Heaters, electric

Such a resistance device is usually called an electrical heater but, since there is no means of measurement at the boundary between the resistance and the material in contact with it, it is easier to regard the resistance as being inside the system, i.e. a part of it. Energy enters the system in the fomi of work where the wire breaches the wall, i.e. enters the container. 

Note that in this special case, the heat absorbed directly measures a state fiinction. One still has to consider how this constant-volume heat is measured, perhaps by an electric heater , but then is this not really work Conventionally, however, if work is restricted to pressure-volume work, any remaining contribution to the energy transfers can be called heat . 

Consequently traces of these unstable peroxides are present in samples of all the lower aliphatic ethers unless the samples have been freshly distilled. If these ethers when being distilled are heated on, for example, an electric heater, the final residue of peroxide may become sufficiently hot to explode violently. The use of a water-bath for heating, as described above, decreases considerably both the risk of the ether catching fire and of the peroxide exploding. 

The sample solution is pumped along a narrow capillary tube, the end of which becomes the nozzle of the nebulizer. On the outside of the capillary near its nozzle end, an electrical heater rapidly... 

Maintenance of isothermal conditions requires special care. Temperature differences should be minimised and heat-transfer coefficients and surface areas maximized. Electric heaters, steam jackets, or molten salt baths are often used for such purposes. Separate heating or cooling circuits and controls are used with inlet and oudet lines to minimize end effects. Pressure or thermal transients can result in longer Hved transients in the individual catalyst pellets, because concentration and temperature gradients within catalyst pores adjust slowly. 

Electric heaters have also been directly immersed in the molten zone. Zone refining has been accompHshed with a single hehcal heater rotating in an annular sample space (71). 

Electric Tracing An electric tracing system (see Fig. 10-178) consists of an electric heater placed against the pipe under the thermal insulation, the supply of electricity to the tracer, and any control or monitoring system that may be used (optional). The supply of electricity to the tracer usually consists of an electrical panel and electrical conduit or cable trays. Depending on the size or the tracing system and the capacity of the existing electrical system, an additional transformer may be required. 

C. 3-Hydroxyquinoline. A 1-1. beaker is fitted with a thermometer and mechanical stirrer and clamped firmly on an efficient electric heater (Note 14). Diethyl succinate (400 ml.) (Note 15) is placed in the beaker and heated to boiling (215-220°) with stirring. 3-Hydroxycinchoninic acid (part B) (94.6 g., 0.5 mole) is added in portions to the boiling solution by means of a metal spoon or Scoopula. Care is taken to prevent too vigorous evolution of carbon dioxide. The addition requires 2-3 minutes, during which time a temperature drop is noted unless good heating is maintained. 

Decomposition of trichloroethylene can occur upon contact with naked flames, red-hot surfaces, hot elements of electric heaters, or intense UV light with the generation of acidic and highly-toxic products. The presence of reactive contaminants, e.g. acids, strong alkalis, highly-reactive metals, may also result in decomposition to similar products. 

Tanks containing liquefied gases that are kept liquid by refrigeration sometimes have electric heaters beneath their bases to prevent freezing of the ground. When such a heater on a liquefied propylene tank failed, the tank became distorted and leaked—but fortunately, the leak did not ignite. Failure of the heater should activate an alarm. As stated in Section 5.2, frequent complete emptying of a tank can weaken the base/wall weld. 

A reactor was cooled by a molten salt. At startup the salt was heated to reaction temperature by an electric heater. During one startup the temperature of the salt rose at only half the usual rate. Obviously one of the heaters was faulty, but no fault could be found. The problem was finally traced to a nitrogen valve, which had been left open. The flow of nitrogen through the reactor was taking away half the heat. 

The inherently safer solution is to use a source of heat that is not hot enough to ignite the plastic, for example, hot water, low-pressure steam, or low-energy electric heaters [9]. 

---