Cooling flow-induced

Fig. 8. Transverse cross-sectional view of double-flow induced-draft cooling tower. Courtesy of The Madey Co.

Natural convection is self-induced and is created by the density differences, which are temperature related the boiling of water in a kettle is an example of free convection. Forced convection is caused by an external force being applied by mechanical means such as a fan or pump the cooling of a warm bottle in cool flowing water is an example of forced convection. 

Figure 9-105. Cross-flow Induced draft cooling tower. Used by permission of The Marley Cooling Tower, a United Dominion Co.

Flow field and cooling condition between injection molding and compression molding are essentially different. In particular, the flow-induced molecular orientation and/or the distorted shape of the dispersed phase have to be considered seriously in the injection molding. This part deals with the relation between morphology and mechanical properties in the injection-molded products for iPP and iPP/EHR blends (65). This is directly important for the industrial application. The characteristics of these samples are summarized in Table 9.5. 

Induction heating uses a medium- or high-frequency electric coil (water cooled) to induce a current in a metal load. (See figs. 3.1 and 3.2.) The flux lines are most concentrated just below the surface of the load. Conduction distributes the heat across the load. The heat flow is not reduced by surface resistances as with convection and radiation. 

Somani RH, Yang L, Zhu L, Hsiao BS (2005) Flow-induced shish-kebab precursor structures in entangled polymer melts. Polymer 46 8587-8623 Sorrentino A, De Santis F, Titomanlio G (2007) Polymer crystallization under high cooling rate and pressure a step towards polymer processing conditions. Lect Notes Phys 714 329-344 Stocker W, Magonov SN, Cantow HI, Wittmann JC, Lotz B (1993) Contact faces of epitaxially crystallized a- and y-phase isotactic polypropylene observed by atomic force microscopy. Macromolecules 26 5915-5923... 

The double layer pad has been tested by Bahr (31) and Kawaike et al. (32) and found to be very effective. An attractive feature is that the cooling flow is passively induced, without a pump. Kawaike found that the flow velocity in the channels was 0.15 the rotor velocity, which compares well with the approximate velocity of 0.015 over the back of standard pads. Higher convection coefficients will result. In addition, the conduction resistance (k/t) is substantially reduced, particularly if the plate is of copper alloy. The four cases in Table II have the common basis ... 

Mechanisms of coalescence in polymer blends are generally not well understood [56, 57]. Flow induced coalescence has been discussed briefly above. Under quiescent conditions such as cooling of a strand or an injection molded part, mechanisms such as Smoluchowski coalescence or Ostwald ripening may be important [58]. However, under manufacturing conditions, relaxation of flow stresses and interfacial tension driven changes in domain shape are probably of more importance. 

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