Experimental Analysis Of Two-phase Flow In
Domestic Central Heating Systems:
Micro Bubble Characteristics
Author(s)
A. M. Fsadni, Y. T. Ge & A. G. Lamers
Abstract
Domestic central heating systems result in micro bubble nucleation and
detachment at the boiler wall due to the presence of supersaturated conditions in
the system. Such conditions originate due to the widespread use of untreated tap
water in such systems and due to the air leakage into the system’s closed loop
circuit during the daily thermal cycling. The presence of air bubbles in such
systems results in a number of undesired effects such as corrosion, blockages,
noise and the filling of radiators with air due to the deposit of the micro bubbles
in the radiators. As a result, a loss in the heat transfer area of the radiator occurs
thus resulting in an inefficient use, consequently increasing the carbon footprint
of such widely used systems. Therefore, the capture of micro bubbles at the exit
point of the boiler should result in improved system efficiencies. A
comprehensive knowledge of the expected bubble production rate and bubble
size is important for an efficient deaeration system. To date, no studies have been
published on the fundamentals of bubble production and size in wet central
heating systems, therefore, the importance of this paper for the building services
industry. Experimental results on a test rig incorporating a typical 19 kW (rated)
domestic gas fired boiler show typical micro bubble production rates ranging
between 0.03 to 0.47 litres of nitrogen gas per hour with a shift in the system
heating load. An analysis of the expected bubble diameters was done at different
system conditions. Bubbles with average diameters within the range of 0.13 and
0.39 mm were observed. A comparison with Winterton’s finite angle force
balance model resulted in reasonable predictions.
Keywords: micro bubbles, supersaturated solutions, central heating, dissolved
gasses, space heating.
Keywords
micro bubbles, supersaturated solutions, central heating, dissolved
gasses, space heating
Related Book
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