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Powell–Eyring Rheology

Mathematical Modelling — Fluid Dynamics & Heat TransferContinuum mechanics; boundary-layer similarity theory

ML⁻¹T⁻²

A non-Newtonian constitutive law capturing shear-thinning between Newtonian limits through the material constant β and characteristic shear rate ς; the stretching rate c is unrelated.

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Dimension:ML⁻¹T⁻² (kg m⁻¹ s⁻²)Maths:ℝ scalar(·, ·, ·) — A single number (real numbers), depending on another quantity, another quantity, another quantityDimensionally verifiedMathematically verifiedFully reduced to base quantities

In words:minus.

Open full derivation chain: 2 stepsDerivation
  1. 1
    Open Step 1: Given / definition · The exact Powell–Eyring shear stress: a Newtonian part plus the inverse-hyperbolic-sine kernel …
    The exact Powell–Eyring shear stress: a Newtonian part plus the inverse-hyperbolic-sine kernel — shear-thinning between two Newtonian limits.Given / definition
    Level 0 · more available
    Brief — named quantities
    About levels

    Why the levels load one at a time

    Only level 0 travels with this article. The complete expansion is several megabytes, so deeper levels are fetched one at a time when you ask for them — and how deep it goes is not known until you get there.

    To go deeper still, open any quantity in the reading as its own concept card — it carries its own derivation and its own depth ladder.

    How many levels remain is not yet known — the depth is discovered one level at a time.

  2. Open Step 2: Taylor expansion / truncation · Truncate the kernel: sinh⁻¹(z) ≈ z − z³/6 for |z| ≪ 1, i.e. (1/ς)|∂u/∂y| ≪ 1 — the truncated la…
    Truncate the kernel: sinh⁻¹(z) ≈ z − z³/6 for |z| ≪ 1, i.e. (1/ς)|∂u/∂y| ≪ 1 — the truncated law feeding the momentum equation. Outside that shear-rate range the model understates the true stress.Taylor expansion / truncation
    Open term-change ledger: 1 records
    Open record 1: μ∂u/∂y + (1/β)sinh⁻¹((1/ς)∂u/∂y) → (μ+1/(βς))∂u/∂y + (1/(6βς³))(∂u/∂y)³
    Consumes:L0L0Produces:L0L0sinh⁻¹(z) ≈ z − z³/6 for |z| ≪ 1: the kernel’s linear part 1/(βς)·∂u/∂y joins the Newtonian stress to form the effective linear stress (μ + 1/(βς))∂u/∂y, and its cubic remainder becomes the shear-thinning correction (1/(6βς³))(∂u/∂y)³; higher-order terms are discarded within the stated validity range.
    Level 0 · more available
    Brief — named quantities
    About levels

    Why the levels load one at a time

    Only level 0 travels with this article. The complete expansion is several megabytes, so deeper levels are fetched one at a time when you ask for them — and how deep it goes is not known until you get there.

    To go deeper still, open any quantity in the reading as its own concept card — it carries its own derivation and its own depth ladder.

    How many levels remain is not yet known — the depth is discovered one level at a time.

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Reads as: Powell–Eyring Rheology

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Mathematical Analysis

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Step 1 — given
Step 2 — taylor expansion

Essence

S1It interpolates between Newtonian behaviour at low and high shear through β and the characteristic shear rate ς; c belongs only to the stretching kinematics. [1.1]

Dimension I

Definition

What it is — and what it is not

What it is
  • S2A non-Newtonian constitutive law for a shear-thinning fluid. [1.1]
  • S3The exact constitutive law: τ = μ ∂u/∂y + (1/β) sinh⁻¹((1/ς) ∂u/∂y).
    • S3.1essenceThe sum of μ∂u/∂y and (1/β)sinh⁻¹((1/ς)∂u/∂y). [1.1]
Wisdoms
  • S4Unlike a power law, it has a sound molecular-kinetic basis and Newtonian limits. [1.1]
  • S5The truncated law used by the boundary-layer model: τ ≈ (μ + 1/(βς)) ∂u/∂y − (1/(6βς³)) (∂u/∂y)³, valid for (1/ς)|∂u/∂y| ≪ 1.
    • S5.1essence(μ+1/(βς))∂u/∂y reduced by (1/(6βς³))(∂u/∂y)³. [1.1]

Dimension II

In practice

How to deal with it

No practical guidance recorded yet.

Sub-topics 4

References

  1. Powell & Eyring (1944); applied in Aziz et al. (2021).

    • 1.1

      Powell–Eyring model — The exact stress uses the material constant β and characteristic shear rate ς: τ=μu_y+(1/β)asinh(u_y/ς). The stretching rate c is not a constitutive constant.

      AmbiguityCorroborated

      The original Powell–Eyring paper, seeded separately in the process provenance, is the primary source; Aziz is only an application.

  2. Powell & Eyring (1944), Nature 154, 427–428.

    • 2.1

      Nature 154, 427–428 — The relaxation-theory stress law with the sinh⁻¹ kernel — the constitutive origin of the ε and δ terms.

      Established
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