On Monday, 14 November Tian Lei from DTU Energy successfully defended his PhD thesis with the title: ”Modeling of active magnetic regenerators and experimental investigation of passive regenerators with oscillating flow”.
Some materials can change their temperature in response to an external field, e.g. a magnetic or electric field. Such ‘caloric’ materials can be used for high-efficiency refrigeration and heating where the use of conventional gaseous refrigerants are avoided. DTU Energy is heading ENOVHEAT, a large project funded by Innovation Fund Denmark, whose aim it is to develop a heat pump based on magnetocaloric materials.
Read more about project Enovheat here
Tian Lei had the important task in the project to improve the understanding of the active component in the heat pump, the so-called active magnetic regenerator. He used both models and an oscillating flow test apparatus to investigate the regenerator.
“Most magnetocaloric materials only exhibit a temperature change of less than 5 degrees with a 1.5 tesla permanent magnet, so we need to use the concept of regeneration to enlarge the temperature span. There are a lot of different materials and designs, and it is important to apply the materials in the right way to get the best performance. This is where I come in. I use computer simulations to see how it all works out to find the best designs”, says Tian Lei.
"There are a lot of different materials and designs, and it is important to apply the materials in the right way to get the best performance. This is where I come in. "
Tian Lei, postdoc at DTU Energy
Tian Lei worked with regenerative engines/coolers before starting his PhD at DTU Energy, a concept that is important in active magnetic regenerators. In his thesis, Tian Lei looked at the performance of a regenerator using either magnetocaloric materials with a first or second order phase transition (FOPT or SOPT), which exhibit different characteristics.
Compared to SOPT materials, FOPT materials have a higher magnetocaloric effect but a much more narrow working temperature region. The thesis quantifies the impact of these differences.
“Based on my investigations, I show how to implement layers of typical FOPT and SOPT materials. Based on simulations, I quantify the losses and analyze the loss mechanisms inside the active magnetic regenerators”, says Tian Lei.
Tian also had to address the problem that some magnetocaloric materials are very brittle. As a result, he developed epoxy bonded regenerators and tested their heat transfer characteristics using a test apparatus built by Tian himself.
Tian Lei successfully defended his thesis ”Modeling of active magnetic regenerators and experimental investigation of passive regenerators with oscillating flow” on Monday 14 November. He will continue at DTU Energy as a postdoc studying electrofunctional materials.
Read more about DTU Energys research in magnetic cooling and heating here