Cross circulation

Air Drying Equipment. Tunnel kiln dryers (70) are long furnaces comprised of several zones of different temperature, humidity, and air flow through which the ware travels on a moving car or belt. These kilns afford continuous processing. Periodic kiln cross-circulation dryers (70) are box furnaces in which ware is stacked on permanent racks or on a car that can be shuttled in and out of the furnace. Fans or jets are used to circulate heat uniformly through the ware. The process is not continuous, but production rates can be enhanced by shuttling multiple cars. 

Values of critical moisture contents for some representative materials are given in Table 12-7 for diying by cross circulation and in Table 12-15 for diying by through circulation. The tabulated values are only approximate, since critic moisture content depends on the drying histoiy. It appears that the constant-rate period ends when the moisture content at the surface reaches a specific value. Since the critical... 

Bumell JM, Dennis MB Jr, Clayson KJ, et al. 1976. Evaluation of dogs of cross-circulation in the treatment of acute hepatic necrosis induced by yellow phosphoms. Gastroenterology 71 827-831. 

Cross-circulation Homologous cross-circulation with healthy volunteers was first attempted by J.M. Burnell et at in 1965. Due to multiple problems, S.C.W Bosman et at introduced heterologous cross-circulation using a baboon in 1968 baboons are the only animal species which can tolerate human blood for 5 to 7 days. 

Batch tray Particulate Cross-circulated tray Cross-circulation Atmospheric tray... 

Continuous tray Particulate Turbo-tray Cross-circulation Rotating tray/snelf, Wyssmont Turbo-dryer... 

Continuous band/tunnel Particulate Tunnel Cross-circulation Moving truck/trolleys... 

No agitation, e.g., tray and band dryers. This is desirable for friable materials. However, drying rates can be extremely low, particularly for cross-circulation and vacuum drying. 

Classification Batch, nonagitated layer convective (cross-circulation or through-circulation) or contact/conduction. 

Classification Continuous nonagitated (except for turnover when falhng between trays) layer convective (cross-circulation or through-circulation) or contact/conductiou vertical solids movement by gravity and mechanical agitation. 

Mebutamate - The mechanism of the hypotensive action of mebutamate was investigated in cross circulation experiments in anesthetized dogs. The results suggested that the initial and transient hypotension may be largely due to the direct vasodilator action and that the sustained effect may be accounted for by an inhibition of the sympathetic vasomotor tone at the spinal and ganglionic levels. ... 

Gas is blown across the surface of a bed or slab of solids or across one or both faces of a continuous sheet or film. This process is called cross-circulation drying (Fig. 24.1fl). 

Gas is blown through a bed of coarse granular solids that are supported on a screen. This is known as through-circulation drying. As in cross-circulation drying the gas velocity is kept low to avoid any entrainment of solid particles (Fig. 24.16). 

MASS TRANSFER IN DRYERS. In all dryers in which a gas is passed over or through the solids, mass must be transferred from the surface of the solid to the gas and sometimes through interior channels of the solid. The resistance to mass transfer, not heat transfer, may control the drying rate. This is most often true in cross-circulation drying of slabs, sheets, or beds of solids. From the standpoint of the gas, this kind of drying is much like adiabatic humidification from that of the solid it is like evaporation when the solid is very wet and like solvent desorption from an adsorbent when the solid is nearly dry. 

Mass transfer between the solid surface and the gas is covered by the relations discussed in Chap. 21. The drying rate of solids containing internal liquid, however, depends on the way the liquid moves and on the distance it must travel to reach the surface. This is especially important in cross-circulation drying of slabs or beds of solids. Drying by this method is slow, is usually done batchwise, and has been displaced by other faster methods in most large-scale drying operations it remains important, however, in the production of pharmaceuticals and fine chemicals, especially when drying conditions must be carefully controlled. 

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