研究目的
To evaluate the effect of using two paraffin waxes with different solidification points as PCMs, stored in soda cans and sequentially distributed, on the discharge efficiency of solar thermal energy accumulators at laboratory and prototype scales.
研究成果
Using two PCMs with sequential distribution based on solidification points enhances discharge efficiency, with optimal configuration placing lower melting point PCM in initial rows and higher in final rows. The mathematical model effectively predicts outlet air temperatures, allowing for design optimization. Efficiency was higher in controlled laboratory conditions (up to 92%) compared to outdoor pilot scale (up to 61%) due to environmental factors.
研究不足
Variability in environmental conditions (e.g., ambient temperature, wind) affected results, especially in the outdoor pilot scale accumulator, leading to discrepancies in simulations. Heat losses to the environment and from the accumulator structure were not fully accounted for in the model, causing deviations in predicted temperatures.
1：Experimental Design and Method Selection:
A 2^3 factorial experimental design with replicates was used to analyze the effects of PCM type distribution in rows on discharge efficiency. The mathematical model from a previous study was adapted for multiple PCMs to predict outlet air temperatures.
2：Sample Selection and Data Sources:
Two paraffin waxes with melting points of 41°C (P-41) and 56°C (P-56) were used as PCMs, stored in recycled soda cans with added aluminum stripes. Data were collected from laboratory and pilot scale accumulators.
3：List of Experimental Equipment and Materials:
Laboratory scale accumulator (chamber: 32 cm x 35 cm x
4：5 cm, 12 cans), pilot scale accumulator (chamber:
2.9 m x 1.2 m x 12.5 cm, 300 cans), infrared lamps (200 W or 250 W for charging), data acquisition system (NI 9211 with NI Compact DAQ Chassis), thermocouples, fans, polystyrene insulation, aluminum stripes (0.4 cm x 10 cm), paraffin wax, soda cans.
5：9 m x 2 m x 5 cm, 300 cans), infrared lamps (200 W or 250 W for charging), data acquisition system (NI 9211 with NI Compact DAQ Chassis), thermocouples, fans, polystyrene insulation, aluminum stripes (4 cm x 10 cm), paraffin wax, soda cans.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: For laboratory scale: Charge accumulator with infrared lamps until PCM temperature >70°C, insulate, open air inlet/outlet, set air velocity to
6：02 m/s and mass flow to 01 kg/s, monitor discharge for 140 min. For pilot scale:
Charge with solar energy until PCM temperature ~80°C, insulate, set air velocity to 0.3 m/s and mass flow to 0.06 kg/s, monitor discharge for 4 hours.
7：3 m/s and mass flow to 06 kg/s, monitor discharge for 4 hours.
Data Analysis Methods:
5. Data Analysis Methods: Discharge efficiency calculated as ratio of heat absorbed by air to total heat stored. Statistical analysis using ANOVA. Numerical model solved to predict temperatures, with comparisons using R2 and RMSE.
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