Synchronization of self-sustained thermostatic oscillations in a thermal-hydraulic network

Flow and temperature oscillations occur under normal conditions in a thermal system with thermostatic control. We present experimental results of the synchronization of multiple oscillators in the secondaries of a thermal-hydraulic network. The test facility is composed of three secondary loops with heat exchangers that exchange heat with a primary heating loop on one side and a primary cooling loop on the other. A thermostatic controller senses the temperature at the outlet of a heat exchanger and modulates the flow rate in that loop. The flow valve is partially closed if the temperature goes above an upper limit and is completely opened if it falls below a lower limit. As a consequence a self-sustained flow and temperature oscillation is set up in that secondary. The frequency of the oscillation depends on the dead-band between the upper and lower temperature limits. Coupled oscillators are set up by the simultaneous action of multiple controllers on different branches. Frequency locking, phase synchronization as well as phase slips are observed to occur due to thermal-hydraulic coupling between the controllers. The phenomenon is a function of the detuning between them which is altered by changing the dead-band of the controllers.