Packings calculation

If it is desired to evaluate a change in performance on an existing tower, knowing the required conditions and numbers of decks and kind of packing, calculate KaV/L for we assumed values of L /G. ... 

Assume that the actual volume of the aggregates in the nitrogen adsorption experiments is 60% of the total volume (with the rest accounting for pore space between aggregates in the packing). Calculate the fractal dimension of the aggregates. 

Table 10.2. Projected (along c-axis) PTFE Phase II Unit Cell Parameters from Rigid Chain Packing Calculations Utilizing Parameter Sets I-IV...

Figure 10.4 (A) The DNA interaxial distance dDNA and the interlayer distance d in the L°a phase (Figure 10.2) plotted as a function of Lipid/DNA (UD) (wt/wt) ratio at the isoelectric point of the0 complex DOTAP/DNA=2.2. dDNA is seen to expand from 24.5 A to 57.1 A. The solid line through the data is the prediction of a packing calculation where the DNA chains form a space rilling one-dimensional lattice. (B) Schematic drawing of DNA-membrane multilayers showing the increase in distance between DNA chains as the membrane charge density is decreased (i.e., as DOpc increases) at the isoelectric point (Adapted from Raedler et al., 1997 Kohover etal., 1999).

Based on molecular packing calculations with and without symmetry constraints the lattice dimensions for RDX crystal have been reproduced to within 0.9% deviation relative to experimental results and with a very small translation and rotation (less than 1.1°) of the molecules inside the unit cell. Additionally, the lattice energy was found to be practically identical to the static lattice energy estimated based on the experimental enthalpy of sublimation (E AH S0M + 2RT). 

As molecular packing calculations involve just simple lattice energy minimizations another set of tests have focused on the finite temperature effects. For this purpose, Sorescu et al. [112] have performed isothermal-isobaric Monte Carlo and molecular dynamics simulations in the temperature range 4.2-325 K, at ambient pressure. It was found that the calculated crystal structures at 300 K were in outstanding agreement with experiment within 2% for lattice dimensions and almost no rotational and translational disorder of the molecules in the unit cell. Moreover, the space group symmetry was maintained throughout the simulations. Finally, the calculated expansion coefficients were determined to be in reasonable accord with experiment. 

N2 molecules (radius = 1.84 x 10-10m) are adsorbed on the surface of a Ti layer. Assuming that they are hexagonally close-packed, calculate the amount of N2 (in units of mbar L) adsorbed per unit area of the Ti. 

The requirement that components be of compatible size is a crystal-packing requirement. The horror vacui which Kitaigorodskii16 explored in crystal packing calculations [40] means that, with the best designed donors and acceptors, if they are of very different sizes, good compact structures with charge transfer are not achieved. This is why there are few interesting salts with TCNE and so many with TCNQ TCNE is too small an electron acceptor, compared with most donors, while literally hundreds of salts are known with TCNQ. 

Mutation Distance (A) AG (meV) Packing Calculated log rate Experimental log rate... 

The 30 successive packing calculations consumed, respectively for zeolite Li-A(BW) and zeolite 4A, some 3s and 12s on a workstation, with each structure optimization then reqmring an additional 2 or 8 min. respectively. In the latter case, in which the local structure provided by the simulations and the sample-averaged structure yielded by difiraction differ, the modeling results also allow the local effects of the site disorder to be explored. These encouraging results set the stage for extensions to still more complex systems and to structures for which less direct experimental data are available. 

The applications were extended to mixed molecular crystals such as tetracene contained as a dilute impurity in anthracene. Choudhury and Ganguly [213] had measured the absorption spectmm of tetracene at 480 nm and interpreted it with the assumption, later confirmed by crystal packing calculations, that the molecules are held in the anthracene lattice in almost the same position and orientation as the molecules they replace. They made the remarkable discovery that the intensity ratio for absorption along the b and a crystal axes was not 7.7 1 expected on the oriented gas model, but around 2 1. We later refined the measurements [84] to give values close to 3 1. 

When after formation of photoproduct at one of the two sites the crystal was heated and cooled the photoreaction was reversed. We were able to conclude with the help of the packing calculations of sec. 3.2 and other experimental results that those impurity molecules that reacted could not be those that replaced anthracenes in the regular lattice, but must be at dislocations or regions of abnormal packing, where the host and guest were in face-to-face positions. The reaction is thus belongs to the class of the photodimerizations of anthracene, and 9-cyanoanthracene, not of dimers formed topochemically in the normal lattice. 

Structural Disturbance and Lattice Relaxation in Molecular Crystal Packing Calculations. 

Dynamic Instabilities in Excited Molecular Crystals. Packing Calculations in Anthracenic Systems. 

Mixed-Crystal Packing Calculations. 9-Methoxyanthracene in Host 9-Cyanoanthracene. 

Karfunkel HR, Wu ZJ, Burkan A, et al. Crystal packing calculations and Rietveld refinement in elucidating the crystal structures of two modifications of 4-amidoindance guanylhydra-zone. Acta Cryst B 1996 52 555-561. 

Vehicle Battery Type EV/HEV Pack Power (kW) Pack Energy (kWh) Pack Voltage (V) Pack Capacity (Ah) Modules/ Pack Calculated Pack Volume (L) Total Pack Mass (kg)... 

Design a tower packed with 50-mm ceramic Hiflow rings for the carbon disulfide scrubber of Problem 5.11. Assume isothermal operation and use a liquid rate of 1.5 times the minimum and a gas-pressure drop not exceeding 175 Pa/m of packing. Calculate the tower diameter, packed height, and total gas-pressure drop. Assume that Ch for the packing is 1.0. 

The first experimental data show that the tetragonal lattice is not realized for lithium [89]. This can be explained by means of packing calculations. The Li ion is much smaller than the holes in the most closely packed form of the lattice proposed (see Table 1.3 and Figure 1.9). Na is only slightly smaller, K just fits nicely, while Rb and Cs" ions leads to some expansion. Though Li-doped polyacetylene has been called amorphous at first, Leitner et al [95] demonstrate diffraction from Li-doped Durham polyacetylene. A number of possibilities for the location of the lithium ions is considered, based on a unit cell almost undistorted by doping [96]. 

Depero [9-50] has summarized the various approaches developed historically in molecular packing calculations. Her scheme has the following five subdivisions ... 

The value of this work goes well beyond measmement. The compressibility data will provide a better basis for compressor design and testing. Reservoir engineers should find the expanded range of particular value. Line pack calculations will be more precise. This work is really a key step in basic knowledge. 

---