Transient Numerical Analysis of Different Finned Tube Designs for Use in Latent Heat Thermal Energy Storage Devices

Abstract

In this paper the results of a numerical investigation of the melting and solidification process of sodium nitrate, which is used as phase change material, will be presented. For the heat transfer to the sodium nitrate different finned tube designs, namely helical-, transversal- and longitudinal finned tubes, are used. The numerical results of the melting and solidification process for the different design cases will be compared. The numerical analysis of the melting process has shown that apart from the first period of the charging process natural convection is the dominant heat transfer mechanism. The numerical analysis of the melting process has also shown that for a fast melting process heat exchanger tubes should be designed in such a way that an unrestricted natural convection is guaranteed. The numerical investigation for the solidification process has shown that the dominant heat transfer mechanism is heat conduction. The investigation has also shown that the solidification front grows more uniformly from the tube surface to the outer shell compared to the melting front. Therefore no significant differences between the different tube designs are detected concerning the solidification process.

Transient Numerical Simulation of the Melting and Solidification Behavior of NaNO3 Using a Wire Matrix for Enhancing the Heat Transfer

“…As we can see from Figure 11 the solidification process starts at the bottom of the computational domain and along the outer tube surface. This result is in good agreement with numerical results presented in [9,10,48,49] and experimental work in [46,47]. In all references a single vertical arranged shell-and-tube heat exchanger is investigated.…”

“…This indicates that the melting front moves from the top to the bottom. This behavior was also observed experimentally by [46,47] as well as numerically by [9,10,48].…”

“…In all numerical simulations, the volume change of the PCM during phase change due to density changes is neglected, the outer shell of the computational region is considered as adiabatic, and the mushy zone constant used for the calculations is C = 10 5 . The numerical simulation presented in [9,10,49] In Figure 11, the development of the liquid fraction of the sodium nitrate during the solidification process at different time steps is depicted. As we can see from Figure 11 the solidification process starts at the bottom of the computational domain and along the outer tube surface.…”

“…In all references a single vertical arranged shell-and-tube heat exchanger is investigated. For improving the heat transfer longitudinal [9,10,46,47,49] and transversal [48,49] fins are used. The numerical investigations are done three-dimensionally, except [48], which was two-dimensionally.…”

“…A widely used method to overcome this heat transport limitation in LHTES is to increase the specific surface of the heat exchanger tubes. Various techniques, like fins [4][5][6][7][8][9][10][11], dispersed high-conductivity particles inside the PCM [12,13], metal and graphite-compound matrices [14][15][16], micro-encapsulation [17][18][19] as well as a combination of metal foam made of copper and sandwich structure fins [20] have been suggested and were analyzed.…”