Determination of drying characteristics of apples in a heat pump and solar dryer

Both a heat pump and solar dryer were designed and manufactured. They were experimentally analyzed by drying apples, and a comparison was made between the two. Apples were sliced 4 mm thick, and dried from 4.8 (g water/g dry matter) moisture content to 0.18 (g water/g dry matter) at 3.3 kg/m2s–2.4 kg/m2s mass air velocity for 3.5 h in a heat pump dryer. Apples were also dried at the range of 3.3 kg/m2s and 2.9 kg/m2s mass air velocity from 4.8 (g water/ g dry matter) moisture content to 1 (g water/ g dry matter) moisture content in the same period in a solar dryer. Effective moisture diffusivity was found to be 2.36×10!8 m2/s in the heat pump dryer, and 1.03×10!8 m2/s in the solar dryer. For both systems, the moisture ratio was analyzed with the Statgraphic program by using semitheoretical models and compared to the empirical values. Correlation coefficients of the equations were calculated and standard error of estimation (SEE) and R2 values were obtained.