This study investigates triplex-tube phase change thermal storage units. First
the variation trends of liquid phase fraction and average temperature during the heat storage process for single- and double-tube filled models with phase change material (PCM) filling rates ranging from 30% to 80% are analyzed. The total heat storage capacity
melting time
and average heat storage rate of the PCM are compared. Secondly
using melting time and total heat storage capacity as evaluation metrics
the entropy weight method (EWM) and the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) method are applied to assess the optimal PCM filling rate. The results show that a 60% PCM filling rate yields the best thermal performance. Further analysis of the temperature field and vorticity evolution reveals the mechanism by which gravity-driven natural convection enhances heat transfer. In addition
a single-tube model with a 60% PCM filling rate is used to study the influence of the radial position of PCM on heat transfer performance. The results indicate that as the PCM filling rate increases
the unit heat storage rate decreases
while the total heat storage capacity increases. When the filling rate exceeds 40%
the vortex generation rate in the single-tube model becomes faster than in the double-tube model
leading to enhanced natural convection by the vortex. Therefore
the single-tube filling model exhibits superior thermal storage performance compared to the double-tube model. Furthermore
a radial PCM filling method closer to the outer tube wall promotes vortex formation. Under constant outer tube diameter and PCM filling rate
the closer the PCM is to the outer tube
the shorter the complete melting time and the better the melting performance.
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references
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