PhD defence: Magnetocaloric materials for use in heat pumps

torsdag 29 sep 16

Magnetocaloric materials and first order phase transitions

Main supervisor: Christian Bahl

Co-supervisors: Kaspar Kirstein Nielsen, Anders Smith

The Ph.D. project was carried out as part of the ENOVHEAT project which is funded by Innovation Fund Denmark (Contract No 12-132673).

On Thursday 29 September 2016 Henrique Neves Bez successfully defended his PhD thesis with the title “Magnetocaloric materials and first order phase transitions” at DTU Energy.

Magnetocaloric materials change their temperature in response to an external magnetic field. Such materials can be used for the active component of a heat pump. Henrique Neves Bez has for the past three years investigated a class of promising magnetocaloric materials in great detail. His work was done within the project ENOVHEAT which will ultimately result in a prototype heat pump for a single-family house.

“I have been looking at the new materials as part of my PhD. Each material has a relatively narrow active temperature range, but a large magnetocaloric effect, meaning that we have a higher efficiency and can take out a higher amount of heat”, Henrique explains.

“The narrow temperature range is a problem for applications. However, if we change the composition of the material slightly, we can shift the active temperature range. By using several layers of different compositions of the same material, we can make a component which is active over a wide temperature range. My part has been to study the properties of the different materials that might compose the different layers.”

One of the problems of the materials is that they undergo a volume change when changing their magnetic state. This may lead to cracks and mechanical failure, making it unfit for long term use in machines. To address this problem, Henrique investigated the thermal properties of the material and how the magnetic and structural behaviour of the materials are interconnected.

Henrique Neves Bez is quite satisfied with his work and his results. 

“I have improved my knowledge considerably during the study here at DTU Energy and I have also found some areas where I was lacking. That was good knowledge, as I can improve those areas, and I did several things that I didn’t think I was able to do. So I have exceeded my own expectations and I believe I have helped the scientific community. I like that.”

Even though his PhD studies at DTU has come to an end, Henrique is not finished with magnetocalorics: Next up will be a postdoc position at Ames Laboratory in the USA where a major research consortium called CaloriCool has just been launched. 

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