Thermal conductivity measurements of copper-coated metal hydrides (LaNi5, Ca0.6Mm0.4Ni5, and LaNi4.75Al0.25) for use in metal hydride hydrogen compression systems

doi:10.1016/j.ijhydene.2009.01.078

International Journal of Hydrogen Energy

Volume 34, Issue 7, April 2009, Pages 3185-3190

https://doi.org/10.1016/j.ijhydene.2009.01.078 Get rights and content

Abstract

This study was performed to supplement the limited data on metal hydrides by experimentally determining the thermal conductivity of various metal hydride powder pellets that underwent a copper coating process. Three different metal hydride powders were tested (LaNi₅, Ca_0.6Mm_0.4Ni₅, and LaNi_4.75Al_0.25) for their thermal conductivity, with variations in testing parameters, and with copper coating processes that varied from 30 to 60 s A testing apparatus was specifically designed for this experiment, and the study reported thermal conductivity values of 3–6 W/m-K.

Introduction

A significant challenge in the practical use of hydrogen as an energy source is its low energy density. To make hydrogen gas a viable option, high storage pressures are required. Current methods in hydrogen compression typically comprises of mechanical compressors operated on electricity derived from fossils fuels, which poses higher energy costs. With the implementation of metal hydrides for hydrogen compression, energy density and efficiency can be increased while reducing costs. This investigation stems from the ability of metal hydrides to charge and discharge hydrogen at relatively fast rates. In a practical view, this aspect of metal hydrides will become increasingly important as the usage of hydrogen gas becomes more commercialized and the demand spreads to the consumer level. Therefore, improvements in heat and mass transfer are desirable and are highly dictated by the thermal conductivity and permeability of the hydride material [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. In this experimentation, the metal hydride samples will be processed with a copper encapsulation method of different fractions in order to understand optimization methods.

One of the earliest studies conducted in analyzing the effective thermal conductivity of porous metal hydrides was done by Ron et al., in which LaNi₅ powders were immersed in an aluminum matrix (0.075–0.3 mass fraction), activated, compacted into a cylindrical pellet, and subsequently sintered under high pressure (200–300 atm) hydrogen [1]. The thermal conductivity from this method was on the order of 8–23 W/m-K.

An alternative method to the aluminum matrix combined with metal hydride was introduced by Kim et al. [2], [3] where the metal hydride particles are copper-coated by chemical plating and then compacted into cylindrical pellets with varying amounts of Sn binder. In this work, the mass fraction of copper and compaction force was varied from 0.05 to 0.15 and 27.0 to 45.0 kpsi, respectively. The study reported thermal conductivity values of 3–6 W/m-K.

The goal of this study is to supplement the limited data on metal hydrides by experimentally determining the thermal conductivity of various metal hydrides powder beds treated in a similar manner accomplished by Kim et al. while varying the applied force in situ.

Section snippets

Experimental setup

In approaching the quantification of the thermal conductivity of porous metal hydride samples, an apparatus was constructed to make such experimental measurements possible. The apparatus implements the comparative method of thermal conductivity measurements. The test sample is placed between two reference materials (i.e., copper) with well-established thermal conductivities. Its strength allows for variances in compaction pressure of the sample. A constant cold temperature heat sink can be

Results

The resulting data for LaNi₅ in a raw powder (virgin intermetallic) form and also coated in 40 and 50 s processes is shown in Fig. 7. The thermal conductivity data displays a strong correlation between the compaction pressure and the coating of copper. With greater pressure, the thermal conductivity increases, as expected, since the contact area between the particles increases and the void spaces decrease. It is also important to note that the length of the sample was adjusted with the

Discussion

Porous metal hydride powders were tested for their thermal conductivity, with variations in testing parameters. The three different metal hydrides used were LaNi₅, Ca_0.6Mm_0.4Ni₅, and LaNi_4.75Al_0.25 with copper coating process varying from 30, 40, 50, and 60 s. While the thermal conductivity data for Ca_0.6Mm_0.4Ni₅ and LaNi_4.75Al_0.25 are limited for comparison purposes, they were found to have values ranging from 0.80 to 2.82 W/m-K and 1.78 to 4.29 W/m-K, respectively. On the other hand, the thermal

Acknowledgements

The authors extend sincere thanks for the financial support from the U.S. Department of Energy via National Renewable Energy Laboratory in connection with the NSWEP program (NDJ-6-66271-01).

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Thermal conductivity measurements of copper-coated metal hydrides (LaNi5, Ca0.6Mm0.4Ni5, and LaNi4.75Al0.25) for use in metal hydride hydrogen compression systems

Abstract

Introduction

Section snippets

Experimental setup

Results

Discussion

Acknowledgements

Journal of Less-Common Metals

Powder Technology

International Journal of Hydrogen Energy

International Journal of Hydrogen Energy

International Journal of Hydrogen Energy

Thermal conductivity measurements of copper-coated metal hydrides (LaNi₅, Ca_0.6Mm_0.4Ni₅, and LaNi_4.75Al_0.25) for use in metal hydride hydrogen compression systems