Experimental Analysis of a Latent Heat Thermal Energy Storage Unit Enhanced by Branched Fins

Abstract:

The world is pivoting to develop new technologies to replace fossil fuels with renewable energy. The major limitation of renewable energy is that electricity generation and storage do not satisfy energy consumption; one contributing factor being the unpredictability of sources such as wind or solar. Using thermal energy storage in solar applications can allow energy to be stored and released on demand. Recently, research has focused on latent heat thermal energy storage (LHTES) because of the high energy storage density of phase change material (PCM) compared to sensible heat storage material. Despite their high energy storage density, most common PCMs are limited by their thermal conductivity. To improve heat transfer (HT) within PCM, passive HT enhancement techniques can be employed. Many recent studies have focused on the numerical analysis of branched fins with minimal experimental evaluations present. The aim of this analysis is to experimentally determine the thermal enhancement of PCM using branched fins. Three copper fin configurations- one simple radial and two branched will be used in the experimental setup of the LHTES unit. The novelty of the study is the varied geometry yet constant volume of copper between each configuration. The shell and tube LHTES system consists of an acrylic cylinder that houses PCM, Rubitherm RT-55. A copper pipe with attached fins passes through the center of the cylinder and allows for the passage of heat transfer fluid (HTF), water. The fin configurations were tested for charging, at 70°C and 2 gpm, and discharging, at 20°C and 1 gpm, processes and are considered complete when all PCM is fully molten or solidified. Twelve k-type thermocouples are inserted into the PCM at varying depths and heights to continuously monitor the temperature of the PCM. Two 100 Ohm Class A RTDs measure the HTF’s inlet and exit temperatures. The 4 radial fin formation was utilized as the simple radial configuration. The first branched configuration includes 4 radial Y-shaped fins with two branches per fin. The final fin configuration takes the shape of a snowflake with 4 radial fins and three branches per fin. The fin configurations will be compared based on total charging and discharging times, as well as the system energy response.