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Kingston Hot Press: Process Improvements

1,398 bytes added, 09:30, 16 April 2010
Heat transfer
The Kingston Hot Press presents a particularly challenging heat transfer system to model. Six 750W Omega [ OT-2107] strip heaters are clamped to the two "press" plates which transfer heat and pressure to the mold and tile composite material. A cork rubber gasket provides insulation between the press plates and the steel weldments which provide the necessary structural support for the device. A simple on/off controller regulates the temperature of the center of the plate with a thermocouple transducer. Standard setpoints range between 150°C and 250°C. Since a tile (or film) can be pressed within 5-35 minutes depending on the thickness of the mold, the problem almost certainly falls within the transient time period. However, the plates are preheated to the setpoint temperature, and so a steady state model can assist in determining the ideal performance of the heating plates upon the initiation of the press cycle.
A preliminary 2D model of the plate was developed to allow for a general understanding of the behaviour of the plate which could be made accessible for the community through open office. Using a 2D finite element control volume approach<ref>===Plate Optimization===Due to the computational limitations, only the top half of the Kingston Hot press was analyzed in SolidWorks. The components included in the meshing and analysis were the: *Top plate*Top gasket*Top heaters*Top weldment The mesh shown below was generated automatically through the SolidWorks mesh function. [[image:Mesh.JPG]] The thermal analysis carried out through COSMOWorks utilized the following Load/Restraints: *Each strip heater was assumed to be producing 250W of heat at the plate contact. This assumption was based on the pseudo-steady state condition reached by the press after pre-heat, and the fact that the controller acts to regulate the 750W heaters to maintain the setpoint temperature.*It was assumed the setpoint temperature was successfully maintained at 150°C at the interface between the heaters and the plate. This is a strong assumption as only one thermocouple is held against the top plate surface at the edge of the plate.*It was assumed that the outer walls of the weldment had a convection coefficient of 10W/m<sup>2</sup>K to the ambient air.*It was assumed that the outerweldment walls radiated heat energy to the surroundings using a [ view factor] of 1<ref>Incropera, F.P. et al., 2007. Fundamentals of Heat and Mass Transfer 6th ed., Hoboken, NJ: John Wiley & Sons.</ref>.</ref>, a rough estimate of the temperature distribution can be arrived at in a simple spreadsheet. Using each cell as a finite control volume the energy balance equation can be used to derive an equation for the control volume (spreadsheet cell) temperature.
The energy balance equation for a 2D control volume is given by:

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