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Packed Beds

Pressure Drop and Temperature Measurements in Packed Beds

Determination of the Hydraulic Diameter of Irregular Shaped Materials by Pressure Drop Measurements
Flooded air through a packed bed of particles accrues a pressure drop. By using the pressure drop in the Ergun equation it is procurable to approximate a particle’s diameter.

Building up a setup (Fig. 1) that measures the pressure drop of spherical and non- spherical particles was the first goal of the experiment. Testing irregular shaped particles is more interesting, because most of the real applications work with that kind of materials. It is not easy to define a (fictive) diameter of an irregular shaped particle, but the achievements of the measurements show very plausible results.(8% maximum aberration to the real diameter).

In future we want to produce measurements with packed beds consisting of mixed sized particles. We will distinguish between mixed beds and laminated beds. Results for these heterogeneous measurements already exist, but it’s not possible to evaluate them due to the fact that there are too less test readings done up to now.

Temperature Measurements in Packed Beds
The main focus of attention of that measurement this year was placed on temperature measurements in packed beds. As you can see at Fig.1 there are also temperature sensors and a heating system installed. We wanted to find out the temperature change through the packed beds as a function of the time and several heights.

Fig. 1: Measurement setup

The first results showed, that the particles need a lot of time to get heated(especially at the height from 1 meter over the heating system).

A really big problem we were confronted with was the temperature difference at the bottom of the packed bed between the inner wall and the middle of the wall measurements. The difference was about 20 degrees Celsius, which has been too high to get a qualitative measurement input. After several trials to get the problem under control it turned out that the best solution is to design and install circulation grids around the heating system (Fig. 2). Therefore it appeared that the problem of the temperature difference was caused by irregular air flow through the bed. At Fig.3 and Fig.4 you can see the high impact of the circulation grid. During the further procedure we will try to survey different materials and try to calculate the temperature coefficients of the tested particles.

Fig. 2: Heating system

Fig. 3: Heat transfer measurement without circulation grid

Fig. 4: Heat transfer measurement with circulation grid

(Niklas Hofer)