtained from modelling of drying kinetics for tomatoes are in the range of values obtained by other authors who worked on forced convective solar drying experiments
The values we found for effective diffusivity ( Deff ) of water (2.918E−09 m2/s under V1 and 3.921E−09 m2/s under V2) are in the range of values (1E−10 to 1E−8 m2/s) agreed by majority of authors we reviewed
Summary
The FAO [2] has estimated the gross production of tomatoes in 2012 in Niger at 188,767 tons. In order to avoid post harvest losses of tomato production, improve quality of dried tomatoes and respond to the significant demand of dried tomatoes in Niger, solar drying appears to be an effective method. Solar tunnel dryer reduces crop losses, improves the quality of dried product significantly and is economically beneficial compared to traditional drying methods. Few authors concluded that drying of tomatoes is occurring only in the falling rate phase. Other authors have rather established that drying of tomatoes is occurring in both a constant rate and a falling rate phases. We found that tomato slices drying was occurring in both constant rate and falling rate phases. All experiments were conducted under climatic conditions of Niamey (Niger) during the first week of January 2019
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