Key Thermophysical Properties Research Articles

BF3 Complexing Phosphate/Phosphonate Ionic Liquids: Synthesis, Characterization and Thermophysical Properties.

A new group of BF3 complexing phosphate/phosphonate ionic liquids (ILs) [Emim][X(BF3)2] (X=dimethyl phosphate, diethyl phosphate, methyl phosphonate, and ethyl phosphonate) were synthesized and characterized. Key thermophysical properties of the new complex ionic liquids, including density, viscosity, conductivity, surface tension, solid-liquid phase transition, and thermal stability were determined and compared with those of [Emim][X]. Some other important thermophysical properties such as isobaric thermal expansion coefficient, molecular volume, standard molar entropy, and lattice potential energy were obtained from measured density data, and the free volume was estimated by a linear equation presented in this article, while critical temperature, normal boiling temperature, and enthalpy of vaporization were estimated from measured surface tension and density data. Furthermore, Fragility study shows that [Emim][X(BF3)2] should be considered as fragile liquids, while [Emim][X] could be considered as extremely fragile liquids. The ionicity of [Emim][X(BF3)2] was predicted by Walden rule, and the result shows that these ILs fit well with Walden law. The key features of these complex ILs are their extremely low glass transition (-95.33~-98.46 °C) without melting, considerably low viscosities (33.876~58.117 mPa ⋅ s), and high values of free volume fraction (comparable to [Omim][BF4], [Emim][NTf2], and [Emim][TCB]).

Density measurement and uncertainty evaluation of elemental and alloy liquids using electrostatic levitation

Liquid density is a crucial parameter in physical models, numerical simulations, and a key thermophysical property essential for understanding various physical phenomena. Although density measurements of liquid metals have been carried out with various methods, it is still hard to give consistent and precise results, particularly at high temperatures. In this study, we systematically perform the precise density measurements for 34 elemental and alloy liquids using electrostatic levitation (ESL). Through a comprehensive review of density data in the literature, we propose recommended density values for fourteen transition metal liquids. Notably, we observe significant discrepancies in density measurements between ESL and electromagnetic levitation (EML). After conducting careful uncertainty evaluation and error analysis, the discrepancies are attributed to the shape deformation of the liquids, which seriously influences the density and its temperature coefficient measurements. The present work not only provides high-quality density data but also helps to develop standards for archiving density datasets and improve the density measurements of high-temperature molten melts.

Thermal stability and durability of solar salt-based nanofluids in concentrated solar power thermal energy storage: An approach from the effect of diverse metal alloys corrosion

Concentrated Solar Power (CSP) technology has witnessed substantial growth, with forecasts predicting an increase of 3.4 GW between 2019 and 2024. This expansion necessitates the installation of energy storage systems to meet the growing demand. Solar molten salts, specifically a mixture of 60 % NaNO3 and 40 % KNO3, have emerged as the primary thermal energy storage (TES) medium in commercial CSP plants. However, a significant challenge lies in the corrosive nature of molten salt at high temperatures, which poses limitations in TES applications. The literature has explored a promising solution: reducing corrosion rates by incorporating nanoparticles into molten salts, creating nanofluids. To assess the viability of nanofluids for CSP, it is essential to understand how they perform under working conditions, especially regarding their thermal stability and durability. This study presents further evidence of nanofluid interactions with component materials under static working conditions. Specifically, focus on the impact of corrosion products precipitated during corrosion tests on the physical and thermal properties of Solar Salt-based silica dioxide nanofluids. In this research, nanofluids in contact with stainless steel, nickel‑chromium alloy, and carbon steel were examined before and after subjecting them to a 90-day thermal exposure at 500 °C. These findings provide valuable data on key thermo-physical properties during service, contributing to the design of more precise TES systems and enhancing their overall efficiency and effectiveness.

Transport Properties of Equiatomic CoCrFeNi High-Entropy Alloy with a Single-Phase Face-Centered Cubic Structure

The key thermophysical properties necessary for the successful design and use of CoCrFeNi alloy in thermophysical applications have been measured experimentally, and the results have been compared with literature values and results previously obtained for commercial Ni-Cr alloys and equiatomic CoCrFeNi alloy. In particular, the thermal diffusivity, coefficient of thermal expansion (CTE), and specific heat capacity were measured for the as-cast and homogenized equiatomic CoCrFeNi alloy over a temperature range allowing the thermal conductivity to be calculated up to 1173 K. The thermal conductivity and thermal diffusivity of the equiatomic CoCrFeNi alloy were found to deviate from monotonic behavior in the temperature range from 773 to 1100 K. Such a deviation was previously observed in the behavior of the temperature dependence of CTE and specific heat capacity of the equiatomic CoCrFeNi alloy. The non-linear behavior is primarily the result of order/disorder phenomena for the as-cast and homogenized sample, as well as non-equilibrium solidification under arc melting conditions for the as-cast sample. The measured data of thermophysical properties are provided for thermally differently treated samples, and it is shown that there is a difference in the behavior of the temperature dependences of CTE, thermal diffusivity, and heat capacity.

Study on performance evaluation framework and design/ selection guidelines of working fluids for subcritical organic Rankine cycle from molecular structure perspective

Organic Rankine cycle (ORC) is a promising power cycle to convert low-grade thermal energy. The quick and easy evaluation of the potential working fluids lacking thermophysical property data is important for the working fluid selection of ORC. This paper proposes a systematic framework of working fluid evaluation from the molecular structure perspective, which couples the quantitative structure property relationship (QSPR) and universal equations of state. The thermodynamic performance of ORC is first correlated with four key thermophysical properties based on universal equations of state. Then, these thermophysical properties are obtained from the corresponding QSPR models based on the molecular structure of working fluids. The influence factors of ORC performance at a micro level are investigated using the QSPR models. Moreover, the effects of molecular characteristics on thermal efficiency are analyzed. The criteria for working fluid design/selection are recommended aiming at the improvement of thermal efficiency. The proposed framework shows sufficient accuracy with the relative errors of −0.41 - 15.85% and mean absolute error of 8.29% compared with the results based on REFPROP. It is found that the cyclization of carbon chain is an ideal method for the working fluid design based on alkanes and alkenes. This work can provide new insights for the evaluation, selection, and design of working fluids on the molecular structure level.

Uncertainty analysis and performance evaluation of thermophysical property measurement of liquid Au in microgravity

A new method for quantifying facility performance has been discussed in this study that encompasses uncertainties associated with thermophysical property measurement. Four key thermophysical properties: density, volumetric thermal expansion coefficient, surface tension, and viscosity of liquid Au have been measured in microgravity environment using two different levitation facilities. Levitation experiments were conducted using the Electrostatic Levitation Furnace (ELF) onboard the ISS in Argon and air, and the TEMPUS Electromagnetic Levitation (EML) facility on a Novespace Zero-G aircraft parabolic flight in Argon. The traditional Maximum Amplitude method was augmented through the use of Frequency Crossover method to identify the natural frequency for oscillations induced on a molten sample during Faraday forcing in ESL. The EML tests were conducted using a pulse excitation method where two techniques, one imaging and one non-imaging, were used to study surface oscillations. The results from both facilities are in excellent agreement with the published literature values. A detailed study of the accuracy and precision of the measured values has also been presented in this work to evaluate facility performance.

Prediction Models of Saturated Vapor Pressure, Saturated Density, Surface Tension, Viscosity and Thermal Conductivity of Electronic Fluoride Liquids in Two-Phase Liquid Immersion Cooling Systems: A Comprehensive Review

As the carriers of massive data, data centers are constantly needed to process and calculate all kinds of information from various fields and have become an important infrastructure for the convenience of human life. Data centers are booming around the world, accompanied by the problems of high power consumption and poor heat dissipation. One of the most effective solutions to these problems is to adapt a two-phase liquid immersion cooling technology, which is a more energy-saving and efficient method than the traditional cooling methods; the reason for this is mainly that in two-phase liquid immersion cooling technology, the heat transfer caused by the phase change of liquid coolants (electronic fluoride liquids) helps to cool and improve the temperature uniformity of electronic components. However, the requirements for the electronic fluoride liquids used in two-phase liquid immersion cooling systems are strict. The thermophysical properties (saturated vapor pressure, density, surface tension, viscosity, thermal conductivity and latent heat of vaporization, etc.) of the liquid coolants play a very key role in the heat dissipation capacity of two-phase liquid immersion cooling systems. However, it is not always easy to obtain new electronic fluoride liquids under many actual conditions and reasonable prediction models of their thermophysical properties could contribute to the preliminary screening of the coolants. Thus, the prediction models of their key thermophysical properties (saturated vapor pressure, saturation density, surface tension, viscosity and thermal conductivity) are reviewed, and the accuracy and practicality of these prediction models in predicting the thermophysical properties of electronic fluoride liquids (FC-72, HFE-7100 and Novec 649) are evaluated. This work will provide a valuable reference for actual engineering applications.

Thermophysical characterization of paraffin-based PCMs for low temperature thermal energy storage applications for buildings

Trustworthy information about the thermophysical properties of phase-change-materials (PCMs) is vital for designing low temperature thermal energy storage systems for buildings and for modelling their thermal behaviour. However, data provided by manufacturers are recurrently optimistic, insufficient and/or uncertain for developing reliable numerical approaches, which requires further investigation. This paper aims to assess the key thermophysical properties of ten paraffin-based PCMs: microencapsulated and bulk paraffins.The melting/solidification peak temperatures, the enthalpy of fusion/solidification and the specific heat capacity were measured by Modulated-Differential-Scanning-Calorimetry. The Transient-Plane-Source-method was used to estimate the variations of the thermal conductivity/diffusivity with temperature. The thermal stability was assessed by High-Resolution-Thermogravimetric-Analysis. The microstructures of the microencapsulated PCMs were examined via Scanning-Electron-Microscopy.It was concluded that some information provided in the datasheets is roughly corroborated by the experimental results. However, in some cases, it was too optimistic (particularly the enthalpy of fusion/solidification), incoherent (mainly the melting/solidification peak temperatures) or scarce (e.g., the values of the thermal conductivity and the specific heat of the solid/liquid phases). The major contribution of this work is a reliable dataset for upcoming numerical modelling, saving time and resources in future studies. The results can also be used as a reference for future inter-laboratorial comparison studies.

Evaluation of Liquid Heat Capacity of Latest Low Global Warming Hydrofluoroolefins (HFOs): A Comparison of a Cubic Equation of State, Fundamental Equations of State, and a Corresponding State Equation

Isobaric heat capacity is one of the key thermophysical properties for working fluids in thermal systems and plays an important role in the development of equation of state. Due to the lack of experimental data for promising hydrofluoroolefins (HFOs), we carried out theoretical predictions for condensed liquid phase with three different methods: traditional cubic equation of state (CEOS), fundamental equations of state (FEOS) explicit in Helmholtz free energy and a corresponding state equation (CSE). Both CEOS and CSE are generalized models that only need several characteristic parameters to conduct calculation, while FEOS are specific models in which the structure and parameters are regressed from experimental data of one certain fluid. Liquid heat capacity data of 9 HFOs were calculated, including well-known R1234yf, R1234ze(E), and latest prospective R1123, R1216, R1243zf, R1234ze(Z), R1336mzz(Z), R1141, and R1125zc. A critical comparison was carried out between different calculation methods. The comparison showed that both CSE and FEOS predicted available experimental data well with AADs % less than the reported experimental uncertainties. For refrigerants without experimental heat capacity, CSE and FEOS showed good agreements with AADs % less than 3.6 %. The selected CEOS always provided relatively larger predictions than experiments or the other two methods. Despite that, calculated data of CEOS showed a strong linear relation with the other two methods, which suggested that there might be a potential linear modification or correlation for CEOS in improving its heat capacity calculations. Furthermore, when there were no experimental data available, CSE used in this study could be a useful preliminary evaluation tool for the liquid heat capacity of hydrofluoroolefins, considering its accuracy and easy application characteristics.

Performance of binary zeotropic mixtures in organic Rankine cycles (ORCs)

Compared to pure fluids, zeotropic mixtures have the potential to lower the irreversibilities in low temperature Rankine cycles by better temperature profile matching of the working fluid with the heat source/sink. However, having a gliding temperature does not guarantee performance boost over pure fluids, as many factors influence the exergy efficiency of the cycle. In this study, 25 pure fluids and 104 binary mixtures of natural working fluids are analyzed in subcritical ORCs with heat source temperature range of 125–300 ℃ and different condensing conditions and the results are investigated within two frameworks: (1) comparing the mixtures to their pure constituents, (2) comparing the mixtures to the best performing pure fluid. In one behavior type, the performance of the mixture falls between the performance of its pure constituents for all evaporator pressure range, and the mixture provides no benefit. However, some mixtures could provide performance boost in a specific evaporator range. Therefore, the maximum allowable evaporator pressure plays an important role in the performance comparison of zeotropic mixtures to their pure constituents. Mixtures which outperform their pure constituents in the first perspective, are further analyzed in the second perspective. Finally, a screening method is presented to map the binary mixtures with performance boost compared to their pure constituents and high absolute exergy efficiency. This method is based on the key thermophysical properties of the fluids including critical temperature and normal boiling point, as well as working conditions such as heat source and heat sink temperature and PPTD in the evaporator and the condenser.

Protocol for selecting exemplary silicate deposit compositions for evaluating thermal and environmental barrier coatings

AbstractA protocol for selecting representative silicate compositions for comparative testing of gas turbine coating materials is presented. It begins with a curated dataset of compositions of engine deposits and naturally occurring siliceous debris including volcanic ashes, sands, and dusts. The compositions are first reduced to the five major oxides—those of Ca, Mg, Fe, Al, and Si—and then distilled further using principal component analysis and k‐means clustering. The process ultimately yields four classes of possible deposits with common chemical characteristics. Each class is represented by a composition centroid and a range in Ca:Si ratios. Key thermophysical properties of the possible deposits are calculated and related to the glass network connectivity, characterized by the Si:O ratio. Finally, deposits from each of these classes are compared in terms of their reactions with prototypical thermal and environmental barrier oxides, with due consideration of the effects of composition variations within each deposit class. The protocol is, in principle, adaptable to datasets compiled by OEMs and researchers in gas turbine coatings.

Perspective: Temperature-Dependent Density And Thermal Expansion Of Cryoprotective Agents

Density is a key thermophysical property, affecting the response of materials to temperature changes in different ways, consistent with the phase of state. In fluids, temperature variation across the domain leads to colder areas being heavier than warmer areas, where buoyancy effects drive fluid flow and thereby increase heat transfer. This phenomenon is known as natural heat convection, which in general is a more efficient heat transfer mechanism than heat conduction in the absence of flow. In solids, where the material is locked in place, colder areas tend to contract while warmer areas tend to expand, leading the material to deform. When this deformation is constrained by the geometry of the domain and/or its container, mechanical stresses develop. This phenomenon is known as thermomechanical stress (or thermal stress), which can lead to structural damage such as fractures. The picture becomes even more complex during vitrification (or glass formation), where the material gradually changes from liquid to an amorphous solid over a significant temperature range. There, due to temperature variation across the domain, fluid mechanics and solid mechanics effects may coexist. It follows that characterization of the density as a function of temperature is crucial for the analyses of thermal, fluid, and mechanical effects during cryopreservation, with the goals of protocol planning, optimization, and preserving structural integrity. For this purpose, the current study focuses on the density of the material and its companion property of thermal expansion. Specifically, this paper reviews literature data on thermal expansion of cryoprotective agents (CPAs), discusses the mathematical relationship between thermal expansion and density, and presents new calculated density data. This study focuses on the CPA cocktails DP6, VS55, M22, and their key ingredients at various concentrations, including DMSO, propylene glycol, and formamide. Data for DP6 combined with a selection of synthetic ice modulators (SIMs) are further presented.

A review of the thermophysical properties and potential of ionic liquids for thermal applications

Key thermophysical properties of ILs were evaluated and compared leading to their classification by thermal conductivity and viscosity behavior into groups according to their cation types and also providing insights for their thermal applications.

Exploration of Basalt Glasses as High-Temperature Sensible Heat Storage Materials.

Thermal energy storage (TES) systems are a key technology that utilizes renewable energy and low-level thermal energy to ensure continuous and stable operation in concentrated solar power plants, family heating, and industrial waste heat recovery fields. It solves the intermittent problem of solar radiation and significantly improves energy efficiency and economic benefits. Three varieties of natural basalt ores have been selected, namely, intermediate, basic, and ultrabasic basalt, which have been prepared into basalt glasses by the melt-quenching method. The applicability of basalt glass to high-temperature heat storage applications is studied. In the present paper, the chemical composition and structure of basalt glasses have been determined. The effect of temperature and composition on key thermophysical properties such as density, heat capacity, thermal diffusion, thermal conductivity, and thermal expansion has been analyzed during a series of thermal cycles. It has been confirmed that basalt glass has extremely high heat storage performance and thermal stability, and its working temperature is as high as 1000 °C such that it can be used as a solar energy heat storage material.

Thermodynamic and thermophysical effects enabling high-forced convection heat transfer coefficients in supercritical fluids

The strong variation of thermophysical properties of working fluids operating in the vicinity of the critical point makes this thermodynamic domain attractive to several energy applications. Therefore, herein a two-dimensional numerical method is used to investigate the effect of local thermophysical property variations on the local and overall thermal performance of internal convective heat transfer in a pipe in 324 operational conditions. Focusing on carbon dioxide and water as heat transfer fluids, an association of the variation of key thermophysical properties with thermohydraulic performance metrics is proposed, namely: (a) the local and (b) mean convective heat transfer coefficient and (c) the maximal temperature obtained at the tube wall. It is shown that there is an optimal combination of parameters such as mass flow rate, operating pressure, wall heat flux, and inlet temperature that, when properly selected, allow for a minimal maximal wall temperature. As expected, optimality is strongly associated with the Widom—or pseudo critical—line that extends from the critical point. Interestingly, however, contrary to what is observed in constant-property fluids, high heat transfer coefficient or minimal maximum temperature lead to different sets of optimal operating conditions. This difference is explained by how thermophysical properties vary locally along heat exchangers, which significantly affects overall heat transfer.

Features and results of assessment the thermal conductivity of building materials and products by the active method of thermal non-destructive testing

Thermal control (passive and active) is a non-destructive testing method. During passive thermal control, the test object is characterized by a temperature field formed during its operation. In active thermal control, the test object is additionally thermally stimulated. This technique is widely used in various areas of construction, energy, mechanical engineering, transport. This paper proposes a variant of active thermal non-destructive assessment of the thermal conductivity coefficient of building materials and products on the example of a fragment of a building structure made of silicate bricks. The test object is subjected to thermal stimulation by an external source of thermal energy before reaching a steady-state thermal regime. Thermography of the test object surfaces is carried out. The average integral temperatures of surfaces or individual sections of the test object are calculated. The coefficient of thermal conductivity of the test object is determined, which is used to calculate its thermal resistance (resistance to heat transfer). After that, the coefficient of heat transfer is calculated. The method was implemented in laboratory conditions. It can be used in natural and operational conditions for accurate and quick determination of the key thermophysical properties of building materials and products.

Possibilities of complex experimental study of thermophysical and thermodynamic properties of selected steels

In this paper, selected key thermophysical and thermodynamical properties of steels (three alloys based on Fe–C–Cr) such as solidus (TS) and liquidus (TL) temperatures, peritectic transformation temperatures (TP), heats of fusion (ΔHF), specific heat capacities(cP), surface tension (σ), and wettability expressed by the wetting angle (θ) of liquid steel on alumina substrate were experimentally determined in a high-temperature area up to the temperature of 1600°C. The effect of the temperature and the chemical composition of steel on these properties was investigated using 3D heat flux DSC (Differential Scanning Calorimetry) and a sessile drop method. The interaction of the steel samples with the alumina substrate was studied by SEM, EDX and XRD methods. To assess the influence of the major elements (carbon and chromium), the steels with different carbon and chromium content, which varied in the range of 0.077–0.381wt.% and 0.049–4.990wt.%, were chosen. It was shown that increasing carbon and chromium content led to a decrease in phase transformation temperatures and thermal capacities, as well as an increase in the heat of fusion, surface tension, and wetting angle. Furthermore, the rising temperature increases the thermal capacities and wetting angles. Whereas the surface tension followed the opposite trend.

Thermodynamic characterisation of aqueous alkanolamine and amine solutions for acid gas processing by transferable molecular models

The development of new alkanolamines/amines is a topic which has attracted a great deal research interest, particularly as absorbents for the removal of acid gases from industrial sources and CO2 capture applications. One of the major challenges when evaluating the techno-economic performance of selected new single amines or blends is the lack of experimental data on the thermophysical properties required for a reliable process design and simulation. In this contribution, a robust theoretical framework for the description of key thermophysical properties of aqueous solutions of single and mixed alkanolamines/amines at relevant gas separation process conditions is proposed. The approach is based on the coupling of the Free-Volume Theory and the Density Gradient Theory with a molecular-based equation of state (soft-SAFT) for the integrated modelling of phase behaviour, enthalpies, densities, viscosities and interfacial tensions. The alkanolamines and amines investigated differ in their family and structure, and included primary (monoethanolamine), secondary (diethanolamine), tertiary (methyldiethanolamine), sterically hindered (2-amino-2-methyl-1-propanol) and cyclic amines (piperazine). The study was performed in a systematic manner, starting from the development of the models for the pure amines, the description of their thermophysical properties, and the properties of the aqueous mixtures. Compared to other models described in literature, the present modelling approach preserves the effects due the chemical structure and key intermolecular interactions of the examined alkanolamines/amines through a set of molecular parameters obtained from pure substance data, whenever available, or transferred from substances of different chemical families. This enabled the development of a consistent modelling framework which can provide reliable thermodynamic property predictions of both single and blended amine solutions over a broad range of temperatures (298–373 K) and compositions (0–50 wt% amine). The proposed approach is well-suited for implementation and extension to other alkanolamines and amines, making it a valuable tool for having reliable process simulations as well as for the screening and discovery of new amine systems, which will be required for the deployment of more economical acid gas removal processes.

Effects of key thermophysical properties on the curing uniformity of carbon fiber reinforced resin composites

AbstractKey thermophysical properties of the thermosetting resin, including density, conductivity coefficient and specific heat that evolve with resin curing, are related to temperature and curing degree fields of the fiber/resin composite material. However, their effects on heat transfer inside composite materials, consequently on the curing non-uniformity in thick-section laminates, are not well understood. The focus of this study is on the effects of key thermophysical properties of resin on the curing uniformity of AS4/3501-6 composite by means of the coupled thermochemical analysis with the method of numerical simulation. The results clearly indicate that the conductivity coefficient and specific heat of resin have obvious influence on curing uniformity, especially for thick laminates, while the density of resin has no noticeable effect on the curing uniformity. The simulation results can help to guide the material preparation of industrial production.

Anisotropic thermal expansion of Ni3Sn4, Ag3Sn, Cu3Sn, Cu6Sn5 and βSn

The directional coefficient of thermal expansion (CTE) of intermetallics in electronic interconnections is a key thermophysical property that is required for microstructure-level modelling of solder joint reliability. Here, CTE ellipsoids are measured for key solder intermetallics using synchrotron x-ray diffraction (XRD). The role of the crystal structure used for refinement on the CTE shape and temperature dependence is investigated. The results are used to discuss the βSn-IMC orientation relationships (ORs) that minimise the in-plane CTE mismatch on IMC growth facets, which are measured with electron backscatter diffraction (EBSD) in solder joints on Cu and Ni substrates. The CTE mismatch in fully-intermetallic joints is discussed, and the relationship between the directional CTE of monoclinic and hexagonal polymorphs of Cu6Sn5 is explored.