Comparative Analysis of Temperature Fields in Railway Solid and Ventilated Brake Discs

A new approach to numerical simulation using the finite element method (FEM) for the rotational motion of discs for railway vehicle disc brake systems was proposed. For this purpose, spatial models of transient heating due to the friction of such systems with solid and ventilated discs were developed. The performed calculations and the results obtained allowed justification of the possibility of simplifying the shape of the ventilated brake disc through elimination of ventilation channels. This contributes to a significant reduction in computational time, without compromising the accuracy of the results. The spatial and temporal temperature distributions in the ventilated and the solid disc of the same mass were analyzed. The share of energy dissipated due to convection and thermal radiation to the environment in relation to the total work done during a single braking was investigated. The maximum temperature values found as a result of computer simulations were consistent with the corresponding experimental results.

The Spatiotemporal Evolution of Temperature During Transient Heating of Nanoparticle Arrays

Nanoparticle (NP) are promising agents to absorb external energy excitation and generate heat. Cluster of NPs or NP array heating have found essential roles for biomedical applications, diagnostic techniques and chemical catalysis. Various studies have shed light on the heat transfer of nanostructures and greatly advanced our understanding of NP array heating. However, there is a lack of analytical tools and dimensionless parameters to describe the transient heating of NP arrays. Here we demonstrate a comprehensive analysis of the transient NP array heating. Firstly, we developed analytical solution for the NP array heating and provide a useful mathematical description of the spatial-temporal evolution of temperature for 2D, 3D and spherical NP array heating. Based on this, we proposed the idea of thermal resolution that quantifies the relationship between minimal heating time, NP array size, energy intensity and target temperature. Lastly, we define a dimensionless parameter that characterize the transition from confined heating to delocalized heating. This study advances the understanding of nanomaterials heating and provides guidance for rationally designing innovative approaches for NP array heating.

Efficient Thermal Energy Management of Hollow Pin Fin Heat Sinks with and without Phase Change Material

Electronic devices need to be cooled efficiently. Phase change material (PCM) could be incorporated into a conventional fin heat sink (FHS) for such a purpose. This paper reports experimental results obtained on the thermal performances of four FHSs fabricated with different arrays and numbers of hollow aluminium pin fins with various lengths and diameters. Tests were conducted with and without filling them with PCM. Heat input was kept on for 2 hours and varied from 1W, 5W and 10W. Transient heating surface temperatures were recorded on a data logger and plotted every 5 minutes. The results showed that the PCM-filled FHS resulted in faster cooling rates and lower heating surface temperatures. Long and large diameter pins performed better than small and short pins. Efficient fin heat sinks for electronic cooling are essential in view of the weight and size of the component. Hence the findings of this paper would be beneficial for electronic cooling and useful to the electronic industry for efficient thermal energy management.

A Revised Description of the Cosmic Ray Induced Desorption of Interstellar Ices

Nonthermal desorption of ices on interstellar grains is required to explain observations of molecules that are not synthesized efficiently in the gas phase in cold dense clouds. Perhaps the most important nonthermal desorption mechanism is one induced by cosmic rays (CRs), which, when passing through a grain, heat it transiently to a high temperature—the grain cools back to its original equilibrium temperature via the (partial) sublimation of the ice. Current cosmic ray induced desorption (CRD) models assume a fixed grain cooling time. In this work, we present a revised description of CRD in which the desorption efficiency depends dynamically on the ice content. We apply the revised desorption scheme to two-phase and three-phase chemical models in physical conditions corresponding to starless and prestellar cores, and to molecular cloud envelopes. We find that, inside starless and prestellar cores, introducing dynamic CRD can decrease gas-phase abundances by up to an order of magnitude in two-phase chemical models. In three-phase chemical models, our model produces results very similar to those of the static cooling scheme—when only one monolayer of ice is considered active. Ice abundances are generally insensitive to variations in the grain cooling time. Further improved CRD models need to take into account additional effects in the transient heating of the grains—introduced, for example, by the adoption of a spectrum of CR energies.

RECURSIVE FORMULAE FOR DROPLETS TRANSIENT HEATING AND EVAPORATION MODELS VIA A COMBINED METHOD OF INTEGRAL TRANSFORMS

The transient heating of a spherical droplet at rest in a hot gas environment, is analysed when the temperature distribution is initially assumed to be non uniform inside the droplet. A combined method of integral transforms, namely the classical Fourier cosine transform together with the unilateral Laplace transform, is used in solving the resulting initial-boundary value problem, stated in the dimensionless form. Explicit solutions of the problem are first obtained in the Laplace domain, and then analytical approximations in short time limits (timessteps) are derived for the droplet internal and surface temperature fields. The analytical approximation for the droplet internal temperature during the time step is proven to be highly accurate, while the innovative recursive formula obtained for the droplet surface temperature may lead to computationally efficient droplets and sprays vaporization models.