The effects of thermistor linearization techniques on the T-history characterization of phase change materials

Phase Change Materials (PCMs) are increasingly being used in the area of energy sustainability. Thermal characterization is a prerequisite for any reliable utilization of these materials. Current characterization methods including the well-known T-history method depend on accurate temperature measurements. This paper investigates the impact of different thermistor linearization techniques on the temperature uncertainty in the T-history characterization of PCMs. Thermistor sensors and two linearization techniques were evaluated in terms of achievable temperature accuracy through consideration of both, non-linearity and self-heating errors. T-history measurements of RT21 (RUBITHERM® GmbH) PCM were performed. Temperature measurement results on the RT21 sample suggest that the Serial–Parallel Resistor (SPR)1 linearization technique gives better uncertainty (less than ±0.1 °C) in comparison with the Wheatstone Bridge (WB)1 technique (up to ±1.5 °C). These results may considerably influence the usability of latent heat storage density of PCMs in the certain temperature range. They could also provide a solid base for the development of a T-history measuring device.

► We evaluated two thermistor linearizing techniques for PCM T-history measurements.
► MATLAB® models were developed in order to optimize the linearization circuits.
► PCM T-history measurements using thermistors were performed.
► High temperature accuracy in PCM measurements was achieved.
► High temperature precision in the evaluation of PCM heat density was achieved.