Track model

Front-tracking model for in situ combustion oil recovery [1515]... 

P. S. Rocha, M. A. Miller, and K. Sepehmoori. A succession-of-states front-tracking model for the in-situ combustion recovery process. In Situ, 21(1) 65-100, February 1997. 

There is a large body of known radiation-physical and radiation-chemical phenomena, the existence or explanation of which requires a track model. With the exception of the consideration of electron escape (ffee-ion yield), these phenomena... 

The areas where the use of the track model has been found particularly expedient are (1) LET variation of product yields in the radiation chemistry of liquids (2) the yield of escaped ions and its variation with particle LET (3) energy loss in primary excitations and ionizations (4) radiation-induced luminescence and (5) particle identification. 

In liquefied rare gases (LRG) the ejected electron has a long thermalization distance, because the subexcitation electrons can only be thermalized by elastic collisions, a very inefficient process predicated by the small mass ratio of the electron to that of the rare gas atom. Thus, even at a minimum of LET (for a -1-MeV electron), the thermalization distance exceeds the interionization distance on the track, determined by the LET and the W value, by an order of magnitude or more (Mozumder, 1995). Therefore, isolated spurs are never seen in LRG, and even at the minimum LET the track model is better described with a cylindrical symmetry. This matter is of great consequence to the theoretical understanding of free-ion yields in LRG (see Sect. 9.6). 

Figure 10.19 Contact-tracking model in sales business.

The thermalization path length of subexcitation electrons has been the object of many discussions from the time the first track models appeared up to this day. The reason is that for quite a long time there were no direct methods of measuring the path lengths of slow electrons, while the corresponding theoretical analysis is very difficult owing to the need to take into account all the processes relevant to retardation of subexcitation electrons. 

The particle tracking is therefore divided into two phases. In the first the acceleration within the fast gas jets that are found in and just above the erupting bubbles is simulated and in the second the accelerated particles are followed through the freeboard. In practice this means an average gas jet velocity and the time and distance the particle spends within that jet are estimated from the fluidised bed model, and then put into the particle tracking model. This gives an initial particle velocity for tracking... 

The terminal velocity that particles reach when in free fall is an important particle characteristic. It is also fairly straightforward to measure and was therefore used to check the accuracy and validity of the particle tracking model. The measurement technique is entrainment of a small sample of a particular size class in a narrow tube taking the average of the band within which 90% of the small sample are entrained. In the computational modelling of the particle tracks the upper end of the class size is used as the particle diameter and the particles are started from rest and from a falling velocity greater than their terminal velocity. 

M. Bussmann, J. Mostaghimi, S. Chandra, On a three-dimensional volume tracking model of droplet impact, Physics of Fluids, vol. 11,1406-1417,1999. 

Lee (1995) has proposed a model for fast-track diffusion to explain the effects of combined lattice diffusion and diffusion along fast diffusion pathways through the lattice such as defects. Lee proposed that the combined diffusion could be modeled as two parallel diffusion mechanisms with argon atoms partitioning between the two. The mathematical model produces realistic release patterns, but does not currently take account of the distances between fast track pathways and the time taken for atoms to reach one (cf. Arnaud and Kelley 1995). Future development of the fast track model may provide very fruitful avenues for research. 

Track Model Energy Partition Between Core and the Emergent Secondary Electrons... 

Further developments using track models presented here will be reported later. We propose to include (1) diffusion kinetic studies based on present track models, (2) discussion of thermalization lengths of electrons generated in these tracks, and (3) detailed description of fission fragment tracks. 

Dijkhuizen, W., Roghair, L, van Sint Annaland, M., and Kuipers, J.A.M. (2010), DNS of gas bubbles behaviour using an improved 3D front tracking model—model development, Chemical Engineering Science, 65(4) 1427-1437. 

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