In physics, chemistry and materials science, percolation (from Latin percolare, "to filter" or "trickle through") refers to the movement and filtering of fluids through porous materials. It is described by Darcy's law. Broader applications have since been developed that cover connectivity of many systems modeled as lattices or graphs, analogous to connectivity of lattice components in the filtration problem that modulates capacity for percolation.
Darcy's law
Defines the relationship between the instantaneous flux q (q = Q/A, unit: (m3 of fluid/s) / m2) through a porous medium, the permeability k of the medium, the dynamic viscosity of the fluid μ , and the pressure drop ∇ p over a given distance L
This equation, for single phase (fluid) flow, is the defining equation for absolute permeability (single phase permeability).
Those of you who have worked with Darcy's law may not have encountered it in the form above: it is often shown in a simpler form where the pgh term is ignored, because it is often applied in a context where the pressure applied on the fluid is much more important than the fluid's weight (as is the case with espresso). But for pour over coffee, we are in a context of gravity-driven flow, and therefore this more general form of Darcy's law is useful.
The most dramatic one is permeability; in the context of pour over, it is affected by the following variables:
• The grind size (coarser coffee is more permeable, finer coffee is more resistive);
• The permeability of the coffee filter (affected by its pores and thickness);
• The ridges on the inside of the brewer's wall and filter creping (they allow air to flow upward outside the filter and increase permeability);
• The saturation of the coffee bed (a coffee bed saturated with water increases its permeability, which is probably the most important reason why we bloom).
Question: adding 1/4 teaspoon of 10% phosphoric acid to 19 litres of water, what will be the pH? Let's go through the calculations step by step. Step 1. Convert mass ( or volume) of 10% phosphoric acid to mole per litre ( mol/L) The above calculation shows that 1/4 tsp of H3PO4 acid is 6.97e-5 mol/L Step 2. Input this value to BATE (or other app) to calculate pH The answer: pH = 4.16, ie too acidic !? If you use pipette instead of teaspoon, 1 drop = 0.05ml. So 1/4 TSP means roughly 25 drops If you actually aim for pH 5.6 (which is optimum pH for mashing), conc will be 2.51 e-6, or 1/100 tsp , 0.044 ml, roughly 1 drop Let's roll back a bit. From recipes of BarleyWine , summer rye , hefe Gordon Strong suggested to use 1/4 teaspoon of 10% phosphoric acid, which is targeting pH of 5.5..... Discussion on homebrewtalk forum. However using online BF water calc , Sparge pH would be 4.6. but he also added 1 tsp of CaCl2. 2H20. Mash pH change from 5.7 t...
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