Phase Change Material Heat Storage Research Articles

A study on novel dual-functional photothermal material for high-efficient solar energy harvesting and storage

The solar-heat storage efficiency of devices based on phase change materials (PCMs) is limited due to the light absorption and internal heat transfer within the PCMs, unclear thermal conductivity-enhancement mechanism within nanocomposite PCMs, and uncontrollable photothermal-interface modulation. Therefore, a novel controllable strategy was proposed in this study to fabricate dual-functional photothermal storage three-dimensional (3D) phase change blocks (PCBs) with higher thermal conductivity (27.98 W/m·K) and spectral absorption (98.03%) compared to those of most previously reported PCM-based devices. The as-synthesized PCBs contained millimeter-sized graphite plates with horizontal Van der Waals bonds and oriented micro/nanoscale graphite nanosheets. The structural properties of thin PCM layers between the PCB sheets have synergistically reduced the internal interfacial thermal resistance of the PCBs. Laser-controllable induction was used to fabricate integrated biomimetic-forest 3D optical absorbers on the high thermal conductivity interface of the PCBs, which significantly reduced the thermal resistance of the optical-thermal interface. The resulting 3D-PCBs, integrated with thermoelectric generators, powered portable electronic devices, expanding the applications of traditional PCM heat-storage devices. Therefore, this study will guide the future design of high-performance solar-thermal storage PCMs with a wide range of practical applications.

Thermal performance of an active casing pipe macro-encapsulated PCM wall for space cooling and heating of residential building in hot summer and cold winter region in China

Phase change material (PCM) wall is expected to match the building type and its climate region effectively. In order to meet the space cooling and heating of residential buildings in hot summer and cold winter regions in China, a new active casing pipe macro-encapsulated PCM wall is proposed, in which the cold storage and heat storage PCMs are sealed between the inner pipe and outer pipe with no leakage. To obtain the optimal structure parameters and better thermal performance of the PCM wall, the mathematical model of the PCM wall is established and validated by experiment, and the effects of PCM filling pattern, structural parameter of casing pipe, water temperature in inner pipe and indoor setting temperature are simulated and analyzed. The results show that the optimal PCM filling pattern is to fill the cold storage PCM and heat storage PCM in the gap between the inner pipe and outer pipe separately; the optimal PCM filling thickness is 13 mm; the optimal structural parameters are inner pipe diameter of 20 mm and casing pipe centre spacing of 61 mm. The water temperature in the inner pipe and PCM energy storage/release time reasonably match the indoor setting temperature. Under the optimal operating conditions, the average PCM wall surface temperatures of 20.5 and 26.8 ℃ and the PCM wall surface heat fluxes of 45.9 and 57.2 W/m2 can be obtained in summer and winter conditions, respectively. The research provides an optimized casing pipe macro-encapsulated PCM wall system that can reliably and efficiently meet both the space heating and cooling demands of residential buildings in hot summer and cold winter regions in China.

Study on thermal storage performance of a novel conical spiral tube heat storage system

Due to the structural advantage of the conical spiral tube, which is narrow at the top and wide at the bottom, it helps to improve the thermal response rate of the heat storage system. Therefore, this study proposes a novel conical spiral tube heat storage system. The software Fluent is used to conduct three-dimensional unsteady state calculations and investigate the effects of the conical ratio, taper, and length-to-diameter ratio on the phase change material (PCM) thermal storage performance. The results indicate that when the conical ratio is increased from 1.0 to 3.0, the PCM heat storage capacity is reduced by 1.05%, the melting time is shortened by 17.60%, the average heat storage rate is increased by 20.10%, and the heat storage efficiency is reduced by 0.10%. Continuing to increase the conical ratio, the optimization of the performance is not obvious. Subsequently, a conical ratio of 3.0 heat storage tank is used as the reference unit. When the tank taper is increased from 0 to 0.22 and the length-to-diameter ratio is increased from 1.44 to 1.85, the melting time is shortened by 7.59% and 32.62 %, the heat storage capacity is reduced by 3.45% and 9.24%, the average heat storage rate is increased by 4.47% and 34.69%, and the heat storage efficiency is reduced by 0.02% and increased by 7.99%, respectively. Continuing to increase the taper from 0.22 to 0.32 does not result in an effective improvement of the performance. This study is a good guide for the optimization of the thermal storage performance of spiral tube heat storage systems and the efficient use of solar energy.

Microencapsulation of Al-Si-Fe alloys for high-temperature thermal storage with excellent thermal cycling performance

Metal-based phase change heat storage materials have become a potent candidate to regulate supply and demand of thermal energy due to their high conductivity, latent heat and stability. With the development of high-efficiency energy storage systems, materials with higher phase change temperatures are in demand urgently for more effective energy storage, which had not been achieved. Herein, the industrial Al-Si-Fe alloy with phase change temperature of 869 °C was chosen as heat storage material in this research. Furthermore, to prevent the alloy from the inherent problems such as liquid leakage, oxidation and corrosion at high temperature, a new and simple strategy was developed to micro-capsulate the alloy. The prepared process of microcapsules involved two steps: pre-coated of aluminum hydroxide along with hydrothermal carbon and heat treatment in nitrogen atmosphere. The composition, morphology, and thermal performance of the microcapsules were characterized by XRD, SEM, TEM, and TG-DSC. The results indicated the shell below 1 μm was composed of α-Al2O3 strengthened by network AlN fibers formed through the V-S mechanism. The latent heat of microcapsules reached 187.6 J·g−1 which was 82.9 % relative to raw material. Moreover, the total latent heat of the microcapsules did not change much after 300 cycles between 500 and 900 °C, although the phase transition behavior was altered. Overall, this research provides a novel idea for the encapsulation technology and the application of thermal energy storage materials from preparation and structure, which is conducive to promote the application of high-temperature phase change materials.

Thermal management of honeycomb heat sink filled with phase change material for smart lighting applications

Recently, thermal management of LEDs lamps has become increasingly essential due to the widespread integration of LEDs in smart lighting applications. In this work, we focus on the thermal analysis of convective heat transfer using a honeycomb heat sink designed for LEDs lamp cooling. Three different heat sink geometries were examined: an aluminum-filled honeycomb radiator, a hollow honeycomb radiator, and a hollow honeycomb radiator incorporating a phase change material (PCM) layer. The results obtained from numerical simulations using COMSOL Multiphysics® showed that the third heat sink geometry, when employed in short-duration lighting applications, led to a 25% reduction in temperature for a 20W power lamp. We also determined the optimal operational time, during which the temperature drop is maximum. Moreover, we observed that the integration of a PCM-filled honeycomb radiator in cyclic lighting applications (involving on/off cycles and high/low power settings) significantly mitigates temperature rise in the lamp by leveraging the PCM's heat storage capacity. This approach effectively prevents thermal shocks, ensures prolonged LEDs performance, and contributes to energy savings in the lighting sector. By addressing the thermal management challenges associated with LEDs lamps through innovative heat sink designs and the utilization of PCM, our research offers valuable insights for enhancing the overall performance and efficiency of LED lighting systems.

Thermal performance of solar flat plate collector using energy storage phase change materials

AbstractThe present study has been carried out to improve the overall efficiency of a conventional flat plate solar collector (FPSC) using two different heat storage phase change materials (PCMs). Two grades of paraffin wax—Paraffin‐P116 (PCM‐1) and Paraffin‐5838 (PCM‐2) as PCM are selected for the analysis based on their high heat fusion rate, low thermal conductivity, and suitable phase transition temperature. The present code has been validated with experimental results and it showed a maximum error of 6.43% in predicting the water outlet temperature. Absorber plate temperature, useful heat transfer rate, water outlet temperature and efficiencies are estimated to improve the performance of FPSC with and without PCM for various flow rates (15 lph and 30 lph) with two different weights of PCM (9 kg and 14 kg) for three different locations in India, [Chennai (13.0827° N, 80.2707° E), Bengaluru (12.9716° N, 77.5946° E), and Delhi (28.7041° N, 77.1025° E)]. The maximum increment in the efficiency of FPSC with the use of PCM‐1 is 19.59% and with the use of PCM‐2 is 16.53%. Using 14 kg of PCM‐1 with the conventional FPSC at water inlet flow rate of 15 lph increases the overall thermal efficiency up to 19.59% compared with conventional FPSC. The maximum increase in the percentage of efficiency with PCM‐1 from conventional FPSC for different cases of 15 lph‐09 kg is 16.34%, 15 lph‐14 kg is 19.59%, 30 lph‐09 kg is 14.57% and 30 lph‐14 kg is 18.45%. From the present study, it can be concluded that the overall efficiency of FPSC is increased with the use of 14 kg of PCM‐1 with conventional FPSC at the inlet water flow rate of 15 lph.

Experimental study of breathable and heterogeneous phase change material (B&H-PCM) wall for all-season thermal performance enhancement

Physical parameters of existing building walls are relatively stable, making it difficult to meet the thermal requirements under different seasons. In this study, phase change materials (PCMs) with different thermal conductivities and melting points were adopted to form a breathable heterogeneous phase change material (B&H-PCM) wall to achieve the year-round heating and cooling load reduction. The effects of operation parameters on B&H-PCM and ventilated block (VB) wall were experimentally analyzed. As the hot air inlet temperature rose from 30 to 80 °C in winter, the heat storage capacity and liquefaction ratio continuously increased. The PCM heat storage rate was maximized at 50 °C with 26.7 %, and the liquefaction ratio of internal PCM was 100 % at 60 °C. As the air inlet velocity went up in winter/summer, the heat storage/dissipation capacity increased and the heat storage/dissipation rate changed oppositely. The maximum heat storage rate was 36 % at 0.5 m/s in winter, and the maximum heat dissipation rate was 58.7 % at 3 m/s in summer. The external/internal heat capacity and thermal resistance of B&H-PCM wall were 5.9/7.2 and 1.1/0.8 times of VB wall respectively, indicating that B&H-PCM wall had a better heat storage and resistance capacity both in winter and summer.

Analysis of thermal characteristics and thermal storage performance of energy-saving phase change thermal storage materials in buildings

In order to explore the thermal characteristics and thermal storage performance analysis of energy-saving phase change heat storage materials in buildings, taking the common exterior wall insulation composite wall structure in southwestern China as an example, the influence of insulation board structure thickness design on the total cost of residential air conditioning energy consumption and insulation board cost is studied, thus clarifying the concept and calculation origin of economic insulation thickness. The experimental results show that by drawing mathematical functions of energy consumption cost, total cost, and insulation material cost in the same 2-D coordinate, it is intuitively demonstrated that the minimization of total cost can be ensured when the insulation thickness is in an economic state, and the specific economic thickness can be accurately calculated through example data. Therefore, specific measures for improving external wall insulation from refined insulation structure design are proposed. It has been proven that the design of the exterior wall insulation layer structure is an important way to improve the overall energy-saving benefits of building exterior wall insulation.

Thermal performance analysis and thermal environment creates effect of a novel solar hot-air phase change bed

Comprehensive heating provides a comfortable indoor but consumes significant energy. Temporal-spatial partitioned heating can meet differentiated thermal demands while reducing energy consumption. A novel solar hot-air phase change bed heating system has been proposed for achieving temporal-spatial partitioned heating. Theoretical analysis models have been established to study the heat transfer process of the hot-air phase change heating bed, and numerical simulations have been conducted to analyze its thermal performance and creation of a comfortable environment. The results demonstrate that at the end of the heat storage, the bed board temperature increased by 1.5 °C for every 5 °C increase in the wind temperature. The maximum temperature difference of the bed board reached 6.1 °C under three different wind speed schemes. During heat release, the bed board heat flux was affected by the phase change material heat storage difference, and the maximum temperature difference of the bed board reached 4.3 °C ∼ 6.7 °C under different schemes. After the first cycle, both indoor and bed board temperature were higher than the initial values. During the daytime, there was excessive heat indoors, and the maximum environmental temperature exceeded the comfortable range by 8.7 °C. At night, the bed was covered with a high-temperature layer, and the bed surface temperature was uniformly distributed, remaining in the thermal comfort zone for 3.8 h to 5.1 h. The research results provide a basis and guidance for utilizing solar hot-air phase change beds to improve differentiated thermal demands.

Optimization research on battery thermal management system based on PCM and mini-channel cooling plates

A phase change materials (PCM) coupled mini-channel cooling plates model was established for the optimization of the battery thermal management system (BTMS). Specific cooling strategies with different discharge rates of the battery were discussed. For a discharge rate of under 2C, using PCM can meet the heat dissipation needs. Particularly, for a discharge rate below 1.2C, external cooling was not necessary. For a discharge rate above 2C, active cooling should be added to compensate for the lack of heat storage of PCM. In the research of optimization structure, it was found that the scheme of four cooling plates and each cooling plate with two mini-channels was the most ideal in this research, which not only reduced the battery temperature efficiently but also maintained a good temperature uniformity of the battery. For the optimization parameters, the effect of the ethylene glycol solution temperature, ethylene glycol solution volume fraction and the start-up time of active cooling on the maximum temperature of the battery and the melting fraction of PCM were discussed. After the multi-factor parameters optimization by Response Surface Methodology, three optimization schemes were put forward, which could reduce the driving power consumption by 35% – 40%. The research could provide valuable information support and optimization suggestions for the design of BTMS.

Energy storage investigation of solar pond integrated with PCM and nanoparticles during winter season in Chennai

Solar energy is a highly regarded renewable energy sources that are attracting substantial attention owing to its potential to alleviate climate change and provide sustainable energy. Solar ponds are one approach to collect solar energy by capturing and storing thermal energy inside a pond. However, the effectiveness of solar ponds has been hampered by reasons such as heat loss, evaporation, and inadequate heat transmission. Researchers have investigated the use of phase change materials (PCMs) and nano-additives to improve the performance of solar ponds in order to overcome these issues.Large amounts of heat can be stored and released by substances known as phase change materials as they transition between two states. By adding PCMs into solar ponds, heat may be retained throughout the day and released at night when the sun is not shining. Alternatively, nano-additives have the potential to enhance the efficiency of a solar pond by improving the heat transfer properties of the fluid present in it.To measure the thermal efficiency of the solar pond, multiple phases of an experiment have been undertaken to establish the degree of thermal efficiency. During the experiment, various parameters were employed to measure and track the temperature variations in the lower convective zone (LCZ) of the solar pond. These measurements were recorded on a daily, weekly, and hourly basis, taking into account the depth of the solar pond as a determining factor. There was also an experiment carried out using micro PCMs and paraffin waxes (PCMs) that were combined into the matrix. In this study, nanoparticles with high thermal conductivity, such as carbon nanotubes (CNTs), and hybrid nanoparticles, such as AgTiO2, were utilized.The solar pond without phase change material (PCM) had an average temperature of 45 °C in the lower convective zone (LCZ). When PCM was added to the solar pond, the maximum temperature in the LCZ increased by 2 °C compared to the previous 24 h. Furthermore, when carbon nanotube (CNT) nanoparticles were incorporated into the solar pond with PCM at the base, the temperature was observed to be 1.3 °C higher compared to a typical solar pond that only used PCM for heat storage. In another scenario, the solar pond with PCM and a combination of CNT and AgTiO2 nanoparticles had an average temperature of 52.5 °C in the LCZ during the first week of observation.

Research on performance of radiant floor heating system based on heat storage

With the development of the economy, improving energy efficiency and saving energy have become important issues that need to be addressed. In terms of building energy efficiency, combining phase change heat storage material with floor radiation heating is an effective way to improve energy utilization efficiency. In this paper, a composite phase change heat storage material used in radiant floor heating was introduced. Based on the selected materials, experiments on floor radiation heating system based on heat storage in different environments during the heating season were conducted. The results showed that thermal conductivity of composite phase change heat storage material increased by a maximum of 97.2%, and the maximum heat release time can be obtained 6 h. By using this radiant floor heating system, a balance between heating comfort and economy has been achieved, so this system will have a good applied foreground.

Experimental Study of Simultaneous Charging and Discharging Process in Thermocline Phase Change Heat Storage System Based on Solar Energy

As a renewable energy power generation method, concentrating solar power generation has a broad application prospect. Weather and fluctuation significantly affect the output power of concentrating solar power generation. A heat storage system can stabilize this fluctuation and generate continuous and stable power. Therefore, the research on heat storage systems is of great significance to the development of concentrating solar power generation. This paper mainly studies the operating characteristics of the heat storage system based on solar energy in simultaneous charging, the influence in the change in solar radiation intensity on the charging power and the discharging outlet temperature, and the feasibility of the heat storage tank as an inertial link to stabilize the fluctuation in solar energy and the discharging outlet temperature. In this study, an experimental system for heat storage was established, in which solar energy was used as the heat source, water was used as the heat transfer fluid, and paraffin was used as the phase change heat storage material. When the initial temperature is 50 °C and the charging flow rate is maintained at 0.7 m3/h, at the same time the discharging flow rate is 0.1 m3/h, 0.3 m3/h, and 0.5 m3/h, respectively. The results show that when the solar radiation intensity is lower than 548 W/m2, the curve of heat storage power is almost parallel to the curve of solar radiation intensity; when the solar radiation intensity is lower than 535 W/m2, the moving direction of the thermocline will change; the average discharging outlet temperature in each case is higher than the phase change temperature of the phase change material and this system can continuously supply hot water at more than 69 °C for more than 3 h 32 min; and increasing the discharging flow rate will increase the whole charging and discharging time, thicken the thermocline, and disturb the temperature field in the tank. The experimental analysis will be conducive to profoundly understanding the operation characteristics of the thermocline heat storage tank under the solar heat source and has reference value for the subsequent design of a more efficient heat storage system.

Heat transfer and storage characteristics of a hexagonal close structured packed-bed thermal storage system with molten salt phase change materials

The phase change material (PCM) spheres using 316SS as the ball shell and solar salt (NaNO3-KNO3, 60–40 wt%) as the PCM were arranged in an orderly pebble-bed arrangement. The charging performance, energy and exergy of PCM spheres in the packed ball thermal energy storage system (PBTES) were investigated using CFD simulation in order to solve the problem of heat storage at 300 °C–500 °C. The results show that the total melting time of PCM spheres slightly decreases from 1455 s to 1319 s with the inlet velocity increasing. The average heat storage efficiency of PCM spheres and PBTES are improved with the inlet temperature increasing. When the inlet flow rate increases from 0.01 m/s to 0.10 m/s, the energy efficiency of PBTES increases approximately 5.06 times, and the exergy efficiency increases from 17.91 % to 99.55 %. However the heat energy storage and exergy efficiency of PCM spheres are not affected by the inlet velocity changing. The energy efficiency of PBTES increases about 2.09 times, and the exergy efficiency increases from 30.29 % to 70.93 % with the inlet temperature grows from 300 °C to 500 °C. It provides an idea for the design of the medium-high temperature and high-efficiency molten salt PCM heat storage system.

Investigation of high-enthalpy organic phase-change materials for heat storage and thermal management

The growing interest in phase-change materials (PCM) is related to their possible role in thermal energy storage and thermal management. The choice of materials depends strongly on the required temperature range, whereas the latent heat of solid–liquid phase transition has to be as high as possible. Among other organic PCM, sugar alcohols have gained some attention due to their availability and certain advantageous properties. However, the thermal processes in these materials still require investigation. In the present work, we focused on the materials with solid–liquid phase change within 80 °C–100 °C. A comprehensive literature survey was conducted to elucidate the available sugar alcohols relevant to this range. It was found that the use of pure materials of this type is not very practical, because of their scarcity in the required range and their specific features, like difficulties with crystallization and solidification. On the other hand, based on the literature, we have discerned three eutectic mixtures of erythritol with other organic materials, namely, erythritol–xylitol, erythritol–urea and erythritol– trimethylolethane (TME). In all those cases, it is remarkable that while the components commonly have rather high melting temperatures, the eutectic mixtures had the phase transitions in the required range. Still, each of these mixtures has its own peculiar features, especially at cooling and solidification. An extensive experimental study was performed to provide detailed visualization of these major processes. The results revealed the melting temperature and latent heat of the mixtures to be: 84 °C and 190 J g−1 for erythritol–xylitol, 82 °C and 227 J g−1 for erythritol–urea. Erythritol–TME has two phase transitions at 82 °C and 97 °C, with total latent heat of 198 J g−1. Based on the present findings, the erythritol–urea mixture is the best PCM candidate for the melting range within 80 °C–100 °C.

Liquid-structure coupled simulation study on impacts of HTF temperature on discharge and mechanics performances of PCM heat storage system

This paper presents an influence estimate of typical factors on heat release and mechanics performances of the latent thermal energy storage (LTES) tank with phase change material (PCM) by using the liquid-structure coupled calculation approach. Two heat transfer material temperatures are evaluated, including the cold molten salt temperature (MST) and hot MST. The results demonstrate that when the cold MST decreases from 610 K to 530 K, the HR duration will be reduced, the total heat release quantity (HRQ) increases, the average heat release power (HRP) increases from 3.22 MW to 7.98 MW, but the peak maximum mechanical stress (MMS) of the tank wall also rises. As the hot MST rises from 730 K to 810 K, the HRQ increases obviously, the average HRP increases from 5.09 MW to 6.63 MW, but the peak MMS also increases to 159.6 MPa. Hence, to improve the HR performance of the LTES system, under the condition of ensuring the structural safety of the LTES system, the hot MST should appropriately be increased, and the cold MST should be decreased properly.

Experimental Research on a Solar Energy Phase Change Heat Storage Heating System Applied in the Rural Area

Thermal energy storage technology can effectively promote the clean heating policy in northern China. Therefore, phase-change heat storage heating technology has been widely studied, both theoretically and experimentally, but there is still a lack of engineering application research. According to the characteristics of heating load in northern rural areas, a kind of solar heating system using phase-change materials (PCMs) for heat storage is proposed. Furthermore, a farmhouse is used to demonstrate the practical engineering applications of the heating system. The heating system consists of the phase-change heat storage device (PCHSD), solar thermal panels, and a floor radiant heating terminal, which can realize the effective utilization of solar energy. Considering solar power generation capacity, heating load characteristics of farm buildings, and the local electricity price model, four potential operation modes of the heating system are established. Then, the corresponding control strategies are proposed for the four operating modes. The actual operation data of the heating system under different operating modes were collected continuously, and the application effect of the heating system was evaluated from the aspects of thermal efficiency of the device, the renewable energy efficiency, thermal comfort level, and economy. The experimental results show that: (1) The thermal efficiency of the device is mainly affected by the heating load, which can reach more than 80% during the test period; (2) the renewable energy efficiency of the system is positively correlated with the solar radiation intensity, and the maximum can reach 100% when the solar radiation is sufficient; (3) the system maintains excellent thermal comfort in all conditions, with the average and the highest thermal comfort time accounting for 80% and 100%, respectively; (4) compared with the average level of existing clean heating technology, the annual operating cost of the system is reduced by 27.3%, and the economy is significant. The results show that the system achieves effective performance during the test period.

Fabrication of Biobased Advanced Phase Change Material and Multifunctional Composites for Efficient Thermal Management

In this study, an advanced phase change material (PCM) was fabricated to combine the properties of a biobased thermoplastic polymer and the heat storage of PCM to overcome the limitations of the existing PCM composites. The novel PCM of erythritol (ET)-grafted polylactic acid (PLA) (ETPLA) was prepared by the in situ polymerization of ET and PLA. The thermally conductive ETPLA composites were fabricated by injection molding using a hybrid filler system of oxidized carbon fiber (CF-OH) and aluminum nitride (AlN), which showed a high through-plane thermal conductivity of 4.25 W/mK, a tensile strength of 16.4 MPa (1953% enhancement comparing pure ET), an elongation at break of 4.4% (189% enhancement comparing pure ET), and latent heat of 170.7 J/g. Thus, the ETPLA/CF-OH/AlN composites facilitate efficient thermal management to combine heat saving and heat dissipation through the large latent heat and high thermal conductivity. Thus, the fabricated PCM composites have potential applications in thermal management systems of next-generation electronic devices.

Long-term heat-storage materials based on λ-Ti3O5 for green transformation (GX).

Effective reuse of waste heat energy is an important energy savings issue for green transformation. In general, phase-change heat storage materials cannot store energy for a prolonged period. If a solid material could conserve the accumulated thermal energy and release it only on demand, then its heat-storage application potential is considerably widened. From this angle, in 2015, we proposed the concept of a long-term heat-storage material, in which latent heat is preserved until the material is triggered by an external stimulus. This feature article describes long-term heat-storage ceramics composed of lambda-trititanium-pentoxide (λ-Ti3O5) from their discovery to heat-storage properties and future applications.

Effect of Tube Bundle Arrangement on the Performance of PCM Heat Storage Units

The results of a comprehensive study on the charging and discharging of latent heat storage systems (LHSS) are presented. Multi-tube shell-and-tube units with variable layouts of tube bundles are examined. Two tube arrangements—in-line and staggered—are tested. A variable number of tubes and different tube positions in a bundle are investigated. Moreover, two pitch ratios are studied. Three commercially available substances are used as phase change materials (PCM). The results show that increasing the number of tubes reduces both the charging and discharging times. It is found that for a bundle of seven tubes with a pitch ratio s/d = 4.5, the in-line tube arrangement results in a shorter charging time, but the discharging time is shorter for a staggered tube arrangement.