# CFD-Simulink Modeling of the Inflatable Solar Dryer for Drying Paddy Rice  
[PERSON]  
1 Tropics and Subrophysics Group (440e), Institute of Agricultural Engineering, University of Hohenheim,  
70599 Stuttgart, Germany; 1  
[PERSON]  
2 Tropics and Subrophysics Group (440e), Institute of Agricultural Engineering, University of Hohenheim,  
70599 Stuttgart, Germany; 1  
[PERSON]  
1 Tropics and Subrophysics Group (440e), Institute of Agricultural Engineering, University of Hohenheim,  
70599 Stuttgart, Germany; 1  
[PERSON]  
2 Tropics and Subrophysics Group (440e), Institute of Agricultural Engineering, University of Hohenheim,  
70599 Stuttgart, Germany; 1  
Footnote 1: [[https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci)]([https://www.mdpi.com/journal/applsci](https://www.mdpi.com/journal/applsci))  
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The dissemination of flat-bed dryers for paddy rice has been promoted since the 1970s in the Republic of the Philippines, but this technology was not well received by farmers. Some of the reasons behind the lack of adoption were the higher operating and maintenance costs compared to traditional sun drying practices [14]. As an alternative, in the 1980s, the solar tunnel dryer was tested for paddy rice at the International Rice Research Institute (IRRI) in the Republic at the Philippines headquarters. Despite the drying performance being promising, mixing the grains along the tunnel dryer was challenging [9; 15]. Several interventions followed that offered alternative drying practices. However, in most instances, energy usage and loading capability restricted the acceptance of these technologies. Therefore, under this scenario, the inflatable solar dryer (ISD) was developed through a collaboration of the University of Hohenheim, the IRRI, and GrainPro Philippines Inc., who manufactured the dryer (trade name \"Solar Bubble Dryer\"M\") [16]. The ISD is a further development of the solar tunnel dryer, which was developed by the University of Hohenheim in the 1980s. The ISD design characteristics are: ease of transport and installation; simple operation compared to mechanical dryers; low maintenance since it is made of plastic material. Currently, the ISD has been successfully tested on paddy rice [16; 17], amaranth leaves [18], mushrooms [19], and maize [20]. However, information on airflow distribution or heat and mass transfer of the ISD is still lacking. According to [PERSON] and [PERSON] [21], four methods are widely used to model and analyze solar dryer systems. The first method is thermodynamic modeling using semiempirical equations. The second method is to establish differential equations that are solved by using computational fluid dynamics (CFD). The third method is based on statistical methods that use a series of experiments to develop empirical equations. The fourth method is the reacting engineering approach based on the chemical reaction subject to the drying process. Researchers such as [PERSON], et al. [22] have mostly used the first method for modeling solar tunnel dryer designs. Their study provided an approach for the simulation of a solar tunnel dryer, considering heat transfer and mass transfer equations to predict temperatures, product temperature, and moisture content. The numerical solution was programmed in BASIC language. A similar method was reported by [PERSON], et al. [23]. The study generates a comprehensive numerical solution programmed in Compaq Visual Fortran. The results showed a good agreement between the simulated and the experimental values of temperatures and moisture content. [PERSON] [24] combines the first and second modeling methods where the program ESATAN was applied to solve the thermal model around the solar tunnel dryer. The simulated crop temperature and moisture content were in good agreement with the experimental data.