Infrared temperature measurements and DEM simulations of heat transfer in a bladed mixer

Abstract

An understanding of heat transfer in a bladed mixer is important for drying of pharmaceutical drug crystals. This study presents thermal imaging experiments of the particle bed surface in a bladed mixer to investigate how the impeller speed influences the rate and the uniformity of heat transfer. Next, the process is simulated using the discrete element method. The bed thermal properties are lumped into an effective thermal conductivity, that is calibrated for one impeller speed. The experiments and the simulations show the same trends and generally agree well for all agitated beds. However, to obtain good agreement of the rate of heat transfer between the simulations and experiments in a static bed, we need to adopt a higher thermal conductivity than for the agitated beds. Finally, we discuss the implications of these results for the design of operating protocols.

Experimental investigation of heat generation during the mixing of granular materials in an overhead stirrer

“…However, bladed mixers (e.g., the overhead stirrers) possess the advantage of their simpler design and relatively shorter blending time [15]. Moreover, such mixers are extensively used in applications that require high input power, e.g., in blending solid pellets to melt and mix the polymer [7] and their blending performance was examined by many researchers [7,8,[16][17][18]. However, these studies focused mainly on the impeller torque and power consumption [7,8], flow behaviour [16,17], and heat transfer [18].…”

“…Moreover, such mixers are extensively used in applications that require high input power, e.g., in blending solid pellets to melt and mix the polymer [7] and their blending performance was examined by many researchers [7,8,[16][17][18]. However, these studies focused mainly on the impeller torque and power consumption [7,8], flow behaviour [16,17], and heat transfer [18]. Little attention was paid to the energy dissipation and thermal response of the granular bed.…”

“…Despite valuable insights into bladed mixers, the link between operating parameters and the thermal response of granular media is not explored in-depth. Few studies examined the influence of operating parameters on the drying process for bladed mixers with heating jackets [18,43]. However, such studies were only limited to the heat transfer phenomenon in the presence of external heat sources, ignoring the heat generation induced by energy dissipation.…”

Experimental investigation of heat generation during the mixing of granular materials using an overhead stirrer

“…15 Moreover, such mixers are extensively used in applications that require high input power, for example, in blending solid pellets to melt and mix the polymer 7 , and their blending performance was examined by many researchers. 7,8,[16][17][18] However, these studies focused mainly on the impeller torque and power consumption, 7,8 flow behavior, 16,17 and heat transfer. 18 Little attention was paid to the energy dissipation and thermal response of the granular bed.…”

“…7,8,[16][17][18] However, these studies focused mainly on the impeller torque and power consumption, 7,8 flow behavior, 16,17 and heat transfer. 18 Little attention was paid to the energy dissipation and thermal response of the granular bed.…”