Hi, I am trying to do this workshop as shown in the attached picture. I am a new user to MathCAD and it needs to be done using MathCAD. It is an iterative calculation to find parameters related to the terminal velocity in a settling equation. In this case, the desired terminal velocity of the particle is known, I am trying to find what the associated diameter D for that velocity would be, given a certain particle density p_subp. Reynolds number is R, Drag coefficient is C, as defined by the equations in the picture. you can rearrange the velocity equation in terms of v or D as desired. The physics part is easy but I am having the following issues.
Since C is a piecewise function based on value of R, I have used if/else statements to determine value. However, MathCAD highlights the inequality Re<1 for C <-- if Re <1 and says "This value must be a scalar" This also comes up for the R<1000, R<200000 terms. Any fix for this?
If that can be fixed, it is part of a while loop I have shown in two alternate ways, either until v converges to a desired v (0.5m/s or I can show as the variable v_terminal), or by convergence of the drag coefficient C, which I have tried to compare to the last iteration via a dummy variable K, within 5% or 0.05. Since C, R, and D are all interdependent, I would appreciate any feedback on how I should set these loops up, or where to state a return v or return C or return D, etc.
This should be done for an range of particle densities from 800 to 8000kg/m3, as stated in the question. Further help on how to set this up as one smooth calc is appreciated. I was thinking of using a 10x1 matrix of arbitrary values 1001,1600....4000,7000,8000 kg/m3 (you will see below why I don't start at 800)
Lastly!!! I need to plot this as a function of particle diameters than be separated as a function of density. Note of course, that since the fluid density is 1000kg/m3, there is no possible diameter that can be separated for particle density of 800-1000kg/m3 range, so I would start the plot at somewhere above 1000kg/m3 where the scale makes sense (or I might have to figure out if Log scale is best to illustrate). Would appreciate any amount of help, ESPECIALLY for the C<-- R<1 error.
Hopefully, I've described the big picture problems. Please let me know if you think you can help within the next few days.
Much Obliged.
Solved! Go to Solution.
One problem are the square brackets around the number 1111 in the definition of p.p. Square brackets create a matrix/vector - in your case a 1x1 matrix and this matrix cannot be compared to a number as you do when you write "if R<1". Hence the error message you show in the picture only.
Fest step
See if the attached file helps, and read up on solve blocks as functions. File is Prime 4.0 Express.
Thanks, I appreciate the research you put in. And the Prime 4.0 Express file was able to open on my class computer, which I tihnk is using Prime 4.0
One problem are the square brackets around the number 1111 in the definition of p.p. Square brackets create a matrix/vector - in your case a 1x1 matrix and this matrix cannot be compared to a number as you do when you write "if R<1". Hence the error message you show in the picture only.
The brackets were the main problem. Things went more smoothly after this. Thanks a lot.