Nichrome heating coil

Forced-convection pit furnaces are employed for heat-treating small metal parts in biuk. Small pieces are suspended in a mesh-bottom basket, while larger pieces are placed on racks. Air heating is by means of Nichrome electric coils set in refractory walls around the... 

Metallic chromium is an ingredient of several important alloys. Some forms of stainless steel, for example, contain about 12% Cr. Nichrome, which is commonly used for heating coils, has about 15% Cr in addition to 60% Ni and 25% iron. Both these alloys are quite resistant to chemical oxidation. 

Although two reactors are shown in Figure 1, they were not used simultaneously. The reactor shown in the center was the fixed bed reactor which is of primary interest in this contribution. It consisted of a 12.7 mm diameter X 250 mm long steel tube packed with 40/50 mesh catalyst (0.3 mm average particle diameter). The reactor was heated by a nichrome wire coil and was well insulated. The coil spacing was adjusted and was packed in insulation with the intent of making the reactor crudely adiabatic. A variac controlled heater on the reactor inlet and a thermocouple sensor kept the feed to the reactor at the nominal reaction (or feed inlet) temperature of 400°C. The tube of the fixed-bed, reactor was fitted with 12 thermocouples to record the axial temperature profile in the bed (Figure 1). 

Forced-convection pit furnaces are employed for heat-treating small metal parts in bulk. Small pieces are suspended in a mesh-bottom basket, while larger pieces are placed on racks. Air heating is by means of Nichrome electric coils set in refractory walls around the periphery of the pit. A high-velocity fan beneath the basket circulates heated air up past the cons and then down through the basket. Some heat is radiated to the outer basket shell, but most is transferred by direct convection from the circulating gas to the solids. 

The bath temperature may be controlled by heating with an immersed loop of Nichrome resistance coil, such as the heating element from an electrical appliance. The coil is connected to a 110-volt line in series with a 27-ohm 5-ampere variable resistor and a 600-watt heater element, which may be cut out of the circuit to lower the fixed resistance. An ammeter in the circuit helps to determine the proper adjustment of the sliding contact of the resistor. To avoid an excessive load on the coil,... 

The furnace heating coil is wound non-induc-tively to avoid magnetic interactions between the coil and the sample. Coils are made from various materials, such as nichrome (T < 1300 K), platinum (T > 1300 K), platinum-10% rhodium (T < 1800 K) and silicon carbide (T < 1800 K). The furnaces consisting of an infrared (IR) ray heater instead of a standard coil heater are also used. An IR furnace is routinely used up to 1800 K. Using an elliptical reflector or parabolic reflector, IR... 

In this type of system a resistively heated platinum or nichrome wire coil or ribbon is used to rapidly heat the sample. The wire is continuously swept with carrier gas, whereupon the pyrolysis vapors are transported into the chromatographic column. Heating times are relatively large (up to 20 s) for this system, which may lead to nonrepeatable pyrograms and secondary reactions. The pyrolysis conditions, sample size, and location must be carefully controlled to obtain repeatable data. Two possible heating modes are available for this system pulse mode or programmed mode. For most forensic applications the pulse mode has been used. 

Aerosols generated by electrical heating of a coil of nichrome wire Aerosol Size Range 0.01 - 0.08 urn (radius)... 

Radiation in the infrared region of the spectrum is obtained from heated ceramic devices such as the Nemst glower or Globar. The Globar is made of silicon carbide and is heated to approximately 800-1500°C to emit black-body radiation in the infrared region of the spectrum. Coils of nichrome wire also emit infrared radiation when electrically heated. 

The checkers used a Hoskins tube furnace, type FD303A (Central Scientific Co.), 17 in. long. The heater for the sublimation vessel was wound in two sections with heating wire in such a way that a decreasing temperature gradient in the direction of the pyrolysis oven was maintained. The open end of the heater was closed by an asbestos end plate which could be heated independently by a small nichrome coil. 

The first pump removes air at a rate of 500 1/min and the second at about 300 1/min. The pressure in the first vacuum-lock is maintained at about 1 to 20 torr and that in the second about 0.1 to 0.5 torr. As a consequence the mass spectrometer source can be easily operated at about 10 torr. Flash vaporization of the solute occurs by radiant heating in a small chamber that butts directly onto the solid probe entrance to the ionization chamber and the vapor passes through a small hole directly into the ion source. The flash heater is either a nichrom coil or a quartz heater tube. The slots in the vacuum-locks are made of sapphire strips. An example of the use of the belt interface to monitor the separation of a pesticide mixture is shown in figure 20. 

A Wood s metal bath contains a metal alloy (50 per cent bismuth, 25 per cent lead, 12.5 per cent tin, and 12.5 per cent cadmium) with a low melting point ( 70°) which may be used up to quite high temperatures ( 400°). The metal is easily oxidized at the higher temperatures and, therefore, is usually covered with a protective layer of carbon. An electrically heated bath is recommended, since the temperature is then easily controlled. This may be made by taking an ordinary tin can (preferably low and wide), covering it with asbestos paper, and winding a coil of nichrome wire around it. The wire is covered with more asbestos paper held in place by some coils of copper wire. The entire assembly is placed inside a metal container such as... 

Coiled nichrome wire 18 to 20 8 to 10 1,500 Initially lowest cost is very inefficient, and heats nonuniformly with use. 

Electrically heated oil baths, which typically contain either mineral oil or silicone oil, are commonly employed in the laboratory. These baths are heated either by placing the bath container on a hot plate or by inserting a coil of Nichrome resistance wire in the bath. In the latter case, the resistance wire serves as the heating element and is attached to a transformer with an electrical cord and plug (Fig. 2.24). Thermal equilibration within the bath is maintained by placing a paper clip or stirbar in the bath and using a magnetic stirrer (Sec. 2.11). 

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