Manifold external heating

Other options for gas dispensing cryogenic tanks are manifolds that can connect two to six cylinders together. These manifolds can provide flow rates of 250 cfh (cubic feet per hour), can set up a reserve of gas for uninterrupted flow when changing cylinders, and (with an economizer circuit) can cut loss due to evaporation. For extra-high-capacity gas demands, there are external vaporizing manifolds, which are a combination of the external heat exchanger and manifold n... 

Additionally, space is required for manifolding and heat insulation while space is also required at the top and bottom of the module so as to gain maximal profit of the available membrane surface area. Fig. 2.14. A module vessel consisting of an insulated double wall has the advantage of minimization of expensiveheat- and oxygen-resistant stainless steel, used for relatively thin inner walls, and therefore reduction of the total costs of the module. Accommodation of the pressure inside the module is reached by a thick cold external wall that can be manufactured from cheap steel. 

Reactors for conventional thermally activated CVD are of two types cold-wall and hot-wall reactors, respectively internally and externally heated. The disadvantage of a hot-wall reactor is deposition on the wall and partial depletion of reactants leading to nonuniform coatings. A correct reactor geometry and gas inlet manifold can compensate for gas depletion in hot-wall reactors. There is no limit to the form of the objects to be coated, but sizes are restricted. In a cold-wall reactor the substrates to be coated are heated by a graphite susceptor that is inductively heated by an rf generator. Only the hot parts are coated and not the reactor walls, which remain relatively cold. 

Hot-manifold mold n. An injection mold equipped with an internal heater located in the center of the melt stream in the manifold and nozzle system. This type of mold was developed for thermally sensitive resins to provide gentler heating and avoid the decomposition problems experienced with external heating techniques because of excessive temperature differences. 

From these basic components stacks were assembled as shown in Fig. 20.10. The supply and removal of the liquid heat transfer media and the distribution on every cell is provided by externally mounted manifolds. The heat transfer fluids flow from the top downwards through the straight channel structure on the back of the cathode side half-shell. 

The operating principle of externally-heated manifolds has already been described in Chapter 1.2. This is the traditional manifold design, which is still the dominant one in the market. 

In practice, hybrid systems are increasingly frequently encountered, where the manifold is simultaneously bolted on and clamped down, which reduces the risk of seal failure. Much attention is given to ensuring that manifolds with external heating can withstand leakage. Manifolds with screw-in nozzles have been developed for this reason. 

The heaters used for external heating of plate manifolds are of the cartridge or tubular resistance type operating on 230 V AC current. Tubular manifolds are heated by 230 V coil heaters or low-voltage 24 V or 5 V, heaters. 

It depends not only on the heating method, but also on the insnlation method and the way the manifold is supported, i.e., its cooling curve. Typical of externally-heated manifolds is rapid cooling of the ends of the manifold (measurement points 1 and 6). This is why a certain minimum distance K between the nozzle and the end of the manifold is maintained. 

In the classic D-M-E version, the manifold has large-diameter (24-50 mm) drilled flow channels in which cartridge heaters in a tubular body are located. The melt thus flows through an annular channel between 4 and 9 mm wide (see Chapter 1). Because of the heating pipe in the centre of the channel, the channels cannot cross over as in externally-heated manifolds, but must be connected adjacently. Torpedoes must also be connected with a butt joint to the flow channels. This creates certain restrictions as regards the mould cavity arrangement, and it is not easy to achieve a natural flow balance (see Figure 4.91). 

The choice between internal and external heating, particularly of the manifold (see... 

A system with external heating enables the channels to be purged relatively quickly. A system with internal heating does not allow the channels to be purged completely, and in some cases it is necessary to take the manifold apart and clean the channels, torpedoes and insulation chambers manually. Some systems are designed in such a way as to allow the channels to be opened up (see Figure 4.91) sometimes this can even be done on the machine without removing the mould. 

The difficulties with color change restrict the field of application of internally heated systems. The following combination can be found more often Externally heated manifold and internal heating in the nozzle area, equivalent to the design of the gate elements as a torpedo or as a thermal conductive tip. 

FIGURE 1.46 Externally heated hotrunner in the standard design with floating manifold a Manifold b support disk c tubular heating elements d centering pin e heating coil of the nozzle [24]... 

Fig. 4. Schematic of a hemodialyzer. The design of a dialyzer is close to that of a sheU and tube heat exchanger. Blood enters through an inlet manifold, is distributed to a parallel bundle of fibers, and exits into a coUection manifold. Dialysate flows countercurrent in an external chamber the blood and dialysate are separated from the fibers by a polyurethane potting material. Housings are typically prepared from acrylate or polycarbonate. Production volume is...

Injection The injection blow moulding machine is based on an extruder barrel and screw assembly which melts the polymer. The molten polymer is fed into a manifold where it is injected through nozzles into a hollow, heated preform mould. The preform mould forms the external shape and is clamped around a mandrel (the core rod) which forms the internal shape of the preform. The preform consists of a fully formed bottle/jar neck with a thick tube of polymer attached, which will form the body. 

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