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Parametric Thermodynamic Models of Parchment Coffee Beans during HARC2S Dehydration

Rodríguez RF and Francisco M

Parametric thermodynamic models have been developed to predict the temperature and moisture content wet base (M.C. (w.b.)) of parchment coffee beans during dehydration process in a hot air recirculation controlled-closed system (HARC2S). The principals of energy and mass transfer conservation during dehydration are the basis of the models. Experimental data of the moist air dry-bulb temperatures, relative humidity, and barometric pressure of the air entering and leaving the coffee beans are used to calculate the air thermal physical properties. These properties are used in the temperature prediction model. The coffee mass aspect ratio as determined by the HARC2S organic material chamber, predicted temperature, water-coffee effective diffusivity coefficient, and initial measured moisture content are required in the M.C. (w.b.) model. The experimental temperature data profile behavior appeared to be of a lumped-capacitance nature, while the M.C. (w.b.) experimental data had a linear constant rate decent behavior during dehydration. The linear decent appears to be an inherent characteristic property of the HARC2S dehydration process. The models prediction average errors as compared to the experimental data were, ± 1.8803% error for the temperature, and ± 1.8599% error for the M.C. (w.b.). The coffee processors will directly benefit from the developed thermodynamic models. They will have the capacity to continually monitor the parchment coffee beans temperature and M.C. (w.b.), while keeping the environmental integrity of the HARC2S during dehydration processes. The integrity is maintained by not opening the HARC2S until the desired M.C. (w.b.) of 10% to 12% is reached. Maintaining the environmental integrity of the HARC2S has the following advantages: (1) system energy efficiency is maintained within quasi-adiabatic environment; (2) coffee contamination from foreign objects is eliminated; (3) potential of bacterial and/or fungal growth are minimized. Thus, using the HARC2S has the potential benefit of insuring coffee bean safety and quality.