Conductivity Of Gas Research Articles

Model Based Exploration of Physical Parameters for Liquid Hydrogen System Insulation Performance

Cryogenic Systems require a highly efficient insulation so as to limit the heat ingress and boil-off, which is generally achieved through the use of vacuum combined with an insulated media. The performance of Multi layer Insulation (MLI) will be investigated with detailed thermal models developed to account for all the heat transfer contributions, solid conduction, gaseous conduction and radiation. Results are presented for an usual cold vacuum pressure (CVP) corresponding to high vacuum (<10−6 torr) and compared with available experimental measurements for state of the art technologies. The nominal thermal performances are then evaluated for a cold temperature of 20K (representative of liquid hydrogen storage temperature), for a degraded CVP with hydrogen and nitrogen as residual gasses and for increased hot boundary temperatures. Other parameters are also discussed such as, the number of layers, material, layers density, venting options, assembly process and material optical properties. Finally, a sensitivity of the thermal performance is also presented with a pressure gradient through the insulation thickness, that could be induced by cryopumping, materials outgassing, pumping times or small leakages.

Tree waste based advanced thermal insulation – Vacuum insulation panels – For application at up to 70 °C

Vacuum Insulation Panels (VIPs), despite being the best performing thermal insulation, face the challenges of high cost and environmental concerns associated with the core material, which typically consists of fumed silica (FS) or glass fibres. This study experimentally assessed the suitability of two novel core materials, which were generated from waste tree-based natural fibres (TNF), as potential substitutes for the expensive and widely used fumed silica. A series of composite samples were developed by mechanically mixing TNFs with FS and compressed to manufacture cores (150 mm × 150 mm). Samples were investigated for their radiative, gaseous and solid conductivities using extensive experimental techniques to identify the most cost-effective core composite for VIPs exposed to temperatures up to 70 °C. The spectral extinction coefficient of TNFs was determined by the use of Fourier Transform Infrared Spectroscopy and results indicated that TNFs exhibited a greater spectral extinction coefficient compared to fumed silica within the short infrared wavelength range of 2.5–7.5 μm. The radiative conductivity of fumed silica at a temperature of 70 °C was determined to be 3.33 mWm−1K−1, whereas the radiative conductivity of TNF composites varied between 0.53 mWm−1K−1and 0.39 mWm−1K−1. The VIP sample, which consisted of 100% FS material, had a thermal conductivity 7.84 mWm−1K−1 when measured at an average temperature of 20 °C. The observed value exhibited a substantial increase with the rise in temperature, reaching 11.58 mWm−1K−1 at a temperature of 70 °C. VIP containing 30 % tree-based natural fibre had the lowest thermal conductivity of 6.75 mWm−1K−1 and 8.28 mWm−1K−1 at 20 °C and 70 °C, respectively, among all composites studied. For this sample, VIP core material cost decreased from £3.46 kg−1 per R-value (100% FS) to £2.19 kg−1 per R-value at 20 °C. The study has concluded that a content of 30% of TNF is optimum for FS cores to deliver the most cost-effective VIP.

Electrostatically actuated all metal MEMS Pirani gauge with tunable dynamic range

An electrostatically actuated all-metal microelectromechanical systems (MEMS) Pirani gauge with a tunable dynamic range is proposed. Contrary to the conventional fixed gap Pirani gauges, an electrostatic mechanism is employed to tune the gaseous conduction gap. Due to the electrostatic force between the heating element and heat sink, this tuning results in shifting the transition pressure to a higher pressure. As a result, the operating range of the Pirani gauge can be tuned depending on the magnitude of the actuation voltage. Theoretical estimation of the transition pressure corresponding to different gaseous conduction gaps is also presented. Depending on the available margin of gap tuning, the electromechanical and electrothermal analyses are carried out in COMSOL Multiphysics. The analytical approach is validated by experimentally characterizing the fabricated device. The experimentally tested device with the proposed actuation mechanism shows an 11.2 dB increase in dynamic range in comparison to the conventional design. In a complementary metal-oxide-semiconductor (CMOS)-compatible fabrication process flow, the proposed gauge can be used to monitor vacuum from 40 Pa to 5 × 105 Pa with the electrostatic actuation.

Why and which opacifier for perlite based vacuum insulation panels (VIPs) in the average temperature range of 10–70 °C

Little is known on the effect of opacifiers in perlite core vacuum insulation panels at lower temperatures in the range of 10–70 °C, which are important for applications like refrigerators, transport boxes, buildings, and domestic hot water storage tanks. This paper shows that the effect of opacifier on perlite core Vacuum Insulation Panels (VIPs) is radically different than that on fumed silica VIPs. Identifying an optimum proportion of opacifiers for perlite core VIPs is not a trivial task because of a concomitant rise in solid conductivity as the radiative conductivity decreases. Further, the effect of opacifiers on temperature dependent thermal conductivity of VIPs has been resolved. Opacifiers in perlite are shown to yield clear benefits by reducing the overall thermal conductivity for insulation exposed to ≥70 °C. This was not the case for ≤20 °C. Several VIPs were manufactured using a low-density expanded perlite and 3 different proportions of 4 opacifiers i.e., carbon black, graphite and two variants of silicon carbide (SiC I, SiC II). These VIPs were tested at various combinations of sealing pressure and four different average temperatures i.e., 10 °C, 20 °C, 40 °C and 70 °C. A novel methodology has been developed to derive the evacuated thermal conductivity of perlite core VIPs by curve fitting technique, in order to eliminate the effect of gaseous conduction. The results were also compared with fumed silica core vacuum insulation panels with different proportions of carbon black as opacifier. Among the opacifiers tested (carbon black, graphite, SiC I and SiC II) in this research, Silicon carbide I with a mean particle size of 20 μm was found out to be the best opacifier, with one of its composite resulting in a 50% lower thermal conductivity at 70 °C in comparison to pristine perlite core VIPs.

Surfactant Assisted In Situ Synthesis of Nanofibrillated Cellulose/Polymethylsilsesquioxane Aerogel for Tuning Its Thermal Performance

Back Cover: In article 2200628, Pradip K. Maji and co-worker show that the thermal conductivity depends upon solid and gaseous conductivity. The red and blue color gradients in aerogel slab distinguish hot and cold region. Green color fibers and spherical particles symbolize nanofibrillated cellulose and polymethylsilsesquioxane, respectively. The navy blue color air molecules diffuse into aerogel pores due to Knudsen effect. The structure of aerogel slab represents the thermal insulator.

Multi-scale thermal, energetic and economic analysis of composite insulating materials made of silica aerogel in a fibrous inorganic mat

Composite materials made of silica aerogel in a fibrous inorganic mat, hereafter called “aerogel blankets”, represent promising insulating materials that can overcome the low mechanical resistance of monolithic aerogels, while preserving their very low thermal conductivity. Firstly, this paper details an experimentally validated mathematical model to predict the aerogel blankets’ effective thermal conductivity, as a function of the blankets' density, fiber volume fraction, and temperature. Secondly, an experimental test building retrofitted internally with a layer of needle glass fiber (NGF) aerogel blanket is monitored, and its thermal behavior is compared to the baseline case before the retrofit. The retrofitted wall U-value is derived from experimental data series using stationary and transient parametric methods. Then, a validated whole building Energy Plus numerical model is used to predict the annual energy consumption of a detached single-family house retrofitted with an NGF aerogel blanket, in the climates of Brussels (Belgium), Nice (France), and Stockholm (Sweden). Lastly, a 1-D COMSOL multiphysics model evaluates the economic profitability of installing the blanket as an interior thermal insulation system. Results show that the aerogel blankets have an effective thermal conductivity of about 0.0165 W.m−1.K−1. The designed mathematical model can reliably predict the gaseous conduction in the blanket, but deviations from the experimental measurements appear when considering the radiative and solid conduction components. The blanket's effective thermal conductivity increases with fiber volume fraction and temperature while its dependency curve to density is concave, with a minimum for densities of around 140 kg.m−3. Retrofitting a wall with 2.5 cm of NGF aerogel blanket as an internal insulation system almost doubles the thermal resistance of the experimental wall and decreases the heating load by more than 40 % in all tested climates. Internal thermal insulation with aerogel blankets is more profitable than conventional insulation materials, in places of high floor area price, because it can preserve the indoor living space.

Thermal transport in solar-reflecting and infrared-transparent polyethylene aerogels

Polyethylene aerogels (PEAs) present a unique combination of optical (solar-reflecting but infrared-transparent) and thermal properties that are ideally suited for applications requiring infrared-transparent thermal insulation such as atmospheric radiative cooling and condensation-free radiant cooling. As the material's thermal resistance plays a large role in these systems’ performance, better understanding of thermal transport within the material is crucial to guide future material development. In this work, we characterize thermal transport in PEAs, elucidating contributions of different heat transfer mechanisms and identifying pathways to further improve their thermal insulation performance. We first present a theoretical model that separates thermal transport via solid conduction through the polyethylene backbone, gaseous conduction within the porous structure and radiative transfer through the semi-transparent material. We then fabricated PEA samples of densities ranging from 12.0 kg/m³ to 82.2 kg/m³ and experimentally characterized their thermal conductivity using a custom-built guarded-hot-plate thermal conductivity setup, with pressures ranging from vacuum to 1 atm, in three gas environments (nitrogen, argon and carbon dioxide), and with low and high emissivity boundaries. The experimental and modeling results indicate that conduction in the gas phase and radiative transfer (for the high emissivity boundary case) dominate heat transfer through the material. We find that reducing the pore size and gas pressure, using lower thermal conductivity gases, adding infrared opacifiers and maintaining low density could all provide significant reduction in thermal conductivity.

Digital holographic interferometry for the measurement of temperature distribution around textile conductive yarn embedded in heating garments

Due to the development of wearable smart/electronic integrated textiles, the heating compression bandages, conductive fabrics, and electrically heated garments have been extensively used in many fields. Heating garments could be widely applied in the field of body warming and physical therapy. To impart heating therapy through garments, we need to select conductive yarn to be incorporated into the fabric. In addition to this, voltage supply, resistance, temperature distribution, temperature gradient, heating area, and spacing between the two consecutive conductive yarns are some major factors that have to be optimized for heating garments. Therefore, identifying the proper conductive yarn and approximate spacing between them is important in the electrically heated garments. The measurement of temperature and temperature profile around heated textile conductive yarn is demonstrated using digital holographic interferometry (DHI). DHI has been widely used to measure temperature and temperature profile of gaseous flames and heat conduction studies, etc., as it is more accurate, precise, and provides better spatial resolution. DHI is chosen to measure temperature distribution around copper and stainless-steel yarns used in textiles. DHI is a noncontact, noninvasive, full-field, and almost real-time interferometric technique. We have chosen copper and stainless-steel yarn to study the temperature profile and uniform heating to approximate spacing between two yarns.

Measurement and analysis of thermal conductivity of ceramic particle beds for solar thermal energy storage

A systematic study was performed to measure the effective thermal conductivity of ceramic particle beds, a promising heat transfer and thermal energy storage medium for concentrating solar power (CSP). The thermal conductivity of the ceramic particle beds was measured using a transient hot-wire (THW) method within a temperature range of room temperature to 700 °C, the target operating temperature of the next-generation CSP systems. Two different types of ceramic particles were examined: (1) CARBOBEAD HSP 40/70 and (2) CARBOBEAD CP 40/100 (also known as ACCUCAST ID 50) with the average particle sizes of ~405 μm and ~275 μm, respectively, and thermal conductivities ranging from ~0.25 W m −1 K −1 to ~0.50 W m −1 K −1 from 20 °C to 700 °C in both air and N 2 gas. The gaseous pressure dependence of the thermal conductivity of the ceramic particle beds was also studied in the N 2 environment to differentiate the contributions from gas conduction, solid conduction, and radiation. Calculations using the Zehner, Bauer, and Schlünder (ZBS) model showed good agreements with the measurements. Based on the model, it is concluded that the effective thermal conductivity of the packed particle beds is dominated by the gas conduction while the solid conduction and radiation contributes to about 20% of the effective thermal conductivity at high temperature. • First thermal conductivity measurement of CARBOBEAD HSP 40/70 and CP 40/100 up to 700 °C. • Analysis of thermal conductivity from temperature and gaseous pressure dependence. • Quantification of relative contributions from gas, solid contacts, and radiation at various temperature. • Gaseous conduction is found to be the dominant mechanism.

Thermal radiation shielded, high strength, fire resistant fiber/nanorod/aerogel composites fabricated by in-situ growth of TiO2 nanorods for thermal insulation

• Vertically aligned TiO 2 nanorods were synthesized directly on the surface of microfibers by in-situ growth. • A novel ‘fiber/nanorod/aerogel’ composite was constructed for thermal insulators. • The composite with low thermal conductivity exhibited significantly enhanced infrared radiation shielding. • In-situ growth of TiO 2 nanorods reduced the gaseous conductivity by increasing the interfacial adhesion force. Fiber/aerogel composites attract considerable interest as thermal insulation materials due to their low thermal conductivity. However, in practice they deliver unsatisfactory performance due to their high infrared radiation transmittance and poor interfacial adhesion. Herein, we report a simple strategy for constructing vertically aligned 1D rutile TiO 2 nanorod arrays (TiO 2 -NRAs) directly on the surface of quartz fibers (QFs) by in-situ growth. A novel ‘fiber/nanorod/aerogel’ composite was synthesized by filling the pores of QF/TiO 2 -NRAs with SiO 2 -Al 2 O 3 aerogels (ASAs) through vacuum impregnation. The QF/TiO 2 -NRAs/ASA composite exhibited excellent thermal insulation (0.071 W·m −1 ·K −1 at 1100 °C), infrared radiation shielding performance (an extinction coefficient greater than 150 cm −1 and an infrared reflectivity greater than 95%), fire resistance (more than 1200 °C), and compressive strength (0.37 MPa, 10% strain). In-situ growth of TiO 2 -NRAs can reduce the gaseous thermal conductivity by increasing the interfacial adhesion force between fibers and aerogels, and reduce the radiation heat transfer by shielding infrared radiation. This strategy is applicable to multi-type fibers reinforced silica-based aerogel materials used for insulation and protection in extreme environments.

Theoretical modeling of thermal conductivity of alumina aerogel composites based on real microstructures

As compared with silica aerogels, alumina aerogels have excellent high-temperature stability, and hence, are regarded as a promising candidate for high-temperature thermal insulation materials. However, heat transfer mechanisms for such materials remain insufficiently explored. In this study, based on real material microstructures, an analytical thermal conductivity model for alumina aerogel-fiber-opacifier composites is developed via a modified parallel-series equivalent electrical circuit approach. The model takes into account solid, gaseous, and solid-gas coupling heat conduction in aerogels, solid heat conduction in both fibers and opacifier particles, and radiation in aerogels, fibers, and opacifier particles. The model is validated by comparing its predictions with measured thermal conductivity data. The model predictions reveal that there are two kinds of solid-gas coupling heat transfer mechanisms, which occur in the corner regions between interconnected secondary particles and in the slit regions between adjacent chains, respectively. Because of this coupling, the contribution of gaseous heat conduction is comparable to that of solid heat conduction and radiation of aerogels, fibers, and opacifier particles, which is well supported by experimentally measured data of thermal conductivity. The model is also used to analyze effects of various parameters on the thermal insulation performance of the composites, such as diameters and volume fractious of both fibers and opacifier particles.

APPLICATION OF STUDSVIK’S CMS5 CODE SYSTEM TO ACCIDENT TOLERANT FUEL CORE DESIGN AND ANALYSIS

The possible deployment of Accident Tolerant Fuels (ATF) for currently-operating Light Water Reactors (LWR) has prompted interest in the use of Studsvik’s CMS5 code system to support the analysis of such advanced ATF core designs. Various ATF concepts have been proposed; for example, uranium silicide (U3Si2) fuel, together with iron-based (FeCrAl) cladding. The purpose of this work is to showcase the application of the CMS5 code system, which includes the CASMO5 advanced lattice physics code and the SIMULATE5 three-dimensional nodal simulator, to the analysis of a U3Si2/FeCrAl ATF concept. Given that the CMS5 code system was designed from inception to enable the analysis of advanced core designs, only minor changes to the CASMO5 lattice physics code and SIMULATE5 core simulator are necessary. The current CASMO5 586 energy-group nuclear data library provides all the necessary data to support the generation of homogenized data for downstream use by SIMULATE5 for ATF. The SIMULATE5 nodal code, which features a simplified fuel pin model, requires updating various thermophysical properties corresponding to the U3Si2/SiC ATF fuel and the gaseous conductance models. An equilibrium core for the Integral Inherently Safe (I2S) LWR design developed by the Georgia Institute of Technology was selected. The results of the CMS5 simulation were compared with those in the literature and were found to be in good agreement, giving us confidence that the CMS5 package can be used in the modeling of LWR systems with ATF technology.

Vacuum enclosures for solar thermal panels Part 2: Transient testing with an uncooled absorber plate

Creating a vacuum (<1 Pa) around a solar absorber in a flat plate solar thermal collector can increase efficiency by minimising gaseous conduction and convection between the absorber plate and the glass cover. High performance and architecturally attractive flat plate solar thermal collectors are appealing to building owners and designers for supplying clean and renewable energy cost effectively produced via the façade of the building.This two part paper describes the construction techniques and thermal performance of two vacuum enclosures, fabricated at Ulster University, as prototype components for evacuated flat plate solar collectors. The enclosures were tested at three conditions: 0.0033 Pa, 17 Pa and atmospheric pressure. The first enclosure consisted of two glass panes, sealed to an edge spacer and separated by an array of support pillars on a regular square grid to form a narrow evacuated space. The second enclosure, incorporated an uncooled copper plate to represent a solar thermal absorber. Part 1 of this paper has described the fabrication techniques and compared results from hot-box calorimeter and IR thermography testing of the first enclosure with numerical and analytical predictions.Part 2 describes solar simulator testing of the second enclosure which incorporated an uncooled copper plate. Testing under a solar simulator showed a higher stagnation temperature in the high vacuum test (0.0033 Pa) in comparison with the low vacuum (17 Pa) and atmospheric pressure tests. Curve fitting of a heat transfer model to the transient response data demonstrated that radiation and gas conduction were close to predictions. Simulated results were in close agreement with both the transient response and the steady-state asymptotic plate temperatures.

Thermal conditions and heat transfer characteristics of high-temperature solid oxide fuel cells investigated by three-dimensional numerical simulations

Elucidating internal thermal conditions of high-temperature solid oxide fuel cell (SOFC) stacks is essential for obtaining a substantial thermal efficiency and reliability for long-term operations prior to their commercialization. To examine simultaneous heat transfer and its generation and their effect on the local thermodynamic state, a high-fidelity physical model that resolves spatially the three-dimensional structure of planar, anode-supported SOFC stacks is used in this study. Results show that thermal conduction through metallic interconnects plays a key role in transferring the heat produced by joule heating and electrochemical reactions and thus determining the internal thermal conditions. The heat generated from the electrolyte and thin reactive electrode layers is transferred to the interconnect predominantly by gaseous convection and conduction through materials in the anode and cathode, respectively. The interconnect subsequently transports this heat conductively towards gas inlets and/or surrounding repeating units, influencing temperature increments, its profile and hot spot formation. Its effect on the internal thermal conditions was further examined by a parametric study with respect to the thermal property and geometry of the interconnect which determine its thermal resistance. They indeed affect significantly heat generation and its transfer within the cell, through its boundaries, between repeating units and to incoming gases.

An analytic model employing an elliptical surface area to determine the gaseous thermal conductance of uncooled VOx microbolometers

This work presents a detailed overview of the analytic methods for calculating the beam and gaseous thermal conductance components associated with uncooled VOx microbolometers. The conventional method to calculate the gaseous component relies on the assumption that the entire plate is maintained at a uniform temperature, thus the surface area of the plate is used for the calculation. We have observed using an industry leading multiphysics simulator that this assumption is not strictly true for VOx microbolometers as the conduction pattern exhibits an elliptical shape. Based on this, we have developed and propose an analytic method that employs an elliptical surface area scaled appropriately with the device dimensions to obtain an estimate of the average temperature conduction pattern. Prototype devices were manufactured and experimentally characterised. The devices exhibit thermal conduction characteristics comparable to those in literature and industry, and we could achieve 0.5μW/K under vacuum conditions and 15μW/K at atmospheric pressure with a TCR of −1%/K. However, both simulated and experimental result sets of the gaseous thermal conductance exhibit large deviations from the conventional analytic method, on average approximately 40%. The proposed method reduces this average error significantly to less than 10% when compared to the simulated results.

Endogenous regulation of night-time water relations in hybrid aspen grown at ambient and elevated air humidity

Although night-time water relations have been studied in different plant species in the last decade, there is limited information about the impact of climate variables on endogenous regulation of night-time water relations in trees. The aim of the current study was to elucidate how long-term exposure to increased air humidity impacts night-time gaseous and liquid phase conductance and gas exchange in cut shoots of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) sampled from the free air humidity manipulation experimental site and measured at constant air relative humidity (RH) level in a growth chamber. Neither the early-night leaf conductance (g n1) nor canopy conductance (g c) differed (P > 0.05) between the humidification (H) and control (C) treatments. However, there was a significant (P < 0.01) difference in predawn leaf conductance (g n5) and shoot hydraulic conductance (K 5) between the treatments, with the shoots from the H treatment opening their stomata more efficiently before dawn. Both the early-night dark respiration (R 1) and height increment of stump sprouts were significantly higher (P < 0.01) in the control than in the H treatment. Although the relationship between g n5 and predawn dark respiration (R 5) was statistically significant (P < 0.01) in the H treatment, the gn5 did not depend on R 5 in the C treatment. Our findings suggest that endogenous increase in predawn water flux associates with decreased growth rate of hybrid aspen grown at elevated RH. Thus, regional changes in air humidity may potentially impact night-time water relations in fast-growing tree species like hybrid aspen.

The influence of gaseous heat conduction to the effective thermal conductivity of nano-porous materials

A thermal conductivity test apparatus based on transient plane source method is built and developed to measure effective thermal conductivity of open porous materials at different gas pressures. The effective thermal conductivity of open nano-porous silica materials with porosity of 88.5% is measured under gas pressures ranging from 0.001Pa to 1MPa. The contribution of gaseous heat conduction to the effective thermal conductivity of materials is decomposed by subtracting the effective thermal conductivity at ultimate vacuum from that at different gas pressure. It is found that the contribution of gaseous heat conduction is much different with the gas thermal conductivity in nano-porous materials and that in free space. The result is also demonstrated by theoretical analysis and numerical simulation.

Centre of Panel Thermal Conductivity Performance Analysis of Aerocor-Centrifugal Hybrid Ultrafine Glass Fiber VIP Core Materials

This paper includes analysis on the recent advancement of glass fiber core based vacuum insulation panels (VIPs) in China, including the experimental development of mixed ultrafine fiberglass prototype core material consisting of Centrifugal and Aerocor glass wool mixture at different ratios. Pore sizes exhibited by these prototypes generally range between 15-25μm. Extensive centre of panel thermal conductivity (Kcop) were performed from which thermal performance graphs were extracted and analyzed prudently. Kcop analysis verified superior performance of the prototypes over traditional glass fiber core samples, hinting greater service life. The study concludes that in order to optimize the long term performance of current industrial glass fiber core material reduction of pore size at less than 10μm range as well as reduction of x-z axis fiber orientation angle to less than 450 would potentially decrease core structural sensitivity towards both gaseous and solid conductivity at increase of internal pressure.

Effects of stomata clustering on leaf gas exchange.

A general theoretical framework for quantifying the stomatal clustering effects on leaf gaseous diffusive conductance was developed and tested. The theory accounts for stomatal spacing and interactions among 'gaseous concentration shells'. The theory was tested using the unique measurements of Dow et al. (2014) that have shown lower leaf diffusive conductance for a genotype of Arabidopsis thaliana with clustered stomata relative to uniformly distributed stomata of similar size and density. The model accounts for gaseous diffusion: through stomatal pores; via concentration shells forming at pore apertures that vary with stomata spacing and are thus altered by clustering; and across the adjacent air boundary layer. Analytical approximations were derived and validated using a numerical model for 3D diffusion equation. Stomata clustering increases the interactions among concentration shells resulting in larger diffusive resistance that may reduce fluxes by 5-15%. A similar reduction in conductance was found for clusters formed by networks of veins. The study resolves ambiguities found in the literature concerning stomata end-corrections and stomatal shape, and provides a new stomata density threshold for diffusive interactions of overlapping vapor shells. The predicted reduction in gaseous exchange due to clustering, suggests that guard cell function is impaired, limiting stomatal aperture opening.

Thermal conductivity of powders used in continuous casting of steelPart 2 – Powders

Measurements of the thermal conductivity of casting powders are needed to determine the magnitude of the vertical heat flux in the powder bed of a continuous casting mould. The thermal conductivities and thermal diffusivities of four mould powders have been determined using the transient plane source (TPS) and the transient hot wire (THW) methods. The values reported in this investigation are in good agreement with the results of earlier studies which used the THW method. However, the results were significantly different from λeff values obtained in thermal insulation tests. This was attributed to the large contribution to λeff from gaseous conduction which arises from the large temperature gradient across the sample. It was found that the thermal conductivity (λpowd) of the powders had a mean value of 0.125±0.025 W m−1 K−1 for the four powders studied; this value is in good agreement with two other studies; it increased as the temperature increased with a mean temperature coefficient of (dλ/dT = 9×10−5 W m−1 K−2 for the range 295–1100 K and increased as the bulk density increased (λ295 = 0.010+1.69×10−4ρbulk W m−1 K−1).