Experimental investigation of a weir-type cascade solar still with built-in latent heat thermal energy storage system

With the pressing need to decarbonize, industries are turning to renewable energy and energy saving technologies in a bid to reduce emissions. Latent Heat Thermal Energy Storage (LHTES) systems is an enabler for waste heat energy storage, solar power storage, district heating and cooling. By tapping on the high latent heat capacity of Phase Change Material (PCM), LHTES systems can store heat energy for later use. An in-depth review of the current state-of-the-art on the application of various metallic fins in several geometries is presented, together with the working and design principle of the application of fins, detailed explanations of key fin parameters, effect of natural convection on LHTES performance, corrosion, and numerical model assumptions. The occurrence of dead zones, the slowest region of LHTES system to melt or solidify, causes non-uniform melting and temperature profile. The location, volume and quantity of dead zones varies depending on the geometry of the LHTES system and location of heat transfer surface. To mitigate the adverse effects of dead zones, metallic fins are employed to achieve thermal penetration into said zones at an early stage to promote more uniform melting and temperature profile. To improve natural convection flow, angled metallic fins were proposed on a side-wall heated LHTES system. Experiment and numerical models were built to investigate the efficacy of angled metallic fins, and to study the combined effects of varying fin length and angle. With respect to horizontal fins, positively inclined fins of +15º and +30º delayed the full melt time by 3.8% and 4.0%, respectively, while negatively inclined fins at -15º and -30º improved the melt fraction difference by up to 5.2%. Three fin lengths corresponding to dimensionless lengths of 0.375, 0.625 and 0.875 were numerically studied together with varying angles. Results indicate that the longest fin with a downward angle of -15º yielded the best improvement in melt time. The study shows that long, downward tilted fins enhance PCM transient melting in a rectangular LHTES and the considerations that go along with these parameters. Apart from applying metallic fins in LHTES systems, varying geometry of LHTES is often an overlooked aspect of improving system performance. Recovery of waste heat from exhaust gases, analogous to heat recovery in Combined Cycle Gas Turbines (CCGT) is an excellent way to improve Gross Turbine Heat Rate (GTHR); enhancing such operations will go a long way in reducing gas consumption and improving efficiency. To increase heat transfer surface area, while maintaining the same PCM volume, protrusion and concave designs were proposed by varying the side wall angles of a rectangular enclosure. The protrusion geometry (133.8º) reduced melt time by 24.9% compared to the baseline rectangular geometry (90º). Application of parallel fins in horizontal annular LHTES systems is a common way to improve melt time. Multiple sectioned parallel fins were proposed to increase fin surface area, without reducing PCM volume (for parallel fin of same volume). A numerical model was built and validated to conduct parameter study on the proposed designs. Two main arrangements, half section (1 split) and quarter section (3 splits) were investigated using an annular LHTES system employing RT42 as PCM. The melt time of proposed designs improved by 64.2% and 4.3%, respectively, when compared to parallel and no fin case. The sections created additional pathways for liquid PCM to flow in the longitudinal direction. Future recommendations call for standardized design parameters for fins in various geometries and wider, system level research, lifetime assessments, partial charge capabilities, for wide spread adoption of LHTES.

Multi-objective RSM optimization of fin assisted latent heat thermal energy storage system based on solidification process of phase change Material in presence of copper nanoparticles

Performance study of a novel funnel shaped shell and tube latent heat thermal energy storage system

An experimental and numerical study on phase change material melting rate enhancement for a horizontal semi-circular shell and tube thermal energy storage system

Energy storage is an effective approach to bridging the gap between energy supply and demand created due to the sporadic nature of solar energy. Thermal performance enhancement is a key research subject for effective energy storage using latent heat thermal energy storage (LHTES) systems. This paper focuses on the analysis-based design of suitable LHTES system components for solar absorption-based cooling applications with a working temperature of up to 200 °C. Initially, the medium-temperature range (80 °C to 200 °C) phase change material (PCM) is selected using the Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). Further, a suitable heat transfer fluid (HTF) is selected along with the design of a geometrical assessment and an appropriate LHTES system. Finally, the effect of the stirrer on the thermal performance of the LHTES system has been discussed. The melting time of PCM reduces by 58% while input energy increases by 20 kJ with an increase in HTF inlet temperature from 180 °C to 190 °C. However, input energy increases faster with a further increase in HTF inlet temperature while melt time does not reduce significantly. Therefore, selecting optimum HTF inlet temperature is an important criterion for efficient LHTES system design. Implanting a rotating stirrer at 200 RPM inside a PCM tube decreases the net-input energy by 73 kJ. Using back-of-the-envelope calculations, the analysis-based selection of key components of the LHTES system will pave the way forward to designing an application-specific LHTES system. Further, this study can be instrumental in theoretically scrutinizing the stirring effect on PCM charging before experimental analysis.

An experimental investigation of the heat transfer and energy storage characteristics of a compact latent heat thermal energy storage system for domestic hot water applications

Performance enhancement of finned heat pipe assisted latent heat thermal energy storage system in the presence of nano-enhanced H2O as phase change material

Response surface method optimization of V-shaped fin assisted latent heat thermal energy storage system during discharging process

Response surface method optimization of innovative fin structure for expediting discharging process in latent heat thermal energy storage system containing nano-enhanced phase change material

Latent heat thermal energy storage (LHTES) systems can be used to combat the limited collection and long-term storage of renewable energy sources. The key component of an LHTES system is its phase change material (PCM), which thermally stores energy. Despite extensive research on thermal conductivity enhancement within PCM, little attention has been paid to the heat transfer fluid (HTF) within the system. This study aimed to observe the impact of variable HTF flow rates and temperatures on the speed of charging and discharging an LHTES system enhanced with annular fins. Two copper fin configurations of 10 and 20 annular fins were tested within an LHTES system with Rubitherm RT-55 PCM. The configurations were tested during charging processes with HTF parameters of 65 °C and 70 °C at 1, 2, and 3 gpm. Discharging processes were tested with HTF parameters of 15 °C and 20 °C at 0.5, 1, and 1.5 gpm. The system energy response and PCM temperature were recorded throughout the tests. The results of the study revealed that a higher flow rate produced a shorter processing time, but furthermore, that a larger temperature gradient between the PCM and HTF caused a more significant decrease in charging and discharging times.

Estimation of thermal performance and design optimization of finned multitube latent heat thermal energy storage

An improved, generalized effective thermal conductivity method for rapid design of high temperature shell-and-tube latent heat thermal energy storage systems

Transient performance analysis of concentrating solar thermal power plant with finned latent heat thermal energy storage

Experimental investigation on latent heat thermal energy storage system for stationary C.I. engine exhaust

The error of neglecting natural convection in high temperature vertical shell-and-tube latent heat thermal energy storage systems