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 2.36×10−8m2/s in the heat pump dryer, and 1.03×10−8m2/s in the solar dryer. For both systems, the moisture ratio was analyzed with the Statgraphic program by using semi-theoretical 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.