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The aim of this work was the determination of desorption isotherms from cocoa beans at different temperatures (20°C, 30°C, 35°C, 40°C and 45°C), moisture ratio (10% and 90%). Gravimetric method and different temperatures were used to get the experimental moisture ratio at equilibrium. Experimental data were adjusted to mathematical isotherm models frequently used for the hygroscopic representation of agricultural products. Cocoa beans varied from 0 to 13% moisture ratio equilibrium. Obtained results showed that the moisture ratio at equilibrium decreases as temperature increases for the same relative humidity. Statistical parameters, modified the Oswin model, GAB, Iglesias Chirife Hasley and Chungs Pfost modified model better represented hygroscopic balance for cocoa beans than Henderson modified and Harkings Jura models. Desorption isotherm models are important for the determination of desorption energy and drying models. The desorption isotherms of cocoa beans were satisfactorily modeled by modified Oswin, GAB, Iglesias, Chirife, Halsey, and modified Chungs Pfost, which can be used as tools in the prediction and optimization of storage conditions in a wide range of water activities and temperatures.

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Solar drying is used to reduce post-harvest losses. An indirect solar dryer with oriented air is presented. It provides the ability to store energy. This work predicts the outlet temperature at the collector in the single-face and bifacial modes of collector. The heat balance applied to each element is determined taking into account the temporal term which characterises storage in the material. The simulation is done using Matlab software. Both models of the collector are validated by comparing the experimental and theoretical curves. The results show that the two curves of outlet temperatures have the same profile when the global heat transfer coefficient loss is 2.94 W.m -2 .K -1 , the contact resistance between the absorber and the insulator is 0.025 W -1 .m2.K and the velocity is 0.2 m.s -1 . The contact resistance has a significant influence on the outlet air temperature but not accessible for controlling temperature compared to the velocity. G.B. Tchaya et al.Martin Kamta is an Associate Professor in Electronics at the University of Ngaoundere. His main range of scientific interests is physics of semiconductor devices, electronics and photovoltaic systems. He has published three articles in electron spin resonance (ESR) of defects in III-V materials, three articles in superconducting materials, one article and six communications about photovoltaic systems. He has supervised several PhD, several Master's degree theses and several Master engineering.Michel Havet received his Doctorate in Aerodynamics, Fluid Mechanics, Combustion and Thermal from the University of Poitiers in 1995. He is currently in charge of Food Process Engineering Department at ONIRIS, France. His research activities concern the aerodynamics and increased transfers in food processing. He has published close to 25 papers in refereed journals and has supervised several Masters and PhD theses.César Kapseu is a Professor of Process Engineering at the University of Ngaoundere. He has published close to 100 papers in refereed journals and is a holder of more than ten prestigious awards. He has supervised several Masters and PhD theses. He has equally held several posts of responsibilities at the University of Ngaoundere.

This work presents the regulation of temperature in an indirect multitrays solar dryer with oriented flux under the irradiance fluctuation. The temperature regulator using a negative temperature coefficient (NTC) as a sensor and fans is designed, and a similar device is also used to measure humidity through a sensor. Inlet and outlet dryer temperature and temperature on the three trays have been recorded with the regulation system according to different airflow modes. Irradiance and humidity have also been recorded. The model of outlet temperature with energy storage was given by using heat transfer equations. The results have shown that in the linking airflow mode, the average temperature on the three trays is 51.3 ± 1.5a°C, 52.18 ± 1.4a°C, and 51.9 ± 1.2a°C, respectively, with 52°C as setpoint temperature and NTC fixed on tray number 2. With temperature sensor in the same tray and 51°C as setpoint temperature, the average temperatures on the three trays are 51.86 ± 1.54°C, 51.60 ± 1.16°C, and 50.42 ± 1.13°C, respectively, in mixed mode, whereas in crossing airflow mode, the temperature gradient does not allow regulation on all trays. The regulation is possible when the temperature in the dryer chamber exceeds the set point temperature by more than 5%. The proportional type corrector is suitable for the temperature controller in indirect solar dryers. When the energy source is unstable, humidity which is a variable parameter is used to mark the end of drying instead of time.