Liners temperature control

Hot wall reactors have the advantage of close temperature control. A disadvantage is that deposition occurs everywhere, on the part as well as on the walls of the reactor, which require periodic cleaning or the use of a disposable liner. 

In Fig. 7.2 a thermoplastic filament winding process consisting of a material rack, a tension controller, a preheating zone, a main heater, a consolidation roller and a mandrel is shown schematically. Beside the material used, the most adjustable process parameters are winding velocity (which is defined by mandrel rotation and crosshead movement), roving tension, temperature, winding angle and mandrel/liner (material and temperature control). 

In some cases, especially for pressure vessels (connection quality), or the usage of slightly volatile mediums, a liner as mandrel is used. The liner can be a vital part of the product which is also considered by the requirements. The filaments are wound on the liner, which remains in the application. Materials for the liner manufacturing depend on the end-use of the application. Liners can be made, for example, of polymer, aluminum alloy or steel. Also like the dissolvable core the liner cannot be temperature controlled. 

As a blow moulding material, nse of HDPE has been very successful. In order to work at the lowest practical temperatures, very good temperature control is necessary for all stages of the process, and in addition machines should be of robust construction because high pressures are developed in the barrels. To minimise wear the extruder barrels should have a continuous hardened steel liner. 

Temperature changes in layered composites lead to shape distortion via spatial differences in material properties. Our original interest in the phenomenon was motivated by quality control during the manufacturing of the boxes for refrigerators and freezers. These boxes are made from a steel sheet as an outside layer, a plastic liner and urethane foam in the middle. In our case, the liner was made from... 

Permeability of an FML is evaluated using the Water Vapor Transmission test.28 A sample of the membrane is placed on top of a small aluminum cup containing a small amount of water. The cup is then placed in a controlled humidity and temperature chamber. The humidity in the chamber is typically 20% relative humidity, while the humidity in the cup is 100%. Thus, a concentration gradient is set up across the membrane. Moisture diffuses through the membrane, and with time the liquid level in the cup is reduced. The rate at which moisture is moving through the membrane is measured. From that rate, the permeability of the membrane is calculated with the simple diffusion equation (Fick s first law). It is important to remember that even if a liner is installed correctly with no holes, penetrations, punctures, or defects, liquid will still diffuse through the membrane. 

Area 300 is controlled using a distributed control system (DCS). The DCS monitors and controls all aspects of the SCWO process, including the ignition system, the reactor pressure, the pressure drop across the transpiring wall, the reactor axial temperature profile, the effluent system, and the evaporation/crystallization system. Each of these control functions is accomplished using a network of pressure, flow, temperature, and analytical sensors linked to control valves through DCS control loops. The measurements of reactor pressure and the pressure differential across the reactor liner are especially important since they determine when shutdowns are needed. Reactor pressure and temperature measurements are important because they can indicate unstable operation that causes incomplete reaction. 

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