Melt layer temperature

In the older method, still used in some CIS and East European tar refineries, the naphthalene oil is cooled to ambient temperatures in pans, the residual oil is separated from the crystals, and the cmde drained naphthalene is macerated and centrifuged. The so-called whizzed naphthalene crystallizes at ca 72—76°C. This product is subjected to 35 MPa (350 atm) at 60—70°C for several minutes in a mechanical press. The lower melting layers of the crystals ate expressed as Hquid, giving a product crystallizing at 78—78.5°C (95.5—96.5% pure). This grade, satisfactory for oxidation to phthaHc anhydride, is referred to as hot-pressed or phthaHc-grade naphthalene. 

The combustion wave structure of ADN consists of three zones the melt layer zone, the preparation zone, and the flame zone. The temperature remains relatively unchanged in the melt layer zone, then increases rapidly just above the melt layer zone to form the preparation zone, in which it rises from about 1300 to 1400 K. At some distance above the melt layer zone, the temperature increases rapidly to form the flame zone, in which the final combustion products are formed. 

Figure 4-34 is a phase diagram for the system titanite-anorthite. Suppose a crystal of titanite is initially in contact with a crystal of anorthite. The two are heated to 1350°C. Either phase by itself would not melt. But because the temperature is higher than the eutectic point of the two phases, at the interface there is melting. As melting proceeds, a thin melt layer would form between the two crystals. The melting of the two phases continues and the rate may be controlled by different factors. The rate would depend on the controls, as outlined below. 

We now discuss the residence times and temperature increases of layers close to the die wall using the preceding equations At r — Ra 0.1 mm and r — R 0.01 mm, the residence time and the temperature increase of the two layers are, respectively, 0.008 s, 77°C and 0.082 s, 704°C. On the other hand, on the core surface (r — Rf), the residence time is 0.0005 s, and the temperature increase only 38°C. It is obvious that the closer the melt layer is to the die wall, the residence time is longer and the melt temperature during transit increases in an exponential fashion. Despite the very high temperature increases, the residence time of the melt layers near the wall is short and much shorter than the degradation induction time 0(T) (see Fig. E5.1(a), which is for unplasticized PVC). Thus, degradation is not likely to occur, and the wall melt layer has such a small viscosity that it precludes melt fracture. 

If the melt viscosity is considered as a function of temperature, then the momentum and energy equations will have to be solved simultaneously. Nevertheless, the results concerning the temperature increase of the melt layers near the wall will be only slightly different from that just given. The resulting polymer coat thickness can be calculated by equating the volumetric flow rates inside and outside the die, namely ... 

Fig.2.11. Plots of layer thickness against dipping time.197 1, thickness of Layer I 2, thickness of Layer H 3, total thickness of both layers. Temperature 700°C, melt A1 + 2.5 % Fe and corresponding amounts of other elements from the steel.

For metals, such as W, an additional erosion mechanism exists due to the formation of a melt layer on the PFC surface, once the surface temperature exceeds the melting temperature of the metal. This layer can reach a width of several tens of microns for W under energy fluxes of 1 M J/m2 sustained during several hundreds of microseconds. The stability of this layer in realistic tokamak geometries and in contact with the plasma is difficult to describe by... 

Fig. 3.25. Heat flux histories following an ELM of 1MJ/m2 with a power flux triangular waveform (curve 1) with ramp-up and ramp-down phases lasting 300 ds each on a 10mm thick W target under an inter-ELM power flux of 10MWm 2. Curves. (1) incident heat flux load (2) conducted heat flux into the material (3) heat flux spent in melting of the material (the evaporation and black-body radiation heat fluxes are comparatively small and not shown). Curve (4) shows the surface target temperature and (5) shows the temperature of the melt layer. Curve (6) shows the vaporized thickness (amplified of a factor of 1000) and (7) the melt layer assuming that no losses of molten material occur during the ELM [3]...

The impact of the temperature gradient on metamorphism explains many of the features of Figure 1. The typical HGM-type metamorphism of the taiga snowpack eventually transforms most of the snowpack into depth hoar, " while the QIM-type metamorphism of the maritime and Alpine snowpacks forms, in the absence of melting, layers of small rounded grains 0.2 to 0.4 mm in diameter. However, considering the effects of other climate variables such as wind speed is necessary to explain features such as the presence of windpacks formed of small rounded grains in the tundra snowpack. 

Figure 2 Temperature distribution near the interface during formation of the melted layer. This picture implies constant temperature in the metal and in a thin water layer.

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