Simultaneous heat and mass transfer studies in drying ammonium chloride in a batch-fluidized bed dryer

Abstract

Simultaneous heat and mass transfer occurs during drying. Fluidized bed drier, unlike other types of dryers is more sensitive to the variation of moisture content of the material being dried. Ammonium chloride is used for this study. Heat and mass transfer studies were carried out using the experimental set up which consists of a well-insulated glass fluidized column with calming section and a fluidized section of height 435 mm and diameter 55 mm. Experiments were carried out with the variables- (i) size of ammonium chloride particles from 495 to 912 microns, (ii) inlet air velocity from 1.136 to 1.391 m/s, (iii) temperature of inlet air to the fluidized bed dryer from 60 to 75°C, (iv) initial moisture content of ammonium chloride to the fluidized bed dryer from 0.04 to 0.06 kg of water /kg of bone dry ammonium chloride, (v) bed hold of 0.090 to 0.130 kg. Humidity of the inlet air to the fluidized bed is determined by measuring the dry and wet bulb temperatures and using the psychrometric chart. Microsoft Excel spreadsheets are used for the calculations. A correlation between Nusselt number and Reynolds number was developed using the least square method. A simplified unsteady state mass transfer equation was developed to determine the diffusion coefficient.