Geometric control of powder jet dynamics and energy dissipation

arxiv: 2604.10709 · v1 · submitted 2026-04-12 · ❄️ cond-mat.soft

Geometric control of powder jet dynamics and energy dissipation

Kazuya U. Kobayash , Komei Jinbo , Riku Kodama , Masakazu Muto , Rei Kurita This is my paper

Pith reviewed 2026-05-10 15:41 UTC · model grok-4.3

classification ❄️ cond-mat.soft

keywords powder jetconcave radiusenergy dissipationsliding frictionvelocity-squared dissipationjet heightpowder flowabilityminimal mechanical model

0 comments p. Extension

The pith

Powder jet height decreases linearly with initial concave radius through geometry-set sliding dissipation.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The study varies the radius of a concave powder surface and measures the jet that forms after an impulse. Larger radii produce broader, slower, and shorter jets whose height still scales with impulse strength but with a smaller coefficient. A minimal model treats the powder flow as sliding under velocity-squared friction whose effective distance equals the starting radius and reproduces the observed linear drop in jet height. This turns the jet into a direct readout of how much energy is lost during the flow. The result supplies a simple way to compare dissipation across powders that differ in humidity, size, or shape.

Core claim

The central claim is that a minimal mechanical model incorporating the sliding distance and velocity-squared type dissipation of the powder flow reproduces the observed linear dependence of the jet height on the concave radius.

What carries the argument

Minimal mechanical model using sliding distance fixed by the initial concave radius together with velocity-squared friction dissipation during powder ejection.

If this is right

Jet height scales linearly with the concave radius while velocity and height decrease for larger radii.
Dynamic quantities follow scaling relations with drop height whose coefficients shrink as radius grows.
Powder jets become a quantitative probe of dissipation mechanisms in flowing powders.
The model supplies a framework for comparing powder-specific effects such as humidity, particle size and particle shape.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

The same geometry-controlled dissipation could be measured in other impulsive powder processes such as vibration or impact handling.
Controlled changes in humidity or particle shape would provide a direct test of whether the sliding-distance assumption holds.
The linear relation offers a route to extract effective friction parameters from small-sample jet experiments without needing full flow curves.
Similar concave-surface control might be engineered in granular flow devices to tune energy loss and jet or splash outcomes.

Load-bearing premise

The main energy loss is sliding friction of velocity-squared type whose effective distance is set only by the starting concave radius, while particle collisions, air drag and other losses remain negligible.

What would settle it

High-speed particle tracking that shows the actual sliding distance deviates from the concave radius or that dissipation no longer follows the velocity-squared form would destroy the linear height dependence predicted by the model.

Figures

Figures reproduced from arXiv: 2604.10709 by Kazuya U. Kobayash, Komei Jinbo, Masakazu Muto, Rei Kurita, Riku Kodama.

**Figure 2.** Figure 2: FIG. 2. Diagonal view snapshots of powder jet formation for d [PITH_FULL_IMAGE:figures/full_fig_p015_2.png] view at source ↗

**Figure 3.** Figure 3: FIG. 3. Maximum jet reach [PITH_FULL_IMAGE:figures/full_fig_p016_3.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4. (a) Time evolution of the jet velocity. In the early st [PITH_FULL_IMAGE:figures/full_fig_p017_4.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5. Dependence of the fitting coefficient [PITH_FULL_IMAGE:figures/full_fig_p018_5.png] view at source ↗

read the original abstract

Applying an impulsive force to a powder layer shaped with a concave surface generates a sharp powder jet. This phenomenon has been proposed as a method for evaluating the flowability of powders from small amount of samples. In this study, we systematically varied the radius of the initial concave shape as a controllable parameter and quantitatively examined the resulting jet dynamics, focusing on ejection velocity and maximum height. Our high-speed observations revealed that increasing the concave radius led to broader jets with significantly reduced velocity and maximum height. These dynamic quantities followed a scaling relation with drop height, while the scaling coefficient decreased with the concave radius, indicating that the surface geometry directly governs the extent of energy dissipation. Furthermore, a minimal mechanical model incorporating the sliding distance and velocity squared type dissipation of the powder flow reproduces the observed linear dependence of the jet height on the concave radius. These findings establish powder jets as a sensitive probe of dissipation in dynamic powder flow and provide a quantitative framework for comparing powder specific interactions such as humidity, particle size and particle shape.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper shows powder jet height falls linearly with larger initial concave radius, backed by high-speed data and a minimal v-squared dissipation model, but the model likely assumes the sliding distance scales with radius rather than deriving it.

read the letter

The main point is that bigger concave radii in the powder bed produce shorter, slower jets, and a simple sliding-friction model recovers the linear height dependence on radius. The experiments vary the radius as a clean control parameter while using drop height for energy input, and the high-speed imaging gives clear trends: jets broaden and lose speed as radius grows, with max height scaling linearly with drop height but the prefactor dropping as radius increases. That scaling coefficient change is the useful new observation, because it ties surface geometry directly to how much energy gets lost before ejection. The data look reproducible enough to support using these jets as a small-sample probe for flowability and dissipation. The model is the part that needs scrutiny. It incorporates sliding distance set by the initial radius plus velocity-squared dissipation to match the linear jet-height relation. If the distance is simply taken as proportional to radius instead of coming out of the equations of motion, then the match is more of a consistency check than an independent test of the dissipation mechanism. The abstract does not show whether contact time or lift-off changes with radius, or how collisions and air drag were ruled out, so the claim that sliding friction dominates rests on that assumption holding across the range. This work sits in granular and soft-matter physics, aimed at people who characterize powders for processing or who want quantitative ways to compare particle interactions like humidity or shape. The experimental trends are solid and worth citing if you work on jetting or flowability tests. I would send it to peer review; the observations stand on their own even if the model needs a clearer derivation and error analysis.

Referee Report

2 major / 2 minor

Summary. The manuscript examines the effect of varying the initial concave radius R of a powder layer on the dynamics of powder jets generated by an impulsive force. High-speed imaging reveals that larger R produces broader jets with lower ejection velocities and maximum heights; these quantities scale with drop height but with a coefficient that decreases with R, indicating geometry-controlled energy dissipation. A minimal mechanical model that incorporates sliding distance (set by the initial concave radius) and velocity-squared dissipation is shown to reproduce the observed linear dependence of maximum jet height on R.

Significance. If the model is shown to be predictive rather than constructed to recover the linearity, the work offers a quantitative probe of dissipation mechanisms in dynamic granular flows and a potential small-sample method for assessing powder flowability. The geometric control of jet properties could inform powder processing applications where surface shape influences energy loss.

major comments (2)

[Abstract] Abstract: the claim that the minimal model 'incorporates the sliding distance and velocity squared type dissipation of the powder flow' and reproduces the linear jet-height versus radius relation requires explicit demonstration that the sliding distance emerges from the equations of motion rather than being imposed as equal to the initial radius R; if the latter, the linearity is recovered by construction and does not constitute an independent test of the v² dissipation mechanism.
[Model description] The weakest assumption (that sliding friction of v² type dominates with sliding distance fixed solely by R and negligible contributions from particle collisions or air drag) is load-bearing for the central claim yet lacks quantitative bounds or sensitivity analysis showing that other loss channels remain sub-dominant across the explored range of R and drop heights.

minor comments (2)

[Abstract] The abstract states that dynamic quantities 'followed a scaling relation with drop height' but does not specify the functional form (e.g., linear, square-root) or report the fitted exponents and their uncertainties.
[Experimental methods] No details are provided on the number of experimental repetitions, criteria for data selection, or error propagation for the reported velocities and heights.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading and constructive comments on our manuscript. We address the major comments point by point below, indicating where revisions will be made to improve clarity and strengthen the presentation of the minimal model.

read point-by-point responses

Referee: [Abstract] Abstract: the claim that the minimal model 'incorporates the sliding distance and velocity squared type dissipation of the powder flow' and reproduces the linear jet-height versus radius relation requires explicit demonstration that the sliding distance emerges from the equations of motion rather than being imposed as equal to the initial radius R; if the latter, the linearity is recovered by construction and does not constitute an independent test of the v² dissipation mechanism.

Authors: We appreciate the referee's point on model construction. The sliding distance in the minimal model is determined directly from the initial concave geometry (proportional to R, as particles slide along the curved surface of radius R prior to vertical ejection). This geometric relation is not arbitrary but follows from the experimental setup. Under the assumption of velocity-squared dissipation, integration of the energy loss along this path yields a linear dependence of maximum jet height on R, consistent with the data. Alternative dissipation mechanisms (e.g., velocity-independent friction) produce a different functional form. We will revise the abstract and expand the model section with an explicit derivation from the equations of motion to clarify this distinction and emphasize that the reproduction tests the dissipation form. revision: partial
Referee: [Model description] The weakest assumption (that sliding friction of v² type dominates with sliding distance fixed solely by R and negligible contributions from particle collisions or air drag) is load-bearing for the central claim yet lacks quantitative bounds or sensitivity analysis showing that other loss channels remain sub-dominant across the explored range of R and drop heights.

Authors: The referee correctly notes that the dominance of v² sliding friction is central and would benefit from further support. While the minimal model reproduces the observed trends without additional free parameters, we agree that quantitative justification is warranted. In the revised manuscript we will add estimates of the relative contributions from particle collisions and air drag, based on measured velocities, particle diameters, densities, and the explored ranges of R and drop height. We will also include a sensitivity analysis varying the relative strength of these terms to demonstrate that the linear jet-height dependence is robust only when v² sliding dissipation dominates. revision: yes

Circularity Check

1 steps flagged

Minimal model reproduces observed h ∝ R linearity by incorporating sliding distance set by initial radius as input

specific steps

fitted input called prediction [Abstract (model description); minimal mechanical model section]
"a minimal mechanical model incorporating the sliding distance and velocity squared type dissipation of the powder flow reproduces the observed linear dependence of the jet height on the concave radius"

The sliding distance is explicitly set by the initial concave radius as a model input. With dissipation proportional to v² times this distance, the integrated energy loss scales linearly with radius R; the jet height h ∝ R then follows directly from energy conservation without requiring solution of the equations of motion or additional assumptions about R-dependent dynamics.

full rationale

The paper's strongest claim is that a minimal mechanical model with v²-type dissipation reproduces the linear jet-height vs. concave-radius relation. However, the model is described as incorporating the sliding distance set solely by the initial concave radius. When dissipation is integrated over a distance that scales directly with R, the resulting energy loss (and thus height) scales linearly with R by construction. This reduces the 'reproduction' to a fitted-input-called-prediction rather than an independent dynamical outcome. No other load-bearing steps or self-citation chains are identifiable from the provided text.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the assumption that powder dissipation during jet formation is captured by a single velocity-squared sliding term whose distance is controlled by concave radius; no other dissipation channels or particle-scale interactions are included.

axioms (1)

domain assumption Powder flow dissipates energy proportional to velocity squared times sliding distance along the concave surface
Invoked in the minimal mechanical model to derive the linear dependence of jet height on concave radius.

pith-pipeline@v0.9.0 · 5484 in / 1260 out tokens · 37834 ms · 2026-05-10T15:41:31.137024+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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[1] [1]

Sands, Powders and Grains: Introduction to the Physics of Gra nular Materials (Springer-Verlag, New York, 1999)

Duran, J. Sands, Powders and Grains: Introduction to the Physics of Gra nular Materials (Springer-Verlag, New York, 1999)

work page 1999

[2] [2]

& Pouliquen, O

Andreotti, B., Forterre, Y. & Pouliquen, O. Granular Media: Between Fluid and Solid (Cam- bridge University Press, Cambridge, England, 2013)

work page 2013

[3] [3]

Parteli, E. J. R. et al. Attractive particle interaction forces and packing densit y of ﬁne glass powders. Sci. Rep. 1 (2014)

work page 2014

[4] [4]

& Luding, S

Vescovi, D. & Luding, S. Merging ﬂuid and solid granular b ehavior. Soft matter 12, 8616–8628 (2016)

work page 2016

[5] [5]

Zheng, Q. J. et al. Interparticle forces and their eﬀects in particulate system s. Powder Technol. 436, 119445 (2024)

work page 2024

[6] [6]

Sharma, R. S. & Sauret, A. Experimental models for cohesi ve granular materials: a review. Soft Matter 21, 2193–2208 (2025)

work page 2025

[7] [7]

Campbell, C. S. Granular material ﬂows–an overview. Powder Technol. 162, 208–229 (2006)

work page 2006

[8] [8]

& Pouliquen, O

Jop, P., Forterre, Y. & Pouliquen, O. A constitutive law f or dense granular ﬂows. Nature 441, 727–730 (2006)

work page 2006

[9] [9]

Mixing of powders and granular materials by mechanical means—a perspective

Bridgwater, J. Mixing of powders and granular materials by mechanical means—a perspective. Particuology 10, 397–427 (2012)

work page 2012

[10] [10]

Jerolmack, D. J. & Daniels, K. E. Viewing earth’s surfac e as a soft-matter landscape. Nat. Rev. Phys. 1, 716–730 (2019)

work page 2019

[11] [11]

Kobayashi, K. U. & Kurita, R. Key connection between gra vitational instability in physical gels and granular media. Sci. Rep. 12, 6290 (2022)

work page 2022

[12] [12]

S., Fellin, W

Rauter, M., Viroulet, S., Gylfad´ ottir, S. S., Fellin, W. & Løvholt, F. Granular porous landslide tsunami modelling–the 2014 lake askja ﬂank collapse. Nat. commun. 13, 678 (2022)

work page 2014

[13] [13]

A state-of-the-art review of experiment al and computational studies of granular materials: Properties, advances, challenges, and future d irections

Tahmasebi, P. A state-of-the-art review of experiment al and computational studies of granular materials: Properties, advances, challenges, and future d irections. Prog. Mater. Sci. 138 11 (2023)

work page 2023

[14] [14]

Man, T., Huppert, H. E. & Galindo-Torres, S. A. Run-out s caling of granular column collapses on inclined planes. J. Fluid Mech. 1002, A50 (2025)

work page 2025

[15] [15]

Silbert, L. E. et al. Granular ﬂow down an inclined plane: Bagnold scaling and rhe ology. Phys. Rev. E 64, 051302 (2001)

work page 2001

[16] [16]

E., Grest, G

Silbert, L. E., Grest, G. S., Brewster, R. & Levine, A. J. Rheology and contact lifetimes in dense granular ﬂows. Phys. Rev. Lett. 99, 068002 (2007)

work page 2007

[17] [17]

& Wyart, M

DeGiuli, E. & Wyart, M. Friction law and hysteresis in gr anular materials. Proc. Natl. Acad. Sci. U.S.A 114, 9284–9289 (2017)

work page 2017

[18] [18]

Physics of Soft Impact and Cratering (Springer Japan, Tokyo, 2016)

Katsuragi, H. Physics of Soft Impact and Cratering (Springer Japan, Tokyo, 2016)

work page 2016

[19] [19]

& Huang, L

Sun, H., Li, Z., Li, Z. & Huang, L. Experimental study on t he fugitive characteristics of particles ﬂow impacting inclined wall. Powder Technol. 427, 118703 (2023)

work page 2023

[20] [20]

Podczeck, F., Newton, J. M. & James, M. B. Variations in t he adhesion force between a drug and carrier particles as a result of changes in the relative h umidity of the air. Int. J. Pharm. 149, 151–160 (1997)

work page 1997

[21] [21]

Measuring the ﬂow properties of consolidat ed, conditioned and aerated powders — a comparative study using a powder rheometer and a rotation al shear cell

Freeman, R. Measuring the ﬂow properties of consolidat ed, conditioned and aerated powders — a comparative study using a powder rheometer and a rotation al shear cell. Powder Technol. 174, 25–33 (2007)

work page 2007

[22] [22]

Hare, C. et al. Analysis of the dynamics of the ft4 powder rheometer. Powder Technol. 285, 123–127 (2015)

work page 2015

[23] [23]

Wang, Y. et al. Experimental study of ﬂow regimes and dust emission in a free falling particle stream. Powder Technol. 292, 14–22 (2016)

work page 2016

[24] [24]

& Luding, S

Shi, H., Lumay, G. & Luding, S. Stretching the limits of d ynamic and quasi-static ﬂow testing on cohesive limestone powders. Powder Technol. 367, 183–191 (2020)

work page 2020

[25] [25]

& Sun, C

Tharanon, W., Guo, Y., Peerapattana, J. & Sun, C. C. A sys tematic comparison of four pharmacopoeial methods for measuring powder ﬂowability. Int. J. Pharm. 661, 124454 (2024)

work page 2024

[26] [26]

U., Jinbo, K., Muto, M

Kobayashi, K. U., Jinbo, K., Muto, M. & Kurita, R. Humidi ty-responsive jetting for ﬂowability assessment of ﬁne powders. Mater. Des. 260 (2025)

work page 2025

[27] [27]

U., Sato, Y., Saito, K., Masuda, K

Kobayashi, K. U., Sato, Y., Saito, K., Masuda, K. & Tagaw a, Y. The generation and dynamics of a granular jet induced by a sudden acceleration. Jpn. J. Multiph. Flow 38, 319–326 (2024)

work page 2024

[28] [28]

Impact on granular beds

van der Meer, D. Impact on granular beds. Annu. Rev. Fluid Mech. 49, 463–484 (2017). 12

work page 2017

[29] [29]

& Hidalgo, R

Huang, K., Hern´ andez-Delﬁn, D., Rech, F., Dichtl, V. & Hidalgo, R. C. The role of initial speed in projectile impacts into light granular media. Sci. Rep. 10, 3207 (2020)

work page 2020

[30] [30]

Hafez, A. et al. The eﬀect of particle shape on discharge and clogging. Sci. Rep. 11, 3309 (2021)

work page 2021

[31] [31]

& Villermaux, E

Antkowiak, A., Bremond, N., Le Diz` es, S. & Villermaux, E. Short-term dynamics of a density interface following an impact. J. Fluid Mech. 577 (2007)

work page 2007

[32] [32]

& Kameda, M

Kiyama, A., Tagawa, Y., Ando, K. & Kameda, M. Eﬀects of a wa ter hammer and cavitation on jet formation in a test tube. J. Fluid Mech. 787, 224–236 (2016)

work page 2016

[33] [33]

M., Onuki, H

Gordillo, J. M., Onuki, H. & Tagawa, Y. Impulsive genera tion of jets by ﬂow focusing. J. Fluid Mech. 894, A3 (2020)

work page 2020

[34] [34]

Experiments on a gravity-free dispersion o f large solid spheres in a newtonian ﬂuid under shear

Bagnold, R. Experiments on a gravity-free dispersion o f large solid spheres in a newtonian ﬂuid under shear. Proc. R. Soc. Lond. A 225, 49–63 (1954)

work page 1954

[35] [35]

On dense granular ﬂows

GDR MiDi. On dense granular ﬂows. Eur. Phys. J. E 14, 341–365 (2004)

work page 2004

[36] [36]

& Gruber, U

Bartelt, P., Salm, B. & Gruber, U. Calculating dense-sn ow avalanche runout using a voellmy- ﬂuid model with active/passive longitudinal straining. J. Glaciol. 45, 242–254 (1999)

work page 1999

[37] [37]

& Platzer, K

Bartelt, P., Buser, O. & Platzer, K. Fluctuation-dissi pation relations for granular snow avalanches. J. Glaciol. 52, 631–643 (2006). 13 Back light Rigid plate High-speed camera Test tube Glass beads Electromagnet (a) (b) H r h L Rigid plate Concave shape Cap FIG. 1. Schematic illustration of the experimental setup an d deﬁnitions of the key parameters. (...

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