Thermophysical Characterization Research Articles

Cooling potential of cement concrete pavements based on their thermophysical properties

Impermeable paving surfaces constitute one of the main causes of the aggravation of the urban heat island phenomenon. The replacement of such surfaces with cool pavements represents an innovative and promising approach to mitigate this phenomenon. In this study, the investigated cool pavements allow to restrict the rise in the surface temperature by facilitating the evaporation of water through capillary pores. This process occurs from the water-supplied base to the surface exposed to solar radiation. The pavement's cooling potential is quantified by its surface temperature, influenced by various factors, including prevailing weather conditions, thermophysical properties of the pavement, and its initial temperature and saturation state. Within the scope of this research, the pavement’s qualification for its cooling potential is carried out based on the results of an experimental thermophysical characterization. The main objective is to identify the thermophysical properties governing the surface temperature of the pavement under external climatic conditions.To achieve this objective, 21 cement concrete pavements with different formulations are initially identified. These pavements are categorized into two series: the first (denoted as BS) comprises 8 pavements made from recycled sand and containing hydrophilic materials, while the second (denoted as BI) includes 13 pavements made from structural insulating concrete. The methods employed for pavement characterization are outlined, and the corresponding results, encompassing thermophysical properties measurements and surface temperature values, are presented. Analysis of these results reveals new correlations between thermophysical properties and surface temperature. These correlations highlight the coupling between pavement properties, that dictate surface temperature under real summer conditions, contingent on whether the pavement is draining or non-draining. Furthermore, a robust negative linear correlation (R2= 0.92) is identified between surface temperature and evaporation rate under controlled conditions. This underscores the pivotal role of evaporation in substantially regulating the surface temperature of both types of pavements.

Geraniol and hydrophobic geraniol:thymol eutectic mixtures: Structure and thermophysical characterization

The properties of essential oils as food preservatives are well-established. These components have also been used as neoteric solvents to prepare eutectic mixtures. Their high capacity to dissolve poorly water-soluble substances makes them particularly interesting in the biotechnology industry. To implement them, it is essential to determine the structural and chemical-physical properties, as well as develop models to predict the behaviour under any operational condition. Herein, pure geraniol and geraniol/thymol mixtures are studied. Nuclear magnetic resonance experiments and molecular dynamics are used to evaluate the fluid structure. In addition, seven thermophysical properties are measured and correlated. The experimental densities, surface tensions, and viscosities were lower than 952 kg m–3, 33 mN m–1, and 36 mPa s, respectively. These values were adequate for the industrial application of these mixtures. PC-SAFT equation of state well predicted the density with an average deviation of 0.13 %, and the isobaric molar heat capacity with a deviation of 6.9 %. Greater compaction was observed at higher thymol molar ratios and dispersive interactions were predominant. Depending on the composition, geraniol was both an acceptor and donor of hydrogen bonds; conversely, thymol acted as a donor. The article provides the necessary knowledge to be able to use these mixtures and design new ones, as ecological solvents in different applications including those in the agri-food sector.

Thermophysical Characterization of Protic Ionic Liquids: Density Measurements, Group Contribution Method, and PC-SAFT Modeling Application

Thermophysical Characterization of Protic Ionic Liquids: Density Measurements, Group Contribution Method, and PC-SAFT Modeling Application

Micro-encapsulated phase change material suspensions for heat and mass transfer: A thermo-physical characterization

Despite the growing popularity of phase change materials (PCM) and suspensions of micro-encapsulated phase change materials (mPCM) in both industrial and scientific applications, their properties characterization remains partial and mainly limited to thermal properties. The characterization of such suspension is a crucial aspect for comprehending their behavior and optimizing their performance. This paper is dedicated to a wide characterization of two suspensions containing micro-encapsulated phase change material. In pursuit of a thorough understanding, we also extend our characterization efforts to the bulk PCM encapsulated within the particles.Our primary focus is on determining the materials thermal properties such as latent heat and specific heat capacity using differential scanning calorimetry. Different cooling and heating rates have been employed in our measurements. Regarding our experiments, the bulk phase change material is predominantly identified as octadecane. Results obtained from calorimetry are then compared between the bulk PCM and the mPCM suspensions. By comparing the magnitudes of latent heat obtained for suspensions with the bulk material, we can accurately determine the mass fraction of PCM within each suspension. Noteworthy, during the solidification process an additional latent heat peak is observed only for the encapsulated PCM.The density of the materials is also measured. The phase change of PCM included in the capsules can be observed in densimetry: within the studied temperature range (283.15–306.15 K), the most significant density variations occur during intervals associated with phase change transitions. In ranges where the PCM, included in the capsules, is in a single-phase state (solid/liquid), we provide linear laws that account for density variations with temperature.Finally, our characterization work focuses on the rheological properties of the materials. While the bulk PCM in liquid phase exhibits a Newtonian viscosity, mPCM suspensions present a non-Newtonian viscosity. Both shear-thinning and shear-thickening behaviors are observed depending on the suspension particle volume fraction ϕ of mPCM. This paper concludes with a full comparison of our characterization results with models and correlations proposed in the literature.

Examining the Thermophysical Impact of Low Concentrated Nanoparticles Hexagonal Boron Nitride Embedded in Phase Change Material for Photo to Thermal Energy Conversion

Phase change materials (PCMs) have garnered substantial interest for their use in thermal energy storage. However, restricted thermal conductivity of PCMs hinders their effectiveness in application. The objective of this work is to integrate hexagonal boron nitride (h‐BN) in low concentration with RT38 PCM for thermophysical characterization and photo to thermal energy conversion. The composites are prepared by adding 0.03–0.07 weight percent (wt%) nanoparticles with RT38 PCM through two‐step technique. As per the results, prepared samples remain chemically and thermally stable. Besides, addition of 0.05 wt% of h‐BN nanoparticles with PCM (RT38‐0.05) enhances thermal conductivity to 43%. Additionally, latent heat of melting remains at 137 Jg−1 for 0.05 wt% nanoparticle integrated nanocomposite in comparison to base 140 Jg−1 with slight variation in its melting temperatures. Further, PCM and nanocomposites exhibit zero weight degradation on thermal‐stability analysis up to 160 °C. The research examines thermal energy storage behaviour of base PCM and RT38‐0.05 nanocomposite by applying 800 Wm−2 irradiations. The analysis shows that RT38‐0.05 nanocomposite reaches 49 °C in 9 min, whereas base PCM achieves 43 °C. Thus, the integration of h‐BN nanoparticles in PCM results in improved thermophysical properties and greater conversion of photo to thermal energy.

Synthesis and thermophysical property characterization of aqueous graphene quantum dot dispersions for air-conditioning applications

Air-conditioning systems are on track to demand most of the electricity consumed by buildings around the world. The authors propose that dispersing quantum dots into the chilled water loops of air-conditioners represents a path towards improving the efficiency of air-conditioners. As such, the thermophysical properties of carbon-based quantum dot ‘nanofluids’ (e.g., nanoparticles dispersed in liquids) are presented in this study for sub-ambient temperatures (5–15°C)—an under-explored temperature range which requires understanding for air-conditioning applications. This study also explores dispersion stability and materials compatibility—another under-explored area in the literature which is required for commercial uptake. In this study, carbon quantum dots were synthesized via the hydrothermal route and characterized with UV–Vis, FT-IR, Raman spectroscopy, and TEM. Next, the thermophysical properties of specific heat capacity, thermal conductivity, and viscosity of the nanofluids were experimentally measured between 5 and 15°C (not previously reported for aqueous quantum dots). The highest thermal conductivity enhancement was ∼11% (compared to DI water) for 0.3 wt.% at ∼11 °C. Finally, the stability of the fluid was monitored over time and after exposing the fluids to common materials used in air-conditioning systems (e.g., copper, brass, and stainless steel). Unchanged UV–Vis spectra and the lack of sedimentation indicate that the developed dispersions are indeed suitable for chilled water air-conditioning applications.

Thermophysical characterization and reliability analysis of binary composite nano doping on stearic acid-acetamide eutectic PCM

Organic phase change materials (PCM) have been extensively studied and employed for thermal energy storage applications, especially in the last decade. Wide range of melting temperature with high latent heat of fusion and absence of super cooling have made them highly desirable for energy storage applications, yet their intrinsic low thermal conductivity has been a major drawback in practical implementation. This study intends to address this and study the thermophysical characteristics of an organic PCM through composite nano doping. Stearic acid-acetamide eutectic PCM with a melting temperature of 65.73 °C and a latent heat of 203.72 J/g, was incorporated with a binary blend of Aluminum Oxide nanoparticles and multi-walled carbon nanotubes (MWCNT). The addition of metallic oxide and carbonaceous nanoparticles increased the melting temperature of the eutectic mixture by 2.9 °C and a highly advantageous increment in latent heat of fusion by 10% was observed, due to the improved molecular interaction introduced by the nanoparticles. Composite nano doping enhanced the thermal conductivity of the eutectic PCM by a 132.7% and also resulted in high optical absorption properties. The prepared eutectic mixtures were chemically stable and the eutectic PCM showed an improved final degradation temperature and thermal stability, with composite nano doping. Thermal reliability was analyzed through accelerated thermal cycling test and the eutectic mixtures could retain their thermal characteristics and chemical stability even after 500 thermal cycles. Composite nano doping proved to be a reliable thermophysical characteristics enhancement technique for organic eutectic PCM.

Quenching optimization of a hot stamping line for aluminum automotive components

The rising cost of fuel and harder environmental regulations driving the need for more eco-friendly vehicles have compelled automotive manufacturers to search for innovative lightweight solutions. Consequently, hot stamped aluminum alloys are gaining prominence due to their exceptional specific strength and improved formability compared to cold formed components. Unfortunately, the current state of knowledge in the field lacks the necessary depth to establish a reliable, fast and optimized process for aluminum hot forming. To address this gap, a collaborative effort between Mondragon Unibertsitatea (knowledge provider), Fagor Arrasate (hot stamping line supplier), and Batz (tool manufacturer) has been initiated. The collaborative endeavour aims to conduct semi-industrial trials involving the hot stamping of an authentic automobile bumper employing high-strength 6xxx and 7xxx aluminum alloys. The hot stamping trials have been performed under different in-die quenching times and mechanical properties of the stamped bumpers have been empirically tested. These results have helped to define the optimal quenching time. With that aim, first, a thermophysical and rheological characterization of the aluminum has been performed, followed by the development of a model to predict mechanical properties of aluminum alloys. This predictive model, together with the aluminum material data, has been then integrated into the simulation framework to enable accurate forecasting of mechanical properties and, consequently, the identification of the optimal quenching duration. The results revealed that quenching times as brief as 1 second could be employed while maintaining acceptable mechanical properties in a rapid cycle hot stamping process. These expedited quenching times have the potential to boost production by an impressive 70 % when compared to the conventional hot stamping process applied to the equivalent steel bumper.

Simulation test platform for the controlled storage and transfer of liquid hydrogen

Clean-energy propulsion machines, including trucks, tractors, ships, and aircraft, for heavy-duty and long-range mobility have moved, by necessity, to onboard liquid hydrogen (LH2). However, the established method of storage and transfer is problematic due to losses and for any duty-cycle of a sporadic or on/off nature. Integral servicing system methodology is needed for both safety and cost effectiveness in the key drivers of time savings, product savings, and venting exposures. Modern controlled storage technology enables quick and effective vehicle servicing at the point of use. Simulations of controlled storage/transfer (CS/T) methodologies are performed using a multi-purpose LH2 simulation test platform comprised of two primary systems: Cryostat CS900 tank and transfer system and the LS20 liquefaction/refrigeration and storage system. Testing includes both steady-state and transient modes of operation to demonstrate both zero boiloff (ZBO) and zero-loss transfer (ZLT) modes. Technical areas of use include product development for tanks, refrigeration, transfer systems (lines, dispensers, pumps, valves); experimental validation of analytical models and thermofluidic properties; thermal insulation performance test data under relevant conditions; thermophysical characterization of materials and structures; instrumentation and sensors development; tank boiloff and heat flux engineering design data. Descriptions and preliminary test results are given along with thermal performance analyses from real-world testing and experimentation.

Thermo-physical Characterisation of Plasters Containing Phase Change Materials (PCMs)

The integration of phase change materials (PCMs) within building materials is an interesting strategy to improve the thermal performance of buildings, thus reducing the energy demand for heating and/or cooling. To do so, the thermo-physical characterisation of the new enhanced materials is of outmost importance which, however, is difficult to carry out due to several limitations related to the most used techniques. To overcome these, a new alternative set up was realized, which allowed the thermo-physical characterization of different plaster samples enhanced with granular organic PCM. A steady-state test was conducted maintaining constant thermal gradients through which the thermal conductivity of the materials used was estimated. Then, a two-step ramp unsteady-state test was conducted through which the specific heat and the latent heat were estimated, showing a good agreement with values provided by the PCM suppliers. The estimated properties were then validated against experimental data acquired during the monitoring activity under real outdoor conditions of different wall samples on which the PCM-enhanced plasters were applied. With the estimated properties, RMSE values were lower than 1 °C for temperatures and lower than 2.50 W·m−2 for heat fluxes.

Cu-Graphene water-based hybrid nanofluids: synthesis, stability, thermophysical characterization, and figure of merit analysis

Hybrid nanofluids are emerging as an alternative to conventional heat transfer fluids and nanofluids for improving the thermal efficiency of heat exchanging devices synergistically due to their outstanding thermophysical properties associated because of the dispersion of different types of nanoparticles as compared to mono nanofluids. This will help in optimizing fluid characteristics in different flow regimes for several applications. However, enhancing the thermal energy efficiency of heat exchangers is challenging owing to the deprived stability of hybrid nanofluids at greater volume concentrations. This work concentrated on the synthesizing, thermophysical depiction, and thermal performance estimation of stable water-based Cu-graphene hybrid nanofluids using very low volume concentrations of Cu and graphene hybrid nanostructures. Cu-graphene hybrid nanofluid was successfully synthesized by dispersing the synthesized Cu and graphene nanostructures (keeping the Cu concentration constant at 0.04 vol % and varying the graphene concentration from 0.01 to 0.1 vol %) in water. Hybrid nanofluids display excellent stability against aggregation for up to 7 weeks, as proven by higher zeta potential values. Thermophysical characteristics of the prepared hybrid nanofluids were effectively measured. The thermal conductivity of Cu-graphene hybrid nanofluids shows exceptional enrichment (~ 35%) at minimal concentrations of hybrid nanostructures. Viscosity of the water-based hybrid nanofluids shows remarkable enhancement as compared to water and represents the increasing trend in viscosity of the base fluid with respect to the increase in concentration of hybrid nanostructures. The thermal and rheological properties of hybrid nanofluids are effectively validated with existing theoretical models. In addition, the specific heat and pumping power of Cu-graphene hybrid nanofluids with respect to the volume concentration of hybrid nanostructures are calculated using the existing theoretical equations. A figure of merit (FOM) analysis was conducted for the synthesized hybrid nanofluids to gauge thermal efficiency and evaluate the applicability of these hybrid nanofluids under laminar and turbulent flow conditions.

Thermophysical characterization of innovative and recyclable composites, being developed and considered for battery boxes mass production

This paper describes the results of preliminary thermophysical characterization carried out on recyclable & biobased Fibre Metal Laminates (FML) for lighter, more sustainable & safer battery box production, with higher fire resistance. These FMLs are designed to be suitable for the low and medium end automotive. In particular, the specific heat and the thermal conductivity of four different types of FMLs were analysed and assessed depending on temperature. The results show increasing trends of specific heat by increasing temperatures and thermal conductivity values increasing both with temperature and the density of the samples. Further studies will be carried out both to optimise the composition of the FMLs and to provide extensive assessment of the thermal and mechanical properties of the solutions so as to guarantee high thermal and mechanical performances and durability of battery boxes for electric vehicles.

Manipulation of the thermo-rheological properties of stable Fe3O4 nanoparticles-embedded PCM nanoemulsions

Phase Change Material (PCM) nanoemulsions offer numerous benefits as thermal energy storage systems, including high energy storage capacity, rapid thermal response, enhanced stability, and easy integration into existing thermal management systems. This study focuses on producing nanoemulsions with fine droplets of commercial paraffin RT42, stabilized with the anionic surfactant sodium dodecyl sulfate (SDS) using the sonication method. The impact of formulation of PCM nanoemulsions on its thermophysical and rheological characterization has been investigated. The results indicated that the degree of supercooling declined from 12.8 °C to 8.6 °C as the PCM volume fraction varied from 10 to 45 vol%. This decrease was attributed to the enlargement of PCM droplet size from 110 to 164 nm while maintaining a constant PCM-to-surfactant ratio of 10:1. By incorporating Fe3O4 nanoparticles as a nucleating agent at two different concentrations of 1 and 4 %, the supercooling degree decreased from 10.2 °C to 8.2 °C when 4 % Fe3O4 nanoparticles were added. The samples exhibited remarkable stability throughout a period of one year of storage and under dynamic conditions, including 50 freeze-thaw cycles. Rheological investigations and the gelation mechanism through estimation of the attractive and repulsive interaction forces among droplets revealed that nanoemulsions with volume fractions ≥30 % transformed from fluid-like states to viscoelastic gels due to the depletion attractions caused by SDS micelles in the continuous phase. These findings contribute to a better understanding of the factors influencing the formation of viscoelastic PCM nanoemulsion gels and their potential applications across various fields.

Thermo-Physical Properties and Characterization Studies on Vacuum Hot-Pressed Boron Carbide Ceramics

Thermo-Physical Properties and Characterization Studies on Vacuum Hot-Pressed Boron Carbide Ceramics

High-Throughput Thermophysical Characterization of Semiconductors

High-Throughput Thermophysical Characterization of Semiconductors

Thermophysical Characterization of Local Materials from a Locality in Chad for Use in Eco-Building

Thermophysical Characterization of Local Materials from a Locality in Chad for Use in Eco-Building

Thermophysical characterization of concrete reinforced with baobab trunk fibers (Adansonia digitata L.) for thermal insulation of buildings

This work deals with characterizing concrete based on baobab trunk fibers for thermal in- sulation in buildings. The aim is to study the effect of the fiber content and the type of fiber treatment on the hygroscopic and thermo-physical properties of the concrete. Therefore, two types of treatment were carried out: an alkaline treatment and a thermo-alkaline treatment. Hygroscopic test results (34.25% to 54.92% for fiber content ranging from 14% to 28%) show that adding fibers to concrete makes them more sensitive to water. However, thermochemical treatment of the fibers reduces this water sensitivity. The thermal conductivities of concrete range from 0.202 to 0.086 W/m.K for the same fiber content. These results show that these biomaterials can be used in construction to improve building insulation.

Thermophysical characterization of 1-propylpyridinium 1,1,1-trifluoromethanesulfonate, effect of alkyl chain length of the cation, and anion structure

Thermophysical characterization of 1-propylpyridinium 1,1,1-trifluoromethanesulfonate, effect of alkyl chain length of the cation, and anion structure

Analyzing the thermal potential of binary 2D (h-BN/Gr) nanoparticles enhanced lauric acid phase change material for photovoltaic thermal system application

Thermal energy storage as latent heat is an effective strategy to preserve the excessive energy available. In this aspect, fatty acid phase change materials (PCMs) are promising materials since they have a high latent heat, nontoxic, and little sub-cooling. However, their inherently low thermal conductivity severely restricts their applicability. Herein, hexagonal boron nitride (h-BN) and graphene (Gr) binary nanoparticles (NPs) are taken as nano-additives to enhance thermal conductivity of lauric acid (LA). The NPs added PCM known as nano-enhanced phase change material (NePCM) is prepared by two-step method for thermo-physical characterization. According to an optical performance investigation using ultraviolet-visible spectroscopy (UV–Vis); optimal composite LBG2% (LA with 3 % h-BN and 2 % Gr NPs) displayed 78 % reduction in transmissibility compared to base LA. Further, LBG2% composites exhibited elevated thermal conductivity of LA by 97 %. Additionally, differential scanning calorimeter (DSC) observed a slight variation in latent heat and melting temperature. Latent heat for composite LBG2% found to be as 176 Jg−1 with a reduction equal to NPs weight% as compared to base LA. Moreover, the preferred composite LBG2% displays chemical stability and thermal reliability after 500 heating/cooling cycles. The addition of LBG2% NePCM to a photovoltaic thermal system increased electrical and thermal efficiency to 9.41 % and 69 %, respectively, as compared to the photovoltaic thermal system alone, which was 7.1 % and 64 %. It can be concluded, the binary NPs enhanced composite LBG2% exhibited improved photoabsoprtion and thermal conductivity, along with thermal reliability and higher latent heat. The composite has significant application potential within the melting temperature range of 50 °C for employment in solar photovoltaic systems and other applications.

Incorporation of graphene nanoplatelets with organic phase change materials – Studies on thermal conductivity enhancement, and thermal and chemical stability

Phase change materials (PCMs) have the capability to store energy in form of latent heat, along with exceptional chemical and thermal stability. However, their main limitation lies in their thermal conductivity, which hampers the rate at which energy can be stored and released. In the current work, we have chosen graphene nanoplatelets (GNP) as the thermal conductivity enhancer and organic PCM melting at 21, 30, 35, and 46 °C and a hydrated salt melting at 24 °C. Melt blending technique was used to develop GNP-enhanced PCM, and their chemical and thermal properties were studied. Thermal conductivity was studied in the temperature varying from 25 to 50 °C and we observed a substantial upsurge in thermal conductivity with an upsurge in concentration of GNP. Specific heat was found to increase with an upsurge in concentration of nanoparticles. DSC thermograms depicted a minor upsurge in melting and solidification temperatures and a decline in their latent heat concerning an upsurge in GNP concentration. Subcooling temperature of all pure and GNP-enhanced composites was found to be less than 10 °C. FTIR spectrum peaks designated the presence of physical interaction with the nonappearance of chemical interaction between GNP and PCM. TGA thermograms depicted a minor weight loss till 165 °C and rapid weight reduction in temperature range of 165 – 270 °C which conveys that incorporation of GNP has enhanced thermal stability of PCM. From thermophysical and chemical characterization of pure and GNP-enhanced PCM, we can conclude that GNP-enhanced composites can be used for enhanced heat transfer applications.