•Pressure exerts a negligible effect on most TIMs when pressure exceeds 0.3 MPa.•Surface roughness exerts little effect the performance of PCMs and LMPAs.•PCMs and LMPAs show good performance at low ...pressure.•Thermal pads and carbon-based materials can hinder heat transfer when surface is smooth.
Using thermal interface materials (TIMs) is generally considered an effective way to reduce thermal contact resistance. In this paper, effects of surface roughness, temperature and pressure on TIMs’ performance are investigated. A variety of TIMs including thermal pads, carbon-based materials, phase change materials (PCMs) and low-melting-point alloys (LMPAs) are experimentally studied, and their performance is compared with the case without using any TIM. Results indicate that, when pressure is below 0.3 MPa, the interface thermal resistance (ITR) decreases when the pressure increases, but such a trend is not obvious when pressure exceeds 0.3 MPa. The increase of surface roughness causes the ITR of thermal pads and carbon-based materials to increase, but does not affect the performance of PCMs and LMPAs. Interface thermal resistance of carbon-based materials decreases a little as temperature increases and that of thermal pads is not affected by temperature in test range. The ITR of PCMs and LMPAs sharply decreases when temperature exceeds phase change point. When surface roughness is 0.8 μm, thermal contact resistance of aluminum is 189 mm2·K·W−1 at 0.2 MPa and 153 mm2·K·W−1 at 0.4 MPa, but the ITR of thermal pads is 136–395 mm2·K·W−1 at 0.3 MPa and the ITR of one carbon-based material is 165 mm2·K·W−1 at 0.5 MPa.
In this study, we propose a highly accurate and rapidly analyzable electrothermal modeling for the observed self-heating effect (SHE) characteristics in multinanosheet FETs (mNS-FETs) anticipated for ...use after FinFET. This modeling aims to provide a comprehensive understanding of the SHE in mNS-FETs. In particular, thermal resistance model capable of accurately depicting the thermal profile of mNS-FETs with not only a single structure but also those with multistack (MS) and multifinger (MF) configurations, analyzing their self-heating characteristics, for the first time. The model considers variations in self-heating behavior based on the introduction of a bottom-isolation process, which can reduce leakage current. Electrothermal model constructed with this thermal resistance network accurately captures the lattice temperature distribution within the device due to SHE, allowing for precise depiction on circuit simulators. This capability can enhance the accuracy of reliability analysis for mNS-FET devices during circuit operation, demonstrating its potential utility in assessing the reliability of the components. We propose a thermal resistance formula model suitable for MS and MF configurations of mNS-FETs to be incorporated into the industry-standard SPICE model used for circuit simulations. This provides an accurate modeling methodology for circuit design, ensuring that the thermal characteristics of mNS-FETs with MS and MF structures are appropriately represented in the SPICE model for reliable circuit simulations.
•A micro heat pipe array-air cooling battery thermal management system is proposed.•An equivalent thermal resistance model is developed for MHPA based on thermal circuit method.•Accuracy of the ...thermal circuit model is verified by experiments;•The cooling effect of the system is compared with air cooling under different operating conditions.
An effective battery thermal management system is crucial for electric vehicles because the performance of lithium ion battery is sensitive to its operating temperature. In this study, a thermal management system equipped with micro heat pipe array (MHPA) is designed. An equivalent thermal resistance model is developed for MHPA based on thermal circuit method. The accuracy of the proposed model is validated by comparing the simulation results with experimental data under steady and dynamic and operating condition. A validated lumped thermoelectric model is adopted for prismatic lithium ion battery. The proposed thermal resistance model is combined with the battery model in order to predict the transient temperature distribution of a battery pack based on MHPA cooling. Simulations are conducted for air-cooled MHPA thermal management system. Temperature rise and temperature gradients of the designed cooling system are compared with direct forced convection. Simulation results demonstrate that the MHPA-based battery thermal management provides a quick response to ensure the temperature stability during rapid changing operating condition.
•Compare heat gain and loss for TW-PCM with or without night insulation.•Relate recommended additional thermal resistance with outdoor climate.•Obtain thermal resistance of closed air cavity under ...different wall emissivities.•Obtain SHF–SLR of TW-PCM buildings with night insulation in different climates.
A Trombe wall with a phase change material (TW-PCM) is a practical and low-carbon passive solar heating method. However, the heat efficiency is not high due to the large amount of heat loss at night. Insulation on the outside of the cavity is a suitable solution, but the design method has not been obtained, which hinders the realization of zero energy buildings. In the present study, we analyzed the thermal performance of a TW-PCM with insulation on the outside of the cavity at nighttime to develop the design approach. A mathematical model was established and validated based on experiments. This model was used to analyze the heat efficiency in different outdoor climates for a TW-PCM with insulation on the outside of the cavity. As well, the solar heating fraction (SHF) was analyzed. The results indicated that insulation on the outside of the cavity could significantly improve the thermal performance due to the reduced heat loss during the nighttime. The recommended additional thermal resistance due to the insulation on the outside of the cavity was negatively correlated with the average outdoor air temperature in January based on the analysis of various climates in China. The thermal resistance of the closed air cavity, formed by the TW-PCM and the insulation component, at the same wall emissivity was similar under the recommended additional thermal resistance in different outdoor climates. The SHF was improved significantly for the TW-PCM buildings with insulation on the outside of the cavity and it had a linear relationship with the solar heating load ratio (SLR).
•Combined effects of K1, K2,V1, V2, R*c1 and R*c2 are considered.•ETC is largely independent of R*c1/R*c2 when the R*c1 + R*c2 is less than 10−4.•ETC is not affected by the TC of filler-1 when K1 ...exceeds a critical value of 103.•The effect of Rc on ETC is influenced by K.•For each sum of Rc, there exists a critical value of R*c1/R*c2.
There has been significant interest in enhancing the effective thermal conductivity (ETC) of polymer by incorporating spherical hybrid fillers. However, the effect of interface thermal resistance (Rc) on the ETC of composites has not been investigated. In this paper, this effect is investigated. Meanwhile, the combined effects of filler thermal conductivities (K1, K2), filler sizes (V1, V2), the Rc sum (R*c1 + R*c2) and the Rc ratio (R*c1/R*c2) are also considered. The results show that for a given K1, K2 and R*c1 + R*c2, the ETC is largely independent of R*c1/R*c2 when the R*c1 + R*c2 is less than 10−4. However, when the R*c1/R*c2 ranges from 10−2 to 10, the competing effects of hybrid fillers Rc have a significant effect on the ETC. The ETC is not affected by the TC of filler-1 when K1 exceeds a critical value of 103, instead becoming dependent on K2. For each sum of Rc, there exists a critical value of R*c1/R*c2 where the ETC reaches its nadir, this critical value is influenced by the R*c1 + R*c2, V and K of two fillers. The Rc of fillers with high K is <10−2, it is not feasible to improve the ETC by continuing to reduce its Rc, this value is 10−4 for fillers with low K.
•Thermal performance of a copper made microchannel heat sink is investigated.•Silver nanoparticles are synthesized and used in the cooling loop.•37% enhancement in overall thermal performance of the ...system is reported.•Small penalty for friction factor and pressure drop is reported.•Fouling was found to reduce the thermal performance of the system.
Thermal performance of a copper-made heat sink with rectangular microchannel was assessed within laminar flow regime. Silver nanoparticles were synthesized and dispersed into the deionized water as a potential coolant. Pressure drop, friction factor, heat transfer coefficient and fouling thermal resistance parameter of the system were experimentally investigated for mass concentrations of 0.01%, 0.05%, and 0.1%. Results showed that the heat transfer coefficient of the microchannel is enhanced when deionized water (as a traditional coolant) is replaced with the nanofluid. Importantly, a small increase in pressure drop, friction factor and fouling thermal resistance parameter were reported when nanofluid is used in the system. With an increase in the flow rate and mass concentration of nanofluid, the heat transfer coefficient and pressure drop of the Microchannel Heat Sink (MCHS) increased. Likewise, the local heat transfer coefficient and overall thermal resistance of the microchannel decreased along with the length of the microchannel. The highest heat transfer coefficient (as a thermal performance index) was also seen in the entrance region of the microchannel. The highest value for the fouling thermal resistance parameter was observed for the highest mass concentration of nanofluid which was 1.07 for wt.% = 0.1. The flow rate of fluid was found to enhance the fouling thermal resistance parameter over the 1000 min of the operation. Despite the enhancement in the fouling thermal resistance parameter and friction factor, there was an optimum concentration for silver-water nanofluid in which the overall thermal performance of the system was maximized such that the overall thermal performance of the system can be enhanced up to 37% at Reynolds number 1400 and at wt.% = 0.05.
For advanced thermal interface materials (TIMs), massive inorganic addition for high isotropic thermal conductivities conflicts with suitable rheological viscosity for low contact thermal resistance. ...Traditional strategies rarely resolve such a contradiction, and it remains an academic and industrial challenge. Herein, inspired by the structure and function of the bone joint, a best‐of‐both‐worlds approach is reported that endows a standard polydimethylsiloxane/alumina (PDMS/Al2O3) TIM with simultaneously enhanced rheological mobility and thermal conductivity. It is conducted by employing morphology‐controllable gallium‐based liquid metal (LM) to the surface of Al2O3 by a scalable mechanochemical process. At the typical polymer‐LM‐Al2O3 interface, LM droplets with low cohesive energy can release the freedom for macromolecular chain relaxation and reduce the viscosity, successfully allowing the high‐loading TIMs (79 vol.%) to keep the thixotropic state and effectively reducing its contact thermal resistance with a copper substrate by 65%. At the same time, adjacent LMs merge to thermally bridge separate Al2O3 particles, which facilitates the interfacial thermal conduction and enhances the thermal conductivity from 5.9 to 6.7 W m−1 K−1. Along with additional electrical insulation, this filler modification strategy is believed to inspire others to develop high‐performance polymer‐based TIMs for future advanced electronics.
A joint‐inspired interfacial engineering strategy is reported through on‐demand employing liquid metal to alumina by a scalable mechanochemical process, leading the original hard and non‐conductive polymer–alumina interface change into the liquid yet thermal conductive counterpart. It successfully resolves the traditional paradox that thermal conductivity and contact thermal resistance of a thermal interface material is hardly improved simultaneously.
As demand on the safety and quality of the product in food packaging is increased, nanocellulose based transparent paper with resistance against microbial activity becomes more important. In this ...study, transparent cellulose film was prepared from ginger nanofiber with chemicals and ultrasonication. After purification using acid hydrolysis, ginger fiber had high cellulose content (88%). Ultrasonication of the suspension of the chemically treated fibers for 1 h decreased their diameter to 54.3 nm. Drying of the nano-sized fiber suspension resulted in a transparent film with 5 μm thickness. This film transmitted 83.3% of the light at 650 nm and showed antimicrobial activity. It had high thermal stability with the maximum decomposition temperature peak at 353 °C. This was 17% higher than that of raw ginger fiber (302 °C). The transparent film had a crystallinity index of 48%, and lower moisture resistance than film from chemically treated cellulose fiber. This study promoted transparent nanocellulose film with good antimicrobial properties from abundant and available ginger fibers.
Drying of the nano-sized fiber suspension resulted in an optically transparent film showing antimicrobial activity. Display omitted
•Ginger nanofibers were prepared with chemical treatment and ultrasonication.•Drying of the nano-sized fiber suspension resulted in an optically transparent film.•This transparent film had high thermal stability and showed antimicrobial activity.
Highlights
Bottlenecks in the field of thermally conductive polymer composites are raised, and corresponding reasons are analysed.
Three possible directions for breaking through such bottlenecks are ...put forward, and current advances in these three directions are illustrated.
Future development trends and demands are foreseen to help the development of thermally conductive polymers and their composites.
Rapid development of energy, electrical and electronic technologies has put forward higher requirements for the thermal conductivities of polymers and their composites. However, the thermal conductivity coefficient (
λ
) values of prepared thermally conductive polymer composites are still difficult to achieve expectations, which has become the bottleneck in the fields of thermally conductive polymer composites. Aimed at that, based on the accumulation of the previous research works by related researchers and our research group, this paper proposes three possible directions for breaking through the bottlenecks: (1) preparing and synthesizing intrinsically thermally conductive polymers, (2) reducing the interfacial thermal resistance in thermally conductive polymer composites, and (3) establishing suitable thermal conduction models and studying inner thermal conduction mechanism to guide experimental optimization. Also, the future development trends of the three above-mentioned directions are foreseen, hoping to provide certain basis and guidance for the preparation, researches and development of thermally conductive polymers and their composites.
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