Info

" 650

1 600 ro

Figure 8. Overall heat transfer coefficient between solid food particles in a canned liquid and the heating medium as influenced by particle concentration during end-over-end rotation. Source: Ref. 28.

for economical reasons in small production volume. Due to slow movement of the liquid from natural convection, heating times required for sterilization are somewhat long. Steam is generally the heating medium, however, hot water is also used.

Flow and Temperature Profiles

In natural convection heat transfer, the liquid moves only due to the buoyancy induced by the change in temperature. This couples the flow and temperature fields and makes their computation a challenging task, as can be seen for pasteurization of beer in bottles (31) and sterilization of canned Newtonian (32) and non-Newtonian (33,34) fluids. Figures 10 and 11 show the typical flow patterns and temperature profiles in such nonagitated heating starting from a fluid at rest at a uniform temperature and raising its walls to the retort temperature. The liquid next to the sidewall, the top wall, and the bottom wall receives heat from the hot walls. As the liquid is heated, it expands and thus gets lighter. Liquid farther from the sidewall is still at a much lower temperature. The buoyancy force created by the liquids at different temperatures forces the hot liquid, next to the wall, upward. A sharp drop in temperature occurs from the wall to the core, creating a boundary layer. The buoyancy force resulting from this large temperature difference contributes to the largest velocities near the wall. The hot liquid going up is interrupted by the top wall and then travels radially toward the core. The core liquid, being heavier, moves downward and toward the wall. Thus a recirculating flow is created with a boundary layer at the sidewall, core flow at the centerline, and a mixing region at the top. Because the liquid is going up only through a small cross-sectional area (the thickness of the boundary

Figure 8. Overall heat transfer coefficient between solid food particles in a canned liquid and the heating medium as influenced by particle concentration during end-over-end rotation. Source: Ref. 28.

Figure 9. Overall heat transfer coefficient between solid food particles in a canned liquid and the heating medium as influenced by particle size during end-over-end rotation. Source: Ref. 28.
The Mediterranean Diet Meltdown

The Mediterranean Diet Meltdown

Looking To Lose Weight But Not Starve Yourself? Revealed! The Secret To Long Life And Good Health Is In The Foods We Eat. Download today To Discover The Reason Why The Mediterranean Diet Will Help You Have Great Health, Enjoy Life And Live Longer.

Get My Free Ebook


Post a comment