Temperature and curvature-dependent thermal interface conductance between nanoscale-gold and water from molecular simulation

Plasmonic gold nanoparticles (AuNPs) can convert laser irradiation into thermal energy and act as nano heaters in avariety of applications. Although the AuNP-water interface is an essential part of the plasmonic heating process,there is a lack of mechanistic understanding of how interface curvature and the heating itself impact interfacial heattransfer. Here, we report atomistic molecular dynamics simulations that investigate heat transfer through nanoscalegold-water interfaces. We confirmed that interfacial heat transfer is an important part of AuNP heat dissipation inAuNPs with diameter less than 100 nm, particularly for small particles with diameter≤10 nm. To account forvariations in the gold-water interaction strength reported in the literature, and to implicitly account for differentsurface functionalizations, we modeled a moderate and a poor AuNP-water wetting scenario. We found that thethermal interface conductance increases linearly with interface curvature regardless of the gold wettability, while itincreases non-linearly, or remains constant, with the applied heat flux under different wetting conditions. Our analysissuggests the curvature dependence of the interface conductance is due to the changes in interfacial water adsorption,while the temperature dependence is caused by heat-induced shifts in the distribution of water vibrational states.Our study advances the current understanding of interface thermal conductance for a broad range of applications.

Identification of the Thermal Conductance of a Hidden Barrier from Outer Thermal Data

Hidden defects affecting the interface in a composite slab are evaluated from thermal data collected on the upper side of the specimen. First we restrict the problem to the upper component of the object. Then we investigate heat transfer through, the inaccessible interface by means of Thin Plate Approximation. Finally, a Fast Fourier Transform is used to filter data. In this way, we obtain a reliable reconstruction of simulated flaws in thermal contact conductance corresponding to appreciable defects of the interface.

Experimental investigation on steam/nitrogen condensation characteristics inside horizontal enhanced condensation channels

In order to investigate heat transfer characteristics of steam/nitrogen condensation inside horizontal enhanced condensation channels (HECCs), experiments have been performed, respectively, inside HECC and horizontal circular channel (HCC). HECC is formed by inserting different reinforcers into HCC including horizontal multi-start straight channels (HMSSCs) and horizontal spiral channels (HSCs). Effects of nitrogen mass fractions on average condensation heat transfer coefficients (CHTCs), average outlet condensate mass flowrates (CMFRs), and average steam-side pressure drops (SSPDs) are analyzed, respectively. The results indicate that HECC has better condensation performance than HCC under the same conditions, while average SSPDs of HECC will increase slightly. Then, HMSSC is compared against HCC, and enhancement factors of average CHTCs and average outlet CMFRs are about 1.45 and 1.12, respectively, while the enlargement factor of average SSPDs is about 1.16. Similarly, HSC is compared against HCC, and enhancement factors of average CHTCs and average outlet CMFRs are about 1.25 and 1.05, respectively, while the enlargement factor of average SSPDs is about 1.12.

Tunable analog thermal material

Naturally-occurring thermal materials usually possess specific thermal conductivity (κ), forming a digital set of κ values. Emerging thermal metamaterials have been deployed to realize effective thermal conductivities unattainable in natural materials. However, the effective thermal conductivities of such mixing-based thermal metamaterials are still in digital fashion, i.e., the effective conductivity remains discrete and static. Here, we report an analog thermal material whose effective conductivity can be in-situ tuned from near-zero to near-infinity κ. The proof-of-concept scheme consists of a spinning core made of uncured polydimethylsiloxane (PDMS) and fixed bilayer rings made of silicone grease and steel. Thanks to the spinning PDMS and its induced convective effects, we can mold the heat flow robustly with continuously changing and anisotropic κ. Our work enables a single functional thermal material to meet the challenging demands of flexible thermal manipulation. It also provides platforms to investigate heat transfer in systems with moving components.

Investigation of heat transfer in porous channels

Purpose This paper aims to investigate the heat transfer in porous channels. Design/methodology/approach Finite element method is used to simulate the heat transfer in porous channels. Findings The number and width of channels play a key role in determining the heat transfer of the porous channel. The heat transfer is higher around the channel legs. Smaller base height is better to get higher heat transfer capability. Originality/value This study represents the original work to investigate heat transfer in a porous domain having multiple channels.