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Model-based Analysis of Lubricants for High-Temperature Heat Pumps with Refrigerant Mixtures
This thesis allows you to contribute to our research on high-temperature heat pumps with refrigerant mixtures. Heat pumps have the potential to decarbonize substantial shares of industrial heat supply and with refrigerant mixtures the efficiency and flexibility could be increased. However, critical challenges remain and are yet to be researched, one of which is the knowledge gap around lubrication.
In your thesis, you will assess the lubrication challenge by developing and using thermodynamic models, thereby enabling potential issues in an early development stage.
The decarbonization of industrial heat generation is a pressing issue. High-temperature heat pumps have the potential to meet a substantial portion of the industrial heat demand by supplying heat up to 200 °C. However, current industrial high-temperature heat pumps emerged mainly from household applications, are hardly customized to industrial applications, and hence lack the required efficiency and flexibility. Increasing the efficiency and flexibility of high-temperature heat pumps thus is crucial. Recent research in our group and the literature has shown that refrigerant mixtures can increase efficiency and application flexibility by exploiting the non-isothermal phase change, known as temperature glide.
While the potential benefits of refrigerant mixtures are known, practical implementation faces significant challenges. A particular challenge regards the lubrication in the heat pump cycle which is critical to prevent the wear of moving parts in the compressor. Identifying suitable lubricants, hence, is a vital task in the development of novel refrigerants. Heuristics exist mapping suitable lubricants to refrigerant classes. While these heuristics work for pure refrigerants, lubrication remains a critical knowledge gap for refrigerant mixtures, particularly for mixtures of dissimilar refrigerants that show beneficial thermodynamic properties for high-temperature heat pumps.
This master thesis aims to fundamentally examine the interactions between refrigerant mixtures of different polarity and common lubricants. As a result of this master thesis, we envision understanding the emerging challenges in lubrication when using refrigerant mixtures. The gained understanding yields a first step towards incorporating an oil-compatibility assessment in a molecular and process design frame-work. For this purpose, the PC-SAFT equation of state shall be employed to describe equilibrium proper-ties of the pure refrigerants, lubricants, and ternary refrigerant-refrigerant-lubricant mixtures. Parameters of the equation of state shall be fitted to experimental vapor pressure data. Based on the obtained equations of state and the theory of entropy scaling, viscosities of the refrigerants-lubricant systems shall be estimated and validated against experimental data. The estimates for the equilibrium and transport properties directly yield insights into the interactions between the refrigerant mixtures and the considered lubricants. In particular, miscibility plots and so-called “Daniel plots”, comprising the solubility of the refrigerant in the lubricant and the corresponding viscosities, yield practically relevant insights.
The decarbonization of industrial heat generation is a pressing issue. High-temperature heat pumps have the potential to meet a substantial portion of the industrial heat demand by supplying heat up to 200 °C. However, current industrial high-temperature heat pumps emerged mainly from household applications, are hardly customized to industrial applications, and hence lack the required efficiency and flexibility. Increasing the efficiency and flexibility of high-temperature heat pumps thus is crucial. Recent research in our group and the literature has shown that refrigerant mixtures can increase efficiency and application flexibility by exploiting the non-isothermal phase change, known as temperature glide.
While the potential benefits of refrigerant mixtures are known, practical implementation faces significant challenges. A particular challenge regards the lubrication in the heat pump cycle which is critical to prevent the wear of moving parts in the compressor. Identifying suitable lubricants, hence, is a vital task in the development of novel refrigerants. Heuristics exist mapping suitable lubricants to refrigerant classes. While these heuristics work for pure refrigerants, lubrication remains a critical knowledge gap for refrigerant mixtures, particularly for mixtures of dissimilar refrigerants that show beneficial thermodynamic properties for high-temperature heat pumps.
This master thesis aims to fundamentally examine the interactions between refrigerant mixtures of different polarity and common lubricants. As a result of this master thesis, we envision understanding the emerging challenges in lubrication when using refrigerant mixtures. The gained understanding yields a first step towards incorporating an oil-compatibility assessment in a molecular and process design frame-work. For this purpose, the PC-SAFT equation of state shall be employed to describe equilibrium proper-ties of the pure refrigerants, lubricants, and ternary refrigerant-refrigerant-lubricant mixtures. Parameters of the equation of state shall be fitted to experimental vapor pressure data. Based on the obtained equations of state and the theory of entropy scaling, viscosities of the refrigerants-lubricant systems shall be estimated and validated against experimental data. The estimates for the equilibrium and transport properties directly yield insights into the interactions between the refrigerant mixtures and the considered lubricants. In particular, miscibility plots and so-called “Daniel plots”, comprising the solubility of the refrigerant in the lubricant and the corresponding viscosities, yield practically relevant insights.
In this master thesis, you will identify the emerging challenges in lubrication when using refrigerant mix-tures for high-temperature heat pumps. You will get insights into the molecular interactions of refrigerant-refrigerant-lubricant systems by using state-of-the-art property prediction models. Furthermore, you will learn how to parametrize these property prediction models by regression using experimental data and a numerical solver. Your master thesis will contribute to researching decarbonization technologies for industrial applications.
In this master thesis, you will identify the emerging challenges in lubrication when using refrigerant mix-tures for high-temperature heat pumps. You will get insights into the molecular interactions of refrigerant-refrigerant-lubricant systems by using state-of-the-art property prediction models. Furthermore, you will learn how to parametrize these property prediction models by regression using experimental data and a numerical solver. Your master thesis will contribute to researching decarbonization technologies for industrial applications.
If you are interested in this thesis, please contact Carl Hemprich (chemprich@ethz.ch). To apply for the project, please attach your CV and transcript of records.
If you are interested in this thesis, please contact Carl Hemprich (chemprich@ethz.ch). To apply for the project, please attach your CV and transcript of records.
