Talk:Mass balance

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[edit] Mass balance models

I noticed through a Google search that someone had put up a request for Mass balance models. Rather than moving my contribution mass balance I made a redirect since I think that mass balance is a better term than mass balance models, I'll try to explain why: The term model can be interpreted in many, many ways, so many that the term has almost lost its meaning. What I as a chemical engineer do (in this field) is to write down mass balances (and energy balances) for my systems. In doing that I have to make simplifications and assumptions, i.e. the mass balance is a model of reality, not reality itself. Once I have my balances for mass and energy I translate that into a computer model, either a standalone computer program, or as a routine that can be used inside another program. From a more philosophical point of view, everything we experience is a model, since we have no (?) way of knowing for sure that anything exist.

So, to put it short, I rather see a mass balance entry in the wikipedia than a mass balance models entry. Saittam 12 Aug 2005

  • I keep doing newbie mistakes and fail to see them directly. Unfortunately I have to give less attention to wikipedia for a while so I leave things as they are Saittam 11.30 17 Aug 2005 (CET)

[edit] Mathematical statement of conservation of mass

Can someone provide a mathematical statement of the conservation of mass, in the form of partial derivatives or some kind of governing equation? Maybe what I'm looking for is a continuity/conservation type of equation. Problem is, I don't know what I don't know! User 202.156.6.54 January 1, 2006

I've added a link to Continuity equation but hesitate to add much in the Mass balance article: I haven't looked to closely, but I think the following equation is still lacking in wikipedia:

{\partial C_A \over \partial t} + v \nabla C_A = D_{AB} \nabla^2 C_A + R_A

which relates the derivative of substance A ({\partial C_A \over \partial t}) with the convection (v \nabla C_A), the diffusion of substance A in substance B (D_{AB} \nabla^2 C_A) and the reaction rate at which substance A is produced (RA). I hesitate, not because I think it shouldn't be in wikipedia somewhere, but because I don't know where to put it. If the equation above is to be included, I think it would be only proper to explain what it means, e.g. how to interprete it in different coordinate systems e.g. the cylindrical

{\partial C_A \over \partial t} + v_r {\partial C_A \over \partial r} + v_\theta {1 \over r} {\partial C_A \over \partial \theta} + v_\phi {1 \over r \sin\theta } {\partial C_A \over \partial \phi} = D_{AB} \left( {1 \over r^2} {\partial \over \partial r} \left(r^2 {\partial C_A \over \partial r}\right) + {1 \over r^2 \sin \theta } {\partial \over \partial \theta} \left(\sin \theta {\partial C_A \over \partial \theta }\right) + {1 \over r^2 \sin^2 \theta} {\partial^2C_A \over \partial \phi^2}\right) + R_A

one might then continue to explain different simplifications, e.g. steady-state, no convection, etc. How to make this into a wikipedia entry rather than a wikibook entry is somewhat beyond my imagination though… Saittam Jan 3, 2006 19:14 CET

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