An introduction to heat transfer

Boundary-layer flow of a nanofluid past a stretching sheet

A universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion (macroscopic in both space and time), wave (macroscopic in space but microscopic in time), phonon-electron interactions (microscopic in both space and time), and pure phonon scattering The model is generalized from the dual-phase-lag concept accounting for the laging behavior in the high-rate response While the phase lag of the heat flux captures the small-scale response in time, the phase lag of the temperature gradient captures the small-scale response in space The universal form of the energy equation facilitates identifications of the physical parameters governing the transition from one mechanism (such as diffusion or wave) to another (the phonon-electron interaction)

A Unified Field Approach for Heat Conduction From Macro- to Micro-Scales

Bonding mechanism in cold gas spraying

Heterogeneous catalysis is of paramount importance in chemistry and energy applications. Catalysts that couple light energy into chemical reactions in a directed, orbital-specific manner would greatly reduce the energy input requirements of chemical transformations, revolutionizing catalysis-driven chemistry. Here we report the room temperature dissociation of H2 on gold nanoparticles using visible light. Surface plasmons excited in the Au nanoparticle decay into hot electrons with energies between the vacuum level and the work function of the metal. In this transient state, hot electrons can transfer into a Feshbach resonance of an H2 molecule adsorbed on the Au nanoparticle surface, triggering dissociation. We probe this process by detecting the formation of HD molecules from the dissociations of H2 and D2 and investigate the effect of Au nanoparticle size and wavelength of incident light on the rate of HD formation. This work opens a new pathway for controlling chemical reactions on metallic catalysts.

Hot Electrons Do the Impossible: Plasmon-Induced Dissociation of H2 on Au

This work introduces a new concept in heat transfer, developing a transient model describing the fast-transient process of heat transport in solids with micro-structures. In describing the microstructural interaction effect in the short-term response, it extends the "macroscopic" concept that practisings engineers are already familiar with. The dual-phase-leg model covers the existing macroscopic and microscopic models in the same framework, including the classical diffusion model employing the Fourier's law and the thermal wave model for dielectric films, insulators, and semi-conductors, and the photon-electron interaction model for metals (microscopic). Chapters cover the current status of microscale heat transfer, the lagging behaviour in the transient response, experimental evidence supporting the lagging behaviour in heat transport under various circumstances, the high-order effect of phase legs in the delayed response, and the possible effect of lagging responses in the related fields of elasticity and forced convention.

Macro- to Microscale Heat Transfer: The Lagging Behavior

This work contains three major components: a thorough review on the research emphasizing engineering applications of the thermal wave theory, special features in thermal wave propagation, and the thermal wave model in relation to the microscopic two-step model. For the sake of convenience, the research works are classified according to their individual emphases. Special features in thermal wave propagation include the sharp wavefront and rate effects, the thermal shock phenomenon, the thermal resonance phenomenon, and reflections and refractions of thermal waves across a material interface. By employing the dual-phase-lag concept, we show that the energy equation may be reduced to that governing the heat transport through the metal lattice in the microscopic two-step model

On the Wave Theory in Heat Conduction

The generalized lagging response in small-scale and high-rate heating

This work examines the lagging behavior for heat transport in small-scale and fast-transient processes. The experimental result by Qiu et al. for the femtosecond transient response in gold films and that by Bertman and Sandiford for the temperature pulse traveling through superfluid liquid helium are re-examined with emphasis on the lagging behavior. The model employing the phase-lag concept provides as competent or even better results when describing the special response observed in these experiments.

Da Yu Tzou

Papers

A Unified Field Approach for Heat Conduction From Macro- to Micro-Scales

Macro- to Microscale Heat Transfer: The Lagging Behavior

On the Wave Theory in Heat Conduction

The generalized lagging response in small-scale and high-rate heating

Experimental support for the lagging behavior in heat propagation