Nozzles coil heater

Mineral-insulated cable heaters are often coiled and used on hot sprue bush-ing/runnerless molding nozzles. The coil heaters are capable of high operating temperatures, up to 815°C. 

Coil heaters fitted onto the casing usually have external insulation in the form of a jacket of polished or nickel-plated steel sheet which reflects thermal radiation. Coil or band heaters fastened to the nozzle flange are similarly insulated by reflective band clips. 

There is a trend for coil heaters of increasingly small diameter (Hotset) to be introduced, as this enables the nozzle pitch to be made smaller. New developments in 220/230 V heaters of type (d) (see Figure 5.1) are beginning to compete successfully with low-voltage heaters. The durability of 230 V and 5 V heaters is also becoming comparable. 

The hydrocarbon gas feedstock and Hquid sulfur are separately preheated in an externally fired tubular heater. When the gas reaches 480—650°C, it joins the vaporized sulfur. A special venturi nozzle can be used for mixing the two streams (81). The mixed stream flows through a radiantly-heated pipe cod, where some reaction takes place, before entering an adiabatic catalytic reactor. In the adiabatic reactor, the reaction goes to over 90% completion at a temperature of 580—635°C and a pressure of approximately 250—500 kPa (2.5—5.0 atm). Heater tubes are constmcted from high alloy stainless steel and reportedly must be replaced every 2—3 years (79,82—84). Furnaces are generally fired with natural gas or refinery gas, and heat transfer to the tube coil occurs primarily by radiation with no direct contact of the flames on the tubes. Design of the furnace is critical to achieve uniform heat around the tubes to avoid rapid corrosion at "hot spots."... 

The G.P. chamber is equipped with an air cooler of about 5500 BTU size (Item 3) is located about 1.8 meters off the floor. An evaporator control valve (Item 2) on the refrigerate line allows temperature control of the air cooler condenser coils. Temperature of the coils is maintained just above the dew point for 50% relative humidity. An electric baseboard heater (Item 6) is equipped with a hydrastatic thermostat control (Item 11). The base board heater is placed near the floor and opposite of the chamber door. A humidifier (Item 4) is located approximately 1.8 meters above the floor and just to the right of the air cooler. The nozzle of the humidifier is pointed slightly toward the back of the chamber. A humidistat (Item 10) is centered between the floor and end walls on the same side as the humidifier. A strategically located recording hygrothermograph is used to monitor both temperature and humidity. 

The second version of the nozzle 4.55(b) is a design with two improvements. The heater coil is elongated in the centre to cause a more even temperature distribution. To improve insulation, the support ring is made of titanium alloy, but these changes have not made a lot of difference. 

A heater with a coil of rectangular cross-section (b), or more often a flattened oval cross-section, has a greater contact area with the nozzle, which allows some of the heat to be transferred by conduction. This reduces the heat load and improves the thermal balance. The thermal density used is 6-15 W/cm. ... 

The basic airflow system for flotation dryers is shown in Figure 40.10. It consists of three basic components (1) supply fan (2) exhaust fan and (3) heater. The supply fan is sized for the air volume required by the open area of the dryer nozzles and the maximum nozzle outlet velocity. It blows hot air through the air-bar nozzles onto the coated web surface. The spent air is exhausted by an exhaust fan. The heater can be a direct-fired gas burner for air temperatures up to 400°C or high-steam coils for air temperatures up to 200°C. When drying aqueous coatings, the exhaust is led to a recirculation system where part is bled to the atmosphere and the remainder reheated for recirculation. When solvents are involved, this spent air may be incinerated or led to a solvent-recovery unit. 

A cabinet performing such tests should be equipped with a solid-state humidity sensor reading the current humidity condition and a feedback controller. The mechanism that controls the humidity t5q3ically moves chamber air via a blower motor and passes it with an atomizer nozzle over a heater coil at the bottom of the chamber (Fig. 11.32). 

FIG. H-24 Coil-type stab-in tank heater. This type heater is installed through a side entering tank nozzle, and differs from the bayonet type in that usually more pipes or tubes than one are used, requiring therefore a tubesheet and bonnet, or a continuous coil to allow for usually lower flow of heating medium such as heat transfer oils, diphenyl, etc. Rns are helical for natural convec tion. (Source Armstrong Engineering Associates.)... 

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