Latent Heat Thermal Energy Storage Unit Research Articles

Improving phase change heat transfer in an enclosure partially filled by uniform and anisotropic metal foam layers

Anisotropic metal foams exhibit exceptional potential for improving the efficiency of latent heat thermal energy storage (LHTES) units by enhancing heat transfer and thermal energy storage rates. This study explores the largely uncharted area of thermal behavior of anisotropic metal foams in varied configurations and enclosure designs. The research focuses on an LHTES unit with a specific channel configuration, constructed using copper and containing three layers of copper metal foam, one of which is anisotropic and infused with paraffin wax. The finite element method was utilized to manage the complexities emerging from phase change, and the anisotropic angle varied from 0 to 90° in three different placements of the AMFL: top, middle, or bottom of the enclosure. The ideal design was achieved with an AMFL in the middle with a 0°angle, resulting in a 3.7 % reduction in melting time and approximately a 2.3 % reduction in solidification time. However, AMFL designs at the middle placement with a 75° anisotropic angle were less effective, hampering the melting and solidification processes, thus potentially extending charging and discharging times. The study concludes that the placement and angle of the AMFL layer are vital for the heat transfer capabilities of phase change materials. AMFL at the middle with a 0° angle optimally leverages temperature gradients, enhancing heat transfer compared to other investigated cases. An AMFL in the middle with a 0° angle exhibits approximately 7.1 % and 6.3 % improvements for melting fractions of 0.9 and 0.95, respectively, underscoring its potential for efficient thermal energy storage.

Natural convection and field synergy principle analysis of the influence of fins redistribution on the performance of a latent heat storage unit in a successive charge and discharge

The present study focuses on analyzing the impact of enhancing the heat exchanges on the shell side by surface extension on the kinetics of melting/solidification in a latent heat thermal energy storage (LHTES) unit. Particular attention is paid to the influence of fins redistribution on the performance of the LHTES unit, natural convection, and Phase Change Material (PCM) melting/solidification kinetics. The particularity of this study lies in the improvement of the LHTES unit performances in a successive charging-discharging operation by only redistributing the fins while keeping the same total heat transfer surface, PCM volume, and compactness. The first part of the study consists of evaluating the impact of fin redistribution for the same total heat transfer surface on the LHTES unit performance. Attention was paid to the fully charging and discharging times and the heat duty absorbed or released during the melting or solidification process. For this purpose, 4 configurations of LHTES units having 4 and 8 radial fins with the same total transfer surface were analyzed, with the aim of ensuring a maximum performance on charging process. In a second part, an improved configuration was proposed in order to minimize the successive charging and discharging time for a cyclic operation of the LHTES unit. The coordination factor derived from the field synergy principle, PCM liquid fraction, the heat duty exchanged, phase change kinetics, and liquid PCM velocity were used as performance key factors. They were used to analyze and compare the different configurations in order to find the best configuration for a successive charging-discharging operation. The selected improved configuration has been found to enhance both the charging and discharging processes. It leads to the reduction of the successive charging-discharging overall duration by 10 % to 47 % compared to the other configurations investigated with the same heat transfer surface. The enhanced LHTES unit developed in the present study is intended to improve the thermal comfort of buildings by valorizing and storing renewable and waste energies.

Numerical investigation and optimization of the melting performance of latent heat thermal energy storage unit strengthened by graded metal foam and mechanical rotation

In this paper, a combined passive graded metal foam and active mechanical rotation strategy is proposed to simultaneously solve the problem of slow melting rate and non-uniform phase change problem of the latent heat thermal energy storage (LHTES) technology. The enthalpy-porosity method and fixed grid structure are employed to numerically investigate the effects of porosity range, the number of graded layers, and the rotational angular velocity. Moreover, the response surface method (RSM) is further selected to optimize the structural parameters and obtain the function of melting performance and various factors. The result shows that there is an optimal porosity range and the total melting time decreases first and then increases with the increase of porosity range. When the porosity range is 12 % and the graded layer is three, it can shorten the melting time by 35.54 % and increase the thermal energy storage rate (TESR) by 51.57 %. In addition, the melting performance is gradually improved as the number of graded layers increases. The strengthening effect of graded metal foam with just four layers is close to that of the maximum layers considered in this paper. The trend of the influence of rotation speed on the melting performance of the LHTES unit is consistent with the porosity range, indicating the existence of the optimal rotational speed. The RSM optimization structure, with a 14.969 % porosity range, 5-layer graded number, and 2.267 rpm rotational speed, shortens the melting time by 42.42 % and increases the TESR by 62.75 % compared with the stationary case with uniform metal foam. This work verifies the effectiveness of active rotation coupling with passive graded porous structures, which could provide a new strengthening approach to enhance LHTES.

Numerical study of solidification and melting behavior of the thermal energy storage system with non-uniform metal foam and active rotation

This paper focuses on the strengthening study of the latent heat thermal energy storage (LHTES) unit and proposes a coupling strengthening method with non-uniform graded metal foam and active rotation. The non-uniform graded metal foams are employed to enhance heat conduction, and the rotation method is selected to make full use of natural convection. The solidification and melting behavior under the coupling effect of non-uniform metal foam and active rotation are numerically analyzed. The aluminum foam is partially concentrated and divided into two parts (concentrated part and diluted part) and is divided into the even-layered or uneven-layered porous structures according to the different regions area. Under the same volume of phase change material (PCM), the effects of layered forms (even-layered and uneven-layered approach), concentrated porosity, concentrated ratio, and rotational speed are performed. It can be concluded that the metal foam should concentrated near the inner tube and the uneven-layered structure can further improve the phase change heat transfer performance compared to the even-layered structure. Moreover, the thermal performance of the LHTES unit improves firstly and then decreases as the concentrated porosity, concentrated ratio, and rotational speed increase. The optimal values are obtained at 0.86 concentrated porosity, 0.3 concentrated ratio, and 0.5 rpm rotational speed. Compared with the static case with uniform metal foam, the melting time, solidification time, and total melting and solidification time can be significantly reduced by 40.30 %, 28.66 %, and 33.18 %, respectively. Similarly, the thermal energy storage rate can be correspondingly increased by 62.57 %, 40.82 %, and 54.11 %, respectively.

Investigation of phase change heat transfer in a rectangular case as function of fin placement for solar applications

This paper attempts to maximize solar energy utilization by employing a latent heat thermal energy storage (LHTES) unit integrated with a solar receiver of concentrating collectors or thermal management unit for photovoltaic panels. The study investigated an LHTES unit with a rectangular shape and equipped with a T-shaped fin subjected to heat flux. The paper examined the effect of eight T-fin positions under the applied heat flux on the thermal performance of phase change material (PCM). The PCM melting process was modeled using the enthalpy-porosity method using the finite element approach. The obtained numerical results revealed that PCM melting rate strongly depends on fin position, with superiority for fins located at the upper part of the chamber when heat flux is used as the primary heating source. Under applied heat flux, locating the fin at the upper section of the vertical LHTES unit enhanced the melting rate of the PCM, reaching 10 % better than the fin's middle and bottom positions, which is against the cases reported for the fixed temperature heating process that prefer bottom fins. Thus, these results recommend using T-shaped fins in the upper parts of PCM-based units used for solar collector receivers and thermal management of photovoltaic panels.

Design and experimental investigation of topology-optimized fin structures for enhanced heat transfer in latent heat thermal energy storage units

In order to enhance the heat exchange rate between the heat transfer fluid and the phase change material (PCM), the placement of fins in the latent heat thermal energy storage (LHTES) unit is an effective means. To this end, this paper introduces a novel fin structure that can evolve along the optimization process using a topology optimization strategy, aiming to optimize the spatial layout of the fins and maximize the thermal performance of the LHTES unit. The numerical results demonstrate that the topological fins (TOF) outperform the conventional rectangular fins (CF) in effectively enhancing the temperature and liquid phase fraction of the PCM. Following this, the TOF was fabricated using selective laser melting and tested in an experimental platform containing three types of LHTES units to examine its thermal properties. The findings from the experiments indicate that the TOF exhibits superior thermal performance and can achieve a more uniform heat exchange with the PCM. Specifically, under the heat storage and release conditions of 90 °C–60 °C, the heat transfer efficiency of the TOF unit is enhanced by 57.8 % compared to that of the finless unit, and by 25.26 % compared to that of the CF unit. Similarly, under the heat storage and release conditions of 85 °C–65 °C, the heat transfer efficiency of the TOF unit is improved by 67.54 % compared to the finless unit, and by 22.84 % compared to the CF unit. Consequently, in engineering applications, LHTES units equipped with TOF can achieve faster heat storage and release, and exhibit greater responsiveness to load changes in the energy system.

Improving heat storage performance of shell-and-tube unit by using structural-optimized spiral fins

Spiral fins have been widely used to enhance the heat transfer of latent heat thermal energy storage (LHTES) systems. However, owing to the inhomogeneous melting of solid-liquid phase change materials (PCMs) driven by convective heat transfer, the uniform spiral fins always have poor enhancing performance. In the present work, we proposed structural-optimized spiral fins, including optimized fin thickness, optimized fin height, and optimized fin pitch, to uniformly and efficiently transfer the heat from fins to PCM. By comparing their melting results with the original-uniform model, we found that negative models with larger fin volume at the bottom are more efficient in accelerating the melting process, and they can maximally reduce the complete melting time of PCM by 15.01% compared with the original one. On the contrary, the positive model with a smaller fin volume at the bottom slows down the melting of the LHTES unit. The heat transfer mechanism along the whole melting process is analyzed by comparing the thermal parameters (including liquid fraction, average temperature, average liquid velocity, and heat flux) of the original and optimized models. The enhancements of the negative models are owing to their benefits to the developments of convective heat transfer in the top region and conductive heat transfer at the bottom. According to the results of this paper, researchers can design novel high-performance LHTES systems using optimized spiral fins.

Design and assessment on a bottom-cut shape for latent heat storage tank filled with metal foam

The utilization of phase change materials (PCMs) holds tremendous potential of heat storage domain. The PCM's refractory at the latent heat thermal energy storage (LHTES) unit bottom hinders the heat storage efficiency, despite the significant improvement in thermal conductivity achieved through the addition of metal foam. This study employs numerical simulation to examine the impact of applying bottom cross-cut on PCM's spatial distribution in a horizontal LHTES unit. The manuscript analyzes parameters including melting fraction, complete melting time, Rayleigh number, natural convection heat transfer gain, melting phase interface, velocity and temperature distributions, and heat storage. The findings indicate that the proximity to the heating tube results in a reduction of solid volume at the LHTES unit bottom. A 0.6 bottom cross-cut ratio leads to an 18.84 % faster heat storage rate compared to a concentric-circle unit. Furthermore, a bottom cross-cut ratio of 0.5 enhances natural convection heat transfer gain by 3.28 times.

Design and Research of Heat Storage Enhancement by Innovative Wave Fin in a Hot Water–Oil-Displacement System

Energy storage technology provides a new direction for the utilization of renewable and sustainability energy. The objective of this study is to introduce a novel, wavy, longitudinal fin design, which aims to improve heat transfer in the melting process of a Latent Heat Thermal Energy Storage (LHTES) unit. The main goal is to mitigate the negative effects caused by the refractory zone at the end of the melting phase. A two-dimensional numerical model of LHTES unit is established by using the enthalpy porosity method and verified by experimental data. Through the quantitative comparison between the traditional rectangular fin and the innovative wave fin, the influence of wave fin on the heat transfer mechanism in the heat storage process is revealed. The results show that the average heat storage rate of five and six wave fins is 3.70% and 12.98% higher than that of conventional rectangular fins, respectively, and the average temperature response of six wave fins is 17.78% higher than that of conventional rectangular fins. The addition of the wave fin weakens the negative effect of the refractory zone, but prolongs the heating time of the initial melting point.

Numerical analysis and optimization of the heat transfer enhancement from the heat transfer fluid side in a shell-and-tube latent heat thermal energy storage unit: Application to buildings thermal comfort improvement

This study investigates the impact of enhancing the convective heat transfer on the Heat Transfer Fluid (HTF) side by passive flow manipulation on the melting and solidifying kinetics of a Phase Change Material (PCM) in a shell-and-tube Latent Heat Thermal Energy Storage (LHTES) unit. The PCM used is PureTemp 23 (PT23), a commercial bio-sourced product. The targeted application is the development of a LHTES unit for improving the thermal comfort in buildings through a combined heating and cooling approach. The study is carried out using the commercial code STARCCM+ and the enthalpy-porosity method, with appropriate implementation of the buoyancy source term. The numerical approach used for phase change modeling has been validated by comparisons with reference data from the open literature. Delta Wing pairs (DWg) and Delta Winglet pairs (DWt) vortex generators (VGs), were first inserted into the tube in which the HTF flows. Parametric analysis on the aspect ratio, position, and VGs number were performed, and optimization was done on the attack and rolling angles. The Performance Evaluation Criteria (PEC) index, which takes into account the heat transfer enhancement achieved and the related pressure losses, was used as an assessment criterion to evaluate the heat transfer augmentation of the studied enhanced tube with VGs. The results show that maxima can be reached for the different parametric studies carried out. While PEC increases with the attack angle until a maximum beyond which it decreases, it decreases consistently with the rolling angle. Once the enhanced optimal tube equipped with a shell containing the PCM, the results of the detailed study made on the kinetics for charging and discharging period of the enhanced LHTES unit reveal important gain for the storage unit. The heat transfer enhancement achieved result into more than 110 % increase in the PCM's melting/solidifying kinetics in the shell, thanks to an increase in the heat duty exchanged between the HTF and the PCM, leading to a considerable reduction of complete melting/solidification time. It was observed that the enhanced and optimized LHTES unit developed in the present study has a huge potential for improving buildings seasonal thermal comfort.

Study of storage thermal energy of latent heat Application to the solar collector

The energy production provided by a heat excess or discontinuous source (solar, waste heat...) involve the utilization of a thermal storage in the thermodynamic or recuperation chain. These last years, studies on thermal storage systems have been developed in order to bring technical and economic elements. The study includes two parts. The first one concern a numerical analysis of a latent-heat thermal energy storage unit is conducted. The element of storage is a rectangular closed cavity filled with a phase change material (PCM) initially at the solid state. At t = 0 a heat flux is applied through one of the vertical walls of the cavity. Other one, experimental steady treats a new type of solar collector was developed and tested to valid numerical models.

The Effect of Different Configurations of Copper Structures on the Melting Flow in a Latent Heat Thermal Energy Semi-Cylindrical Unit

Utilizing latent heat thermal energy storage (LHTES) units shows promise as a potential solution for bridging the gap between energy supply and demand. While an LHTES unit benefits from the latent heat of the high-capacity phase change material (PCM) and experiences only minor temperature variations, the low thermal conductivity of PCMs hinders the rapid adoption of LHTES units by the market. In this regard, the current work aims to investigate the thermal behavior of a semi-cylindrical LHTES unit with various copper fin configurations (including horizontal, inclined, and vertical fins) on the melting flow. The novelty of this research lies in the fact that no prior studies have delved into the impact of various fin structures on the thermal performance of a semi-cylindrical LHTES system. The nano-enhanced phase change material (NePCM) fills the void within the unit. The warm water enters the semicircular channel and transfers a portion of its thermal energy to the solid NePCM through the copper separators. It is found that the system experiences the highest charging capability when the fins are mounted horizontally and close to the adiabatic upper wall. Moreover, the presence of dispersed graphite nanoplatelets (GNPs) inside the pure PCM increases the charging power and temperature of the LHTES unit.

An in-depth study on melting performance of latent heat thermal energy storage system under rotation mechanism by fluctuating heat source

The Organic Rankine Cycle (ORC) is a reliable and efficient means of converting solar energy into electricity. The challenges brought about by the unpredictable nature of solar energy can be effectively mitigated by utilizing latent heat thermal energy storage (LHTES) technology, specifically by implementing heat source pretreatment. This paper investigates the thermal storage properties of a rotating triplex-tube LHTES unit under different sinusoidal fluctuating heat sources. A transient numerical model is built to analyze the effects of sinusoidal wall temperature amplitude and angular velocity on the melting characteristics of the unit, including melting time, heat storage rate, and temperature response. The design is further analyzed using the Taguchi method. The results show that the angular velocity of the sinusoidal wall temperature has a greater effect on the average heat storage rate and melting time than the amplitude. When the amplitude is set to 10 and the angular velocity to 0.02, the melting time is decreased by 8.7%, while the average heat absorption rate and average temperature response increase by 10.21% and 12.27%, respectively. Additionally, the sensible and total heat energy absorption increase by 2.23% and 0.62%, compared to the initial heat source condition. Furthermore, the heat transfer is enhanced through the introduction of Al2O3 nanoparticles at varying percentages. The unit heat storage rate improves significantly with an increasing percentage of nanoparticles. Specifically, when 2.5% and 5% Al2O3 nanoparticles are added, the melting time of the unit is reduced by 3.77% and 15.07%, respectively, while the average heat absorption rate increases by 2.43% and 10.39%.

Comprehensive performance analysis and structural improvement of latent heat thermal energy storage (LHTES) unit using a novel parallel enthalpy-based lattice Boltzmann model

Latent heat thermal energy storage (LHTES) utilizing phase change material (PCM) is one of the critical enablers in developing sustainable and low-carbon energy systems. To fill the knowledge gap, this paper presents an enthalpy-based solid–liquid model through the lattice Boltzmann method (LBM) with a multi-relaxation-time (MRT) approach, aiming to simulate convective phase change in LHTES units with and without porous media in Cartesian or axisymmetric domains. To improve accuracy and efficiency, the model integrates a differential scanning calorimetry (DSC) correlated equation for enthalpy modeling, couples with a 1D heat-transfer-fluid (HTF) model for boundary treatment of HTF side, and employs a parallel LBM scheme for efficient parametric studies. The validation demonstrates the model’s success in predicting PCM phase change, with errors below 10%. A comprehensive numerical analysis is then conducted to quantitatively evaluate the effect of convection on PCM melting. Novel metrics, such as acceleration rates (ac) of PCM melting and threshold Rayleigh numbers (Radc) at various aspect ratios, are introduced. Furthermore, PCM melting in the porous cylindrical unit is explored. Findings reveal up to 86% acceleration in melting compared to pure PCM at 80% energy storage, and the porous media with porosity above 0.9 is recommended for thermal enhancement. Moreover, this paper analyzes the negative effect of uneven temperature distributions caused by convection on LHTES unit efficiency. A modified LHTES unit geometry is proposed to offset this negative effect, and the study demonstrates successful mitigation of uneven temperature distributions, achieving up to 57 % acceleration in PCM melting.

The heat transfer enhancement of the converging-diverging tube in the latent heat thermal energy storage unit: Melting performance and evaluation

Latent heat thermal energy storage (LHTES) has emerged as a promising approach to settle the intermittent and fluctuant of renewable energy but heat transfer enhancement is necessary due to the low thermal conductivity of the phase change material (PCM). This study numerically investigated the heat transfer enhancement effect of the typically converging-diverging tubes (CDTs) inside a shell-and-tube LHTES unit. The evolution of melting behavior was analyzed to describe the heat transfer enhancement mechanism of the CDT. Based on the enhancement effect and pump power consumption associated with the CDT, a modified performance evaluation criterion (PEC) was established to evaluate the feasibility of current designs. The arrangement of CDTs was found to significantly improve the heat transfer performance of LHTES. The triangle CDT exhibited the maximum melting time reduction of 20.77%. The heat transfer enhancement effect of CDT was attributed to the enhanced natural convection of PCM and forced convection of heat transfer fluid. The analysis of the evaluation ensures the feasibility of the new criterion and its specific application field. Moreover, it was worth to note that the triangle CDT achieved the best cost performance of 0.363 ω, where ω represented the return factor.

Experimental and numerical investigations on the thermal performance enhancement of a latent heat thermal energy storage unit with several novel snowflake fins

This article introduces a novel snowflake fin inspired by the crystal structure of snowflake to enhance the heat transfer performance of Latent Heat Thermal Energy Storage (LHTES) units. Initially, a numerical simulation model for transient heat transfer units with snowflake fin was established in a shell and tube LHTES unit. The accuracy and dependability of the model are verified through comparison with experimental results. Then, the effects of three placement methods of LHTES unit (vertical, horizontal-Ⅰ, and horizontal-Ⅱ) on melting and solidification performance are explored. Additionally, the effects of traditional longitudinal fins, snowflake fin, and four novel snowflake fins on melting and solidification behaviors are quantitatively compared. The single-factor method and response surface methodology (RSM) were employed to further optimize the selected optimal novel snowflake fin design. The research results show that the heat transfer performance of the vertically placed LHTES unit is the best. In comparison to traditional longitudinal fins and conventional snowflake fin designs, the novel snowflake fin design reduced the total melting and solidification time by 45.15% and 18.14%, respectively. The optimal size of the branch fins is a radial length of the root of 22.9 mm, self-length of 8 mm, and an angle of 60.3°.

Parameter optimization of unevenly spiderweb-shaped fin for enhanced solidification performance of shell and tube latent-heat thermal energy storage units

This paper investigates the solidification process of fin-strengthened shell and tube latent-heat thermal energy storage unit (LTESU). An unevenly spiderweb-shaped fin is proposed to fit better with shell and tube structures. This new type of fin is connected to the radial fins by annular fins. The uneven arrangement is achieved by varying the distance between the annular fins and the width ratio of the annular fin to the radial fin. Numerical simulation is used to investigate the strengthening effect of the novel fin on the solidification performance of LTESU. Moreover, to achieve better solidification properties, three parameters of the spiderweb-shaped fin are optimized for an equal share of metal fins (the position of the outermost annular fin γ, decreasing common difference of distance between annular fins ψ, and width ratio δ). The results show that there are optimum values for all three parameters to enable LTESU to achieve the shortest complete solidification time and the highest thermal energy release rate (TERR). The optimized spiderweb-shaped fin has a structure with larger annular fin spacing close to the inner tube, smaller annular fin spacing away from the inner tube, and thicker radial fins, thinner ring fins. It is recommended that the configuration parameters for the spiderweb-shaped fin are γ = 0.94, ψ = 0.05, and δ = 0.10. Compared to conventional rectangular fins, it ultimately reduces the complete solidification time by 88.9 % and increases the TERR by 7.8 times.

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.