Experimental Investigation of a Finned Mono Tube — Latent Heat Thermal Energy Storage (LHTES)

Abstract

The present experimental investigation covers the construction of a latent heat thermal energy storage system (LHTES), which uses sodium nitrate (NaNO3) as phase change material (PCM). The storage unit is filled with 300 kg of the PCM. For the heat transfer a vertically arranged bimetallic mono tube with longitudinal fins is used. The fins increase the heat flux into/from the PCM. Thermal oil is used as a heat transfer medium, as it allows working temperatures up to 400°C. This thermal energy storage is able to store 60 kWh of thermal energy and can be loaded with a power up to 200 kW. One part of the investigation results presented in this paper was the determination of the storable energy and the comparison with data from literature and calculations. Additionally, the melting behavior of the PCM was measured with temperature sensors located at different positions over the height of the storage unit. Finally, the entrance of the heat transfer medium was changed from the top to the bottom of the thermal energy storage unit and a different melting behavior could be detected.

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].…”

“…This intensifies the described asymmetric melting process. However, the results of experimental investigations, e.g., [46,47], show the same effect. The measured temperature at the top of the storage device with vertical heat exchanger tubes increases faster compared to the temperature at the bottom.…”

“…With the development of the first small liquid layer of PCM along the outer tube surface the temperature difference between the heat transfer fluid and the liquid PCM decreases and therefore, also the heat flux decreases. After this typical rapid decrease of power (see also measurement data in [46,47]), the charged power is approximately constant up to about 1000 s after simulation start (in this analyzed case). During this period of time the volume averaged temperature increases close to the melting temperature (see Figure 4).…”

“…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.…”