Heat Transfer Distance Research Articles

Non-diffusive thermal transport in GaAs at micron length scales

We use a transient thermal grating technique in reflection geometry to measure the effective thermal diffusivity in GaAs as a function of heat transfer distance at three temperatures. Utilizing heterodyne detection, we isolate the “amplitude” grating contribution of the transient grating signal, which encodes the thermal transport dynamics. As the thermal grating period decreases, and thus the heat-transfer distance, we observe a reduction in the effective thermal diffusivity, indicating a departure from diffusive behavior. Non-diffusive behavior is observed at room temperature, as well as low temperature (180 K) and high temperature (425 K). At the shortest thermal grating period measured corresponding to a heat transfer distance of approximately 1 μm, the effective diffusivity drops to a value roughly 50% of the bulk thermal diffusivity. These measurements show the utility of the reflection transient thermal grating technique to measure thermal transport properties of opaque materials.

Nanoscale heat transfer in direct nanopatterning into gold films by a nanosecond laser pulse

We investigate nanoscale heat transfer and heat-flux overlapping effects in nanopatterning through interactions between interferogram produced by 5-ns laser pulses at 355 nm and gold films. These mechanisms played different roles in direct writing of gold nanolines with different periods. Continuous gold nanolines were produced for large periods, where heat-flux overlapping is too small to effect the laser-metal interactions. Thus, the heat-transfer distance and direct laser-ablation determined the width of resultant gold nanolines. However, gold nanolines consisting of isolated gold nanoparticles were produced for small periods, where the overlapped heat-flux exceeds the threshold for removing or melting gold films.

Heat Transfer From Freely Suspended Bimaterial Microcantilevers

Bimaterial atomic force microscope cantilevers have been used extensively over the last 15 years as physical, chemical, and biological sensors. As a thermal sensor, the static deflection of bimaterial cantilevers, due to the mismatch of the coefficient of thermal expansion between the two materials, has been used to measure temperature changes as small as 10−6 K, heat transfer rate as small as 40 pW, and energy changes as small as 10 fJ. Bimaterial cantilevers have also been used to measure “heat transfer-distance” curves—a heat transfer analogy of the force-distance curves obtained using atomic force microscopes. In this work, we concentrate on the characterization of heat transfer from the microcantilever. The thermomechanical response of a bimaterial cantilever is used to determine the (1) thermal conductance of a bimaterial cantilever, and (2) overall thermal conductance from the cantilever to the ambient. The thermal conductance of a rectangular gold coated silicon nitride cantilever is Gc=4.09±0.04 μW K−1. The overall thermal conductance from the cantilever to the ambient (at atmospheric pressure) is Ga=55.05±0.69 μW K−1. The effective heat transfer coefficient from the cantilever to the ambient (at atmospheric pressure) is determined to be ≈3400 W m−2 K−1.

Miniature loop heat pipes for electronics cooling

The paper is devoted to the development of miniature loop heat pipes (mLHPs) with a nominal capacity of 25–30 W and a heat-transfer distance up to 250 mm intended for cooling electronics components and CPU of mobile PC. It gives the results of investigating several prototypes of mLHPs incorporated into remote heat exchanger (RHE) systems in different conditions. It has been established that in the nominal range of heat loads orientation does not practically affect the mLHPs operating characteristics. Under air cooling the total thermal resistance of such a system is 1.7–4.0 °C/W and depends strongly on the cooling conditions and the radiator efficiency. In this case the mLHP’s own thermal resistance is in the limits from 0.3 to 1.2 °C/W, and the maximum capacity reaches 80–120 B t. The obtained results make it possible to regard mLHPs as quite promising devices for RHE systems providing thermal regimes for electronics components and personal computers.