Ultra-High Temperature Thermal Conductivity Measurements of a Reactive Magnesium Manganese Oxide Porous Bed Using a Transient Hot Wire Method

Abstract

The effective thermal conductivity of packed beds of magnesium-manganese oxide pellets is a crucial parameter for engineering Magnesium Manganese Oxide (Mg-Mn-O) thermochemical energy storage devices. We have measured the effective thermal conductivity of a packed bed of 3.66 ±0.516 mm sized magnesium manganese oxide (Mn to Mg molar ratio of 1:1) pellets in the temperature range of 300 to 1400°C. Since the material is electrically conductive at temperatures above 600°C, the sheathed transient hot wire method is used for measurements. Raw data is analyzed using the Blackwell solution to extract the bed thermal conductivity. The effective thermal conductivity standard deviation is less than 10% for a minimum of three repeat measurements at each temperature. Experimental results show an increase in the effective thermal conductivity with temperature from 0.50 W/m °C around 300°C to 1.81 W/m °C close to 1400°C. We propose a dual porosity model to express the effective thermal conductivity as a function of temperature. This model also considers the effect of radiation within the bed, as this is the dominant heat transfer mode at high temperatures. The proposed model accounts for micro-scale pellet porosity, macro-scale bed porosity, pellet size, solid thermal conductivity (phonon transport), and radiation (photon transport). The coefficient of determination between the proposed model and the experimental results is greater than 0.90.

Enhancing the Chemical Energy Flux in a High-Temperature Tubular Counterflow Solid Fuel Synthesis Reactor Using a Bypass

“…The new limiting factor for the storage flux is now the residence time. Increasing the tube diameter would help with the particle residence time; however, the radial heat conduction 18 restricts the extent to which the diameter can be increased. A numerical study on the impact of different tube diameters for this setup was done by Korba et al 19 Instead, a longer reduction zone would be an effective method.…”