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Simulation of a Safe Start-Up Maneuver for a Brayton Heat Pump

Oehler, Johannes and Tran, A. Phong and Stathopoulos, Panagiotis (2022) Simulation of a Safe Start-Up Maneuver for a Brayton Heat Pump. In: ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition, GT 2022. ASME 2022, 13.-17. Juni 2022, Rotterdam, Niederlande. doi: 10.1115/GT2022-79399. ISBN 978-079188612-0.

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Official URL: https://asme.pinetec.com/gt2022/data/pdfs/trk-6/GT2022-79399.pdf


With about 50 % of the final energy used as heat in Europe, reducing fossil fuel consumption in this sector is crucial to achieve significant greenhouse gas emission reduction. Heat pumps using renewable electricity can potentially cover the heat demand below 500 °C. The DLR’s prototype CoBra (Cottbus Brayton cycle heat pump) aims at demonstrating the feasibility of a turbomachine driven closed-loop Brayton cycle heat pump with a thermal output of 200 kW and a heat sink temperature of up to 350 °C. In order to achieve safe operation, transient operation of the heat pump, such as start-up, must be analyzed. Temperature gradients must be kept below a limit, defined mostly by thermal stresses in the heat exchangers. At the same time, compressor surge and resonant frequencies of rotating components must be avoided during transient maneuvers of the system. In the current work, the heat pump prototype has been modeled with Modelica based on the component geometries and with the use of compressor and turbine maps obtained from 3D CFD simulations. For the start-up of the prototype, a suitable control strategy is developed and analyzed in order to minimize operational risks. Control parameters are compressor shaft speed, secondary mass flows and the turbine bypass. It is shown that a turbine bypass is necessary to avoid compressor surge during start-up. The conflicting requirements of crossing natural frequencies quickly while ensuring tolerable temperature gradients in the heat exchangers can be met. The results also show that pressure rise delay through volume dynamics is in the order of seconds. Slow transient effects in the evolution of fluid and heat exchanger temperatures arise from the thermal inertia of the heat exchangers.

Item URL in elib:https://elib.dlr.de/188724/
Document Type:Conference or Workshop Item (Speech)
Title:Simulation of a Safe Start-Up Maneuver for a Brayton Heat Pump
AuthorsInstitution or Email of AuthorsAuthor's ORCID iDORCID Put Code
Oehler, JohannesUNSPECIFIEDhttps://orcid.org/0000-0001-6226-5328UNSPECIFIED
Tran, A. PhongUNSPECIFIEDhttps://orcid.org/0000-0002-3365-5500UNSPECIFIED
Date:16 June 2022
Journal or Publication Title:ASME Turbo Expo 2022: Turbomachinery Technical Conference and Exposition, GT 2022
Refereed publication:Yes
Open Access:Yes
Gold Open Access:No
In ISI Web of Science:No
Keywords:high temperature heat pump, reverse Brayton cycle, process heat, Modelica, transient process simulation
Event Title:ASME 2022
Event Location:Rotterdam, Niederlande
Event Type:international Conference
Event Dates:13.-17. Juni 2022
Organizer:American Society of Mechanical Engineers
HGF - Research field:Energy
HGF - Program:Materials and Technologies for the Energy Transition
HGF - Program Themes:High-Temperature Thermal Technologies
DLR - Research area:Energy
DLR - Program:E SP - Energy Storage
DLR - Research theme (Project):E - Low-Carbon Industrial Processes
Location: Cottbus
Institutes and Institutions:Institute of Low-Carbon Industrial Processes > High-Temperature Heat Pumps
Institute of Low-Carbon Industrial Processes > Simulation and Virtual Design
Deposited By: Oehler, Johannes
Deposited On:24 Nov 2022 10:27
Last Modified:27 Feb 2023 14:50

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