We are always learning. After studying more about compressor datasheets, I realized that I forgot to include the superheat in yesterday’s post. Let’s fix that. The main problem is that, in every calculation, I took the inlet state as saturated vapor in the given evaporating temperature, when in reality the datasheet specifies that the vapor always enters at 32.

When selecting a compressor for a refrigeration system, the engineer usually has to browse through datasheets to select the most appropriate machine. The user must select a compressor that works with the selected refrigerant (chosen for environmental and cost reasons) and is able to deliver the required cooling capacity when operating between evaporating and condensing temperatures; these are linked to the cold and hot source temperatures (that is, the low temperature that is to maintained and the hot ambient temperature over which we have no control) through heat exchangers, but for this text we will ignore that and assume ideal heat exchangers.

In a previous post, we performed a First-Law Analysis, calculating work and heat transfer, of a mixture of ideal gases. Now we have a more realistic situation, taken from Exercise 13-99 from [1]: a mixture of 4 kg of \(\mathrm{He}\) and 8 kg of \(\mathrm{O_2}\) is kept in a rigid tank initially at 170 K and 7 MPa and pressure.

This is exercise 16-89 from [1]: a mixture of 1 mol of \(\mathrm{H_2O}\), 2 mols of \(\mathrm{O_2}\) and 5 mols of \(\mathrm{N_2}\) is heated up to 2200 K and 5 atm of pressure.

This is exercise 13-97 from [1]: a mixture of gases composed of 55% of nitrogen gas and 45% of carbon dioxide (in mass) is originally at 200 kPa and 45 ˚C.