Abstract
A series of experimental measurements has been conducted in order to investigate the bubble behaviours through the horizontal pipe line of the domestic wet central heating systems. Obtained results exposed the effect of 90 degree bend, buoyancy forces on bubbly two phase flow patterns and effect of velocity on void fractions and bubble diameters. Distance chosen for the first sight glass (HSG0) was sufficient enough to note the effect of 90 degree bend on void fraction patterns. Due to the effect of 90 degree bend, position of the peak void fractions across the pipe section lowers, with an increase in bulk fluid velocity. Bubbles tend to flow for longer distance at the bottom of the pipe section. Buoyancy force effect is demonstrated with figures for highest bulk fluid velocity at three different positions. Analysis of four different flow rates at two different saturation ratios show reduction for average bubble diameters and void fractions when bulk fluid velocity increases. An attempt to predict bubble dissolution rates across the horizontal pipeline of the system is made, however results show some uncertainties.
Highlights
Bubble formation in wet central heating systems is due to the supersaturated conditions which occur on the primary heat exchanger wall of the boiler
Bubble distributions across pipe section are shown in the following log of void fraction versus focal plane figure 11-13
Peak void fraction positions at HSG0 gets closer at the bottom of the pipe with an increase in bulk fluid velocity
Summary
Bubble formation in wet central heating systems is due to the supersaturated conditions which occur on the primary heat exchanger wall of the boiler. Dissolved gases in the flowing liquid are released as bubbles when they encounter high temperatures These bubbles tend to escape to the higher parts of the system (low pressure) and cause cold spots, and maintenance or noise problems. Little data exists in the literature for two-phase flow characteristics, for central heating systems, to assist companies to improve such devices. In this regard, investigation of bubble behaviours in central heating systems becomes important to help enhance the design of deaerators
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