Space- and time-resolved interferometric measurements of the thermal boundary layer at a periodically magnetized gadolinium plate

• Two thin flat gadolinium (Gd) plates immersed into n-decane are periodically magnetized.
• A Mach-Zehnder interferometer is used to monitor the 2D transient temperature field.
• The thermal fronts emanating from the Gd plates after magnetization obey a t1/2-dependence.
• A finite time of de-/magnetization causes a spatially delayed propagation of the thermal fronts.
• The evolution of temperature profiles and heat flux into n-decane is provided in detail.

By means of a Mach-Zehnder interferometer we examine the transient dynamics of heat transfer from two periodically magnetized gadolinium (Gd) plates into a heat transfer fluid (n-decane). We demonstrate that the propagation of the thermal fronts emanating from the Gd plates after magnetization or demagnetization obeys a t-dependence. A finite time required for magnetization and demagnetization causes a spatially delayed propagation of the thermal fronts. The diffusive heat flux, derived from the temperature profiles, experiences a drop down by about 80% after first 3 s while the percentage of thermal energy transferred into n-decane experiences a maximum there. Although limited to heat transfer into a stagnant fluid, the present works provides reasons for lower bounds of geometry and operation frequency of a simplified parallel-plate structure in the diffusive limit. In this way, the results are instructive for an efficient design of a parallel-plate magnetic regenerator with forced convection.