Drying displacement

Values of m/n for various test gas mixtures were determined in exactly the same way as for pure hydrocarbons. The test gas flowrates were calculated by using a flowrate conversion factor computed on the basis of known test gas composition (ref 7). These computed flowrates were in agreement with the values obtained by direct measurements with a positive displacement dry test meter. The results for the various test gas mixtures are summarized in Table V. 

Fluid displacive drying and resin-embedding of wet sediments... 

Additionally, this is a spot-free drying technique that leaves no trace of moisture on the material surface, which is especially important when drying films, plastics, polished metals, ceramics, and so forth. So far, displacement drying has found application in the field of electronics (printed circuit boards, relays, semiconductors, TV tubs), optics (eyeglass frames and lenses, films, cameras), electromechanics (copiers, electric motors), and mechanics (tools, cutlery, medical instruments). According to Devine (1980), in 1980 there were over 600 drying systems in operation in Europe, ranging in capacity from 40 liters to several cubic meters. 

Two alternative mechanisms have been proposed to explain displacement drying (Brandreth and Johnson, 1980) ... 

Figure 18.1 Mechanism of displacement drying (a) roll-up of water droplet (b) water-solvent interfacial tension lowering, (a) Water contact angle increases due to adsorption of a hydrophobic surfactant, (b) Water break-up by lowering interfacial tension between bquid phases.

In most cases, both mechanisms contribute to the overall displacement effect although to different extents. Because displacement drying is based on the surface phenomena, it is clear that internally bound water at molecular level, osmotically bound water or crystal water cannot be removed by this technique. It is possible, however, to remove water held in small pores. 

Figure 18.3 Comparisons of energy consumption for hot-air and displacement drying.

Table 18.1 Energy Consumption Versus the Number of Extraction Stages for Displacement Drying of Veneer in Ethanol...

Brandreth DA, Johnson RE Jr. Displacement drying. In Mujumdar AS, ed. Drying 80. Vol. 1. Washington Hemisphere Publishing Corp. 1980, pp 304-307. 

Actually a more relevant example of Class II cosolvent machines, and of the kerosene dryer, is the fluorocarbon-based dryer for removal of water from part surfaces. Flere the substrate is to be dried by displacement. Drying in this manner avoids an energy consuming drying step (evaporation of water) and can greatly expedite subsequent processing of the substrate component. No thermal stresses are applied to components on surfaces. 

Yet, some commercial fluorocarbon-based displacement drying fluids are augmented with surfactants whose function is to chelate with the water so that it does not form emulsions with the fluorocarbon. Surfactant-fluorocarbon compositions have been patented to alleviate this condition, especially on non-metallic surfaces. Useful surfactants are ... 

Displacement drying uses anhydrous fluids, such as IPA (isopropanol), anhydrous ethyl alcohol denatured with acetone or methanol, or a commercial drying agent, to displace the... 

Fig.5. (Above right) SANS from zirconia gels, (a) Wet gel in water, o, (b) butanol displacement dried gel reimmersed in water, , and (c) gel dried in air then reimmersed in water, .

Fig.6. SANS contrast variation results for solvent displacement dried gels of (a) titania, (b) an equimolar mixture of titania and zirconia and (c) zirconia. Intensity correspond to Q/A of 2.5xl0. ...

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