Low Supercooling Degree Research Articles

Thermal performance of a novel composite phase change material for solar-assisted air source heat pump packed bed thermal energy storage application

The thermal properties of the heat storage medium in the solar-assisted air source heat pump (SAASHP) systems must be aligned with the system’s heat generation temperature while satisfying the heat demand. In this study, a novel composite phase change material (CPCM) for efficient heat storage in SAASHP systems was developed. Our investigation revealed that the incorporation of 8 wt% KNO3, 1.5 wt% thickener, and 1.0 wt% Al2O3 nanoparticles into sodium acetate trihydrate resulted in the manifestation of desirable properties suitable for SAASHP systems. The compound exhibited a suitable melting point of 48.66 °C, high latent heat of 235.97 kJ/kg, low supercooling degree of 2.25 °C, and good thermal conductivity of 0.905 W/(m·K). Furthermore, the novel CPCM demonstrated exceptional thermal stability, with only an 8.64 % loss of latent heat after undergoing 200 cycles, while maintaining a supercooling degree within a range of 6 °C for each cycle. Moreover, molecular dynamics simulation results further indicated that the presence of KNO3 weakened the interaction between CH3COONa molecules and water molecules, leading to a reduction of the melting point. Additionally, numerical analysis revealed that the total heat storage capacity and exergy storage capacity of the packed bed thermal energy storage (PBTES) system filled with the novel CPCM are 358.8 MJ and 25.1 MJ, respectively. With an increase in the heating power of the SAASHP system from 10 kW to 30 kW, the cycle heat storage time of the PBTES system can decrease by 38.8 %, while an increase in the flow rate from 2 m3/h to 6 m3/h can reduce the time by 26.3 %. These findings have significant implications for the selection and composition design of thermal storage materials in SAASHP systems.

Comparison of UiO-66(Zr) and its derivate in shape stabilized phase change materials: Thermal storage performance and characterizations

In this study, UiO-66(Zr) and its derivative (UiO-66-C) are employed as supports to prepare shape stabilized PCM (U/SA-X and UC /SA-X) for resolving the melting leakage and poor thermal conductivity of stearic acid (SA). Thermal storage performance, including phase change enthalpy, supercooling degree, phase change temperature, thermal conductivity, and shape stability of U/SA-X and UC/SA-X, are compared. Preliminary characterization reveals that the physicochemical property evolution of the support impacts the thermal storage performance of SA. UiO-66 with microporous structure is unfavorable to enhance the shape stability of SA. U/SA-X exhibits low thermal storage efficiency and high supercooling degree owing to nanoconfinement and hydrogen bonding. By contrast, UiO-66-C possesses mesopores and graphitic structure that allows for a remarkable thermal storage performance of UC/SA-X. In detail, UC/SA-50 exhibits an ideal thermal storage performance, where the thermal conductivity (0.531 W/(m·K)) increases by 141 % in comparison to SA with a high phase change enthalpy of 93.6 J/g and low supercooling degree of 0.24 °C. It also shows satisfying thermal reliability that the thermal property of UC/SA-50 maintains stability even after 100 thermal cycles. In addition, the photothermal conversion efficiency of UC/SA-50 is up to 83.06 %.

Incorporated surfaces and confined spaces of Na2HPO4·12H2O–Layered vermiculite nanosheets for phase change materials with enhanced thermal properties

The phase change process of hydrated salts with a large latent heat and non-flammable characteristics is a promising route for achieving energy-efficient devices. To improve the reliability of the inorganic phase change material (PCM) system, excellent heat storage capacity, low supercooling degree, and good stability of hydrated salts are required. In this study, novel Na2HPO4·12H2O (DHPD)–vermiculite nanosheet (VMTNS) composite PCMs (CPCMs) possessing both surfaces and confined spaces were theoretically designed and synthesized. Incorporating the environmentally friendly VMTNSs, a new type of nano-reinforced fillers with multiple active sites, into DHPD hydrated salt results in excellent crystallization, great diffusion ability (33.277 × 10−11 m2/s), a low supercooling degree (0.8 °C), a high latent heat of melting (260.7 J/g), and great thermal stability of CPCMs. The DHPD arrangement both in the confined spaces and on the surfaces of the VMTNSs was simulated via molecular dynamics calculations. It was found that the adsorption energy of DHPD in the confined spaces of the VMTNSs and on their surfaces is –5.991 and –5.543 eV, respectively. This study provides an innovative method to construct novel CPCMs for efficient energy storage.

Influence of manganese alloying on the structure and properties of electrospark coatings of EP741NP heat-resistant nickel LPBF alloy

The paper investigates the impact of Mn content (Mn = 0; 0.5; 0.6; 1; 1.5 at.%) in the composition of the electrodes of the Al–Ca–Mn system on the structure and properties of electrospark coatings formed on LPBF substrates made of EP741NP alloy. It was found that the highest weight gain of the substrate (5.8·10–4 g) was recorded when the Al–7%Ca–1%Mn electrode with a low degree of supercooling of the melt (Δt = 5 °C) was subject to electrospark treatment (EST). EST with this electrode with a fine eutectic structure enables the formation of coatings with minimal surface roughness (Ra = 3.51±0.14 μm). The nanocrystalline structure of the coatings was confirmed by transmission electron microscopy, including HRTEM. Comparative tribological tests revealed that the coating with maximum hardness (10.7±0.8 GPa) formed during EST with an electrode containing 1.5 at.% Mn had the minimal wear rate (1.86 ·10–5 mm3/(N· m)). We proved that EST with Al–Ca–Mn electrodes enables to reduce the specific weight gain of the LPBF EP741NP alloy during isothermal (t = 1000 °C) curing in air due to in situ formation of a complex thermal barrier layer consisting of oxides (α-Al2O3, CaMoO4) and intermetallides (γ ′-Ni3Al and β-NiAl). We determined the concentration limit of Mn (1.0 at.%) in the electrode, at which the barrier layer retains its integrity and functionality.

Adjustment of phase change temperature using KCl to develop composite phase change materials based on super absorbent polymer as carrier for use in building energy conservation

In the present work, a Na2HPO4·12H2O–KCl/SAP composite phase change material (CPCM) adapted to the comfortable indoor temperature of the human body has been successfully prepared. The CPCM was developed by physical mixing of Na2HPO4·12H2O (DSP) as the main PCM, KCl as temperature regulator and super absorbent polymer as carrier. In addition, the CPCM was characterized by various techniques, and its thermal properties were analyzed. The results showed that the phase change temperature (Tm) of DSP could be adjusted from 35.8 °C to 32.7 °C by KCl and the DSP-KCl mixture containing 4 % KCl had a high enthalpy value (241.5 kJ kg−1). The cooling curve test found that adding 0.75 % nano-α-Al2O3 as nucleating agent could greatly reduce the supercooling degree of DSP-KCl mixture to 3.39 °C. Adding 14 % SAP into the mixture can solve the leakage and reduce the supercooling degree and thermal conductivity. The resulting CPCM with 14 % SAP added had appropriate Tm (26.9 °C), high enthalpy value (153.5 kJ kg−1), low supercooling degree (1.34 °C) as well as thermal conductivity (0.3079 W K−1 m−1) and excellent thermal reliability. These results indicated that the CPCM was suitable for the field of building energy conservation.

Supercooling degree decrease of barium hydroxide octahydrate employing 3D porous silver foam as supporting material

Inorganic hydrated salts possess high latent heat of phase transition and are promising phase change materials (PCMs). However, the issues of supercooling, low thermal conductivity, susceptibility to leakage, and phase separation significantly impediment the practical applications of inorganic hydrated salts. In this study, it is proposed to decrease the inorganic hydrated salt supercooling degree by increasing the surface roughness of the porous material and to load the nucleating agent silver (Ag) onto polydopamine (PDA) modified melamine foam (MF) by electroless plating to obtain 3D porous Ag foams, which are then utilized as support materials. The results demonstrated that the 3D porous Ag foam compounded with barium hydroxide octahydrate (BHO) can ameliorate the shortcomings of leakage and reduce the supercooling degree in the cooling process. The composite not only exhibits high enthalpy of over 248.5 J/g and high thermal conductivity of 1.82 W·m−1·K−1 but also has a low supercooling degree of 0.21 ℃. Furthermore, the composites exhibited superior shape stability and thermal cycling stability. This study provides an effective method for reducing the supercooling degree of inorganic hydration salts.

Shape-stabilized phase change materials of barium hydroxide octahydrate based on Cu‐coated melamine foam

Hydrated salt phase change materials (PCMs) have the advantages of high energy storage density and low cost, and have great application prospects in the field of phase change energy storage. However, the problems of supercooling, phase separation and leakage of hydrated salt PCMs limit their further applications. In this work, we designed and fabricated Cu-coated melamine foam (MF)/barium hydroxide octahydrate (BHO) shape-stabilized phase change materials (SSPCMs) with low supercooling. MF was used as supporting material and Cu as a nucleating agent and thermal conductivity enhancer by loading it onto MF via electroless plating. BHO was then encapsulated into the MF@Cu skeleton through vacuum impregnation to obtain BHO@MF@Cu SSPCMs. The results demonstrated that BHO@MF@Cu SSPCMs not only present very low supercooling degree of 0.12 °C and high thermal energy capacity of 247 J/g, but maintained a latent heat of phase transition of 229.3 J/g with little change in enthalpy after 100 thermal cycles. Moreover, compared to BHO, SSPCMs exhibited high thermal conductivity of 1.687 W m−1 K−1, excellent shape stability, and thermal cycling stability. In summary, BHO@MF@Cu SSPCMs with low supercooling degree were prepared by electroless plating and vacuum impregnation in this study, which provides a new strategy to reduce the supercooling degree of hydrated salt PCMs.

A metal-based microencapsulated phase change material (MEPCM) with high thermal reliability and its performance regulation

An ideal microencapsulated phase change material (MEPCM) should have the characteristics of high thermal reliability, low supercooling degree and high thermal conductivity. Herein, we report a novel metal-based MEPCM with high thermal reliability based on “double-layer coating, sacrificial inner layer” method, solving the problem of MEPCM cracking caused by thermal expansion. Furthermore, synergistic regulation of supercooling and thermal conductivity was studied by loading nanoparticles into shell. The results showed that the supercooling degree was reduced by 81.8% when the nano-Co loading was 0.8%, which achieved the best supercooling suppression effect so far, and the properties kept stable after 200 thermal cycles. Furthermore, thermal performance of MEPCM loaded/unloaded with 0.8% Co was compared. The results demonstrated that the MEPCM loaded with 0.8% Co showed a 12.6% increase in thermal conductivity and a faster thermal response rate. This paper provides a novel strategy for the preparation and performance regulation of metal-based MEPCM.

Encapsulating an inorganic phase change material within emulsion-templated polymers: Thermal energy storage and release

Phase change materials (PCMs) based on hydrated salts are promising candidates for energy storage and release applications owing to their relatively high latent heats per volume, their high thermal conductivities, and their nonflammability. The use of these PCMs, however, is limited owing to incongruent melting, significant supercooling during crystallization, and irreversible phase transformations. PolyHIPEs, polymers templated within high internal phase emulsions (HIPEs), were proven to be effective at encapsulating aqueous solutions and organic liquids. Here, calcium chloride hexahydrate (CCHH) was successfully encapsulated within elastomeric, acrylate-based, emulsion-templated polymers by using free-radical polymerization within molten-salt-in-oil HIPEs. The effects of adding a nucleating agent to the internal phase to reduce supercooling and the effects of enhancing HIPE stability through modification of the external phase were investigated. The crosslinking and stabilization modifications made to enhance the original polyHIPE formulation successfully enhanced the encapsulation efficiency. The most promising system, 75% CCHH dispersed as relatively uniform internal phase droplets of 100–300 μm in diameter, exhibited melting and crystallization heats of ⁓120 J/g, a relatively low degree of supercooling, and negligible transformation to calcium chloride tetrahydrate. This work, demonstrating that molten salt hydrates can be successfully encapsulated within elastomeric, emulsion-templated monoliths, can be used as a blueprint for the encapsulation of other salt hydrates.

Hydrate salt/fumed silica shape-stabilized composite phase change material with adjustable phase change temperature for radiant floor heating system

Radiant floor heating system combined with hydrate salt phase change materials (PCMs) can obtain energy savings along with improving thermal comfort. However, the inappropriate phase change temperature and the leakage of PCM limit its further applications. Here, sodium acetate trihydrate (SAT)-potassium chloride (KCl)-urea composite phase change material (CPCM) was composited with fumed silica (SiO2) to prepare shape-stabilized CPCM (SSCPCM) with adjustable phase change temperature for use in floor radiant heating. The effects of the mass fraction of SiO2 on phase change properties, and shape-stabilized ability of SSCPCM were emphatically studied. Besides, the morphology, porous structure analysis and chemical compatibility and related thermal properties of SSCPCM were discussed detailedly. The results manifested that SiO2 could not only regulate the melting temperature of SAT-KCl-urea CPCM, but also stabilize CPCM into its porous structure with large surface area and high porosity. Meanwhile, SSCPCM with 30 wt% SiO2 exhibited a good shape stability, and melted at 40.85 °C with high latent heat of 132.6 J/g, low supercooling degree of 0.29 °C as well as good thermal stability and thermal reliability. The result comparison of two test rooms confirmed that phase change floor radiant heating system can effectively increase the duration of indoor thermal comfort. All good thermal properties of SSCPCM make it prospective potential in radiant floor heating system for building energy efficiency.

The microscopic contact morphology of ice crystal on substrate and its effect on heterogeneous nucleation/icing

As one of the long-standing crucial theoretical assumptions of the heterogeneous nucleation and substrate icing theory, the tiny shape of an ice tip on the substrate commands further detailed experimental observation. In this paper, the morphology and growth processes of ice on different near-thermal insulation surfaces at a low supercooling degree were observed by microscope. Experimental results show that the contact angles of the dendritic ice tip on the substrates are all obtuse under a lower supercooling degree, and decrease with temperature as a Sigmoid function. Moreover, the analysis of ice growth on different substrates reveals that the surface property can affect substrate icing by altering the ice tip; that is, as the ice contact angle increases, the radius will increase and the influence of the thermal conduction of substrate on the ice tip will decrease, ultimately leading to a slower growth rate. Significantly, heterogeneous nucleation experiments illustrate that the obtained ice contact angle is close to the ice nucleus contact angle. Consequently, compared with previous theories, the temperature-dependent ice contact angle could be used to accurately predict the nucleation rate and ice growth.

Phase change temperature adjustment of CH3COONa·3H2O to fabricate composite phase change material for radiant floor heating

Hydrated salts phase change materials (PCMs) have a great potential for use in floor radiant heating considering outstanding cost competitiveness and remarkable energy storage density. However, their inappropriate phase change temperatures and the limited methods for temperature adjustment have hindered their widespread applications. Herein, using the formation of non-eutectic mixture to realize phase change temperature adjustment, a novel composite PCM used in the floor radiant heating was developed based on sodium acetate trihydrate (SAT) as main PCM, glycine as temperature modifier and Na2HPO4·12H2O as nucleating agent. The temperature regulation mechanism was discussed and properties of the composite PCM were investigated. The results showed that glycine could regulate melting temperature of SAT from 48.34 to 58.38 °C, ascribing to the formation of hydrogen bond between them. Thereinto, the mixture containing 12% glycine melted at 48.62 °C with enthalpy of 258.5 J g−1, making it applicable to the floor radiant heating. With the addition of 0.5% Na2HPO4·12H2O, the crystallization behavior of the composite PCM was promoted with a low supercooling degree (3.62 °C). The composite PCM presented a melting temperature of 47.55 °C with enthalpy of 256.5 J g−1, good thermal stability and reliability, indicating that the material can be promisingly engineered into the floor radiant heating.

Synthesis of shape stabilized phase change material with high thermal conductivity via in situ N-doped carbon derived from chitin

Stearic acid (SA) is recognized as a promising phase change material (PCM). Nevertheless, poor thermal conductivity and leakage are great challenges for SA in practical application. To this end, the shape stabilized PCM (CTX/SA) with high thermal conductivity is fabricated by impregnating SA into the in situ N-doped carbon (CTX) derived from chitin (CH). The thermal storage performance of CTX/SA is investigated to acquire the optimal carbonization temperature for CTX. Meanwhile, characterizations of FTIR, XRD, SEM, and N2 isothermal adsorption-desorption are conducted to reveal the influence of CTX on thermal storage performance. The synthesized CT800/SA exhibits high thermal conductivity of 0.461 W/(m·K) and thermal storage efficiency of 92.84 % with a low supercooling degree of 1.06 °C. CT800/SA also has desirable thermal stability and reliability even after 200 repeated thermal cycles. Moreover, the photothermal conversion of CT800/SA is 74.12 %.

High-performance macro-encapsulated composite for photothermal conversion and latent heat storage

The request for green circular economy stimulates the use of solar energy. Capture and storage-release of solar energy can be simultaneously achieved by integrating photothermal conversion particles into phase change materials (PCMs) to obtain dual functional composites. Herein, a simple, cheap strategy for preparing 3D macro-encapsulated composite is proposed. Firstly, based on sizes difference, in situ grow nanoscale CuS coating on the surface of foamy Cu. The obtained CuS-Cu porous carrier adsorbs Na2S2O3·5H2O-CH3COONa·3H2O eutectic PCM to form semi-shape-stabilized PCM@CuS-Cu. Then, CuS-B4C modified epoxy resin (MEP) thin-layer macro-encapsulates PCM@CuS-Cu to fabricate PCM@CuS-Cu@MEP permanent shape-stabilized composite. The uniform distribution of CuS particles improves the heat transfer and photothermal conversion abilities of composite, as well as its exothermic accuracy shown as a low supercooling degree of only 0.740 °C. Photothermal conversion efficiency of PCM@CuS-Cu@MEP is 81.83 %, increased by 12.70 times compared with that of PCM (5.97 %). The MEP helps the composite to have leak-free performance under 60 °C for 72 h, and thermal reliability revealed as consistent thermal properties, crystal phase, composition after 100 heating-cooling cycles. The job provides a novel strategy to uniformly disperse PCM and photothermal conversion particles in space, ensuring the efficiently conversion and storage-release of energy.

Polyurethane template-based erythritol/graphite foam composite phase change materials with enhanced thermal conductivity and solar-thermal energy conversion efficiency

In this paper, we report a kind of composite phase change materials (PCMs) fabricated by the vacuum impregnation method in which ER functions as the filter and graphite foams (GFs) serve as the supporting framework, which is fabricated from polyurethane (PU) foam. Polyvinyl alcohol (PVA) and multi-wall carbon nanotubes (MWCNTs) serve as modifiers. Compared with pure ER, the ER/GFs show an excellent performance improvement; the resulting supercooling degree was reduced by ∼59 °C and thermal conductivity was improved to 56.93 W m−1 K−1, more than 86-folds that of pure ER, resulting in a tremendous latent heat-releasing percentage enhancement of 77.09%. This demonstrates that such ER/GFs composites can be used for efficient solar-thermal energy conversion, and have a low supercooling degree, good leakage resistance, and high thermal conductivity, mitigating the severe issues of ER and presenting a new strategy for enhancing the solar energy storage performance.

Single Crystals Self‐Assembled to Sector‐Face Dendritic Aggregates by Synchrotron Microbeam X‐Ray Analysis on Poly(ethylene succinate)

Poly(ethylene succinate) (PESu), upon crystallization with a morphology-modulating diluent and at low degree of supercooling, forms peculiarly novel sector-face dendritic aggregates. Delicate dissection by various microscopic techniques is used to confirm the unique differences of these two faces in the PESu dendrites. Powerful synchrotron-source generated X-ray microbeam analysis is performed to prove without doubt the nature of the single crystals that self-assemble into these two sectors, respectively. Both microscopy results and 1D/2D wide-angle X-ray patterns collectively confirm that one sector-face of the PESu dendrites is composed all fully flat-on with the single-crystal's basal face contacting the substrate and branching growth with mutual perpendicular ≈90° angle intersections; the second face is composed fully edge-on with the prism face contacting the substrate and growth with mutual oblique 5–30° angle intersections. The growth intersection angles are also proved by the azimuthal angles in 1D and 2D X-ray patterns.

Preparation and characterization of a solar-driven sodium acetate trihydrate composite phase change material with Ti4O7 particles

Thermal energy storage using phase change materials has received much attention as it can effectively relieve the contradiction of renewable energy between supply and demand. The novel bifunctional sodium acetate trihydrate (SAT) composite phase change materials with photo-thermal conversion and heat storage properties were developed to promote the thermal utilization of solar energy. The Ti 4 O 7 particles were selected as photo-thermal conversion media with full spectral absorption of sunlight and efficient photo-thermal conversion performance. 5 wt% disodium hydrogen phosphate dodecahydrate (DSP) and 3 wt% carboxymethyl cellulose were used to decrease supercooling and restrain phase separation of SAT, respectively. The as-prepared SAT composites with different content of Ti 4 O 7 possess a low supercooling degree of 0.9–1.5 °C and high latent heat of 228.6–257.7 kJ kg -1 . Ti 4 O 7 has a stable absorption capacity covering the full solar spectrum (200–2500 nm) and the absorption capacity of SAT and DSP in the infrared light even more than Ti 4 O 7 at 1900 nm–2500 nm. The SAT composite sample with 10 wt% Ti 4 O 7 has the best total solar absorption capacity of 93.33% more than Ti 4 O 7 of 92.76% because SAT and DSP have outstanding absorption capacity in the long-wave infrared wavelength. The photo-thermal storage efficiency of all SAT composite photo-thermal conversion phase change materials exceeds 50%, of which the composite with 10 wt% Ti 4 O 7 has the optimal photo-thermal conversion storage efficiency of 76.63%. The composite photo-thermal storage phase change materials have potential applications in solar energy systems. • The SAT-based composites have optical absorption and thermal storage properties. • The absorption capacity of the composite phase change materials is 93.33%. • The optical photo-thermal conversion and storage efficiency is 76.63%. • Ti 4 O 7 was a vital component in facilitating solar to heat for phase change materials.

Excellent heat transfer and phase transformation performance of erythritol/graphene composite phase change materials

As a phase change material, erythritol has two main disadvantages: low thermal conductivity and high supercooling degree. In this study, we proposed a novel erythritol/graphene composite phase change material, and its thermal properties were predicted by molecular dynamics simulation. The effects of the graphene mass fraction, size and number of layers on the thermal conductivity and phase transition characteristics, including the melting point and supercooling degree, were analyzed. The mechanism behind the above phenomena was revealed from a micro perspective. The results show that graphene can not only improve the thermal conductivity of the composites but also reduce the supercooling degree, thus improving the thermal properties of erythritol. The thermal conductivity of the composites increases with increasing graphene amount, size and number of layers. When the mass fraction of graphene increased to 8 wt%, the thermal conductivity doubled. The melting point of erythritol can be effectively controlled by changing the amount, size and number of layers of graphene. This study can provide guidance for the design and application of erythritol-based composite phase change materials. • Thermal properties of erythritol/graphene composite were calculated by MD method. • Thermal conductivity of the composite can reach twice of that of pure erythritol. • Graphene can significantly suppress the supercooling degree from 68 °C to 21 °C. • The microscopic mechanism of thermal performance improvement was revealed.

Development of diatomite-based shape-stabilized composite phase change material for use in floor radiant heating

The utilization of phase change materials (PCMs) in floor radiant heating system can reduce energy consumption along with enhancing thermal comfort by reducing indoor temperature fluctuations. However, the leakage and poor thermal performance of PCM limit its further applications. Here, to solve the above problems, sodium acetate trihydrate (SAT)-acetamide (AC)-micron/nano aluminum nitride (AlN) composite phase change material (CPCM) was composited with heat-treated diatomite to prepare diatomite-based shape-stabilized CPCM (SSCPCM) for use in floor radiant heating. The effect of treating temperature on diatomite’s porous structure was analyzed by porosity analyzer to determine the optimal heat-treated diatomite as supporting material. Subsequently, the effects of the mass fraction of diatomite on phase change properties, and shape-stabilized ability of diatomite-based SSCPCM were investigated. Meanwhile, the morphology, chemical compatibility analysis and thermal properties of SSCPCM were discussed in detail. Results indicated that diatomite calcined at 400 °C had large surface area and high porosity, giving it good adsorptive capacity for SAT-AC-AlN CPCM. SSCPCM with 37.5 wt% diatomite had a good shape stability, which melted at 46.5 °C with high latent heat of 162.5 kJ/kg, low supercooling degree of 0.33 °C and good thermal stability and thermal reliability, making it prospective potential in floor radiant heating.

Effect of additives on the cyclic thermal stability and thermal properties of sodium acetate trihydrate as a phase change material: An experimental study

As a low-cost and high-density heat storage material, sodium acetate trihydrate with sodium carboxymethyl cellulose (CMC) as a thickening agent and disodium hydrogen phosphate dodecahydrate (DSP) as a nucleating agent has the advantages of good thermal cycle stability and low supercooling degree. However, the optimal concentration and mechanism of the additives are unclear. In this study, the effects of viscosity grades of CMC and additives (CMC and DSP) of different concentrations on the cyclic thermal stability, thermal properties and phase change behavior of cPCMs were examined. The results showed that CMC with a high viscosity has a remarkable ability to maintain the thermal cycle stability of the cPCMs. However, a poor phase change behavior (decreased latent heat and increased supercooling degree) was observed with high-viscosity CMC as the thickening agent. It was also observed that excessive use of CMC or DSP results in a poor thermal stability and high supercooling degree. In addition, the viscosity of the cPCMs decayed irreversibly after several thermal cycles because of the degradation and weakened entanglement, which challenges the ability of CMC to cope with long thermal cycle environments.