Experimental investigation of a thermally powered central heating circulator: Pumping characteristics

A thermally powered circulator based on a two-phase thermofluidic oscillator was constructed and operated successfully as a replacement for a central heating hot water circulator coupled to a domestic gas-fired boiler. During regular operation the thermally powered circulator demonstrated a pumped flow-rate that decreased monotonically as the head applied across it increased. A maximum measured flow-rate of 850 L/h was achieved at zero head, and a maximum head of 8.4 mH2O was attained at near-stalling (zero flow-rate) conditions. In agreement with previous modelling studies of the technology, increased inertia in the load line seems to lead to improved circulator performance. Further, the oscillating circulator exhibited an operational frequency between 0.24 and 0.33 Hz, which was mostly determined by the circulator configuration. The pumping capacity was strongly affected by the oscillating liquid amplitudes in the power cylinder that defined the positive displacement amplitudes of the liquid piston into and out of the hot water circuit. The best circulator configuration was associated with lower operation frequencies and relatively large ratios of suction to discharge displacement.