Dielectric loss of coal as a function of temperature and frequency
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Adsorbed water has various effects on tan δ for coals. If tan δ ≈ ≈ 0.5, ɛ and tan δ increase with the water content. If tan δ ≈ 50, ɛ increases but tan δ decreases.
The dielectric loss along the bedding in a dried coal exceeds that across the bedding by a factor 10–100. The loss across the bedding is mainly of relaxation type, while conduction dominates tan δ along the bedding (especially at low frequencies).
The ɛ along the bedding for a dried coal is much greater than that across the bedding and is very much dependent on frequency. This difference almost vanishes at high frequencies. Ion displacement contributes to ɛ along the bedding at low frequencies.
The temperature dependence of tan δ indicates that coal has a very open structure along the bedding and that conduction dominates the loss in that direction.
KeywordsBedding Dielectric Loss Adsorbed Water Open Structure Relaxation Type
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