Thermal Conduction Losses Research Articles

Core–shell spherical graphite@SiC attenuating agent for AlN-based microwave attenuating ceramics with high–efficiency thermal conduction and microwave absorption abilities

A core–shell structured spherical graphite (SG)@SiC attenuating agent with a tunable silicon carbide (SiC) shell thickness was synthesized via in-situ solid-liquid reaction of SG and Si. Then, fully dense 10 wt%SG@SiC/AlN microwave attenuating composite ceramics were prepared through hot-pressing sintering, and the morphology of SG@SiC particle was well maintained. By moderately modulating the thickness of the SiC shell with relatively low complex permittivity and thermal conductivity, an effectively inhibited solid solution of SiC into AlN, weakened dipole and electron polarization, enhanced conduction loss, and an improved impedance matching, thermal conductivity and microwave loss capacity were simultaneously achieved. Thus, the SG@SiC/AlN composite exhibit excellent and impressive thermal conductivity of 63.92 W m−1·K−1 and minimum reflection loss of −34.2 dB. The outstanding performance of SG@SiC/AlN composite indicates that the composite is promising microwave attenuating ceramic with excellent thermal conduction and microwave absorption ability. This work opens up a new core–shell structure strategy for designing and developing a high-efficiency attenuating agent and microwave attenuating ceramic.

Data-driven assessment of magnetic charged particle confinement parameter scaling in magnetized liner inertial fusion experiments on Z

In magneto-inertial fusion, the ratio of the characteristic fuel length perpendicular to the applied magnetic field R to the α-particle Larmor radius ϱα is a critical parameter setting the scale of electron thermal-conduction loss and charged burn-product confinement. Using a previously developed deep-learning-based Bayesian inference tool, we obtain the magnetic-field fuel-radius product BR∝R/ϱα from an ensemble of 16 magnetized liner inertial fusion (MagLIF) experiments. Observations of the trends in BR are consistent with relative trade-offs between compression and flux loss as well as the impact of mix from 1D resistive radiation magneto-hydrodynamics simulations in all but two experiments, for which 3D effects are hypothesized to play a significant role. Finally, we explain the relationship between BR and the generalized Lawson parameter χ. Our results indicate the ability to improve performance in MagLIF through careful tuning of experimental inputs, while also highlighting key risks from mix and 3D effects that must be mitigated in scaling MagLIF to higher currents with a next-generation driver.

Thermodynamic and Magnetic Topology Evolution of the X1.0 Flare on 2021 October 28 Simulated by a Data-driven Radiative Magnetohydrodynamic Model

Solar filament eruptions, flares, and coronal mass ejections (CMEs) are manifestations of drastic releases of energy in the magnetic field, which are related to many eruptive phenomena, from the Earth’s magnetosphere to black hole accretion disks. With the availability of high-resolution magnetograms on the solar surface, observational data-based modeling is a promising way to quantitatively study the underlying physical mechanisms behind observations. By incorporating thermal conduction and radiation losses in the energy equation, we develop a new data-driven radiative magnetohydrodynamic model, which has the capability of capturing the thermodynamic evolution compared to our previous zero-β model. Our numerical results reproduce the major observational characteristics of the X1.0 flare on 2021 October 28 in NOAA active region 12887, including the morphology of the eruption, the kinematics of the flare ribbons, extreme ultraviolet (EUV) radiations, and the two components of the EUV waves predicted by the magnetic stretching model, i.e., a fast-mode shock wave and a slower apparent wave, due to successive stretching of the magnetic field lines. Moreover, some intriguing phenomena are revealed in the simulation. We find that flare ribbons separate initially and ultimately stop at the outer stationary quasi-separatrix layers (QSLs). Such outer QSLs correspond to the border of the filament channel and determine the final positions of flare ribbons, which can be used to predict the size and the lifetime of a flare before it occurs. In addition, the side views of the synthesized EUV and white-light images exhibit typical three-part structures of CMEs, where the bright leading front is roughly cospatial with the nonwave component of the EUV wave, reinforcing the use of the magnetic stretching model for the slow component of EUV waves.

Polytetrafluoroethylene Nanocomposites with Engineered Boron Nitride Nanobarbs for Thermally Conductive and Electrically Insulating Microelectronics and Microwave Devices

The demands for effective thermally conductive dielectric composite materials continue to increase due to high speed and low-loss signal propagation required in microwave frequency applications. Composites of polytetrafluoroethylene (PTFE) and boron nitride are promising for these applications. Here, for the first time, recent generation surface-engineered boron nitride nanobarbs (BNNB) material was evaluated at a low filler content in PTFE to achieve the desirable high thermal conductivity and low dielectric loss requirements which are typically difficult without a strong filler–matrix interaction and high filler loading. Composites of modified BNNB and modified PTFE were also fabricated and evaluated. These composites exhibited higher thermal conductivity (1.2–1.3 W/mK) with a lower concentration of boron nitride nanoparticles than those reported in the literature. The data were analyzed by theoretical models and interfacial thermal resistance was the lowest for the composite made from the modified PTFE and modified BNNB. Additionally, the composites displayed excellent dielectric properties including a dielectric constant ≈2.3 and loss tangent of less than 0.005 at frequencies of 1–3 GHz. These results indicate that such thermally conductive and low-loss dielectric composites have significant potential as materials for thermal management and dielectric components in microelectronics, 5G, and microwave devices.

Development of a Phase Change Backfill Material with High Heat Capacity and High Thermal Conductivity Used for Ground Source Heat Pumps

To solve the problems of phase change materials (PCM) including low thermal conductivity and easy washout and loss after liquefaction in current studies on borehole backfill materials, capric acid-lauric acid/expanded graphite (CA-LA/EG) PCM admixture with high thermal conductivity and high heat capacity was developed by using expanded graphite as the carrier. The PCM admixture is mixed with original sands (drilling debris) to make phase change backfill materials (PCBM). When the PCM backfilling is applied, the key issue is to dissipate the large amount of heat stored as latent heat in boreholes to the surrounding formation in time; otherwise, serious heat accumulation would be induced. Numerical simulation of application of the PCBM in multiple intermittent operation cycles was conducted when the admixture percentages and thermal conductivities are different. The result shows that compared with conventional low-conductivity PCM admixtures and ordinary backfill sands such as drilling debris, the CA-LA/EG admixture can mitigate the temperature fluctuation in borehole and improve its heat exchange rate. The heat exchange rate was increased by 11.6% when 30% of CA-LA/EG admixture was added. However, the improvement declined as the number of operation cycle increased, so the intermittent operation mode is suggested to match the PCBM application since the heat in borehole should be dissipated in time to reserve storage capacity in the next operation cycle and continuously utilize the high heat capacity of the PCM.

Hydroxyl-group decreased dielectric loss coupled with 3D-BN network enhanced high thermal conductivity epoxy composite for high voltage-high frequency conditions

The rapid development of electrical and electronics industry puts forward new requirements for high thermal conductivity and low dielectric loss of insulating materials. However, the traditional strategies to improve thermal conductivity of insulating materials with high thermal additives quantity usually accompany with the huge increase in dielectric loss, which will eventually lead to thermal breakdown and cannot meet the real demand under high voltage-high frequency conditions. Herein, in-situ bubble-induced self-assembled strategy was used to fabricate 3D boron nitride (BN) network/epoxy composites. The cellulose with rich hydroxyl groups could both crosslink with epoxy group and form hydrogen bonding with the hydroxyl groups on BN, which restricts the polymer chain movement and ensures the low dielectric loss. Improved thermal conductivity (1.62 W/(m·K), 8 times higher than that of EP) and decreased dielectric loss (0.00597, 18.1% lower than that of EP at 46.4 kHz, 20 °C) of the as-prepared composites contribute to the significant extension of the thermal breakdown time (411.4% higher than that of EP at 44 kHz). In addition, the partial discharge inception voltage of the composites is 8.9% higher than that of EP. These advantages make it attractive to high reliability of thermal management applications in the electrical and electronics industry.

Hydroxy silicone oil modified boron nitride for high thermal conductivity and low dielectric loss silicone rubber composites: experimental and molecular simulation studies.

Polymer-based composites are widely used in microelectronics and wireless communications, which require high thermal conductivity and low dielectric loss for effective heat dispersion and signal transmission. Different lengths of hydroxyl silicone oil chains modified boron nitride/silicone rubber composites were explored and prepared in this work. Experiments demonstrate that the long-chain modified BN improves the thermal conductivity and decreases the dielectric loss of composites. A molecular dynamics simulation was employed to study the mechanism and affecting variables. The calculated results indicated that the improvement of the thermal and dielectric properties is mainly related to the interfacial behavior, including interfacial compatibility, interfacial bond strength, and phonon matching. Based on the simulated interfacial behavior and thermal conductivity, the thermal and dielectric properties of different chain-length modified boron nitride/silicone rubber composites have been anticipated. The results show that the longer-chain modified boron nitride/silicone rubber composites have better thermal and dielectric properties. This research may give a theoretical foundation for the development of materials with designable performance for electronic devices.

Characterization of GaN HEMTs' Aging Precursors and Activation Energy Under a Wide Range of Thermal Cycling Tests

In this paper, 650 V / 7.5 A rated enhancement-mode (E-mode) Gallium Nitride (GaN) high-electron-mobility-transistors (HEMTs) with integrated gate drivers are characterized under thousands of accelerated thermal cycles (ATC) at different junction temperature stresses. This research helps in developing fundamental insights into GaN HEMTs' aging characteristics through the degradation of ten devices under ATC tests. For over 20,000 thermal cycles, the forward and reverse conduction losses, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> GSS, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> oss, and the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RDS</i> on are experimentally measured to identify the parameter shifts and the corresponding precursors. Results indicate that both <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">IGSS</i> and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</i> oss do not deviate much, but the values of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RDS</i> on, the forward and reverse conduction losses vary considerably with device aging. This paper also presents an empirical method to estimate the correlation between the acceleration factors of the GaN FETs' degradation process and the thermal cycling conditions. The value of the activation energy of the tested GaN HEMT devices is also derived using the empirical equations to be about 1.13 eV under the applied stress factors. This study finds that the degradation process of GaN HEMTs with age facilitates a reasonable correlation with different failure mechanisms, which further helps in reliability improvement.

Evaluation of insulated gate bipolar transistor valve converter based unified power flow controller reliability and efficiency

The effectiveness and reliability of the unified power flow controller (UPFC) are determined by the insulated gate bipolar transistor (IGBT) valve. Thermal losses, conduction losses, and switching losses in the IGBT valve all affect the efficiency of UPFC. The failure rate of the converter valves is influenced by junction temperature, which has an impact on the converter's reliability. Piecewise linear electrical circuit simulation (PLECS) was used to simulate two IGBT valve-based converter legs working at 12000 Hz, part number GT30F123. By reference to the switching characteristics produced by PLECS, switching losses, conduction losses, and thermal losses are analyzed. Simulation results are corroborated with analytical measurements. The chance of achieving 100%, 50%, and 0% functioning modes are among the reliability indices that are analyzed. The chance of achieving a hundred percent, fifty percent, or zero percent functioning mode is assessed. The frequency of achieving the state probability and mean time to failures (MTTF) are obtained from probabilities using the Markov model. The thermal losses, failure rate, and lifetime of the UPFC are all quantified to give a complete picture of the UPFC's performance.

Dielectric polymer composites with ultra-high thermal conductivity and low dielectric loss

Polymer based dielectric materials with simultaneously high thermal conductivity and low dielectric loss are highly desirable in various applications like energy storage, thermal management and electronic packaging. Polymer dielectrics generally benefit from good electrical insulation, high breakdown strength, high toughness and low density but suffer from very low thermal conductivity (0.1–0.5 W m −1 K −1). Herein we propose a new strategy to overcome this compromise; solid-state drawing of ultra-high molecular weight polyethylene (UHMWPE) films doped with a small amount of nanodiamonds (NDs). The resulting orientation of UHMWPE macromolecules and the nanofiller significantly improves the thermal conductivity along the stretching direction, while the dodecane surface functionalization of the NDs endows a robust interface between the matrix and filler, which minimizes the thermal resistance and dielectric loss. Our composites film (2 wt% NDs) shows an ultra-high thermal conductivity of 60 W m −1 K −1 in the drawing direction and very low dielectric loss, both at low and high electric field. More generally, herein we demonstrates that the interfaces introduced by the nanofillers do not necessarily cause an increase in dielectric loss at high electric field and a decrease in thermal conductivity, providing a new direction for the design of novel polymer based dielectric and functional materials.

Flexible substrate based on sandwich-structure hydrocarbon resin/aligned boron nitride composites with high thermal conductivity and low dielectric loss

Flexible circuit board materials with low dielectric constant (εr), low dielectric loss (tanδ) and high thermal conductivity (TC) were highly desired for high-frequency and high-speed electronic equipment. Herein, hexagonal boron nitride (h-BN) sheets were filled into highly elastic styrene ethylene butylene styrene (SEBS) matrix and oriented along in-plane direction regularly by hot-pressing method. SEBS/h-BN films exhibited high TC and outstanding flexibility except relatively high tanδ and water absorption. The sandwich structure was designed utilizing pure cyclic olefin copolymer (COC) films as outer surface layers and SEBS/h-BN film as interlayer. The introduction of COC films reduced the tanδ and water absorption of SEBS/h-BN film without reducing original TC obviously. Hybrid SEBS/COC/BN films owning the same components with sandwich-structure films were also fabricated to verify the advantages of designed structure. Sandwich-structure films always kept good flexibility and exhibited low εr (2.7–3.6), low tanδ (<1 × 10−3, 10 GHz), high TC (3.8–17.6 W m−1 K−1) and low water absorption (<0.1%). These films were also fabricated into flexible copper clad laminates and patch antenna operated in sub-6G band. The antenna exhibited a return loss of −32.8 dB and a gain of 7.04 dBi. The flexible substrates show great potential and satisfy large-scale production demand in high TC flexible circuit board materials field.

Thermal rectification in polytelescopic Ge nanowires

Herein we served non-equilibrium molecular dynamics (NEMD) approach to simulate thermal rectification in the mono- and polytelescopic Ge nanowires (GeNWs). We considered mono-telescopic structures with different Fat-Thin configurations (15-10 nm-nm or Type (I); 15-5 nm-nm or Type (II); and 10–5 or Type (III) nm-nm) as generic models. We simulated the variation of thermal conductivity against interfacial cross-sectional temperature as well as the direction of heat transfer, where a higher thermal conductivity correlating to thicker nanowires, and a more significant drop (or discontinuity) in the average interface temperature in the positive (or negative) direction were detected. Noticeably, interfacial thermal resistance followed the order of Type (II) (48 K/μW, maximal) ˃ Type (III) ˃ Type (I) (5 K/μW, minimal). In the second stage, a series of polytelescopic nanostructures of GeNWs were born with consecutive cross-sectional interfaces. Surprisingly, larger interfacial cross-sectional areas equivalent to smaller diameter changes along the GeNWs were responsible for higher temperature rectification. This led to a very limited thermal conductivity loss or a very high unidirectional heat transfer along the polytelescopic structures - the key for manufacturing next generation high-performance thermal diodes.

Design and development of novel LiCl–NaCl–KCl–ZnCl2 eutectic chlorides for thermal storage fluids in concentrating solar power (CSP) applications

Molten chloride mixtures are of great scientific and technical interest for sensible heat storage in solar power generation. In this work, the condensed phases in a LiCl–NaCl–KCl–ZnCl 2 multicomponent system were critically evaluated and predicted via literature review and simulations of LiCl–KCl and KCl–ZnCl 2 systems. Two innovative LiCl–NaCl–KCl–ZnCl 2 quaternary chloride systems with low melting points were proposed and developed on the basis of a thermodynamic design. The thermal–physical properties of these two eutectic compositions, including melting point, mixing enthalpy, specific heat capacity, density, thermal conductivity, and mass loss, were then experimentally determined. The experimental results were consistent with the theoretical predictions. The novel quaternary eutectic chlorides with excellent thermophysical properties developed herein are potential candidates for thermal energy storage and transfer materials in concentrating solar power plants. • Thermodynamic prediction of LiCl–NaCl–KCl–ZnCl 2 system was performed via CALPHAD. • Two novel quaternary eutectic chlorides were successfully designed for thermal energy storage and transfer. • Thermophysical properties of the system were determined by experiment and classical prediction method. • Thermodynamic performance of the novel chlorides was substantially improved compared with other potential materials. • The novel quaternary eutectic chlorides were proposed as potential candidate materials in CSP applications.

The Effect on Energy Efficiency of Yttria-Stabilized Zirconia on Brass, Copper and Hardened Steel Nozzle in Additive Manufacturing

This study aimed to investigate if a thermal barrier coating (TBC) affected the energy efficiency of 3D printers. In accordance with this purpose, the used TBC technique is clearly explained and adapted to a nozzle in a simulation environment. Brass, copper, and hardened steel were selected to be the materials for the nozzles. The reason for the usage of a thermal barrier coating method is that the materials are made with low thermal conductivity, which reduces the thermal conductivity and energy losses. Yttria-stabilized zirconia was used to coat material on brass, copper, and hardened steel. To prevent temperature fluctuations, yttria-stabilized zirconia together with a NiCRAl bond layer was used and, thus, heat loss was prevented. Additionally, the paper addressed the effects of the coating on the average heat flux density and the average temperature of the nozzles. In addition, by means of the finite element method, steady-state thermal analyses of the coated and uncoated nozzles were compared, and the results show that the thermal barrier coating method dramatically reduced energy loss through the nozzle. It was found that the average heat flux was reduced by 89.4223% in the brass nozzle, 91.6678% in the copper nozzle, and 79.1361% in the hardened steel nozzle.

Performance Evaluation of Solar-Powered Atmospheric Water Harvesting Using Different Glazing Materials in the Tropical Built Environment: An Experimental Study

Water scarcity is a global issue, and its severity is expected to worsen in the near future, prompting further efforts to find new sources of freshwater. Solar-Powered Atmospheric Water Harvesting (SPAWH) is a promising passive approach for atmospheric water generation. This study aims to examine the thermal performance of different glazing materials and water production in SPAWH. The research consists of two phases: a laboratory test of various glazing materials and an experimental study to assess system efficiency in producing water in the tropics. The preliminary results indicated that glass demonstrated better thermal performance than acrylic in the lab, with higher thermal conductivity and less heat loss. The experimental findings showed that the maximum water produced by the proposed SPAWH (60 cm length, 60 cm width and 30 cm height) placed on a 30° tilt angle using glass (3 mm) and acrylic (3 mm) was 0.61 L/m2/day and 0.44 L/m2/day, respectively. The cost analysis revealed that produced water costs $0.18/kg for glass and $0.40/kg for acrylic, respectively. Atmospheric water could be harvested using SPAWH in the tropics, which would help to provide new opportunities for sustainable water supplies and development in these regions.

Thermal performance of stable SiO2 nanofluids and regression correlations to estimate their thermophysical properties

The present work investigates the best mix ratio of Glycerol in Water as a medium to prepare a stable nanofluid. Increasing the proportion of glycerol enhances the aqueous mix's dynamic viscosity and improves the prepared nanofluid's stability. The thermal conductivity and viscosity of the Glycerol and Water mixtures determination were undertaken at various Glycerol ratios. The best percentage of glycerol in the mixture is found to have the least amount of thermal conductivity loss and the optimum viscosity gain. Silica (SiO2) nanofluid of 0.25%, 0.5%, 1%, and 1.5% weight concentrations was prepared with this optimal mixture of Glycerol and Water. The stability of these SiO2 nanofluids is evaluated by determining the zeta potential at different time intervals. The nanofluids prepared were observed to be stable for one month. The thermal conductivity and viscosity of the nanofluids are measured between the temperature limits of 30°–70°C. A peak increment of 32.1%and 46.3% in thermal conductivity and viscosity is observed. Furthermore, when the percentage enhancement ratio (PER) and Mouromtseff ratio of these nanofluids is examined, it is observed that they have more excellent thermal performance at higher temperatures. Regression correlations are developed to estimate the thermal conductivity and viscosity of the prepared nanofluids with a maximum deviation of 9%.

Construction of coronal hole and active region magnetohydrostatic solutions in two dimensions: Force and energy balance

Coronal holes and active regions are typical magnetic structures found in the solar atmosphere. We propose several magnetohydrostatic equilibrium solutions that are representative of these structures in two dimensions. Our models include the effect of a finite plasma-β and gravity, but the distinctive feature is that we incorporate a thermal structure with properties similar to those reported by observations. We developed a semi-analytical method to compute the equilibrium configuration. Using this method, we obtain cold and under-dense plasma structures in open magnetic fields representing coronal holes, while in closed magnetic configurations, we achieve the characteristic hot and over-dense plasma arrangements of active regions. Although coronal holes and active regions seem to be antagonistic structures, we find that they can be described using a common thermal structure that depends on the flux function. In addition to the force balance, the energy balance is included in the constructed models using an a posteriori approach. From the two-dimensional computation of thermal conduction and radiative losses in our models, we infer the required heating function to achieve energy equilibrium. We find that the temperature dependence on height is an important parameter that may prevent the system from accomplishing thermal balance at certain spatial locations. The implications of these results are discussed in detail.

Flexible and quasi-isotropically thermoconductive polyimide films by guided assembly of boron nitride nanoplate/boron nitride flakes for microelectronic application

• A hierarchical “brick and plank” structure is fabricated by dopamine modified h -BN nanomaterials. • This special structure can be used to improve the performance of polyimide. • The modified PI films have quasi-isotropic thermal conductivity and high thermal stability. • The modified PI films have good flexibility and excellent electrical insulation. • The modified PI films show faster shape memory response time reducing 50 %. Currently, the application of polyimide (PI) based materials often demands mutual additional properties, such as high thermal conductivity, good flexibility, high thermal stability and low dielectric constant and loss, etc. . Herein, a well-aligned hierarchical “brick and plank” architecture by rational assembly of dopamine modified hexagonal boron nitride flakes and nanoparticles (PDA-BNF@BNNPs) which can effectively improve the thermal conductivity, thermal stability, electrical conductivity, dielectric properties and shape memory performance of pure PI. The alternating stacking of vertically arranged h -BNNPs and horizontally laid h -BNFs yield a quasi-isotropic thermal conductivity of PI films with a high through-plane thermal conductivity of 6.43 W/(mK) and an in-plane thermal conductivity of 11.85 W/(mK) because of the simultaneously vertical and horizontal phonon scattering enabled by the vertically arranged h -BNNPs and horizontally laid h -BNFs. Besides, this special structure also endues PI films high thermal stability of over 560 °C, prominent electrical resistance of over 1.40 × 10 -13 Ω•cm, and low dielectric loss of less than 0.02 in the high frequency. Moreover, the PDA-BNF@BNNP/PI films exhibit excellent flexibility and shape memory performance with faster recovery response time reduced over 50 % comparing with that of pure PI film. These outstanding properties combining with the facile and scalable fabrication process make PDA-BNF@BNNP/PI films are very promising in diverse electronic device applications, especially in flexible electronic devices or circuits requiring additionally high thermal conductivity and low dielectric loss.

A Thermopile Detector Based on Micro-Bridges for Heat Transfer.

A thermopile detector with their thermocouples distributed in micro-bridges is designed and investigated in this work. The thermopile detector consists of 16 pairs of n-poly-Si/p-poly-Si thermocouples, which are fabricated using a low-cost, high-throughput CMOS process. The micro-bridges are realized by forming micro trenches at the front side first and then releasing the silicon substrate at the back side. Compared with a thermopile device using a continuous membrane, the micro-bridge-based one can achieve an improvement of the output voltage by 13.8% due to a higher temperature difference between the hot and cold junctions as there is a decrease in thermal conduction loss in the partially hollowed structure. This technique provides an effective way for developing high-performance thermopile detectors and other thermal devices.

Carbon as a solution for nanocellular foam superinsulation

This work demonstrates the substantially improved thermal radiation blocking capability of polymer foams with the utilization of carbonaceous nanoparticles to overcome the limitation of the nanocellular foam's thermal insulation capability to achieve superinsulation. Without carbon, the radiation heat transfer becomes extremely high through thin and transparent cell walls and struts of the low-density nanocellular foams. However, this high radiative heat transfer can be successfully reduced by incorporating multi-walled carbon nanotubes (MWCNTs). The effect of carbon on heat transfer in foams was mathematically modelled and experimentally verified. The model includes contributions of thermal transport through conduction and radiation, while convection is negligible. The effects of MWCNTs on thermal conductivity, refractive index, absorption index, dielectric permittivity and dielectric loss of the solid were studied using two examples of polystyrene/MWCNT and PMMA/MWCNT nanocomposite foams. It was found that, with carbon, the radiation blocking capability is significantly improved and nanocellular foams could achieve superinsulation level through the Knudsen effect. The optimal cellular structure at which heat transfer is minimized was investigated with the aim of manufacturing superinsulation. The foam's total heat transfer decreased while the optimal expansion ratio increased with the filler content, which is preferable for manufacturing high performance insulation with less polymer.