Latent Heat Thermal Energy Storage Unit Research Articles

Enhancing the performance of a greenhouse dryer with natural dolomite powder-embedded latent heat thermal energy storage unit and air-to-air heat recovery system

Greenhouse drying systems (GDSs) are grouped in direct-type solar dryers and are widely utilised because of their easy applicability, high product drying capacity and cost-effectiveness. In the present work, it is aimed to improve the drying performance of a GDS by using natural dolomite powder-embedded latent heat thermal energy storage unit (LHTESU) and air-to-air heat recovery system (HRS). In this context, three different types of GDSs have been designed and manufactured including a GDS with paraffin-based LHTESU, a GDS with natural dolomite powder-embedded LHTESU and a HRS-assisted GDS with natural dolomite powder-embedded LHTESU. Designed and manufactured GDSs have been experimentally analysed under the same environmental conditions. According to the experimentally achieved findings, combined utilisation of HRS and dolomite powder in the LHTESU reduced the drying time approximately as 36.36%. Moreover, highest instantaneous outlet air temperature was achieved as 51.4 °C in the system that used natural dolomite-embedded LHTESU and HRS. The exergetic efficiency of the GDS was upgraded as 46.21% by using the mentioned modifications in comparison to the base case (the system contains only paraffin-based LHTESU). In addition, specific moisture extraction rate for the analysed GDSs was attained between 0.96 and 1.52 kg.kWh−1.

Enhanced heat transfer in a latent heat thermal energy storage unit using a longitudinal fin with different structural parameters

The latent heat thermal energy storage (LHTES) unit can be used to resolve the imbalance between energy supply and demand. To boost heat storage efficiency, a model with longitudinal fins was developed to accelerate the melting process. Based on the finite volume method (FVM), the effect of fin angle and number on melting performance was evaluated. Further, the response surface methodology (RSM) was applied to optimize the longitudinal fin by maximizing its melting rate. Results demonstrate same heat transfer capacity at the fin angles θ and θ1(θ1=90−θ). The complete melting time at a θ values of 0°was reduced by 46.66%, compared with a θ value of 45°. The optimized case (θ = 0°, N =16 fins) reduced the total melting time by 62.59%. The melting rate of the upper region of the LHTES unit was higher than that of the lower region in all cases. Further, the study quantified the temperature uniformity of the system using mathematical methods, which showed that the integrated mean value of temperature uniformity at a θ value of 0° was the smallest (12.51°C), suggesting excellent temperature uniformity at a rotation angle of 0°.

Exergy Analysis of a Shell and Tube Energy Storage Unit with Different Inclination Angles

To optimize the utilization of solar energy in the latent heat thermal energy storage (LHTES) system, this study conducts exergy analysis on a paraffin-solar water shell and tube unit established in the literature to evaluate the effects of different inclination angles, inlet temperatures, original temperatures, and fluid flow rates on the exergy and exergy efficiency. Firstly, the thermodynamic characteristics of the water and the natural convection effects of the paraffin change with different inclination angles. When the inclination angle of the heat storage tank is less than 30°, the maximum exergy inlet rate rises from 0 to 144.6 W in a very short time, but it decreases to 65.7 W for an inclination angle of 60°. When the inclination angle is increased from 0° to 30°, the exergy efficiency rises from 86% to 89.7%, but it decreases from 94% to 89.9% with the inclination angle from 60° to 90°. Secondly, under the condition that the inclination angle of the energy storage unit is 60°, although increasing the inlet temperature of the solar water enhances the exergy inlet and storage and reduces the charging time, it increases the heat transfer temperature difference and the irreversible loss of the system, thus reducing the exergy efficiency. As the inlet water temperature is increased from 83 to 98 °C, the exergy efficiency decreases from 94.7% to 93.6%. Moreover, increasing the original temperature of the LHTES unit not only reduces the exergy inlet and storage rates but also decreases the available work capacity and exergy efficiency. Finally, increasing the inlet water flow rate increases the exergy inlet and storage rates slightly. The exergy efficiency decreases from 95.6% to 93.3% as the unit original temperature is increased from 15 to 30 °C, and it is enhanced from 94% to 94.6% as the inlet flow rate is increased from 0.085 to 0.34 kg/s with the unit inclination angle of 60°. It is found that arranging the shell and tube unit at an inclination angle is useful for improving the LHTES system’s thermal performance, and the exergy analysis conducted aims to reduce available energy dissipation and exergy loss in the thermal storage system. This study provides instructions for solar energy utilization and energy storage.

Melting performance enhancement in a thermal energy storage unit using active vortex generation by electric field

Latent heat thermal energy storage (LHTES) devices aid in efficient utilization of alternate energy systems and improve their ability to handle supply–demand fluctuations. A numerical analysis of melting performance in a shell-and-tube LHTES unit in the presence of a direct current (DC) electric field has been performed. The governing equations of fluid flow, heat transfer, electric potential and charge conservation are solved using a customized finite-volume solver built in the open-source framework of OpenFOAM. Enthalpy-porosity method based fixed grid approach is used to track the melt interface. Primary objective of the study is to highlight the interface and flow morphology evolution in the presence of electric field induced flow and to evaluate the melting performance of the LHTES unit. The transient evolution of the melting process in the presence of electric field has been mapped in terms of total liquid fraction, kinetic energy density and mean Nusselt number. The charge injection from the tube surface generates multiple electrohydrodynamic (EHD) flow vortices in the liquid region. Thus, the inherent uni-cellular flow structure of the natural convection driven melting is disrupted. The multi-cellular flow structure with stronger velocity distribution enhances mixing and heat transfer. Melting performance at various levels of applied voltages (0≤V≤10kV) in both vertical and horizontal orientations of the LHTES unit has been quantified in terms of charging time and total power storage. The charging time gets shorter and total power storage gets higher with increasing applied voltages. In the vertical orientation, a maximum 82.52% reduction in charging time and 80.85% increase in net power storage is achieved. In the horizontal orientation, weaker buoyancy force leads to stronger influence of the electric field. A maximum of 89.61% reduction in charging time and 88.35% increase in power storage is achieved in the horizontal orientation. The results of this study aid in understanding the mechanism of EHD flow assisted melting and provide a reference for design of a shell-and-tube LHTES unit with improved performance.

Improving the energy release of a latent heat storage with multiple phase change materials loading and partition shaping

This paper presents a theoretical study of the integration of two selected phase change materials (PCMs) into a vertical shell and tube latent-heat thermal energy storage unit. Various cell shapes and PCM arrangements are analyzed for their heat release characteristics and compared to a reference unit. Using the finite volume method with an enthalpy-porosity formulation, the study simulates conjugate heat transfer between an isothermal wall and PCMs. This approach examines the impact of both the delay of the phase transition and the layout of the PCM cavities on natural convection. The findings indicate that these factors have a significant influence on energy transport. Delaying the solidification process near the cold wall can lead to a substantial reduction in the phase transition time. Furthermore, triangular cross-section cells improve convection and increase the solidification and complete energy discharge times by 42.7% and 25.3%, respectively. The energy charging performance is also enhanced by 39.7%.

Improving the melting performance of phase change material (PCM) in a latent heat thermal energy storage unit via a non-uniform arrangement of longitudinal fin

The application of latent heat thermal energy storage (LHTES) technology in solar energy utilization is greatly restricted by the low thermal conductivity of phase change material (PCM). This paper proposed a non-uniform arrangement of a longitudinal fin in a typical LHTES unit to improve the melting performance of PCM. Water is used as the heat transfer fluid (HTF) and paraffin (RT35) is selected as the PCM. A three-dimensional computational model is built to simulate the melting process of PCM, and its result is verified by experimental data. Firstly, the melting performance of PCM in the LHTES unit with four kinds of fin arrangements is comparatively studied, and its heat transfer mechanism is characterized via the maximum velocity of liquid PCM. In addition, the influences of HTF inlet temperature and flow rate, as well as heat transfer tube material on the complete melting time of three typical fin arrangements are also investigated. The results implied that the complete melting time of the non-uniform arrangement of the longitudinal fin reduces by 30.91% relative to the conventional longitudinal fin (Case 2). The results also revealed that the melting rate of PCM is related not only to the intensity of natural convection but also to the distribution of natural convection in the whole melting process.

Effect of twisted fins on the melting performance of PCM in a latent heat thermal energy storage system in vertical and horizontal orientations: Energy and exergy analysis

• Performance of a LHTES unit in the presence of twisted fins is studied. • Different number of fins in vertical and horizontal orientations were considered. • Paraffin wax was used as PCM. • Triple fin and double fin outperformed other cases in vertical and horizontal cases. • The best case is a trade-off between the fin number and length of fins. Solar energy and other renewable energy resources are of great importance to solve the energy crisis in the 21th century. In this regard, the energy storage systems play a vital role as a means of harnessing solar energy. In this study, performance enhancement of a shell and tube latent heat thermal energy storage (LHTES) system in terms of energy and exergy has been assessed by implementing twisted fins in a PCM enclosure with both vertical and horizontal orientations by using Finite Volume Method and the Enthalpy-Porosity method has been used for simulating the melting process. The fins have constant heat transfer surface with different configurations including single, double, triple and quadruple fins along with a case study about effect of penetrating the fin inside the tube. Paraffin wax was used as PCM. The results have been presented in terms of melt fraction, temperature and velocity magnitude contours, melt fraction and temperature curves, average Nusselt number and total melting time for both horizontal and vertical orientations. In order to better evaluate the optimizations made, exergy analysis has also been performed and the exergetic efficiency has also been presented. It was revealed that the triple fin in vertical orientation and double fin in horizontal orientation have the best effect on melting enhancement of PCM with 11.2% and 10.7% of enhancement in melting time in comparison with the worst finned case, and 37.4% and 30.5% enhancement in comparison with the base case. It was also shown demonstrated that the triple fin in vertical orientation and double fin in horizontal orientation have the best exergy efficiency.

Low-Temperature Industrial Waste Heat (IWH) Recovery Using a New Design for Fast-Charging Thermal Energy Storage Units

The dynamic melting of CuO–coconut oil was addressed in a latent-heat thermal energy storage unit loaded with copper foam. In a new design, the thermal storage unit is made of a shell-tube-shaped chamber, in which a liquid flow of hot phase-change material (PCM) is allowed to enter the chamber from a port at the bottom and exit at the top. A fin is mounted in the chamber to forward the entrance PCM liquid toward the solid regions. The control equations were solved using the finite element method. The impact of foam porosity, inlet pressure, fin length, and the concentrations of CuO nanoparticles on the thermal charging time of the chamber was investigated. A fast-charging time of 15 min with a foam porosity of 0.95 was achieved. A porosity of 0.95 can provide a maximum thermal charging power of 15.1 kW/kg. The inlet pressure was a significant parameter, and increasing the inlet pressure from 0.5 kPa to 4 kPa reduced the melting time by 2.6 times. The presence of the fin is not advantageous, and even a long fin could extend the thermal charging time. Moreover, dispersed nanoparticles were not beneficial to dynamic melting and extended the thermal charging time.

Assessment on the effect of longitudinal fins upon melting process in a latent heat thermal energy storage unit

Latent heat thermal energy storage(LHTES) unit are an effective technical means to balance the demand and supply of energy. To enhance the heat transfer efficiency of the phase change material(PCM) in the LHTES unit, a series of novel three-tube heat exchangers with longitudinal fins was designed. The study was carried out in terms of the number, length, thickness, and arrangement of fins. Results demonstrate that the thickness change of fins has a significant effect on reducing the melting time of the whole PCM. The thin long fins have a higher melting rate. The complete melting time of the thin long fins was 10.6 % faster than that of the short thick fins. By studying the effect of fin length on the heat storage performance, it was found that the structure appeared to be more reasonable at L = 30 mm and the heat storage time was shortened by 18.0 %. In addition, the use of the lower long and upper short fin arrangement can strengthen the heat transfer. Considering that the amount of heat storage capacity decreases as the number of fins increases, N = 20 is considered as the best fin number. Therefore, we give an optimal combination of fin design parameters (N = 20, L = 30, W = 1), which shortens the total melting time of PCM by 71.2 %. To be conclusive, it is more beneficial to add fins to heat transfer enhancement than to have no fins, saving more energy charging time.

Effective estimation of the state-of-charge of latent heat thermal energy storage for heating and cooling systems using non-linear state observers

An effective quantification of the energy absorbed and supplied by latent heat thermal energy storage (LHTES) units is critical to maximise their use within thermal systems. An effective control of the charging and discharging processes of these units demands an accurate estimation of the state-of-charge (SoC). However, a direct and reliable SoC estimation requires incorporating internal sensors to monitor the temperature gradient of the phase change material (i.e. the storage medium), resulting in higher instrumentation costs and technical specifications. These issues may be relieved by adopting state observers for SoC estimation to drastically reduce the number of measurements. This paper bridges this gap by presenting a novel and direct method for estimating the SoC of LHTES units, both for heating and cooling applications, based on a non-linear state observer. The observer is based on a simple one-dimensional dynamic model of the thermal store and the thermophysical properties of the storage medium and the heat transfer fluid, which are usually provided by manufacturers. This enables the estimation of the internal temperatures of the LHTES unit and, in turn, SoC calculation. The observer implementation is simple as it requires three measurements only as input variables (i.e. the mass flow rate and the input and output temperatures of the heat transfer fluid). The SoC estimation approach is assessed through dynamic simulations of two LHTES units: one for a heating application and one for a cooling application. The results show that the SoC can be estimated with root mean square and mean absolute errors of less than 4.6% and 3.62%, respectively, compared with experimental measurements.

Simulation study on charging performance of the latent energy storage heat exchanger with a novel conical inner tube

The application of a latent heat thermal energy storage (LHTES) system can effectively solve the problem of the mismatch between the energy supply and demand. However, most studies focus on the traditional cylindrical configuration with a low heat storage rate, which limits the wide application of LHTES systems. The configuration optimization of a vertical shell-and-tube LHTES unit is carried out in this paper to enhance heat storage rate, and the effects of cone angle values (0–10°) in the conical shell and conical tube configurations on the heat storage performance are explored by numerical simulations. The results show that these two kinds of conical configurations both significantly improve the melting rate of the phase change material (PCM) compared with the cylindrical unit. However, when the cone angle is the same, the heat transfer enhancement effect of the latter is found to be superior to that of the former. Moreover, the complete melting time is shortened by 46 % as the cone angle of the inner tube increases from 0° to 10°. More importantly, a novel conical tube configuration design is proposed to eliminate the hard-to-melt zone at the bottom of the LHTES unit with the conical tube, then the effects of different tilting heights (60–170 mm) and bottom annulus distances (0–10 mm) are investigated. The results demonstrate that the melting rate increases with the increase in the tilting height, but the increased amplitude of that gradually reduces. Besides, the average heat storage rate shows a trend of first increasing and then decreasing with the increase in the distance of the bottom annulus. When the bottom annulus distance is 2 mm, the average heat storage rate reaches the maximum value, which is 94.84 W. The research results can provide a reference for the engineering design and configuration optimization of the vertical shell-and-tube phase change heat exchanger.

Effect of shell shape on the charging and discharging performance of a vertical latent heat thermal energy storage unit: An experimental study

In this paper, the effect of shell shape on vertical latent heat thermal energy storage (LHTES) unit is experimentally investigated to alleviate the heat transfer lagging region and enhance its charging and discharging performance. A cylindrical (CYL) and two conical (CON-I and CON-II) LHTES units are designed and fabricated, and they have the same heat transfer area and internal volume. Paraffin with a narrow range of phase change temperature and high enthalpy was selected as phase change material (PCM), and water is used as heat transfer fluid (HTF). The thermal behaviors of CYL, CON-I and CON-II such as evaluation of melting and solidification fronts, temperature response characteristics, heat transfer characteristics and energy and exergy conversion are comparatively studied. A correlation is developed to predict the entire melting and solidification time of different LHTES units under different HTF flow rates and temperatures. The results demonstrate that CON-I and CON-II can provide a better temperature field uniformity and enhance the heat transfer rate between HTF and PCM. When compared with CYL, the entire melting/solidification time is reduced by 16.95 %/8.07 % and 29.94 %/23.22 % for CON-I and CON-II, and the time-averaged heat transfer rate is increased by 20.69 %/23.61 % and 35.87 %/41.24 % for CON-I and CON-II during the melting/solidification processes. In addition, the developed correlation is able to well predict the entire melting and solidification time of PCM in the LHTES unit with a relative error of ±5 %.

A Numerical Parametric Study of a Double-Pipe LHTES Unit with PCM Encapsulated in the Annular Space

Latent heat thermal energy storage (LHTES) with Phase Change Materials (PCM) represents an interesting option for Thermal Energy Storage (TES) applications in a wide temperature range. A tubular encapsulation model of an LHTES with PCM was developed, and the calculated data were analyzed. In addition, a parametric analysis for the preferable system geometry is presented. Organic paraffin RT18 with a melting point of 18 °C was utilized as PCM for different geometries of LHTES, and the addition of internal and external fins and their influence on LHTES thermal conductivity was investigated. One-step heat exchange from outdoor air to PCM and from PCM to water characterizes the LHTES system in solidification and melting processes, respectively. A 2D axisymmetric model was developed using Comsol Multiphysics 6.0. The LHTES unit performance with PCM organic paraffin RT18 encapsulated in electrospun fiber matrices was analyzed. The study results show that longer internal fins shorten the melting and solidification time. Direct contact of PCM electrospun fiber matrix with 23 °C water showed instant melting, and the phase change process was accelerated by 99.97% in the discharging cycle.

Anisotropic metal foam design for improved latent heat thermal energy storage in a tilted enclosure

The metal foams are a promising candidate for the enhancement of heat transfer in latent heat thermal energy storage (LHTES) units. These foams can be synthesized with engineered local properties such as improved thermal conductivity or permeability in a specified direction. However, the impact of using anisotropic metal foams for thermal energy storage has not been addressed yet. In the current research, an anisotropic metal foam was modeled mathematically with engineered local properties in perpendicular directions. The solid-liquid phase transition of the copper-coconut oil LHTES unit was simulated using the finite element method. The anisotropic metal foam was defined by using an anisotropic parameter and angle. The simultaneous impact of the mounting tilt angle and the anisotropic angle of the copper foam were addressed in the phase transition behavior and charging time of the LHTES unit. The results revealed that the anisotropic angle could notably impact the thermal energy storage power. An optimum tilt angle of -45° or +45° along with a 0° anisotropic angle could lead to the maximum charging power. Thus, designing an LHTES unit using an anisotropic metal foam could save the charging about 15% (for a -45° inclination angle) and 20% (for zero inclination angle) compared to a regular metal foam. Such save in the charging time is without any penalty on the weight increase or capacity reduction for the LHTES unit.

Effects of various types of nanomaterials on PCM melting process in a thermal energy storage system for solar cooling application using CFD and MCMC methods

• A vertical shell and tube LHTES unit where D-mannitol was utilized as the PCM on the shell side was numerically analyzed. • Ag, Cu, Al 2 O 3 , CuO, TiO 2 , GNP, MWCNT, and SWCNT were added to PCM to enhance its thermophysical properties. • CFD and, a method based on Bayesian inference, was adopted by coding the Bayesian MCMC simulation for predicting the melting time. • Adding carbon-based nanomaterials to pure PCM reduced the melting time by about 50%, while metal nanoparticles impaired the melting performance. • Adding metal oxide nanoparticles did not add any essential advantage to the LHTES system. Latent heat thermal energy storage (LHTES) systems are attractive for bridging the energy supply and demand gap. In such systems, reducing storage time is critical, especially for solar applications. Accordingly, this study mainly aims to employ various nano-additives, including metal (Ag and Cu) and metal-oxide (Al 2 O 3 , CuO, and TiO 2 ) nanoparticles and carbon-based nanomaterials (GNP, MWCNT, SWCNT), to improve the thermophysical properties of pure phase change materials (PCM) to accelerate the melting process. For this purpose, the energy storage performance was numerically analyzed in a vertical shell and tube LHTES unit where D-mannitol was utilized as the PCM on the shell side. Dynalene-ht was employed as a heat transfer fluid (HTF) in the tube. Using computational fluid dynamics (CFD) modeling, transient variations in liquid fraction, PCM temperature, and total melting time were investigated under the impact of the following parameters: the thermophysical properties and volume fraction of nanomaterials, Re and the inlet temperature of HTF. In addition, a methodology based on Bayesian inference was adopted by coding the Bayesian MCMC simulation to create proper models for predicting the melting time. The numerical results showed that adding carbon-based nanomaterials to pure PCM reduced the melting time by about 50%, while metal nanoparticles impaired the melting performance. It was also observed that adding metal oxide nanoparticles did not add any essential advantage to the LHTES system. This research will help design TES applications in the operating temperature range of 160–200 °C, especially in solar cooling systems.

Enhancement of the part-load thermal charging performance of a latent heat thermal energy storage unit with variable length fins at effective locations

Rapid thermal charging of the latent heat thermal energy storage unit (LHTESU) based on phase change material (PCM) is restricted by the material's low thermal conductivity. The numerical investigation for the thermal charging process of LHTESU considering a rectangular enclosure under the high-temperature gradient is presented. Constant and variable length fins with different locations are considered inside the enclosure with one vertical sidewall at a constant temperature. For various part-load thermal charging operations, a two-dimensional transient model with enthalpy-porosity technique is employed with natural convection current to evaluate the thermal charging rate and melting characteristics. The simulation outcomes manifest that convective heat transfer significantly impacts PCM melting in the case of variable length fins. Uniform distribution of Variable length fins with the most extended fin near the base of the container has 20% superior thermal charging performance than of constant length in full load thermal charging operations. However, in half-load thermal charging operations, constant-length fins with uniform distribution in the enclosure reduce the maximum thermal charging time and the average temperature of the PCM domain. Further, the result indicates that Cases VF-2 (most extended fins placed significantly close to the bottom and remaining fins inserted with equal gap) and VF-3 (fins insertion only in the lower half of the container) minimized the sensible heating of liquid PCM by directing the heat towards solid PCM. Case VF-3 demonstrated the most robust thermal charging performance by taking the least melting time in all cases for a 90% thermal charging of the system.

Experimental investigation on the charging and discharging performance enhancement of a vertical latent heat thermal energy storage unit via snowflake fin design

The application of latent heat thermal energy storage (LHTES) technology in solar energy systems is greatly restricted by the poor thermal conductivity of the phase change materials (PCM). Inspired by the natural snowflakes, a snowflake fin is designed to enhance the charging and discharging performance of the LHTES unit in this paper. The phase interface, temperature response, thermal energy storage and release characteristics, as well as the entire melting and solidification time of LHTES unit with the same material volume but varying fin designs, e.g., nullity fin, longitudinal fin and snowflake fin, are experimentally compared. Paraffin is selected as the PCM, which is filled into the annular region between the brass finned tube and the transparent acrylic shell to enable visual observation of the melting and solidification processes. Water is used as the heat transfer fluid (HTF), whose effects of various flow conditions on the charging and discharging performance of the LHTES unit were inspected. The preliminary results show that the snowflake fin design significantly reduces the entire melting and solidification time by 32.23∼51.81% as compared to the longitudinal fin. In addition, snowflake fin is found to be more beneficial for the discharging process, since the time-averaged heat transfer rate of HTF only increases by 12.27% for charging but increases by 179.81% for discharging if compared to the traditional longitudinal fin.

Heat Transfer Enhancement of Phase Change Material in Triple-Tube Latent Heat Thermal Energy Storage Units: Operating Modes and Fin Configurations

The inherent low thermal conductivity of phase change materials (PCMs) serious limits the thermal performance of latent heat thermal energy storage (LHTES) systems. In this study, the author proposed two operating modes (inside heating/outside cooling and inside cooling/outside heating)and designed seven fin configurations to improve the thermal performance and flexibility of the triple-tube LHTES unit. A transient two-dimensional numerical model was established to study the energy storage, release and simultaneous storage and release processes, and local and global entropy generation was analyzed. A comprehensive evaluation was used to propose the optimal combination of operating mode and fin configuration. Considering various performances, the combination of the operation mode of inside cooling/outside heating and the staggered fin configuration shortened the total time by 66.6% and increased the heat transfer rate by 5.6%, providing the best performance in both the continuous and simultaneous storage and release process.

Investigation of different topology-optimized fin structures in a cylindrical latent heat thermal energy storage unit

Latent heat thermal energy storage (LHTES) has received great attention from many researchers due to the high energy density of phase change materials (PCM), which helps to store more energy while allowing for a compact storage volume. However, most of these PCMs have low thermal conductivity, which requires enhancement techniques to efficiently distribute and store heat inside the LHTES unit. Therefore, different structures of finned heat exchangers have been investigated in the literature. Still, most of these structures are intuitive designs, which makes the literature very lacking in terms of non-intuitive heat exchanger designs for LHTES units. In this paper, we will use topology optimization to efficiently distribute the fins in the PCM domain. Afterwards, we will examine numerically the performance of different topology optimized fin designs, that were obtained through radial topology optimization and a novel axial topology optimization approach. The PCM used in this study is paraffin RT35 with water used as heat transfer fluid (HTF). The results presented in this study show a significant increase in performance by the topology-optimized designs with a maximum increase in performance of 86.3%. Additionally, the radially finned structure has proved to be a better enhancement in this specific case with a fin distribution that’s occupying 20% of the initial PCM volume for large-scale applications.

Phase change heat transfer and energy storage in a wavy-tube thermal storage unit filled with a nano-enhanced phase change material and metal foams

Latent heat thermal energy storage plays a key role in the thermal management of heat transfer systems, shifting thermal loads, and developing renewable systems. A latent heat thermal energy storage (LHTES) unit can store/release a significant amount of heat in a compact space. However, the main issue of LHTES units is their poor heat transfer characteristics. Thus, the thermal response time of most LHTES is low, and they cannot absorb/release the required energy in a timely manner. Hence, the heat transfer enhancement approaches such as using nano additives, metal foams, and extended, wavy surfaces are promising approaches to improve the heat transfer capability of LHTES. The present study aims to address the impact of using wavy tubes in a composite phase change material and metal foam LHTES unit. A phase change heat transfer model based on enthalpy-porosity was introduced and solved via the finite element approach. The influence of nanoparticle volumetric fraction (VFna), tube wave amplitude (A), tube wave number (N), and the porosity coefficient (ε) was investigated on the charging time, stored energy, and heat transfer behavior of the LHTES unit. According to the findings, employing metal foams and nanoparticles enhances heat transmission and decreases charging time. A simple tube with no wavy surface produces lower pressure drop and better charging power compared to a wavy tube.