Heating electrical resistance heaters

Heating and Cooling. Heat must be appHed to form the molten zones, and this heat much be removed from the adjacent sohd material (4,70). In principle, any heat source can be used, including direct flames. However, the most common method is to place electrical resistance heaters around the container. In air, nichrome wine is useflil to ca 1000°C, Kanthal to ca 1300°C, and platinum-rhodium alloys to ca 1700°C. In an inert atmosphere or vacuum, molybdenum, tungsten, and graphite can be used to well over 2000°C. 

Low-voltage electric resistance heater cables fixed to the structural floor slab and then protected within a 50 mm thickness of cement and sand to give a suitable surface on which the floor vapour barrier can be laid. The heating is thermostatically controlled, and it is usual to include a distance reading or recording thermometer to give visual indication of the temperature of the floor at several locations below the insulation. 

The next step involves heating the mold while it is rotating. Molds can be heated by a heated oven, a direct flame, a heat-transfer liquid (either in a jacket around the mold or sprayed over the mold), or electric-resistance heaters placed around the mold. With uniform heat transfer through the mold, the plastic melts to build up a layer of molten plastic on the molds inside surface. 

Typically, a FW tank temperature of 180 to 190 °F (82-88 °C) is preferred and can be achieved by the direct application of live steam (from a LP steam supply or from a flash steam recovery system) through a perforated sparge pipe or by indirect heating via steam, gases of combustion, or electrical-resistance heaters. Each temperature rise of 10 °F (5.6 °C) results in at least a 0.3 to 0.4% fuel saving. Tanks should, of course, be properly designed and lagged. 

The second study was done in a cold-wall reactor12-13 using the same reactants. The reactor was a single-wafer system, similar to the tube reactor of Figure 18 in Chapter 2, with the wafer heated by an electrical resistance heater in the pedestal. In this case, the sublimator was operated at 88°C with a 10 seem flow of H2. The influence of SiH4 flow rate on the film stoichiometry and resistivity (after anneal) are shown in Figure 11. 

An electrical resistance heater with more turns at the tube ends (to compensate for heat losses) surrounds each tube. There is a vertical laminar flow hood over the loading area to minimize particle contamination of the wafers being loaded. As we can see, there are temperature controls for the furnace tubes, and a power module to provide the electrical power. When operated as a LPCVD system, a unit including both the gas flow and vacuum systems is positioned on the right side. Such a unit is shown in Figure 8. Here we can see the vacuum pumps on the left, and the mass flow controllers on the right. The vacuum pump oil recirculation systems are shown in the slide out drawers. As can be seen in Figure 9, this system, as well as most current similar systems, operate under computer control. 

A recuperative bayonet sulphuric acid decomposition reactor has been designed by researchers at Sandia National Laboratories (SNL) that features all-silicon carbide (SiC) construction for the heated parts, can be made from readily available SiC shapes, makes the most use of heat recuperation, and has all of its fluid connections at sufficiently low temperatures that conventional seal materials can be used. Bench-scale experiments using electric resistance heaters as the energy source have verified that the design functions as intended. 

The thermal rockets, other than chemical rockets,. currently at the furthest state of development are surface heat transfer rockets. The term surface heat transfer is used to imply that thermal energy is transferred to the propellant through a material wall. Many sources of the thermal energy are possible and include solid core nuclear reactors, radioisotopes, electrical resistance heaters, and solar heaters. 

One of the most versatile and robust heating techniques is the use of electrical resistance heaters. They are used in as varied heating approaches as hot plates, mantles, heat strips, immersion heaters, and even blankets. 

Hot Plates. These devices have a metal (cast aluminum, stainless steel, or some alloy), ceramic, or pyroceramic top. Underneath the top is an electric resistance heater. Hot plates are used for heating flat-bottom containers such as beakers and Erlenmeyer flasks. Because hot plate tops are non-porous, there are fewer concerns for spills affecting the heating elements as there are with heating mantles. Magnetic stirring devices are commonly included with hot plates. 

Heat is added to the fluid from the electric resistance heater the rate of energy input is determined from the resistance of the heater and the current passing through it. The entire apparatus is well insulated. In practice there are a number of details which need attention, but in principle the operation of the flow calorimeter is simple. Measurements of the rate of heat input and the rate of flow of the fluid allow calculation of values of AH between sections 1 and 2. 

A layer of material of known thickness and area can be heated from one side by an electric resistance heater of known output. If the outer surfaces of the heater are well insulated, all the heat generated by the resistance heater will be transferred through the material whose conductivity is to be determined. Then measuring the two surface temperatures of the material when steady heal transfer is reached and substituting them into Bq. 1-21 togelher with other known quantities give tlie thermal conductivity (Fig. 1-26). 

Water is heated in an insulated, constant diameter tube by a 7-kW electric resistance heater. If the water enters the heater steadily at 15°C and leaves at 70 C, determine the mass flow rate of water. 

A 2-kW electric resistance heater submerged in 30-kg water is turned on and kept on for 10 min. During the process, 500 kJ of heat is lost from the water. The temperature rise of water is... 

Consider a water pipe of length A = 17 m, innet radius r, = 15 cm, outer radius = 20 cm, and thermal conductivity k 14 w/m C. Heat is generated in the pipe material uniformly by a 25-kW electric resistance heater. The inner and outer surfaces of the pipe are at Tj = 60 C and T2 80°C, respectively, Obtain a general relation for leraperature distribution inside the pipe under steady conditions and determine Ihe temperature at the center plane of the pipe. 

A thick aluminum block initially at 20 C is subjected to constant heat flux of 4000 W/in by an electric resistance heater whose top surface is insulated. Determine how much the surface temperature of the block will ri.se after 30 minutes. 

Water is to be heated from 15 C to 65 C as it flows through a 3 cm-internal-diameter 5-m-long tube (Fig. 8-30). The tube is equipped with an electric resistance heater that provides uniform heating throughout the surface of the tube. The outer surface of the heater is well insulated, so that in steady operation all the heat generated in the heater is transferred to the water in the tube. If the system Is to provide hot water at a rate of 10 L/min, determine the power rating of the resistance heater. Also, estimate the inner surface temperature of the tube at the exit. 

SOLUTION Water is to he heated in a tube equipped with an electric resistance heater on its surface, The power rating of the heater and the inner surface temperature at the exit are to be determined. 

An electrical resistance heater starts radiating heat soon after it is plugged in, and we can feel the emitted radiation energy by holding our.hands against the heater. But this radiation is entirely in the infrared region and thus cannot... 

A 2.75-m-liigh room with a base area of 3,7 m X 3.7 ui is to be heated by electric resistance heaters placed on the ceiling, which is maintained at a uniform temperature of 32°C at all limes, The floor of the room is al 17°C and has an emissivity of 0.8. The side surfaces arc well insulated. Treating the ceiling as a blackbody, determine the rate of heal loss from the room through the floor. 

Because evaporation of a liquid phase usually requires addition of large amounts of thermal energy, the method of transferring this heat to the liquor tends to dominate evaporator capital cost. The source of heat for evaporators is usually a medium such as hot combustion gases or a condensing vapor, typically steam. Molten salts and electrical resistance heaters are less commonly used sources of thermal energy. 

Argon gas in an insulated plasma deposition chamber with a volume of 2 L is to be heated by an electric resistance heater. Initially the gas, which can be treated as an ideal gas, is at 1.5 Pa and 300 K. The lOOO-ohm heater draws current at 40 V for 5 minutes (i.e., 480 J of work is done by the surroundings). What is the final gas temperature and pressure at equilibrium The mass of the heater is 12 g and its heat capacity is 0.35 J/(g)(K). Assume that the heat transfer to the chamber from the gas at this low pressure and in the short time period is negligible. 

In industrial processes heat energy is transferred by a variety of methods, including conduction in electric-resistance heaters conduction-convection in exchangers, boilers, and condensers radiation in furnaces and radiant-heat dryers and by special methods such as dielectric heating. Often the equipment operates under steady-state conditions, but in many processes it operates cyclically, as in regenerative furnaces and agitated process vessels. 

In this equation, q",.dA is the net radiative heat flux at the moving material surface imposed by external sources such as radiant burners/heaters or electric resistance heaters. Both parabolic, boundary layer [80], and full, elliptic [61,81] problem solutions have been reported. Because of the nature of the problem, the heat transfer results can t be given in terms of correlations. The interested reader is referred to Refs. 62 and 79 for citation of relevant references. 

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