Some structural properties of packed bed systems on both the local and overall scales which are available in the literature and of interest in chemical engineering applications are discussed. Regular and random packings of uniformly sized spheres are initially analyzed as a basis for the later examination of the more general case of random packed beds containing particles of various sizes and shapes, with or without restraining surfaces.

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The effects of temperature and other factors on the thawing of frozen lamb shoulders in both water and air were evaluated by determining thawing time and changes in bacterial count, appearance and palatability characteristics.Water thawing is suitable for a short-time batch or continuous process immediately prior to boning and gives a net weight gain which partially offsets the previous weight loss during cooling and freezing. The optimum conditions are immersion in water at 45 & 3°C (113 rf: 5°F) for 2-2.5 hr, followed by equilibration and surface drying for 0.5 hr in air at 10°C (50°F) prior to boning. Provided a high standard of hygiene is maintained the water can be reused for up to 4 hr.Air thawing is suitable for a batch process with a cycle time between 8 and 60 hr, which determines the air temperature required in the range 2-18°C (35-65°F). A high relative humidity is required to minimize weight loss.Thawing times in both water and air can be theoretically predicted by a modified form of Plank's freezing equation.