Hot Disk Thermal Constant Analyzer Research Articles

Analysis of thermal properties of main sedimentary rocks in the Beijing area

The Beijing area is abundant in geothermal resources, yet there has been limited research on the thermal properties of rocks and their influencing factors. This paper focuses on the thermal properties of sedimentary rocks in the region, conducting experimental analysis to investigate these properties and their influencing factors. The experiment involved collecting primary sedimentary rock outcrop samples from around Beijing, testing the thermophysical parameters of 48 samples using a Hot Disk thermal constant analyzer. By combining this data with the standard stratum profile and historical information about Beijing, the thermal conductivity of the formation was calculated using the harmonic mean method, allowing for an analysis of the thermal properties of primary sedimentary rocks in the study area. The results indicate that overall distribution of thermal conductivity for sedimentary rocks in the Beijing area ranges from 1.48 to 6.55 W/(m·K), while thermal diffusivity ranges from 0.76 × 10−6 to 4.04 × 10−6 m2/s, and specific heat distribution ranges from 0.57 to 2.52MJ/(m3·K). Furthermore, according to harmonic mean calculations, it was found that Jixian formation exhibits the highest thermal conductivity value, whereas Triassic formation displays the lowest. This study on the thermal properties of sedimentary rocks provides valuable insights for the geothermal field research in the Beijing area.

Thermal Conductivity of Loess: Experimental Studies and Empirical Model

Soil thermal conductivity is an important indicator for developing and utilizing geothermal resources. In this study, the impact of underground environmental factors on the thermal conductivity of loess was explored by studying the thermal conductivity of saturated and unsaturated loess under varying water content, dry density, and temperature using the Hot Disk thermal constant analyzer. The results show that the thermal conductivity of unsaturated undisturbed and remolded loess presents different growth trends as the water content increases. When the water content is less than 9%, the thermal conductivity of undisturbed soil increases slowly. The thermal conductivity of unsaturated loess gradually increases with temperature. When the temperature rises above 30°C, the latent heat transfer of steam gradually strengthens, accelerating the increase in thermal conductivity, which is most noticeable at intermediate saturation. However, the thermal conductivity of saturated loess rises slowly as the temperature rises. A weighted geometric average model is proposed in this study to predict the thermal conductivity of loess under temperature conditions, considering the effects of soil water content, dry density, and mineral content. The model accuracy was corroborated by the measured soil thermal conductivity and the data collected from six regions.

Characterization of the physicochemical and thermal properties of different forest residues

The assessment of the variability of the fuel properties is essential information to understand combustion behavior and to develop mathematical models. This work comprehensively investigates the physicochemical and thermal properties of four different forest residues (eucalyptus, pine, acacia, and olive). Each fuel is fully characterized in terms of chemical composition by proximate and ultimate analysis and its calorific value. Furthermore, this study examines the variation in terms of the thermal properties and the ash elements to evaluate the tendency for slagging and fouling. Selected samples of the solid biomasses were tested using the Hot Disk Thermal Constants Analyzer TPS 2500S to measure the thermal conductivity, which was found in the range of 0.239–0.404 W/mK. In addition, the heat capacity was evaluated within 0.855–2.442 MJ/m3K, and the thermal diffusivity was between 0.187 and 0.258 mm2/s. The ultimate and proximity analyses were carried out on the fuel samples using LECO TruSpec CHN Macro and LECO CS-200 equipment and a muffle furnace, respectively. The results revealed a higher reactivity of eucalyptus, which was around 2 times higher than the other fuels, and the propensity of acacia to produce pollutant emissions (mostly Nitrogen based) and ash deposition problems due to their chemical composition.

Improving the Thermal and Photothermal Performances of MXene-Doped Microencapsulated Molten Salts for Medium-Temperature Solar Thermal Energy Storage

Molten salts are widely used as thermal energy storage materials for solar thermal applications, but they suffer from low photothermal conversion efficiency and potential leakage and corrosion issues. In this paper, MXene doping was proposed to improve the thermal properties and photothermal conversion efficiency of microencapsulated molten salts. MXene nanomaterials, which have excellent thermal conductivity and photothermal conversion efficiency, were used to dope the molten salts. The results tested by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) indicate that MXene was well doped in the molten salt microcapsules. Fourier transformation infrared (FT-IR) spectroscopy was used to confirm that the microencapsulation of the molten salt by silica is a physical action. The results of X-ray diffractometry (XRD) show that the crystal structure of the molten salt maintained stability. The results obtained from the Hot Disk thermal constant analyzer and photothermal conversion experiments showed that thermal conductivity and photothermal conversion efficiency of the MXene-doped microcapsules were increased by 156.2% and 169.4%, respectively. The differential scanning calorimeter (DSC) results indicated that the MXene-doped microcapsules had a reduction of 49.6% in the supercooling degree. The thermal reliability of the MXene-doped microcapsules was 94.0% after 50 thermal cycles. This approach provides a promising solution for improving the thermal properties and photothermal conversion efficiency of microencapsulated molten salts for medium-temperature solar thermal energy storage.

The effect of expanded natural graphite added at different ratios of metal hydride on hydrogen storage amount and reaction kinetics

In this study, metal hydride pellets were formed to accelerate the hydrogen charge/discharge processes. The heat transfer in hydrogen storage material was improved by employing Expanded natural graphite (ENG). The ideal grinding time for LaNi5 material was determined to be 5 h. In the study, LaNi5 alloy was mixed with ENG in 1%, 5%, 10%, and 20% proportions by weight. The amount of hydrogen stored in the reactor by each mixture at 10 bar pressure was measured depending on time. Within the scope of experimental studies, the thermal conductivity coefficient of LaNi5 materials containing 20% ENG by weight was increased by 1380%. Thus, hydrogen charge/discharge processes were accelerated. Storage materials were characterized by XRD and SEM. The thermal conductivity coefficients were measured with the Hot Disk Thermal Constants Analyzer device, and the densities were measured with the Helium Pycnometer device. LaNi5 was chosen as the storage material in the study. It was found that 1–5 wt% ENG addition increased the reaction kinetics without significantly reducing the hydrogen storage capacity in storage alloys. However, in alloys with higher ENG concentrations, the hydrogen storage capacity decreased. The reaction kinetics were increased in the range of 135–260%.

Thermal properties of radiant floor surface materials and numerical evaluation of the thermal performance

A Hot Disk thermal constant analyzer was used to obtain the thermal parameters of composite boards, solid wood floor, and ceramic tiles (CT). FLUENT software was used for the model establishment and the temperature field simulation, and the effects caused by different surface materials were analyzed. A 2D unsteady model was constructed to analyze floor surface temperature and indoor temperature fields in an enclosure space. Comparison of temperature fields caused by different materials showed that both steady indoor temperature and surface temperature of CT were the highest, which is due to its good thermal properties. Thermal conductivity and thermal capacity are the two main factors affecting floor thermal performance in the initial hours, while thermal conductivity is the key factor in the steady period. For the compared floor materials, CT and Sindora glabra (SG) are the optimal choices from the perspective of thermal performance, while composite boards are almost the same in thermal performance.

The effect of copper coated metal hydride at different ratios on the reaction kinetics

In this study, the process parameters that affect the improvement of hydrogen storage material properties were investigated. In order to accelerate the hydrogen charge/discharge processes and to obtain the required hydrogen at the desired flow rates in a short time, the thermal conductivity of the storage materials has been improved, and density analyses have been made. The ideal grinding time has been determined for the LaNi5 material. Within the scope of the experimental studies, the thermal conductivity coefficients of LaNi5 coated with copper and LaNi5 ground for 5 h and coated with copper were increased by 500–750%, and the copper plating ratios were optimized. The materials obtained were characterized by XRD, SEM, and their density was measured with the Helium Pyknometer device and their thermal conductivity coefficients with the Hot Disk Thermal Constants Analyzer. In addition, the hydrogen storage of materials with increased thermal conductivity was investigated experimentally in the metal hydride reactor at the determined pressure. In the study, it was seen that the storage material coated with copper increases the heat transfer, reduces the hydrogen charging time in the metal hydride reactor, and increases the stable discharge time.

Multiscale analysis on the anisotropic thermal conduction of laminated fabrics by finite element method

In this paper, we present a novel “Two-scale finite element method” (tFEM) based on virtual fiber models to investigate the heat conduction behavior of stacked quartz woven fabrics and predict their anisotropic thermal conductivity. Considering the random fiber distribution and the twisted characteristic of yarns, the yarn-scale model was established. Furthermore, the single-layer fabric was composed of interwoven virtual yarns, which are stacked to be the multi-laminate fabric-scale model. Both the yarn-scale model and the fabric-scale model were combined with air matrix to form the two-phase composite model. Hot-Disk thermal constant analyzer was used to measure the anisotropic thermal conductivity of yarns and woven fabrics. Excellent agreement between simulations and experiments is obtained, which indicates the multiscale finite element models in this paper is accurate. The innovations of the study are that not only the effects of fiber numbers and diameters on the thermal conductivity of twist yarns and quartz ply-fabrics are analyzed, but also the detailed heat flux distribution and temperature distribution between fibers and the air are simulated and analyzed. Moreover, the isotropic thermal conductivity of the yarn radial direction and the anisotropic thermal conductivity of quartz fabrics are illustrated.

Improving the thermal performance of novel low-temperature phase change materials through the configuration of 1-dodecanol-tetradecane nanofluids/expanded graphite composites

To improve the thermal conductivity (λ) of organic phase change materials (PCMs) in air-conditioning systems, a series of novel organic PCMs were prepared via a two-step method, including high-speed emulsification and natural physical adsorption. The effect of the mass ratio of the 1-dodecanol-tetradecane nanofluids to the expanded graphite (EG) onmass loss percentage and thermal stability of 1-dodecanol-tetradecane/EG composite PCMs was investigated. Differential scanning calorimetry, Hot Disk thermal constants analyser, and thermogravimetric analysis, as well as scanning electron microscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction were employed to analyse the thermal performance, surface topography, surface functional groups, and crystal structure of 1-dodecanol-tetradecane nanofluids/EG composite PCMs. The molar ratio of the 1-dodecanol and tetradecane with in the nanofluids was determined to be 26.3:73.7, while the optimal EG additional amount was 7 wt%. The results show that the melting and solidification temperatures (Tm and Ts) of the nanofluids are 3.43 °C and 4.17 °C, respectively, whereas the corresponding latent heats of melting and solidification (Hm and Hs) are 212.96 J/g and 213.00 J/g, respectively. After the natural adsorption process, the Tm and Ts of the 1-dodecanol-tetradecane/EG composite PCM with an optimal mass ratio of 93:7 are 3.63 °C and 7.71 °C, respectively, while the corresponding Hm and Hs decrease to 197.95 J/g and 198.81 J/g, respectively. Notably, the λ values of the nanofluids and the 1-dodecanol-tetradecane/EG composite PCM are 0.2186 W/(m∙K) and 2.4070 W/(m∙K), respectively, thereby indicating a tenfold increase in λ. The present study confirms that the 1-dodecanol-tetradecane/EG composite PCM is a potential candidate for cold energy storage in air-conditioning system and cold chain logistics.

Preparation and effective thermal conductivity of a Paraffin/ Metal Foam composite

In this work, a paraffin- metal foam composite were prepared by the vacuum impregnation method. Aluminum and nickel foams were used. The aim of this study is to characterize the thermal behavior of these composites with a view to their use for the thermal management of Li-ion batteries. First, thermal conductivities and diffusivities in solid state were evaluated using a Hot Disk Thermal Constants Analyzer (TPS 2500S) and the Transient Guarded Hot Plate Technique (TGHPT) was used to determine thermal conductivity in liquid state. Next, the effective thermal conductivity of the composite was modeled as a function of the structure of the foam, the thermal conductivity of the metal foam and the thermal conductivity of the PCM. The results show a high impact of thermal conductivity of metal foam and a minor impact of pore size on the effective thermal conductivity.

Effect of Different Firing Temperature on Thermal Conductivity of Ceramic Tiles

The aim of this study is to investigate the effect of different firing temperature on thermal conductivity of ceramic tiles. The body formulation powders of ceramic tiles were made according to the formulation given by company and compacted at 18 MPa using pressing machine in order to obtain button shape specimen with 50 mm diameter. The button shape specimen was fired at different firing temperature which 1150°C, 1175°C, 1200°C and 1225°C. Then, the thermal conductivity of fired specimens was measured by using Hot-Disk Thermal Constant Analyzer. Thermal conductivity result shows that the ceramic tile body fired at 1150 °C producing the lowest thermal conductivity values (0.97 W/mK) in comparison with other specimens. This low thermal conductivity performance is due to the high porosity value in the specimen as a result of more trapped air and implies delaying the heat transfer either inward or outward from the ceramic tiles. Therefore, this study proved that by altering firing temperature, different thermal conductivity values of ceramic tiles were obtained.

Preparation and characterization of sodium thiosulfate pentahydrate/expanded graphite phase change energy storage composites

AbstractIn order to solve the problems of high supercooling, poor thermal conductivity and phase separation after repeated use of Na2S2O3·5H2O with additives. In this paper, Na2S2O3·5H2O is used as the matrix phase change material, and 1% sodium carboxymethyl cellulose, 3% SrCl2·6H2O, and 10% expanded graphite (EG) are added to prepare the modified Na2S2O3·5H2O composite phase change energy storage material. Based on the existing research, the effects of reducing supercooling, improving thermal conductivity, and improving stability are further optimized. The phase change temperature, supercooling degree, heat release time, phase change latent heat, and thermal conductivity of the material are tested by temperature data acquisition instrument, differential scanning calorimeter, hot disk thermal constant analyzer, and other instruments. The effect of EG on the thermal conductivity of the Na2S2O3·5H2O composite phase change energy storage material was explored from the microstructure through a digital scanning electron microscope; Fourier transform infrared spectroscopy verified the composition of the composite phase change materials. After 200 cycles of melting and solidification, the improved composite phase change material has a phase change temperature of 43.49°C, a supercooling degree of 2.19°C, a phase change latent heat of 198.7 J/g, and a thermal conductivity of 3.42 W/m·K. Composite phase change material shows good thermal stability and provides strong support for phase change energy storage technology.

Influence of chain interaction and ordered structures in polymer dispersed liquid crystalline membranes on thermal conductivity

Abstract Polymer dispersed liquid crystalline (PDLC) membrane with intrinsic thermal conductivity was prepared by dispersing liquid crystalline polysiloxane containing crosslinked structure (liquid crystalline polysiloxane elastomer (LCPE)) into polyvinyl alcohol (PVA). Chemical structures were characterized by Fourier transform infrared (FT-IR) and 1H-NMR, and microscopic structures were analyzed by polarizing optical microscope (POM), scanning electron microscope (SEM) and X-ray diffraction (XRD). The thermal conductivity of PDLC membrane was characterized by hot disk thermal constants analyzer, and the tensile properties were measured by tensile testing machine. Thermal properties were characterized by differential scanning calorimeter (DSC) and thermal gravimetric analyzer (TGA). The results show that LCPE was dispersed in PVA uniformly, and the mesogenic monomer of LCPE formed microscopic ordered structures in PDLC membrane. Meanwhile, hydrogen-bond interaction was formed between LCPE and PVA chain. Both microscopic-ordered structure and the hydrogen-bond interaction improved the phonon transmission path, and the thermal conductivity of PDLC membrane was up to 0.74 W/m⋅K, which was 6 times higher than that of pure PVA film. PDLC membrane possessed proper tensile strength and elongation at break, respectively 5.18 MPa and 338%. As a result, PDLC membrane can be used as thermal conductive membrane in electronic packaging and other related fields.

Enhanced Heat Transfer of Carbon Nanotube Nanofluid Microchannels Applied on Cooling Gallium Arsenide Cell

Carbon nanotube nanofluids have wide application prospects due to their unique structure and excellent properties. In this study, the thermal conductivity properties of carbon nanotube nanofluids and SiO2/water nanofluids were compared and analyzed experimentally using different preparation methods. The physical properties of nanofluids were tested using a Malvern Zetasizer Nano Instrument and a Hot Disk Thermal Constant Analyzer. Combined with field synergy theory analysis of the heat transfer performance of nanofluids, results show that the thermal conductivity of carbon nanotube nanofluids is higher than that of SiO2/water nanofluids, and the thermal conductivity of nanofluid rises with the increase of mass fraction and temperature. Moreover, the synergistic performance of carbon nanotube nanofluids is also superior to that of SiO2/water nanofluids. When the mass fraction of the carbon nanotube nanofluids is 10% and the SiO2/water nanofluids is 8%, their field synergy numbers and heat transfer enhancement factors both reach maximum. From the perspective of the preparation method, the thermal conductivity of nanofluids dispersed by high shear microfluidizer is higher than that by ultrasonic dispersion. This result provides some reference for the selection and use of working substance in a microchannel cooling concentrated photovoltaic and thermal (CPV/T) system.

TEOS and Na2SiO3 as silica sources: study of synthesis and characterization of hollow silica nanospheres as nano thermal insulation materials

Hollow structured material (HSM) consisting of monodisperse hollow silica nanospheres (HSN) shows a promising potential for construction insulation due to its affordable cost and simple process. Yet the studies of high-yield and low-energy for the synthetic of HSN are still insufficient. This research reported the comparison of morphology and performance of synthesize HSN utilizing TEOS and Na2SiO3 as silica source. The average yield of Na2SiO3-based samples can reach 93.75%, which is about 10 times higher that of TEOS-based samples. Transmission electron microscopy (TEM) and Scanning electron microscopy (SEM) results revealed that the shell morphology of TEOS-based samples was raspberry-like or smooth structure, while the shell of the Na2SiO3-based samples was round honeycomb-like structure. Hot Disk thermal constant analyzer results demonstrated that the thermal conductivity of the Na2SiO3-based samples was lower than that of the TEOS-based samples with similar inner-diameter and shell thickness. Thereafter, the influence mechanism of the morphology on thermal insulation performance was also investigated. The prepared HSN as filler significantly enhanced the thermal insulation of acrylic coating. This research confirms that the synthesis route with Na2SiO3 was a greener method which can solve the low yield and high energy consumption caused using TEOS as a silica source. Excellent thermal insulation properties indicate HSN will have a broad application prospect in heat-insulating and energy-saving construction.

Thermophysical Properties of a Novel Nanoencapsulated Phase Change Material

Thermophysical properties are important parameters that influence the performance of phase change materials (PCMs) and heat transfer fluids. Micro/nanoencapsulation is an effective technique for preventing leakage and enhancing thermophysical properties of PCMs. In the present study, novel d-mannitol nanocapsules with inorganic shells were synthesized as a medium-temperature PCM. The nanocapsulation was confirmed by scanning electronic microscopy. The specific heat and thermal diffusivity of the nanocapsules and their suspension with heat transfer oil as base fluid were measured by a differential scanning calorimeter and light flash apparatus. The thermal conductivity of the nanocapsule suspension was measured using a hot-disk thermal constants analyzer. The viscosity of the nanocapsule suspension was measured by a rotational rheometer. The results show that the thermal conductivity and thermal diffusivity of the nanocapsules were enhanced compared to the bulk of the PCM due to the inorganic shell. The specific heat, thermal conductivity, and viscosity of the nanocapsule suspension were increased compared to the base fluid. The potential of the nanocapsule suspension as a heat storage and transfer fluid was evaluated.

Thermal properties of shape-stabilized phase change materials based on Low Density Polyethylene, Hexadecane and SEBS for thermal energy storage

In this work, a Shape-stabilized phase change materials were prepared by absorbing hexadecane into the network of styrene-b-(ethylene-co-butylene)-b-styrene (SEBS) tri-block copolymer and coating them with a low-density polyethylene (LDPE). The four composites were prepared at different mass fractions of Hexadecane/SEBS (80/5, 75/10, 65/20, 55/30, w/w %) with 15% of LDPE by the melt-mixing method. Thermal conductivities and diffusivities were evaluated using a Hot Disk Thermal Constants Analyzer (TPS 2500S) and the Transient Guarded Hot Plate Technique (TGHPT) was used to investigate thermal storage and release capacity of the composites. Results were compared to DSC/TGA data. The thermal properties of the composite were improved by the incorporation of the Hexadecane, where the latent heat of composites increased from 106.15 kJ/kg to 179.76 kJ/kg for the composite containing 80% PCM. Interestingly, the mass fraction of Hexadecane could reach approximately 80% with a good form stability, which surmounts almost all mass fraction values reported in the literature.

The Influence of Environmentally Friendly Flame Retardants on the Thermal Stability of Phase Change Polyurethane Foams.

To improve thermal insulation, microencapsulated phase change materials (micro-PCMs), expandable graphite (EG), and ammonium polyphosphate (APP) were introduced into polyurethane foam (PUF) to enhance the thermal stability and improve the thermal insulation behavior. The morphology of the PUF and micro-PCM was studied using a scanning electronic microscope (SEM), while the thermophysical properties of the PUF were investigated using a hot disk thermal constants analyzer and differential scanning calorimetry (DSC). The thermal stability of the PUF was investigated by thermogravimetric analysis (TGA), and the gas products volatilized from the PUF were analyzed by thermogravimetric analysis coupled with Fourier transform infrared spectrometry (TGA-FTIR). The results revealed that the thermal conductivities of the PUF were reduced because micro-PCM is effective in absorbing energy, showing that the PUF functions not only as a thermal insulation material but also as a heat sink for energy absorption. Moreover, the EG and APP were found to be effective in improving the thermal stabilities of the PUF, and the optimized formulation among EG, APP, and micro-PCMs in the PUF showed a significant synergistic effect.

Thermal conductivity enhancement of sodium thiosulfate pentahydrate by adding carbon nano-tubes/graphite nano-particles

Abstract Phase change materials are great thermal energy storage medium, while their low thermal conductivity presents the main obstacle for their potential applications. Improvement of the thermal conductivity and specific heat of Sodium Thiosulfate Pentahydrate as a base phase change material with joining Carbon Nano tubes CNT and Graphite Nano particles GNP as Nano-fillers was investigated in this work. CNT and GNP Nano-fillers added in a mass fraction of 1, 3, 5 and 7% in Sodium Thiosulfate Pentahydrate. Thermal conductivity and specific heat were measured by Hot Disk Thermal Constants Analyzer Instrument. Results have shown that increasing the mass fraction of Nano-fillers increases the composite's thermal conductivity. Thermal conductivity of the composite containing: 7% GNP was 2.944 W/m.k with 155.33% enhancement, in the other hand, thermal conductivity of the composite containing: 7% CNT was 4.031 W/m.k with 249.61% enhancement. Moreover, the charging/discharging rates have been enhanced by adding Nano-fillers to Sodium Thiosulfate Pentahydrate.

Graphene-filled versus ionic liquid-filled poly(vinylidene fluoride-co-hexafluoropropene) electrolytic membranes for high energy devices: thermophysical and electrochemical aspects

The recent developments of membrane technology that requires the composite membrane to work effectively in high energy devices have prompted the inclusion of graphene (GO) and N-butyltrimethylammonium iodide (IL) into a poly(vinylidene fluoride-co-hexafluoropropene) (PVDF-co-HFP) host polymer. From the characterizations that were conducted using FTIR, SEM, TGA, DSC, universal testing machine, Hot Disk Thermal Constants Analyser and the RF impedance spectroscopy, the IL-filled PVDF-co-HFP membrane (1P/IL) was found to have a better dielectric and thermal conductivity, while the decreased porosity of the 1P/GO membrane was discovered to have contributed to its better mechanical performance. Apart from the moieties, which had filled the gaps of the porous architecture and formed a firmer configuration from the chemical junctions with the PVDF-co-HFP, the IL in the membrane was also observed to have increased the density of the accumulated charge carriers and polarization with a better crystallinity control, porosity and ion transportation of the dielectric constant. Based on the above results, the introduction of an ionic liquid (with its plasticizing effect, well-dispersed assembling and diffusional motions) can thus be regarded as significantly improving the properties of the PVDF-co-HFP and particularly in the hi-tech targeted applications of high energy devices such as those of the high-energy Li-ion batteries.