Extent Of Heat Transfer Research Articles

A novel approach to correlate heat transfer and pressure fluctuation in gas–solid spouted bed

Statistical analysis of pressure fluctuations in spouted beds has been used as a well-established diagnostic tool to determine bed and flow characteristics because of its smooth operation. However, in many recent and conventional applications of spouted beds such as drying, coal gasification, catalytic conversion, biomass treatment, and chemical vapor deposition, direct estimation of the heat transfer rate from the solid bed to the gas or vice versa has proven to be difficult. A variance and spectral analysis of pressure fluctuation is extended here to characterize the heat transfer phenomena in a spouted bed. In the present study, zirconia and alumina were used as the bed materials, and argon and nitrogen were used as the spouting gases. Experiments were conducted at various heating rates for different superficial gas velocities for a range of temperatures up to 300°C. Significant changes in the gas density and viscosity with different extents of heat transfer were observed to affect the momentum diffusivity and gas–particle interaction, which in turn led to local pressure fluctuations, causing the bed to behave differently. In the present work, a novel approach is proposed to establish a link between local pressure fluctuation and the extent of heat transfer in the bed. This method shows potential for correlation of the statistics of pressure fluctuation with the thermal properties of individual solids and gases. Thus, the technique can be extended to many industrial applications for the indirect estimation of the extent of heat transfer and prediction of unknown thermal properties of products in solids or gases.

Characterization of the pierce two-node model under exercise load by parameter optimization toward construction of a modified thermal model for persons with spinal cord injury.

In this study, we attempted to develop a thermal model for estimating a body temperature in persons with spinal cord injury (SCI) during exercise. To clarify requisites for the SCI thermal model, we compared actual body temperature of SCI subjects with that calculated with a standard thermal model, that is, the Pierce two-node model. Model optimization by the parameter search method was able to fit the model-estimated skin and core temperature with those in able-bodied subjects during repeated exercise and rest. However, there remained a phase shift between actual and model-estimated core temperature trends in SCI subjects even after the optimization. The comparison of the optimized parameter combinations revealed that the Pierce two-node model was able to express loss of sweating in the SCI subjects, but unable to express delay in heat accumulation and dissipation. These results suggest that SCI thermal model requires additional nodes that express the speed and extent of heat transfer in the body of SCI persons.

Silver-gold alloy nanoparticles as tunable substrates for systematic control of ion-desorption efficiency and heat transfer in surface-assisted laser desorption/ionization.

Systematically controlling heat transfer in the surface-assisted laser desorption/ionization (SALDI) process and thus enhancing the analytical performance of SALDI-MS remains a challenging task. In the current study, by tuning the metal contents of Ag-Au alloy nanoparticle substrates (AgNPs, Ag55Au45NPs, Ag15Au85NPs and AuNPs, ∅: ∼2.0 nm), it was found that both SALDI ion-desorption efficiency and heat transfer can be controlled in a wide range of laser fluence (21.3 mJ cm-2 to 125.9 mJ cm-2). It was discovered that ion detection sensitivity can be enhanced at any laser fluence by tuning up the Ag content of the alloy nanoparticle, whereas the extent of ion fragmentation can be reduced by tuning up the Au content. The enhancement effect of Ag content on ion desorption was found to be attributable to the increase in laser absorption efficiency (at 355 nm) with Ag content. Tuning the laser absorption efficiency by changing the metal composition was also effective in controlling the heat transfer from the NPs to the analytes. The laser-induced heating of Ag-rich alloy NPs could be balanced or even overridden by increasing the Au content of NPs, resulting in the reduction of the fragmentation of analytes. In the correlation of experimental measurement with molecular dynamics simulation, the effect of metal composition on the dynamics of the ion desorption process was also elucidated. Upon increasing the Ag content, it was also found that phase transition temperatures, such as melting, vaporization and phase explosion temperature, of NPs could be reduced. This further enhanced the desorption of analyte ions via phase-transition-driven desorption processes. The significant cooling effect on the analyte ions observed at high laser fluence was also determined to be originated from the phase explosion of the NPs. This study revealed that the development of alloy nanoparticles as SALDI substrates can constitute an effective means for the systematic control of ion-desorption efficiency and the extent of heat transfer, which could potentially enhance the analytical performance of SALDI-MS.

Nanosecond UV Laser Ablation of Gold Nanoparticles: Enhancement of Ion Desorption by Thermal-Driven Desorption, Vaporization, or Phase Explosion

The phase transition of surface-assisted laser desorption/ionization (SALDI) substrates has been identified as a driving process for ion desorption in many previous SALDI fundamental studies. Here, the effects of various phase transition stages, including substrate melting, vaporization, and phase explosion, on SALDI ion desorption efficiency and extent of heat transfer were investigated. We employed molecular dynamics to simulate the phase transition (from melting, vaporization, to phase explosion) of gold nanoparticles (AuNPs, ⌀: 2.5 nm) upon laser-induced heating and experimentally probed the corresponding SALDI ion desorption efficiency and extent of heat transfer to a chemical thermometer, benzylpyridinium (BP) salt (using 355 nm solid-state laser, pulse width: 6 ns, laser fluence range: 21.3 to 125.9 mJ/cm2). The results showed that substrate phase explosion has the most significant effect on enhancing the ion desorption efficiency and lowering the extent of heat transfer, which were reflected by an...

水中溶接における冷却過程の解析

Underwater welding techniques have been of growing importance as a number of new projects for offshore structures are underconsideration and some of them are being put into practice. Underwater“wet type”welding is especially useful for the repair and maintenance of those structures. In the previous paper, fundamental characteristics of wet welding such as heat transfer from plate to surrounding water have been evaluated using mixed gas shield welding, and the extent of heat transfer was quantitatively estimated in terms of coefficients of heat transfer. In addition, three dimensional Finite Difference Analysis was attempted to obtain temperature distributions within the plate. In this paper, cooling process for underwater welding is compared with that for welding in air, where the effects of welding conditions such as welding speed and plate thickness are discussed. It is also shown that the cooling rates for underwater welding could be analyzed within acceptable engineering accuracy using three dimensional FDM.

Criteria for recirculation in confined jet flames

Recirculation is an important phenomenon in furneces. This paper discusses two methods of predicting when recirculation will occur in a cylindrical confined-jet combustion chamber. One of these methods is based on the Thring-Newby number [1], and the other is based on an extension of the theory developed by Curtet [2] for confined jets without combustion. In each case, use of the criterion developed requires knowledge of the value of a parameter which is an empirical measure of the extent of heat transfer from the furnace. Experiments were carried out to test these criteria and determine the values of the empirical “furnace design factors” for the combustion chamber used in the tests. Temperatures were measured, and recirculation was detected by means of a flow visualization technique in which boron trifluoride was used to produce smoke. Both criteria were found to be valid, although the one based on the work of Curtet is expected to be applicable to a wider variety of flow conditions than that based on the Thring-Newby number.