Measurable latent heat storage systems - Determining heat content with piezoelectric elements

Latent heat storage systems, also called phase-change material or PCM storage, are heat accumulators that can store a large part of the heat energy they receive in the form of transformation enthalpy, the necessary energy for transition from one phase (solid/liquid/gas) to another. The problem is that energy thus stored cannot be detected by temperature, as it can in sensitive heat accumulators. A joint invention from the Bochum University of Applied Sciences and the Westfälischen Hochschule solves this problem.

Piezo elements are used to determine the energy in latent heat storage systems. These elements are influenced by the storage system’s change of phase, which affects their vibration behavior. An electromechanical impedance spectrum makes this change measurable, which in turn allows determination of the current degree of phase-change material crystallization. A second piezo element allows calculation of the heat content by means of a transfer function. This is done by sending a signal from one element to the other through the heat accumulator. The frequencies used here can be adjusted individually for the phase-change material. This invention can also be used to monitor the overall condition of the latent heat storage system. Piezo elements or piezoelectric sensors have been used for decades in structural health monitoring to monitor buildings, pressure tanks, and machines. In this application, they can also exercise their monitoring function.