Search

As one of the phase change materials (PCMs), paraffin is widely used in solar energy storage and utilization; however, there are limitations to its use due to poor photothermal properties of paraffin with low thermal conductivity and weak spectral absorption. In this present work, an experimental investigation on improving the photothermal properties of PCMs by producing hybrid PCM-based nanofluid with paraffin wax incorporating zinc (Zn) and zinc oxide (ZnO) nanoparticles was carried out. The two-step method was considered for the preparation of the Zn–ZnO/paraffin hybrid nanofluid, and the thermal and optical properties of the hybrid nanofluid were experimentally investigated. The impacts of nanoparticle concentration and solar radiation intensity on the photothermal properties of hybrid nanofluid were also studied. The results show that the addition of Zn and ZnO nanoparticles enhances thermal conductivity and specific heat capacity compared with pure paraffin. On the other hand, the transmission of nanofluid reduces with optical length and nanoparticles concentration increasing. Zn–ZnO/paraffin hybrid nanofluid can promote the photothermal properties in lower concentrations and higher irradiance range, and the maximum photothermal conversion efficiency of Zn–ZnO/paraffin hybrid nanofluids is 42.97%. [ABSTRACT FROM AUTHOR]

The use of phase change materials (PCMs) for thermal storage, thermal management, and thermal insulation has been widespread for many years. Thermal storage systems (TES) based on PCMs can be improved and optimized by adding nanoparticles (NPs) to them. Throughout this study, PCM nanocomposites (NCs) based on paraffin wax (PW) loaded by anatase titania (TiO2) NPs were fabricated and characterized to examine their thermal performance as phase change materials. The as-synthesized TiO2 NPs were obtained by hydrolysis technique and showed a well-defined spherical shape with a diameter in the nanoscale range and a crystallite size ~ 22.75 nm. Throughout the used concentrations of TiO2 NPs, 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.5%, the morphological feature for the PW/TiO2 NCs revealed a good dispersion of NPs in PW. The non-isothermal differential scanning calorimetry (DSC) measurements at a constant heating rate of 10 °C min−1 were used in order to get the melting point (Tm), latent heat of fusion (LH), and latent heat rate (LHR) as a function of TiO2 NP concentrations for the investigated PW/TiO2 NCs. Both LH and LHR values for PW/TiO2 NCs are higher than those obtained for a pure PW sample. The significant enhancement in LH and LHR values for PW/TiO2 NCs was found to be 21.2% and 134.3% in comparison with the pure PW sample, respectively. The thermal stability of the investigated PW/TiO2 NCs was examined using thermal gravimetric (TG) scans. It is found that the thermal stability varies with TiO2 NP concentrations with a non-monotonic trend. At concentrations up to 0.25 mass%, the thermal stability improved. For concentrations over 0.25 mass%, the degradation process became rapid. [ABSTRACT FROM AUTHOR]

Solar energy is the most plentiful renewable energy source that has the capability to keep up with the growing demand. When the sun's energy is not available, thermal energy storage (TES) using phase change material (PCM) is a promising technique for storage and utilization. However, PCM's low thermal conductivity may limit its use. The use of nanomaterials to enhance the thermal conductivity is one of the prominent solutions to overcome this issue. This research work reports that graphene nanoparticles (0.1%, 0.3%, 0.5%, 0.7% and 1% mass) enhanced paraffin wax (PW) to improve the thermophysical properties and transmittance capability. Thermogravimetric analyzer (TGA), differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible spectroscope (UV–VIS) were used for the characterization of the base PCM and nano-enhanced phase change materials (NePCM) composites. A significant improvement of 110% in thermal conductivity was obtained at 0.7% mass ratio compared to base PW without compromising the prepared composites' latent heat storage (LHS) capacity. TGA and FTIR outcomes demonstrated excellent thermal and chemical stability, respectively. To check the thermal reliability of composite, the PW and nanocomposite were subjected to repeated thermal cycling. The outcome evidence that the NePCM composite had consistent thermal energy storage properties even after repeated thermal cycles. The composite's light transmission was drastically lowered by 56.34% (PW/Gr-0.5) compared to base PW, resulting in PW/Gr composite has better thermal reliability in relation to thermal conductivity and LHS than base PCM, which can be used specifically in photovoltaic thermal systems and TES. [ABSTRACT FROM AUTHOR]

Devices of solar water desalination confront many problems including the low thermal properties of phase change materials (PCMs) such as heat transfer, storage of heat capacity, charging and discharging capability. Thus, these properties need to be improved by using a simple and novel procedure. So, incorporation and dispersion of hybrid nano-powders inside PCMs is considered a simple and novel procedure to improve the thermal properties of solar water desalination devices. The present article is focused on incorporating different nano-powders of MWCNTs and Al2O3 inside PCMs to improve the thermal characteristics of solar water desalination applications. Different nano-powders of MWCNTs and Al2O3 have been incorporated as: (i) 1.0 mass% Al2O3, (ii) 1.0 mass% MWCNTs, and (iii) hybrid 1.0 mass% of Al2O3 + 1.0 mass% MWCNTs, inside a constant amount of 250 gm RT-65HC paraffin wax. An innovative prototype was designed and produced to measure the thermal characteristics of solar water desalination devices. Various analyses have been carried out to study the influence of nano-powders scattering on the morphological, microstructural observations, chemical and thermal characteristics, including SEM, XRD, FT-IR, TGA, DSC, thermal conductivity, and infrared thermography. Microstructural observations showed that the excellent dispersion of nano-powders was at hybrid nano-additives of 1.0 mass% MWCNTs + 1.0 mass% Al2O3 inside PCMs. The uniform scattering of hybrid 1.0 mass% MWCNTs + 1.0 mass% Al2O3 inside PCMs assists to eliminate any defects. Finally, thermal characteristics of hybrid nano-additives phase change materials (NAPCMs) were improved specially in thermal stability, latent heat temperature, and thermal conductivity at 89%, 80%, and 32.8%, respectively. [ABSTRACT FROM AUTHOR]

Nano-sized high conductive particles are extensively used in many engineering applications to achieve enhanced thermal performance. Paraffin wax is regarded as the most promising phase change material (PCM) for energy storage applications. However, the low thermal conductivity of paraffin poses a challenge which decreases the performance of storage system. In this work, composite PCMs consisting of paraffin and copper (Cu) nanoparticles were synthesized at different mass percentages (0%, 0.5%, 1%, 2% and 3%) and the thermo-physical properties were examined experimentally. The field emission scanning electron microscope (FESEM) results showed that the dispersion of nanoparticles in the PCM is homogeneous. The differential scanning calorimeter reports revealed that the effect of nanoparticle addition on phase change temperature is insignificant. On the other hand, reduction in latent heat is observed. The addition of nanoparticles is found to be critical in prolonging the thermal degradation of the storage medium which ensures the thermal and chemical stability of nano-Cu–paraffin composites. Moreover, the thermal conductivity of solid PCM is enhanced by 7%, 14%, 24% and 30.5% with the nanoparticle loading of 0.5%, 1%, 2% and 3%, respectively. In case of liquid PCM, the enhancement is found to be 8%, 15%, 28% and 31.5% with mass fraction of 0.5%, 1%, 2% and 3%, respectively. Altogether, the obtained results have revealed that the enhanced properties make nano-Cu–paraffin composite PCM as right candidate for solar thermal energy storage. [ABSTRACT FROM AUTHOR]

The research article addresses the effect of multi-wall carbon nanotube (MWCNT) and nano-boron nitride (NBN) hybrid composite powders on thermal properties of the paraffin wax for thermal storage applications. Five different phase change material (PCM) samples were prepared with 100 paraffin wax, 99.5 paraffin wax + 0.5 MWCNT, 99.5 paraffin wax + 0.5 BN, 99 paraffin wax + 0.5 MWCT + 0.5 BN and 98 paraffin wax + 1 MWCNT + 1 BN mass percentage compositions. The size of the secondary particles MWCNT and NBN was assessed using transmission electron microscope (TEM). After PCM preparation, the morphology and distribution of the secondary particles were evaluated using field emission scanning electron microscope (FE-SEM). The phase change of MWCNT and NBN was evaluated using X-ray diffraction (XRD) technique. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and thermal conductivity tests were carried out on the PCMs to assess physical and thermal properties. The results revealed that hybrid nano-composite powders with paraffin wax provide better thermal conductivity of paraffin wax which increased from 0.18 to 0.31 W m−1 K−1. However, the distribution of MWCNT and NBN extended the thermal degradation of paraffin wax and solidification temperature. Increasing the mass % of MWCNT and NBN reduced the melting point of paraffin wax from 64.70 to 62.52 °C. Further, the solidification temperature of paraffin wax increased while increasing the mass % of MWCNT and NBN from 56.01 to 60.13 °C. This research revealed that thermal properties of paraffin wax were significantly increased with the increment of mass % of composite powders (MWCNT and NBN) addition. [ABSTRACT FROM AUTHOR]

In this work, a novel type of stearic acid-modified exfoliated graphite (SEG) with strong lipophilicity, rich pores and good economic efficiency is synthesized in order to improve the decline of heat storage capacity, poor dispersion stability and thermal cycle stability of paraffin (PA)-based composite phase change materials (PCMs) after multiple cycles. With a small amount (≤ 4 mass%) of SEG as a thermal performance enhancement additive, PA/SEG composite PCMs with comprehensive thermal performance is prepared. DSC, TG and other experimental analysis methods are used to evaluate the thermal performance of composite PCMs before and after multiple cycles (up to 500 cycles). It is found that the thermal conductivity of composite PCMs is more than 2 times higher than that of pure PA. Most importantly, after 500 heat storage and release cycles, the heat storage capacity of composite PCMs would hardly decrease, where the melting and cooling enthalpy of PA/SEG4 is up to 188.3 J g − 1 and 186.6 J g − 1, respectively, which are 5.5% and 4.4% higher than that of 0 cycle, and it still has outstanding dispersion stability and excellent thermal cycle stability. These results may provide a feasible strategy of successfully synthesizing novel high-performance composite PCMs and further enhancing energy storage efficiency. [ABSTRACT FROM AUTHOR]

In this work to increase the thermal capacity and performance of pristine paraffin wax (phase change material), it is mixed with COOH group functionalized graphene. The various concentrations of graphene mixed with paraffin wax are 0.25 volume percent to 1 volume percent at an increment of 0.25 volume% at three different volumetric flow rates of 6.25 mL s−1, 12.5 mL s−1, and 25 mL s−1. The charging performance is analyzed, and Fourier transform infrared spectroscopy (FTIR), X ray diffraction (XRD), differential scanning calorimetric (DSC) analysis, Thermo gravimetric analysis (TGA), field effective scanning electron microscopy, with energy dispersive spectroscopy are done for characterizing chemical structure, crystal structure, enthalpy, thermal stability, and microstructure, along with elemental composition, respectively. The results indicated that with increasing percentages of COOH group functionalized graphene the charging time decreases by 6.25–25% for the HTF flow rate 6.25 mL s−1, 6.67–26.67% for HTF flow rate 12.5 mL s−1, and 15.38–38% for HTF flow rate 25 mL s−1 over pure paraffin wax owing to increasing percentage and thermal conductivity of COOH group functionalized graphene in paraffin wax. This advanced material with the help of XRD and FTIR also showed that the functionalized COOH graphene was chemically inert and did not lead to any new product being formed. Through TGA the advanced functional materials manifested that they were thermally very stable and by DSC it showed that it was having very high enthalpy of melting. [ABSTRACT FROM AUTHOR]

The present numerical study addresses the buoyancy assisted transient two-dimensional early-stage heat transfer and melting process of PCM's in a square enclosure. Two PCM materials are used namely pure paraffin wax and paraffin with 1 mass % fraction of SiC nano particles. The square enclosure walls are subjected to a constant temperature of 65 °C (Hot wall) and 27 °C (Cold wall) at bottom and top side, respectively, while remaining sides of the enclosure are perfectly insulated. A finite volume (FVM)-based Ansys fluent software along with enthalpy-porosity method is used to capture the phase change process from solid to liquid. The pressure–velocity coupling is performed by coupled scheme, while pressure correction is done by PRESTO method. The transient variation of PCM liquid fraction, temperature, velocity and enthalpy are plotted. The results obtained shows that a notable difference is confined between early melting stages of both paraffin and nano-enhanced paraffin materials. The close observation of velocity vectors clearly shows that the addition of SiC nanoparticles in pure paraffin improves the convective heat transfer rate with time. The addition of SiC nano particles in paraffin reduces the melting time of paraffin but contrary influence the uniformity in temperature distribution and heat transfer characteristics. The presence of SiC nanoparticles increases the liquid fraction and temperature rise by 33% as compared with pure paraffin. [ABSTRACT FROM AUTHOR]

Modern electronic devices need an efficient thermal management system to remove heat effectively under different heat loading conditions. The present paper reports the thermal performance of different heat sink (HS) configurations with various cavities (1, 4, 9, 16, 25, and 36) formed by rectangular cross plate fins arrangement integrated with phase change material (PCM) through experimental investigation. Here, paraffin wax and aluminum are used as PCM and heat sink materials, respectively; tests are conducted for three different heat flux values ( q ″ = 1.5, 2.0, and 2.5 kW m−2) and different PCM volume fractions ( φ = 0.0, 0.5, 0.8, and 1.0). Results are presented in the form of the transient temperature variation in the HS base, the time required to reach the required set point temperature, enhancement ratio, thermal capacity, and thermal conductance values. The maximum reduction in temperature is found to be 19 and 19.5% for HS with 36 cavities compared to HS with a single cavity at q ″ =1.5 and 2.0 kW m−2, respectively. In addition, HS with 36 cavities exhibits the maximum enhancement ratio of 6.5 at q ″ =1.5 kW m−2 for SPT of 65 °C and heat capacity of 1.63 during post-sensible heating for q ″ = 2.0 kW m−2. The thermal performance is found to increase with the increase in the number of cavities and PCM volume fractions. The study suggests that the solidification time takes approximately twice that of the melting time; forced convection cooling needs to be applied to enhance the cooling rate of PCM. [ABSTRACT FROM AUTHOR]

In this study, a nano-graphite/paraffin composite is used to augment the cooling performance of a PV panel, which significantly increases the output power due to decreasing the thermal stresses and current mismatching problems. The constructed composite is a phase change material (PCM). In order to retard the melting of PCM, a finned tube-heat exchanger is inserted inside the PCM. At first step, pure paraffin and finned tube-heat exchanger are used for cooling of a PV panel and secondly, graphite nanoparticles (ϕ = 0.002–0.012 (w/v)) are combined with PCM. The results of temperature, voltage–ampere curves and the maximum power output of the PV panel using PCMs are compared with no cooling device. Results show that using the nano-graphite/paraffin composite has significantly added benefits over using pure paraffin. By increase in water flow rate, the surface temperature of the PV panel is decreased because of increase in the heat transfer rate between the water and PCM around the tubes. Average surface temperature of the PV module is reduced from 336.15 to 310.25 K by using nano-graphite PCM with ϕ = 0.01 (w/v) and the highest value of water flow rate (Q = 100 mL s−1). The maximum enhancement in the power output of the PV/nano-PCM system by using the efficient conditions is 21.2%. The proposed system not only boosts considerably the output electrical power, but also reduces the PV panel temperature while keeping it uniform for each cell. [ABSTRACT FROM AUTHOR]

This paper shows the results of a novel research conducted with the overall aim of developing a system that can provide continuous desalination. Productivity enhancement of solar stills is regarded as the main purpose of the investigators in desalination field. This paper represents the experimental results in a new approach of paraffin + graphene oxide nanoparticles mixture. The paraffin mixture in a semicircular, triangular and rectangular absorber with paraffin + graphene oxide of 0.1, 0.3 and 0.5 mass% has been investigated. The finding indicated that for all absorbers, the use of paraffin + graphene oxide in higher mass fractions enhances daily freshwater production. The results showed that the thermal performances are greater applying graphene oxide + paraffin of 0.5 mass% with semicircular absorber compared to triangular and rectangular absorber. The achievement of the present paper can be implemented to design more efficient absorbers for solar still parts. [ABSTRACT FROM AUTHOR]

In this research work, novel hybrid graphene-silver (Gr-Ag) nanomaterial has been used for first time with paraffin wax as a phase change material (PCM) to improve its thermo-physical properties. Thermal and electrical energy efficiencies of the novel synthesized nanocomposite (PCM/graphene-silver) has been investigated in solar thermal collector systems (CPV/T). This paper focuses on preparation, characterization, thermo-physical properties and energy efficiency in concentrated photovoltaic/thermal (CPV/T) system of new class of nanocomposites induced with hybrid Gr-Ag nanomaterial in three different concentrations. The specific heat capacity (cp) of hybrid PCM/graphene-silver nanocomposite increased by introducing hybrid Gr-Ag nanomaterial. Electrical and thermal energy performance of the hybrid PCM/graphene-silver is investigated in a CPV/T system using MATLAB 2017b program. The improvement of cp is found to be ~ 40% with 0.3 mass% of hybrid Gr-Ag nanomaterial loaded in PCM. The highest thermal conductivity increment is found to be ~ 11% at 0.3 mass% concentration of hybrid Gr-Ag nanomaterial in PCM. The endothermic enthalpy value of the hybrid PCM/graphene-silver nanocomposite is found to be ~ 75.6 J g−1 at 0.1 mass% loading concentration of hybrid Gr-Ag nanomaterial. Melting point of hybrid PCM/graphene-silver nanocomposite with loading concentration of 0.3 mass% is measured to be 73.2 °C. The highest thermal efficiency using the hybrid graphene-silver nanoparticles reached the value of 39.62% which represents 4.16% increment in comparison with the pure PCM. The equivalent electrical efficiency is improved by 2.8% at the loading concentration of 0.3 mass% of the hybrid Gr-Ag nanomaterial. These new class of nanocomposites represented the capability of enhancement in the performance of the CPV/T system consisting of lower PV temperatures, higher temperature gains across the cooling fluid and higher electrical and thermal efficiencies. [ABSTRACT FROM AUTHOR]

In this study, we focus on important global issue containing both environmental pollution control and energy saving. High density polyethylene (HDPE) is utilized as supporting material to load paraffin, while Al2O3 nano-powder is added into composite behaving as thermal conductivity enhancement to form composite phase change materials (paraffin-Al2O3/HDPE composite PCMs). By the adsorption test and differential scanning calomeritry (DSC) curves, the loading ratio of paraffin in paraffin/HDPE composite is 60%, via taking phase change enthalpy and thermal conductivity into integrated consideration, the adding ratio of Al2O3 is 3% in paraffin-Al2O3/HDPE composite. And CMT4304 universal tester results manifest paraffin-Al2O3/HDPE composites have high compressive strength. For paraffin-Al2O3/HDPE composite with 3 mass% Al2O3, Fourier transformation infrared (FT-IR) result indicates no chemical interaction among raw materials but physical combination. DSC results identify composite PCM happens solid–solid phase transition at 33.3 ºC with enthalpy value of 10.7 J g−1 and melts at 48.8 ºC with enthalpy value of 95.1 J g−1, and thermal cycling measurements demonstrate the form-stable composite PCM with adequate stability after 300 times melting/freezing cycles. Furthermore, the thermal conductivity of paraffin/HDPE composite is enhanced by 119.4% to attain 0.419 Wm−1 K−1 after addition of Al2O3. To sum up, form-stable and tough paraffin-Al2O3/HDPE composite PCMs look promising for application in building field as solar energy utilization materials. [ABSTRACT FROM AUTHOR]

Conventional photovoltaic thermal (PVT) systems provide unstable thermal energy, which changes throughout the day. In PVT systems, phase change materials (PCMs) and heat storage materials could be used to make thermal energy more stable and provide longer-term thermal energy. In the present study, exergoeconomic analysis of PVT systems integrated with natural zeolites has been firstly carried out, and the results were compared with the results of PVT systems integrated with PCM and conventional one. PVT systems integrated with paraffin and stearic acid, common PCMs and conventional PVT systems were analyzed by specific exergy costing method, systems were compared exergoeconomically and suggestions were made to improve the economic performance of PVT systems. As a result of the analyzes conducted with 297 data obtained experimentally, the average energy efficiencies were calculated as 33%, 40%, 37% and 32% for paraffin, natural zeolite, stearic acid and conventional PVT system, respectively. Besides, average exergy efficiencies were 24%, 24%, 22% and 22% for paraffin, zeolite, stearic acid and conventional PVT system, respectively. The average entropy generation of the PVT based paraffin; natural zeolite, stearic acid and conventional one were found as 2.11, 2.29, 2.18 and 2.07 W K−1, respectively. According to the exergoeconomic analysis, specific exergy flow cost values were found as 0.206, 0.176, 0.204 and 0.206 € kWh−1 for the PVTs based on paraffin, natural zeolite, stearic acid and the conventional PVT. It was concluded that the natural zeolite-based PVT system was found as the best system exergoeconomically. [ABSTRACT FROM AUTHOR]

Energy storage plays an important role in improving the applicability of a wide range of energy systems. Buildings could be considered as a desirable place for this purpose. Incorporating phase change materials (PCMs) as form-stable composites into the building materials has been widely taken into consideration in recent years. However, there are still some shortcomings in applying this technique. In this study, we focused on a surface modification method to prevent leakage of PCM from porous aggregates during heating/cooling cycles. Paraffin (PA) as phase change material was impregnated into the expanded perlite (EP) particles by vacuum impregnation method, and prepared EP/PA composite was coated by a layer of polystyrene. Thermal characterization of obtained composite samples was conducted by DSC and TG analysis. Also, a simple apparatus was prepared to evaluate thermal behavior of a concrete block made by these modified form-stable PCMs during the heating process. Oozing circle method and visual observation for leakage were conducted for surface-modified EP/PA particles and final concrete blocks, respectively. Finally, compressive strength test was applied to evaluate the feasibility of using concretes made by EP/PA composites as structural concrete. The results showed that using polystyrene as a coating material for EP/PA particles was a promising method for PCM leakage prevention. Latent heat value decreased about 18% for surface-modified EP/PA but no leakage trace was observed; also in spite of decreasing in compressive strength up to 40%, it is still in acceptable range for structural purposes. [ABSTRACT FROM AUTHOR]

The biggest challenge in dispersion of nanoparticles in phase change materials (PCMs) is the physical stability of these particles in PCM. Numerous studies have evaluated the effect of different parameters on the stability of nanoparticles in PCM, but the effect of PCM polarity has rarely been investigated. In this study, the stability of functionalized and pristine multi-walled carbon nanotubes (MWCNTs) in three different PCMs with various polarity levels was investigated. The utilized PCMs were paraffin wax (nonpolar), stearic acid (partially polar), and polyethylene glycol (polar). Two different methods of functionalization of MWCNTs, with stearic acid and hexadecyl amine, were used to compare their stability in PCMs. The FTIR analysis and FESEM images reveal that the surface modification reactions were done thoroughly and MWCNTs are well dispersed in PCM. The results showed that pristine MWCNT is more stable in nonpolar PCMs (paraffin and stearic acid), while the samples containing functionalized MWCNT or surfactant had higher stability in polyethylene glycol. The three most stable samples were used to measure their thermal conductivity and heat release/storage capability. The addition of nanoparticles to all kinds of PCMs led to higher rate of heat storage and release. Moreover, the thermal conductivity of all PCMs improved by the introduction of nanoparticles. In both liquid and solid phases, nanoenhanced PCM had higher thermal conductivity compared to pure PCM with stearic acid containing 1 mass% of pristine MWCNT having the highest rate of enhancement at 16.82% for solid phase. [ABSTRACT FROM AUTHOR]

In this paper, an experimental and numerical study has been performed on melting process of commercial Iranian paraffin wax, with melting temperature of about 60 °C, inside a plate heat exchanger. A 500 × 100 mm plate thermal storage system and 22 mm thick phase change material has been designed. Experimental and numerical results are compared with each other in three different inlet temperatures of heat transfer fluid (HTF), which are 343, 348, and 353 K, and three different volume flow rates, which are 15, 30, are 45 L min−1. The temperature contours of paraffin wax at various time steps are presented to investigate the conduction and convection effects of melting process with respect to time. It has been shown that the melting rate of paraffin wax is higher at the upper part of the system due to the presence of natural convection. Results showed that increasing HTF temperature enhances the amount of heat transfer and reduces the melting time up to 37%. Also, by increasing volume flow rate of HTF, the melting time reduced up to 0.9%. [ABSTRACT FROM AUTHOR]

Present experimental investigation focuses on the performance analysis of metallic foam and phase change material (PCM)-based heat sink at variable heat loads. High porosity (97%) copper and nickel foams are used with PCM (RT-54HC) to enhance the surface area for the heat transfer. Experimental results reveal that metallic foam-based heat sink embedded with PCM can reduce the base temperature of the heat sink efficiently. Copper foam is recognized to be more promising when compared to nickel foam in lowering base temperature for all heat loads (8 W, 16 W and 24 W). It was found that copper foam embedded with 0.8 volume fraction of PCM reduced the base temperature by 26% as compared to that of nickel foam without PCM at 24 W. Furthermore, when the PCM fraction is increased, final temperature of the heat sink gets lessened at the end of charging process while discharging process remains almost intact. So, in this study, copper foam with 0.8 volume fraction is determined to be an optimized configuration. [ABSTRACT FROM AUTHOR]

In this paper, the melting properties such as the thermal energy storage capacity and phase-change temperatures of paraffin are investigated. The paraffin is also modified as nano-PCM by dispersing small fractions (0.2% and 0.5% mass fractions) of highly conductive nanoparticles. The material used in this study has a melting temperature of 22 °C, making it suitable for domestic building applications. Additionally, the thermal conductivity and heating rate of the paraffin and paraffin with multiwall carbon nanotubes (MWCNTs) are studied experimentally. The results show that the paraffin with 0.2% and 0.5% mass fractions of MWCNTs could increase the thermal conductivity by 35% and 49% with respect to pure paraffin. The maximum thermal conductivity of 0.203 W m−1 K−1 is observed for the paraffin with 0.5% mass fraction of MWCNTs. Additionally, the heat of fusion slightly reduced by increasing the mass fraction of MWCNTs. The result implies that the materials used in this study could be used for building applications. [ABSTRACT FROM AUTHOR]

The most critical part and barrier of phase change material (PCM) applications are the accuracy of simulations and the control of the process. The state of the PCM and the momentarily stored energy cannot be estimated easily unless numerous temperature sensors are used. There are a lot of models used by researchers, but most of them focus solely on the full charging or discharging of the PCM thermal energy storage. In a real working environment, the phase change is often interrupted so this phenomenon should also be modelled with high accuracy. The aim of this paper is to present the newly developed diagonal model validated by differential scanning calorimetry measurements, which can model what occurs inside the hysteresis of the solid–liquid two-phase state. The model was created and validated by using paraffin wax (P53) and was further tested with coconut oil (C.oil20), which has a very wide hysteresis. The modelling accuracy of the different models was compared with each other, and the evaluations were carried out. [ABSTRACT FROM AUTHOR]

In this study, a mixture of nano-encapsulated phase change materials in water has been used as the working fluid in a pulsating heat pipe in order to investigate its thermal performance. The results of the experiments showed that using the nano-encapsulated paraffin dispersed in water as working fluid improves heat transfer and decreases the thermal resistance of the pulsating heat pipe. On the other hand, among the tested concentrations for nano-encapsulated paraffin, there is an optimal value in which increasing the concentration causes an increase in the thermal resistance of the pulsating heat pipe due to the increased dynamic viscosity of the fluid. Enhancement in the thermal performance of the pulsating heat pipe by adding paraffin nanocapsules is attributed to the increase in effective specific heat of the fluid mixture as a result of the latent heat of paraffin nanocapsules. Higher effective sensible heat leads to an augmentation of convective heat transfer which has the main role in heat transfer of heat pipes. Moreover, the existence of nano-encapsulated paraffin can result in more mixing which is another reason for heat transfer enhancement. In addition, the use of nano-encapsulated phase change paraffin at high concentrations causes a cessation in the dry-out phenomenon at higher heat input compared with water or, in other words, increases the operating range of the pulsating heat pipe, which is due to an increase in the heat capacity of the fluid. In addition, the effect of inclination angle (30°, 60°, and 90°) on the thermal performance of the PHP at an optimum concentration among tested concentrations of nano-encapsulated paraffin was investigated, which was equal to 6.25 g L−1. It was observed that the PHP had its best thermal performance at the vertical position. The lowest measured thermal resistance of the PHP was 0.86 K W−1 in a vertical orientation and 50 W heat input. Moreover, at 30°, the thermal resistance of the PHP sharply increased, which can be attributed to the reduced effect of gravity in fluid return from the condenser to the evaporator. The maximum thermal resistance of the PHP observed in the case of inclination angle equal to 30° and 10 W heat input was 5.38 K W−1. [ABSTRACT FROM AUTHOR]

High thermal conductivity in phase change materials (PCM) is preferred in thermal energy storage (TES) systems. Carbon additives are considered as suitable materials for this purpose; however, some important issues such as price and stability for these materials should be considered. In this study, graphite powder and multiwall carbon nanotubes as an inexpensive and a relatively expensive carbon additives were used to improve the thermal conductivity of a long-chain paraffin (P) with a melting peak point of 64 °C. Also an amine functionalization method was applied to enhance the dispersion of CNTs into the non-polar paraffin medium. At first, the thermal conductivity and stability of the materials, as important and critical properties, were evaluated. In the next step, atmospheric impregnation method was conducted to incorporate modified PCM into the expanded perlite (EP) particles and finally, a lightweight concrete was constructed by these form-stable EP/P composites. Thermal behavior of the final concrete sample was studied by a simple handmade apparatus. Also, DSC analysis was conducted to determine the melting/freezing point and latent heat value for modified paraffin and form-stable PCM composites. The maximum allowable volume percent of EP usage for having a structural concrete was also determined by compression strength analysis. Thermal behavior analysis showed promising results for TES of the concrete block containing modified paraffin as phase change materials; also it was found that in form-stable technique, the stability of the additives is not significantly effective due to the narrow pores and channels, which reduce the effect of particles precipitation. [ABSTRACT FROM AUTHOR]

This present work contributes to the improvement in thermal energy storage capacity of an all-glass evacuated tube solar water heater by integrating it with a phase change material (PCM) and with a nanocomposite phase change material (NCPCM). Paraffin wax as PCM and a nanocomposite of paraffin wax with 1.0 mass% SiO2 nanoparticles as NCPCM had been used during the experiments. The results were acquired through the real-time experimental measurements on the all-glass evacuated tube solar water heater integrated with built-in thermal energy storage, functioning under thermosyphonic flow. Three different cases, namely, without PCM, with PCM, and with NCPCM, were considered. The testing procedure involved the observation of total temperature variation in the tank water from 6.00 a.m. to 6.00 a.m. of next morning. Meanwhile, the water was completely renewed for every 12 h. The system performance was studied using energy efficiency, exergy efficiency, and temperature of hot water supply during the next morning, for all the three cases. The investigation exemplifies that the tank water temperature at 6.00 a.m. after one complete day of operation was notably improved to 37 °C and 39.6 °C, respectively, with PCM and NCPCM, whereas it was 33.1 °C for the case without PCM. The energy efficiencies for the three cases were found to be 58.74%, 69.62%, and 74.79%, respectively, and exergy efficiencies of the system were determined as 19.6%, 22.0%, and 24.6%, respectively, for without PCM, with PCM, and with NCPCM. Also, it was evidenced that the thermal conductivity of paraffin wax was considerably increased to 22.78% through the diffusion of SiO2 nanoparticles. Put together, this indicates that the incorporation of PCM and explicitly the dispersion of SiO2 nanoparticles in NCPCM had been significantly improved the thermal performance of the system. [ABSTRACT FROM AUTHOR]

Highly conductive nanoparticles were proposed to be dispersed into phase change materials (PCMs) such as paraffin wax for heat transfer enhancement. The mixture, often referred to as nanoparticle-enhanced phase change material (NePCM), has been studied extensively for latent heat energy storage but with conflicting results. This study attempts to understand this problem by investigating the stability of NePCMs under multiple thermal (melting-solidification) cycles, which has not been well explained in previous studies. We believe that stability of a NePCM is prerequisite for any experimental investigation of its thermal properties or application. In this study, paraffin wax was chosen as the base material. Three different types of nanoparticles were tested, i.e., multi-walled carbon nanotubes, graphene nanoplatelets, and aluminum oxide nanoparticles (Al2O3). The nanoparticles were dispersed into paraffin wax at varying mass fractions using mechanical dispersion methods (sonication, stirring) with and without different surfactants. Stability of different mixtures was investigated after consecutive thermal cycles performed in an environmental chamber. Significant coagulation and deposition of nanoparticles were found after a few thermal cycles regardless of the nanoparticle type, concentration, or dispersion method. Different boundary conditions in heating were also examined for their effects. None of these methods led to long-term stable NePCMs. The "negative" results from this study indicate that long-term stability of NePCM (at least for the paraffin wax and nanoparticles tested) remains a major challenge and requires further research with a multidisciplinary approach. [ABSTRACT FROM AUTHOR]

The effective and facile microencapsulation of paraffin with poly(styrene) was conducted using emulsion polymerization. The optimal independent variables using response surface methodology were paraffin wax/styrene mass ratio of 0.39, SDS/styrene mass ratio of 0.032 and the stirring rate of 1500 rpm which are different from those of in the previous works. The thermal characterization of the optimal sample was carried out using TG and DSC analysis. Microcapsules produced using this method show less mass loss during the heating process. The microencapsulation ratio ( ER) reached to 87.8 ± 0.2% under the optimal conditions. The morphology of the optimal microcapsules was considered by SEM analysis. The results showed that the obtained microparticles were smaller, smoother and have greater microencapsulation ratios than was the case for those produced in previous studies. Thus, the optimal encapsulated paraffin with the maximum ratio and good stability can be considered to have good potential for energy storage. [ABSTRACT FROM AUTHOR]

In this study, paraffin-/ultrasonic-treated diatomite was characterized for use as phase change material (PCM) for thermal energy storage in buildings. The diatomite was treated with ultrasound at various periods of time. The diatomite treated with ultrasound for 60 min (DA-60) was the optimum condition providing the highest surface area without structural degradation. The melting point and latent heat of the paraffin/DA-60 composite PCM were 59 °C and 45.90 J g, respectively. The obtained form-stable PCM had good thermal reliability after 500 cycles of thermal cycling test. The thermal performance of PCM was tested by incorporating the paraffin/DA-60 composite PCM into gypsum board. The results showed that the gypsum board containing the paraffin/DA-60 composite PCM had better thermal energy absorption and release characteristics than those of the control sample. The incorporation of paraffin/DA-60 composite PCM into suitable building materials could thus considerably reduce the energy consumption of cooling system in buildings. [ABSTRACT FROM AUTHOR]

The addition of carbon nanofillers to phase change materials (PCMs) has received much attentions recently. The shape effects of carbon nanofillers on the thermal properties of paraffin were investigated in this work. Four types of nanocomposite PCMs were prepared by mixing paraffin with multi-wall carbon nanotubes (MWCNTs), graphitized MWCNTs, nanographene with different layer numbers (GNP-B, GNP-C). It shows that phase change enthalpy of nanocomposite PCM decreases gradually with the increasing of the loading of carbon nanofillers. Due to the nucleating action of carbon nanofillers, the supercooling degree of nanocomposite PCM slightly decreases. The microstructure of the nanofillers plays an important role in enhancing the thermal conductivity of paraffin. It is the flaky structure of GNP shows a more significant effect on enhancing the thermal conductivity of paraffin than the tubular structure of CNTs, which is confirmed by comparing the melting/freezing time of PCM. In the four kinds of carbon nanofillers, GNP-C shows the greatest thermal conductivity enhancement up to 52.4 % at the loading of 3 mass%. [ABSTRACT FROM AUTHOR]

Thermal energy storage plays a key role in improving the efficiency of solar applications. In this study, the energy storage behavior (melting or charging) and energy removal process (solidification or discharging) are investigated in the presence of paraffin wax as a phase-change material (PCM) in a horizontal shell-and-finned tube. The horizontal shell-and-finned tube comprises 24 and 48 radial fins for investigation in the laminar regime. The effect of external fin surface area on the heat transfer between the PCM and heat transfer fluid (HTF), distilled water, was studied. To realize this issue, the PCM charging and discharging times at different Reynolds number of HTF were investigated in the presence of both series of fins (24 and 48 fins). Along with a significant improvement in heat transfer with higher number of fin, the results concluded that a change in the HTF flow rate presents more influence on the PCM charging process as compared with discharging process. Also, the charging time was reduced 58 and 76 % by increasing HTF flow rate and fins density, respectively. [ABSTRACT FROM AUTHOR]

In this study, thermal and heat transfer characteristics of the newly prepared composite as phase change material (PCM) comprising paraffin and hybrid nanomaterials (50 % CuO-50 % TiO) have been investigated for solar heating systems. Composite PCMs with 0.25, 0.5, 0.75, and 1.0 mass% of hybrid nanomaterials were prepared individually for assessing their better performances than paraffin alone. Sodium dodecylbenzene sulfonate (SDBS) was preferred as the surfactant to ensure the dispersion stability of the nanomaterials in the paraffin and mass fraction of SDBS was 1.2 times of the mass fraction of hybrid nanomaterials in the paraffin. The thermal properties of the composite PCMs were determined by differential scanning calorimetry in terms of mass fractions of hybrid nanomaterials and number of thermal cycles. The thermal stabilities of the paraffin and composite PCMs were tested by thermogravimetric analyzer. The thermal conductivity and viscosity of the paraffin due to the addition of various mass fractions of CuO, TiO, and hybrid nanomaterials were determined by LFA 447 NanoFlash analyzer and Brookfield DV-III Ultra programmable rheometer, respectively. The experimental results proved that the heating and cooling rates of composite PCMs were faster due to the dispersion of hybrid nanomaterials. For composite PCM with 1.0 mass% of hybrid nanomaterials, the melting and freezing times were reduced by 29.8 and 27.7 %, respectively, as compared with the paraffin. [ABSTRACT FROM AUTHOR]

The thermal properties of paraffin as phase change material (PCM), combined with layered zinc hydroxide nitrate (LZHN) and intumescent flame retardant (IFR), have been studied by thermogravimetric analysis (TG), TG-Fourier transform infrared spectrometry (TG-FTIR), cone calorimeter (CONE),and differential scanning calorimetry (DSC). The TG results indicated that the thermal stabilities of the paraffin and paraffin/IFR composites could be improved when dodecyl sodium sulfate-modified LZHN (ds-LZHN) was incorporated. The TG-FTIR results indicated that ds-LZHN could reduce the release of combustible gases for paraffin and paraffin/IFR. The CONE results showed that the flame-retardant efficiency of IFR could be improved in the paraffin/IFR system owing to ds-LZHN. DSC results presented that the phase change temperatures and latent heats of the composites were determined by the dispersed paraffin with their mass percentage. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the melting/freezing characteristics of paraffin by adding Cu nanoparticles. Cu/paraffin composite phase change materials (PCMs) were prepared by a two-step method. The effects of Cu nanoparticles on the thermal conductivity and the phase change heat transfer of PCMs were investigated by the Hot Disk thermal constants analyzer and infrared monitoring methods, respectively. The maximum thermal conductivity enhancements up to 14.2% in solid state and 18.1% in liquid state are observed at the 2 wt% Cu/paraffin. The photographs of infrared monitoring suggest that the melting and freezing rates of Cu/paraffin are enhanced. For 1 wt% Cu/paraffin, the melting and freezing times can be saved by about 33.3 and 31.6%, respectively. The results provide that adding nanoparticles is an efficient way to enhance the phase change heat transfer of PCMs. [ABSTRACT FROM AUTHOR]

This communication presents the experimental study and performance analysis of a solar air heater with and without phase change material (PCM) viz. paraffin wax and hytherm oil. There are three different arrangements viz. without PCM, with PCM and with hytherm oil to study the comparative performance of this experimental system. Inlet, outlet temperatures and radiation with respect to time have been recorded and found that the output temperature in case with thermal energy storage (TES) is higher than that of without TES, besides, the outlet temperature with paraffin wax is slightly greater than that of with hytherm oil. Also there is no energy gain in the evening in case of without TES but in case of with TES there is a heat gain for around 4 h in the evening which gives the backup for hot air for around four more hours which is the main advantage of this systems with TES. Based on the data, the efficiency of the system has been calculated and it is noted that the efficiency in the case of heat storage is higher than that of without TES, besides the efficiency in the case of the paraffin wax is slightly higher than that of the hytherm oil case. [ABSTRACT FROM AUTHOR]