Spiral heat exchanger construction

Spiral heat exchangers are constructed by winding two long strip of plate metal around a center to form a spiral body, which then contains two concentric channels. Each channel is welded closed at alternate sides (see Fig. 27.1). Covers are then bolted over each side of the spiral body to complete the unit. When both of these covers are removed, the entire surface area of the exchanger is available for manual cleaning. 

Plate evaporators may be constructed of flat plates or corrugated plates, the latter providing an extended heat transfer surface and improved structural rigidity. Two basic types of heat exchangers are used for evaporation systems plate-and-frame and spiral-plate evaporators. Plate units are sometimes used because of the theory that scale will flake off such surfaces, which can flex more readily than curved tubular surfaces. In some plate evaporators, flat surfaces are used, each side of which can serve alternately as the liquor side and the steam side. Scale deposited while in contact with the liquor can then be dissolved while in contact with the steam condensate. There are still potential scaling problems, however. Scale may form in the valves needed for cycling the fluids and the steam condensate simply does not easily dissolve the seale produced. 

FIGURE 6.37 Schematic diagrams of spiral-plate heat exchangers (a, b) basic construction for two fluids in counterflow, (c) configured for condensation or reboiler service. 

Based on different mechanical construction, the common types of heat exchanger used in industry are doublepipe or multi-tube hairpin, shell and tube, air cooler, plate and frame, and spiral. Only the tirst three types of heat exchanger will be discussed in this chapter. 

The experimental equipment (35] for P(VDF/1>FE) copolymer was constructed by the combination of the controlling system of the lest copolymer and the managing system of the heat flow, in which the spiral stack including t copolymer specimen was used. As shown from the top view in Figure 21, the spiral was wound around a central support rod and consists of alternate layers of plastic sheet and nylon separator screen. The copolymer specimen was wrapped into tbe stack. The nylon separator screen allows beat exchange fluid (a hi -dieled -strength silkone) to flow over the surface of tbe plastic sheet and specimen. 

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