Fluid thermodynamic properties lab

Description

The fluid thermodynamic properties lab deals with the thermodynamic properties of environmentally friendly refrigerants and their blends using specific experimental setups. Nowadays, the research activity is focused on the study of Hydrofluoroolefins (HFO) which are new generation refrigerants with low Global Warming Potential (GWP) and a short atmospheric lifetime. HFOs are of great interest to the refrigeration industry since they could ensure both good thermodynamic performance and excellent environmental properties. Therefore, they are considered potential substitutes of Hydrofluorocarbons (HFC). The activity research in low GWP refrigerants is driven by international agreements (Kyoto protocol and Kigali agreement) and governmental regulations (European Union (EU) F – Gas Regulation No 517/2014) which aim to decrease the emissions of greenhouse gases. In particular, the thermodynamic properties are measured through three experimental apparatus. An isochoric experimental setup allows to measure pressure, volume and temperature properties (PvT) for pure refrigerants and pressure, volume, temperature and composition properties (PvTx) for refrigerant blends along an isochoric curve both in the two-phase and superheated vapor regions. A Burnett experimental apparatus allows to accurately measure PvT and PvTx properties of pure fluids and blends, respectively, along an isotherm curve in the superheated vapor region. An experimental setup for the analysis of Solid Liquid Equilibrium (SLE) of refrigerants and their blends allows to measure their thermodynamic properties at very low temperatures (until -150 °C). In particular, this apparatus ensures the measurement of the triple point properties for pure fluids and the determination of the SLE behaviour and eutectic point for blends. Additionally, the lab deals with novel and reliable mathematical models used to determine the most significant fluid thermophysical properties. Specifically, new empirical and semi-empirical equations are proposed to determine:

surface tension;
thermal conductivity;
dynamic viscosity;
equations of state of gases.

The equations are defined using the corresponding states principle, the group contribution theory and artificial neural networks. Among all the fluids under study, new generation refrigerants are kept in particular consideration.

Research ares

The aim of the fluid thermodynamic properties lab is the measurement of the thermodynamic properties of low GWP refrigerants and their blends. Specifically, measurements of pure fluids and their blends are carried out both in the two-phase and in the superheated vapor regions. Additionally, the triple point properties of pure refrigerants are investigated, together with the determination of Solid Liquid Equilibrium (SLE) and eutectic point of their blends. The research activity is also involved in the study of mathematical models used to determine the thermophysical properties of fluids (surface tension, thermal conductivity, dynamic viscosity) and the equations of state of gases.

Facility

The experimental measurements are performed by means of three apparatus:

An isochoric apparatus which allows to measure the thermodynamic properties that define the thermodynamic state of pure fluids (PvT) and blends (PvTx) in the temperature range from -50 °C to 110 °C. The samples can be studied both in the two-phase and the superheated vapor regions.

Fig. 1 Isochoric apparatus

Fig. 2 Schematic view of the isochoric apparatus

Fig. 3 P-T data of a pure fluid in the two-phase and superheated vapour regions

Fig. 4 Graphical user interface of the acquisition software

A Burnett apparatus which allows to measure the thermodynamic properties of the samples in the superheated vapor region (up to 120 °C) through isothermal transformations.

Fig. 5 Schematic view of the Burnett apparatus

An experimental apparatus for the study of the Solid Liquid Equilibrium (SLE) which allows to measure the thermodynamic properties of refrigerants near their triple point (from -150 °C to -50 °C). Moreover, it is possible to define the SLE behaviour and the eutectic point of blends of refrigerants.