Types of Grids

Koch Flextgrid 2 (or Koth HIglwCapacity Rexigrid (Rg. 8.14d). This 

Rgui 8.14 (Continued) Common grid packings, (g) Perform Grid. (Part g from K. Hoppe, J. Keller and L. Krell, Chem, Zn r., Fd rua, 1978, p. 110 reprinted courtegy of the tution, of Chemietd Engineers, UK.) 

Perfonn grid (Fig. 8.14. This grid is made of eiqianded metal components. The direction of orientation of small form-punched orifices 

Pressure drop.. Due-to.ite high open area and high capacity, grid is one of th lo i t-pressure-i devices. Compared to 2-in PsiU rings, grids typically have a pressure drop three to five times lowra some 

Wetting. The minimum liquid rate recommended for adequate wetting is about 0.2 to 0.3 gpm (44), although rates down to 0.1 gpm/f have been successfully used (45,46). These rates are low and are comparable to the minimum wettii rates for corrugated-sheet structured packittgs (Sec. 8.1.10). Grids therefore can achieve higd turndown and perform well at low liquid rates. 

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Table 5.12 Comparison of measured data with predictions for different bundles and types of grids...

The shorter grid span gives higher DNB hat fluxes with the same type of grid. 

The following equations can be used to design perforated plates, spargers, and bubble-cap types of grids ... 

To proceed with the design, it is necessary to select a hole size (judgement call). For the purpose of this example, a hole size of 0.025 m will be chosen to compare the different grid types. This hole diameter does not result in an excessive number of holes for either type of grid. 

Having selected the numerical method, it is necessary to generate an appropriate grid, i.e. discrete representation of the solution domain and discrete locations at which variables are to be calculated. Two types of grids, namely structured and unstructured grids, are briefly discussed here. In a structured grid, there are families of grid lines... 

An obvious solution to minimize the number of grid points NK is to introduce symmetry. Consider for example an inversion point such as the point x = 0 in the harmonic oscillator. The eigenfunctions can be classified as being either even or odd with respect to parity i j(<7) = i i(— < ) one restricts the calculation to one class of functions the computational effort can be reduced by a factor of 2 by using a fast cosine transform for even functions and a fast sine transform for odd functions (52). The same symmetry considerations should work for other types of grids. 

The finite volume method uses the integral form of the conservation equations. The solution domain is subdivided into a finite number of control volumes and the conservation equations are applied to each volume. The method can accommodate any type of grid, so it is suitable for complex geometries. The method is conservative by construction. 

There is a facility of settings where the user can choose different options as per their requirement. The number of site points for a site (15 default) and the number of sites to be found (5 default) should be specified. Three types of grid are available— fine, standard and coarse—defined based on the distance between two points in the grid. Here, standard grid, the default option, is used. One can also choose between a more restrictive and less restrictive option for defining the hydrophobic regions. Two types of force fields are available of which Optimized Potentials for Liquid Simulations (OPLS) 2005 is the default one. In the given example, all default options are used (Fig. 5.3). 

The different types of grids used for the experiments are characterized in Table 1. 

The turbulence measurements were performed for all types of grids with two different flow velocities, and the measured turbulence intensities and macro length scales of the different turbulence producing grids were compared to each another (see Turbulence Measurements in a Steady Nonreacting Flow). 

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