Ribbon heater

Insulating substrate in ribbon heaters in combination with a pyrolytic graphite resistance heating element. 

For a horizontal ribbon heater, as used by Lienhard and Keeling (1970), L = W, the width of ribbon heater,... 

A—ribbon heater B—flow meter C—thermocouple D—jacket... 

The cooking performance is also influenced by the type of heating element. So far, for the greater part, heat flow and energy transfer have been discussed for the most common type of heating element - the ribbon heater, which has... 

Another type of heating element is the halogen heater (radiation peak at 1.1 pm), which has a shorter reaction time during the heat-up phase. This heater type is disappearing more and more from the market because of its high costs and the continual performance improvement of the ribbon heater. 

Electrical heating is accomplished with resistance bauds or ribbons which must be electrically insulated from the machine body but in good thermal contact with it. The heaters must be carefully spaced to avoid a succession of hot and cold areas. Sometimes they are mounted in aluminum blocks shaped to conform to the container walls. Their effective temperature range is 150 to 500°C (about 300 to 930°F). Temperature control is precise, maintenance and supervision costs are low, and conversion of electrical energy to useful heat is almost 100 percent. The cost of electrical energy is usually large, however, and may be prohibitive. 

Edge of heater ribbon visible at left (2). Vapor streamers from edges of heater ribbons (3). Fluctuating surface temperature. 

The thermal conductance of each glue spot below 150 mK was very low because of the two contact resistances Rc (Kapton-glue and glue-copper), and the power Ph delivered to the copper sample did not flow through the Kapton foil. To be sure of that, however, 1 mm large, 56 xm thick copper ribbon was internally glued around the upper end of the Kapton support. A heater Hk and a thermometer Tk (Fig. 11.6) were fixed on the ribbon and a power Pk was delivered to the Kapton support in such a way that T = Th. 

Figure 12 shows the CTL-based sensor element. The platinum ribbon wire (0.2 mm in width and 0.02 mm in thickness) is spot-welled on the screen-printed substrate as heater lead wires, and the sensor chip is suspended on a plastic frame by the lead wires. In order to measure the catalyst temperature, very thin thermocouple wires are fixed on the substrate using ceramic cement. 

In these experiments a sample of cobalt/molybdenum disulfide was mounted on the heater ribbon in close proximity to a cobalt/graphite specimen, which was positioned in the path of the electron beam. All specimens were initially treated in 1.0 Torr hydrogen for l.Q hours at 360°C. and under these conditions the cobalt film nucleated to form particles. 2.5 - 5.0 nm diam. on the graphite surface. At the same time these particles were being exposed to hydrogen disulfide produced during the cobalt catalyzed hydrogenation of molybdenum disulfide, a reaction which had been previously found to proceed at appreciable rates at ten ratures above 250°C (ref. 16). 

Electrical interconnections between the boards are made using a backplane and ribbon cables between rear I/O cards. Ribbon cables on the front side of the chassis connect the reactor boards to the heater driver circuit boards. The rear I/O cards are custom-built PC boards that are used to transfer signals from cables connected to the control computer to the system boards on the front. Ribbon cables are used to transfer connections between the rear I/O cards because there were not enough lines available in the backplane to make all of the required connections. 

The electronics needed to operate six temperature sensors on each microreactor channel are located underneath these cards. The ribbon connector, which is also visible in Fig. 12.8, is used to transfer electrical signals directly from the reactor board to the heater circuit board (described below). Serial communications for the Redwood flow manifolds is provided by two, four-conductor RJ-11 jacks on the front. The front of the board has gas inlets for the reactor feed and the purge gas. In addition, there are two gas outlets, one for each reaction channel. The inlet and outlet fittings are 1/16-inch type 316L stainless steel. The tubing assembly component having the greatest pressure sensitivity is the microreactor membrane. 

Figure 4 Advanced boosted heated-filament pyrolyzer with thermocouple feedback. The chromel-alumel thermocouple wires d, 25 pm) attached to the nichrome ribbon have a small thermal capacity with a fast response time. When mounted on the GC, the chamber Is surrounded by a heater jacket. (Reproduced with permission from Lehrle RS, Robb JC, and Suggate R (1982) European Polymer Journals 443-461 Elsevier.)...

Rod, wire, and ribbon resistance heaters are also used. Silica carbide, quartz, and graphite heating elements are also available. 

FIGURE 19.76 Schematic of wax transfer process (a) Intimate contact between printhead, ribbon, and paper is required for successful transfer, (b) design elements of thin-film thermal printhead. Thermal barrier insulates heater for the duration of the heat pulse but allows relation of heater temperature between pulses. 

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