PERFORMANCE OF FLAMCOVENT DEAERATORS

Transcription

1 PERFORMANCE OF FLAMCOVENT DEAERATORS An extract from: PERFORMANCE EVALUATION OF DEAERATORS FOR CENTRAL HEATING SYSTEMS A report on the enquiry on the basis of the MSc thesis of E.D. Vis van Heemst, TU Delft, the Netherlands, November 1995 Compiled for FLAMCO B.V. Author: Dr. Z. Olujic TU Delft Laboratory for process equipment Leeghwaterstraat CA Delft The Netherlands Delft, April

2 PERFORMANCE OF FLAMCOVENT DEAERATORS INTRODUCTION Several years ago, Flamco BV developed a continuously working deaerator, which received the name Flamcovent, in co-operation with the Laboratory for Process Equipment of the Technical University of Delft, the Netherlands. The Flamcovent proved to be very efficient in practice; it was able to remove air bubbles from central heating and refrigeration units. However, there was no specific process for measuring the performance of this deaerator in the area of micro-bubbles. For that reason, Flamco BV offered the Technical University of Delft the opportunity to carry out an experimental examination, which, in turn, could help in quantifying the performance of the Flamcovent. This examination was carried out on a closed cold water circuit with controlled air injection and concentrated itself essentially on attempts to separate micro-bubbles. To this end, laser diffraction technology and hardware were used, which were developed for particle sizing by Malvern Instruments. The results of these tests leave clear conclusions in respect of the depth of the process of air separation down to the smallest bubbles, the separation of which can still be expected from a Flamcovent deaerator.

3 QUANTIFICATION OF THE EFFECTIVENESS OF THE FLAMCOVENT The way in which the Flamcovent deaerator works lies in a patented process of separation of gases from fluids (water). As shown in the diagram below (fig. 1), fillers (pall rings) are used in this process and must have the following qualities: - Large surface area per unit of volume, - Large possibility for collision and adhesion, - Low flow resistance. (fig. 1) The working method of a Flamcovent was simulated in a closed cold water circuit with controlled air injections. These air injections cause an increase in pressure in the test circuit. As soon as the Flamcovent starts to remove air from the system, the circulation pressure begins to fall. Figure 2 shows the typical course of pressure reduction relative to time as measured during testing. The initial, steeply falling part of the curve, shows primarily the deaeration due to removal of macro-bubbles; separation of micro-bubbles is shown in the latter part of the curve.

4 De-aeration De-aeration and separation Separation Pressure (bar) (fig. 2) Time (sec) Macro-bubble separation Macro-bubbles (Ø > 500 µm) are primarily separated from the fluid as a result of the flow delay realized in the main part of the Flamcovent. Due to the water s low flow speed through the Flamcovent; the air bubbles can swim upwards into the air chamber of the Flamcovent, from which they can be blown off into the ambient air through a swim/valve mechanism. Micro-bubble separation The occurrence of separation of micro-bubbles from the fluid, which happens in the Flamcovent, is known as the coalescence effect. This means in practice that the micro-bubbles have a tendency to stick to the surface of the pall rings and then to grow into larger air bubbles, which easily separate from the pall rings up into the air chamber of the Flamcovent, from which they can be blown off into the ambient air through a swim/valve mechanism.

5 MEASUREMENT OF BUBBLE SIZE DIVISION Measurement of bubble size division in a continuous fluid flow is, in practice, carried out with the Malvern Particle size Analyzer, a unit that uses the small diffraction angle of laser light to establish the maximum size of the air bubbles in the system. The tests were repeated with an entry speed of 1.25 m/s constant static pressure and constant temperature. Each measurement was carried out three times to establish the result. The measurements, lasting up to six hours, showed that the size of the largest bubbles remaining in the system after approximately one hour appeared to stabilize at µm ( mm), which leads to the conclusion that almost all air bubbles larger than the measured size are removed from the system by the Flamcovent. CLOSING COMMENTS The measurements have shown that after some 60 seconds (10 15 times passing through the Flamcovent) all macro-bubbles, i.e. bubbles with diameters in excess of 500 µm (> 0.5 mm) are removed from the system. From this point onwards, air separation appears to play the main role due to the coalescence effect. It was shown that the pall rings, which accentuate this effect, have the ability to remove all bubbles larger than µm. This size class may be viewed as a reliable indicator for the depth of deaeration which can be realized in practice with the Flamcovent micro-bubble separator.