Fluctuations In Temperature Field Research Articles

Laboratory-scale experiments relevant to coal spontaneous combustion: Temperature variations in loose rock heated by an internal source

To understand the distribution of temperature fields in loose rock heated by internal heat sources with constant power, two experiments under both no ventilation and negative pressure ventilation conditions were performed and the properties and geometry of the temperature fields analyzed. The results show that there is a core heating area during heating where the temperature gradient is uniform and the area encompassed by the core heating zone increases linearly as long as heat is supplied. During heating, the temperature gradient changes linearly over time. Temperature gradient under ventilation is lower than the temperature gradient under nonventilated conditions. The rock closer to the heat source has a shorter temperature response time and the greater the distance between the rock and the heat source, the greater the temperature field fluctuations. And the maximum temperature difference of 5 cm is nearly 200 °C.

Solidification dynamics under random external-temperature fluctuations

The nonlinear dynamic mechanisms of solid-phase formation with a phase transition region are studied under periodic and random fluctuations of the cooling-boundary temperature. It is theoretically shown that a mushy zone can form even at close liquid and cooling-boundary temperatures due to random temperature field fluctuations. The growth of a solid phase with the mushy zone is investigated as a function of the autocovariance characteristics of random noises.

Numerical study of the effect of turbulence on rate of reactions in the MILD combustion regime

In this paper, the importance of fluctuations in flow field parameters is studied under MILD combustion conditions. In this way, a turbulent non-premixed CH4+H2 jet flame issuing into a hot and deficient co-flow air is modeled using the RANS Axisymmetric equations. The modeling is carried out using the EDC model to describe the turbulence-chemistry interaction. The DRM-22 reduced mechanism and the GRI2.11 full mechanism are used to represent the chemical reactions of H2/methane jet flame. Results illustrate that although the fluctuations in temperature field are small and the reaction zone volume are large in the MILD regime, the fluctuations in temperature and species concentrations are still effective on the flow field. Also, inappropriate dealing with the turbulence effect on chemistry leads to errors in prediction of temperature up to 15% in the present flame. By decreasing of O2 concentration of hot co-flow air, the effect of fluctuations in flow field parameters on flame characteristics are still significant and its effect on species reaction rates does not decrease. On the other hand, although decreasing of jet inlet Reynolds number at constant inlet turbulence intensity addresses to smaller fluctuations in flow filed, it does not lead to lower the effect of turbulence on species distribution and temperature field under MILD combustion conditions.

Time-Resolved Heat Transfer Measurements on the Tip Wall of a Ribbed Channel Using a Novel Heat Flux Sensor—Part I: Sensor and Benchmarks

A novel heat flux sensor was tested that allows for time-resolved heat flux measurements in internal ribbed channels related to the study of passages in gas turbine blades. The working principle of the atomic layer thermopile (ALTP) sensor is based on a thermoelectric field created by a temperature gradient over an yttrium-barium-copper-oxide (YBCO) crystal (the transverse Seebeck effect). The sensors very fast frequency response allows for highly time-resolved heat flux measurements up to the 1MHz range. This paper explains the design and working principle of the sensor, as well as the benchmarking of the sensor for several flow conditions. For internal cooling passages, this novel sensor allows for highly accurate, time-resolved measurements of heat transfer coefficients, leading to a greater understanding of the influence of fluctuations in temperature fields.

Observations on fluctuations of sound transmission and temperature field from the ASIAEX 2001 South China Sea experiment and inversion of the characterizations of internal tides (waves)

Abstract Two conclusions are obtained by analyzing the fluctuation data of the temperature field and the sound transmission in the South China Sea from ASIAEX 2001 volume interaction experiment. First of all, the peak-to-peak value of the particle vertical mean displacement due to the internal waves exceeds 40m. Secondly, the peak-to-peak value of the sound transmission fluctuations represented by the pulse leading-edge fluctuations of the travel-time average exceeds 100 ms. Based on that, the major components of the internal waves are obtained by analyzing the spectrum of the temperature field fluctuations. The spectrum structures of the temperature field fluctuations in the across-shelf and the along-shore directions are compared respectively, and the spectrum structures of the sound transmission in such two different directions are also compared. The multi-path signals and the travel-time of the pulse are respectively used to capture the information of the sound transmission fluctuations, and their spe...

Temporal evolution of the temperature field in the beam interaction zone during laser material processing

This paper presents a numerical simulation of the temperature field resulting from the impingement of a laser beam on a metal surface. The calculations were based on a hydrodynamic physical model of laser-material interaction, which includes the effect of evaporation recoil pressure on melt flow and the related convective heat transfer. The computations follow an experimentally verified physical model of melt hydrodynamics and the model of laser-induced evaporation developed by Anisimov. The simulations indicate that convective heat transfer which is induced by recoil pressure is significant for absorbed laser intensities from 0.5 MW cm-2 to 10 MW cm-2. This range corresponds to laser welding, cutting and drilling due to melt ejection (hydrodynamic drilling). The simulations also show that the motion of the melt from the centre of the beam interaction zone towards the periphery results in a secondary maxima in the temperature distribution, which in turn can lead to instability of the melt flow and temperature field fluctuations. The model also predicts that the cooling rate in and around the fusion zone is strongly influenced by the recoil-pressure-induced melt flow. At the centre of the beam interaction zone, the cooling rate is much higher (~10 times), and at the periphery, much slower than predicted by a pure heat conduction model.