Thermofluids Air Conditioning Unit TS diagram

[Mechaman]

Homework Statement

To plot a TS diagram given the relevant data here http://imgur.com/Q9RNL8P for an air conditioning unit.

Homework Equations

R134a is being used in an air conditioning unit, steam tables for -5hf 0hf and -5sf 0sf written below in exrapolation.

The Attempt at a Solution

I've extrapolated the -2.7 to find the base pressure that goes into the evaporator from point 4 here http://imgur.com/zl4eIGJ

And finally this is my plot from what I understand http://imgur.com/XE4HVtt

I can see that point one is superheated so wouldn't I take the lower pressure as the -2.7degrees.

• But the pressure at -2.7 degrees is 2.7006 bar
• and the pressure of 5.2 degrees is 2.554 bar

How is the warmer temperature a lower pressure?
Am I right in setting the bottom pressure line at the -2.7 degrees?

Thanks for reading I would appreciate any help with this.

 

[KataKoniK]

Hello! I would suggest using a thermodynamic software or a steam table to accurately plot the TS diagram for the given data. The extrapolation method may not give accurate results and can lead to errors in your analysis. Additionally, it is important to consider the thermodynamic properties of the refrigerant being used (in this case, R134a) and the specific processes involved in the air conditioning unit.

To address your specific questions, the pressure at a warmer temperature can be lower because it depends on the specific volume of the refrigerant. As the temperature increases, the specific volume also increases, resulting in a decrease in pressure. It is also important to note that the pressure values given in the steam table are for saturated conditions, so you may have to use interpolation to find the actual pressure at a specific temperature.

To accurately plot the TS diagram, I would suggest using the enthalpy-entropy (h-s) diagram instead of the temperature-entropy (T-s) diagram. This is because the h-s diagram takes into account the changes in specific volume and is more suitable for refrigeration and air conditioning systems.

Hope this helps! Good luck with your analysis.