Planar High Temperature Heat Pipes for SOFC/SOEC Stack Applications

Abstract

Targeting transient operation of high temperature solid oxide cell (SOC) systems this paper proposes an enhanced heat management mechanism using planar high temperature heat pipes that can be integrated into the SOC‐stack structure. Flat heat pipes with thicknesses down to 4 mm filled with liquid alkali metals for almost isothermal 2D heat spreading, even for intense heat transfer rates, are demonstrated. A new pathway towards a temperature gradient shrinking in SOC‐stacks without using large amounts of additional air‐cooling is shown. The paper will present latest development results on design concepts, size reduced fabrication and filling procedure. An experimental study demonstrates the heat spreading capabilities and power limitations of planar heat spreaders for high temperature applications as in SOEC/SOFC stacks.

Performance of compressed nickel foam wicks for flat vertical heat pipes

“…( 5 ), provided that the contact angles of the respective fluids on the wick surface are known: If it is assumed that there is no evaporation of liquid from the wick, the maximum rise of liquid in the wick can be determined by balancing the capillary pressure to the hydrostatic pressure of the liquid in the wick [14]:…”

“…( 5 ). From the contact angle calculations performed, a contact angle of 58.4º was used for the heptane on the wick surface.…”

“…Overviews over established materials, structures and working fluids suitable for different working temperatures are available in textbooks [1][2][3][4]. Recently Dillig et al [5] carried out experiments with planar heat pipes using sodium as working fluid and different types of wick structures (screen mesh, sintered plates and grooves). The capillary limitation was identified as one of the main challenges in their study, underlining the importance of the wick structure optimization.…”

Integration of Planar Heat Pipes to Solid Oxide Cell Short Stacks

“…Heat pipe interconnector design bases on the planar heat pipe design developed at the institute of energy process engineering (EVT) 18. The casing was milled into CROFER 22H sheets, with the flow fields machined on the external side.…”

“…Figure 1 explains the basic idea behind this concept. The heat pipe functionality is directly incorporated into the flat metal interconnectors 18, which are stacked into the SOC stack among normal interconnectors with a certain frequency. Thus, these heat pipes are in close thermal contact to the planar SOC cells.…”