Experimental investigation on volumetric heat transfer coefficient during intermittent spray drying of mannitol solution

Abstract

The paper presents a detailed experimental investigation on volumetric heat transfer during intermittent spray drying of a 20% w/w of mannitol solution in a custom-made spray dryer. Unlike the conventional intermittent drying process, which achieves intermittency by pulsating the properties of the carrier gas medium, the present works achieve intermittency by pulsating the nozzle spray. The estimated volumetric heat transfer coefficient varies between 0.8 and 2 kW/m³K, and the volumetric mass transfer coefficient is between 0.6 and 2.5 s⁻¹. The correlation for heat and mass transfer coefficients is evolved that relates the heat and mass transfer coefficient with the flow properties and thermophysical properties of both the carrier gas and the precursor fluid in terms of Ohnesorge number and Nusselt number. The investigation uses response surface analysis to analyze the effect of Reynolds number of air and Ohnesorge number of precursors on the volumetric heat transfer coefficient. The results show that a decrease in Reynolds number for a wide range and Ohnesorge number causes the volumetric heat transfer coefficient to increase.

Keywords:

• spray drying
• multicomponent spray
• nozzle
• volumetric heat transfer coefficient
• intermittent drying