9 replies to this topic

[Francisco Angel]

The pressure drop for random packing can be estimated knowing both liquid and gas superficial velocities and densities, liquid kinematic viscosity and a packing parameter termed packing factor.

The procedure involves reading the pressure drop from level curves. I developed a spreadsheet that automates the pressure drop estimation. The operational point is plotted in the original graph for visual comparison with the reported value.

The spreadsheet is available here:

https://www.dropbox....v6/DP.xlsx?dl=0

 

Any thoughts or comments are appreciated.

Best regards.

[Bobby Strain]

Francisco,

       Did you compare the results with software from Sulzer and Koch-Glitsch?

Bobby

[Francisco Angel]

Francisco,

       Did you compare the results with software from Sulzer and Koch-Glitsch?

Bobby

Dear Bobby:
I used the Perry's graph (on which I based the spreadsheet) a couple of times, so I decided to automate the interpolation process. What are your thoughts about this?, I wasn't aware of the Sulzer software, do you think it was worth the effort?

Best regards.

[Bobby Strain]

I never use a spreadsheet developed by others. Especially if I can't see all the sheets and code. And I advise others to do the same.

 

Bobby

[Francisco Angel]

I never use a spreadsheet developed by others. Especially if I can't see all the sheets and code. And I advise others to do the same.

 

Bobby

 

Bobby:

I understand you in a sense. But isn't the same with software?, there are software that doesn't have its code open.

In this case the calculation is simple, and you can see the operational point in the graph and decide if the interpolated value makes sense. I wanted to share the spreadsheet, it can be useful for someone.

Best regards.

Edited by Francisco Angel, 30 November 2016 - 05:52 PM.

[Bobby Strain]

Spreadsheets are not fit for any serious purpose without extensive validation and control. And, if the spreadsheet uses cell formulas, they are impossible to trace and validate. Even the developer has no idea what is in the sheet after a few weeks. You can make them a bit more secure by doing everything in code with VBA or VB or even C#, using the spreadsheet only for input and output. And, you seem to think that your work is secure with a password. Nothing is further from the truth. Even using VBA project, you should not protect the code with a password, because it is easily cracked. If you insist on using spreadsheets with cell formulas, you should limit them to your own use. Most people don't understand how risky they are, are are happy to collect all manner of garbage. So, you should spend your time learning to code in a more secure environment like VB.NET or C#. It will serve you well.

 

Bobby

[Francisco Angel]

Spreadsheets are not fit for any serious purpose without extensive validation and control. And, if the spreadsheet uses cell formulas, they are impossible to trace and validate. Even the developer has no idea what is in the sheet after a few weeks. You can make them a bit more secure by doing everything in code with VBA or VB or even C#, using the spreadsheet only for input and output. And, you seem to think that your work is secure with a password. Nothing is further from the truth. Even using VBA project, you should not protect the code with a password, because it is easily cracked. If you insist on using spreadsheets with cell formulas, you should limit them to your own use. Most people don't understand how risky they are, are are happy to collect all manner of garbage. So, you should spend your time learning to code in a more secure environment like VB.NET or C#. It will serve you well.

 

Bobby

 

A per the lack of extensive validation, I concede.

I know passwords can be cracked, but I'm not worried about this, as I said before, the calculation is a simple interpolation, so no mysteries there.

I know some VBA, I didn't want to use it, because, again, the calculation is simple, and also because some people feel uncomfortable when spreadsheets contain code (the pop up " activate macros" and what not).

As for the general usage of spreadsheets, this same site contains a repository of them http://www.cheresour...filter_key=free

so, in some cases, it must be worth using them, I'm wrong?

I can't understand what is your main critique, it is the fact that I hide the calculation details?

I would like to declare that I have not obscure intentions in sharing the spreadsheet "As-Is".

Best regards.

[Bobby Strain]

Francisco,

        I think your succinct summary, "As-Is", is perfect. I believe that description also applies to spreadsheets that you will find on this site. Or anywhere on the web. They are somewhat like a free kitty. So, you should take care in sharing spreadsheets with others. Many of the site users have no experience and they are desperate for spreadsheets. No matter the risk. Take a look at the applications available on my website. Just Google my name to find it. These are all coded in VB.NET or C#. You might even compare one or two with spreadsheets that you have acquired. Maybe this will help to convince you that you should further develop your coding skills, and go beyond "=A1+B6/R2*D2".

And take a look at some of Harvey Wilson's wares at katmar.com.

 

Bobby

[katmar]

We all have our biases and prejudices. In my own paradigm, online calculators like Bobby's are less trustworthy than spreadsheets because even if I spent hours verifying its results last week I have no guarantee that the version that is online today is the same as the one I tested. I am sure that Bobby will disagree with this analysis. What does help is to have a good reputation. I know that Bobby is an experienced and competent engineer, so I would be more likely to trust his calculator than one from an unknown (to me) author. But we all have to start somewhere and it takes years to develop that reputation.

A healthy dose of scepticism is required whatever design method you use - even if it is a well-known commercial product or a "trusted" publication like Perry or the Crane TP410 piping manual. They all contain mistakes. It is for this reason that professional engineering design contractors insist that all calculations be done by at least two independent methods. Even when I am using a program or spreadsheet that I know and have some trust in, I will use other less-known spreadsheets and online calculators as a cross check. If the results disagree then I have to dig a bit deeper.

On the question of protecting cells containing formulas from being edited, I believe this practice is good and is for the protection of the end-user as much as it is to protect the work of the author. I have been approached several times by companies asking me to convert a spreadsheet into a compiled program and the reason is always along the lines of "we have so many versions of this spreadsheet floating around with each user's customizations and we no longer know which one to trust". The ease of editing a spreadsheet is one of its strongest points, but also one of its weakest.

In developing software (spreadsheets or other) testing against reputable sources is important. If you only test against the original source you may be replicating their mistakes. Try the programs Bobby has recommended and please also try my Packed Column Calculator. Even though it has been around for 18 years and nobody has ever reported a mistake I would regard your testing as a verifaction of both of our work. My AioFlo pipe sizing program generated so many queries of "how accurate is it?" that I put a collection of 12 calculations online comparing its results against known and trusted sources. This has helped greatly in generating trust and you could consider putting worked examples from known sources in the documentation for your spreadsheet.
 

[Francisco Angel]

Francisco,

        I think your succinct summary, "As-Is", is perfect. I believe that description also applies to spreadsheets that you will find on this site. Or anywhere on the web. They are somewhat like a free kitty. So, you should take care in sharing spreadsheets with others. Many of the site users have no experience and they are desperate for spreadsheets. No matter the risk. Take a look at the applications available on my website. Just Google my name to find it. These are all coded in VB.NET or C#. You might even compare one or two with spreadsheets that you have acquired. Maybe this will help to convince you that you should further develop your coding skills, and go beyond "=A1+B6/R2*D2".

And take a look at some of Harvey Wilson's wares at katmar.com.

 

Bobby

Bobby:

Regarding coding skills, as I said before, I think that in this particular case it was not justified to code anything, I'm not against coding in general. Regarding desperate users, I tend to be optimistic about the good judgement of users, I prefer to offer the tool and let people decide if it is worth instead of neglecting the tool.

 

 

We all have our biases and prejudices. In my own paradigm, online calculators like Bobby's are less trustworthy than spreadsheets because even if I spent hours verifying its results last week I have no guarantee that the version that is online today is the same as the one I tested. I am sure that Bobby will disagree with this analysis. What does help is to have a good reputation. I know that Bobby is an experienced and competent engineer, so I would be more likely to trust his calculator than one from an unknown (to me) author. But we all have to start somewhere and it takes years to develop that reputation.

A healthy dose of scepticism is required whatever design method you use - even if it is a well-known commercial product or a "trusted" publication like Perry or the Crane TP410 piping manual. They all contain mistakes. It is for this reason that professional engineering design contractors insist that all calculations be done by at least two independent methods. Even when I am using a program or spreadsheet that I know and have some trust in, I will use other less-known spreadsheets and online calculators as a cross check. If the results disagree then I have to dig a bit deeper.

On the question of protecting cells containing formulas from being edited, I believe this practice is good and is for the protection of the end-user as much as it is to protect the work of the author. I have been approached several times by companies asking me to convert a spreadsheet into a compiled program and the reason is always along the lines of "we have so many versions of this spreadsheet floating around with each user's customizations and we no longer know which one to trust". The ease of editing a spreadsheet is one of its strongest points, but also one of its weakest.

In developing software (spreadsheets or other) testing against reputable sources is important. If you only test against the original source you may be replicating their mistakes. Try the programs Bobby has recommended and please also try my Packed Column Calculator. Even though it has been around for 18 years and nobody has ever reported a mistake I would regard your testing as a verifaction of both of our work. My AioFlo pipe sizing program generated so many queries of "how accurate is it?" that I put a collection of 12 calculations online comparing its results against known and trusted sources. This has helped greatly in generating trust and you could consider putting worked examples from known sources in the documentation for your spreadsheet.
 

 

You are right on the spot about reputation, we young engineers must start from the simple and gradually approach complex programs/problems. I agree that verification of the results will be a valuable addition to the spreadsheet, I can be done by me in V2 or maybe another person.

Protecting the cells is a compromise decision like almost anything, I could have made the automation using Python, this would limit the user base, but then again you don't need to own Excel to run it, so which one is better?. There will always be a damaged side.

Best regards.