Drying System Configurations

Figure 11.2 Typical configurations of the Vacu Jet Drying System. (Reprinted with permission of Hosokawa Micron Corporation, Japan.)...

Figure 14.10 Basic configuration of the Pulse-Dryer. (Courtesy of Pulse Drying Systems, Inc., Portland, Oregon.)...

In a typical configuration of a drying system, small solids (e.g., fine metal or plastic parts) are sunk into displacement fluid (Figure 18.2). Larger parts may be sprayed with a solvent, whereas solid structures like textile fibers or particulate materials can be washed with a drying fluid forced through the solid matrix. 

Any dehumidifying drying system will include the dryer itself, the hopper in which the material is actually dried, and a means to deliver dry material to the processing machine feed throat. Beyond that, there are several different ways to configure these system components, and each has definite advantages and disadvantages. 

The intrinsic structure of a liquid-vapor interface resembles the surface of a polymer liquid in contact with a nonattractive solid substrate at the pressure where the liquid coexists with its vapor. In the latter case, the system is in the vicinity of the drying transition and a layer of vapor intervenes between the substrate and the polymer liquid. There is, however, one important difference between the vapor-polymer interface and the behavior of a polymer at a solid substrate the local position of the interface can fluctuate. Let us first consider the case where the film is very thick and the solid substrate does not exert any influence on the free surface of the film in contact with its vapor. The fluctuations of the free surface are capillary waves. Neglecting bubbles or overhangs, one can use the position of the liquid-vapor interface, z = h x,y), as a function of the two lateral coordinates, x and y, parallel to the interface to describe the system configuration on a coarse scale. In this Monge representation, the free energy of the interface is given by the capillary-wave Hamiltonian " ... 

The three towers usually are sized to a common diameter that will give a pressure drop of 0.10 in. to 0.15 in. H20/ft of packed depth, because the overall pressure drop desired for the entire drying system is only 4 in. to 5 in. H2O. This process largely is gas-film-controlled, as expected. It is desirable to keep the packed depth in each of the three columns the same. To accomplish this configuration, an iterative design procedure is necessary. The driving force for mass transfer is the difference between the partial pressure of water vapor in the gas stream and the vapor pressure of water above the liquid phase. Because of the high liquid flow rate, as a first approximation, the acid concentration and temperature in eath tower can be assumed constant in order to establish the amount of water vapor removed in each column, and thereby the acid concentration. 

Polymers and Coatings Advances ia polymer chemistry have resulted ia many successful medical devices, including diagnostic assays (26). Polymers (qv), which can be manufactured ia a wide range of compositions, ate used to enhance speed, sensitivity, and versatiUty of both biosensors and dry chemistry systems to measure vital analytes. Their properties can be regulated by composition variations and modifications. Furthermore, polymers can be configured iato simple to complex shapes. 

The hrst step in theoretical predictions of pathway branching are electronic structure ab initio) calculations to define at least the lowest Born-Oppenheimer electronic potential energy surface for a system. For a system of N atoms, the PES has (iN — 6) dimensions, and is denoted V Ri,R2, - , RiN-6)- At a minimum, the energy, geometry, and vibrational frequencies of stationary points (i.e., asymptotes, wells, and saddle points where dV/dRi = 0) of the potential surface must be calculated. For the statistical methods described in Section IV.B, information on other areas of the potential are generally not needed. However, it must be stressed that failure to locate relevant stationary points may lead to omission of valid pathways. For this reason, as wide a search as practicable must be made through configuration space to ensure that the PES is sufficiently complete. Furthermore, a search only of stationary points will not treat pathways that avoid transition states. 

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