Diffusion Definition and 476 Threads

I've been looking into compressed Hydrogen storage, and it seems that the high pressure containers have a lot of layers on the inside to keep the Hydrogen from leaking out/diffusing over the lifetime. However now I'm curious as to whether you could use a tank to store high-pressure Hydrogen (in...

Homework Statement $$\frac{\partial U}{\partial t}=\nu \frac{\partial^{2} U}{\partial y^{2}}$$ $$U(0,t)=U_0 \quad for \quad t>0$$ $$U(y,0)=0 \quad for \quad y>0$$ $$U(y,t) \rightarrow {0} \quad \forall t \quad and \quad y \rightarrow \infty$$ Homework Equations This is a diffusion problem on...

Homework Statement I'm trying to derive an analytical expression for the photon backscatter flux in finite turbid media using the diffusion equation and the method of images. What I want to write is: for a given volume (x,y,z), where a coherent light source is incident on the x-y plane and z is...

Hi, I am trying to model a counter flow diffusion flame using ansys fluent with fuel/oxidiser as methane/air. The problem is that the flame temperature(800 K) is much lower than what it should be(>1600 K). I am using Non premixed combustion module with steady diffusion flamelet and adiabatic...

Hello I am a lower-intermediate user of MCNP and I do not know how to obtain the diffusion coefficient (or maybe the angle of scattering) using tallies. I also have read a paper (Multigroup Scattering Matrix Generation Method using Weight-to-Flux Ratio Based on a Continous Energy Monte Carlo...

Are there any noteworthy papers that explain in detail why diffusion occurs, or suggest the reason for the existence of the second law of thermodynamics?

Hi In diffusion equation ,if we have a infinite slab of moderator with thickness ±a and the sources is s(x)= cos(x) i think the first boundary flux( ±a ) = 0 what will be the second boundary condition ??

Hey, I’m currently stuck at my research and I’d like to ask for some help. First I’ll try to introduce the measurement and the setup and then I’ll get straight to the problem. The goal is determining the diffusion length of charge carriers quantitatively in different materials. For this...

Hello! Double heterostructures are used in LEDs and lasers to provide both the confinement of the charge carriers and the confinement of the generated light. This image is a comparison between a homojunction and a heterojunction. As regards the unbiased junctions, when the n region and the p...

Consider I have a packed column of length L filled with known characteristic adsorbent. I am putting a mixture of N components in it and I am solving for concentration of each component in mobile phase at the outlet of the column. The equations which are to be generalised are as follows: An...

Homework Statement Prove that the diffusion constant D of an ideal gas can be expressed as D=1/3λv(v bar) where λ is the mean free pass of the gas molecule. And v bar is the average speed of the gas molecules obtained from the kinetic theory of gases.(Use the picture to setup the net flux...

Disclaimer: This is a homework problem I need to analytically solve the diffusion equation for a 1d 1 group slab with width a, and source distribution Se^(-k(x+a/2)) I've gone through the math, and come up with my homogeneous and particular solution and attempted to apply the boundary...

Homework Statement Hello, I don't understand the solution of an exercise Let P(x) be a continuous function such that |P(x)|≤Ceax² . Show that formula (8) for the solution of the diffusion equation makes sense for 0 < t < 1/(4ak), but not necessarily for larger t. Homework Equations Equation...

Hello Everyone, I have a question regarding the diffusion of a gas (or mixture of gases) into an evacuated space. The situation I am picturing is one where you have two vessels of equal volume, one contains a gas at room temperature, some known pressure (say ~760torr), and the other at static...

Homework Statement A Ti Rod is to be put into a furnace to try and increase the carbon content of the rod. Initially, the carbon content of the rod is 0.2%wt. The carbon content of the furnace is 1.0%wt. What would the temperature have to be in order to get a final carbon content in the Ti rod...

I am running a general circulation model (EPIC, which uses isentropic vertical coordinate system, potential temperature) and need to add vertical diffusion to the zonal velocity U. The vertical coordinate is theta (Θ, potential temperature) and there is no vertical height coordinate in z but I...

Homework Statement Consider the diffusion of a drop of ink in a water vase. The density of the ink is ## \rho (\vec{r}, t) ##, and the probability ##P(\vec{r}, t)## obeys the diffusion equation. What is the relationship between ##\rho (\vec{r}, t)## and ##P(\vec{r}, t)##? Homework...

Hi guys, I have functioning MATLAB code for my solution of the 3D Diffusion equation (using a 3D Fourier transform and Crank-Nicolsen) that runs just from the command window and automatically plots the results. However, it seems like my solution just decays to zero regardless of what initial...

Hello. I have some questions regarding the equation: k\frac{\partial}{\partial x}\left( u\frac{\partial (u-r(x,t))}{\partial x} \right) = \kappa \frac{\partial u}{\partial t}. u is positive. r(x,t) is given as an input. I have implemented this non-linear diffusion equation using backward Euler...

Homework Statement Exercise: Hexachlorobenzene (C6Cl6) is a highly toxic waste product of pesticide manufacturing. It is resistant to biodegradation. Sediments at the bottom of a reservoir in the Upper Mississippi River catchment have been found to contain high C6Cl6 concentrations. The...

I want to model the diffusion-controlled combustion of a small carbon particle. The system I want to model is similar to this one However, I'm not going to use the stagnant gas film model as shown in the figure, since I lack data for the film thickness, and I want to evaluate the problem...

Homework Statement Is the oxygen required by the single-celled organisms obtained by diffusion or osmosis through the surface membrane of the cell? Homework Equations The Attempt at a Solution I'm thinking osmosis since there's a membrane through which the oxygen passes. But I've been...

Hi, PF! I recently solved a problem from BSL which asked to analyze the following system used for determining the diffusivity of a binary mixture of gases. The left portion of the system, from the left bulb up to the stopcock at the middle of the tube, is filled with gas A. The right portion...

Homework Statement Problem 18B.13 from Transport Phenomena, BSL. Tarnishing of metal surfaces. In the oxidation of most metals the volume of oxide produced is greater than that of the metal consumed. This oxide thus tends to form a compact film, effectively insulating the oxygen and metal from...

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Homework Statement A (spherical) rubbery balloon of 20 cm in diameter is filed with helium. The rubber balloon wall has a thickness of 0.05 cm and diffusivity of 0.1x10-10 cm2 /s for helium. When the balloon is left in the air at 25°C, helium leaks into the air by diffusion through the rubbery...

At Earth's 1g, is the rate of diffusion equal to the rate of sedimentation for cellular molecules (or proteins)? The diffusion rate is higher, correct? Thanks.

OK the atmosphere by definition envelopes the earth.The force keeping it here is solely gravity. The "force" opposing this is diffusion across a pressure gradient into the vacuum of space. Assuming that is correct how could I prove this other than looking out the window. Newton's law of...

Homework Statement What is the difference between diffusion and osmosis? Homework Equations 3. The Attempt at a Solution I am guessing that diffusion means that particles spread out. And osmosis is when particles spred out in a cell membrane. [/B] Osmosis can be "diffusional" but...

This is my attempt at the solution. I have been told that the given function is a solution. I just need to prove it. As you can see that I am stuck. What am I doing wrong?

https://en.wikipedia.org/wiki/Mass_diffusivity http://webwhiteboard.com/#4j3pn87a In the equation specified in Wikipedia for gases. http://imagebin.ca/v/2A0LjLEf0qyT The Average Collision Diamteter & Integral are said to be tabulated and there is a book referenced. Is it possible to get an...

I'm right now working with modelling a system, where atoms diffuse along a coordinate z until they reach a certain point z=z0 at which they are taken out of the system. The diffusion equation is: ∂n/∂t = D∂2n/∂z2 The question is now what boundary conditions to use for the concentration profile...

Hello, I am trying to solve the following simple diffusion equation using the method of lines: du/dt=D(du2/dx2)function k=func1() k = [0, 0, 0, 0, 0, 0, 0.4380, 0, 1e5]; %k(9) initial value of the molecules end %k(7) D/dx2 function...

Hello all, I have a Varian M4 diffusion pump that has a 6 inch diameter opening at the top, is it okay for me to connect that to a reduced size opening like just 2 or 3 inches diameter so that I can use a smaller valve? I am only trying to pump down a cubic foot or two sized chamber. I am...

1. A sheet (with a thickness of 0.05 cm) of MgO lies in between layers of Ni and Ta to avoid reaction between these two metals . At 1400 ºC, ions of Ni are created and diffuse through the ceramic MgO to the Ta. Find the number of ions that go through the MgO per second, knowing that the...

Hello everyone, I have a question concerning the following: There is a relationship for diffusion concerning the RMS: <x^2>= 2\cdot D \cdot T for one dimension and there is also Fick's 2nd Law. When does the above formula apply? What I don't understand is that in the RMS formula there is...

We solved a simple looking heat diffusion problem because it describes an apparatus used in an NIH sponsored research project. It resembles problems discussed in textbooks and in many papers on the web. A textbook method solves all those problems but a straight forward application of that...

Hi, I'm just an average guy here, mostly self educated, and am looking for experts to verify my theories on developing revolutionary impact protection. If I disrupt direct impact to the head using a highly elastic layer of material, does that create an inelastic impact interruption? A helmet...

Hello everyone, I've been stuck on this problem for three days now I just can't seem to make it work out to a reasonable value Homework Statement Consider a horizontal glass tube with an inner diameter of 5 mm and a length, L, of 500 mm filled with pure nitrogen gas at a temperature of 25C...

Homework Statement Mono-energetic sources of neutrons emitting S neutrons/cm^3 sec are distributed uniformly throughout an infinite material (characterized by a macroscopic absorption cross section Σa and a diffusion coefficient D). An infinite sheet of very thin absorber, of thickness t and...

I'm trying to understand how a diode works and for this I've used(among other resources) the book written by Albert Malvino, Electronic Principles. Everywhere I read about this topic, it says that when the N-type and P-type semiconductors are joined together, the free electrons from the N-type...

The diffusion distance for a Brownian particle is given as x^2 = 2Dt D: diffusion coeficient, t: time However, not all textbooks include the factor 2 (i.e. they just write x^2=DT). Is there a difference or are they just beeing sloppy? I run into trouble when I want to calculate the length of a...

Homework Statement A slab of radioactive material of thickness L lies in the x-y plane surrounded by a material that can be thought of as extending to +/- infinity from -L/2 and +L/2. The system is in steady. Find the general solution for the diffusion equations in each region(ok). Find the...

I am trying to understand about glucose metabolism! I have been researching this stuff forever! X( Would you see if my explanations are right, and if not, tell my why? Thank you SO much! That would be a HUGE help! Is it true that uptake and release of gas/nutrients only occur in the...

Homework Statement The goal is to derive the heat equation with convection, ut=α2uxx-vux but for the case where u(x,t) instead models concentration changes by diffusion and convection. The idea is to use conservation of mass to do this. Homework Equations We are given: Change of mass inside...

Hello, The diffusion current in a semiconductor is caused by difference in concentration of holes and electrons. My question is it related to Coulomb's law (electric force due to electric field) ? Thank you

Show by direct calculation that Eqs. (4-134) and (4-137) in the textbook by Duderstadt and Hamilton hold, i.e.:(a) ∫ dΩΩiΩj= 4π/3 δij; i,j = x,y,z; 4π(b) ∫ dΩΩxΩyΩz = 0, if l, m, or n is odd. 4π The integrals are over 4π. This is part of the derivation of the diffusion equation...

Can I make diffusion pumps from aluminum? I am going to create parallel connected diffusion pumps for many UHV purposes. I see that aluminum that is treated to prevent outgassing is used for UHV valves, chambers, and reactors. I'd like to know what temperature diffusion pumps boil their...

Hi, I understand that an exciton must reach the D/A interface within the Exciton diffusion length to prevent recombination, however, what are the factors during device fabrication that can affect the Exciton diffusion length of a P3HT:PCBM BHJ OSC?

Hello everybody. I should solve a modified version of second Fick's law in nondimensional spherical coordinates; t is the time and rho [0,1] the nondimensional radius. In this equation the diffusion coefficient is vraiable with t and rho. The equation is the following: dC/dt =...