A transient technique to determine heat transfer in small packed beds

Abstract

A transient technique is proposed for measuring the mean thermal conductivity of a small bed of solid particles. Such beds are used in different catalytic rate studies or for a temperature-programmed desorption apparatus. The lower bound of conductivity for a thin bed of 47% by weight nlckel/slllca catalyst was 2.6 W/(m K), In orderof-magnitude agreement with published data. If methane were produced catalytically from a CO/H2 mixture in such a catalytic bed at typical flow conditions, the calculated difference between center line and wall temperatures should not exceed 4 °C.

Transient temperature technique applied to study activity pattern changes during the hydrogenation of CO over nickel/silica catalysts

“…The temperature of the bed was measured at the center. A uniform temperature distribution has been demonstrated to exist through the catalyst bed (Huang, 1984;Huang et al, 1986a). A flow rate of 100 cm3/min of premixed H2/CO, having a ratio of 20:1, was used.…”

“…The temperature was then modulated in a sinusoidal wave around this common temperature with an amplitude of ±5 K. The procedures used to accomplish the desired temperature variation required a balance between the power input to the oven and the water flow rate in a coil surrounding the reactor. The cycle time for the temperature wave was 240 s. For this modulation time and these reaction conditions, it was previously shown (Huang et al, 1986a) that the effective thermal conductivity of the catalyst bed was 2.6 W/(m K) which ensured a uniform temperature through the bed and that the conversion would be less than 10% over the wide range of reaction temperatures studied. Kinetic data similar to those reported in detail here were found for cycle times of 300 and 360 s, which was also consistent with the earlier measurements (Huang et al, 1986a).…”

“…The cycle time for the temperature wave was 240 s. For this modulation time and these reaction conditions, it was previously shown (Huang et al, 1986a) that the effective thermal conductivity of the catalyst bed was 2.6 W/(m K) which ensured a uniform temperature through the bed and that the conversion would be less than 10% over the wide range of reaction temperatures studied. Kinetic data similar to those reported in detail here were found for cycle times of 300 and 360 s, which was also consistent with the earlier measurements (Huang et al, 1986a).…”

“…Because the reaction conditions used in this study were free from mass-and energy-transfer limitations (Huang et al, 1986a), only the direct surface suppression model was considered. Here the surface is considered to be altered by a less active carbon, which is formed from the reactive carbon pool by a unidirectional reaction.…”