Transient Plane Source Method Research Articles

Thermophysical Characterization of Materials for Energy-Efficient Double Diaphragm Preforming

The Double Diaphragm Preforming (DDPF) process uses vacuum pressure and heat to pre-shape dry carbon fabric reinforcements between flexible diaphragms in liquid composite molding (LCM). Accurate modeling of heat transfer within DDPF requires knowledge of the thermophysical properties of the constituent materials under processing conditions. This study investigates the thermal conductivity of silicone diaphragms and carbon fabrics with embedded thermoplastic binder webs, utilizing transient plane source (TPS) and modified transient plane source (MTPS) methods, respectively. Additionally, the specific heat of silicone, carbon fibers (both chopped and powdered), and binder were measured using differential scanning calorimetry (DSC). Mixed samples comprising chopped fibers with 1.8 wt% binder and powdered fibers with 3.6 wt% binder was also analyzed with DSC. This study also examined the influence of reheating cycles on the specific heat of carbon fiber—3.6 wt% binder samples—and the effect of compaction and vacuum on the thermal conductivity of carbon fabrics with an embedded binder. While silicone exhibited linear-specific heat behavior, the thermoplastic binder showed non-linearity due to phase change. The combined carbon fiber-binder samples demonstrated slight non-linear specific heat variations depending on reheating cycles. The thermal conductivity of the fabric preforms decreased with the addition of thermoplastic binder and under vacuum-compaction conditions. The established temperature-dependent specific heat relationships and thermal conductivity provide valuable data for optimizing DDPF preforming parameters and enhancing energy efficiency in composite manufacturing.

Determining thermal properties of beech and fir wood samples in longitudinal direction via modified transient plane source method

The increasing use of wood leads to the need for a better understanding of its thermal properties with the aim of quantitatively identifying the exchange of thermal energy between wood and the surrounding solar radiation as precisely as possible. Reliable and rapid measurement of thermal conductivity is one of the most important current industrial requirements. The aim of this study is to examine the validity of using the modified transient plane source method (MTPS), which uses the principle of one-sided heating of the sample, and is defined by the ASTM D7984-21 (2021) standard, for determining the thermal conductivity of complex biocomposite composite materials such as wood. The analysis of the available literature shows a lack of data on the thermal conductivity of the type of wood originating in Croatia. In this study, the thermal conductivities of beech and fir wood samples in the longitudinal direction was determined by the MTPS method depending on the temperature and moisture content in the samples. Measurements were made on samples with a moisture content of 0%, 10%, and 20% in the temperature range from 20 to 80 °C.

Heat-Transfer Properties of Additively Manufactured Aluminum Lattice Structures in Combination with Phase Change Material.

Compared to sensible heat storage, latent heat storage provides higher energy density due to the enthalpy difference of the storage medium undergoing a phase change. However, the heat storage capability of phase change materials is opposed by low thermal conductivity. To enable sufficient heat transfer within a latent heat storage unit, phase change materials can be used in combination with a metallic matrix. One approach is the infiltration of phase change materials into additively manufactured metallic lattice structures. In this work, the fabrication of aluminum lattice structures through laser powder bed fusion is described. During fabrication, the cell size and the strut diameter were varied to obtain specimens of different geometries. To obtain the thermal conductivity of the fabricated lattices, measurements were conducted based on the transient plane source method. Additionally, finite element simulations were carried out to evaluate the effect of fabrication and measurement uncertainties. The thermal conductivity of the fabricated lattices was found to be between 3 W/(m·K) and 130 W/(m·K). The numerically and analytically performed calculations provide good estimations of the experimentally obtained data.

Assessment of the Thermal Properties of Gypsum Plaster with Plastic Waste Aggregates.

Building material manufacturers must support new production models that encourage the manufacture of more efficient and sustainable products. This includes thinking about savings in the use of raw materials, a contribution to the energy efficiency of buildings during their useful life, and a reduction in the generation and deposit of waste in landfills. In this research, an analysis of the thermal properties of gypsum composites added with plastic waste is carried out using the most common methods, the steady state method and the transient plane source method, and the effect of water saturation on these composites is tested. The results show an improvement in the thermal performance of the composites (values reduced with respect to the reference by 4-7%), despite their heterogeneity, as well as a variation in the measurements carried out, depending on the method used for the measurements (variation up to 10%). It is also found that the degree of humidity negatively affects the thermal conductivity coefficient but, on the contrary, this coefficient is not altered in the composites with plastic waste, due to their lower hygroscopicity. Therefore, it is considered that the proposed eco-plasters are a good alternative to traditional plasters, with which to contribute to the achievement of the objectives of the current European directives on waste and circular economy.

Intricacies of high temperature thermal characterization of Silicaf/Silica composites

In this paper, we discuss the unique challenges posed by Silicaf/Silica composite while measuring their thermal conductivity by using Transient Plane Source (TPS) method and specific heat by Differential Scanning Calorimeter (DSC). The measured thermal conductivity values were found reaching a plateau followed by a reduction at temperatures 800 °C and above. Thermal expansion characteristics as measured in Thermomechanical Analyzer (TMA) exhibited strong dependency on static force applied during experiments. Keeping in view the real life application of the developed Silicaf/Silica composite, a novel method of sample preparation was implemented which restricted the sample compression at elevated temperatures during TPS experiments. Experiments utilizing DSC under linear and step heating with sample placement in alumina crucible yielded inconsistent values of specific heat (Cp). With further experimentation, the combination of step heating and direct placement of sample in platinum crucible was found most appropriate for accurate measurement of specific heat of Silicaf/Silica.

Experimental and Computational Study of the Thermal Insulation Properties of Hollow Glass Microspheres

Hollow glass microspheres (HGM) are expected to be used in cryogenic liquid storage tanks as an insulating material with better insulation performance and lower maintenance cost instead of perlite. Obtaining the effective thermal conductivity of HGM can help to improve the insulation performance of cryogenic tanks. Herein, a test system based on the transient plane source method is designed and constructed, and the effective thermal conductivity of six models of HGMs from four suppliers at 200–300 K is measured. The results show that under atmosphere pressure of 200 K, the effective thermal conductivity of HGM is only 25.87–35.84 mW m−1 K−1. The effective thermal conductivity at room and low temperatures is calculated using the derived system of equations for integrated thermal conductivity and radiative heat transfer, with the error of no more than 13% from the current experimental results. The integrated thermal conductivity is still dominant in low pressure and low temperature, and the reduction of the true density contributes to the improvement of the HGM insulation performance.

Analysis of heat flow in modified transient plane source (MTPS) measurements of the thermal effusivity and thermal conductivity of materials.

An iterative algorithm for the diffusion of heat in layered structures is solved in cylindrical coordinates for the geometry used in measurements of thermophysical properties of materials by the modified transient plane source (MTPS) method. This solution for the frequency-domain temperature response is then used to model the transient temperature excursion and evaluate the accuracy of the measurements. We evaluate when the MTPS method is capable of separately determining the thermal conductivity and heat capacity per unit volume of a material. For a typical sensor design, data acquisition, and data analysis, the MTPS measurement has a small sensitivity to the thermal diffusivity of the sample when the thermal diffusivity is <5 mm2 s-1. We analyze the propagation of errors from uncertainties in the thermal contact between the sensor and the sample and evaluate the limitations of the MTPS method in accurately measuring samples with extremely low thermal effusivity, e.g., low density foam insulation. We find that uncertainties in the thickness of the contact region limit the accuracy of MTPS measurements when the data are analyzed in a conventional manner based on a single parameter, m-1, the inverse of the slope of the temperature excursion as a function of the square root of time.

Experimental Investigation of the Anisotropic Thermal Conductivity of C/SiC Composite Thin Slab

Fiber-reinforced composites possess anisotropic mechanical and heat transfer properties due to their anisotropic fibers and structure distribution. In C/SiC composites, the out-of-plane thermal conductivity has mainly been studied, whereas the in-plane thermal conductivity has received less attention due to their limited thickness. In this study, the slab module of a transient plane source method is adopted to measure the in-plane thermal conductivity of a 2D plain woven C/SiC composite slab, and the test uncertainty is analyzed numerically. The numerical investigation proves that the slab module is reliable for measuring the isotropic and anisotropic slabs with in-plane thermal conductivity greater than 10 W⋅m−1⋅K−1. The anisotropic thermal conductivity of the 2D plain woven C/SiC composite slab is obtained within the temperature range of 20–900 °C by combining with a laser flash analysis method to measure the out-of-plane thermal conductivity. The results demonstrate that the out-of-plane thermal conductivity of C/SiC composite decreases with temperature, while its in-plane thermal conductivity first increases with temperature and then decreases, and the ratio of in-plane thermal conductivity to out-of-plane thermal conductivity is within 2.2–3.1.

Study on the effect of semi-transparency on thermal insulation performance of silica aerogel composites

This paper centralizes its focus on elucidating the distinctive thermal insulation performance of silica aerogel composites, emphasizing their semitransparent attributes under diverse heating methodologies. Firstly, the theoretical prediction of conductive thermal conductivity is undertaken utilizing the spherical hollow cube model and Davies model. Subsequently, the radiative thermal conductivity is numerically derived employing the two-flux approximation model, integrating experimental measurements of optical radiation characteristic parameters. The prediction results under high-temperature are validated by the measured data via a Hot Disk instrument, utilizing the transient plane source method. Finally, the influence of semitransparent properties of the aerogel composites on thermal insulation performance is exhaustively investigated. This is conducted through a meticulous examination of temperature responses resulting from distinct heating modalities, namely contact heating, quartz lamp heating, and arc heated wind tunnel heating. The findings discernibly illustrate that these diverse heating mechanisms significantly impact the thermal insulation performance of aerogel composites endowed with semitransparent characteristics.

Thermo-optical characterization of novel MXene/Carbon-dot hybrid nanofluid for heat transfer applications

Nanofluid has emerged as a promising heat transfer fluid (HTF) due to their significant thermophysical, and optical characteristics enhancement over base fluids. Hybrid nanofluids with multiple nanomaterials have the advantage of synergistic properties in comparison to monocomponent nanofluids. The present study proposes an energy-efficient and cleaner synthesis method for developing carbon quantum dot (C-dot), MXene, and a hybrid MXene/C-dot hybrid nanofluids, for heat transfer application. In-situ microwave pyrolysis technique and two-step method were adopted for nanomaterial and nanofluid synthesis. The morphological, phase structural, chemical, and elemental compositional analysis of the nanomaterials was performed. The material characterization confirms the hybridization of C-dot on MXene nanosheets. The thermal conductivity and volumetric heat capacity of the nanofluids were measured using the transient plane source (TPS) method. Thermal conductivity was observed to increase with nanofluid concentration and temperature. Results indicate that MXene has the highest thermal conductivity enhancement (50 %) over water, followed by hybrid (42.2 %) and C-dot nanofluid (33.2 %). The volumetric heat capacity of nanofluids decreased with concentration and temperature. A semi-empirical correlation, as a function of nanofluid concentration and temperature, was coined for predicting thermal conductivity and volumetric heat capacity. Optical property characterization study shows that C-dot nanofluid exhibited considerable absorption along the UV range, while MXene nanofluid showed absorption in the visible and near-infrared (NIR) region. Hybrid nanofluids demonstrated complementary absorption properties of C-dot and MXene nanofluids.

Measuring Thermal Conductivity of Single Thickness Fibrous Gas Diffusion Layers Using Transient Plane Source Method

In a proton exchange membrane fuel cell (PEMFC), the gas diffusion layer (GDL) is a porous material placed between the flow field plates and the catalyst layer. Its primary responsibility is to distribute reactants evenly across the surface of the catalyst layer while allowing for the removal of excess water and heat produced during operation. The GDL is typically made of a carbon-based material, such as carbon paper or carbon cloth, which is treated with polytetrafluoroethylene (PTFE) to become hydrophobic. This treatment allows it to repel water and facilitate the transport of gases such as hydrogen and oxygen during operation. The thermal conductivity of the GDL plays a crucial role in managing the heat and water of PEMFCs.The Guarded Heat Flow (GHF) technique is a well-established steady-state method for measuring the thermal conductivity of carbon fiber papers. This is achieved by testing two different thicknesses of a material that have an identical structure [1-3]. Using this two-thickness method, as per ASTM standard C177-19e1 [4], enables the bulk thermal conductivity to be deconvoluted from the thermal contact resistance at the interface between the sample and the measurement device's surface (an interfacial phenomenon). However, materials with identical structures for two-thickness measurements are not always available for commercial GDLs. In this study, we compare the transient plane source (TPS) thin film method, which measures the thermal conductivity of single thickness GDL samples, with the two-thickness GHF method for measuring thermal conductivity.In this study, GDL samples with the same bulk structure and manufactured in two thicknesses were used: Sigracet series 24BA and 34BA with original thicknesses of 190 µm and 280 µm, respectively. A custom-built Thickness Under Compression and Resistance Under Compression machine (TUC-RUC) was utilized to measure the thickness of the samples under loads ranging from 0.35 MPa to 2 MPa. The thickness under compression was measured for five samples (25.4 mm diameter) of each type of GDL. The standard deviation for each sample thickness was below 4%. As shown in Fig. 1, the stress-strain response of the GDL samples was measured and analyzed to assess the similarity in their mechanical structures. Consistent with the assumptions that both samples have the same structure, the GDL samples with two different thicknesses displayed identical stress-strain behavior under compression, as shown by the curve-fit for stress-strain behavior in proposed Fig. 1.The thermal conductivity of the samples was measured using both the TPS thin films method, as per ISO 2207-2:2022 [5], and the GHFM. On the TPS, three samples of each type of GDL were measured three times. The measured thermal conductivities increased with compression, ranging from 0.15 to 0.47 W/mK, with a standard deviation of less than 5% for each measurement. The results from the TPS technique for a single thickness of GDL were compared with the two-thickness measurements conducted using the GHFM, as shown in Figure 2. The GHFM tests were conducted on three samples of each type of GDL at five compressive loads, and the standard deviation on the deconvoluted thermal conductivity was less than 7% for each measurement. The values measured by the two techniques were found to be in good agreement, with a relative difference of within 6%. This study demonstrates that the transient plane source (TPS) method, when combined with an accurate thickness measurement technique, is a precise technique for determining the bulk thermal conductivity of commercial GDLs produced in a single thickness.[1] H. Sadeghifar, N. Djilali, and M. Bahrami, “Effect of Polytetrafluoroethylene (PTFE) and micro porous layer (MPL) on thermal conductivity of fuel cell gas diffusion layers: Modeling and experiments,” Journal of Power Sources, vol. 248, pp. 632–641, Feb. 2014, doi: 10.1016/j.jpowsour.2013.09.136.[2] M. Ahadi, M. Andisheh-Tadbir, M. Tam, and M. Bahrami, “An improved transient plane source method for measuring thermal conductivity of thin films: Deconvoluting thermal contact resistance,” International Journal of Heat and Mass Transfer, vol. 96, pp. 371–380, May 2016, doi: 10.1016/j.ijheatmasstransfer.2016.01.037.[3] E. Sadeghi, N. Djilali, and M. Bahrami, “Effective thermal conductivity and thermal contact resistance of gas diffusion layers in proton exchange membrane fuel cells. Part 1: Effect of compressive load,” Journal of Power Sources, vol. 196, no. 1, pp. 246–254, Jan. 2011, doi: 10.1016/j.jpowsour.2010.06.039.[4] “Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus.” ASTM International. Doi: 10.1520/c0177-19e01.[5] “ISO22007-2, Plastics-determination of thermal conductivity and thermal diffusivity-part 2: transient plane heat source (hot disc) method”, 2022. Figure 1

Estimating the Thermal Conductivity of Thin Films: A Novel Approach Using the Transient Plane Source Method

Abstract The conventional transient plane source (TPS) method for thin films is used for films and adhesives with thicknesses between 50 and 200 μm. Measurements with the conventional TPS method are usually inaccurate due to thermal contact resistance between the insulating sensor layers, the film and the sensor, and the film and the background material. A new approach to measuring thin films with the TPS is introduced, where the heat flow is constrained to one dimension, and a slab layer made from the same background material is introduced between the thin film and the TPS sensor. This decouples the effects of the thermal contact resistance (TCR) of the sensor to the thermal resistance of the film. The new approach is tested on four different thin films with stainless steel as the background material. The results are compared to guarded heat flowmeter measurements. Excellent agreement (&amp;lt; 12% error) between the two methods is achieved, showing that the new method proposed is fast, accurate, and convenient alternative for determining the thermal conductivity of thin films.

Thermal insulation of phenolic resin modified fly ash geopolymer

Phenolic resin has been widely used owing to its excellent thermal insulation performance. However, the application of phenolic resin in the field of geopolymer remains unexplored. Here, the foamed fly ash geopolymer samples with high porosity were prepared using phenolic resin for the purpose of foaming materials. The thermal insulation properties of these samples were evaluated by Transient Plane Source Method, and the effect of phenolic resin on pore characteristics was investigated by Mercury Intrusion Porosimetry (MIP), aim to explore how phenolic resin affects the thermal conductivity by changing the pore characteristics of geopolymer. In addition, considering that the internal gas thermal conductivity of pores with different pore sizes is also different (Knudsen effect), in order to predict the thermal conductivity more accurately, this research proposes an iterative calculation method to establish a thermal conductivity model. The results show that phenolic resin can improve the thermal insulation effect of geopolymer, and the minimum thermal conductivity of the sample is 0.17 W/m·K. In addition, according to the test results of MIP, it can be found that phenolic resin mainly promotes the porosity of micron pores (>1 μm) whereas there is slight inhibition on nano pores (<1 μm), but the beneficial effect of the increase of micron-sized pores (>1 μm) on the thermal insulation performance of geopolymer is greater than the negative influence effect of the disappearance of nano pores. Moreover, according to the results of MIP, phenolic resin can narrow the throat in the pore of the ink bottle, limit the thermal convection of the gas between the pores, and reduce the thermal conductivity. Finally, the newly modified Russell model considering the Knudsen effect can effectively predict the thermal conductivity by using the experimental data. This study provides a new method to improve thermal insulation performance of geopolymers and offers a new building insulation product.

Thermal conductivity of dried biocemented sand at higher calcification

Thermal conductivity of dried biocemented sand at higher calcification

Evaluation of transient measurements of thermophysical parameters using Finite Elements Method.

The transient plane source (TPS) method was used to measure the thermal diffusivity and conductivity of silica glass and polymethyl methacrylate (PMMA). The results were evaluated by an analytical model and also by a numerical model created by the finite elements method (FEM). The results of both models and both materials were compared, and the difference was less than 0.4%.

3D FE modeling of a real-world energy piled foundation

3D FE modeling of a real-world energy piled foundation

Thermal conductivity of the cell wall of wood predicted by inverse analysis of 3D homogenization

This work proposes an accurate prediction of the directional thermal conductivity of wood at the cell wall scale. To that purpose, the strategy combines the physical characterization at the macroscopic scale, the description of the cellular morphology, homogenization calculations and an inverse analysis. The first step consisted in measuring the macroscopic thermal conductivity using the Transient Plane Source (TPS) method in the three material directions of spruce and poplar. The values range from 0.10 to 0.31 Wm−1K−1 depending on direction and species. The 3D morphology was acquired by micro-tomography and subsequently processed to generate a digital representation of the cellular structure. This representation is the input geometry in an homogenization procedure. Based on the results of this algorithm, the measurements of the solid fraction and the macroscopic values, we are able to determine the microscopic thermal conductivity of the cell wall λ0s, which is impossible to measure directly. λ0s was also found to be anisotropic with respective values of 0.6 and 1.0 Wm−1K−1 in the transverse plane and the longitudinal direction.

Thermal and mechanical properties of bio-cemented quartz sand mixed with steel slag

The aim of this study is to disclose the feasibility of improving the thermal conductivity and mechanical strength of quartz sand steel slag mixtures treated by enzyme-induced carbonate precipitation (EICP). In this work, the effects of steel slag content (SSC) and number of treatment cycle (N) on the thermal conductivity and mechanical strength of EICP-treated specimens were investigated. The immersion method was adopted for specimen preparation. The thermal conductivity was measured by transient plane source method (TPS) and the unconfined compressive strength (UCS) was obtained through a uniaxial compression test. Moreover, the SEM test was conducted to obtain the morphology and deposition characteristics of calcium carbonate crystals. The result shows that the thermal conductivity and UCS of EICP-treated sands increase before decreasing as the SSC increases. Consequently, the maximum values of thermal conductivity and UCS are 1.28 W/(m⊡K) and 6.31 MPa, respectively, corresponding to the optimal parameter of 20% SSC at 12 N. The optimal thermal conductivity and UCS increase by 367% and 137%, respectively, compared to that of EICP-treated sand with no addition of steel slag. The SEM analysis indicates that the spherical calcium carbonate exists in the range of 0–20% SSC, whereas there is mainly amorphous calcium carbonate when the SSC varies from 40% to 80%. It also demonstrates that the UCS is more sensitive to the variation of calcium carbonate content than that of thermal conductivity.

Characteristics of geothermal field and evaluation of geothermal resource potential in the Yingjiang Basin

Geothermal resource, a green and sustainable energy resource, plays an important role in achieving ‘emission peak’ and ‘carbon neutrality’ targets. The Yingjiang Basin is located in the eastern branch of the Mediterranean-Himalayan high-temperature geothermal belt and exhibits considerable potential for geothermal resources. However, current investigations into the distribution of deep geothermal resources in this region are somewhat limited. In this paper, the transient plane source (TPS) method is used to measure the thermal conductivity parameters of 31 rock samples within the study area. Additionally, the one-dimensional steady-state heat conduction equation is employed to calculate the deep geothermal field, considering the constraints of rock thermal properties and terrestrial heat flow in the study area. Furthermore, the “stripping method” is used to determine the contribution rate of sedimentary layer to terrestrial heat flow, while the volume method is applied to estimate the geothermal resources at burial depths of 3000–5000 m. The results show that (1) The heat generation rate of granite is the highest with an average value of 4.52 μW/m3, followed by gneiss with an average value in the range of 2.0–3.5 W/(m·K), mudstone and sandstone being the lowest with an average value between 1.0 and 2.0 W/(m·K). (2) The main contributor of terrestrial heat flow in the study area is mantle heat flow, and the contribution of sedimentary layers to terrestrial heat flow only accounts for about 2%. (3) The geothermal resources in Yingjiang Basin within the depth range of 3000–5000 m is 93.6 × 1015 kJ, or 3.2 × 109 tonnes standard coal equivalent (SCE).

Investigation of thermal properties of pykrete

Experimental investigation of the thermal properties of ice reinforced with sawdust is presented in this paper. Mechanical properties of pykrete are fairly covered in literature, while there are no data about its thermal properties. For the purposes of this examination, ice made of 215 ml of tap water was reinforced by adding 35 g of sawdust. Transient Plane Source (TPS) method was employed to measure the thermal conductivity and thermal diffusivity in a temperature range from -15 °C to -33 °C. Blocks of pykrete were placed in an expanded polystyrene (EPS) box in the freezer where the measurements took place. Thermal conductivity of pykrete was observed to vary from 1.64 Wm−1K−1 at -15 °C to 1.75 Wm−1K−1 at -33 °C while thermal diffusivity in the same temperature interval exhibited growth at a larger scale, from 0.88 mm2s−1 to 1.10 mm2s−1. Measured values showed an average decrease of approx. 21% in thermal conductivity and approx. 23% in thermal diffusivity when compared with results obtained for frozen pure tap water. Measured thermal constants were shown to be similar to the ones obtained in literature for concrete.