Tube Latent Heat Thermal Energy Research Articles

Thermal performance enhancement of multiple tubes latent heat thermal energy storage system using sinusoidal wavy fins and tubes geometry modification

In this paper, performance enhancement of a shell and multiple tube latent heat thermal energy storage system (LHTESS) is numerically investigated by implementing sinusoidal wavy fins and different geometrical designs of heat transfer tubes. The annular space of the shell is filled with the paraffin wax RT35 as phase change material (PCM) and absorbs heat from hot water through the multiple tubes. With the constant total cross-section area of all tubes and fins as the constraint condition, the effect of tube number and tube shape incorporated with the proposed fins on the heat transfer properties of PCM during the melting process is evaluated. The computational results demonstrate that the sinusoidal wavy fins can improve the phase change efficiency compared to the conventional straight fins. The double-pitch sinusoidal wavy fins decrease the total melting time by 9.5% compared to the straight fins for the single-tube case. As the number of HTF tubes increased from one to four, the complete PCM melting time decreased by 38.3%. Geometrical design alterations of heat transfer tubes from circular to petal-shaped are proposed to further improve the thermal performance of multiple tubes LHTESS. The melting rate of PCM is accelerated with an increase in the number of petals. The petal tubes with nine petals can save the charging time up to 24 % in comparison with the circular tubes in a four-tube case with double-pitch sinusoidal wavy fins, and up to 57% compared to the base case with a single circular HTF tube and straight fins.

Effect of ternary hybrid nanoparticles (GO-MgO-TiO2) and radiative heat transfer on the solidification process of PCM inside a triplex tube with hollow fins

Nowadays, due to the features such as high latent heat and constant phase transition temperature, the utilization of phase change materials (PCMs) in energy storage and thermal management systems has attracted scholars' attention. However, the low thermal conductivity and solidification process of these materials has always been a challenge for widespread implementation of them in disparate industries. The current research investigates the characteristics of the PCM solidification process within a triplex tube Latent Heat Thermal Energy Storage System (LHTESS) with innovative hollow fins in the presence of ternary hybrid nanoparticles (THNPs) and radiative heat transfer. The governing equations are solved using Galerkin Finite Element Method (GFEM) with various boundary conditions in the outer wall, such as constant temperature, adiabatic, and coolant fluid temperature (triplex), through FlexPDE software. Furthermore, the effect of key parameters, including shape factor and volume fraction of THNPs, and radiative heat transfer on thermal storage performance is scrutinized. Ultimately, the Taguchi method is adopted to determine the optimal point at which the full solidification time (FST) is lowest. Results show that at 400000 s, the triplex case improved total discharging energy by 23% and 4% in comparison to the constant temperature and the adiabatic case, respectively. Additionally, by including THNPs with a volume percentage of 0.1 and a shape factor of 16.1 instead of 3, the required time for FTS reduces by approximately 13.1% and 21.9%, respectively. Also, the overall solidification times of the PCMs decrease to 36% by enhancing the radiation parameter from 0 to 1. These outcomes illustrate THNPs and considered fins are effective for reducing the FST and the shape factor of THNPs and radiation are key parameters that should be considered by designers.

Heat transfer characteristics of PCM inside a modified design of shell and tube latent heat thermal energy storage unit

Shell and tube latent heat thermal energy storage systems are compact and effective among other types of energy storage systems. The present numerical study deals with geometry optimization of a modified design of shell and tube latent heat thermal energy storage system over melting and solidification cycles. The modified design was produced by splitting the single inner tube into three smaller inner tubes arranged in a line array with different orientations. The numerical model covered four different line array orientations: 0°, 30°, 60°, and 90°, along with a storage model consisting of a single inner tube. The surface temperature, perimeter of inner tubes, and mass of PCM in all numerical cases were assumed to be identical. The numerical model has been validated by comparing the melting fraction contours and the PCM temperature with the experimental published data. It has been found that the line array of 0° orientation has the minimum full cyclic duration with an improvement of 44.4% compared to the base case. Conversely, the line array of 90° orientation has the maximum full cyclic time; 15.83% longer compared to the base case of a single inner tube. Lastly, the orientation of the line array is more significant for melting compared to the solidification.

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.

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%.

The effect of conical shell and converging/diverging tube on the charging performance of shell and tube latent heat thermal energy storage system

Latent heat storage is a promising method to overcome the problem of the intermittent nature of renewable sources. However, the main challenge in utilizing phase change materials is their poor thermal conductivity which leads to the slow charging and discharging of latent heat thermal energy storage tanks. Geometric optimization is a passive method to enhance the charging and discharging rate. In this paper, the geometric optimization of a shell and tube storage tank is studied numerically. Different configurations, including conical shell and tube, cylindrical shell and diffuser, cylindrical shell and nozzle, and a combination of conical shell and diffuser with different tilting angles is investigated. The height of all cases is assumed to be a constant number. The melting process is modeled by the enthalpy-porosity method, and the Boussinesq approximation is employed to consider the effect of natural convection. The governing equations are solved by a spatially and temporally second-order finite volume method. It is found that the main determining parameter is the cross-sectional area ratio of the phase change material at the top to its value at the bottom of the tank. By increasing this ratio, the effect of conductive heat transfer is attenuated, but natural convection is augmented. Since the charging rate is affected by these two heat transfer mechanisms, an optimum value of around 10 is obtained for this shape factor which results in an increased storage rate of 25 % compared to the case of cylindrical shell and tube storage tank. The optimum shape factor can be obtained either by a conical shell and tube or by combining a conical shell and a diffuser.

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.

Numerical study of shell and tube latent thermal energy storage partially filled with metal foam and corrugated internal tube with external heat losses

In the present work, a vertical shell and tube Latent Heat Thermal Energy Storage System is analyzed. The cylinder is filled with phase change material and parts of metal foam. The inner face of the cylinder is corrugated, and it is assumed a constant temperature over the melting temperature of the paraffin wax to simulate the heat transfer. The external surface loses heat to the outside and the top and bottom surfaces are adiabatic. Paraffin wax is used as phase change material that melts over a range of temperatures and has a high latent heat of fusion. The thermal conductivity of the phase change material is low and due to this, it is enhanced with metal foam. In this numerical simulation, it is used the aluminum foam. Enthalpy-porosity theory is used to simulate the phase transition process, and the Local Thermal Equilibrium and Darcy-Forchheimer models are used to examine heat transport between the paraffin and the metal foam. Using the commercial code Ansys-Fluent, the governing equations’ solutions are calculated. In the paper, it is considered different conductivity variations on the external wall and the distinct filling ratio of metal foam. The melting time, enthalpy stored, and energy loss from the numerical simulations of the LHTESS charging phase are provided as a function of time and evaluated.

Thermal energy storage based on cold phase change materials: Charge phase assessment

• Experimental study of water–ice energy storage behavior at density inversion temperature . • Experimental analysis of a finned shell & tube latent heat thermal energy storage . • Effect of temperature, mass flow rate and charge direction on storage performance. • Presence of metastable phase is confirmed. Integration of thermal energy storage in energy systems provides flexibility in demand–supply management and in supporting novel operational schemes. In a combined heat and power cycle, it has been shown that integration of cold thermal energy storage is beneficial to fine-tune electric power and heating/cooling production profiles to better match the load demand. Latent heat storage systems have the advantage of compactness and low temperature swing, however storage performance analysis on large scale setup operating around the density inversion temperature is still limited. In this work, a shell & tube, latent heat based cold thermal energy storage was studied around the density inversion temperature of ice-water at 4 °C and the performance was characterized. Sensitivity analyses on heat transfer fluid flow rate, flow direction and inlet temperature were performed. The results show 27% power increase with doubled mass flow and 18% shorter charge time with 2 °C lower charge temperature. Contrary to general expectations during solidification, the cold thermal energy storage actually shows between 5% and 6% better thermal performance and reducing instant icing power jump of 36% due to supercooling with downwards cold heat transfer fluid flow in cooling charge cycle due to buoyancy change around density inversion temperature. This fact highlights the importance of accounting for the buoyancy effect due to density inversion when designing the operational schemes of large size cold thermal energy storage.

Investigation of thermal performance of a shell and tube latent heat thermal energy storage tank in the presence of different nano-enhanced PCMs

Thermal energy storage is crucial for the sustainability of an energy supply system. One of the best thermal energy storage systems is latent heat thermal energy storage tanks. In the present study, a shell and tube heat storage tank is simulated based on computational fluid dynamics. The tank consists of 18 hot and cold tubes and the space between them is filled with paraffin as a phase change material (PCM). The effects of adding SWCNT and GNP nanoparticles are evaluated on the PCM in different heat fluxes. The simulation is implemented by developing the C++ code in OpenFOAM software, and the solution is performed with the PIMPLE algorithm and finite volume method. Results reveal that the melting volume ratio of the PCMs is independent of the inlet heat flux, and increasing the inlet heat flux only accelerates the melting process. Adding SWCNT to the paraffin reduced the melting time by 43% and stored 147% more latent heat energy in comparison to pure paraffin.

Numerical investigation and extensive parametric analysis of cryogenic latent heat shell and tube thermal energy storage system

• Cryogenic latent heat thermal energy storage for boil-off gas reliquefaction. • Phase change numerical modelling using the enthalpy method application on Dymola. • Parametric study on the system geometric design and the fluid mass flow rate. • Study of radial and longitudinal fins as heat transfer enhancement techniques. • Performance evaluation using charging/discharging rates and energy storage data. Latent heat thermal energy storage systems have shown promising energy management solutions in different domains due to their high efficiency and energy density. Nowadays, most studies focus on moderate to high operating temperature applications such as solar power plants, while few studies exist for cryogenic applications such as the liquefied natural gas (LNG) domain. This article aims to assess the thermal performance of a shell and tube latent heat thermal energy storage system. The purpose of this system is to reliquefy the excess boil-off gas (BOG) generated on LNG carriers, using n-Butane as a suitable phase change material (PCM). The system is numerically investigated using Dymola software, where the solidification and melting evolution of the PCM is accounted for by using the enthalpy method and applying the finite volume method discretization technique. This system works on two operating modes: charging and discharging. During charging, the PCM solidifies and stores the cold energy during the LNG evaporation to be discharged at later times to condense the BOG while the PCM melts. An extensive parametric study is carried out to assess the impact of different factors on the system’s thermal performance. Results showed that the existence of natural convection would significantly enhance the PCM performance. Moreover, the selection of the tube diameter, PCM thickness, and the heat transfer fluid mass flow rate is crucial and is a compromise of several factors. On the other hand, radial and longitudinal fins were assessed as heat transfer enhancement techniques, where a parametric study on the fins’ volume, thickness, and number is carried out. The excessive addition of fins is expected to obstruct the natural convection forces; however, a considerable enhancement in the thermal performance, especially for the radial ones, is observed.

Numerical Investigation on Shell and Tube Latent Heat Thermal Energy Storage with External Heat Losses Partially Filled with Metal Foam

Numerical Investigation on Shell and Tube Latent Heat Thermal Energy Storage with External Heat Losses Partially Filled with Metal Foam

Orientation impact on structural integrity of a shell and tube latent heat thermal energy storage system

Latent heat thermal energy storage systems can regulate the intermittency of electricity generation in a grid powered by renewable energy sources. Such systems could be used in conjunction with Brayton power generation cycles operating at high temperatures (520 °C–750 °C) delivering higher efficiency. However, a trade-off of higher thermal efficiency can be higher thermal stresses. The isothermal latent heat thermal energy storage and release can reduce the thermal stresses for a specific design. This study investigates the impact of the orientation on the melting process and the consequent thermal stresses in a lab-scale latent heat shell and tube system using a combination of transient computational fluid dynamics and finite element analyses. With a high temperature phase change material melting at 705.8°C, two initial temperatures of 700°C and 650°C were considered in transient analyses, leading to a 50 K and 100 K initial temperature difference across the tubes, respectively. For the structural analysis, an elastic method was employed for the condition of 50 K temperature difference, and an elastic-plastic analysis for the condition of 100 K to account for plastic deformation. The results of the elastic analysis presented the maximum thermal stresses of 63.5 MPa and 106.7 MPa in tubes in the horizontal and vertical orientations, respectively. The stress in the tube sheet was slightly higher (94.5 MPa) for the horizontal system compared with 90.4 MPa in the vertical position. For the condition of 100 K, the results of the elastic-plastic analysis identified the highest stresses of 172.5 MPa and 147.4 MPa in the tube sheets of the horizontal and vertical systems, respectively. For both initial temperature conditions, the stress level in tubes is lower in the horizontal orientation, which is where most cost occurs in a shell and tube system. Particularly important for the 100 K condition, the results show a lower stress of 100 MPa in tubes for a horizontal system compared with 140 MPa in a vertical orientation. In general, the lowest thermal stress occurs where a melt layer forms around tubes during the early stages of a melting process. A higher stress occurred in parts in contact with argon. The highest level of stress occurred in parts in contact with solid PCM, which has direct implications for larger vessel designs. This study provides insights into hydrothermal and mechanical design of a PCM system to prevent and/or manage localised maximum thermal stresses for a cost-effective thermal energy storage system.

Numerical investigation of using helical fins for the enhancement of the charging process of a latent heat thermal energy storage system

This paper is focused on the enhancement of the thermal performance of a vertically oriented shell and tube latent heat thermal energy storage (LHTES) system by using helical fins. In order to see the improvement made by using the helical fin in a LHTES unit, the performance of the helically finned LHTES system has been compared with those of axially finned LHTES system, and no finned LHTES system. The length of the helical fin in the helically finned LHTES system is considered equal to the total length of the four axial fins used in the axially finned LHTES system and the net volume of the PCM is supposed to be identical for all studied cases. Three different temperatures of 345 K, 355 K, 365 K have been considered for the inner tube wall. Results revealed that for the helically finned TESS, the total melting time of the PCM can be reduced up to 18.25%, 21.5% and 16.75% in comparison with axially finned LHTES system for the inner tube wall temperatures of 345, 355 and 365 K, respectively. The presence of a helical fin causes the penetration of the heat into the core of the PCM inside the container and the motion of the molten PCM will be affected by the result of the buoyancy forces and the centrifugal force. Thus, there will be both transverse convection and longitudinal convection for the helically finned LHTES system. Besides, for the helically finned LHTES system, the PCM receives the needed heat for its full melting (charging) in less time compared to the axially finned LHTES system. This is due to the helicity of the molten PCM and also the formation of the vorticities due to the existence of the helical fin which contributes to deeper penetration of the heat and melt front.

Experimental investigation of shellac wax as potential bio-phase change material for medium temperature solar thermal energy storage applications

Thermal performance of shellac wax as a novel bio-phase change material (BPCM) and Therminol®-55 as heat transfer fluid (HTF) in a vertical shell and tube latent heat thermal energy storage (LHTES) unit is analyzed experimentally. Operational parameters considered, namely HTF flow rate and inlet temperature in the range of 2–5 LPM and 100–120 °C, respectively. The comprehensive study of contours and plots reveals the impact of natural convection and the progress of the melting and solidification front in the charging and discharging process. As the HTF flow rate increases, the charging rate improves considerably, and a maximum reduction in melting time is obtained as 43.6% for 4 LPM. The maximum reduction in melting time and storage efficiency are 42.2% and 73.4%, respectively, at 120 °C and 4 LPM. However, the discharging process's increased flow rate has no significant effect on solidification and discharge efficiency, which attributes the dominant mode of heat transfer is conduction during the solidification. Shellac wax storage efficiency is comparable to existing paraffin wax, stearic acid and palmitic acid-based LHTES unit. In this regard, shellac wax can be a potential Bio-PCM for medium temperature range (60–80 °C) solar thermal applications such as domestic water heating and food drying.

Dominant roles of eccentricity, fin design, and nanoparticles in performance enhancement of latent thermal energy storage unit

In this paper, numerical and experimental investigations of thermal performance enhancement of horizontal longitudinal shell and tube latent heat thermal energy storage unit (LHTESU) via eccentricity (e), fin design optimization, and nanoparticles in the phase change material (PCM) of stearic acid are presented. An enthalpy-porosity-based two-dimensional, transient numerical methodology is used after validating against the experimental results and the literature. Five different eccentric positions, e = 0.14, 0.28, 0.42, 0.56, and 0.63 are investigated by modifying the design of Y-finned tube. The eccentricity and fin design modifications improved natural convection effects as compared to concentric Y-finned tube. Thermal performances of LHTESU are analyzed on the basis of melting time, heat storage capacity, heat storage rate, and performance enhancement ratio. Based on the performance analysis, an optimum eccentric configuration of LHTESU is proposed. For optimized eccentric unit (e=0.42), a reduction of 34.14% in melting time along with 30.7% improvement in thermal energy storage rate is achieved as compared to concentric (e=0) LHTESU. The effect of temperature of the tube on PCM's melting time and heat transfer is also analyzed and two important correlations are proposed. The thermal performance of the optimized eccentric unit is further enhanced by adding nanoparticles of Al2O3 and CuO ranging from 0.5% to 10% by volume in the pure PCM. The nano-enhanced PCM with 1% of Al2O3 further improves melting and energy storage rates of optimum LHTESU by 10%.

Transient Thermo-mechanical analysis of a shell and tube latent heat thermal energy storage for CSP plants

The structural integrity of a lab-scale shell and tube latent heat thermal energy storage under transient conditions was investigated. The system was designed to use sodium at 750 °C as a heat transfer fluid with a high temperature phase change material, melting at 705.8 °C, as the heat storage medium. Stainless steel 347H (SS347H) was used as the tube and shell material. One quarter of the lab-scale system was used for the CFD model (using ANSYS Fluent) while a temperature profile was generated from the CFD modelling which was then linked to the validated ANSYS FEA model. The operating pressure of the system was below 1 bar, therefore, the thermally induced stress–strain due to high temperature gradient (up to 100 K) was the determining factor. The difference between the thermal expansion coefficient of the PCM and metal tubes was found to be of lesser influence as the ullage area provided sufficient space for expansion of the PCM. In the case of 50 K temperature gradients, a thermoelastic analysis showed that the maximum equivalent stress is approximately 106 MPa, which is below the allowable design stress for SS347H. However, the maximum equivalent stress under the 100 K temperature difference was 250 MPa, well above the allowable stress. Therefore, the structural integrity of the system is sound under transient operating conditions within a 50 K temperature gradient for 1000 h. Furthermore, an elastic–plastic (bilinear) analysis showed similar results for operation within a temperature difference of 50 K, however, a lower equivalent stress of 140 MPa for 100 K. Therefore, operation under a higher temperature gradient of up to 100 K is possible considering plastic strain and deformation while the system is reasonably protected against creep failure during the first 1000 h of operation. The current study provides new knowledge and insight into the structural integrity of a shell and tube system, in particular a system using an austenitic steel material, under high operating temperature which can assist in the design of a cost-effective latent heat thermal energy storage system.

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

The latent heat thermal energy storage system (LHTES) utilizes phase change material (PCM) to store energy. The non-uniformity in heat transfer between heat transfer fluid (HTF) and PCM along the height of the widely used vertical cylindrical shell and tube type storage tank causes a reduced thermal performance of the storage. Hence, in the present work, a passive heat transfer enhancement technique is proposed through a novel funnel shaped configuration of the shell and tube LHTES to achieve more uniform temperature distribution in the PCM as compared to the cylindrical shell and tube LHTES. Additionally, longitudinal fins are introduced in the HTF tube further to enhance the heat transfer between HTF and PCM. A numerical model is developed using the enthalpy-porosity technique to analyze the phase change phenomenon. The thermal performance of the funnel LHTES is evaluated using the first and second law of thermodynamics. The funnel LHTES with the lateral shell surface tilting up to a height of 250 mm shows higher melt fraction and energy efficiency by 11.5% and 66.6%, respectively compared to the cylindrical LHTES. The latent heat content of the funnel LHTES with a shell tilt height of 250 mm during the charging and discharging period is improved by 1.72 and 1.11 times, respectively than that of the cylindrical LHTES. A significant improvement in the rate of solidification of PCM during the discharging process is obtained with the funnel LHTES.

Performance investigation of shell and helical tube heat energy storage system with graphene dispersed erythritol PCM

AbstractExperimental investigation on the thermal performance of a shell and helical tube latent heat thermal energy storage system for medium temperature applications is reported in the article. Commercial grade erythritol having a melting temperature of 120°C was employed as the phase change material (PCM). The thermal conductivity of the erythritol had been usually very low (0.73 W/mK) and it results in low heat transfer rates during both charging and discharging processes. In the study, an attempt was made, this inherent limitation of erythritol, high thermal conductive graphene nanoparticles, which are dispersed into erythritol matrix, referred to as nanoparticle dispersed phase change material (NDPCM). The effect of the addition of graphene nanoparticles on the performance of the storage system such as heat flow rate, overall heat transfer coefficient, charging and discharging efficiency and effectiveness was evaluated and compared with the storage system with only base erythritol during both energy storage and retrieval processes. The efficiency of the NDPCM system increased to 16.29% during the storage period and 28.48% during the retrieval period compared with the base PCM system. Further, it was observed that the effectiveness is about 14% greater at the beginning of the melting process and about 12% greater at the beginning of the solidification process for NDPCM.

Design of non-uniformly distributed annular fins for a shell-and-tube thermal energy storage unit

The shell and tube latent heat thermal energy storage systems are widely recognized as one of the most effective ways to store and utilize solar energy due to their high energy density, constant storage/releasing temperature, structural feasibility and rational price. The application of fins is an effective method to enhance heat exchange through extend the heat transfer surface area. However, there existed strong uneven melting behavior including melting fraction, temperature uniformity in a vertical thermal energy storage unit. To improve its uniformity of melting fraction and temperature, this study designed various conditions for fin pitch and positions in a non-uniform pattern to reduce the inhomogeneity for the melting process. Numerical models were established and validated by the experimental measurement conducted in this study. The effects of fin pitch and position on the thermal performance of the melting process were quantified via analyzing the melting front evolution, temperature and velocity distribution, melting rate and temperature uniformity. Results demonstrated that a 62.8% and 34.4% reduction in full melting time and average temperature difference in the phase change material region was separately obtained for the thermal energy storage unit with non-uniformly distributed annular fins, compared to the original case with uniform fins. Besides, the melting rate uniformity was also improved by 84.7%. The non-uniform design on fin position and pitch give a perspective to enriching the design methods for practical application in engineering.