Experimental results on mass transfer obtained during the constant rate period of the through-circulation drying of packed beds, were analyzed. The results, expressed as / factors, were correlated using a theoretical model for fluid-particle mass transfer in fixed beds. A good agreement was found, which allows us to deduce that a laminar boundary layer exists over the range of Reynolds numbers investigated.

The drying characteristics of Laminaria digitata frond and stipe have been studied and are compared with those of L. cloustoni frond and stipe.A striking similarity was found in the shapes of the curves of time versus air velocity for the fronds and-stipes respectively of the two species. The empirical equations for fronds were similar in type and those for the stipes were also similar. It was concluded that the physical differences between the two parts of the same plant had a greater influence on the drying time than the differences between the three common sublittoral species.The close agreement between the species was most marked in the effect of bed depth on the drying time. This relationship was apparently independent of any particle-shape factor since fronds (either minced, shredded, pre-dried or wet) gave the same general type of curve, i.e. concave upwards. The bed-depth curves for minced or sliced stipe were in general agreement, but were in contrast with the frond curves.These physical properties of stipes and fronds have been compared with those of other vegetable materials (hops, potatoes, carrots and brewer's spent grain) and it has been shown that the time versus bed-loading curves for all these materials can be classified into three groups, depending on whether the material is compressible or rigid.The output versus bed-loading curve for the first group (materials similar t o fronds) reaches an optimum value, and mathematical considerations have demonstrated that the optimum drying time is about twice the minimum time. The minimum time for throughcirculation drying is the period required to dry a single layer of the material, and is represented by the intercept of the smooth curve (of time versus bed-loading) on the time axis.The effect of agitation on the reduction of drying time was.investigated for two-inch beds of L . dzgitala frond. Agitation was carried out a t equal time-intervals and has been expressed as effective stages. In the first half of the run (T = 7 to T = 3, where T = total water content, lb. of water/lb. of bone-dry solid) three effective stages reduced the time to only 95% of the corresponding static time, whereas a reduction to about 40% was obtained in the range 3 to 0 . 1 .Bed-depth experiments suggest that L. digitata plants dry faster than, and L. saccharina slower than, L. rloustoni. Internal temperatures of a #-in. slice of L . cloustoni stipe during a drying run have been measured. The effect on drying time of storage between harvesting and drying has been found for L. digitata frond. IntroductionIn a previous paper1 the physical and chemical differences between the two parts of the plant, i.e. stipe and frond, were compared and contrasted. Physical differences between the three common sublittoral seaweeds used in the drying tests are described below.Z L. cloustoni has a sturdy stipe with a circular cross-section. The epidermis, or outer skin, of the stipe is rough and often has adherent parasitic growths. The stipe is surmounted by a flat palmate frond. The plant ancho...

h graphical design method is proposed for calculating the drying time, throughput rates and specific evaporation for double-and triple-stage conveyor through-circulation driers. The method is illustrated with examples based on the unit wet-bulb depression drying curves for Laminaria cloustona stipe and frond.

The drying characteristics of freshly harvested Laminaria cloustoni frond have been investigated in a through‐circulation drier. Drying factors investigated were bed depth (0.5‐4 in.), particle size (minced and shredded), air velocity [3‐7 lb./(sq. ft.) (min.)], air temperature (130–220° F), air wet‐bulb depression (53‐123° F), and the seasonal variation of drying times. In most of the tests reported, the fronds were minced before drying. The general effect of air velocity, air temperature and humidity on the drying time is similar to that for L. cloustoni stipe, and a comparison test showed that minced frond dried slightly faster than the shredded material. Drying rates of frond beds at average water contents of 2.5‐0.2 lb./lb. (dry basis) have been found to be directly proportional to the wet‐bulb depressions of the air.