On the optimization of heat rectification in graded materials

Designing nonlinear thermal devices and metamaterials under the Fourier law: A route to nonlinear thermotics

“…Although the experimental samples in the works mentioned above are usually in millimeter size, the basic ideas to realize thermal rectification based on the different temperature trends of κ [99][100][101][102] and asymmetric/inhomogeneous geometry (mass-gradient, porous structure, etc.) [102][103][104][105][106][107][108][109][110][111] in the two segments can also work at the nanoscale (especially the one/two-dimensional materials like carbon nanomaterials [13][14][15]) as long as the heat flux is expressed by the temperature gradient and the (effective) thermal conductivity, in spite of their various phonon scattering mechanisms. In addition to the mismatch of phonon power spectra we have mentioned in the Introduction part, standing wave and local resonance effects of phonons [109,110]), and phonon localization from defect engineering [111]) are also important mechanisms that have been revealed.…”

Toward a solid-state thermal diode for room-temperature magnetocaloric energy conversion

“…The most common expression used to determine R when ̇f wd > ̇r ev is presented in Eq. (1) 38,39,[41][42][43]46,48,49 .…”

Non rectification of heat in graded Si-Ge alloys

“…The thermal phenomenon that allows the heat to be transferred in a suitable direction in a given material, while the flow is impeded in the opposite direction, is called thermal rectification [1,2]. This is the analogue of the current rectification of the electronic diodes and for this reason any device showing some thermal rectifying feature is called thermal diode.…”

“…In this work we present a detailed analysis of the possibility to get a thermal diode with graded Si-Ge alloys. The investigation is mainly based on the results given in [1], where a systematic approach has been introduced to find the optimal gradation of the species in order to maximize the efficiency of the fin. Our main assumptions are the following ones:…”

“…The paper is organized as follows: in Section 2 we introduce the main equations and the rectification coefficient R. Also, for the sake of clearness and completeness we briefly describe the approach given in [1] to maximize this coefficient. In Section 3 we apply the formulae to a Si-Ge graded wire with variable diameter.…”