Presentation of the exercise

This exercise deals with the study of a 100 kilowatts water chiller, used to keep food at a temperature of a few degrees Celsius. It extends the exercise of session S31En, which showed how to model the cycle.

In this session, we quantitatively analyze the cycle irreversibilities by setting up up its exergy balance, using the spreadsheet presented in session S06En, which you should refer to.

We also suggest you to download the document on the exergy balances available from the link below.

(Session realized on 06/16/11 by Renaud Gicquel)

Simple cycle exergy balance

Simple cycle exergy balance

Simple cycle

Simple cycle exergy balance

Cycle on (T,s) chart

Cycle on (h,ln(P)) chart

Cycle on (xh,s) chart

Summary

Sessions S31En and S32En have enabled you to become familiar with the modeling of refrigeration cycles and the establishment of exergy balances.

The solution files of this exercise are included in the archive that you can download from a link at the bottom of this page.

The interest to model cycles with a software package is that the properties of substances are calculated with great precision and without any difficulty. Once the model is developed, you can quite easily change its settings, allowing you to rapidly make sensitivity studies on the influence of various parameters.

This working manner involves however a risk: that you do not criticize the values provided by the software package, which can lead you to grant a disproportionate confidence to the results it provides.

It can happen that the model is not well built, and that its results are not right, and it is necessary to know to diagnose this type of errors. To do this, you should be able to check by yourself its results, at least in an approximate way.

You will find below a link towards a note entitled “Model construction and verification methodology” intended to provide to the users of Thermoptim a certain number of recommendations based on past experience.