Cooling prediction

A plate of polystyrene is to be injection-moulded. When the cavity is sealed freezing of the gate, the melt is at a temperature and pressure of 120 C and 20 MPa, respective. Assuming uniform cooling, predict the linear mould shrinkage of the plate when it is removed from the mould at 20°C Use the following data for polystyrene. 

Poly(methyl methacrylate) (PMMA) is to be injection moulded. The cavity will be sealed by freezing of the gate when the mass of polymer in the cavity is at 165"C and under the packing pressure of 40 MPa. Assuming slow (uniform) cooling, predict the temp>erature of the melt at which the pressure in the cavity falls to atmospheric, employing the following equation of state which links pressure P (in Pa), specific... 

Equation (Cl.4.35) yields two remarkable predictions first, tliat tire sub-Doppler friction coefficient can be a big number compared to since at far detuning Aj /T is a big number and second, tliat a p is independent of tire applied field intensity. This last result contrasts sharjDly witli tire Doppler friction coefficient which is proportional to field intensity up to saturation (see equation (C1.4.24). However, even tliough a p looks impressive, tire range of atomic velocities over which is can operate are restricted by tire condition tliat T lcv. The ratio of tire capture velocities for Doppler versus sub-Doppler cooling is tlierefore only uipi/uj 2 Figure Cl. 4.6 illustrates... 

Eurther research on convective transport under low Reynolds number, quasicontinuum conditions is needed before the optimal design of such a micro heat exchanger is possible. The cooling heat exchanger is usually thermally linked to a relatively massive substrate. The effects of this linkage need to be explored and accurate methods of predicting the heat-transfer and pressure-drop performance need to be developed. 

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

W. Majewski and D. C. Miller, eds.. Predicting Effects of Power Plant Once-Through Cooling on Aquatic Systems, Technical Papers in Hydrology 20, United Nations Educational, Scientific and Cultural Organization (Unesco), Paris, 1979. 

For practical reasons, the blast furnace hearth is divided into two principal zones the bottom and the sidewalls. Each of these zones exhibits unique problems and wear mechanisms. The largest refractory mass is contained within the hearth bottom. The outside diameters of these bottoms can exceed 16 or 17 m and their depth is dependent on whether underhearth cooling is utilized. When cooling is not employed, this refractory depth usually is determined by mathematical models these predict a stabilization isotherm location which defines the limit of dissolution of the carbon by iron. Often, this depth exceeds 3 m of carbon. However, because the stabilization isotherm location is also a function of furnace diameter, often times thermal equiHbrium caimot be achieved without some form of underhearth cooling. 

Other Effects Stream concentration can have important effects on corrosion rates. Unfortunately, corrosion rates are seldom linear with concentration over wide ranges. In equipment such as distillation columns, reactors, and evaporators, concentration can change continuously, makiug prediction of corrosion rates rather difficult. Concentration is important during plant shutdown presence of moisture that collects during cooling can turn innocuous chemicals into dangerous corrosives. 

A number of current coupled ocean-atmosphere climate models predict that the overturning of the North Atlantic may decrease somewhat under a future warmer climate.While this is not a feature that coupled models deal with well, its direct impact on the ocean s sequestration of carbon would be to cause a significant decline in the carbon that is stored in the deep water. This is a positive feedback, as oceanic carbon uptake would decline. Flowever, the expansion of area populated by the productive cool water plankton, and the associated decline... 

Because C-curves are determined by quench-hold-quench sequences they can, strictly speaking, only be used to predict the micro structures that would be produced in a steel subjected to a quench-hold-quench heat treatment. But the curves do give a pretty good indication of the structures to expect in a steel that has been cooled eontinuously. For really accurate predictions, however, eontinuous eooling diagrams are available (see the literature of the major steel manufacturers). 

To simulate the next summer s condition the plant was run at the desired production rate and two cooling tower fans were turned off. It turned out that the cold water temperature rose to slightly above that predicted for the next summer. A thorough inspection of critical temperatures and the plant s operation indicated that the plant would barely make it the next summer. Process side temperatures were at about the maximum desired, with an occasional high oil temperature alarm on the large machines. 

Calculate N,og and Table 1, from Predict the number of Transfer Units for Cooling Towers, by Kamal Adham Khodaparast, Chemical Engineering Progress, Vol. 88, No. 4, pp. 67-68 (1992). Reproduced by permission of the American Institute of Chemical Engineers. 1992 AlChE. ... 

Classic Side Studies and Their Results. Let s discuss briefly the classic side studies and even predict what the final results might be For air versus water cooling, the optimum temperature will probably lie in the range 120-150°F, so time can be saved by building initial cases therein. 

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