Anthropogenic climate change caused by fossil fuels is a major threat to our planet. Decarbonization of the industry therefore is crucial to achieve the goal of a sustainable future. One way to reduce carbon emissions in the industry is by the use of high temperature heat pumps, which operate with waste heat and small amounts of electricity, thus replacing fossil fuels. However, traditional expansion valves used in heat pumps are inefficient, due to the irreversible dissipation process occurring inside. An alternative expansion device, the ejector, has the potential to improve the COP (Coefficient of Performance) of heat pumps up to 26\%. This makes heat pumps not only more efficient, but also reduces their operational costs. Utilizing Numerical Fluid Dynamics, ejectors for the use in an industrial heat pump with R1233zd(E) as a refrigerant are investigated in this thesis.To reduce the computational demand of simulating the two-phase flow inside the ejector, the Homogeneous Equilibrium Model (HEM), which assumes thermal and mechanical equilibrium between both phases, is applied. This model was implemented into the commercial software Ansys Fluent. From the simulations it was found that ejector geometries can be scaled with the same factor in all coordinate directions without changing the performance. This leads to an increased mass flow rate, therefore increasing the maximum power output. Thus, for heat pumps which have a power output different from the one for which the ejector was originally designed for, the ejector geometry must simply be scaled accordingly.The testing of 300 different geometries in 2D axisymmetric simulations led to a geometry with a theoretical ejector efficiency of ≈0.3907.It was shown that if the heat pump cycle allows an adaption of the operating conditions, the efficiency can further be increased, as the suction pressure ratio directly influences the ejector efficiency. By a comparison of the 2D simulations with 3D simulations, it was concluded that the 2D simulations give a valuable first result and thus first steps can be taken to optimize the geometry. However for further investigations 3D simulations are recommended, especially if tangential suction inlets are chosen.
|Qualifikation||Master of Science|
|Betreuer/-in / Berater/-in|
|Datum der Bewilligung||23 Jan. 2023|
|Publikationsstatus||Veröffentlicht - 1 Feb. 2023|
- Efficiency in Industrial Processes and Systems