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# Calculation speed

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# Calculation speed

PoreXpert calculations are computationally very demanding, and can take significant amounts of time - minutes, hours or days.  Under sections detailing particular types of calculation, speed warnings are given next to a snail symbol.

The calculation times increase with unit cell size quite dramatically. Let n be the number of pores along each edge of a unit cell - for example for a 15x15x15 unit cell, n = 15.  Then the number of void features N in a particular unit cell (pores and throats) is given by N = n3 (1 + c/2), where c is the connectivity. Then the calculation time for permeability varies as calculation time nexponent where exponent is in the range 8 to 9, or Nexponent1   where exponent1 is in the range 2.7 to 3.  So for example the permeability of a 25x25x25 unit cell will take around 96 times longer to calculate than for a 15x15x15 unit cell.

For tortuosity, exponent is around 7.5, and exponent1 is around 2.5.

For fitting a percolation curve, the dependencies are given by exponent  3.3. and exponent1 2.0.

The table below shows typical times for the calculation of absolute permeability.

If you want to measure exactly how long a calculation takes, then run it in Batch mode.  After the calculation has completed, from the Home / Operations list screen, save the list of operations as an uncompressed *.porexpert file .  Then open the file with an editor capable of handling it - we suggest Notepad++.  In the example below, the Building operation listing has been shrunk by clicking the minus sign next to it. Then the TimeStamp shows that the permeability calculation for water took 1 hour 30 minutes 30 seconds for a 20x20x20 unit cell with c set to 5.5 , so that N = 30000.