Simulations for the Analysis of High Temperature Heat Pumps

AIT Austrian Institute of Technology sees itself as a bridge between research and industry, helping to lower barriers to adopting new technologies. One current project example is the optimization of high temperature heat pumps for industrial processes. The aim is to significantly reduce the carbon footprint of industrial companies by directly utilizing waste heat from existing processes. Simulation plays a crucial role for AIT, both for designing the heat pump’s refrigeration cycle and for optimizing the ejector used in the system.

Reducing the Carbon Footprint of Industrial Operations

Household heat pumps are already widespread and gaining momentum. In contrast, process heat in industry is still often generated with natural gas. To change this, AIT is working to optimize high temperature heat pumps for these industrial applications. In addition to natural gas, waste heat from existing processes can be used directly for heating. This waste heat can be raised to a higher energy level and integrated back into the processes. The result: energy savings.

Especially in the high temperature range, the technology is still relatively new, meaning that very few industrial companies dare to take the first step. This is why convincing pilot projects are needed, supported by demonstrator systems that show that the technology works.

Understanding the Ejector’s Operating Principle Through Simulations

To achieve this, AIT chose a classic research driven approach: first gaining a full understanding of the system before developing any improvement concepts. The required detailed analyses were performed with simulation support to gain deep insight into the ejector’s operating principle.

Operating principle of the ejector | © AIT Austrian Institute of Technology GmbH

Robust and Accurate Simulation Models Analyze Multiphase Behavior

Several complex physical phenomena occur simultaneously: on the one hand, supersonic speeds and the associated strong turbulence; on the other hand, evaporation. To design ejectors efficiently, highly robust and accurate simulation models for analyzing multiphase flow had to be developed.

AIT worked on both the calculation of the heat pump’s refrigeration cycle and the detailed design of the ejector. In the primary inlet, the liquid refrigerant is accelerated to supersonic speed, while the gaseous medium is drawn in through the secondary inlet. After both streams mix, a pressure increase occurs in the diffuser.

To analyze this phenomenon, comprehensive flow simulations were carried out using Ansys Fluent. This made it possible to examine the ejector’s behavior and then design it optimally based on the findings.

Integrating Material Data Is Essential for Simulations

In the initial phase, simulation stability problems occurred, leading AIT engineers to engage in intensive discussions with experts from CADFEM and industry representatives about their previous results. This exchange was extremely valuable and encouraged the engineers to not only focus on improving the simulation workflow but also to significantly enhance the integration of material data.

Initially, simplified external material databases – so called lookup tables – were used and integrated into the simulation software. Due to the limited resolution of these material models for the refrigerant in the ejector, stability issues occurred because two phases had to be considered: liquid and vapor.

Velocity analysis with improved database integration | © AIT Austrian Institute of Technology GmbH 

“User Defined Real Gas Models” Solve the Stability Issue

The material databases were then integrated with much higher resolution. This resulted in greater stability and at the same time increased accuracy and computational speed. Through the intensive exchange with CADFEM support, AIT engineers gained a much better understanding of Fluent’s internal material handling. Working together with CADFEM, they developed an optimized solution using “User Defined Real Gas Models”, which integrate the material databases in this way.

Analysis of vapor fraction and velocity | © AIT Austrian Institute of Technology GmbH 

Brick Manufacturing Plant Reduces CO₂ Emissions by 88 Percent

A joint project between AIT and Wienerberger aimed to develop and build a decarbonized brick plant. AIT engineers mainly supported the company by conducting simulations – both for the electrification of the kiln and for optimal integration of a heat pump that uses the kiln’s waste heat for the drying process.

Wienerberger’s new plant is now up and running. Initial measurements show that primary energy consumption has been reduced by around 30 percent, while CO₂ emissions have been cut by 88 percent at the same time.

The AIT technology is highly transferable. Since similar kilns are used in other industrial sectors, high temperature heat pump technology can be implemented there with only minor adjustments. Given the massive documented CO₂ savings, there is now active exchange with other manufacturing companies in Austria – including steel, ceramics, paper, and pharmaceuticals.

Watch the interview with Manuel Schieder (Junior Research Engineer, AIT Austrian Institute of Technology GmbH) an: