The Colombian coffee growers face many complications when using traditional open-sun drying techniques such as post-harvest process delays or incomplete grain dryness because of climate conditions. Therefore, local workshops began fabricating low-capacity dryers simulating the industrial equipment working principles. One of the most commercialized units is a triple tray rectangular-shaped dryer with a 31.25 kg capacity of dry parchment coffee per batch, providing the issue with an acceptable solution. However, it was redesigned into a circular shape holding a lower grain bed thickness and a vertical air inlet with a diffusive tray. Both units were simulated using the Thompson and the Michigan State University grain drying mathematical models to obtain their theoretical drying time. Then, a computational fluid dynamics simulation was conducted, attaining the unit's drying air behavior, the circular dryer exhibited notable drying times reduction and even air distribution, optimizing the dryer's performance, representing a benefit for the coffee-growing farmers. Practical ApplicationsA cylindrical arranged coffee dryer with a vertical air inlet reduces the drying time of the grain, allowing a better rentability of the grower and improves the air distribution inside the equipment, meaning that the moisture removal will occur uniformly, safeguarding that the product's final moisture content meets the required conditions for safe storage.
HighlightsThe forced and natural convection drying processes of a single coffee grain can be predicted.The moisture distribution profiles depict the drying phenomena and water concentration zones.With accurate predictive drying curves, coffee growers can ensure high-quality coffee beans.Abstract. Different coffee drying technologies face complex tasks in ensuring an acceptable final seed moisture content. This research performed a Finite Element Analysis (FEA) study, simulating a single coffee bean's drying process as a transient mass diffusion model under mechanical and natural convection conditions, so the drying behavior and data of both case scenarios can be foreseen and controlled by a predictive Finite Element Model (FEM). A wet bean was 3D-scanned and digitized as the FEA simulation geometry; the water diffusion between the grain and the atmosphere was defined by a diffusion coefficient subject to the drying air temperature and the grain's moisture content. Three cases were studied: mechanical grain drying at three different temperatures (50, 45, and 40°C) in a forced convection environment; variable natural convection drying under environmental conditions (wet and dry season); and constant natural convection (wet and dry season), including the variation in day/night temperature and relative humidity. The results agree well with the data found in the literature, obtaining the graphical moisture distribution of the phenomena, predictive drying curves, diffusion coefficients, and isotherms. Both simulated drying scenarios provide essential information for coffee growers to improve and control their drying processes, thus obtaining high-quality grains, reducing contamination by microorganisms, and ensuring the integrity of their products. Keywords: Coffea arabica, Coffee Drying, Coffee Seed, Finite Element Model, Moisture Diffusion.
The thermophysical properties of coffee have a special partaking during the drying process since a material‐depending heat and mass transfer occurs between the bean and the drying air. Conditional to the thermophysical properties of the parchment coffee, the drying can be more or less efficient, affecting the final quality and seed safety. Several coffee varieties have been studied; however, the National Coffee Research Center of Colombia has developed new highly productive coffee varieties resistant to different diseases: Cenicafé 1 and Castillo®. Nevertheless, the thermophysical properties of these specific varieties were not yet investigated; moreover, the availability of information related to these properties of different coffee varieties in the literature is relatively scarce. Thus, this study targeted to determine the parchment coffee thermophysical properties of these new varieties at five different moisture contents % (wb): 53%, 42%, 32%, 22% and 11%, using optimized techniques and methods to ensure high accuracy and exactness. It was found that the new varieties have larger, heavier, and denser beans; it was also seen that the bulk thermal conductivity and the bulk‐specific heat are higher in these varieties than in the older ones. It was also revealed that the length, width, thickness, and surface area did not change as the moisture was removed, whereas the bulk density, kernel density, mass, bulk‐specific heat, and bulk thermal conductivity decreased as the moisture was reduced. Displaying better thermophysical properties will improve the drying and roasting processes; hence, a better final product can be expected from these varieties. Practical applications Knowing the thermal and physical properties of these new varieties will allow the growers and coffee processing facilities to predict, simulate and control different post‐harvesting processes such as pulping, fermentation, drying, storing, and roasting. Also, the already developed mathematical models to estimate coffee drying times can be updated, improving the accuracy of the predictions, bed porosities, mass, and heat transfer in order to safeguard the innocuousness of the product.
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