Cooling nonuniform

Crystalline polymers undergo a discontinuous decrease in volume when cooled through (Fig. 4). This can lead to nonuniform shrinkage and warping in molded objects. On the other hand, it also causes the polymer to "lock on" to reinforcing fibers, eg, glass (qv), so that crystalline thermoplastics benefit much more than amorphous thermoplastics from fiber reinforcement. 

Some concerns directly related to a tomizer operation include inadequate mixing of Hquid and gas, incomplete droplet evaporation, hydrodynamic instabiHty, formation of nonuniform sprays, uneven deposition of Hquid particles on soHd surfaces, and drifting of small droplets. Other possible problems include difficulty in achieving ignition, poor combustion efficiency, and incorrect rates of evaporation, chemical reaction, solidification, or deposition. Atomizers must also provide the desired spray angle and pattern, penetration, concentration, and particle size distribution. In certain appHcations, they must handle high viscosity or non-Newtonian fluids, or provide extremely fine sprays for rapid cooling. 

Type IV (Low Heat of Hydration). Type IV is used where the rate and amount of heat generated from hydration have to be minimised, ie, large dams. Compared to Type I, Type IV Pordand cement has only about 40 to 60% of the heat of hydration during the tirst seven days and cures at a slower rate. In large stmctures such as dams where the heat of hydration cannot be readily released from the core of the stmcture, the concrete may cure at an elevated temperature, and thermal stresses can build up in the stmcture because of nonuniform cooling that weakens the stmcture. U.S. production of Type IV Pordand cement is less than 1%. 

Equipment which is electrically driven and operated with metal temperatures exceeding 425 K should be provided with auxihaiy drives or power sources. Loss of rotation of a heated calciner or high-temperature dryer carrying a hea y bed of hot solids will quickly result in sagging of the cyhnder due to nonuniform cooling. 

Local air motion is another thermal nonuniformity that can cause a local cooling of the skin and the feeling of a draft. Draft discomfort from local air motion increases as the air temperature decreases below skin temperature. Fluctuations in the local air motion increase the perception of drafts and should be avoided. The unsteadiness of air motion is often described in terms of its turbulence intensity (Tu) ... 

High supply air velocities or cool supply air can cause uncomfortable drafts on the worker. Nonuniform supply air velocities with high turbulence intensity may result in decreased capture efficiency, increased contaminant spread, and increased thermal discomfort. 

Hetsroni G, Mosyak A, Segal Z (2001) Nonuniform temperature distribution in electronic devices cooled by flow in parallel micro-channels. IEEE Trans Comp Packag Technol 24(1) 16-23 Ho CM, Tai Y-C (1998) Micro-electronic mechanic systems (MEMS) and fluid flows. Ann Rev Fluid Mech 30 5-33... 

The more recent Thomas model [209] comprises elements of both the Semenov and Frank-Kamenetskii models in that there is a nonuniform temperature distribution in the liquid and a steep temperature gradient at the wall. Case C in Figure 3.20 shows a temperature distribution curve from self-heating for the Thomas model. The appropriate model (Semenov, Frank-Kamenetskii, or Thomas) is determined by the ratio of the heat removal from the vessel and the thermal conductivity in the vessel. This ratio is determined by the Biot number (Nm) which has been described previously as hx/X, in which h is the film heat transfer coefficient to the surroundings (air, cooling mantle, etc.), x is the distance such as the radius of the vessel, and X is the effective thermal conductivity. 

One of the drawbacks of this CAVERN device is the occurrence of a nonuniform distribution of reactant on catalysts because adsorption occurs on a deep bed of catalyst packed in a MAS rotor. To overcome this problem, we developed several shallow-bed CAVERN devices (95), and Fig. 10 shows a version of one such design. A thin layer of catalyst is supported on a glass trapdoor, and the device is evacuated. A furnace is clamped in place so that the catalyst can be activated if necessary. The catalyst is cooled with a cryogen bath, and a controlled amount of adsorbate is introduced from the vacuum line. The trapdoor is raised, the loaded catalyst falls into the MAS rotor, and the seal is driven into place. Finally the cold, sealed rotor is manually transferred into the cold MAS probe. The added advantages of the shallow-bed CAVERN is that all manipulations can be carried out without using a glovebox in any step. 

Influence of Flow Nonuniformity on the Mass and Heat Transfer Conditions in Cooling Towers)... 

Based on locally nonuniform theoretical distribution of fluids in the range of the inserts it is shown, that not only the nonuniformity of the flow field of the cooling air, but also the nonuniformity of the water to be cooled have to be taken into account in evaluating experimental results and in design. 11 refs, cited. (In German). 

For stage VI, the analysis of inherent (or residual) stresses resulting from nonuniform cooling and heat treatment of final articles appears to be critical.Thus, stages IV to VI should be the subject of mathematical modelling specific to reactive processing (chemical molding processes). 

The third factor is the nonuniform temperature field in the gap, because the outside wall is cooled to secure high enough stresses in the gap, but the rotor is not cooled moreover, viscous dissipation generates heat. All these led to a nonuniform stress field, which once again affects performance. 

The focusing noted above will deteriorate due to (a) the failure of the harmorii j approximation for atoms hitting y points for which Eq. (12.61) does not hold, nonuniform vz distribution, and (c) non-zero v transverse-velocity values, thaiR deviations of the atomic directions from the normal. The last two effects can minimized by cooling the atomic beam and selecting its directionality by ufiirt t sequence of slits. 

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