Notation vary greatly between different subfields and between different text books. The notation we use here is, as always, a compromise given the different subfields we cover in the same course.

Channel moderator here: At 6:02 the text states "if the molar input of O2 is three times larger than the molar input of CH2O"…

The programming environment used here happens to be Anaconda with Spyder, but you can code and execute Python code using various other programming environments

@@PLE_LU i want to learn evaporation sizing through this software, will you help me ?

1. Python is a programming language, not a software. What we demonstrate in this video is _one_ way to solve a set of non-linear of equations 2. The course this video is a part of is not a MOOC (Massive Online Open Course), we just make the videos we use in the course available to the world in the hope they might help more people than just our students. We cannot offer individual support outside of our courses.

I don't think there is a general answer to that question. There might be situations where it is ok, but if you stop the pump diffusion will continue and thus broadening of the front may be substantial. Also, as soon as you change operating conditions in a real life case, all bets are off. The only way to be sure if a change matters is to test if it matters

@@PLE_LU thanks a lot for your reply. Appreciate it :)

I don't think I understand your question. Drawing these lines between the operating lines and the equilibrium curve is analogous to alternating between solving a mass balance and solving the equation for the equilibrium between the phases. Please note that there is a newer playlist on distillation: kzbin.info/aero/PLvpgTFzUKO49J3fwJF9y61q17FSNDdoGN

Level 1 answer: Measure one more thing, e.g. the temperature in flow 3 Level 2 answer: In a real system, the dryer is never fully adiabatic, so measure both temperature and wet temperature in flow 3. Level 3 answer: In a real system you typically want your drying goods to become dry, right? So the underlying assumption that the drying goods is surface wet is violated and the air in the dryer will not follow the adiabatic cooling line and thus you definitely need to measure both the temperature and the wet temperature in flow 3. Compare the video on drying rate: kzbin.info/www/bejne/hKnaZ4Wbpb2qrdk

⁠@@PLE_LU Thank you for your quick response. Btw, I’m currently designing a dryer for my undergraduate thesis and there’s no possible way to measure the temperature at point 3. What should I do to determine the properties at point 3?

Glad that it helped. My guess is that most mathematicians would dislike this video as I am not mathematically rigorous in the explanation 🙂

You need the equilibrium line. You can either interpolate from literature data, or use one of many "curve fits" (in which case you need literature data for the parameters). What curve fit to use depend on the system, van Laar is one of those "curve fits". Compare the video studio.kzbin.infolz-RWsMYx48/edit which explains how you can take the first steps if the system is ideal (which is usually never true). From there you have to find ways to calculate activity coefficients (using e.g. van Laar).

@@PLE_LU Thank you for the advice .

Thanks for the hint, but you are actually incorrect. The probably most common engineering way to express this is still _moist_ air, see e.g. www.engineeringtoolbox.com/moist-air-properties-d_1256.html So, in engineering we talk about moist air versus dry air. Moisture content = kg water/kg dry air, Relative humidity compares the humidity with the moisture content at saturation. How much the terminology varies between countries is beyond my knowledge, but moist air is definitely commonly used in engineering contexts.

Hi, maker of the video here: There is a more recent version of this video if you are interested (kzbin.info/www/bejne/b5i9lpmqirOYoM0) and we do have a playlist on distillation Regarding what we teachers don't mention, I often say to my students "Nature is a bitch" as a short for "reality is usually way more complicated than our models of reality". Deciding what to not mention and how drastic simplifications to make when designing a course is a rather tough task. Jack Cohen and Ian Stewart describes this kind of problem in the drastic term "Lie-to-children" (en.wikipedia.org/wiki/Lie-to-children), a term I personally came across when reading the book "The science of Discworld" that they co-authored with late fantasy writer Terry Pratchett. Other famous quotes on this topic include "The best material model of a cat is another, or preferably the same, cat" (Norbert Wiener) and "All models are wrong. Some models are useful" (G E P Box). Let me take two examples: Should we include in our teaching that the Celsius scale was redefined in 1990 (ITS-90) or that the SI-unit system was redesigned in 2019? Both these facts have interesting consequences for how we do science, but with the limited time we have in a specific course, it might not be the most important for the student to understand. And just a final example, since this is a topic that fascinates me: I recently went through all chemistry text books in our local university library. All but one had an incorrect definition of reaction rate. They define it as a change in concentration over time. You find the same definition all over the internet and in all kinds of books. Even IUPAC (goldbook.iupac.org/terms/view/R05156) states that this is the definition. That does not, however, make the definition correct. In fact rather than a definition, that the reaction rate _equals_ the time derivative of concentration is what you get if all of the following criteria are met * You have only one reaction * That reaction is irreversible * You have a closed system * The volume is constant over time If any of the criteria are not valid, the reaction rate does not equal the time derivative of concentration. If you compress air, the concentration of air molecules increases (PV=nRT => C=n/V=P/RT), but there is no reaction. If you add more water to salt solution, the concentration decreases, but there is no reaction. The oxygen level in the blood of your brain needs to stay fairly constant (the time derivative of concentration being essentially zero) for you to survive, but there is a reaction consuming oxygen. If that reaction stops, you die. Nearly all naturally occurring systems are flow systems and the so called definition of reaction rate that is used by almost everyone is obviously invalid in such systems. Yet the faulty definition is still used and taught and will continue to be used and taught because it is easier to explain for beginners. I myself often say "my jacket is warm" although that's physically incorrect. The correct term is that my jacket is a good insulator. Sorry, went of on a tangent here :D

Editor here: Depends on your definition of "polymer". Lignin is a complex substance, see e.g. en.wikipedia.org/wiki/Lignin

There is more on DoF in the playlist kzbin.info/aero/PLvpgTFzUKO48fgoP6fVAYoDJjsCeuoITr in case you're interested

This video is about the very basics of hygroscopic materials and simplifies in that it divides materials into two distinct categories: hygroscopic materials and non-hygroscopic materials. In reality, the line between the two categories is blurred. As usual, reality is more complex than our models of reality

@@PLE_LU Thank you so much for the reply. Do you have any recommendation websites or public resources that can find info on the properties of hygroscopic of certain substances? like chemical property info in general. I have found sits that list detail info for melting point boling point, but not its hygroscopic info. does hygroscopic is a general property of a substance? or its a phenonmenon will change according to varies condition?

Sorry, I have no good further reading hints apart from that there is information sprinkled in various standard chemical engineering text books. Just to mention one thing, if you have substances that different form of crystals with varying amount of crystal water, you can get behaviour that definitely isn't covered in this video. You can also compare with pF curves for soil, i.e. how much negative pressure you need to apply to suck water out of soil at varying moisture levels. Soil also typically has a moisture threshold under which the structure changes turning it hydrofobic (which you might experience if you forget to water your indoor plants for too long.

@@PLE_LU THANK YOU!!!

Yes, findings have been published and doctoral thesis defended. See portal.research.lu.se/en/persons/alexander-betsholtz/publications/

A Mollier diagram for moist air. There are two competing conventions regarding in which direction to draw the axes, if that's what you're asking. If you're asking who wrote the code for drawing this particular copy of this variant of a Mollier diagram, the simple answer is: I did.

The notation predates the change in the SI-unit system where N_A nowadays should always be Avogadro's number. Here N_A is the total mass transfer OF SUBSTANCE A, i.e. the sum of convective and diffusive transport. As most introductory texts/books/videos on mass transfer it is assumed that we have binary systems, i.e. only two components (A and B). When you introduce a third or more components it gets a bit more complicated.