SHORT COMMUNICATION Sun drying of cocoa with firebrick thermal storage materials Clement A. Komolafe 1 | Mufutau A. Waheed 2 | Sidikat I. Kuye 2 | Babatunde A. Adewumi 3 | Iyiola O. Oluwaleye 4 | Tajudeen M. Adeniyi Olayanju 5 1 Department of Mechanical Engineering, College of Engineering, Landmark University, Omu Aran, Nigeria 2 Department of Mechanical Engineering, College of Engineering, Federal University of Agriculture, Abeokuta, Nigeria 3 Department of Agricultural and Bioresources Engineering, College of Engineering, Federal University of Agriculture, Abeokuta, Nigeria 4 Department of Mechanical Engineering, Faculty of Engineering, Ekiti State University, Ado-Ekiti, Nigeria 5 Department of Agricultural and Biosystems Engineering, College of Engineering, Landmark University, Omu Aran, Nigeria Correspondence Clement A. Komolafe, Department of Mechanical Engineering, College of Engineering, Landmark University, P.M.B 1001, Omu Aran, Nigeria. Email: clemkunle@yahoo.co.uk Summary The thin-layer drying process of N38 cocoa beans using open-sun and a solar drying (SD) system with firebrick heat storage materials (FTSM) has been modeled. The 10 kg capacity force convective SD system was developed and used to carry out the experiments. The choice of the best model was based on a comparison of statistical indicators including determination coefficient (R 2 ), reduced chi-square (χ 2 ), root mean square error (RMSE), sum of square error (SSE), and normalized root mean square error (NRMSE) after fitting the exper- imental results to 11 common thin layer models in the literature. The results revealed that under open-sun drying and SD processes, the Midilli et al model provided the best drying characteristics of cocoa beans. Therefore, in the exper- imental context, this model can be assumed to reflect the solar/sun drying behavior of cocoa. The effective diffusivity values for the open-sun and SD of cocoa with FTSMA and FTSMB were 4.25× 10 -11 , 6.64× 10 -11 , and 5. 95 × 10 -11 m 2 /s respectively. The predicted pre-exponential factor and activation energy were 5.81 × 10 -11 m 2 /s and 22.79 kJ/mol respectively. KEYWORDS cocoa beans, diffusivity, drying kinetics, firebricks, heat storage, modelling 1 | INTRODUCTION Cocoa is one of Nigeria's most important perennial cash crops. In 2000, the Federal Government formed the National Cocoa Development Committee (NCDC) to rejuvenate the production of cocoa in order to diversify its economy. As a follow-up to the inauguration of the committee, a special program tagged cocoa re-birth pro- cess was launched in 2005 by the President Federal Republic of Nigeria. There are a variety of steps in the process of conditioning cocoa beans for industrial use to improve its value. These include pod maturity (appropri- ate maturity), pod cracking, removal of seed, fermenta- tion, drying, sorting, and storing. Fermentation and drying are important elements in pre-shipping processing of cocoa beans after harvest for storage. The steps play vital roles in the formation of high-quality products. Improper drying in many processes can result in irrevers- ible damage to the quality of the product and hence a non-sellable product. Drying is a convoluted thermal process of unpre- dictable heat and moisture transfer simultaneously. Dry- ing generally entails complex processes of heat and mass transfer in which extraction of moisture occur through Abbreviations:D eff , effective diffusivity (m 2 /s); D o , Arrhenius pre- exponential factor (m 2 /s); DR, rate of drying (g /g wet solid h); E, activation energy (kJ/mol) i terms number; M, moisture content (%); N, number of observations; NMRSE, normalized root mean square error; R 2 , coefficient of determination; RMSE, root mean square error; SSE, sum of square error; W, weight of the sample (g). Received: 3 December 2019 Revised: 7 March 2020 Accepted: 8 March 2020 DOI: 10.1002/er.5364 Int J Energy Res. 2020;1–11. wileyonlinelibrary.com/journal/er © 2020 John Wiley & Sons Ltd 1