Abstract
As one of the means for energy saving and environment preservation, a regionally concentrated air-conditioning system using chilled or hot water as a thermal media has recently been reconsidered. And an thermal energy meter has been developed. For the flow measuring element of semimicro meters, tangential rotor wheel type is widely used. Various experimental results of this flowmeter are considered, the following defects are evident: 1) At heating, because bubbles mixed in circulating hot water are retaind over a long time in the casing of rotor wheel, the measuring error remarkably increases. 2) By the frictional resistance of mechanical moving parts, the measuring error occurs in a lower flow rate range. 3) A change in the viscosity of fluid gives a bad influence on the measuring performance. In order to improve the above defects, a new flowmeter using a fluidic oscillator has been built trially for proposal. In addition, the observations for the optimum desgin conditions of the flow path shapes, and the various performances are described. The flowmeter is constructed by both main piping system that is equipped with an orifice and bypass piping system constituted by a feedback fluidic oscillator. This fluidic flowmeter is attached on inside walls near the inlet of feedback duct, unlike the conventional flow path. By the consideration from various experimental results, the following are evident: 1) The measuring error due to the stagnation-accumlation phenomenon can be eliminated. 2) The pressure loss is very little, and this meter is small in size, light in weight and simple in construction. 3) Considering various characteristics of the flow path shapes, the following are evident: a) The optimum position of the inside wall is as follows; each distance from the main nozzle or attachment wall are 13〜20 or 1.5〜2.5 multiplied by the main nozzle width. And the oscillating phenomenon is stable in the lower flow rate range. b) The detecting gain increases proportionally to the distance of the inside wall from the main nozzle. 4) For the oscillating characteristics of the flowmeter, the following are evident: a) The oscillating frequency does not influence very much on the changes of viscosity and density for 20〜75℃. b) The oscillating frequency increases linealy in the wide range, and the measuring accuracy is about ±2% to flow rate of 0.15〜2.2m^8/h. Summarizing the results of the present experiments, it is evident the fluidic flowmeter trially made is very usefull for the flow measuring part of the thermal energy meter. And, the fluidic flowmeter has better performance as compared with previous flowmeter.
