The purpose or objective of this research was to study the behaviour of a thermal store for integration with a heat pump. Two different types of heat exchanger, plate heat exchanger (PHE) and serpentine heat exchanger (SHE), were designed and modular units built in the workshop at the University of Warwick. Both heat exchangers were used to study the effect of the mass flow rate, inlet heat transfer fluid temperature, thickness of phase change material (PCM), thermal properties of the PCM etc. on the behaviour of the thermal energy storage (TES). The PCMs selected for this research had phase change temperatures in the range of 50°C-60°C. Thermophysical properties of four different PCMs were determined in the laboratory. PCMs including RT 52, RT 58, Climsel C58 and a eutectic mix of magnesium hexahydrate and ammonium nitrate that are suitable for use with heat pumps were studied using the differential scanning calorimeter (DSC) and hot disk to determine their thermal behaviour when compared to manufactures’ data. The modular units were charged and discharged at different inlet heat transfer fluid temperatures. The PHE experiment was carried out using both RT 52 and RT 58, while the SHE experiments were carried out using RT 52 only. The heat transfer fluid used in the experiments was water. The PHE was made from polypropylene sheet (a polymer material), with channels that carry the water in and out of the store. The SHE was based on a shell and tube concept, designed and used as a thermal store. A MATLAB model was developed based on the enthalpy method using finite difference to study and compare the temperature profile, charge rate and energy stored in the PHE using the thermal properties of RT 52 or RT58 as PCMs suitable for this thermal energy storage application. The MATLAB model was validated for both the charge process and discharge process, with the inlet HTF temperature from the experiment. Experimental results from the SHE experiment are presented for RT 52. The charge rate and energy stored during charging and discharging processes were analysed for different thicknesses of PCM around each PHE module. Results showed that the greater the PCM thickness, the higher the amount of energy stored in the PHE module and the slower it is for the module to charge or discharge. The model was used to evaluate the performance for when the store was fully charged and half charged and the results presented. To increase the capacity of the store for effective use with a domestic heat pump for a specified period of charging during off-peak tariff periods, a thermal store design using 30mm PCM thickness is proposed. With this PCM thickness, a 32kWh thermal store would require about twenty polypropylene sheets. Twenty-two (22) polypropylene sheets arranged in parallel could be charged at 8.89kW, allowing the store to work in conjunction with an 8kW heat pump. This type of PHE storage module could be installed in suitable locations in the home, such as beneath kitchen cabinets or within ceiling voids, which would accommodate the dimensions of the plate heat exchanger. The sheet capacity and number of sheets required for a store of 32kWh was determined for six different PCM thickness using RT 52. A plot of sheet charge rate or store charge rate against the reciprocal of the thickness was produced that can be used to determine the thickness or charge rate is presented. This enables the required store characteristics (PCM thickness and number of sheets) to be determined quickly and easily from the plot or fitted equation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:752529 |
| Date | January 2018 |
| Creators | Jimoh, Bashir O. |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/106911/ |
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