Three-dimensional Temperature Measurements in Turbulent Reacting Flows

Field temperature measurement technique using the flow visualization with the liquid crystal has been investigated and is applied to the three-dimensional temperature measurement by scanning the thermometry. The color to temperature calibration of the liquid crystal is carried out using the neural networks, where the effect of view angle relative to the light sheet is considered by distributing the networks over the image plane and with an optimum smoothing technique. The calibration error of temperature due to the view angle is much reduced by the present technique and is proved to be useful by application to the temperature measurement of the thermal convection over a heated surface. The three-dimensional temperature distributions of the thermal convection is reconstructed from the measured temperature field and the structure of thermal plumes is examined.

In this study, we propose a three-dimensional (3D) surface temperature measurement method based on the principle of stereoscopic 3D reconstruction and the dependence of phosphorescence lifetime on temperature. A 385-nm UV(Ultraviolet) light was used as the excitation light, and two high-speed cameras were used as the detectors. The phosphor MFG (Mg4FGeO6: Mn4+) was mixed with the binder HPC and sprayed onto the tested 3D surface. The natural texture generated by the surface roughness of the phosphor coating was used as a feature for cross-correlation calculations. The digital image correlation (DIC) algorithm was used to match these feature positions in the phosphorescent images from the two cameras. The effects of the excitation angle and detecting angle were analyzed. The results indicate that the temperature measurement based on phosphorescent lifetime was not affected by the excitation and detecting angle. The method was validated on a turbine blade as an example of a 3D surface to demonstrate the capability. A comparison of the measurement results with the thermocouples proves that the current method can successfully measure the temperature on 3D surfaces with a maximum difference of 1.63°C. The spatial accuracy of the method was obtained by comparing with the measurement results of a 3D scanner, which shows that the maximum absolute error of the 3D reconstruction was 0.350 mm. The current study proposes a promising 3D surface temperature measurement method, which is expected to be widely used in gas turbine blades, Internal Combustion (IC) engine cylinders, complex curved heat exchangers, and other fields due to its non-contact measurement, low susceptibility to infrared radiation interference, high measurement accuracy, and ability to withstand harsh environments.

Compared with conventional camera, the light field camera takes the advantage of being capable of recording the direction and intensity information of each ray projected onto the CCD (charge couple device) sensor simultaneously. In this paper, a novel method is proposed for reconstructing three-dimensional (3-D) temperature field of a flame based on a single light field camera. A radiative imaging of a single light field camera is also modeled for the flame. In this model, the principal ray represents the beam projected onto the pixel of the CCD sensor. The radiation direction of the ray from the flame outside the camera is obtained according to thin lens equation based on geometrical optics. The intensities of the principal rays recorded by the pixels on the CCD sensor are mathematically modeled based on radiative transfer equation. The temperature distribution of the flame is then reconstructed by solving the mathematical model through the use of least square QR-factorization algorithm (LSQR). The numerical simulations and experiments are carried out to investigate the validity of the proposed method. The results presented in this study show that the proposed method is capable of reconstructing the 3-D temperature field of a flame.

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Analytical solution of three-dimensional temperature field for skin tissue considering blood perfusion rates under laser irradiation and thermal damage analysis

Temporal prediction of three-dimensional spatial fields of ocean temperature, salinity and flow is important for a number of civilian and military applications. For accurate prediction of regional ocean environments, combing an accurate dynamic ocean model with optimized in-situ observations of ocean states provided by a network of marine vehicles (such as unmanned surface vehicles, autonomous underwater vehicles, and underwater gliders) is an important approach. To realize fast and accurate three-dimensional spatial prediction of regional ocean environments via ocean models and fast optimization of ocean observation strategies of marine vehicles guided by ocean models, this paper proposes a data driven dynamic model for temporal prediction of three-dimensional regional ocean environments. The proposed model is based on the deep learning method, and is developed based on the Convolutional-LSTM (long short-term memory) network. The feature of the proposed model is that the correlation of temperature, salinity and flow is considered and implemented in the neural network, with which the joint prediction of three-dimensional ocean temperature, salinity and flow fields is achieved. Data set form a numerical ocean model is used to conduct the training of the model and the results demonstrate that the proposed model could provide more accurate prediction than implementing prediction of single ocean temperature, salinity or flow field. The proposed model could be integrated with marine vehicles to form an accurate, high-resolution three-dimensional regional ocean prediction and fast-response adaptive sensing system.

Combustion flame detection based on digital image processing is the popular trend of flame detection technology. In this paper, we propose a modeling method for the distribution of three-dimensional temperature field of combustion flame image based on modified simultaneous algebraic reconstruction technique. The flame image captured by CCD is projected onto the target sheet in three-dimensional space. We investigate the relationship between each pixels of flame image and spatial flame radiation intensity according to the spatial flame radiation of three-dimension. Using the method of reconstruction image based on projection, the simultaneous algebraic reconstruction technique (SART) and the least squared estimation (LSE) algorithm are used to calculate the three-dimensional (3D) temperature field distribution. Numerical calculation and simulation experiments have been done in order to verify the algorithm. The experimental results demonstrated that the algorithm is feasible and effective.

The unique structural design of an arch ring featuring varying inclination angles for individual segments causes variations in the longitudinal distribution of the temperature field d along the arch axis. This study aims to enhance the understanding of temperature fields in reinforced concrete (RC) arch bridges with diverse arch ring structural configurations during their construction phases. A comprehensive investigation into the three-dimensional distribution pattern of solar-induced temperature fields within arch ribs during the construction of RC ribbed arch bridges was conducted. A field test specifically measuring the temperature distribution across arch rib cross-sections was conducted on-site, involving an RC arch bridge constructed using the cable-stayed cantilever cast in situ method. Analyzing the monitored on-site temperature data revealed the distribution characteristics of temperature fields at the arch foot cross-section under solar radiation. By comparing these findings with international standards, a vertical temperature gradient fitting model for arch rib cross-sections under solar radiation was formulated. Drawing upon meteorological records and solar radiation principles, an adaptive numerical simulation finite element model was developed to depict the temperature field within an arch rib section. This model was rigorously verified. Subsequently, a comprehensive analysis of the three-dimensional temperature field of the arch rib under solar radiation was performed. Additionally, a three-dimensional temperature gradient fitting model was proposed, accounting for the longitudinal inclination of the bridge.

A concept for joined three-dimensional temperature and velocity measurements in turbulent gas flows using sub-micron sized thermographic phosphor tracer particles is presented. Such measurements are needed to resolve flow structures commonly encountered in turbulent flows of scientific and industrial interest. While available techniques for simultaneous 3D thermometry and velocimetry are suitable for microfluidic applications or slow liquid flows, the present concept is applicable to macroscopic turbulent gas flows. The feasibility of these measurements is demonstrated using two turbulent heated gas jets. The concept utilizes two sub-systems: a four-view 3D particle tracking velocimetry system combined with a two-view ratiometric phosphor thermometry system. A double-pulse green laser and a single-pulse UV laser are used for illumination and excitation of phosphor luminescence, respectively. Upon imaging the particle-laden flow using the joined camera system, 3D particle positions and velocities are computed from four double-frame Mie-scattering recordings, while the temperature is inferred from two single-frame luminescence-emission recordings. Measurement results using low particle seeding densities successfully retrieve the expected temperature and velocity distributions. This proof-of-concept is a first step towards the ability of resolving 3D turbulent flow structures from individual single-shot recordings using higher particle seeding densities.

The increased severity of the thermal environment of high pressure turbine blades and vanes requires accurate calculations for the successful design of these parts. In this paper, the prediction of the temperature field in the near-cooling-hole region on a film cooled turbine vane is presented. The surface distribution of the heat transfer coefficient and the film cooling effectiveness on the vane in presence of one or several film cooling injections is obtained from boundary layer calculations and via experimental correlations. Cooling jet coalescence is taken into account as well as the main parameters governing this physical phenomenon. The internal boundary conditions result from available correlations. The study was conducted on two different configurations : a flat plate including an injection through two rows of holes and a turbine vane including three injections through two rows of holes on the suction side. Thermal computations using a three-dimensional finite element code yield strong temperature distortions and high temperature gradients around the injection zones. The study also indicates that the three-dimensional temperature field just downstream of the injections becomes two-dimensional when jet coalescence takes place. The influence of one or several obstructed injection holes on the temperature field is studied; important effects are observed when the main flow temperature is high.

Spatially resolved thermometry during laser ablation in tissues: Distributed and quasi-distributed fiber optic-based sensing

When determining the location and intensity of coal spontaneous combustion using the inversion method, the internal temperature field and surface temperature variation of coal under different heat source temperatures must be analyzed. Different coal particle sizes and thermal conductivities affect the temperature transfer of coal. To study the influence of different thermal conductivities on the internal temperature field of a coal body, a three-dimensional active temperature field model of a coal body was established, and the temperature distribution of the internal temperature field and natural convection surface of the coal body was analyzed through numerical simulations. The results showed that the high-temperature area inside the coal body was initially a sphere centered on the heat source. With the extension of the calculation time, when the temperature field inside the coal body reached stability, the high-temperature area in the upper part of the coal body was larger than that in the lower part. The temperature of the upper part of the heat source was higher than that of the lower part. The temperature of the center of the natural convection surface was the highest, whereas the temperatures of the left and right sides were basically symmetrical, which gradually increased from bottom to top to reach the maximum value at X = 0 and then gradually decreased. The influence of different thermal conductivities on the temperature field inside the coal body was mainly reflected in the following: when the thermal conductivity was small, the heating rate of the internal temperature of the coal body was faster, and the heat could not be transferred to the natural convection surface but accumulated in the coal body, forming a high-temperature area quickly. When the thermal conductivity increased, the temperature rise of the coal surface increased, and the temperature rise could be more obviously observed. The research results can provide a reference for determining the location and intensity of underground fires in coal mines using the inversion method.

The vertical turbulent transfer of heat and momentum in the lower atmospheric boundary layer is accomplished through intermittent sweep, ejection, outward interaction, and inward interaction events associated with turbulent updrafts and downdrafts. These events, collectively referred to as sweep–ejection dynamics, have been studied extensively in forested and nonforested environments and reported in the literature. However, little is known about the sweep–ejection dynamics that occur in response to turbulence regimes induced by wildland fires in forested and nonforested environments. This study attempts to fill some of that knowledge gap through analyses of turbulence data previously collected during three wildland (prescribed) fires that occurred in grassland and forested environments in Texas and New Jersey. Tower-based high-frequency (10 or 20 Hz) three-dimensional wind-velocity and temperature measurements are used to examine frequencies of occurrence of sweep, ejection, outward interaction, and inward interaction events and their actual contributions to the mean vertical turbulent fluxes of heat and momentum before, during, and after the passage of fire fronts. The observational results suggest that wildland fires in these environments can substantially change the sweep–ejection dynamics for turbulent heat and momentum fluxes that typically occur when no fires are present, especially the relative contributions of sweeps versus ejections in determining overall heat and momentum fluxes.

An experimental study of the interaction between a shock wave and a boundary layer over a flat plate with a sharp leading edge in hypersonic rarefied gas flow is presented. Experiments in a low-density wind tunnel using an electron beam probe were conducted at the Shock Wave Laboratory, RWTH Aachen, Germany. Rotational temperatures for stagnation temperatures of T0=670∼1000 K and Kn=0.024∼0.028 based on a reference length of 0.05m were calculated using Muntz’s method and Robben and Talbot’s method. The domain of quasi two-dimensional flow over the plate was determined from three-dimensional rotational temperature measurements. Nonequilibrium between translational and rotational temperatures was observed near the leading edge, and the experimental rotational relaxation length explains the rotational collision number of 2∼4.

Proton resonance frequency thermometry is well established for monitoring small temperature changes in tissue. Application of the technique to the measurement of complex temperature distributions within fluid flow is of great interest to the engineering community and could also have medical applications. This work presents an experimental approach to reliably measure three-dimensional (3D) temperature fields in fluid flow using proton resonance frequency thermometry. A velocity-compensated three-dimensional gradient echo sequence was used. A flexible pumping system was attached to an MR compatible double pipe heat exchanger. The temperature of two separate flow circuits could be adjusted to produce various three-dimensional spatial temperature distributions within the fluid flow. Validation was performed using MR compatible temperature probes in a uniformly heated flow. A comparative study was conducted with thermocouples in the presence of a spatially varying temperature distribution. In uniformly heated flow, temperature changes were accurately measured to within 0.5 K using proton resonance frequency thermometry, while spatially varying temperature changes measured with MR showed good qualitative agreement with pointwise measurements using thermocouples. Proton resonance frequency thermometry can be used in a variety of complex flow situations to address medical as well as engineering questions. This work makes it possible to gain new insights into fundamental heat transfer phenomena. Magn Reson Med 76:145-155, 2016. © 2015 Wiley Periodicals, Inc.