Measurement Of Thermal Properties Research Articles

An instrumentation guide to measuring thermal conductivity using frequency domain thermoreflectance (FDTR).

Frequency Domain Thermoreflectance (FDTR) is a versatile technique used to measure the thermal properties of thin films, multilayer stacks, and interfaces that govern the performance and thermal management in semiconductor microelectronics. Reliable thermal property measurements at these length scales (≈10nm to ≈10μm), where the physics of thermal transport and phonon scattering at interfaces both grow in complexity, are increasingly relevant as electronic components continue to shrink. While FDTR is a promising technique, FDTR instruments are generally home-built; they can be difficult to construct, align, and maintain, especially for the novice. Our goal here is to provide a practical resource beyond theory that increases the accessibility, replicability, and widespread adoption of FDTR instrumentation. We provide a detailed account of unpublished insights and institutional knowledge that are critical for obtaining accurate and repeatable measurements of thermal properties using FDTR. We discuss component selection and placement, alignment procedures, data collection parameters, common challenges, and our efforts to increase measurement automation. In FDTR, the unknown thermal properties are fit by minimizing the error between the phase lag at each frequency and the multilayer diffusive thermal model solution. For data fitting and uncertainty analysis, we compare common numerical integration methods, and we compare multiple approaches for fitting and uncertainty analysis, including Monte Carlo simulation, to demonstrate their reliability and relative speed. The instrument is validated with substrates of known thermal properties over a wide range of isotropic thermal conductivities, including Borofloat silica, quartz, sapphire, and silicon.

Comprehensive characterization of the irradiation effects of glassy carbon

Carbon materials have become increasingly diverse, finding applications in high-temperature and high-radiation environments. Glassy carbon, an allotrope known for its exceptional chemical inertness and desirable mechanical properties. However, understanding neutron irradiation effects in glassy carbon has proven challenging, primarily because of its unique nanopore structure. This study presents a highly detailed microstructural characterization investigation of neutron-induced changes in glassy carbon, revealing how changes in nanopore structure and crystallinity impact the irradiation-induced shrinkage. Aberration-corrected scanning transmission electron microscopy (STEM) reveals pore closure that leads to material densification in the irradiated samples. Dimensional analysis combined with comparison to historical data suggest significant length shrinkage to occur. Neutron and in situ electron irradiation experiments suggest that glassy carbon transforms into so-called carbon onions, supporting the concept of shrinkage saturation. Investigating irradiation temperature effects using STEM, electron energy loss spectroscopy, x-ray diffraction, and Raman spectroscopy revealed partial amorphization at 210 °C–230 °C and preserved order in glassy carbon at 860 °C, coinciding with pore closure. Thermal property measurements were also conducted to assess the effects of densification and other changes in the atomic structure of glassy carbon. The results of this study have broad implications in the deployment of glassy carbon to nuclear environments, based around the observed changes in the thermal properties, and demonstrates the operational window for the onset of densification.

Relationship between coking properties measured by automatic Sapozhnikov plastometer with other measurements

ABSTRACT A Sapozhnikov plastometer is equipment that is commonly used, particularly in Asia, for measuring the contraction of the coal bed as well as the plastic layer thickness during the coking process. The relationship between the Sapozhnikov contraction X and the maximum plastic layer thickness Y values and other thermal rheology testing techniques is not fully understood. It leads to difficulties in the interpretation of data using different thermal rheology properties measurement techniques. In this work, a series of coal samples were analyzed in parallel using the automatic Sapozhnikov plastometer, the Gieseler plastometer, and the Ruhr dilatometer. The measurement results were compared to assist in the interpretation of data generated using different coal thermal rheology property measurement techniques. The Sapozhnikov X results are found not comparable due to the difference in sample particle size and testing conditions for component coals with the wide range of maximum mean reflectance (Ro), but a significant linear correlation on the contraction/expansion behavior between Sapozhnikov and Ruhr dilatation test is observed for experimental coal blends Ro between 1.00 and 1.20. Sapozhnikov Y results are linearly related to the melting range from both the Gieseler plastometer and the Ruhr dilatometer for all the experimental single coals and coal blends.

Estimation of heat source, specific heat, and thermal conductivity of insulation materials using modified conjugate gradient method

The use of insulation materials is crucial for minimizing thermal losses in various industries like automotive, building, solar, and aerospace. Plexiglass and Expanded Polystyrene (EPS) foam are popular choices due to their effective temperature regulation, lightweight nature, and cost-effectiveness. Accurate measurement of their thermal properties is vital for achieving conservation goals. While the parallel hot wire technique provides valuable insights, accurately determining heat source strength (HW) poses a challenge, impacting measurement accuracy. To address this, the modified Conjugate Gradient Method (CGM) is employed for simultaneous estimation of thermal conductivity (λ), specific heat (c) and HW of Plexiglass and EPS foam. The direct problem result has been validated with published experimental work that shows deviations less than 2 %. The study investigates the impact of sensor positioning relative to the hot-wire (rm) and introduces artificial Gaussian error with standard deviations (θ) of 0.01 °C, 0.02 °C and 0.1 °C. At θ = 0.1 °C the percentage relative errors in the estimation of λ, c and HW with rm = 5 mm for Plexiglass are 5 %, 1.442 %, and 4.651 % respectively. For EPS foam the corresponding errors are 2.44 %, 1.26 %, and 1.74 %. The modified CGM emerges as a reliable algorithm for the measurement of thermal properties of insulation materials.

Noncontact measurement of density and thermal properties of SS 316L powder bed through flash thermography

PurposePowder bed density is a key parameter in powder bed additive manufacturing (AM) processes but is not easily monitored. This research evaluates the possibility of non-invasively estimating the density of an AM powder bed via its thermal properties measured using flash thermography (FT).Design/methodology/approachThe thermal diffusivity and conductivity of the samples were found by fitting an analytical model to the measured surface temperature after flash of the powder on a polymer substrate, enabling the estimation of the powder bed density.FindingsFT estimated powder bed was within 8% of weight-based density measurements and the inferred thermal properties are consistent with literature findings. However, multiple flashes were necessary to ensure precise measurements due to noise in the experimental data and the similarity of thermal properties between the powder and substrate.Originality/valueThis paper emphasizes the capability of Flash Thermography (FT) for non-contact measurement of SS 316 L powder bed density, offering a pathway to in-situ monitoring for powder bed AM methods including binder jetting (BJ) and powder bed fusion. Despite the limitations of the current approach, the density knowledge and thermal properties measurements have the potential to enhance process development and thermal modeling powder bed AM processes, aiding in understanding the powder packing and thermal behavior.

Effect of boron on the microstructure and performance of HIP-prepared high boron steels

High boron steels containing 2 wt% and 3.3 wt% boron were fabricated using hot isostatic pressing (HIP). The enhanced shielding performance of the steel with higher boron content was quantitatively evaluated through Monte Carlo simulations using software Fluka. The steels were studied with XRD and the phase ratio were calculated using Rietveld refinement method. The microstructure of the materials was investigated using electron backscatter diffraction (EBSD). Comprehensive thermal property measurements, complemented by Hamilton thermal conductivity model analysis, were conducted on high boron steels. The results revealed that the decreased overall thermal conductivity in these materials is primarily attributed to two factors: the increased volume fraction of the boride phase and the enhanced interconnectivity among boride particles. These findings provide crucial insights into the thermal behavior of high boron steels. Room temperature tensile tests indicate that high boron content can cause the fracture mode of the material to transition from ductile to brittle. This study provides a detailed analysis of the effects of boron content on various properties of high boron steels, which can serve as shielding materials in fusion reactors. Advances were proposed for optimizing the thermal performance of high boron steels in this study.

Thermal characterization of thin films: A chip-based approach for in-plane property analysis

Accurate measurement of thermal properties in thin films is crucial for optimizing devices and deepening our understanding of heat transfer at nano and micro scales. This study presents a combined experimental and computational investigation on a chip-integrated technique for the assessment of in-plane thermal properties of thin films. This method stands out by incorporating inherent error cancelation to lessen the impact of radiative heat loss and allows simultaneous, independent determination of both thermal conductivity and diffusivity through straightforward linear fittings from the same dataset, reducing error propagation. We examine an 84 nm thick SiNx membrane over a temperature range from 100 K to nearly 500 K, aligning with previous studies. Further investigations into a conducting polymer film post-doping demonstrate a notable increase in both thermal conductivity and diffusivity, corroborating scanning thermal microscopy observations, confirming the technique's efficacy and reliability.

Response of 11B enriched ZrB2 ultra-high temperature ceramic to neutron irradiation at elevated temperatures

ZrB2, an ultra-high temperature ceramic (UHTC) is being considered for use in fusion reactor first-wall structures, yet its response to irradiation remains poorly understood. This study employed scanning/transmission electron microscopy (S/TEM), synchrotron X-ray diffraction (XRD), finite element calculations, and thermal property measurements to thoroughly investigate the neutron-irradiation effects on 11B-enriched ZrB2. Neutron irradiations were conducted at 220 °C and 620 °C, with a neutron fluence of 2.2 × 1025 neutron/m2 (energy > 0.1 MeV), resulting in 3.9 dpa and 4200 appm He. The study revealed the unusual prevalence of prism loops and a > c anisotropic lattice swelling, likely linked to the low c/a ratio of ZrB2, leading to grain boundary microcracking. Reducing the grain sizes was effective in reducing intergranular cracking and macroscopic swelling. The observation of cavities in ZrB2 irradiated at 620 °C, as opposed to 220 °C, prompts questions about the temperature at which vacancies in ZrB2 become mobile, and the role of neutron absorption by 10B in elevating irradiation temperatures. Isotopic enrichment in 11B proves to be a viable strategy for mitigating helium production in transition-metal diborides, which is a critical consideration for nuclear applications. Irradiation-induced defects reduce the thermal diffusivity and conductivity of ZrB2 by a factor of 4–9, which has important implications for its role as a plasma-facing material in fusion reactors that drive high heat fluxes through first-wall materials. This comprehensive study lays the foundation for understanding ZrB2 behavior under neutron irradiation and highlights important phenomena to consider for various material applications.

Estimation of Thermal Properties of Solid–Liquid Phase Change Material Using Fuzzy Inference Methods

The accurate measurement of thermal properties in phase change materials holds significant importance for engineering applications. This research introduces fuzzy inference methods to estimate the thermal properties of phase change materials. The solution to the coupled heat transfer involving radiation and conduction in material is achieved through a hybrid approach, which combines the finite volume method with the discrete ordinate method. The estimation process is structured as an inverse problem, where the temperature on the material surface acts as the measurement signal for conducting the inverse analysis. Both the fuzzy inference method and the decentralized fuzzy inference method are utilized to address the inverse heat transfer problem. This enables the determination of latent heat and thermal conductivities for both solid and liquid regions within the phase change material. Retrieval results demonstrate that the thermal properties of phase change materials can be accurately estimated using fuzzy inference methods. While both two fuzzy inference methods perform similarly in estimating a single parameter, the fuzzy inference method has limitations in multiparameter estimation tasks. Conversely, the decentralized fuzzy inference method yields accurate results in simultaneous estimation problems. Furthermore, this method proves robust in estimating the thermal properties of phase change materials, even in the presence of noisy data.

Using construction and demolition waste materials to alleviate the negative effect of pavements on the urban heat island: A laboratory, field, and numerical study

In this study, construction and demolition waste (CDW) materials, including waste clay bricks, concrete, and glass, were used as aggregates of chip seal layers to enhance the reflectivity and reduce the temperature of asphalt pavements as an urban heat island (UHI) mitigation policy. UHI is an urban area that has a higher temperature in comparison to its suburbs. As considerable parts of cities are covered with asphalt pavements, their heat absorption and heat release can directly affect the UHI. Four types of chip seal layers, containing CDW aggregates were prepared in this study. The reflectivity and cooling effects of asphalt pavement coated with the developed chip seals were then evaluated with laboratory, field experiments, and computational fluid dynamics (CFD) simulation. Regarding the laboratory methods, UV-Visible-NIR spectrometer reflectance, a trident thermal properties measurement, and solar simulation cooling effect were used. Besides, the albedo and cooling effects of the developed chip seals were evaluated with a pyranometer and thermocouples through a field experiment. The indoor reflectance test showed yellow and red brick chip seals reflected almost 136 % higher than the aged asphalt pavement, followed by concrete chip seals with 80 % higher solar reflectance. Besides, the surface temperatures of yellow brick, red brick, and concrete chip seals were 23 %, 18 %, and 15 % cooler than the hot mix asphalt (HMA) specimens. More importantly, clay brick chip seals had the lowest nighttime heat release, followed by the concrete chip seal. The field test indicated that the albedo of yellow brick was 2 and 6 times higher than the aged and new HMA, causing 17 % and 27 % lower surface temperatures. The numerical models also revealed that using the yellow brick and concrete chip seals decreased the surrounding air temperature at least by 18 % and 14 % respectively. Overall, the numerical modeling, laboratory, and field tests showed similar results, indicating the benefits of using clay bricks and concrete aggregates for chip seal development, which can mitigate the UHI effectively.

Influences of root fragments on soil thermal property measurements with heat pulse method

Heat pulse (HP) method has been widely applied for measuring thermal properties, heat fluxes, and soil–water evaporation for near-surface soil layers. In topsoil layers, the presence of roots violates the underlying assumption of HP method that the soil under test is homogeneous. In this study, numerical and laboratory experiments were conducted to test the influence of root fragments on soil thermal property measurement with HP sensors. Soybean root fragments, with a water content of about 0.74 m3 m−3 and diameters ranging from 0.5 to 4 mm, were carefully repacked into soil samples that were used for HP measurements. Results showed that the effects of roots on soil thermal property measurements depended on root size, root location and directions relative to the heater probe, and the thermal property differences between soil sample and root. Roots showed negligible influence on heat pulse data when the root fragments were positioned outside the HP measurement region (more than probe space away from heater probe), or root diameters (d) were less than 1 mm, or in oven-dried soil samples. On relatively wet soils (i.e., with water content of 0.05–0.25 m3 m−3), when root fragments were located in between the heater and sensing probes (parallel to the probe planes), (1) the heat capacity (C) and thermal conductivity (λ) differences between root-free soil and root-soil mixture increased proportionally with d increased from 1 mm to 4 mm; (2) the differences in absolute values of C and λ between the root-free soil and soil-root mixture were highly dependent on soil water content. The errors in soil C and λ estimates were larger when the root fragment was parallel with than perpendicular to or inclined 45 degrees to the probe plane, and the error overall decreased with a smaller ρb and sand fraction. When the root fragments were positioned within the HP measurement region, or d were larger than 1 mm, or in relatively wet soil samples, it is important to consider root effect when interpreting HP signals.

Modified 3ω conductivity technique for measurements of thermal conductivity in cryogenic fluids

An instrument based on a modification to the 3-omega thermal conductivity technique that allows precise measurement of thermal properties in fluids is presented. Existing hot-wire techniques have difficulty measuring thermal conductivity because of the effects of natural convection distorting the measurement, however the standard 3-omega technique has been used extensively in the measurement of the properties of solids with great success. To address the challenge posed by natural convection in fluids, we modify the boundary condition of the 3-omega device configuration to be finite in extent, thereby restricting fluid motion and enabling a direct high-precision measurement of a fluid’s thermal conductivity. This modified scenario also presents an opportunity for a simultaneous measurement of the thermal diffusivity of the fluid. The behavior of the device is described with the reformed boundary conditions to show how a simultaneous measurement is made. By applying a constant temperature finite boundary condition, the solution characteristic in the frequency domain gains features that allow for simultaneous measurements of the fluid thermal conductivity and diffusivity. Given the density of the fluid, measured separately, the specific heat of the fluid can be calculated. The effects of the thermal properties of the measurement wire influence the measurement characteristic, and only when the wire thermal properties are sufficiently small compared to those of the fluid can a simultaneous measurement be made. Due to limitations in the dynamic reserve of the measurement devices, a setup is described that allows the signal of interest to be extracted and a precise measurement to be made with minimal distortion. Initial data on the thermal conductivity of helium is presented in the 4-300K temperature range. Preliminary specific heat data is also presented. Limitations on the device’s thermal properties prevent a specific heat measurement above 70K. This data is compared with reference fluid properties databases to validate the device performance.

High Accuracy Resisitivity and Temperature Coefficient Measurements of Invar Wire from 5K to 300K

The temperature coefficient of resistivity is a critical element of many AC-based hot-wire measurements of thermal properties. At cryogenic temperatures, most metallic materials suitable for wire and film-based forms have either a temperature coefficient or absolute resistivity that is too small to enable practical, accurate measurements. Invar (36Ni 64Fe) controlled thermal expansion alloy has a significant temperature coefficient of resistance while also maintaining significant absolute resistivity at cryogenic temperatures, and so has seen some use in low temperature 3-omega measurements. Prior data on the temperature coefficient of resistivity of Invar is limited and the uncertainty is high. In this work, we present high-accuracy resistance and temperature coefficient data for this material from 5-300 K.

Thermal Properties of Backfill Material for Underground Heat Exchange Applications

We are investigating the effect of the thermal properties of backfill material on the efficiency of underground thermal energy systems. We have used aluminum to increase the thermal properties of clay-bentonite and to investigate its potential as a backfill material in underground heat exchange applications. The measurements of thermal properties were made at room temperature using the Transient Plane Source (TPS) technique. The measurements were based on an infinite homogeneous medium using different composites of aluminum and clays in amounts of aluminum concentration ranging from 6 to 25 percent of the sample’s weight. The results confirmed an overall relative increase of 170% and 135% in the thermal conductivity and diffusivity, respectively as the Al content increased by 25%. The estimated average of the thermal transmittance (U-value ) of these samples was in the range from 0.40 to 1.1 W/m2K, which was directly proportional to the relative increase in the measured properties. Our findings can be applied to underground thermal energy systems, ground source heat pumps, and solid dielectric underground transmission lines.

Bone density estimation using tissue heat capacity.

Osteoporosis onset is relatively asymptomatic, the condition often being identified only once a significant fracture occurs, leading to a potentially serious prognosis. Currently, early identification of osteoporosis is complicated by the difficulty in measuring bone density without using x-ray absorptiometry or quantitative ultrasound, so a simpler method for estimating bone density is needed. Given that bone is reported to have a lower specific heat than other tissues, we investigated the possibility of estimating bone density using this difference in tissue thermal properties. The tibia medial surface (shin) and medial malleolus (ankle) of 68 healthy volunteers were cooled using an ice bag, and skin surface temperatures and heat flow were recorded. These measurements were then used to calculate the heat energy transferred per unit temperature. Bone density was estimated by quantitative ultrasound using the T score OSISD, which is the participant's osteo sono-assessment index (OSI) compared to the average OSI of young adults. The heat energy transfer per unit temperature at the shin, but not the ankle, showed a significant negative correlation with T score OSISD (r = -0.413, p = 0.001). Multiple regression analysis showed that heat energy transfer per unit temperature at the shin was a significant predictor of T score OSISD, along with age and height. These results show that tissue thermal property measurements are useful for estimating bone density.

An Inductive Method for Comprehensive Estimation of Temperature-Dependent Electrical and Thermal Properties of Conductive Ferromagnetic Materials

Reliable information about the properties of the processed materials has a significant impact on the effects of their processing. In induction heating processes, this also applies to information about the influence of temperature T on these properties. These are both thermal and electro-magnetic properties. Based on previous studies, a comprehensive experimental method is presented for estimating the temperature characteristics of thermal diffusivity, volumetric heat capacity and resistivity on one measurement station, with particular attention to ferromagnetic materials. The estimation process is carried out on an induction heating stand using forcing signals from an inverter generator. In a computer-controlled cycle that changes the base temperature level, basic measurements of thermal and electrical properties are carried out on a material sample in the form of a cylindrical disk. They are the results of the analysis of the temperature and electromagnetic responses of a material sample to short- and long-term step pulses of a sinusoidal excitation signal with a frequency of approximately 40 kHz. The presented estimation method can be treated as a final method or a preliminary procedure for radically narrowing the variability in decision variables inthe optimization process of simultaneous determination of the sought material characteristics.

Optimized measurement of frozen soil thermal properties using a heat-pulse sensor

The measurement of thermal properties in partially frozen soil is crucial for global climate models. As the primary method for soil thermal property measurement, the Dual-Probe Heat-Pulse (DPHP) sensor experiences significant errors when used in partially frozen soils. The application of heat pulses leads to ice melting, and the existing DPHP theory, which does not consider phase changes, fails to accurately determine thermal conductivity (k) and heat capacity (C) in the temperature range of − 5 °C to 0 °C. There is a lack of DPHP theory specifically designed for use in partially frozen soils. The existing DPHP theory employs the Infinite Linear Source (ILS) approximation, which does not account for the melting process and the moving ice-liquid interface in transient heat conduction theory. Currently, there is no effective and reliable method to assess DPHP errors associated with measuring the thermal properties of partially frozen soil. To accurately determine k and C in frozen soil, it is essential to perform an error analysis regarding ice melting caused by a DPHP heat pulse input. In this study, (1) we considered the latent heat of ice melting and a moving ice-liquid interface in finite element simulations and compared the results with an analytical solution presented by Paterson (1952); (2) we performed simulations of DPHP measurements based on the temperature-dependent ice content, liquid water content, and melting latent heat of three frozen soils used by Watanabe and Wake (2009); (3) based on COMSOL simulation results for the three frozen soils, we determined the optimal heating parameter combinations (heating duration, t0, and accumulated heating energy, ΔQ) to minimize DPHP measurement errors in frozen soil. The results showed that (1) Simulations that included the melting phase changes were in agreement with the analytical solution by Paterson (1952). (2) Including the ice-liquid moving interface significantly altered the spatial distribution characteristics of temperature, which were not captured by the ILS model in terms of the temperature distribution near the interface. (3) Below a temperature of − 5.5 °C, the simulations that included phase changes were consistent with measured results; (4) For partially frozen soils with initial temperatures ranging from − 0.5 °C to 0 °C, the relative errors in thermal conductivity fitted by the ILS model exceeded 100 %. To mitigate the influence of ice melting, we recommend using 200 < ΔQ < 400 J m−1 for sand, loam, and silt loam soils with 8 s < t0 < 60 s. For a loam soil with t0 = 60 s, ΔQ = 800 J m−1 should be used. For a silt loam soil with t0 = 60 s, we recommend using ΔQ = 600 J m−1. If the ILS model is chosen to calculate soil thermal properties, we recommend using 200 <ΔQ < 600 J m−1 and 30 s < t0 < 60 s for sandy and silt loam soils. For a loam soil, we recommend using 400 < ΔQ < 800 J m−1 and 30 s < t0 < 60 s.

Data-Driven Contact-Based Thermosensation for Enhanced Tactile Recognition.

Thermal feedback plays an important role in tactile perception, greatly influencing fields such as autonomous robot systems and virtual reality. The further development of intelligent systems demands enhanced thermosensation, such as the measurement of thermal properties of objects to aid in more accurate system perception. However, this continues to present certain challenges in contact-based scenarios. For this reason, this study innovates by using the concept of semi-infinite equivalence to design a thermosensation system. A discrete transient heat transfer model was established. Subsequently, a data-driven method was introduced, integrating the developed model with a back propagation (BP) neural network containing dual hidden layers, to facilitate accurate calculation for contact materials. The network was trained using the thermophysical data of 67 types of materials generated by the heat transfer model. An experimental setup, employing flexible thin-film devices, was constructed to measure three solid materials under various heating conditions. Results indicated that measurement errors stayed within 10% for thermal conductivity and 20% for thermal diffusion. This approach not only enables quick, quantitative calculation and identification of contact materials but also simplifies the measurement process by eliminating the need for initial temperature adjustments, and minimizing errors due to model complexity.

A novel heat transfer characterization method for a thermal management scheme of 3D-IC chips

A novel surface-modified silicon-based thermal management technology has been proposed for 3D IC architecture in this study. 2 × 2 cm2 double sides polished silicon chips’ surface with micro-fin (MF) and micro-pin fin (MPF) structures have been achieved by applying silicon microfabrication technology of deep reactive ion etching, which is applicable to the interlayer of 3D IC packaging technology. By integrating a mini wind tunnel with Raman spectrometer, the transient thermal property measurement system is originally designed to evaluate the cooling capability of the surface-modified silicon interlayer. Finite Element Analysis was involved to confirm this view by taking fluid dynamics and heat transfer into account. The sample with 100 × 100 µm2 MPF structure expresses the appropriate exponential decay time constant τ (with unit of 1), which is 4.71 and 8.53 under cooling and heating measurement conditions, respectively. This also proved that the combination of Raman thermometry with forced gas flow could be a relevant measurement tool for transient thermal property.

Overlooked biocrust impacts on surface soil thermal properties: Evidence from heat‐pulse sensing on large volume samples

AbstractBiocrusts are a critical surface cover in global drylands, but knowledge about their influences on surface soil thermal properties are still lacking because it is quite challenging to make accurate thermal property measurements for biocrust layers, which are only millimetres thick. In this study, we repacked biocrust layers (moss‐ and cyanobacteria‐dominated, respectively) that had the same material as the original intact biocrusts but was more homogeneous and thicker. The thermal conductivity (λ), heat capacity (C) and thermal diffusivity (k) of the repacked and intact biocrusts were measured by the heat pulse (HP) technique at different mass water contents (θm) and mass ratios (Wt), and the differences between repacked and intact biocrusts were analysed. Our results show that biocrusts substantially alter the thermal properties of the soil surface. The average λ of moss (0.37 W m−1 K−1) and cyanobacteria biocrusts (0.90 W m−1 K−1) were reduced by 63.0% and 10.3% compared with bare soil (1.00 W m−1 K−1), respectively. Edge effects including heat loss and water evaporation caused the λ and k of the biocrusts to be underestimated, but the C to be overestimated. The differences in thermal properties were significant (p &lt;0.001), except for the differences in thermal conductivity between repacked and intact cyanobacteria biocrusts, which were not significant (p = 0.379). Specifically, in the volumetric water content (θv) range of 0 to 20%, the λ and k of the repacked moss biocrusts were underestimated by 59.1% and 61.8%, respectively, and the C was overestimated by 23.9% compared with the intact moss biocrusts. The λ and k of the repacked cyanobacteria biocrusts were underestimated by 15.8% and 79.2%, respectively, and the C was overestimated by 34.8% compared with the intact cyanobacteria biocrusts at the θv range of 0 to 30%. Typically, this difference increased as the θv rises between repacked and intact biocrusts. Our new measurements provide evidence that the thermal properties of biocrusts were previously misjudged due to the measurement limitations imposed by their limited thickness when measured in situ. Biocrusts are likely more significant in regulating soil heat and temperature in drylands than was previously assumed.