Design of diatomite‐based hydrated salt composites with low supercooling degree and enhanced heat transfer for thermal energy storage

In this work, diatomite (DM) was calcined at 400°C to obtain the pure surface and pores (DM‐1); then, the three kinds of shape‐stable composite phase change materials (ss‐CPCMs) of CaCl₂·6H₂O (CCH)/DM‐1, CH₃COONa·3H₂O (SAT)/DM‐1, and Na₂SO₄·10H₂O (SSD)/DM‐1 were prepared by impregnation method. The hydrated salts were uniformly adsorbed on the surfaces and into the pores of DM‐1 by capillary action and surface tension. The addition of nucleating agent effectively reduced the supercooling degrees of hydrated salts, and the heterogeneous nucleation mechanism was employed to explain the supercooling suppression. The results showed that the supercooling degrees of the three hydrated salt ss‐CPCMs with optimal nucleating agent were less than or equal to 0.6°C. Moreover, the thermal conductivities of ss‐CPCMs were significantly improved by adding graphite, and the addition of 10 wt% graphite could increase the thermal conductivity of hydrated salt ss‐CPCMs by at least 70%. The package capacity of CCH, SAT, and SSD in three ss‐CPCMs with appropriate contents of nucleating agent and graphite was 58.1, 56.1, and 56.3 wt%, respectively. The DSC results showed that the phase change temperatures of the three ss‐CPCMs were approximately 28.8 to 57.8°C, and the latent heat was approximately 108.7 to 149.4 J/g. The XRD and FT‐IR results exhibited that the three ss‐CPCMs indicated understanding chemical compatibility. In addition, the results of 200 melt‐solidification cycles demonstrated that the ss‐CPCMs had excellent thermal cycle reliability. Thus, the hydrated salt/DM‐1 ss‐CPCMs showed great potential as heat storage materials for various heat storage applications.     

Polyethylene glycol (PEG)/diatomite composite as a novel form-stable phase change material for thermal energy storage

This paper deals with the preparation, characterization, and determination of thermal energy storage properties of polyethylene glycol (PEG)/diatomite composite as a novel form-stable composite phase change material (PCM). The composite PCM was prepared by incorporating PEG in the pores of diatomite. The PEG could be retained by 50 wt% into pores of the diatomite without the leakage of melted PEG from the composite. The composite PCM was characterized by using SEM and FT-IR analysis technique. Thermal properties of the composite PCM were determined by DSC analysis. DSC results showed that the melting temperature and latent heat of the composite PCM are 27.70 °C and 87.09 J/g, respectively. Thermal cycling test was conducted to determine the thermal reliability of the composite PCM and the results showed that the composite PCM had good thermal reliability and chemical stability. TG analysis showed that the impregnated PEG into the diatomite had good thermal stability. Thermal conductivity of the composite PCM was improved by adding expanded graphite in different mass fractions. Thermal energy storage performance of the composite PCM was also tested.     

Development of pentadecane/diatomite and pentadecane/sepiolite nanocomposites fabricated by different compounding methods for thermal energy storage

Global warming is one of the most important consequences of excess energy consumption. Phase change materials (PCMs) have prominent advantages in thermal energy storage owing to their high latent heat capacities and small temperature variations during the phase change process. However, leakage is a major problem that limits the use of PCMs. Leakage may occur in encapsulated PCMs or in composites where the PCM is attached to the surface of a supporting material or within the pores of that material. In this study, pentadecane/diatomite and pentadecane/sepiolite nanocomposites were fabricated by using unmodified and microwave‐irradiated diatomite and sepiolite samples and by using different compounding processes, such as direct impregnation, vacuum impregnation, and ultrasonic‐assisted impregnation methods. The microstructures and the chemical and thermal properties of the composites were characterized by scanning electron microscopy, Fourier‐transform infrared spectroscopy, and differential scanning calorimetry. Subsequently, the thermal reliability and stability and the thermal conductivity of the PCM composites were also investigated. A melting temperature of 9.25°C and a latent heat capacity of 58.73 J/g were determined for the pentadecane/diatomite composite that was prepared with the direct impregnation method using a microwave‐treated diatomite sample. The pentadecane/sepiolite composite prepared in the melting temperature range 7.98°C to 8.53°C and latent heat capacity range 41.05 to 46.02 J/g. The results of the thermal analysis indicate that fabricated diatomite‐based or sepiolite‐based PCM composites have good potential as thermal energy storage materials.     

Latent heat energy storage characteristics of building composites of bentonite clay and pumice sand with different organic PCMs

In the present work, six new kinds of building composite PCMs (BCPCMs), PS/octadecane, BC/octadecane, PS/CA–MA, BC/CA–MA, PS/PEG1000, and BC/PEG1000 composites, were prepared by using vacuum impregnation method. The maximum percent of PCM in the composites was assigned to be 12, 13, 18, 23, 30, and 42 wt%, respectively. The form‐stable BCPCMs were characterized using SEM, FT‐IR, DSC, and TG analysis techniques. The characterization results showed the existence of homogenous dispersion of the PCM into the PBM matrixes. The DSC measurements indicated that the melting temperatures of the form‐stable BCPCMs are in the range of 20–33°C while they have latent heats of melting in the range of about 28–55 J/g. These results make them promising BCPCMs for low temperature‐passive TES applications in buildings. Thermal cycling test indicated that the prepared BCPCMs have good thermal reliability and chemical stability. TG analysis proved that the prepared BCPCMs have good thermal durability. In addition, the thermal conductivity of BCPCMs was enhanced considerably by addition of expanded graphite (EG). The improvement in thermal conductivity of the BCPCMs caused appreciably reduction in their melting times. Copyright © 2014 John Wiley & Sons, Ltd.     

PolyHIPE composite based-form stable phase change material for thermal energy storage

A novel shape-stabilized n-hexadecane/polyHIPE composite phase change material (PCM) was designed and thermal energy storage properties were determined. Porous carbon-based frameworks were produced by polymerization of styrene-based high internal phase emulsions (HIPEs) in existence of the surface modified montmorillonite nanoclay. The morphological and mechanical properties of the obtained polyHIPEs were investigated by scanning electron microscopy analysis and the compression test, respectively. The polyHIPE composite with the best pore morphology and the highest compression modulus was determined as a framework to prepare the form stable n-hexadecane/polyHIPE composite phase change material using the one-step impregnation method. The chemical structure and morphologic property of composite PCM was investigated by FT-IR and polarized optical microscopy analysis. Thermal stability of the form-stable PCM (FSPCM) was examined by TG analysis. The n-hexadecane fraction engaged into the carbon foam skeleton was found of as 55 wt% from TG curve. differential scanning calorimetry analysis was used for determining melting temperature and latent heat storage capacity of FSPCM and these values were determined as (26.36°C) and (143.41 J/g), respectively. The results indicated that the obtained composite material (FSPCM) has a considerable potential for low temperature (18°C-30°C) thermal energy storage applications with its thermal energy storage capacity, appropriate phase change temperatures and high thermal stability.     

Binary mixtures of fatty alcohols and fatty acid esters as novel solid‐liquid phase change materials

The discovery of new eutectic phase change materials (PCMs) will overcome the current PCM challenges such as nonbiodegradability, super‐cooling, and limited thermal stability. This paper reports on the development of new bio‐based PCMs composed of binary mixtures of fatty acid esters and fatty alcohols at their eutectic compositions, which provide potential solid‐liquid PCMs for building applications. Six binary systems, namely 1‐dodecanol (DD) + methyl stearate (MES), DD + methyl palmitate (MEP), DD + methyl laurate (MEL), 1‐tetradecanol (TD) + MES, TD + MEP, and TD + MEL were prepared and their thermal behaviours were deliberated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), long‐term thermal stability test, and mass loss analysis. Amongst the studied systems, phase change transition temperature and latent heat of fusion of the eutectic mixtures of DD‐MES, DD‐MEP, TD‐MES, and TD‐MEP were found to be suitable for the building application with values of 22.46°C/201.91 J/g, 20.34°C/224.45 J/g, 32.05°C/209.38 J/g, and 26.72°C/210.15 J/g, respectively. The average degree of super‐cooling for all PCMs was below 2°C, and no significant changes in thermophysical properties of the developed PCMs were observed after 1000 thermal cycles.     

Enhanced thermal conductivity of copper-doped polyethylene glycol/urchin-like porous titanium dioxide phase change materials for thermal energy storage

A composite phase change material (PCM) of copper-doped polyethylene glycol (PEG) 2000 impregnated urchin-like porous titanium dioxide (TiO₂) microspheres (PEG/TiO₂) was successfully synthesised. The urchin-like porous TiO₂ structures contain hollow cavities that can provide a high PEG loading capacity of up to 80 wt%. Copper nanoparticles were uniformly dispersed on the outer and inner surfaces of the 0.8PEG/TiO₂ as additives to enhance the thermal conductivity of the composite PCM. The latent heat of the Cu/PEG/TiO₂ porous composite PCM reached 133.8 J/g, and the thermal conductivity was 0.58 W/(mK), which was 152.2% higher than that of TiO₂ and 38.1% higher than 0.8PEG/TiO₂. Moreover, the Cu/PEG/TiO₂ porous composite PCM has excellent thermal stability and reliability.     

Preparation of stearic acid/halloysite nanotube composite as form‐stable PCM for thermal energy storage

A novel form‐stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing stearic acid (SA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT‐IR and DSC analysis techniques. The composite can contain SA as high as 60 wt% and maintain its original shape perfectly without any SA leakage after subjected to 50 melt–freeze cycles. The melting temperature and latent heat of composite (SA/HNT: 60/40 wt%) were determined as 53.46°C and 93.97 J g^?1 by DSC. Graphite was added into the SA/HNT composite to improve thermal storage performance, and the melting time and freezing time of the composite were reduced by 65.3 and 63.9%, respectively. Because of its high adsorption capacity of SA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost‐effective latent heat storage material for practical application. Copyright © 2011 John Wiley & Sons, Ltd.     

Preparation and performances of palmitic acid/diatomite form-stable composite phase change materials

Using palmitic acid (PA) as an organic phase change material (PCM), a series of PA/diatomite composite PCMs (CPCMs) composed of PA absorbed into diatomite mesopores with different mass contents were made through direct impregnation method. Nitrogen adsorption-desorption curves indicated the porous structure of diatomite with the specific surface area and the mesopore peak at 40 m²/g and 3 to 5 nm, respectively. The form-stability measurement indicated that the maximum mass loading capacity of PA was 55 wt%. The melting temperature and fusion enthalpy of the PA/diatomite CPCM (55 wt%) were calculated from DSC at 63°C and 88 J/g, respectively. The thermal cycle test implied that the PA/diatomite CPCM with 55-wt% PA loading showed excellent thermal reliability after 1000 thermal cycles. Moreover, the composite has thermal conductivity at 0.5810 W/m·K and enhanced thermal storage/release rate. PA/diatomite CPCM (55 wt% PA) was a suitable candidate for modern building energy saving and industrial solar energy.     

Preparation and properties of caprylic‐nonanoic acid mixture/expanded graphite composite as phase change material for thermal energy storage

To satisfy the application demands for latent heat storage in the temperature range from 5°C to 15°C, an original composite phase change material (PCM), CA‐NA/EG (caprylic‐nonanoic acid/expanded graphite), was prepared and characterized. For CA‐NA/EG, the mass ratio of CA and NA was 8:2, and the mass percentage of the CA‐NA in CA‐NA/EG composite PCM was determined as 90% by leakage test. The melting and freezing points of the CA‐NA/EG were 6.84°C and 9.34°C, and corresponding latent heats were 108.75 kJ/kg and 107.67 kJ/kg. In addition, its thermal conductivity, thermal stability and reliability were investigated by thermal conductivity apparatus (TCA), thermal gravimetric analyzer (TGA), and accelerated thermal cycle test for 100 melt/freeze cycles, respectively. The results showed that the CA‐NA/EG had a good thermal stability and an excellent thermal reliability. Moreover, the thermal conductivity of CA‐NA/EG had an improvement of 25% than that of the CA‐NA. On the other hand, the accelerated thermal cycle test also indicated that the CA‐NA/EG had no supercooling during all melt/freeze cycles. Therefore, the prepared composite PCM, CA‐NA/EG, can be applied for low‐temperature thermal energy storage owing to its proper melting temperature, acceptable latent heat and thermal conductivity, excellent thermal stability and reliability.     

Stearic acid/polymethylmethacrylate composite as form-stable phase change materials for latent heat thermal energy storage

The aim of this research is to prepare of a novel form-stable composite phase change material (PCM) for the latent heat thermal energy storage (LHTES) in buildings, passive solar space heating or functional fluid by entrapping of SA into PMMA cell through ultraviolet curing dispersion polymerization. The composite PCM was characterized using scanning electron microscope (SEM) and Fourier transformation infrared (FT-IR) analysis technique. The results show that the form-stable microencapsulated PCM with core/shell structure was formed and the maximum encapsulated proportion of SA in the composite was 51.8 wt.% without melted PCM seepage from the composite. In the shape stabilized microencapsulated PCM, the polymer acts as supporting material to form the microcapsule cell preventing the leakage of PCM from the composite and the SA acts as a PCM encapsulated in the cell of PMMA resin. The oxygen atom of carbonyl group of skeleton is interacted with the hydrogen atom of hydroxyl group of SA. Thermal properties, thermal reliability and heat storage/release performance of the composite PCM were determined by differential scanning calorimetry (DSC), FT-IR and thermal cycling test analysis. The melting and freezing temperatures and the latent heats of the composite PCM were measured as 60.4 °C, 50.6 °C and 92.1 J/g, 95.9 J/g, respectively. The results of DSC, FT-IR and thermal cycling test are all show that the thermal reliability of the composite PCM has an imperceptible change. This conclusion indicates that the composite has a good thermal and chemical stability.     

Synthesis and thermal properties of poly(styrene-co-ally alcohol)-graft-stearic acid copolymers as novel solid–solid PCMs for thermal energy storage

A series of poly(styrene-co-allyalcohol)-graft-stearic acid copolymers were synthesized as novel polymeric solid–solid phase change materials (SSPCMs). The graft copolymerization reactions between poly(styrene-co-allyalcohol) and stearoyl chloride were verified by Fourier transform infrared (FT-IR) and Proton Nuclear Magnetic Resonance (¹H NMR) spectroscopy techniques. The crystal morphology of the SSPCMs was investigated using polarized optical microscopy (POM) technique. Thermal energy storage properties of the synthesized SSPCMs were measured using differential scanning calorimetry (DSC) analysis. The POM results showed that the crystalline phase of the copolymers transformed to amorphous phase above their phase transition temperatures. Thermal energy storage properties of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and found that they had typical solid–solid phase transition temperatures in the range of 27–30 °C and high latent heat enthalpy between 34 and 74 J/g. Especially, the copolymer with the mole ratio of 1/1 (poly(styrene-co-allyalcohol)/stearoyl chloride) is the most attractive one due to the highest latent heat storage capacity among them. The results of DSC and FT-IR analysis indicated that the synthesized SSPCMs had good thermal reliability and chemical stability after 5000 thermal cycles. Thermogravimetric (TG) analysis results suggested that the synthesized SSPCMs had high thermal resistance. In addition, thermal conductivity measurements signified that the synthesized PCMs had higher thermal conductivity compared to that of poly(styrene-co-allyalcohol). The synthesized copolymers as novel SSPCMs have considerable potential for thermal energy storage applications such as solar space heating and cooling in buildings and greenhouses.     

Hydrate salt/self-curing acrylic resin form-stable phase change materials with enhanced surface stability and thermal properties via the incorporation of graphene oxide

This work presents a novel eutectic hydrate salt/self-curing acrylic resin form-stable phase change materials (PCMs) composite (EHS/SCR) with favorable form-stable performances for heat energy storage. Further, to improve the surface stability, latent heat and thermal conductivity of the EHS/SCR particles, graphene oxide (GO) used as cladding materials is incorporated onto the surface of the EHS/SCR particles to prepare the GO modified EHS/SCR phase change composite (EGO). The obtained results indicate that the GO-targeted absorption model has achieved the enhancements in stability and thermal properties of EHS/SCR while making use of GO in an efficient and economical way. To be specific, with the introduction of GO of only 1.07 wt%, the thermal conductivity of 0.508 W/m·K is achieved, the value shows a significant rise of 128.6% compared with the EHS/SCR of 0.222 W/m·K. Additionally, the maximum latent heat of EGO-6 is up to 90.4 J/g, which exhibits a 3.19-fold increase compared against that of the uncoated EHS/SCR. Moreover, the prepared EGO composite PCM remain a good thermal cycling reliability after 300 thermal cycles. This work provides a novel opportunity to improve the performance of form-stable PCM composites with an intelligent manufacture-oriented pattern.     

Synthesis of solid–solid phase change material for thermal energy storage by crosslinking of polyethylene glycol with poly (glycidyl methacrylate)

Polyethylene glycol (PEG10000)/poly (glycidyl methacrylate) (PGMA) crosslinked copolymer as a novel solid–solid phase change material (SSPCM) was successfully synthesized through the ring-opening crosslinking reaction of end-carboxyl groups in carboxyl polyethylene glycol (CPEG) and epoxy groups in PGMA. Fourier transform infrared spectroscopy (FT-IR), polarizing optical microscopy (POM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and thermogravimetry (TG) were employed to study the chemical structure, crystalline properties, phase transition behaviors and the thermal stability of the copolymer, respectively. The results from WAXD patterns and POM images show that the crystalline form of the copolymer is similar with that of pure PEG, and the PEG soft segment phase transition between crystalline and amorphous states results in heat storage and release of the copolymer. Due to the crosslinking network restricted the free movement of the soft segments, at temperature above the PEG phase melting transition, the copolymer was still solid. The DSC results indicate that the copolymer imparts balanced and reversible phase change behaviors at the temperature range of 25–60 °C, and it has high latent heat storage capacity of more than 70 J/g. The TG results suggest that the copolymer had a much broader applicable temperature range compared with pure PEG.     

Facile functionalized mesoporous silica using biomimetic method as new matrix for preparation of shape‐stabilized phase‐change material with improved enthalpy

Dopamine‐functionalized mesoporous silica (DPMS), which was prepared by using a facile, easy to operate, and environmentally friendly biomimetic method, was synthesized as a new supporter of polyethylene glycol (PEG) to prepare shape‐stabilized phase‐change material (ss‐PCM) of PEG/DPMS with improved enthalpy. The thermal properties of PEG/DPMS were investigated, and the study results demonstrated that dopamine functionalization could regulate the crystallization property of PEG molecules immobilized in PEG/DPMS, and then the enthalpy of PEG/DPMS could be improved effectively. Compared with the ss‐PCM of PEG/SBA‐15 that was synthesized by using unfunctionalized silica molecular sieve (SBA‐15) as the matrix, after dopamine modification, the fusion and solidification enthalpies of 70‐wt% PEG/DPMS increased from 47.25 and 34.96 J/g to 69.77 and 67.54 J/g, respectively. The interaction mechanism study results suggested that the amino groups in the molecule of poly‐dopamines on the surface of DPMS could interact with the oxygen atoms in the molecules of PEG to form hydrogen bonds. Additionally, the PEG/DPMS had favorable thermal reliability and prominent thermal stability. Hence, the DPMS could be applied as a promising supporter for the fabrication of ss‐PCM.     

Thermal characterization of phase change materials based on linear low-density polyethylene,paraffin wax and expanded graphite

Thermal characterization of Phase Change Materials (PCMs) based on linear low-density polyethylene (LLDPE), paraffin wax (W) and expanded graphite (EG) is reported in this paper. Investigated PCMs showed high potential for application in energy storage systems.The latent heat, L_m, sensible heat Q_sens, and the ability of the prepared PCMs to store and release thermal energy were investigated using specific home-made equipment based on the transient guarded hot plane method (TGHPT). The sensible heat of PCM containing 40 wt.% of paraffin wax was investigated in the temperature range 25–35 °C, they exhibited a drop in Q_sens from 31 to 24 J/g depending on the concentration of EG. A similar decrease in sensible heat with increased loading of EG was observed for PCMs containing 50 wt.% of EG.The storage and release of thermal energy during phase change which is associated with the latent heat of the materials were investigated within the temperature range 20–50 °C. PCMs containing 40 wt.% of paraffin wax exhibited latent heat of 36 J/g, whereas the latent heat of PCMs containing 50 wt.% of paraffin wax was 49 J/g. The addition of EG decreased the time needed to melt and solidify PCMs due to increase in thermal conductivity of PCMs with increase in EG content. This behavior was confirmed by the thermal conductivity measurements, where thermal conductivity increased from 0.252 for sample without EG to 1.329 W/m × °C for PCM containing 15 wt.% of EG.The reproducibility of storage and release of thermal energy by PCMs was demonstrated by subjecting them to repeated heating and cooling cycles (over 150 cycles).     

Fabrication and characterization of electrospun fatty acid form-stable phase change materials in the presence of copper nanoparticles

Latent heat storage system using phase change materials (PCMs) has been recognized as one of the most useful technologies for energy conservation. In this study, a novel type of fatty acid eutectic of methyl palmitate (MP) and lauric acid (LA)/polyacrylonitrile (PAN) composite phase change fiber is prepared by single electrospinning method. Additionally, copper nanoparticles (CNPs) with different mass ratio are combined for improving the thermal conductivity of the PCM. The structure and morphology of the fabricated composite PCMs are observed by scanning electron microscopy (SEM), and the thermal properties and performance are also characterized. SEM results show that the liquid fatty acid has been fully stabled by the three-dimensional structure of the fibers. Good compatibility among the components of the composites is also demonstrated. Besides, the addition of nanoparticles leads to an improved thermal conductivity by over 115.2% and a phase transition temperature 21.24 °C as well as a high latent heat of 85.07 J/g. Moreover, excellent thermal reliability of the phase change fiber is confirmed by multiple thermal cycles. Hence, the composite PCM prepared in this study shows a promising potential for thermal energy system such as building insulating and thermal mass regulating textiles.     

污泥掺混木屑水解残渣为载体的复合相变材料循环热性能研究

以污泥水热解残渣资源化为目标,采用真空吸附法将污泥/木屑水热解的残渣吸附三水乙酸钠制备了复合相变储热材料。对水热解残渣进行了BET和粒径分析的表征,通过同步热分析仪、XRD及水浴中熔化-凝固多循环对复合储热材料的储热能力、相变温度、热循环稳定性等性能参数进行分析。实验结果表明,制备的复合相变储热材料无需添加增稠剂或悬浮剂等助剂,借助污泥残渣本身特有的均匀粒径和细微粒度特性以及木屑挥发分析出对残渣的造孔重整,作为载体可有效改善常规水合物储热材料的相变过冷度和相分离问题。封装尺度对储热材料的相变潜热和稳定性影响较小,100次循环后的潜热实际值与理论计算值(219.8 kJ/kg)相差仅为-0.5%～0.4%,化学组分也未有变化,可见该复合储热材料既具有优良的热稳定性也具有可靠的化学稳定性。     

Preparation and characterization of erythritol/polyaniline form‐stable phase change materials containing silver nanowires

Sugar alcohols are promising solid‐liquid phase change materials (PCMs). However, problems such as possible leakage of liquid PCMs, high and unstable supercooling, and low thermal conductivity need to be solved. In this work, a novel form‐stable PCM in which m‐erythritol (ME), polyaniline (PANI), and silver nanowires (Ag NWs) were applied as solid‐liquid PCM, supporting material, and thermal conductive filler, respectively, was successfully prepared in anhydrous ethanol by surface polymerization of aniline. Form‐stable PCM with good form stability could be obtained when the ratio of ME/(aniline + ME) was no more than 78.7 wt%. The melting enthalpy (ΔH_m) of the ME/PANI form‐stable PCMs could attain 234.8 J/g while that of the ME/PANI/Ag NWs form‐stable PCMs was about 220 J/g. In addition, the thermal conductivity of the form‐stable PCM was increased by 61.6% when 7.5 wt% Ag NW was added. Moreover, the supercooling of ME was effectively suppressed from 100°C for pure ME to 60°C, corresponding to an improvement of 40%, for the form‐stable PCM containing 7.5 wt% Ag NWs. The supercooling suppression could be ascribed to that PANI provided great amounts of nucleating centers and improved the nucleation kinetics, and Ag NWs improved the thermal diffusivity and thus increased the crystallization rate.     

Preparation of capric acid/halloysite nanotube composite as form-stable phase change material for thermal energy storage

A novel form-stable composite as phase change material (PCM) for thermal energy storage was prepared by absorbing capric acid (CA) into halloysite nanotube (HNT). The composite PCM was characterized by TEM, FT-IR and DSC analysis techniques. The composite can contain capric acid as high as 60 wt% and maintain its original shape perfectly without any CA leakage after subjected to 50 melt-freeze cycles. The melting temperature and latent heat of composite (CA/HNT: 60/40 wt%) were determined as 29.34 °C and 75.52 J/g by DSC. Graphite (G) was added into the composite to improve thermal storage performance and the thermal storage and release rates were increased by 1.8 times and 1.7 times compared with the composite without graphite, respectively. Due to its high adsorption capacity of CA, high heat storage capacity, good thermal stability, low cost and simple preparation method, the composite can be considered as cost-effective latent heat storage material for practical applications such as solar energy storage, building energy conservation and agricultural greenhouse in the near future.