Composite Phase Change Materials
Mantec has recently undertaken a study – grant funded by the UK Government’s Department for Business, Energy & Industrial Strategy – to address the issue of high energy use at peak power times, i.e. when demand for electricity or gas from the grid is at its highest point.
The research has several domestic and commercial applications, but in this study we aimed at designing a baffle-type phase change heat storage electric heating device.
The device comprises a number of materials (graphite, nitrates and nitride filled paraffin) as the heat storage medium, and encapsulates the composite phase change materials (CPCMs) in a rectangular slab that is directly heated using an electric heating source.
To investigate the impact of the number and thickness of the rectangular plates on the thermal storage and exothermic performance of the device, we performed three-dimensional numerical simulations.
We then made performance and simulation test comparisons with the commonly used shell-and-tube and concentric tube types of heat exchanger. In addition, the designed device was optimized by adding fines to the CPCMs using the orthogonal test method. To verify the heating effectiveness of the device, we simulated the temperature field, PMV (Predicted Mean Vote), and PPD (Predicted Percentage Dissatisfied) of the heating room to represent a household application.
Our investigation confirms continuous heat release of the device for seven hours during the day, which meets home heating requirements. It is also shown that heat storage and exothermic efficiencies reach 85.83% and 90.1%, respectively; after the device was optimized, these efficiencies increased by 8.15% and 6.43% respectively, and the real-time outlet temperature increased by 4.98°C compared with that before the optimization. The average indoor temperature of the heating room is 22.49°C, PMV is 0.55, and PPD is 15.3% – in line with the thermal comfort requirement guidelines.
The device can both deliver and store heat at the same time when the power draw is low, while during the peak period, grid power supply is turned off and the heating is directly supplied by CPCM.
Compared with direct electric heating systems used at peak times, CPCMs can reduce users’ electricity costs significantly. This results in a call for energy from the grid only at low peak times, i.e. used at peak times or when energy level requirements are low which, in turn, switches peak and valley time use resulting in significant household energy costs.
The research Mantec undertook provides a reference for the design and optimization of heat storage devices and their application in practical engineering.