CEE

 Transformations Chemical or biological modifications that influence the composition of a system or structure of a molecule Transport the physical displacement (or movement) of a chemical/ biological species over characteristic distances and timescales fate fate= transport (movement) +transformation (reactions) Advection Fluid acts as a carrier for the material dissolved (molecules) or superspended (particles) in itDef: the transport of material caused by the net flow of the fluid in which a material is suspended (particles) or dissolved (molecules) Formulas:Concentration*Volume/ area *timeor concentration*distance traveled*area/ area* distance traveled/ velocitywhich is concentration*velocity.  overall flux the sum of the advective, diffusive, and dispersive movements. units: mass (or Mol)/ area*time Diffusion molecular diffusion:The net movement of material from a region of high concentration to a region of low concentration caused by the random motion of material Influenced by1.) Temperature2.) size3.) median (^ density, then lower diffusivities) Osmosis Diffusion of water (only) -water molecules move up salt gradients and down water gradients Ficks law Jdiffusivityis proportional to - change in concentration gradient/ change in distance Jdiff= -D (dc/dx) diffusivity is chemical dependent Characteristic distance the distance, x, a molecule or particle will travel in a time t Diffusion/ Brownian motion 1.) results from random motion of the particle and collions with other particles2.) movement from high to low concentrations3.) much slower than molecular diffusion because particles are larger relative to molecules4.) Fick's law applies, but d is more complex Cc the cunningham slip correction factor Stoakes Einstein Relation D=K*T/F   where K is the boltzman constant, f is the friction coefficient and T is the temp in Kelvin F= 3*pie*fluid viscosity*particle diameter/ Cc diffusion occurs faster in? air than water How does transfer occur at boundries Through diffusion b/c advective velocities approach zero at those interfaces k km k is the mass transfer coefficient If Jboundary < 0 then Cboundary > Cbulk and flux is from boundary to bulk fluid If Jboundary >0 Cboundary< Cbulk   and flux is from bulk fluid to boundary Diffusion through a stagnant layer If Jbound= km (Cbulk-Cbound)= -Jdiffthen km= D/L   where D is diffusivity and L is the boundary layer thickness Jdiff Diffusion through  settling particles that stick to the interface Cbulk=CCbound =0Jg= velocity* (Cbulk-Cbound ) = velocity * Ctherefore km = velocity penetration theory accounts for the temporal varience in the concentration gradient as material is lost to the medium Use when contact time b/w the boundary layer and the bulk fluid is less than t=L2/ 20  (ie the time when constant concentration gradient has not yet been established) a time dependent processkm=(D/pie*t)1/2   instantaneous Km  km= 2 (D/pie*t2-t1)1/2   Averaged km where t2-t1 is the time interval of interest film theory a time dependent process Boundary layer Theory 1.) accounts for advection and diffusion 2.) in reality, both adv and diffusion happen simulataneously advection dominates far from boundary layerdiffusion dominates close to boundary layer km= 0.323(u/x)1/2*v-1/6D2/3   at a position x, where u is fluid velocity, x=position, D=diffusivity, v= dynamic fluid viscosity/fluid density Boundary layer averaged over length Lkm=0.646 (u/L)1/2 *v-1/6*D2/3 porosity porosity= pore volume/ total volume porosity of air Density solids density, ps= mass solids/ volume of solids bulk density, pb= mass solids/ total volume pb=ps(1- ) hydraulic conductivity K the stuff that is resisting the flow in the tubeit is measured in Length/timeit is constant for a particular soil/sanddepends on the sand pore size/ grain size  Darcy's Law where K is hydraulic conductivity and A is area and Q is flow velocity Find velocity in a water saturated porous media where U= linear velocity, K=hydraulic conductivity and dh/dl is change in height/ change in length it is - to remind that flow is down the hydraulic gradient Find velocity in any fluid-saturated media where U =linear velocityk= intrinsic permeability = viscositydp/dl= the pressure derivative If Uwater=Uany fluid  -K(dh/dl)= (-k/mu)(dp/dl)  where dP=pw*g (dw) K=k/mu  where mu is viscosity of water and k is intrinsic permeability When can you optimize K? hydraulic conductivity? where K =hydraulic conductivity, k+ intrinsic permeability, pw=pressure of water, g=gravity and mu is viscosity of water Aquifers water in a saturated zone that exists in the subsurface recharge area where surface water can infiltrate the ground. Not much runoff-has high permeability Confined aquifer well will pressure water up How to determine direction of water flow? find hydraulic head ( h) -height hydraulic head h=hp+zhp= pressure headz= elevation head ( distance between some zero level and the bottom of the well where the zero level is deeper) How do you find the water level? hA= hpA+zA   where hpA= pressure head for well A and zA=elevation head for well A What is the hydraulic gradient? With regard to an aquifer, the rate of change of pressure head per unit of distance of flow at a given point and in a given direction.  dh/dl= where hA is water level, and xA-xB is distance  the wells are apart Pressure head symbolized as hpIt is found by the total length of the well-the length of the well before water elevation head distance between some zero level and the bottom of the well, where the zero level is deeper Diffusion in Porous media Jdiffusion= -Deffective diffusivity*(dc/dx) Deffective diffusivity= where theta a is air-filled porosity Dispersion in porous media Jdispersion = - effective difusivity*(dc/dx) eff= h=Deff +U where is dispersivity in porous media, Deff= effective diffusivity, U= filtration velocity 1st order reaction -rxn=-kCw 2nd order reaction -rxn=-k[reactant]Cw accumulation rate accumulation rate=inputs-outputs+formation rxn-rxn dC/dt=QinCin+vsCairA- QoutCw- kCwV Authorhamm.jane ID180807 Card SetCEE Description:,( Updated2012-10-31T01:53:46Z Show Answers