Study of Water Desorption Isotherms from Cocoa Beans (Theobroma Cacao L.) of Cameroon

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

Regulation of Temperature on Multitrays in an Indirect Solar Dryer (ISD) with Energy Storage and Three Airflow Modes

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