Session: 06-06 Heat Pumps-II

Paper Number: 153648

Experimental Exergy Analysis of a High-Temperature Brayton Heat Pump 

High-temperature heat pumps (HTHP) are a promising technology to provide emission-free process heat at high temperatures by utilizing waste heat with renewable electricity especially in industry. HTHPs available on the market can provide process heat up to 150°C. However, many industrial processes, e.g. in food and paper industry, require higher temperatures in the range of 150 – 250 °C.

In order to advance the decarbonization of industry towards climate neutrality, HTHPs must be integrated into industrial processes in an appropriate manner. The development of future HTHPs needs to address the challenge of high achievable temperature levels while maintaining acceptable efficiency. The design of the heat pump cycle and the arrangement of components in relation to each other have a significant influence on the efficiency and play a crucial role for its applicability by the end user.

This study investigates both experimentally and numerically the exergy losses of a reversed Brayton cycle HTHP for a specific operating point in order to provide process heat above 150 °C. For the experimental test, the HTHP pilot plant CoBra at the Institute of Low-Carbon Industrial Processes of the German Aerospace Center (DLR) in Cottbus is used. The pilot plant has two radial compressors, one turbine and three shell and tube heat exchangers, one of which is used as a recuperator. Dry air is used as the working medium and in the secondary cycles.

On the basis of the experimental results, an exergy analysis is carried out to identify the components with the greatest exergy losses and to reveal optimization potential.  Most exergy is lost at the compressors due to low isentropic efficiency and pressure losses between both stages. The heat exchangers’ design for low pressure losses and the gaseous phase on both sides leads to significant exergy losses during heat transfer between primary and secondary cycles. The pilot plant is also modeled using the tool EBSILON^®Professional. The experimental operating point is simulated and the numerical results are then compared with the results obtained experimentally.

This study presents first results of the HTHP experimental facility CoBra. By analyzing the exergy losses in the real plant and comparing them with numerical results, this work contributes to a better understanding of the physics of this heat pump cycle. It is shown that the use of a recuperator is beneficial for the efficiency. Minimizing temperature differences at the heat exchangers as well as insulation of all high temperature areas of the heat pump is a realistic and relevant contribution to the overall efficiency.

Presenting Author: Nancy Kabat German Aerospace Center, Institute of Low-Carbon Industrial Processes

Presenting Author Biography: - M.Sc. Process Engineering at BTU - Cottbus Senftenberg, Germany (2019)
- Plant and process engineer at LUG/ Eta AG Engineering , Germany (2019 - 2020)
- Scientific researcher and ongoing promotion/PHD at German Aerospace Center, Institute of Low-Carbon Industrial Processes, Department of High - temperature heat pumps ( since 2021)
- publication at ASME TE 2023 "INVESTIGATION ON PROCESS ARCHITECTURES FOR HIGH-TEMPERATURE HEAT PUMPS BASED ON A REVERSED BRAYTON CYCLE"

Authors:

Nancy Kabat German Aerospace Center, Institute of Low-Carbon Industrial Processes
Johannes Oehler German Aerospace Center, Institute of Low-Carbon Industrial Processes
Panagiotis Stathopoulos German Aerospace Center, Institute of Low-Carbon Industrial Processes