Resistance heating units

Induction heating systems, skin effect heating, dielectric heating or systems with a current passing through a liquid, an enclosure or pipework are not within the scope of increased safety. However, resistance heating devices 

Enclosure material polyester resin, glass fibre reinforced, or steel, galvanized, or stainless steel Type of protection EEx ed IIC TCertificate PTB Ex-95.D.3155 (for polyester enclosures) PTB Ex-96.D.3148 (for steel enclosures). 

Enclosure dimensions, approx, (height x width x depth)  

Note At the right side/on top, a flameproof enclosure - d is installed. 

Type of protection EEx e l/ll IP code (when installed) IP 68 Air flow at Ap =7000 Pa 14 litres/hour up to 25 litres/hour, depending on size. 

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During the experiment, a layer of catalyst powder (or sieved meshed particles) is packed into the center tube holder. The alumina membrane disc holds the powder sample at the downstream side while allowing the reactant to flow through with minimal resistance. At the upstream side, a small amount of quartz wool is inserted to support the powder. This whole sample holder assembly is fastened to the outer connector and this whole tube assembly is enclosed in the quartz tube that is surrounded by a resistive heating unit. At each end of the tube, X-ray transparent windows are mounted. The thermocouple is placed close to the sample holder. The long gas inlet tube is heated by the tubular furnace, ensuring that the gas is preheated before it reaches the catalyst sample. The upper working temperature is 973 K, which is only limited by the materials of construction. 

The derivatives are hydroxyethyl and hydroxypropyl cellulose. AH four derivatives find numerous appHcations and there are other reactants that can be added to ceUulose, including the mixed addition of reactants lea ding to adducts of commercial significance. In the commercial production of mixed ethers there are economic factors to consider that include the efficiency of adduct additions (ca 40%), waste product disposal, and the method of product recovery and drying on a commercial scale. The products produced by equation 2 require heat and produce NaCl, a corrosive by-product, with each mole of adduct added. These products are produced by a paste process and require corrosion-resistant production units. The oxirane additions (eq. 3) are exothermic, and with the explosive nature of the oxiranes, require a dispersion diluent in their synthesis (see Cellulose ethers). 

Nonferrous alloys account for only about 2 wt % of the total chromium used ia the United States. Nonetheless, some of these appHcations are unique and constitute a vital role for chromium. Eor example, ia high temperature materials, chromium ia amounts of 15—30 wt % confers corrosion and oxidation resistance on the nickel-base and cobalt-base superaHoys used ia jet engines the familiar electrical resistance heating elements are made of Ni-Cr alloy and a variety of Ee-Ni and Ni-based alloys used ia a diverse array of appHcations, especially for nuclear reactors, depend on chromium for oxidation and corrosion resistance. Evaporated, amorphous, thin-film resistors based on Ni-Cr with A1 additions have the advantageous property of a near-2ero temperature coefficient of resistance (58). 

Hitze-einheit,/. heat unit, thermal unit, -ein-wirkung,/. action or influence of heat, hitzeempfindlich, a. sensitive to heat. Hitzeerzeugung, /. heat generation, hitzefest, a. resistant to heat. 

Cl in conjunction with a direct exposure probe is known as desorption chemical ionization (DCI). [30,89,90] In DCI, the analyte is applied from solution or suspension to the outside of a thin resistively heated wire loop or coil. Then, the analyte is directly exposed to the reagent gas plasma while being rapidly heated at rates of several hundred °C s and to temperatures up to about 1500 °C (Chap. 5.3.2 and Fig. 5.16). The actual shape of the wire, the method how exactly the sample is applied to it, and the heating rate are of importance for the analytical result. [91,92] The rapid heating of the sample plays an important role in promoting molecular species rather than pyrolysis products. [93] A laser can be used to effect extremely fast evaporation from the probe prior to CL [94] In case of nonavailability of a dedicated DCI probe, a field emitter on a field desorption probe (Chap. 8) might serve as a replacement. [30,95] Different from desorption electron ionization (DEI), DCI plays an important role. [92] DCI can be employed to detect arsenic compounds present in the marine and terrestrial environment [96], to determine the sequence distribution of P-hydroxyalkanoate units in bacterial copolyesters [97], to identify additives in polymer extracts [98] and more. [99] Provided appropriate experimental setup, high resolution and accurate mass measurements can also be achieved in DCI mode. [100]... 

Kontes/Martin, 1916 Greenleaf St., Evanston, IL 60204 resistive heating is employed in this unit. 

The temperature of the cylinder is regulated with an annular liquid thermostat, i. The heating medium (silicone oil) is constantly circulated to maintain temperature control. A platinum resistance thermometer which operates through a Wheatstone bridge controls the current in the heating unit with the help of a hoop-drop... 

Vertical CVD reactor systems with rotating gas feed over a stationary, resistance-heated plate are manufactured by Phoenix Materials Corporation, Phoenix (500 and 1500 series Vapor Deposition Systems). Units for processing either 26 or 70 5 cm wafers are available (Kern, 1975). 

Monel metal is used in the manufacture of propellers for United States battleships, etc. Owing to its power of resisting heat Germany employs the alloy for locomotive fire-boxes. 

The Pt catalyst was mounted on a copper block and could be translated, tilted and rotated by means of a manipulator fitted with a differentially pumped rotary feedthrough. The Pt foil (Advent, purity > 99.99%) could be resistively heated. The mounting allowed to work in the temperature range 300-1600 K using direct sample heating with a proportional-integral-derivative (PID) control unit. The temperature of the catalyst was measured by a Ni-NiCr thermocouple spot welded to the Pt-foil. Clean platinum surfaces could be obtained by applying several cycles of Ar" " ion... 

In the special case of uniform heat generation, as in the case of electric resistance heating throughout a homogeneous material, the relation in Eq. 2-5 reduces to = eg l/, where e is the constant rate of heat generation per unit volume. 

When two such surfaces are pressed against each other, the peaks form good material contact but the valleys form voids filled with air. As a result, an interface contains numerous air gaps of varying sizes that act as insulation because of the low thermal conductivity of air. Thus, an interface offers some resistance to heat transfer, and this resistance per unit interface area is called the thermal contact resistance, R. The value of is determined experimentally using a setup like the one shown in Fig. 3-15, and as expected, there is considerable scatter of data because of the difficulty in characterizing the surfaces. 

That is, thermal contact resistance is the inverse of thermal contact conductance. Usually, thermal contact conductance is reported in the jiterature, but the concept of thermal contact resistance serves as a better vehicle for explaining the effect of interface on heat transfer. Note that represents thermal contact resistance per unit area. The thermal resistance for the entire interface is obtained by dividing by the apparent interface area/t. 

An instrument performing measurements of D2 (viz. the ratio of the resistivity of ice to that of a product at a given temperature) and implementing DTA (differential thermal analysis) was developed to control freeze-drying processes the principal components are a test chamber, a cooling and heating unit, a digital computer system and a printer. It was used to evaluate the thermal features of a 20% sucrose solution [12]. 

There are several construction principles for pyrolyzers, such as with resistively heated filaments, inductively heated, furnace type, and radiatively heated. Detailed descriptions for instrument construction can be found in literature [1] or obtained from instrument manufacturers. The pyrolysis unit usually consists of a controller and the pyrolyzer itself. The controller provides the appropriate energy needed for heating. A simplified scheme of a pyrolyzer based on the design of a flash heated filament system (made by CDS Inc.) is shown in Figure 3.1.1. 

Electric arc resistance heated furnaces and electrical melting units are mainly used for refractory ceramic fibers, due to the high melting temperatures of the raw materials. In ovens with resistance heating the melt itself acts as the electrical resistance, since silicate melts generally become sufficiently conductive with increasing temperature to transport sufficient current, due to ionic conduction. 

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