This revision removes fabricated service-life, crack-margin and potable-water claims. It keeps a unit-explicit declared Darcy ledger and a connected sealed outside-in candle-filter path while separating hydraulic arithmetic from removal performance, integrity and product safety.
Declared Porous-Media Darcy Explorer
Enter declared pressure drop, media area, thickness, intrinsic permeability and dynamic viscosity. The worksheet reports ideal Darcy flow, flux, superficial velocity and hydraulic resistance; it does not size, certify or assess a water filter.
Equation Used
- The porous layer is homogeneous, saturated and isotropic and the declared intrinsic permeability is constant.
- Flow is steady, one-dimensional and in the laminar Darcy regime.
- Pressure drop is applied only across the declared media thickness; housing, fittings, cake and support losses are excluded.
- Media area is the active area normal to flow and dynamic viscosity is spatially uniform.
- No bypass occurs in the illustrated ideal sealed path; seal condition itself is not calculated.
- Phase moves qualitative tracers only and does not represent the calculated velocity in real time.
- Pore-size distribution, porosity, tortuosity, adsorption, particle capture, contaminant identity/concentration/charge, microbial and chemical removal, log reduction, challenge testing, integrity testing, cracking, burst/collapse pressure, fouling, cake resistance, concentration polarization, backwash, cleaning, temperature-dependent properties, housing/piping loss, service interval, certification, installation, maintenance and safe operation are excluded.
Replaces invented service/crack thresholds with a declared Darcy ledger and removes unsupported treatment and pressure-safety claims.
A sealed housing forces feed through the porous wall
The connected cutaway shows a feed inlet and upstream annulus surrounding a porous candle. End caps and seals isolate that annulus from the clean-water core, so the intended path crosses the porous wall before rising through the core to the outlet.
Moving tracers identify that path only. They are deliberately normalized and do not move at the calculated Darcy velocity.
Hydraulic permeability does not prove treatment performance
EPA defines membrane filtration for drinking-water compliance as a pressure- or vacuum-driven engineered barrier with measurable target-organism removal verified through challenge and direct integrity testing. EPA also warns that nominal or absolute pore size alone does not fully characterize removal.
CDC advises testing the source water and selecting a filter certified for the specific harmful germs or chemicals of concern. Many household filters do not remove germs, and some contaminants require other treatment. Follow the current product certification and manufacturer instructions.
Apply Darcy's law only to the declared ideal layer
USGS gives Darcy velocity proportional to intrinsic permeability and pressure gradient and inversely proportional to dynamic viscosity for laminar flow in isotropic porous media. Multiplying velocity by active area gives volumetric flow.
Flux and resistance are rearrangements of the same declared state. They do not add a fouling, capture or strength model.
A transparent declared-property example
At DeltaP=100 kPa, A=500 cm², L=10 mm, k=1x10^-13 m² and mu=1 mPa*s, ideal Darcy flow is 180.000 L/h. Flux is 3600.000 L/m²/h, Darcy velocity is 1.000000 mm/s and hydraulic resistance is 2.000 GPa*s/m³.
These values are not product ratings and say nothing about treated-water safety.
Measured permeability and verified integrity remain essential
Real elements can have pore distributions, anisotropy, supports, skins, cake layers, concentration polarization, seals and adjacent plumbing losses. Permeability can change with fouling, cleaning, temperature and material condition. Use measurements at the applicable operating state.
EPA requires appropriate challenge and integrity evidence for pathogen-removal claims and notes that membrane construction can limit test pressure. The former universal clean-pressure-drop multipliers, crack limits, safety margins, micron-retention claims, housing factors, service intervals, brand deployments, diagnoses and treatment instructions are removed.
Porous-filter ledger questions
Does the result prove contaminant removal?
No.
Does hydraulic resistance set a replacement threshold?
No. Use product-specific monitoring and service instructions.
Does the pressure input establish a safe housing pressure?
No.
Are the tracer speeds calculated?
No. They only show the intended outside-in path.
Porous-flow and water-filtration references
- USGS Professional Paper 1044-D: Darcy relation using permeability, viscosity and pressure gradient.
- USGS Water-Supply Paper 887: Darcy flow through permeable material.
- US EPA Membrane Filtration Guidance Manual: pressure-driven filtration, challenge testing, integrity and pore-rating limits.
- CDC, Choosing Home Water Filters: target-specific selection, pore ratings, certification and maintenance.
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