Process type electric heaters

There are two basic types of IR heaters electric IR and gas-fired IR (Figure 46.16). The most important element of the IR drying system is the IR emitter. These two types of IR heaters fit into three temperature ranges (1) 343°C-538°C (e.g gas and electric IR) (2) 538°C-1100°C (e.g gas and electric IR) and (3) 1100°C-2200°C (e.g., electric IR only). Electrically heated or natural-gas-heated units are used mainly to preheat the web, although these can be used in principle to carry out the entire drying process. IR temperatures are typically in the 650°C-1200°C range. Improved drying rates can be obtained by a combined radiation-convection system. 

Figure 5.2. Two of the more common types of low pressure CVD reactor, (a) Hot Filament Reactor - these utilise a continually pumped vacuum chamber, while process gases are metered in at carefully controlled rates (typically a total flow rate of a few hundred cubic centimetres per minute). Throttle valves maintain the pressure in the chamber at typically 20-30 torr, while a heater is used to bring the substrate up to a temperature of 700-900°C. The substrate to be coated - e.g. a piece of silicon or molybdenum - sits on the heater, a few millimetres beneath a tungsten filament, which is electrically heated to temperatures in excess of 2200 °C. (b) Microwave Plasma Reactor - in these systems, microwave power is coupled into the process gases via an antenna pointing into the chamber. The size of the chamber is altered by a sliding barrier to achieve maximum microwave power transfer, which results in a ball of hot, ionised gas (a plasma ball) sitting on top of the heated substrate, onto which the diamond film is deposited.

Fig. 3.7 shows a comparison between a capillary thermostat in the right part of the figure and the ever more frequently used NTC temperature sensor whose analogue electrical signal can easily be processed by an electronic control system. The NTC sensor type is increasingly used, particularly in modern European machines that always have their own heater element and sometimes also an additional hot water connection. 

Blanket-type electrical heaters are often used in combination with low thermal mass GRP tools (e.g., in the tooling concept advocated by Plastech TT, UK). The drawback with electrical heaters is that locally very high temperatures can occur. This can damage the tool and give an unacceptable variation in the curing process. 

The heater for the reaction chamber and the conductors were printed on the lowest layer and electrically contacted to the pads on the cover layer by vertical metal-filled vias in every intermediate layer. Still some manual work was necessary to shape the reaction channel from the pre-fired tapes. Also the soldering of clamp-type fittings to the cover layer is certainly difficult to automate. However, a manufacturing process for ceramic foil reactors seems to be within reach. 

In the heat-transfer-type flowmeters, heat is added to the fluid stream with an electric heater, and the resulting temperature rise is detected (Figure 3.73). These types of flowmeters are best suited for the measurement of homogeneous gases (such as H2) and are not recommended for applications in which composition or moisture content is variable, because, for these sensors to work, both the thermal conductivity and the specific heat of the process fluid must be constant. 

The feed pump was a positive-displacement, piston-type metering pump. All liquid transfer lines in the system were traced with electric resistance heaters which allowed us to process heavy SRC solutions. 

PCs are fairly simple devices to operate. If they do not function properly all kinds of problems develop. A checklist for eliminating problems includes nonuniform processed plastic, heater element burnout, location and depth of sensor as related to response time, type of on/off control action such as proportional controller, set point control, and basic electrical component proper selection. It is important to have the proper depth of the sensor in a barrel in order to obtain the best reading for the melt the deeper the better. 

The two general types of downhole heaters employed in the ignition well to start-up the combustion process in the bed are (a) flame heaters, using either natural gas or liquid fuel and (b) AC-powered electric heaters. Variants of these two main types of heaters have been constructed in Russia and abroad. 

Depending on the needs and expectations, one should dedde what type and capadty of the injection equipment to purchase. Usually, the initial investment cost of a flow rate-controlled injection equipment is higher than a pressure-controlled equipment. Figure 9.16a shows a flow-rate controlled injection equipment from Radius Engineering Inc. Its major components are (1) a resin cylinder (with a capacity of 2100 cc for this model) with a heater jacket, (2) an electric stepper motor which drives a piston at a desired resin flow rate, (3) a control console to input the process parameters and monitor process variables, (4) communication interfaces to control the equipment through a personal computer instead of the control console if desired and (5) a frame and stand with wheels. 

Cylinders are usually heated by electrical resistance. Replaceable band-type heaters are fitted at intervals about the periphery of the cylinder, forming different heat zones. Heat requirements along the cylinder length vary and depend upon the material being processed (see Table 4-1). Heat is transferred to the material through the cylinder walls. However, to prevent possible material hang-up, the area of the cylinder which contacts the hopper feed sleeve usually is water cooled to avoid premature softening of the material as it flows from the hopper. 

When using certain gases, it is desirable to maintain them at a set temperature for reasons related to the process and for safety. To do this, there are a number of different types of chillers and heaters. Circulating temperature controllers, use a temperature controlled liquid that is circulated through clam shell t)q)e jackets or coils placed around the cylinder. This type of system can have the actual control unit in a remote location and can easily be used in areas classified as hazardous. Another t5q)e controls the temperature of the air that is circulated through the cabinet. The air either transfers to or absorbs heat from the cylinder. Also available to heat cylinders are electrical resistance t5q)e devices. Some of these electrical devices cannot be installed into areas classified as hazardous. 

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