Numerical and experimental investigation of low temperature heat transfer in an in-line PCM tube bank during air charging and discharging

The performance of air conditioners can be improved by reducing the air temperature before it enters the condenser using a Phase change material (PCM) tube bank. Currently, there is no model available for selecting the optimal tube bank size, PCM type, and quantity to achieve the desired outlet air temperature within the specified operating time. This study conducted both theoretical and experimental analyses to investigate heat transfer in an inline PCM tube bank with air during charging (solidification) and discharging (melting). Two PCMs, Rubitherm 25 high capacity (RT25HC) and Rubitherm 31 (RT31), with different melting points, were examined, focusing on the effects of the number of tube rows and tube diameter on the outlet air temperature and PCM temperatures row-by-row, as well as the duration of the solidification and melting processes. The simulated results showed good agreement with the experimental data, with a deviation of less than 7%. Additionally, a new generalized model of dimensionless correlations for temperature, heat transfer, and time, based on the simulated results under various operating conditions, was developed to support the efficient design of tube bundles and enable quick predictions of air temperatures row-by-row in the PCM tube bank. The calculated outlet air temperatures closely matched the experimental data, with a mean absolute percentage error (MAPE) within 10%. Thus, these correlations are highly beneficial, enabling faster design processes and accurate air temperature estimations within the PCM tube bank.