How to calculate specific entropy, enthalpy, and volume for range of given pressure and temperature values

Hello, I am a novice level matlab user and was wondering if anyone could steer me in the right direction on a problem I am having. I need to calculate the specific entropy, enthalpy, and specific volume of liquids and vapors at a range of pressure and temperature values. Using the XSteam script:

https://www.mathworks.com/matlabcentral/fileexchange/9817-x-steam-thermodynamic-properties-of-water-and-steam

I am not asking anyone to do this for me or mean to post an entire project/assigment. Just wondering if anyone can steer me in the right direction I am completely lost honestly. I have the temp and pressure data in an excel file that I have uploaded to MATLAB but after that I don't know how to proceed. If anyone can offer any help it'd be greatly appreciated. Thank you

[John D'Errico]

You need to make an effort. Sorry, but that is how you will learn. And for here, the only way we know if you are making an effort is to show you are doing something in the right direction.

Does that function do as it says it does? For example, this call:

XSteam('h_pt',1,20) % return the enthalpy of water at 1 bar and 20 degC. 84.0118 kJ/kg

TRY IT!!!!!!!!

You will need to download that toolbox. So do it! MAKE AN EFFORT. All that requires is a click of a button. Then you will need to learn how to install it in MATLAB. So you will use tools like pathtool. Put it on your search path.

You have already been steered in the right direction. Do what you were told to do. Use it. See if it does what it claims to do. Then worry about how to use it for the problem at hand.

The trick to solving a large problem (large is defined as anything too big for you to directly get your head around) in computing is how you eat an elephant. You do it one byte at a time.

[Jacob Carella]

Yes, the XSteam function behaves as it says it does. That is why as of now I guess I will simply just enter XSteam hV_p and hL_p etc. for each pressure and temperature entry.

[John D'Errico]

But is that not exactly what you were told to do? So do it. If you need to use a loop, then use one. TRY IT. I gather you were given a value for each in the spreadsheet. How does it compare to the computed value you get from Xsteam? You were asked to compute a percent difference. Just do it. Can you compute a percent difference? If you don't know how, surely you can look that up.

For example, I just did a search, with the question "how to compute a percent difference". When I did that, MANY pages pop up. I don't know what you don't understand. But it seems like you know what to do, and you just want someone to guide you through this. The fact is though, you need to be your guide. If you will be using MATLAB, you will need to learn how to read the help.

So try it. When you have a problem, THEN ask a question. Show what you did. Tell us what you are doing, and what seems to be wrong. If you get an error message that you don't understand, then show the complete error message, and ask how to fix things. At that point, your question would be one about MATLAB. So far though, this is just your homework assignment, with no effort made.

[Jacob Carella]

Hey thank you for the help.

So far this is what I have:

data = xlsread('SteamTable1.xlsx')

x = data(:,1)

y = data(:,3)

%x value is pressure in bar

%y value is temperature in degrees Celsius

%now using XSteam function

%testing Xsteam function for 2 bar pressure 120.2 degrees Celsius temperature

XSteam('hV_p',2,120.2)

% attempting to calculate XSteam of saturated vapor enthalpy for range of x and y values

XSteam('hV_p',x,y)

So where I am stuck is how can I enter the total range of the x values (about 20 values) and the total range of y values? And have MATLAB calculate XSteam('hV_p') for each value in the range of x and y values?

Answer 1

[Walter Roberson]

XSteam is only designed to handle scalar inputs. If you need to loop up several values according to the data file then you will need to loop, either a for loop or using arrayfun()