Film dryer

If you do not have access to a place to hang the film, say you are on assignment in the middle of the Olympic National Rain Forest, you can rapidly dry film by using a rapid film dryer, such as the one suggested by Paul Lewis (Formulas Miscellaneous Rapid Film Dryer). When you return home, thoroughly wash and dry the film in a normal manner to ensure longterm preservation. 

A related type of equipment is described later under Thin-Film Dryers. ... 

A few types of dryers evaporate solutions and slurries entirely to dryness by thermal means. Typical examples are spray dryers, thin-film dryers, and drum... 

THIN-FILM DRYERS. Competitive with spray dryers in some situations are thin-film dryers which can accept a liquid or a slurry feed and produce a dry, free-flowing solid product. They normally are built in two sections, the first of which is a vertical agitated evaporator-dryer similar to the device illustrated in Fig. 16.3. Here most of the liquid is removed from the feed, and partially wet solid is discharged to the second section, as illustrated in Fig. 24.16, in which the residual liquid content of the material from the first section is reduced to the desired value. 

The thermal efficiency of thin-film dryers is high, and there is little loss of solids, since little or no gas needs to be drawn through the unit. They are useful in removing and recovering solvents from solid products. They are relatively expensive and are somewhat limited in heat-transfer area. With both aqueous and solvent feeds the acceptable feed rate is usually between 100 and 200 kg/m -h (20 and 40 Ib/ft -h). 

Polyvinylidene chloride (PVDC) is typically used as a vapor barrier in food packaging. In these applications, evaporation rates are usually 10-15 kg/h/m with air velocities of 20-40 m/s when utilizing paper substrates and 20-40 m/s when using plastic films. Dryer construction is usually of stainless steel because of the high corrosivity of the coatings and airstream. 

The short residence time category comprises spray dryers, pneumatic dryers, and thin-film dryers in which the residence time may be of the order of several seconds. 

BD Belt dryer DD Drum dryer FB Fluidized-bed dryer CD Conveying dryer BLD Blade dryer PT Plate dryer FFD Falling-film dryer + suitable/good/less + — limited suitability... 

---