Venturi Carpet Technology · Interactive Library

Moisture Gradient & Pruning Front

A live workspace for the working model: hydrothermal resistance, critical drying threshold and predicted pruning-front position.

Moisture gradient and predicted pruning front

The dashed line is the working threshold C_crit. Each dot marks the predicted position z_p ≡ s* where C(s*) = C_crit. The geometric outlet plane is z_h = L in this reference model.

Resistance balance & pruning-front prediction

The same flux J is represented through porous compost, the air gap and the external transfer layer. This is a working design model, not yet a validated physiological law.

Resistances

R_p = ℓ_fD_pA_p R_a = L−ℓ_fD_a^effA_a R_h = 1k_gA_h

Total flow

R_tot = R_p + R_a + R_h
J = C(0) − C_∞R_tot

Front inside compost

z_p ≡ s* = [C(0) − C_crit] D_pA_pJ, s* ≤ ℓ_f

Front inside air gap

z_p ≡ s* = ℓ_f + [C(0) − C_crit − JR_p]D_a^effA_aJ

Geometry reshapes resistance.
The field moves the pruning front.

In this reference model, compost contact changes porous resistance while narrowing and airflow change external transfer. The engineering objective is no longer simply to maximise flow, but to place the predicted pruning front z_p relative to the outlet plane z_h.

z_h = L
Δz = z_h − z_p

Compost contact → R_p

Air-side transfer → R_a, R_h

field balance → predicted zₚ

Contact scenarios & design interpretation

Open cone · f = 0

With no porous segment in this simplified model, R_p = 0 and the gradient is dominated by the air-side path. Treat this as a limiting scenario rather than a recommended operating state.

open · air-dominated · reference limit

Partial contact · f = 0.5

Porous and air-side resistances are both present. This is useful as a comparison state for studying how the predicted pruning front moves as contact and transfer conditions change.

coupled · readable · tunable

Extended contact · f = 0.75

Greater porous length increases R_p in the current model and shifts the concentration profile. The resulting z_p can be compared directly with the outlet plane.

extended · shifted · model-dependent

Design variables to add next

Outlet: diameter d_h and position z_h.
Cone: height H, generatrix angle θ and asymmetric profiles.
Ribs: number, height and orientation as local field modifiers.
Environment: air velocity U, temperature T, relative humidity RH and radiation.

Observation layer

Outer cone: compare visible root termination with the outlet plane.
Inner cone: map root clustering around cone bases and shaded zones.
Condensation: distinguish observed droplets from inferred hydrothermal effects.
Validation: measure surface temperature, RH and moisture before assigning causation.

Working principle

The exit defines the geometry.

The hydrothermal field defines the predicted pruning condition.

Two surfaces. One field. One root response.