Solve Blasius problem in MATLAB 05/10/2012
Problem: Solve Blasius equation: f*f''+f'''=0 BCs: f'(infinity)=1, f(0)=f'(0)=0. Answer: The problem is solved in MATLAB. To do this, the ODE is rewritten as a 1st order ODE set: f1’=f2 , f2’=f3, f3’=-f1f3/2 with the boundary conditions of f1(0)=0, f2(0)=0, f2(∞)=1. Then, define the function set in MATLAB: ===Code Start============================ function df = BlasiusFunc(eta,f) % f() is array of f and its derivatives: f = f(1) f' = f(2) f" = f(3) df = zeros(3,1); % df() is array of the derivatives of f() df(1) = f(2); df(2) = f(3); df(3) = -f(1)*f(3)/2; ===Code End============================= Then the relationship between f’(η) and η is plotted to find f3(10). ===Code Start============================ for i=1:2000 q(i)=i/4000; [t,x]=ode45(@BlasiusFunc, [0,10],[0 0 q(i)]); r(i)=x(length(x),2); end; plot(q,r);grid;xlabel('q');ylabel('r'); ===Code End============================  From the figure, it can be seen that f”(0) =0.3322. Using this number to find f(x). ===Code =========================== [eta,f]=ode45(@BlasiusFunc, [0,10],[0 0 0.3322]); plot(eta,f(:,2));grid, xlabel('eta'); ylabel('df1'); ===Code End======================== The Result:  2 Comments MIT Mathlet 12/17/2011
Find this site when I am preparing for my Engineering Analysis course final exam, it's very helpful. Many details my professor omitted in class were well explained, such as method of undetermined coefficient, it's even better than the wikipedia page. http://tutorial.math.lamar.edu/Classes/DE/UndeterminedCoefficients.aspx 基础化学教学课件/DIDAC 12/05/2011
DIDAC: A five-volume set of technical and didactical high-standard transparencies and accompanying texts for chemistry courses in secondary schools and higher education. I am using it now to reinforce my poor chemistry knowledge :) Chinese version: http://www.cbern.gov.cn/derscn/portal/didac/ English/French/Dutch: http://old.iupac.org/didac/ How a cell battery is made in lab 11/17/2011
Proton-conductive membrane 06/14/2011
When potential difference exists in a conductor, electrical charges move in the direction required to weaken the difference. The property of this conductor is called its electrical conduction. When protons exist in the conductor as the main current carriers, the material is referred to as proton conduction, and the quality or power of the conduction is called proton conductivity. Some membrane materials, typically consisting of such as inorganic compounds of ceramics and/or glass, organic polymer compounds, and inorganic/organic hybrid materials, exhibit high H+ ion conduction. Proton exchange membranes based on fluorinated polymers as typified by Nafion® have been widely used in solid polymer electrolyte fuel cells (PEFCs) due to their high proton conductivity (to 0.1 S cm-1) and chemical stability. --From : http://www.espec.co.jp/english/tech-info/tech_info/pdf/05_10/contents2.pdf Why is Pt a good catalyst? 05/04/2011
1. It can adsorb certain molecules, especially gases. Adsorption is NOT the same as absorption. Adsorption is a process by which a chemical (gases or liquid) physically becomes attached to the surface of an adsorbate (a solid). Once gas molecules are adsorbed on the surface of a catalyst, they are much closer to each other and more likely to react. 2. WHY platinum is good catalyst is a mystery. Presumably, it is good at enhancing the Van der Waals forces that cause adsorption with other molecules, but WHY the platinum family of metals do this better than other metals is not fully understood. 3. It can form partial bonds with other molecules. By forming these partial bonds, the bond in the actual molecule gets weaker and weaker and hence, the bond becomes easier to break. Hence, a smaller amount of energy is needed to break the bond between the original bonds, such as that between 2 hydrogen atoms (the hydrogen molecule). As the amount of energy needed to overcome the bond gets smaller, we say the activation energy for the reaction has been reduced. Edited from Yahoo Answers: http://answers.yahoo.com/question/index?qid=20071024122041AAQhmvv Problem: Solve Blasius equation: f*f''+f'''=0 BCs: f'(infinity)=1, f(0)=f'(0)=0. Answer: The problem is solved in Mathematica by using NDSolver. ===Code Start=== sol = NDSolve[{f'''[t] + R f[t] f''[t] == 0, f[0] == f'[0] == 0, f'[10] == 1}, f, t] Plot[f'[t]/.First[sol],{t,0,10}] ===Code End=== The result:  DMFC activation 04/30/2011
1）先把电池装好 2）配好溶液 一般1M 甲醇溶液 3）调好流量 1ml/min 就可以了 通入电池 4）控温 一般75度就ok 5）1小时后 放电 测IV曲线 6) IV曲线测完后 继续通溶液 过3-5个小时再次一次 IV曲线 7）一般通溶液持续24小时 期间测5次IV放电曲线 8）若最后几次IV曲线 重合了 那电池就是稳定了 活化结束 NOTE: 1. Cathode侧通氧气, 一般 流量100sccm就可以 2. 甲醇溶液要流动着,这24小时内 甲醇不要厅 ,为了节省溶液 不放点的时候你让他循环, 放电测IV曲线的时候 你用另一瓶的新鲜溶液 这样就不影响数据了 | AboutQuike Notes ArchivesMay 2012 CategoriesAll |
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