Thermal properties affecting cooling

It is the cooling operation that sets the shape of thermoplastics. The rate of cooling affects the process in two ways  

An example of the effect on production rates is provided by injection moulding. The longer it takes after injection for solidification of the polymer to occur, the longer will be the overall cycle. (Provided the moulding is not distorted on ejection it will only be necessary to form a rigid skin to the moulding.) 

The solidification time for an amorphous polymer will be determined by  

It should be noted that polystyrene with a number average molecular weight of 50 000 has a Tg only about 2°C less than would be expected of a polystyrene of infinitely high molecular weight. Hence increasing the molecular weight beyond this point in order to raise the Tg would not be very effective and at the same time it would lead to large increases in melt viscosity. 

174 Principles of the Processing of Plastics 8.2.6 Thermal Properties Affecting Cooling 

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Thermal properties that affect the cooling of the polymer. 

Abstract The thermal properties of adhesives affect the rate of cure, whether the latter is by evaporation, cooling, or chemical reaction. In the latter case cure may not go to completion in the sense that not all monomer is reacted, or may not be possible at all above a ceiling temperature. The heat of polymeri2ation is a useful guide to what may happen. 

Common to all air cooled heat exchangers is the tube, through which the process fluid flows. To compensate for the poor heat transfer properties of air, which flows across the outside of the tube, and to reduce the overall dimensions of the heat exchanger, external fins are added to the outside of the tube. A wide variety of finned tube types are available for use in air cooled exchangers. These vary in geometry, materials, and methods of construction, which affect both air side thermal performance and air side pressure drop. In addition, particular... 

The present model takes into account how capillary, friction and gravity forces affect the flow development. The parameters which influence the flow mechanism are evaluated. In the frame of the quasi-one-dimensional model the theoretical description of the phenomena is based on the assumption of uniform parameter distribution over the cross-section of the liquid and vapor flows. With this approximation, the mass, thermal and momentum equations for the average parameters are used. These equations allow one to determine the velocity, pressure and temperature distributions along the capillary axis, the shape of the interface surface for various geometrical and regime parameters, as well as the influence of physical properties of the liquid and vapor, micro-channel size, initial temperature of the cooling liquid, wall heat flux and gravity on the flow and heat transfer characteristics. 

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