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Calculate Refrigerant Saturation Values

wagner saturation temperature

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#1 Pavan4b4

Pavan4b4

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Posted 30 June 2017 - 08:08 AM

Hii all,

 

   I'm newbie to thermodynamics I'm working under a project where we need to project and display saturation temperature at given pressure. So we used antoine equation T= B/(A-ln(P)) - C, Its working but we find some deviation, later we come to know it only works for a limited range. So I found wagner equation gives more accurate results than antoine equation and it have wide range,

        I found wagner equation for calculating saturation pressure but I don't know how to use this formula to calculate temperature.  

 

   Can any one please help me in this regards, or any other suggestion that can work to calculate saturation temperature from pressure for refrigerants is appreciated.

 

Thanks in advance 



#2 Art Montemayor

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Posted 30 June 2017 - 09:09 AM

Pavan:

 

You just joined our Forums, so it’s to be expected that you don’t furnish sufficient information or basic data in your first query.  However, there are some very basic and elementary data and information that our members need in order to help you (or any other engineer - or student) resolve what troubles you.  Therefore, kindly respond with answers and information with regards to this query:

  • Are you a student or a practicing engineer?  Are you a Chemical or another type of engineer?
  • What is the “Wagner” equation?  Is it a means to find the vapor pressures of pure organic substances?  Does it involve using four adjustable parameters?
  • If you are trying to find the saturation pressures for refrigerants, why don’t you use existing, published and available thermodynamic data?  This is found in the literature and databases such as http://webbook.nist....mistry/fluid/. Please state what specific refrigerants you are investigating.  Databases and Mollier diagrams abound.
  • If you are a practicing engineer you can’t be “a newbie to thermodynamics” - especially if you are a ChE graduate.  I don’t know the courses you have to take in India to obtain a ChE degree, but I’m sure you have to successfully pass various thermo courses and Phase Equilibria.  Have you taken (and passed) these courses?

Calculating a refrigeration process should not be a difficult problem in today’s cache of thermodynamic resources.  You should easily have access to the specific database and/or Mollier Diagram that fully defines all the required thermo data and phases for the specific refrigerant.  Tell us the name(s) of the refrigerant and our members can be of direct help in finding the phase data (in this case, vapor pressures) that define the phase envelope in question.  Practicing engineers are not expected to calculate the vapor pressures of a defined refrigerant in order to calculate a refrigeration cycle.   Normally that is the job of research personnel who have all the tools and resources to carry out such work.  Please explain the details of your query in order to respond with help.



#3 MrShorty

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Posted 30 June 2017 - 09:29 AM

Of the vapor pressure equations that I use, the Antoine is the only vapor pressure equation that can be solved explicitly for T. The others, including the Wagner equation, require "trial and error" type root finding algorithms to find T at a given P (https://en.wikipedia...nding_algorithm ).

 

You have not said what kind of computing environment you are working in. Excel has built in goal seek and Solver utilities that can perform this root finding, or you can program your desired root finding algorithm directly in the spreadsheet (a sample I put together for another forum for solving polynomials: http://www.excelforu...find-roots.html). I'm sure other applications like Mathcad have their own root finding commands. Most root finding algorithms are fairly straightforward to code from scratch, if you are working with your favorite programming language. At this point, it is just a matter of looking at your computing environment, selecting the desired tool, and executing the algorithm.






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