Thermohygrometric sensor: a tool for optimizing the spray drying process

The introduction of a thermohygrometer into the outlet air of a spray-drying chamber allows measurement and observation of absolute and relative humidities. As an example, there is no powder stuck in a spray-drying chamber of a three-stage pilot plant when the difference between calculated and measured absolute humidity of the outlet air is below 2 g of water kg(-1) dry air. To obtain a whole milk, skim milk or whey powder at 0.20 +/- 0.02 of water activity (at 25 degrees C), the relative humidity of the outlet air must be equal to 11%+/- 1 for whole milk powder and 7%+/- 1 for whey and skim milk powders. (c) 2004 Elsevier Ltd. All rights reserved