Summary
Raoult’s law is the simplest way of describing vapour pressure of mixtures, but departure from this model is well known in the literature which questions the credibility of this approach in HFA/ethanol mixtures. In this work the predicted temporal expansion chamber pressure and temperature are compared with the measurements. Two distinct models of vapour pressure are incorporated to assess the relative merit of each, being (i) Raoult’s law and (ii) an empirical model. Prediction of temperature was generally satisfactory regardless of the vapour pressure model choice. It was found that incorporation of Raoult’s law to represent mixture vapour pressure, leads to significant underprediction of expansion chamber peak pressure by around 20%. This was attributable to unrealistically large dependency of this model on ethanol composition. Implementation of empirical vapour pressure model resulted in significant improvement in predicted peak pressure with only 4-6% discrepancy compared with measurements. The improvement is a result of incorporation of a departure function in empirical vapour pressure model to represent nonlinear behaviour of this thermodynamic property.
Key Message
When compared with measured data, incorporation of Raoult’s law to represent HFA134a/ethanol vapour pressure, leads to significant underprediction of expansion chamber peak pressure by 20%. Incorporation of empirical vapour pressure model improved predictions with only 4-6% discrepancy compared with measurements. This is, for the first time that such models are implemented and validated for marketed HFA products.