Skip to main content

Questions tagged [transport-phenomena]

Transport phenomenon are mechanisms by which particles or quantities move from one place to another. For example, this could be electrical transport (where electrical charge moves), thermal transport (where thermal energy moves), or molecular diffusion (where mass moves).

Filter by
Sorted by
Tagged with
0 votes
1 answer
46 views

Transformation to replace a Material derivative with a spatial derivative

In the technical paper referenced below, Gringarten et al. claim that the transient energy transport equation in a planar conduit (Eq. 1 in their paper) $$ \rho c \Bigg[ \frac{\partial T(z,t)}{\...
Sharat V Chandrasekhar's user avatar
0 votes
0 answers
18 views

The roles of convection and advection in the absolute flux for species $i$ in mass transfer

I am confused as I have been reading on mass transport on multiple sources and they seem to use "advection" and "convection" interchangeably in the equation for the absolute flux ...
STOI's user avatar
  • 286
2 votes
0 answers
121 views

Is it possible to say that entropy would affect the charge transportation?

I noticed there are a few papers from Dr. Karuppuchamy Navamani, for example: Generalization on Entropy-Ruled Charge and Energy Transport for Organic Solids and Biomolecular Aggregates Theoretical ...
Jack's user avatar
  • 47
0 votes
0 answers
24 views

Green Kubo Relation for viscosity

I am calculating viscosity of WCA fluid using the Green Kubo relation. I am also following the paper of Zhang et al. for the Time decomposition method https://doi.org/10.1021/acs.jctc.5b00351 where, ...
Lifelong Learner's user avatar
0 votes
0 answers
55 views

Why there is steady DC current in a metal under static $E$ field in the presence of Bloch oscillation?

Background: This is a question regarding the Bloch oscillation and the solid state description of shifted Fermi sphere under static electric field. Question: One explanation for a steady current ...
physstudent11's user avatar
1 vote
1 answer
64 views

Carrier Recombination Lifetime in Thermal Equilibrium

All the books I read talk about carrier recombination lifetime when the semiconductor material is pushed out of equilibrium. But let's say the material is in equilibrium ( where generation and ...
Abe 's user avatar
  • 63
0 votes
0 answers
20 views

Confusion regarding quantum point contact conductance

In the Wikipedia Quantum Point Contact (QPC) page the conductance is described as a function if the gate voltage, and has discrete jumps of the size of the conductance quantum $G_0 = 2 e^2/h$. In this ...
peep's user avatar
  • 773
1 vote
0 answers
21 views

What are the benefits/weaknesses of different diffusion models in radiation transport?

Can anyone summarize or point me toward references for why someone would choose one diffusion model over another, particularly in relation to radiation transport during a nuclear blast? The diffusion ...
John's user avatar
  • 11
1 vote
0 answers
25 views

Confusion about Luttinger's transport coefficients

I've started reading three papers, one by Luttinger, one by Eich and by Tatara, and I'm confused to how they relate to one another. My understanding is that in Luttinger's paper a "gravitational&...
electronannihilator's user avatar
1 vote
0 answers
42 views

Does theory impose a limitation on the size of the sample to be used for measuring permeability?

Theory imposes no limitation on the size of the sample to be used but it is evident that in order to minimize effects due to local inhomogeneities in the material such as concretions, small shale ...
Armadillo's user avatar
  • 1,395
1 vote
1 answer
65 views

$p$-like or $s$-like bands

What do people mean by $p$-like or $s$-like band structures? I know that d- or f-type electrons are typically more localized, while p and s-type electrons are typically more delocalized, but how would ...
Chan's user avatar
  • 73
0 votes
0 answers
28 views

Superconductivity vs. energy gap

Many textbooks derive the single-particle excitation energy gap from the BCS mean-field hamiltonian, and then stop there, implying that this gap is sufficient for superconductivity. To be frank, I ...
poisson's user avatar
  • 1,957
4 votes
1 answer
139 views

Is there specific form of Navier-Stokes equation for which mass can cross bounding surface?

In my textbook, we learned that Navier-Stokes (NS) equations can be derived from Reynolds transport theorem where the control volume is assumed to be fixed. But when the control volume is moving, can ...
106207436's user avatar
0 votes
0 answers
39 views

Drude model for electron-hole gas

The Drude formula for the conductivity of the electron gas reads: $$\sigma=\frac{\sigma_0}{1-i\omega \tau}.$$ How should it be modified when the hole or electron-hole gas is under the consideration? ...
freude's user avatar
  • 1,725
0 votes
0 answers
17 views

Semiclassical transport -- can closed orbits be closed outside of the First Brillouin Zone?

In Chapter 12, Ashcroft and Mermin describe the various differences which can arise with bands which have open orbits, these orbits being the path through $k$-space of an electron under a magnetic (...
EE18's user avatar
  • 1,095
1 vote
0 answers
54 views

Does momentum transport occur via diffusion (or random walks)?

Consider a simple gas (or fluid) within a box at thermal equilibrium. I manage to give a kick to one particle within the gas, such that it acquires some momentum. After some time, it should be ...
YoussefMabrouk's user avatar
0 votes
0 answers
39 views

How does evaopration and diffusion affect concentration of solute at the solvent surface?

Imagine a long, thin tube with one end sealed and the other end open. It is filled with a volatile solvent with a dissolved non-volatile solute. As the solvent evaporates at the liquid surface, the ...
YEp d's user avatar
  • 1
1 vote
1 answer
62 views

What physical property does the crossover frequency in an ionic conductor represent; why is conductivity constant below and increasing above it?

After reading an article about ionic transport1, I remain confused about why the behavior illustrated in Fig. 1 of the article happens. (Figure 1 is shown below.) Specifically, why is the conductivity ...
Joseph Thiebes's user avatar
0 votes
0 answers
19 views

How to show that the diffusion of a species is given by $\frac{\dot{m}}{A}=-\rho_i D \ln(C_i)$?

I'm reading a textbook on viscous flow which says that you can go from Fick's Law for the diffusion of a species $$\dot{m_i}/A = -D \nabla \rho_i$$ to an equivalent formulation using the species ...
nwsteg's user avatar
  • 260
0 votes
0 answers
20 views

Scattering processes in $\rm Au$ and $\rm AuPd$

I'm learning about the transport of electrons in solids (especially based on the Drude model), and I was wondering how the different scattering processes that take place in metals vary with ...
user9867's user avatar
  • 221
2 votes
0 answers
218 views

What is the relation between Kubo's formula and the Green-Kubo relations?

In one hand, Kubo's formula is used in linear response quantum mechanics to obtain response functions (conductivity, magnetic susceptibility, dielectric function) and so on in terms of correlation ...
Mauricio's user avatar
  • 5,568
1 vote
1 answer
105 views

On Euler: the vorticity vector is not invariant, but vorticity over density is

I've been reading Frankel's Geometry of Physics but I'm struggling to understand a section devoted to "Additional problems on fluid flow" (Sec. 4.3c in my edition). Consider a fluid flow in $...
Stuart M.'s user avatar
0 votes
1 answer
58 views

Does the Hagen–Poiseuille equation apply to inviscid core/entrance lengt regions?

Does the Hagen–Poiseuille equation apply within the entrance length region of Incompressible, Newtonian fluid flow in a perfect tube?
TheTenthBox's user avatar
2 votes
1 answer
412 views

Onsager relations in Hall conductivity

For Onsager relation $\sigma_{ij}(B)=\sigma_{ji}(-B)$, why should one flip the sign of the $B$-field for reciprocity? In the case of antiferromagnetism, with zero net magnetic moment, can the Onsager ...
steven's user avatar
  • 21
0 votes
1 answer
982 views

How does heat transfer depend on fluid viscosity

I’ve been dealing with a forced convection internal flow (regular vertical pipe) system where viscosity grows significantly through time. The flow is way within laminar region, and I want to predict ...
J Faller's user avatar
0 votes
1 answer
442 views

Calculating the power received by a pixel from a set of rays

I've written a path tracer and am now working on implementing a physically accurate way of simulating the actual sensor response for a given wavelength$^*$, given an exposure time, aperture size, ...
Chris Gnam's user avatar
0 votes
0 answers
158 views

Numerically solving Navier-Stokes-Darcy (Brinkman) equation

I'm trying to learn fluid dynamics in porous media and I need to solve Navier-Stokes-Darcy (Brinkman) equation numerically but I'm not sure how to do that (I was trying to use method of lines for ...
3 votes
0 answers
107 views

How to define the surface current operator of a bulk system?

Consider a bulk uniform system with a boundary (edge, surface, etc.) and we want to study some transport effects mainly due to some boundary states. One possible experimental scenario might be to ...
xiaohuamao's user avatar
  • 3,701
2 votes
2 answers
97 views

Is it possible that the scattering matrix is the minus identity matrix $S=-\mathbb{I}$?

We know that if the scattering matrix is an identity matrix ($S=+\mathbb{I}$), it means that transmission is zero and there is full reflection. My question: Is it possible that the scattering matrix ...
Phys96's user avatar
  • 121
0 votes
0 answers
140 views

Which is uniform at steady state: flux or flow rate?

Background My initial focus was on heat transport, but I tried to gain insight by working with the analogous mass transport equations and I realized my confusion isn't necessary specific to heat ...
electronpusher's user avatar
0 votes
1 answer
67 views

Confused about flux transport

I am confused about a very simple thing: Let's assume you have a 1D flow (fluid), where your flow velocity v$_x (x)$ = -$\frac{1}{x} \hat{x}$, i.e. your speed (= |velocity|) increases as you approach ...
Sajal Gupta's user avatar
0 votes
1 answer
28 views

When are Dufour and Soret effects non-negligible?

Dufour effect is often times excluded from energy equations without mentioning. But there are many papers (out of my iq-league) which study effects of these phenomena in chemically reacting flows. ...
Mukhamejan Baimoldayev's user avatar
1 vote
1 answer
96 views

Mass flux in a multicomponent mixture with a concentration-dependent density

This question concerns how to properly calculate the change in mass in a multicomponent mixture when the mass density is concentration-dependent. For a 1D rod of length $L$ that has a mass density $\...
hingramo's user avatar
1 vote
2 answers
205 views

Fick's Law dependency on concentration or pressure gradients

The question is about the Fick's law dependency on pressure. Would the gas molecules still flow through a membrane in case there is no concentration gradient but still a pressure gradient (e.g. ...
odis's user avatar
  • 49
0 votes
1 answer
32 views

Transport of energy in DC current

In alternating current (AC), electrons barely move a few centimeters along the conductor, with the usual frequencies and intensities in electric lines. That fact, together with Maxwell's equations, ...
Davius's user avatar
  • 1,640
1 vote
1 answer
90 views

Doubts about how to apply Fick's law to gas

According to Fick's law the flux of gas through a membrane depends on the concentration gradient and then on the pressure gradient: $$\Delta P = P_a - P_b$$ where $P_a$ is the pressure of container $A$...
odis's user avatar
  • 49
-1 votes
2 answers
63 views

Transport Phenomena, question on statement in Wikipedia article

The Wikipedia article on Transport Phenomena contains the following statement: Transport phenomena encompass all agents of physical change in the universe. Moreover, they are considered to be ...
Don Foster's user avatar
1 vote
1 answer
109 views

QED in 1+1 dimensions | Transport equation with an imaginary (reaction) source term

I would like to know what is the contribution of the right source term to this fermion component equation of motion: \begin{equation} i(\partial_0+\partial_1)\psi_R= a \psi_R \end{equation} where $a$ ...
Guillermo Abad Lopéz's user avatar
0 votes
1 answer
72 views

The superconductor's electromagnetic response and Meissner current

We know "In the superconducting state, the DC electrical resistivity is zero." But other situations has confused me a bit. There are several situations that superconductors interact with ...
NCX's user avatar
  • 13
1 vote
1 answer
176 views

What is the difference between Collective excitations and quasiparticle in superconductor? How to consider superconductors' optical response?

In the BCS theory, superconductors can be seen as Cooper pair condensates and quasiparticle excitations (Bogoliubov quasiparticle). But in Ginzburg-Landau's theory of superconductivity phenomenology, ...
NCX's user avatar
  • 13
5 votes
2 answers
316 views

Effect of changing $\rm CO_2$-levels on cooling the desert at night

It is known (e.g. as mentioned in this popular article) that the reason why deserts cool down at night so much (to temperature below zero degrees celsius) is that there is much less humidity in the ...
oliver's user avatar
  • 7,504
0 votes
0 answers
118 views

In Reynolds transport theorem, is the integral region simply-connected?

Reynolds transport theorem for a material element (parcels of fluids or solids which no material enters or leaves) reads $^1$ $$ (1):\frac{d}{dt}\left(\int_{\Omega(t)} \mathbf{f}\,dV\right) = \int_{\...
Naghi's user avatar
  • 167
1 vote
0 answers
24 views

An Exotic Transport Phenomena with Zero-Current at Different Voltage Values

I am a researcher working with active matters, and in one of my experiment I've seen a very exotic transport phenomena which we obtain zero-current for many different values of voltage (those values ...
Trung Phan's user avatar
2 votes
0 answers
76 views

Microscopic mechanical energy conservation equation derivation

The transport phenomena book by Bird states that the mechanical energy equation can be derived by taking the dot product of the momentum conservation equation with the velocity vector v. This is the ...
Mateo Acevedo's user avatar
1 vote
1 answer
363 views

What is the difference between 'Equation of motion' and 'Transport equation'?

I think this is a simple question with a not so easily explained answer. What is the difference between the Equation of motion and Transport eq? Is Navier stokes equation an 'Equation of motion' or a '...
GRANZER's user avatar
  • 649
3 votes
0 answers
149 views

Electron transport in fluids VS solids ("structure factor" VS "phonons")

Assume to have a neutral plasma consisting of some ions $X^+$ in a neutralizing gas of electrons $e^-$. Imagine that the $X^+$ can be in a gaseous (G), liquid (L) or solid (S) phase. We want to ...
Quillo's user avatar
  • 5,078
5 votes
1 answer
95 views

Small parameter expansion to obtain convective heat transfer solution of the heat equation

I'm trying to follow along with this paper on perturbative transport analysis. The section I'm stuck on analyzes the heat equation in 1D slab geometry. To get a diffusion-only solution is relatively ...
JSlief's user avatar
  • 163
1 vote
1 answer
133 views

Molecular explanation for pressure

According to this post, viscous stress is the result of molecular diffusion. More specifically, it's a transfer of momentum in a direction perpendicular to the direction of a velocity gradient. This ...
silverbackgorilla's user avatar
0 votes
2 answers
272 views

Is momentum flux scalar or vector?

I'm trying to derive Navier Stokes equation and stacked the linear momentum equation below. The second term is momentum flux, but it seems scalar value for me because it is vector times vector. How ...
Kinnikuman's user avatar
1 vote
0 answers
53 views

Modelling electrical conductivity in low-dimensional nanostructures

I know that the Boltzmann transport equation can be solved under the Relaxation Time Approximation (RTA) to obtain the electrical properties of materials. However, the parameter that I am interested ...
PBH's user avatar
  • 121