Application of Bi–S Drying Correlation to Microwave Drying Data of Pharmaceutical Powders

Abstract

The moisture diffusivities and moisture transfer coefficients characterising the drying of pharmaceutical powders were determined using a correlation proposed by Dincer et al. (2002, Development of a new drying correlation for practical applications. International Journal of Energy Research 26, 245–251). Experimental moisture content data for lactose, Aspirin and Paracetamol samples dried under convective, microwave, combined convective-microwave and combined vacuum-microwave conditions were obtained. The drying coefficients and lag factors were determined from the experimental measurements and incorporated into the model. The mass transfer Bi numbers were found to be in the range 0.058 to 0.194, indicating the presence of finite internal and external resistances. Moisture diffusivity and diffusion coefficient values in the range 0.135 × 10−9 to 102 × 10−9 m2 s−1 and 0.067 × 10−7 to 8.21 × 10−7 ms−1 respectively, were calculated. The predicted moisture profiles showed adequate agreement with the experimental observations, with the average error between experimental and predicted results being ± 15.9%.