City Research Online

Abstract

The existing Phase Change Material (PCM) thermal investigation methods have significant drawbacks and limitations in terms of the correct determination of phase change temperature and enthalpy values. It results in the inaccuracy and sometimes absence of experimental data which are required for the implementation of PCM based Thermal Energy Storage (TES) systems. An advanced T-history method for PCM characterisation was developed to overcome some of the shortcomings of the existing PCM thermal investigation procedures. The advanced T-history setup and the instrumentation system coupled with the LabView virtual instrument, which allows the continuous acquisition of T-history signals, were carefully designed, developed and evaluated. The development process was performed by sequentially addressing all the issues relating to the control and sensing mechanisms of the T-history setup, measurement accuracy and precision, PCM data representation, hysteresis, and finally subcooling. The instrumentation system was iteratively redeveloped and validated in a series of studies until the ±0.5 °C accuracy in PCM related measurements was achieved. Once the desired temperature accuracy was reached the data evaluation technique was implemented in MATLAB to allow the determination of thermo-physical PCM properties from the measured T-history data. Furthermore, detailed studies of PCMs from the RT and PT organic series were performed. These comprehensive PCM investigations revealed various results including the details regarding the materials’ behaviour upon both cooling and heating, the heat release/storage in given 0.5 °C wide temperature intervals, the respective enthalpy-temperature curves, and the total heat released/stored with respect to mass and volume. The comparison of the RT results with the data provided by the manufacturer showed very good agreement in terms of temperature (±1 °C margin) and heat release/storage content (±10 % margin) proving the validity of the advanced T-history method. A new data evaluation technique considering subcooling was implemented in MATLAB to allow correct characterisation of inorganic PCMs and the obtained results were presented accordingly. Moreover, the PT PCM data were re-evaluated showing that subcooling in these materials can be neglected. Finally, pilot optical transmittance studies in a wide wavelength range (from 280 to 700 nm) at different temperatures were carried out and showed that the phase change temperature is one of the most determinative factors of material’s applicability in PCM enhanced glazing units used in solar applications. The results from the PCM characterisation measurements confirmed that a better planned PCM experimental tests in terms of more accurate and precise sensing and control modalities provide more comprehensive and reliable results than those described in the literature so far and hence enable the development of more efficient PCM based TES systems.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	Doctoral Theses School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses

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