Abstract
In this study, heat and mass transfer and the melting process of lauric acid in a two-dimensional region representing a plate fin heat sink with the integration of metal foam are considered. The influence of thermal processes on the cooling of a volumetric heat generation source is numerically analysed for various geometric characteristics of the metal foam and fins.
Keywords : PCM, heat sink, metal foam, numerical simulation
 

1. Introduction

Enhancement of heat transfer in traditional organic PCMs such as fatty acids and paraffins is of great interest to increase the potential of latent heat thermal management. Typically, elements with high thermal conductivity, such as nanoparticles, metal structures, and foams are used for this purpose. However, with the addition of such elements to the system, free convection in the PCM melt weakens, and the balance between increasing the effective thermal conductivity of the system and reducing convective heat transfer in the liquid becomes an important factor [1].
However, adding highly heat-conducting elements allows increasing the performance of cooling systems significantly. In the numerical study [2], a 63.4% reduction in melting time was shown with the addition of fins and metal foam. In [3], a two-dimensional approximation of a rectangular cavity with flat horizontal fins filled with copper foam and KNO₃ as a phase change material was numerically considered. It was shown that the combined use of fins and metal foam as heat transfer enhancers shows the best results: a reduction in the melting-solidification cycle time by 93.34% was achieved. Thus, of particular interest are the processes of convective heat transfer and their interaction with interphase transitions in the complex heat sinks of enhanced metal foam.
 

1. Problem statement, methodology and results

A two-dimensional rectangular model with a metal finned base is considered, the cavity is filled with metal foam and phase change material. A source of volumetric heat generation is adjacent to the lower wall of the region. The side walls and the upper boundary of the heat sink are cooled by air convection, the remaining boundaries of the system are considered thermally insulated. The ambient temperature and the system temperature at the initial moment of time coincide and are lower than the melting temperature of the PCM.


Figure 1. Scheme of the system under consideration

A local equilibrium model is used to describe the properties of the porous media. The perfect thermal contact condition is set at the boundaries between the elements. Convection formed in the melt is considered laminar. The mathematical model describing unsteady heat and mass transfer processes in the system taking into account phase transitions is formulated in the Oberbeck–Boussinesq equations in dimensionless transformed variables: «stream function – vorticity – temperature». The energy equations for the solid and liquid phases were combined using the enthalpy–porosity method. The finite difference method was used to solve the resulting equations.
As a result of calculations, the change in integral and local heat transfer characteristics and the interphase boundary movement were tracked depending on the properties of the metal foam and the geometric parameters of the fins. Figure 2 shows the temperature fields in the region for PCM composite and pure PCM in the finned heat sinks after 15 and 23 minutes of heating. The blue line displays the isotherm corresponding to the interphase boundary in PCM for each case. Comparison of the results for pure PCM and PCM with 92% porosity metal foam shows a significant difference in the heat transfer modes. The melting process in pure PCM begins after the fin temperature reaches the melting point, the interphase front in this case spreads uniformly from the entire surface of the radiator. High effective thermal conductivity is characteristic of metal foam, and PCM melting begins earlier than with pure PCM. Due to more intense heat dissipation, the source does not have time to heat up much due to the high melting rate. As a result, a more uniform temperature distribution is observed in the model, in contrast to the pure PCM heat sink.


Figure 2. Temperature fields in a heat sink with copper fins and copper metal foam when heated by a source with a power of Q = 25 W at times: a) t = 15 minutes; b) t = 23 minutes

1. Acknowledgements

This work was supported by the Russian Science Foundation (Project No. 22-79-10341-P).
 

1. References

[1] Dixit T., Ghosh I. Simulation intricacies of open-cell metal foam fin subjected to convective flow. Applied Thermal Engineering, 2018, 137: 532-544.
[2] Liu G., Du Z., Xiao T., Guo J., Lu L., Yang X., Hooman K., Design and assessments on a hybrid pin fin-metal foam structure towards enhancing melting heat transfer: An experimental study. International Journal of Thermal Sciences, 2022, 182: 107809.
[3] Zhang C., Fan Y., Yu M., Zhang X., Zhao Y. Performance evaluation and analysis of a vertical heat pipe latent thermal energy storage system with fins-copper foam combination. Applied Thermal Engineering,Volume, 2020, 165: 114541.

 

PCM,heat sink,metal foam,Numerical simulation