Temperature control system fluid

One of the major disadvantages is that a very viscous test fluid cannot be subjected to a prolonged period of high shear rate without extensive temperature rise within the test fluid. This effect is due to the fact that the temperature control system cannot cool the test fluid fast enough to counteract the internal heat generation due to fluid flow (J5). 

A typical supercritical fluid extractor includes a supercritical fluid (most often CO2 or CO2 with an organic modifier) source, a means of pressurizing the fluid, a pumping system (for the liquid CO2), an extraction thimble, a device to depressurize the supercritical fluid (flow restrictor), an analyte collection device, temperature-control systems for several zones, and an overall system controller. 

Each of the processes (blown film, sheet, tube, etc.) contains secondary equipment applicable to their specific product lines such as computerized fluid chillers and temperature control systems. Equipment has become more energy-efficient, reliable, and cost-effective. The application of microprocessor and computer compatible controls that can communicate within the extruder line results in the more accurate control of the line. 

Depending on the position of the inductor in or at the mold, the required cavity temperature can be generated near the surface (skin effect). This offers the advantage that much lower amounts of heat are introduced into the mold. In fluid-based temperature control systems, the heat has to be transferred from the interior of the mold in the cavity direction. Therefore, larger mold parts are accidentally heated as well. 

Fluids are usually used for mould temperature control, because both heat extraction and heat supply can be controlled equally well. Electrical heating for soft temperature control is certainly very rapid, but still not fast enough on its own it would cause excessively high temperature variations. In all cases, electrical heating is used in conjimction with fluid temperature control, the latter being there to provide - if required - for sufficiently rapid heat extraction (so as to keep the temperature variations low). This combined temperature control system does indeed obtain the best results, but of course costs are significantly higher, and only rarely economically acceptable. So in what follows only pure fluid temperature control will be considered. 

For higher hard control requirements and for all cases involving soft temperature control, fluid temperature control units (forming units, heating units and cooling units) are used, which pump up a temperature control medium (water and oil) through the temperature control system of the mould. The cycle temperature of the temperature control medium is adjustable, and is adjusted for a pre-set value. 

The accuracy of rheological data obtained using parallel plate measnrements depends on a variety of factors. First, it is essential that sufficient T versns Q and F versus Q data be collected to properly use Equations 8.42 and 8.47. Second, a good temperature control system must be in place to ensure uniform temperatnre throngh-out the gap. Finally, experimental conditions should be chosen to rednce errors from edge fracture, sample expulsion from the gap, wall slip, secondary flow effects due to fluid elasticity and/or misalignment of the plates, and viscous heating. 

Measurement Requirements. Any analysis of measurement requirements must begin with consideration of the particular accuracy, repeatabihty, and range needed. Depending on the appHcation, other measurement considerations might be the speed of system response and the pressure drop across the flow meter. For control appHcations repeatabihty may be the principal criterion conversely for critical measurements, the total installed system accuracy should be considered. This latter includes the accuracy of the flow meter and associated readout devices as well as the effects of piping, temperature, pressure, and fluid density. The accuracy of the system may also relate to the required measurement range. 

Another example of the importance of the VI is the need for a high viscosity index hydraulic oil for military aircraft, since hydraulic control systems may be exposed to temperatures ranging from below — 65°F at high altitudes to over 100°F on the ground. For the proper operation of the hydraulic control system, the hydraulic fluid must have a sufficiently high VI to perform its functions at the extremes of the expected temperature range. 

Green, P.C. and Black, J.C. "High Temperature Stable Viscosifier and Fluid Loss Control System," US Patent 4,486,318(1984). 

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