INTERNATIONAL JOURNAL OF ENERGY RESEARCH Int. J. Energy Res. 2004; 28:739–752 (DOI: 10.1002/er.997) Mathematical modelling of a thin layer drying of apricots in a solar energized rotary dryer E. Kavak Akpinar 1,n,y , C. Sarsılmaz 2,z and C. Yildiz 1,} 1 Mechanical Engineering Department, Firat University, Elazig, 23279, Turkey 2 Mechanical Education Department, Firat University, Elazig, 23119, Turkey SUMMARY In this paper we present a mathematical modelling of a thin layer forced solar drying of apricots. An indirect forced convection solar dryer consisting of a solar heater and a rotary column cylindrical drying (RCCD) cabinet was used in the experiments. Air heated by the solar air heater was forced through the apricots by an electrical fan. Moreover, the natural sun drying experiments were conducted for the comparison at the same time. Fourteen different thin layer mathematical drying models were compared according to their coefficients of determination (r; w 2 ; RMSE) to estimate solar drying curves. The effects of the drying air temperature, velocity and the rotation speed of column on the drying model constants and coefficients were predicted by multiple regressions using a linear type model. Copyright # 2004 John Wiley & Sons, Ltd. KEY WORDS: solar drying; solar dryer; thin layer drying models; forced drying; energy 1. INTRODUCTION Drying is one of the preservation methods of agricultural products (Dincer, 1998) and also a complex thermophysical and biochemical process comprising simultaneous heat and mass transfer between the surface of the material and the surrounding media, and a transfer of heat and moisture within the material (Hossain and Bala, 2002). Cost-effective and hygienic ways of preserving foods is of a great importance given the prevailing insecurity in food supplies throughout the world. The introduction of solar dryers in the developing countries can reduce crop losses and improve the quality of the dried product significantly compared to the traditional methods of drying such as sun or shade drying (Togrul and Pehlivan, 2003). However, properly designed solar dryers not only meet the particular drying requirements of crops of interest but also increase the energy efficiency and the conservation of agricultural management practices. Solar dryers have usage potential all over Turkey because of its high insulation and sunshine duration. Received 12 February 2003 Accepted 12 June 2003 Copyright # 2004 John Wiley & Sons, Ltd. y E-mail: eakpinar@firat.edu.tr n Correspondence to: Dr Ebru Kavak Akpinar, Mechanical Engineering Department, Firat University, 23279, Elazig, Turkey. z E-mail: csarsilmaz@firat.edu.tr } E-mail: cyildiz@firat.edu.tr