A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering

Thesis (M.Eng.) - Asian Institute of Technology, 1996

In this study, a spouted bed dryer with teflon pellets was used to study heat transfer and to produce milk powder. The experiments were carried out to determine the effect of factors such as air and feed flow rates, inlet air temperature and pellet surface area on the surface heat transfer coefficients, using water as feed. Later empirical models for estimating the heat transfer coefficient and outlet air temperature were developed. The values of heat transfer coefficient at various operating conditions ranged from 8.6 to 284.0 W/m2.K. Drying experiments on preconcentrated whole-fat milk varying in concentration of total solids from 20 to 40% were carried out using different inlet air temperatures and flow rates, and liquid feed rates. The quality of dried milk powder sample was analyzed in terms of the moisture content, solubility index and color difference relative to a commercially produced spray-dried sample. The milk powder with overall good quality could be produced at inlet air temperature ranging from 115°C to 130°C, concentration of milk 30 to 40%, air flow rate 221 m3/h, feed rate 1.2 to 1.5 kg/h and mass of teflon pellets as 0.6 kg. The experimental values of heat transfer coefficients during the milk powder production ranged from 14 to 57 W/m2.K and could be estimated as well from the model developed using water as feed. A general comparison of the spouted bed drying process with the spray drying revealed some advantages and disadvantages requiring further study. The main disadvantage appears to be the reduction in the solubility of dried powder. However, the spouted bed dryer can be used for the drying of liquid foods, especially for the small scale operation with less stringent operating requirements.