Thermal Conduction Losses Research Articles

Three-terminal heterojunction bipolar transistor solar cells with non-ideal effects: Efficiency limit and parametric optimum selection

Without fabricating intermediate tunnel junctions or wafer bonding schemes for interconnecting the subcells, heterojunction bipolar transistor solar cells offer a promising new route in solar energy conversion. In this work, an improved theory for the three-terminal heterojunction bipolar transistor solar cell is presented with inclusion of non-ideal effects missing from the previous treatment, namely the non-radiative recombination and the thermal conduction losses that are inevitably present in realistic devices. Following detailed balance theory, the revised analytical formula for the cell conversion efficiency is derived, and the maximum efficiencies under different conditions are further calculated. Under the condition of 100 sun irradiance and 50% injection efficiency, a Gallium arsenide/Gallium antimonide-based solar cell operating at 465 K yields a maximum efficiency of 46.4%. Moreover, the effects of solar concentration, injection efficiency, and other key parameters on the cell performance are analyzed, and, consequently, optimal operating conditions and limiting factors on the conversion efficiency are determined. Simulation results show that such a solar cell operating with low injection efficiency under moderate concentration factor and low cell temperature can significantly boost its conversion performance. This work provides new physical insights for optimal designs, thus paving a route towards the development of low-cost high-performance solar cells.

Working gases based scaling-down limitations for thermoacoustic coolers: Miniaturization approach

Regarding miniaturization of thermoacoustic coolers for thermal management purposes, working gases play a key role as the primary media responsible for producing the so-called “thermoacoustic effect” with their interaction with solid media (i.e., secondary media) within stacks or regenerators. However, the role of working gases in limiting scaling-down of thermoacoustic coolers still needs more investigations compared to addressed operational parameters (i.e., mean pressure, temperature difference across stack, etc.). In the present study, a theoretical computational analysis, based on published literature work, would be conducted to investigate allowable minimum sizes of standing-wave thermoacoustic coolers under the effects of working gases thermo-physical properties with considering adverse effects limitation of thermal conduction losses. Different working gases including air and either pure or mixture noble gases have been used for such geometrical scaling-down analysis under specific operating conditions. Moreover, cooling power was focused here as the more desirable performance indicator rather than the efficiency. The results had revealed the cooling capability at different scale levels based on different working gases, which make gases properties significantly contribute to scalability of thermoacoustic coolers to meet the cooling needs for micro-electronics. In addition, more research work will be devoted to other scaling-down issues of thermoacoustic systems.Regarding miniaturization of thermoacoustic coolers for thermal management purposes, working gases play a key role as the primary media responsible for producing the so-called “thermoacoustic effect” with their interaction with solid media (i.e., secondary media) within stacks or regenerators. However, the role of working gases in limiting scaling-down of thermoacoustic coolers still needs more investigations compared to addressed operational parameters (i.e., mean pressure, temperature difference across stack, etc.). In the present study, a theoretical computational analysis, based on published literature work, would be conducted to investigate allowable minimum sizes of standing-wave thermoacoustic coolers under the effects of working gases thermo-physical properties with considering adverse effects limitation of thermal conduction losses. Different working gases including air and either pure or mixture noble gases have been used for such geometrical scaling-down analysis under specific operating condit...

Structural, thermal and dielectric properties of AlN–SiC composites fabricated by plasma activated sintering

ABSTRACTHighly dense AlN–SiC composites with various SiC additions (0–50 wt-%) were fabricated at 1800°C by plasma activated sintering. The effect of SiC addition on structural, thermal and dielectric properties as well as microwave absorbing performance of the composites was investigated. The thermal conductivity decreases with increasing SiC addition, from 68.7 W (m K)−1 for 0 wt-% SiC to 19.38 W (m K)−1 for 50 wt-% SiC. On the contrary, the permittivity and dielectric loss increase gradually, from 7.6–8.5 to 22–26.7 and from 0.02–0.1 to 0.2–0.53, respectively. AlN–SiC composite with better thermal and dielectric properties in 30 wt-% SiC, whose thermal conductivity and dielectric loss are found to be 24.88 W (m K)−1 and 0.15–0.74, respectively. Furthermore, the composite exhibits microwave absorbing performance with the minimum reflection loss (RL) of −16.5 dB at 15.5 GHz and the frequency range of 2.6 GHz for RL below −10 dB (90% absorption).

Effect of Temperature on Microwave-Absorption Property of Plasma-Sprayed Ti3SiC2/NASICON Coating

The high-temperature dielectric and microwave-absorption properties of Ti3SiC2/NASICON coating have been rarely reported. The coating was fabricated by atmospheric plasma spraying in this work for study of dielectric and microwave-absorption properties from 25°C to 500°C. Results showed that the complex permittivity increased with elevated temperature due to the dielectric relaxation, space charge polarization, thermal ion relaxation polarization and conduction loss. When the temperature ranged from 200°C to 500°C, the coating exhibited a good microwave-absorption property with a wide bandwidth (below −5 dB) with a thickness less than 2 mm, which indicated that Ti3SiC2/NASICON coating can be chosen as a potential candidate of high-temperature microwave-absorption material.

Premixed flame–wall interaction in a narrow channel: impact of wall thermal conductivity and heat losses

The flow physics controlling the stabilisation of a methane/air laminar premixed flame in a narrow channel (internal width $\ell _{i}=5~\text{mm}$) is revisited from numerical simulations. Combustion is described with complex chemistry and transport properties, along with a coupled simulation of heat transfer at and within the wall. To conduct a thorough analysis of the flame–wall interaction, the steady flame is obtained after applying a procedure to find the inlet mass flow rate that exactly matches the flame mass burning rate. The response of the premixed flame shape to various operating conditions is then analysed in terms of flame propagation velocity and flow topology in the vicinity of the reactive front. We focus on the interrelations between the flame speed, the configuration taken by the flame surface, the flow deviation induced by the heat released and the fluxes at the wall. Compared to an adiabatic flame, the flame speed increases with edge-flame quenching at an isothermal cold wall in the absence of a boundary layer, decreases with a boundary layer, to increase again with heat-transfer coupling within the wall. A regime diagram is proposed to delineate between flame shapes in order to build a classification versus heat-transfer properties. Under a small level of convective heat transfer with the ambient air surrounding the channel, the larger the thermal conductivity in the solid, the faster the reaction zone propagates in the vicinity of the wall, leaving the centreline reaction zone behind. The premixed flame front is then concave towards the fresh gases on the axis of symmetry (so-called tulip flame) with a flame speed higher than in the adiabatic case. Increasing the heat loss at the wall through convection with ambient air, the flame shape becomes convex (mushroom flame) and the flame speed decreases below its adiabatic level. Scaling laws are provided for the flame speed under these various regimes. Mesh resolution was calibrated, with and without heat loss, from simulations of one-dimensional detailed chemistry flames, leading to mesh resolution of $12.5~\unicode[STIX]{x03BC}\text{m}$ for detailed chemistry and $25.0~\unicode[STIX]{x03BC}\text{m}$ with a skeleton mechanism. The quality of the resolution was also assessed from multi-physics budgets derived from first principles, involving upstream-flame heat retrocession by the wall leading to flow acceleration, budgets bringing physical insights into flame/wall interaction. Additional overall mesh convergence tests of the multi-physics solution would have been desirable, but were not conducted due to the high computing cost of these fully compressible simulations, hence also solving for the acoustic field with low convective velocities.

Thermal, dielectric, and mechanical properties of h‐BN‐filled PTFE composites

ABSTRACTIn order to obtain materials for improved printed circuit boards (PCBs) with high thermal conductivity and low dielectric losses, hexagonal boron nitride (h‐BN) was incorporated into a polytetrafluoroethylene (PTFE) matrix. The filler loading in the composite was varied up to a filler volume content of 50%. Thermal conductivity and coefficient of thermal expansion (CTE) were investigated with respect to filler orientation. Further dielectric and mechanical properties were investigated. The incorporation of h‐BN improved the heat transport significantly, while the loss factor decreased. Fillers with a higher aspect ratio have a greater effect on increasing thermal conductivity. For a filler volume loading of 30%, the in‐plane thermal conductivity was up to 14 times higher than the thermal conductivity of the matrix, while the loss factor decreased slightly. The permittivity increased with the increasing filler volume content, while the CTE also decreased. Though the filler affects the mechanical properties negatively, 40% of the tensile strength could be maintained if a filler volume content of 30% is not exceeded. Such compositions may be used as raw materials for future printed circuit boards. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46859.

High Current Probe for Ic(B,T) Measurements With ±0.01 K Precision: HTS Current Leads and Active Temperature Stabilization System

The current carrying capabilities of high critical temperature ( Tc ) technical conductors have considerably improved in recent years, and this has practical consequences on the requirements of the measurement equipment. We have designed, constructed, and tested a probe for high-current, high-precision critical current measurements in liquid helium and in gas flow at different temperatures. To minimize the ohmic heating and the thermal conduction losses, the probe employs high-temperature superconductors (HTS) current leads rated at 2000 A, which are cooled by the exhaust helium gas at temperatures below 70 K. An active temperature stabilization system keeps the sample temperature constant at the target during current runs with a precision of ±0.01 K. It consists of a proportional–integral–differential loop that controls heaters close to the sample taking the current-induced heating effects into account. We present the design of the probe and data collected on HTS from different manufacturers, which highlight the performance of the system.

Temperature transient analysis for bounded oil reservoir under depletion drive

The significant pressure and temperature signals at wellbores associated with hydrocarbon production can be very useful for reservoir characterization and production analysis purposes. Temperature transient analysis is emerging partly due to the advancement of the downhole temperature monitoring system. Among different flow regimes encountered during the production of a vertical well, the long-lasting boundary dominated flow is crucial since most oil in conventional reservoirs are recovered during this period. The production induced temperature response behaves transient for boundary dominated pressure response and can be analyzed for reservoir property estimation. In this work, we derive a novel temperature transient analytical solution to model sandface temperature signal under boundary dominated flow. Our approach to obtaining the analytical solution from the governing energy balance equation uses Laplace transform with the input of pseudo-steady state pressure equation. This solution can be integrated with previous temperature transient analytical solutions to model the temperature signal from a depletion drived production well. The temperature modeling results acquired from this analytical solution are validated against those from numerical simulation in multiple cases and present distinct behavior under boundary dominated flow. Compared to the heating Joule-Thomson effect in the transient period near the production well, a cooling effect is observed throughout the reservoir after pressure transient reaches the reservoir outer boundary. The magnitude of this cooling effect is proportional to production time. This finding shows the potential of using temperature data at observation wells away from the production well during boundary dominated flow. Further parametric analyses are conducted on eight reservoir, production, and fluid properties to investigate their impacts on the temperature modeling results. These parameters are categorized based on their sensitivities on periods of transient and boundary dominated flow, in which total compressibility and production drainage area are sensitive to the temperature signals under boundary dominated flow only. Unlike the drawdown test, we find that the buildup temperature behavior under boundary dominated flow is identical to that during the transient period. After presenting the forward temperature modeling results, we extend existing reservoir characterization procedures to incorporate the boundary dominated flow. Drainage area and the distance to the closest boundary from the production well can be estimated from the measured temperature data acquired at both production and observation wells. Decent accuracies of the estimations are achieved for the examples presented in this work. The effects of thermal conduction and heat loss may not introduce significant errors in both forward and inverse thermal modeling for the long-lasting boundary dominated flow period.The temperature transient analytical solution under radial boundary dominated flow introduced in this paper considerably extends the scope for temperature transient analysis. This solution enables observation well temperature transient analysis, which seems promising for field application during the boundary dominated flow period. The analytical solution presented herein helps to advance the temperature transient analysis over the whole well production period and forms a basis for future studies on variable rate temperature transient analysis (rate-temperature transient analysis).

Simultaneous estimation of heat transfer coefficient and reference temperature from impinging flame jets

Heat transfer from impinging flame jets to a flat plate has been assumed to be one-dimensional in most of the investigations and without radiation loss treatment. In the present work, the exact nature of diffusion of heat in the plate is investigated via solution to multidimensional heat conduction problem. Two procedures have been employed – Duhamel theorem and three dimensional transient analytical IHCP. The Duhamel theorem which is analytical model for transient one dimensional heat conduction is applied but its application failed the check of linearity requirement of the convection rate equation. From the solution by analytical IHCP for transient, three-dimensional heat conduction, the distribution of wall heat flux and the wall temperature is perfectly linear. This check confirmed that three dimensional approach has to be used. Experimental data is then analyzed by the three dimensional analytical IHCP for short and larger time intervals. It is found that for short time data, heat transfer coefficient and the reference temperature have oscillatory distribution along the radial direction on the impingement plate and for larger time data the oscillations die out. However, at larger time, radiation loss from the impingement plate becomes significant. The effect of variations in thermal conductivity of the impingement plate with the temperature on heat transfer coefficient and reference temperature is discussed. A novel method is developed to correct the heat transfer coefficient and reference temperature to incorporate radiation losses. The deviation in heat transfer coefficient and reference temperature estimated without considering variable thermal conductivity and radiation loss for large time interval is upto 50%.

Development of an empirical method for determination of thermal conductivity and heat loss for pre-insulated plastic bonded twin pipe systems

Pre-insulated twin pipe systems (PTPS) for heat distribution offer advantages for heat supply companies. Trench dimensions for heat supply systems of District Heating (DH) networks might be reduced using these pipe systems. This reduces costs in civil engineering. Additionally heat loss of the DH network may be reduced, that decreases operational costs of these systems. On the other hand, operational heat losses of PTPS significantly differ in many cases from theoretical heat loss of PTPS. This may inhibit the application of this technology in DH networks.Against this background, a standard measurement procedure of thermal properties of PTPS shall be developed, validated and tested at FFI. These tests shall be based on standard measurement procedures for single pipe systems described in EN ISO 8497 and modified for PTPS. Within this context, preliminary tests are done at FFI. Numerical simulations of heat loss are done at IGTH and iteratively fitted to data generated from measurements at the same time.Numerical simulations of stresses occurring due to operational temperatures for PTPS are done in a second step. Internal stresses due to temperature gradients within PTPS as well as external stresses due to interactions of PTPS with the bedding material and ground will be examined. In addition, interactions of bedding materials, operational conditions and heat losses in situ will be assessed.First results obtained are presented in this paper. Focus of this paper is on development of a standard measurement procedure for thermal properties of PTPS, as well as results of numerical calculations regarding heat loss of these systems. One goal of this project funded by the “BMWi – Federal Ministry for Economic Affairs and Energy”, is to discuss and mirror project results in order to modify existing standards, e.g. EN 15698, EN 15632 and EN 13941. Defined quality standards for PTPS, verified by standardized measurement procedures for PTPS, will increase the acceptance of PTPS in the DH sector. This supports small and medium sized enterprises (SME) using and producing PTPS.

Oscillation analysis and current peak reduction in paralleled SiC MOSFETs

Parallel connection of power metal oxide semiconductor field effect transistors (MOSFETs) is often used in the high current side of power conversion systems to obtain a thermal dispersion and low conduction losses. However, a parallel connection may lead to a current unbalance due to the difference of parasitic parameters and switching characteristics of the paralleled devices. The current unbalance generates current oscillations, and in the worst case, it may lead to complete destruction of the power devices. This study analyses an inherent oscillation of two paralleled SiC MOSFETs, under current unbalance conditions. Based on the proposed analysis, it is found that the parasitic inductance is the main cause of the coupled oscillation, which is composed of two different oscillation frequencies. In this study, the coupled oscillation leads to a difference of peak currents between paralleled devices. The circuit conditions, considering the parasitic inductances, are investigated to suppress the coupled oscillation. As a result, a reduction of the common parasitic inductance allows preventing the coupled oscillation and to suppress the peak combined current of paralleled devices. Moreover, a peak current reduction by 37.8% can be achieved, as a result of eliminating the coupled oscillation.

Development status of a high cooling capacity single stage pulse tube cryocooler

High temperature superconducting (HTS) applications require high-capacity and high-reliability cooling solutions to keep HTS materials at temperatures of approximately 80 K. In order to meet such requirements, Sumitomo Heavy Industries, Ltd.(SHI) has been developing high cooling capacity GM-type active-buffer pulse tube cryocooler. An experimental unit was designed, built and tested. A cooling capacity of 390.5 W at 80 K, COP 0.042 was achieved with an input power of approximately 9 kW. The cold stage usually reaches a stable temperature of about 25 K within one hour starting at room temperature. Also, a simplified analysis was carried out to better understand the experimental unit. In the analysis, the regenerator, thermal conduction, heat exchanger and radiation losses were calculated. The net cooling capacity was about 80% of the PV work. The experimental results, the analysis method and results are reported in this paper.

Mechanism of nucleation and incipient growth of Re clusters in irradiated W-Re alloys from kinetic Monte Carlo simulations

High-temperature, high-dose, neutron irradiation of W results in the formation of Re-rich clusters at concentrations one order of magnitude lower than the thermodynamic solubility limit. These clusters may eventually transform into brittle W-Re intermetallic phases, which can lead to high levels of hardening and thermal conductivity losses. Standard theories of radiation-enhanced diffusion and precipitation cannot explain the formation of these precipitates and so understanding the mechanism by which nonequilibrium clusters form under irradiation is crucial to predict material degradation and devise mitigation strategies. Here we carry out a thermodynamic study of W-Re alloys and conduct kinetic Monte Carlo simulations of Re cluster formation in irradiated W-2Re alloys. We use a generalized Hamiltonian for crystals containing point defects parametrized entirely with electronic structure calculations. Our model incorporates recently gained mechanistic information of mixed-interstitial solute transport, which is seen to control cluster nucleation and growth by forming quasispherical nuclei after an average incubation time of 13.5($\ifmmode\pm\else\textpm\fi{}8.5$) s at 1800 K. These nuclei are seen to grow by attracting more mixed interstitials bringing solute atoms, which in turn attracts vacancies leading to recombination and solute agglomeration. Owing to the arrival of both Re and W atoms from the mixed dumbbells, the clusters are not fully dense in Re, which amounts to no more than 50% of the atomic concentration of the cluster near the center. Our simulations are in qualitative agreement with recent atom probe examinations of ion-irradiated W-2Re systems at 773 K.

Thermal conductivity and air-mediated losses in periodic porous silicon membranes at high temperatures

Heat conduction in silicon can be effectively engineered by means of sub-micrometre porous thin free-standing membranes. Tunable thermal properties make these structures good candidates for integrated heat management units such as waste heat recovery, rectification or efficient heat dissipation. However, possible applications require detailed thermal characterisation at high temperatures which, up to now, has been an experimental challenge. In this work we use the contactless two-laser Raman thermometry to study heat dissipation in periodic porous membranes at high temperatures via lattice conduction and air-mediated losses. We find the reduction of the thermal conductivity and its temperature dependence closely correlated with the structure feature size. On the basis of two-phonon Raman spectra, we attribute this behaviour to diffuse (incoherent) phonon-boundary scattering. Furthermore, we investigate and quantify the heat dissipation via natural air-mediated cooling, which can be tuned by engineering the porosity.

Thermo-mechanical analysis in pulsed laser cladding of WC powder on Inconel 718

An uncoupled thermo-mechanical finite element model is developed to simulate the laser-cladding process of tungsten carbide (WC) on Inconel 718. First, a non-linear three-dimensional transient thermal model is developed, which calculates transient temperature distribution in the local clad area. Thermal load attributed to laser beam is implemented to the workpiece by using a developed subroutine. Thermal and mechanical material properties are introduced temperature dependent. All the major physical phenomena associated to the laser-cladding process, such as heat radiation, thermal conduction, and convection heat losses, are taken into account in the developed model. Subsequently, using the thermal history of the thermal analysis, a mechanical analysis is performed, from which the residual stresses are calculated. Both thermal and mechanical analysis results are verified through experimental works. Results show that the temperature profile and clad dimensions are strong function of the heat source and conductivity of material. It is concluded that the laser power and cladding velocity have significant effect on residual stresses. Also, it is found that the longitudinal stresses are approximately three times the transverse ones. Results of mechanical analysis reveal that by increasing input energy, residual stresses increase and number of cracks decreases in the cladded layer.

Formation of X-ray emitting stationary shocks in magnetized protostellar jets

X-ray observations of protostellar jets show evidence of strong shocks heating the plasma up to temperatures of a few million degrees. In some cases, the shocked features appear to be stationary. They are interpreted as shock diamonds. We aim at investigating the physics that guides the formation of X-ray emitting stationary shocks in protostellar jets, the role of the magnetic field in determining the location, stability, and detectability in X-rays of these shocks, and the physical properties of the shocked plasma. We performed a set of 2.5-dimensional magnetohydrodynamic numerical simulations modelling supersonic jets ramming into a magnetized medium and explored different configurations of the magnetic field. The model takes into account the most relevant physical effects, namely thermal conduction and radiative losses. We compared the model results with observations, via the emission measure and the X-ray luminosity synthesized from the simulations. Our model explains the formation of X-ray emitting stationary shocks in a natural way. The magnetic field collimates the plasma at the base of the jet and forms there a magnetic nozzle. After an initial transient, the nozzle leads to the formation of a shock diamond at its exit which is stationary over the time covered by the simulations (~ 40 - 60 yr; comparable with time scales of the observations). The shock generates a point-like X-ray source located close to the base of the jet with luminosity comparable with that inferred from X-ray observations of protostellar jets. For the range of parameters explored, the evolution of the post-shock plasma is dominated by the radiative cooling, whereas the thermal conduction slightly affects the structure of the shock.

Thermal, mechanical, and acoustic properties of silica‐aerogel/UPVC composites

ABSTRACTThe properties of silica‐aerogel/UPVC composites have been investigated with emphasis on sound and heat insulation. UPVC is a material of construction for window profiles and drainage pipes. Hydrophobic silica aerogels were synthesized using silicate sodium as a precursor through a two‐step sol–gel process. The physical and textural properties of the synthesized silica aerogels such as density, surface area, and particle size were analyzed using SEM and BET analysis. Then, the synthesized aerogels were mixed with Unplastisized Polyvinyl Chloride (UPVC) compound at five different weight ratios in an internal mixer to find out the effects of silica aerogels on the thermal, mechanical, and acoustical characteristics. The prepared UPVC/aerogel composites were characterized for tensile properties, impact strength, hardness, Vicat softening temperature, thermal conductivity, sound absorption, and sound transmission loss. The results revealed that adding silica aerogel in to the matrix of UPVC increases its hardness and softening temperature while decreases impact strength. The thermal conductivity of UPVC was decreased by up to 50% using silica aerogel. The sound absorption property of UPVC was increased up to three times by using silica aerogels due to its high porosity. Silica aerogel increased the maximum sound transmission loss of UPVC in the low frequency range. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44685.

Thermoplastic polypropylene/aluminum nitride nanocomposites with enhanced thermal conductivity and low dielectric loss

Polymer dielectrics with high thermal conductivity and low dielectric loss are highly attractive for applications in electric and electronic industry. In this paper, surface modified aluminum nitride (AlN) nanoparticles were introduced into polypropylene (PP) matrix via melt blending to prepare thermoplastic dielectrics with enhanced thermal conductivity and low dielectric loss. The microstructure, DC conductivity, dielectric properties, breakdown strength, space charge behavior, thermal conductivity and thermal stability of the nanocomposites were investigated. It is found that the inclusion of surface modified AlN nanoparticles results in improved thermal conductivity and thermal stability of PP/AlN nanocomposites. The dielectric constant shows a slight increase with AlN nanofiller content, and the dielectric loss remains at very low level of below 0.003. DC conductivity of PP/AlN nanocomposites increases but shows desirable weak dependence on electric field. DC and AC breakdown strength slightly decrease with the AlN nanoparticle content but it is still high enough for dielectric applications. More importantly, the PP/AlN nanocomposites is a thermoplastic material which is potential to be recycled and has less impact on the environment.

Competition between shock and turbulent heating in coronal loop system

2.5-dimensional magnetohydrodynamic (MHD) simulations are performed with high spatial resolution in order to distinguish between competing models of the coronal heating problem. A single coronal loop powered by Alfv\'{e}n waves excited in the photosphere is the target of the present study. The coronal structure is reproduced in our simulations as a natural consequence of the transportation and dissipation of Alfv\'{e}n waves. Further, the coronal structure is maintained as the spatial resolution is changed from 25 to 3 km, although the temperature at the loop top increases with the spatial resolution. The heating mechanisms change gradually across the magnetic canopy at a height of 4 Mm. Below the magnetic canopy, both the shock and the MHD turbulence are dominant heating processes. Above the magnetic canopy, the shock heating rate reduces to less than 10 % of the total heating rate while the MHD turbulence provides significant energy to balance the radiative cooling and thermal conduction loss or gain. The importance of compressibility shown in the present study would significantly impact on the prospects of successful MHD turbulence theory in the solar chromosphere.

Effect of microwave absorption study on polyaniline nanocomposites with untreated and treated double wall carbon nanotubes

Hexanoic acid (HA) doped polyaniline (PAni) nanocomposites which consist of different contents of untreated double wall carbon nanotubes (u‐DWNT) and carboxyl treated DWNT (c‐DWNT) with titanium dioxide nanoparticles were successfully prepared using template‐free method. Fourier transform infrared, ultraviolet‐visible and X‐ray diffractometer spectra clearly confirmed the chemical structure of PAni nanocomposites. Thermal stability, morphology, conductivity, magnetic properties and reflection loss of PAni nanocomposites were characterized by thermogravimetric analyzer, field emission scanning electron microscope, four‐point probe, vibrating sample magnetometer and microwave vector network analyzer, respectively. From this study, it is shown that electrical conductivity of PAni nanocomposites with u‐DWNT possessed higher conductivity (1.23 × 10–1 to 1.31 × 100 S/cm) compared to c‐DWNT (3.43 × 10–2 to 4.48 × 10–1S/cm). PAni/HA/TiO2/DWNT nanocomposites with 20% of c‐DWNT have been covered by PAni layers to form the highest amount of nanorods/nanotubes. Hence, it shows high heterogeneity that will enhance the dielectric permittivity and contribute to a more disordered motion of charge carriers along the PAni backbone. Therefore, it will eventually contribute to good microwave absorption and potentially apply as an efficient electromagnetic interference shielding material in cell phones. POLYM. COMPOS., 39:1283–1291, 2018. © 2016 Society of Plastics Engineers