Abstract :
[en] A PID controller is introduced into a latent heat thermal energy storage unit to compose a coupling system to control the discharging performance. The outlet temperature of the working fluid can be precisely regulated by means of its inlet velocity variation based on the PID controller. The theoretical model is built by combining heat transfer of the latent heat thermal energy storage unit with the PID controller. Experimental results are used to validate the proposed theoretical model. PID control analysis indicates that its parameters have obvious effects on the performance of the coupling system. Kp of − 0.02 m/(s⋅K), Ki of − 0.15 m/(s2 ⋅K) and Kd of − 0.001 m/K are further optimized according to the dynamic response of the transient outlet water temperature. System parameter analysis exhibits that a higher target temperature produces a larger heat discharging rate, reducing the outlet water flow rate accordingly. The discharging rate and total discharging energy of the latent heat thermal energy storage unit decrease with the augment of the target outlet temperature. An increase in PCM melting point, thermal conductivity and latent heat is favorable for elevating the working fluid velocity. The discharging rate is improved by the PCM melting point, thermal conductivity and latent heat. The latent heat
thermal energy storage units can separately obtain maximum discharging rates of 257.691, 294.437 and 257.603 W at 200 min for a PCM melting point of 327.15 K, PCM thermal conductivity of 0.8 W/(m⋅K) and PCM latent heat of 250 J/g. PCM melting point, thermal conductivity and latent heat are conducive to enhancing the total discharging energy. The largest discharging energy at 200 min is respectively determined
as 1280.409, 1060.105 and 974.153 kJ. System parameters can also substantially affect temperature and phase change contours. In conclusion, the built coupling system is beneficial to efficiently regulate and control discharging performance of latent heat thermal energy storage units.
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