Melting Temperature Of Phase Change Material Research Articles

Preparation and thermophysical properties of three-dimensional attapulgite based composite phase change materials

• Attapulgite based three-dimensional carriers were prepared via “grafting from” method. • Pore size of 3D network can be adjusted by chain length and functional groups of connecting molecule. • SA/TATP have excellent thermal property and thermal reliability. • Melting point and melting latent heat of SA/TATP decrease with the decrease of TATP pore size. • Higher grafting rate of the carrier results in the larger thermal energy storage capacity. Aiming to reveal the relationship between the thermophysical properties of shape-stabled phase change materials (PCMs) with the structure of its matrix, a series of stearic acid/three-dimensional attapulgite (SA/TATP) composite PCMs were fabricated by vacuum impregnation method using TATP as matrix, which prepared via “grafting from” method and employed attapulgite (ATP) as raw material, diphenylmethane diisocyanate (MDI) as modifying agent and amines as linking molecules. The structure of carriers, thermophysical properties of the composite PCMs were analyzed, and the relationship between the thermophysical properties of SA/TATP and characteristics of the carrier were also studied. The results indicated that the thermophysical properties of the composite PCMs were improved significantly due to the introduce of organic bonding agents and the formation of three-dimensional network in the matrix. The latent heat of SA/TATP can be up to 136.81 J/g without leakage, and the maximum thermal conductivity of SA/TATP is 0.4215 W/m•K. The melting temperature and melting latent heat of the composite PCMs degenerate with the decrease of the pore size of the carriers. The relationship between the melting phase transition temperature, melting latent heat of SA/TATP and pore size of TATP can be descripted by the Gibbs–Thomson equation. In addition, the melting enthalpy of SA/TATP is positively associated with the grafting rate of the carrier.

Improving the energy efficiency of passive PCM system using controlled natural ventilation

In recent years, the building sector has been responsible for continuous increase in energy consumption in the world. Space heating and cooling accounts for 34% of this energy consumption in buildings. In this context, using thermal energy storage (TES) can reduce energy consumption for space air conditioning. The use of phase change materials (PCM) as latent heat thermal energy storage (LHTES) system in the building envelope has been of great interest for passive cooling applications due to the high energy storage capacity of this technology. However, in order to utilize the full potential of a PCM, it needs to be fully charged at each cycle. Ventilation during the night is an effective method which can be used in PCM-enhanced office buildings with the aim of charging the PCM every required cycle. In the present study, PCM melting temperature of office building in various climate conditions was optimized using a simulation-based optimization and coupled with free cooling operation. Ventilation control strategies were used to improve the cooling energy performance of the PCM enhanced building integrated into envelopes. It was found that charging PCM with night ventilation, especially when using some specific control strategies of natural ventilation operated by external windows opening results in considerable cooling energy savings. The study was conducted for 15 different cities around the world. It was found that, in hot arid conditions, PCM passive cooling system was ineffective. Although, the energy savings were improved by coupling PCM and natural ventilation in these climate conditions. But the benefits were more or less similar to using natural ventilation only. On the other hand, in temperate condition, the effectiveness of PCM was increased from 3.32% to 25.62% by coupling a PCM passive system with night ventilation. It was further improved to 40% when using PCM with temperature-controlled ventilation. Moreover, it can be said that smart control of ventilation can lead to considerable energy savings.

Multi-objective optimization of cooling and heating loads in residential buildings integrated with phase change materials using the artificial neural network and genetic algorithm

Abstract In this paper, a multi-objective optimization was performed to achieve the minimum cooling and heating loads in a residential building integrated with phase change material (PCM). The methods applied to fulfill this objective were numerical modeling by EnergyPlus, Grouped Method of Data Handling (GMDH) type of Artificial Neural Network (ANN) and Non-Dominated Sorting Genetic Algorithm II (NSGA-II). In this study, design variables were melting temperature and thickness of PCM, thermal resistance of exterior walls, internal gain and infiltration rate. Additionally, objective functions included annual cooling and heating loads of the building that should be minimized. Therefore, first, EnergyPlus software was used to calculate the values of objective functions and to train the neural network. Afterward, the GMDH-type neural network was applied to derive polynomials computing the objective functions from input variables. Then, Pareto optimal points for objective functions were obtained through using these polynomials and NSGA-II multi-objective optimization. Finally, the optimum point was determined by a financial analysis. According to the obtained results, the thickness and melting temperature of the optimum PCM layer in the residential building in Tehran were equal to 0.032 m and 24.58°C, respectively.

Development of eco-sustainable plasters with thermal energy storage capability

In order to limit the energy demand of buildings, a possible strategy consists in the storage of thermal energy using phase change materials (PCMs). In this work, an innovative PCM-enhanced plaster, fully formulated by using materials coming from natural resources, was developed. The PCM (i.e., a biodegradable material from agricultural resources having a melting temperature of 23 °C) was shape-stabilized with a direct absorption method by using a proper combination of different inorganic powders, taking into account also the final cost of the product and the processability issues. The most important physical properties of the plaster were then investigated following the European standards and compared with those of a natural hydraulic lime commercial plaster. The optimized PCM-enhanced plaster could be classified as a lightweight plaster (LW class according to UNI EN 1015-10) with compressive strength CSI (UNI EN 1015-11) and water absorption class W2 (UNI EN 1015-18). Differential scanning calorimetry tests confirmed the thermal energy storage capability of the PCM-enhanced plaster, even though plaster processing operations slightly decreased the specific melting enthalpy of the PCM within the plaster. Moreover, small-scale simulations were performed through the monitoring of the inner temperature of an insulated box, in which a plaster layer was applied on the internal walls, during heating and cooling ramps. These tests confirmed the thermal energy storage capability of the newly developed plaster around the PCM melting temperature interval.

A Numerical Analysis of the Cooling Performance of a Hybrid Personal Cooling System (HPCS): Effects of Ambient Temperature and Relative Humidity.

Hybrid personal cooling systems (HPCS) incorporated with ventilation fans and phase change materials (PCMs) have shown its superior capability for mitigating workers’ heat strain while performing heavy labor work in hot environments. In a previous study, the effects of thermal resistance of insulation pads, and latent heat and melting temperature of PCMs on the HPCS’s thermal performance have been investigated. In addition to the aforementioned factors, environmental conditions, i.e., ambient temperature and relative humidity, also significantly affect the thermal performance of the HPCS. In this paper, a numerical parametric study was performed to investigate the effects of the environmental temperature and relative humidity (RH) on the thermal management of the HPCS. Five levels of air temperature under RH = 50% (i.e., 32, 34, 36, 38 and 40 °C) and four levels of environmental RH at two ambient temperatures of 36 and 40 °C were selected (i.e., RH = 30, 50, 70 and 90%) for the numerical analysis. Results show that high environmental temperatures could accelerate the PCM melting process and thereby weaken the cooling performance of HPCS. In the moderately hot environment (36 °C), HPCS presented good cooling performance with the maximum core temperature at around 37.5 °C during excise when the ambient RH ≤ 70%, whereas good cooling performance could be only seen under RH ≤ 50% in the extremely hot environment (40 °C). Thus, it may be concluded that the maximum environmental RH under which the HPCS exhibiting good cooling performance decreases with an increase in the environmental temperature.

Study on heat transfer performance of a solar double-slope PCM glazed roof with different physical parameters

The glazed roof has better lighting performance and is widely used in modern building design. However, its poorer heat insulation performance can decrease indoor thermal comfort. Therefore, the interlayer of insulating glazed roof is injected with phase change material (PCM) to improve the indoor thermal environment of building and reduce the energy consumption, while obtain sufficient indoor light. Based on enthalpy method, a numerical heat transfer model of double-slope PCM glazed roof was established and verified in this paper. The heat transfer performance of double-slope hollow glazed roof and double-slope PCM glazed roof were compared. Finally, the design of double-slope PCM glazed roof in hot summer and cold winter area was optimized by further studying the roof angle, phase change layer thickness, glazing layer thickness, the melting temperature and phase change latent heat of PCM. The results show that the suitable melting temperature is 26–30 °C under the typical climate of hot summer and cold winter in Wuhan. Increasing the thickness of phase change layer and glazing layer can improve the thermal insulation performance of the roof, but the former effect is more significant. Moreover, a smaller roof angle within a certain range can reduce the amount of solar radiation received by the roof, and a larger latent heat energy of PCM can absorb more solar radiation to improve the heat transfer performance of the roof.

Effect of phase change and ambient temperatures on the thermal performance of a solid-liquid phase change material based heat sinks

Abstract This paper reports the results of experimental and numerical investigations on the effect of phase change temperature and ambient temperature on the overall thermal performance of a composite phase change material(PCM) heat sink with embedded radial plate fins. The heat sinks are filled with different phase change materials, namely n-Eicosane, Docosane, and Tetracosane, which have phase change temperatures of 36, 44, and 52 oC respectively and with almost identical thermophysical properties. The enthalpy porosity formulation is adopted to numerically simulate, visualize the phase change process (melting and solidification) to complement the experimental results and also to quantify the energy apportioning rate in the PCM during the charging and discharging cycles for different heat inputs. The results make it evident that the heat sink with the highest phase change temperature PCM shows superiority in the charging cycle up to 68% over a low phase change temperature PCM at lower heat inputs. However, with an increase in the heat input, the effect of phase change temperature of the PCM on the charging cycle gradually vanishes. In the discharging cycle, the high phase change temperature PCM shows superiority up to 83% over a PCM with lower phase change temperature due to the high-temperature difference between the melting temperature of PCM and ambient. All things considered, the heat sink with a higher phase change temperature shows superiority up to 2.25 times over a PCM with a lower phase change temperature. Additionally, the effect of the ambient temperature on the overall thermal performance of the heat sink is studied. Experiments are conducted on heat sink filled with Tetracosane at ambient temperatures of 20, 24, and 28 oC. From the studies, it is seen that the increase in ambient temperature from 20 to 28 oC reduces the heat sink charging time up to 2.3 times while the discharging time of heat sink is increased up to 3.33 times in terms of reaching the same set-point temperature in the charging cycle and the same ambient temperature in the discharging cycle respectively.

Study of an autothermal-equilibrium metal hydride reactor by reaction heat recovery as hydrogen source for the application of fuel cell power system

This paper proposes a novel autothermal-equilibrium metal hydride reactor as the hydrogen source for the fuel cell power system, which employs phase change material (PCM) to recycle the hydrogen storage heat. A three-dimensional model of the metal hydride reactor coupled with a salt hydrate PCM for heat recovery is developed. Based on the model, the effects of key operating and design parameters on the reactor are investigated for performance optimization, including operating pressure, melting temperature, latent heat and thermal conductivity of PCM. Through the parametric analysis, it is found that increasing the operating pressure is beneficial to accelerate the absorption reaction. The average reaction fraction at 2400 s is increased by 24% with the pressure increasing from 6 to 10 bar. The moderate melting temperature and the thermal conductivity of the PCM that is comparable to that of metal hydride bed contribute to the improvement of hydrogen storage efficiency. Using this kind of hydrogen source reactor in a fuel cell power system, stable hydrogen storage efficiency of approximately 60% in the experiment is presented. In addition, no obvious performance deterioration of the power system occurs after ten cycles.

Performance comparison of two eutectic solder based latent heat storage systems during discharging

Latent heat storage systems consisting of phase change materials (PCMs) offer the advantage of a large thermal energy storage density as compared to sensible heat storage systems. Most recent work has focussed on organic and inorganic PCMs which have problems of subcooling and phase segregation. Metallic PCMs are a recent innovation for medium to high temperature applications due to their high thermal conductivities, high volumetric storage capacities and their low degrees of sub-cooling during the release of latent heat. For medium temperature applications like cooking of food, very limited work has been done on metallic PCMs for energy storage. Solder based PCMs have rarely been investigated for medium temperature applications thus it is necessary to carry out an experimental study on the use of a solder as PCM candidate. No work has ever been reported using the eutectic solder (Sn63/Pb37) as a PCM. Its use is justified since it is low cost and locally manufactured solder worldwide. Another recent innovation is cascaded thermal energy storage (TES), whereby two PCMs with different melting temperatures are used in a single storage tank to improve the efficiency of energy storage. No work has also appeared in recent literature involving metallic solders in cascaded systems. In a bid to investigate the suitability of the eutectic solder as a PCM for medium temperature applications, two eutectic solder (Sn63/Pb37) based systems are experimentally evaluated during discharging cycles. The first system is a single PCM system composed of a packed bed of spherically encapsulated eutectic solder capsules. The other system is a two PCM cascaded system comprising of eutectic solder spherical capsules at the top and erythritol spherical capsules at the bottom in a storage ratio of 50 %: 50 %. Discharging experiments are carried with three different discharging flow-rates to investigate the effect of the flow-rate on the thermal performance. The three discharging flow-rates used are 4 ml/s, 6 ml/s and 8 ml/s. For both storage systems, an increase in the discharging flow-rate increases the peak discharging energy and exergy rates. For both storage systems, an increase in the discharging flow-rate increases the peak discharging energy and exergy rates. The single PCM system shows higher energy and exergy rates for most of the discharging duration compared to the cascaded system. An increase in the flow-rate increases the peak energy and exergy discharging rates for the single PCM and the cascaded PCM storage systems. The single PCM system out-performed the cascaded system during the discharging tests possibly due to the lower melting temperature and lower thermal conductivity of the bottom PCM (erythritol) in the cascaded system. However, for the higher flow-rates (6 ml/s, 8 ml/s), the cascaded system shows a slightly better or comparable performance at the start and at end of discharging.

ENERGY AND FEASIBILITY ANALYSIS OF APPLYING BIO-BASED PHASE CHANGE MATERIALS TO BUILDINGS IN EAST ASIA

ABSTRACT The application of phase change materials (PCMs) in building envelopes can help promote energy efficiency due to its high heat capacity. Our study aimed to provide energy and economic insights for deploying PCM to buildings in eight different regions of East Asia through a series of energy and economic analysis using computer modelling and simulations. The static payback period (SPP) and dynamic payback (DPP) methods were used to evaluate the economic feasibility of applying a PCM at different melting phase temperatures (20°C, 23°C, 25°C, 27°C and 29°C). Results show that the proper choice of a PCM melting temperature is a key factor to improve the performance of the PCM applied to buildings. A melting phase temperature of 29°C achieved the highest economic feasibility in Seoul, Tokyo; Pyongyang; Beijing; and Ulaanbaatar and a melting temperature of 23°C in Hong Kong had the highest economic feasibility. Overall, the combined economic and energy analysis presented in this study can play an important role in improving the energy and economic feasibility of PCM in buildings.

Fabrication of a novel temperature sensitive phase change system based on ZnO@PNIPAM core-satellites and 1-tetradecanol as gatekeeper

Phase change materials (PCMs) with large latent heat capacity and efficient thermal response have great potential for thermal management in various applications. Uniform phase change composite beads were fabricated based on phase change medium 1-tetradecanol (TD) as gatekeeper and core-satellites zinc oxide @ poly(N-isopropyl acrylamide) (ZnO@PNIPAM) using a simple injection device at 50 ℃. It was demonstrated that the ZnO@PNIPAM/TD PCM system possessed a high latent heat value of 230 J g−1. The ZnO nanospheres acted as the core and the phase change material TD was the shell. Furthermore, the satellites PNIPAM nanoparticles acted as a reservoir. The enthalpy values of ZnO@PNIPAM/TD kept high (233.04 J g−1 and 229.41 J g−1) compared with pure TD. The suitable melting temperature of the temperature sensitive PCM is about 38.5℃ close to the human body temperature. The unique core-satellites structure of the system can store small molecules, which not only has its own excellent characteristics but also can give the system rich functionality.

Multivariable optimization of PCM-enhanced radiant floor of a highly glazed study room in cold climates

Hydronic radiant floor systems enhanced with phase change materials (PCMs) could achieve significant energy savings while improving the thermal comfort of occupants in lightweight buildings. However, successful integration of PCMs typically requires comprehensive numerical analysis due to their complex nature. This study aims to investigate two scenarios for optimal integration of PCM into the hydronic floor heating system of a highly glazed study room exposed to cold weather conditions. Scenario 1 includes optimization of two design variables, including PCM melting temperature and thickness. Scenario 2 encompasses optimization of seven design variables, including PCM melting temperature and thickness, insulation thickness and thermal conductivity, floor thickness, thermal conductivity, and solar absorbance. Both scenarios are optimized for the six supply water temperatures, ranging from 35.6 °C to 45.6 °C with a 2 °C step. The overall findings suggest that successful integration of PCMs into the hydronic heating system requires a comprehensive solution tailored for the specific application. Thus, scenario 1 and scenario 2 achieved the highest total energy savings of approximately 17.7% and 20.5% for the lowest supply water temperature of 35.6 °C, whereas under both scenarios the supply water temperature of 43.6 °C provided the best thermal comfort. Furthermore, scenario 1 achieved more substantial cooling energy savings over the wider temperature range (41.6-35.6 °C) compared to scenario 2 (39.6-35.6 °C). The findings also suggest that the addition of the insulation layer in the second scenario reduced the thickness of PCM and payback period for more than 70% compared to the first scenario.

PCM integrated to external building walls: An optimization study on maximum activation of latent heat

Integration of the phase change materials (PCM) into the external building walls is an efficient method for reduction of energy consumption and regulation of energy demands due to increasing thermal inertia of the walls. This study aims to reveal the contribution of latent heat to the thermal performance of the wall and to determine the location, thickness and melting temperature of PCM for the maximum exploitation of latent heat for different climatic conditions. A comparative study is carried out for the wall coupled with PCM and the wall with Phase Stabilized PCM (PSM) to reveal the improvement provided by the latent heat. The influence of location, fusion temperature and layer thickness of PCM on energy saving, decrement factor and time lag was examined. The annually optimized PCM fusion temperature and layer thickness which utilizes the latent heat at maximum level considering both heating and cooling loads are determined for three cities of Turkey. The computed results show that the monthly optimized PCM melting temperature and PCM layer thickness vary from 6 to 34 °C, from 1 to 20 mm depending on climatic conditions. It was concluded that an optimization study should be conducted in order to prevent PCM behaves like PSM.

A parametric study of phase change material characteristics when coupled with thermal insulation for different Australian climatic zones

The development of lightweight structures in the building industry has made the usage of thermal mass more difficult. Hence, phase change materials (PCMs) due to their latent heat storage are a favourable alternative which can be coupled with lightweight constructions. This paper explores the relationship between PCM thicknesses, PCM transition temperatures, insulation, building orientations and energy consumption. For this exploration, a full-scale calorimeter was utilized to validate a model; through numerical simulations, the model was then used for four different climates of Australia. It was found that for all the climates, increasing PCM thicknesses ameliorates the overall energy saving, and the saving proportion is dependent on both the climate conditions and envelope thermal resistance (R-values). For low R-value opaque envelopes, the optimal transitional temperature is contingent upon the PCM thicknesses. Moreover, using insulation in sub-tropical, hot-dry, and cold climates enhances PCM efficiency and stabilizes the optimal PCM melting temperature for differing thicknesses; also, augmenting insulation thickness lowers the importance of PCM thicknesses. However, the use of well-insulated envelopes in tropical climates has an adverse impact on PCM efficacy due to the hindrance of night-time energy release. Finally, the PCM energy saving fully depends upon the building orientation, while the PCM optimum temperature is not conditional on this factor.

Numerical investigation of phase change materials (PCM) optimal melting properties and position in building elements under diverse conditions

The increasing popularity of phase change materials (PCM)-enhanced building products has initiated a scientific discussion concerning specific aspects of their applicability. This study aspires to provide justified answers to the research question of the optimal position of PCM into the building envelope, with emphasis on vernacular buildings, as well as to enlighten aspects of the appropriate melting behaviour of PCM materials. Parameters directly affecting the operation of the PCMs, namely their position within the building envelope, the external environmental conditions and the prevailing interior environmental conditions, have been investigated under diverse climatic conditions with the use of finite element method (FEM). The probability density function (PDF) of the temperature distribution at specific locations within the building envelope, at which realistically PCM layers can exist were derived, revealing the fact that in the case of non-conditioned indoor spaces, the PCM layer should actually be incorporated into the inner surface of the wall. The analysis was also conducted for different orientations and locations of the European continent, providing sufficient answers concerning the appropriate melting temperature of PCMs in the case of non-conditioned buildings. The environmental assessment of building envelopes incorporating PCM building products has also been examined, delivering the energy pay-back time of the PCM-enhanced building products.

Optimization and sensitivity analysis of design parameters for a ventilation system using phase change materials

Ventilation system with thermal energy storage (TES) using phase change materials (PCMs) can be employed to save energy in buildings, which stores outdoor coldness in the PCMs at night and releases this energy to cool down the fresh ventilation air during the daytime. However, its performance depends on the design parameters. This paper presents a detailed parametric analysis to address the separate effect of each design parameter on the cooling energy supply and net electricity saving of the TES system against a conventional ventilation system for the climate of Beijing, by using a computational heat transfer model. A genetic algorithm (GA) is used to optimize the design parameters for maximizing the net electricity saving in four cities of China. The decision variables are related to the PCM melting temperature, PCM slab thickness and cold charging airflow rate. The results show that the saving-optimal solution is not unique and depends on the climate. GA optimization increases the net electricity saving by 10%–54%, with a mean value of 31%. Sensitivity analysis of net electricity saving to the above three variables is carried out. Likewise, the sensitivity of each variable is not unique and depends on the climate.

Heat transfer reduction in buildings by embedding phase change material in multi-layer walls: Effects of repositioning, thermophysical properties and thickness of PCM

Passive latent heat thermal energy storage approach incorporating phase change materials (PCM) is a brilliant technique to tackle high energy consumption issue in buildings. This paper investigated the thermal performance of the conventional walls of buildings in Isfahan, Iran with the inclusion of thirteen different phase change materials. The studied base wall was composed of plaster (2 cm), clay brick (15 cm), and cement (3 cm). The effect of PCM position inside the wall on the heat transfer was assessed in two scenarios, namely: close to the interior and close to exterior. The nonlinear governing equations were solved using the finite volume method. The results show that the performance of PCM-based wall is strongly influenced by the thermal conductivity, phase-change enthalpy and melting temperature of PCM. A PCM can more efficiently reduce the heat transfer to the interior space in case it has a lower thermal conductivity, has a higher latent heat of phase-change, and its phase-change temperature is closer to the room temperature. Moreover, the thermal conductivity has priority over other PCM thermophysical properties. The lower PCM thermal conductivity leads to transfer the lower amount of heat to the interior space. A two-fold increase in the thickness of the PCM leads to less than a twofold reduction in the heat transfer. Among the studied PCMs, the heat transfer reduction by Enerciel 22 was within the range 15.6–47.6%, while this range was 2–7.8% for CaCl2.6H2O.

Numerical Analysis on a Latent Thermal Energy Storage System with Phase Change Materials and Aluminum Foam

A latent heat thermal energy storage system with phase change material (PCM) is numerically studied. To enhance the heat transfer inside the system, a highly conductive metal foam is employed with ceramic nanoparticles. The latter method of enhancement leads to a new class of material called Nano-PCM. The system under investigation is a 70-L tank filled up with pure PCM or Nano-PCM and several pipes are situated where the heat transfer fluid (HTF) flows. The pipe surfaces are assumed at constant temperature above the PCM melting temperature to simulate the heat transfer from the HTF. The enthalpy-porosity theory is applied to simulate the PCM phase change, while the porous media formulation is assumed to describe the metal foam behavior. The nano-PCM is modeled with single-phase model where the properties are the weighted-average between the fluid base and the nanoparticles. The simulations are accomplished for charging-discharging process at different porosities and nanoparticle concentration. The results are given in term of average melting fraction evolution, average temperature as function of time, average stored energy. The metal foam significantly improves the heat transfer between PCM and HTF respect to the addition of nanoparticles, reducing the charging and discharging time more than one order of magnitude.

Examining the effects of microencapsulated phase change materials on early-age temperature evolutions in realistic pavement geometries

This study examines experimentally and numerically the effects of microencapsulated phase change material (PCM) additions on temperature rise and cool-down rate, and the associated impact on reducing the risk of thermal cracking in concrete pavements. Specimens representative of a realistic pavement geometry were exposed to diurnal temperature cycling at early ages while internal temperature evolutions were monitored. In spite of the fact that the lower thermal conductivity of the PCM inhibited heat dissipation, the results showed the presence of PCMs can reduce considerably the temperature rise and cool-down rate in the first 24 h following placement provided the PCM melting temperature is chosen suitably. A transient one-dimensional thermal model of a pavement section suitably captured experimental temperature evolutions and thereby offers the ability to inform the design of concrete pavements containing PCMs that feature early-age thermal cracking resistance.

Assessment of latent heat thermal storage systems operating with multiple phase change materials

Abstract Latent heat thermal storage (LHTS) systems employing phase change materials (PCMs) offer several advantages compared to sensible heat storage units. However, they exhibit an inherent poor thermal performance owing to poor heat transfer, poor thermal conductivity of PCMs, and so on. Methods such as replacing single PCMs with multiple PCMs, addition of fins, micro/macro/nano-encapsulated composite PCMs and dispersion of high conductivity particles to PCMs have been suggested and studied in the past by different authors as a means for performance enhancement of LHTS systems. While extensive literature is available on the last three methods, studies on multiple PCMs are very limited. It is rather difficult at this stage to conclude on the benefits and merits/demerits of the method, given the limited data available in the open literature. Therefore, there is a need for consolidation and compilation of the existing literature to understand and assess the performance of LHTS units operating with multiple PCMs. An attempt is made in this paper to assess the performance of multiple PCM based thermal storage systems by carrying out a comprehensive review of available literature on the topic. Studies have evinced that single PCM units replaced with multiple PCMs offered superior performance with enhanced charging/discharging rates and better energy/exergy efficiencies. Also, past investigations reveal optimal melting temperatures of PCMs, optimal melting temperature difference between PCMs, optimal mass and so on to obtain an optimal performance of multiple PCM systems. Relevant published data were compared and discussed to understand the research trend over the years. Discussions were extended covering the challenges involved with multiple PCMs highlighting the scope for further research. An overall summary based on the survey has been presented for a concise understanding of key findings published in the open literature.