Rice University engineers use Q-switching to release stored heat from a water prototype at 5x prior output
Rice University engineers store heat in two counter-flowing liquid streams and release it as a pulse at constant input power. So far this is a benchtop water prototype.
Engineers at Rice University have described a method called active heat Q-switching, which accumulates heat in a flowing-liquid device and releases it as a short pulse while the input power stays constant. The work was published in Cell Reports Physical Science doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗. In a benchtop water device, the outlet power of one channel rose about five-fold relative to its steady output before the switch
doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗.
How the heat oscillator works
The device uses two thermally connected channels in which liquid flows in opposite directions (a counter-flow heat oscillator). The approach borrows from laser physics, where the quality factor Q measures how well a resonator retains energy. Q-switched lasers store energy and release it as a short, intense pulse. The Rice team applied the same principle of controlled storage and release to thermal energy doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗.
When the flows are matched, heat passes back and forth between the channels and stays inside longer than the liquid takes to pass through. This is the high-Q state, in which energy accumulates doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗. Detuning the flows or reducing the heat transfer between the channels breaks this recirculation. The device then switches to a low-Q state, and the stored heat leaves quickly
doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗. According to the authors, the water stays liquid throughout storage and release, with no melting or freezing of a storage material.
Experiment and model
The experiment used a custom-built benchtop water device heated by an LED lamp. After about five hours of steady heating, the researchers increased the flow rate in one channel. Its peak heat output rose to about five times its output before switching, while the heating input remained constant doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗.
A transient thermofluidic model reproduced the water experiment. For a system with liquid metal as the working fluid, the model predicts a peak about 20 times the input power under the modeled conditions doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗. Modeling also indicates that stacking several oscillators extends the accessible range of stored energy and power
doi.org
Cell Reports Physical Sciencedoi.orgOpen source ↗. The authors note that the extra power in a pulse comes from heat that had already accumulated.
The principle has so far been demonstrated only in water. Study co-author Naomi Halas said the next challenge is making the control reliable over repeated cycles and adapting it to the heat demands of a particular application. The authors name sterilization, cleaning, starting up distillation systems, use of solar or industrial waste heat, and temperature management in microfluidic devices as possible uses.
