Non-uniform Temperature Field Research Articles

Detailed Analysis of the Effects of Viscosity Measurement Errors Caused by Heat Transfer during Continuous Viscosity Measurements under Various Temperature Changes and the Proposed Solution of a Non-Dimensional Parameter Called the Akpek Number

It is extremely important to gather the viscosity behavior of fluids accurately for industries and academia. There is no better method than viscosity measurement to detect changes in the specific characteristics of the materials. However, viscosity measurement is indeed a very sensitive process. In nature, fluids are involved in widely various containers, and they are affected by serious temperature deviations. It is a necessity for viscometers to have the capability to obtain accurate data from all types of containers of fluids even in serious temperature variations in order to understand the natural phenomena inside the fluids. Conventional viscometers mainly neglect the effect of sudden temperature deviations inside the fluids, or they need to use very expensive water bath systems that stabilize the temperature around the test fluids, which is not feasible at all. In this research, the effects of non-uniform temperature fields are analysed detailly to confirm that even in extremely limited amounts, serious viscosity and temperature deviations may occur. Experiments were performed in two parts. The first part was conducted using several thermocouples with different test fluids to find out the effects of thermal conduction and convection. For the second part, particle image velocimetry (PIV) was utilized to comprehend the flow movement within the test fluids. It was shown that even for small volumes and even in very controlled environments, an almost 35% viscosity measurement error (VME) occurs. Finally, as a solution to this problem, a new non-dimensional parameter called the Akpek number was proposed. The Akpek number enables the estimation of VMEs in any possible case. VME is a very crucial obstacle that has urgency to be illuminated by researchers and scientists to improve fluid characteristics. The main goal of this research is to illuminate the importance of this problem and offer a potential solution. The final results are supported by experimental data and numerical simulations using OpenFOAM.

The diffusion characteristics of POSS under electric field and non-uniform temperature field in natural ester insulating oil

The natural ester insulating oil is a green and environmentally friendly liquid dielectric, and nano additives can effectively improve its dielectric and heat transfer performance. However, nano additives are prone to agglomeration, especially under the influence of electric and temperature fields, which can impact the prolonged stable operation of power transformers. In this paper, the diffusion properties of caged Polysilsesquioxane (POSS) molecules in natural ester insulating oil under external electric field and non-uniform temperature field were investigated via simulation, and the effects of temperature and electric field on POSS molecules were expounded from the perspective of interaction. The results show that the high temperature difference and strong electric field can effectively improve the mobility of POSS molecules, and the temperature difference has a greater impact on the diffusion. The decrease of interaction energy is mainly due to the negative positive interaction between Si-O molecules in POSS molecules and insulating oil at high temperature, which counteracts the attraction of branch chains. At the same time, POSS molecules in the electric field will also show obvious polarization due to temperature changes, which further reduces the interaction between POSS molecules and insulating oil molecules. In addition, the electrostatic interaction energy decreases most obviously, which is the main reason that affects the migration characteristics of POSS molecules in natural ester insulating oil. This study provides a theoretical explanation for the migration mechanism of insulating oil in the microenvironment.

Carbon Dioxide Concentration Estimation in Nonuniform Temperature Fields Based on Single-Pass Tunable Diode Laser Absorption Spectroscopy.

We propose a novel technique to accurately predict carbon dioxide (CO2) concentrations even in flow fields with temperature gradients based on a single laser path absorption spectrum measurement and machine learning. Concentration measurements in typical tunable diode laser absorption spectroscopy are based on a ratio of two integrated absorbances, each from a spectral line with different temperature dependence. However, the inferred concentrations can deviate significantly from the actual concentrations in the presence of temperature gradients. Furthermore, it is also difficult to find an analytical expression to compensate for the effect of nonuniform temperature profiles on concentration measurements. In this study, the entire absorption feature was considered since its shape and peak intensities vary with temperature and concentration. Specifically, a predictive model is obtained in a data-driven manner that can identify and compensate for the effect of a nonuniform temperature field on the spectrum. Despite a very detailed understanding of the CO2 absorption spectrum, it is nearly impossible to collect sufficient spectra for model acquisition by varying all temperature gradient conditions. Therefore, the model was obtained using only simulated data, much like the concept of a "digital twin". Finally, the predictive performance of the acquired model was verified using experimental data. In all test cases, the predictive performance of the model was superior to that of the two-line method. Additionally, a gradient-weighted regression activation mapping analysis confirmed that the model utilizes both the peak intensities as well as the change in the shape of absorption lines for prediction.

Freeze‒thaw damage model for concrete considering a nonuniform temperature field

Freeze‒thaw damage model for concrete considering a nonuniform temperature field

SIMULATION OF FLOW AND HEAT EXCHANGE IN A HEAT ACCUMULATOR TANK

The article deals with the research of thermal energy storage tanks. It is proposed to use a «thermal core» to minimize the effects of thermal stratification and high thermal inertia. The thermal core consists of a binary tube placed along the central axis of the tank, filled with a paraffin mixture with a melting point of 45 to 65oC and a density of 0,880 to 0,915g/cm3 at 15oC. In the study the Fluent software package was used to model the temperature distribution in the tank under free convection conditions, the data was then converted to the Transient Thermal module of the ANSYS software package for further calculations of the unsteady temperature distribution in the thermal core. The study showed that a 1400-liter thermal energy storage device, heated for 1 hour by a heat-transfer fluid at 115oC, cools down to 50oC in 4 hours. The research also revealed the need to improve the tank design based on the analysis of the hydrodynamic structure of the flow in the tank, as evidenced by the trajectory distribution of free convective flows. The authors concluded that the use of a heat core, regardless of the type of paraffin used to form it, helps to reduce temperature stratification by height in the tank and that the type of paraffin used has no significant effect on the overall cooling of the tank. However, using ceresin as a core filler results in a slightly higher average tank temperature. Based on the results of the study, the time of complete cooling of the tank was determined by the non-uniform temperature field of all elements of the tank.

A reduced order model for fission gas diffusion in columnar grains

In fast reactors, restructuring of the fuel micro-structure driven by high temperature and high temperature gradient can cause the formation of columnar grains. The non-spheroidal shape and the non-uniform temperature field in such columnar grains implies that standard models for fission gas diffusion can not be applied. To tackle this issue, we present a reduced order model for the fission gas diffusion process which is applicable in different geometries and with non-uniform temperature fields, maintaining a computational requirement in line with its application in fuel performance codes. This innovative application of reduced order models as meso-scale tools within fuel performance codes represents a first-of-a-kind achievement that can be extended beyond fission gas behaviour.

Study on the morphology of liquid–gas interface inside inertial confinement fusion target under the condition of temperature gradient based on Young–Laplace equation

This study investigates the morphology of the liquid–gas interface inside inertial confinement fusion targets with temperature gradients from the perspective of force balance. The effects of contact angle, liquid volume, temperature gradient, and target size on the interface morphology are discussed. The filling of the fuel and the preparation of the ice layer inside the target are carried out near the deuterium–deuterium triple point at 18.71 K, accompanied by temperature gradient distributions of different magnitudes. The morphology of the liquid–gas interface has a significant impact on the subsequent laser experiments. The differential equation for calculating the morphology of the liquid–gas interface under non-uniform temperature field is derived based on the Young–Laplace equation. In order to verify the accuracy and applicability of the model as well as to provide guidance for practical applications such as process optimization, experimental data within a temperature gradient range of 0.69–1.38 K/cm during the fuel filling process were selected. Image processing techniques, including denoising and edge detection, were applied to the experimental images. The obtained structured data were compared with the numerical solutions of the equation for the liquid–gas interface morphology. The accuracy of the equation was verified by the results. Based on this, the morphology of the liquid–gas interface of deuterium–deuterium inside targets under different experimental conditions was calculated. It was found that a smaller target radius, higher filling temperature, smaller contact angle, and larger temperature gradient are more conducive to subsequent experiments.

Optimization of Supply Air Parameters Control Based on Gappy POD Method for Creating Non-Uniform Temperature Fields

This paper explores the implementation and application of non-uniform ambient fields from two perspectives: constant heat source and abrupt heat source variation. On the one hand, the proper orthogonal decomposition (POD) method is used to find the optimum air supply parameters for different target temperatures at multiple demand points. The one-parameter, two-parameter and three-parameter cases were considered, respectively, and the parameters obtained from the search for optimisation were verified, yielding mean deviations of 0.405 K, 0.368 K and 0.380 K and mean errors of 1.48%, 1.61% and 1.68%, respectively. The accuracy of the reconstructed results of the POD method and the reliability of the POD method for finding the best results are verified step by step with the help of the experimental platform. The validation results show that the average error between the reconstructed data and the experimental data for the POD method does not exceed 5%; the average errors between the measured and set demand temperatures at the target point are 1.2% and 0.8%. On the other hand, the gappy POD method is used to accurately fill in the elements of the system with arbitrary missing data and to reconstruct the flow field in the presence of missing (gappy) data with a limited number of sensors combined with POD. The errors of the gappy POD method reconstruction are 0.54% and 1.75%. POD and gappy POD methods can better create non-uniform temperature fields in practical scenarios according to actual needs. The results of the study can provide a methodological reference for real-time reconstruction and real-time control of the indoor flow field environment. It also serves as a help and suggestion for the actual project in terms of end-regulation system and reverse design method.

High-Fidelity Conjugate Heat Transfer Simulation of Micro-Channel Heat Exchanger

In this study, high-fidelity conjugate heat transfer simulations are used to model a micro-channel heat exchanger (MCHE) in a crossflow to study its thermal-hydraulic performance. Three different microchannel geometries, namely circular, triangular, and square with louver-shaped fins, are considered. The local flow field showed a strong coupling between the microchannel flow, solid domain, and crossflow. The flow separation and wake regions formed near MCHE resulted in a large variation in the velocity field and temperature in the crossflow. The interaction of the wake region with the fins introduces significant spanwise variations, leading to variations in the thermal boundary layer. The heat conduction in the solid structure provided a non-uniform temperature field with a higher temperature near the microchannel and a slightly lower temperature near the surface exposed to the crossflow. The microchannel flow analysis showed that the internal geometry affects the pressure drop, which is highest for the triangular MCHE and lowest for the circular MCHE. Based on the effectiveness and performance index calculations, the circular MCHE exhibited the best performance, while the rectangular MCHE showed higher heat transfer effectiveness.

Modeling and calibration of micro/nano FBG temperature probe for scanning probe microscopy.

To accurately measure the local temperatures of the micro-nano area, we propose an optical method using a tapered fiber Bragg grating (FBG) probe with a nano tip for scanning probe microscopy (SPM). When the tapered FBG probe senses local temperature through near-field heat transfer, the intensity of the reflected spectrum decreases, along with a broadening bandwidth and a shift in the central peak position. Modeling the heat transfer between the probe and the sample shows that the tapered FBG probe is in a non-uniform temperature field when approaching the sample surface. Simulation of the probe's reflection spectrum reveals that the central peak position shifts nonlinearly with increasing local temperature. In addition, the near-field temperature calibration experiments show that the temperature sensitivity of the FBG probe increases nonlinearly from 6.2 pm/°C to 9.4 pm/°C as the sample surface temperature increases from 25.3°C to 160.4°C. The agreement of the experimental results with the theory and the reproducibility demonstrate that this method offers a promising approach for exploring micro-nano temperature.

Conformational approach to the crystallization mechanisms of organosilicon liquids of PMS brand in a non-uniform temperature field

The possibility of using the conformational approach to describe the crystallization kinetics during melt-crystal phase transitions in an inhomogeneous temperature field and to determine the molar mass range corresponding to a change in the crystallization mechanism is shown using the example of PMS brand organosilicon liquids. It is established that the curve of dependence of the mean square of the dipole moment of a macromolecule on the average molar mass of an organosilicon polymer contains three sections, each of which has its own crystallization mechanism.

Research on ERS point registration of large-size measurement field based on neural network non-uniform temperature field

PurposeLarge size of aircraft assembly tooling structure and complex measurement environment exist. The laid enhanced reference points (ERS) are subject to a combination of nonuniform temperature fields and measurement errors, resulting in increased measurement registration errors. In view of the nonuniform temperature field and measurement errors affecting the ERS point registration problem, the purpose of this paper is to propose a neural network-based ERS point registration compensation method for large-size measurement fields under a nonuniform temperature field.Design/methodology/approachThe approach is to collect ERS point information and temperature data, normalize the collected data to complete the data structure design and complete the construction of the neural network prediction model by data training. The data learning is performed to complete the prediction model construction, and the prediction model is used to complete the compensation analysis of ERS points. Finally, the algorithm is verified through experiments and engineering practice.FindingsExperimental results show that the proposed neural network-based ERS point prediction and compensation method for nonuniform temperature fields effectively predicts ERS point deformation under nonuniform temperature fields compared with the conventional method. After the compensation analysis, the registration error is effectively reduced to improve registration accuracy. Reducing the combined effect of environmental nonuniform temperature field and measurement error has apparent advantages.Originality/valueThe method reduces the registration error caused by combining a nonuniform temperature field and measurement error. It can be used for aircraft assembly site prediction and registration error compensation analysis, which is essential to improve measurement accuracy further.

Thermo-mechanical coupled behavior of laminated beams with temperature-dependent viscoelastic interlayers

The present research proposes analytical solutions of simply-supported laminated beams bonded by viscoelastic interlayers under both non-uniform temperature field and mechanical loads, in order to study its time-varying thermo-mechanical coupled behavior. The temperature has two effect mechanisms to the laminated beams, including the thermal expansion difference and the temperature-dependent property of viscoelastic interlayer. In the analytical model, the non-uniform temperature field is solved first by the transfer matrix method, based on the heat transport theory. The standard linear solid model is utilized to simulate the time-varying characteristic of the interlayer, which renders the mechanical property of the laminated beam changes over time. Then, the temperature effects on the interlayer modulus degradation are determined according to the Time-Temperature-Superposition-Principle (TTSP). By virtue of the state space method and Fourier series expansion, the general solutions of stress and displacement components are solved with undetermined coefficients. The analytical solutions are solved by means of Laplace transform and Cramer rule. The analysis results indicate that the present solutions are in accordance with the finite element solution and have superior computational efficiency. The influences of temperature, geometric and material parameters on the long-term thermo-mechanical coupled behavior of the laminated beam are studied in detail.

Effect of the reflector system thermal behavior on the pointing accuracy of large radio telescopes

The thermal behavior of the reflector system under solar radiation has great effects on the pointing accuracy of large radio telescopes. To estimate the dynamic pointing error of large radio telescopes caused by the thermal behavior of the reflector system under solar radiation, the nonuniform temperature field and the thermal deformation of the Wuqing 70 m radio telescope (WRT70) on three specific sunny days are first simulated by finite-element (FE) software. Then the pose variations of the reflector system are calculated equivalently based on the FE thermal-structural coupling analysis of the reflector system. Finally, the dynamic pointing errors of the WRT70 on three specific sunny days, caused by the thermal behavior of the reflector system, are estimated according to the beam deviation factor. The research results show that the rotations of the main reflector and the offsets of the subreflector on sunny days have great influences on the pointing error of large radio telescopes. In addition, the pointing error caused by the rotations of the main reflector and the pointing error caused by the offsets of the subreflector cancel each other out, but the pointing error caused by the rotations of the main reflector plays a dominant role. Furthermore, the effect of the thermal behavior of the reflector system on the pointing accuracy of large radio telescopes is less than the influence of the thermal behavior of the alidade. These findings could provide valuable references for the compensation of dynamic pointing errors of large radio telescopes.

Investigation into the heat transfer models for the hot crude oil transportation in a long‐buried pipeline

AbstractBased on reasonable simplifications of a two‐dimensional (2D) energy equation, a basic heat transfer equation in 1D form is obtained for the hot crude oil transportation in a long‐buried pipeline. To enclose the heat transfer equation, the overall heat transfer coefficient and the numerical simulation of temperature fields of pipe wall and soil are introduced, and they together with the basic heat transfer equation constitute 1D and cross‐dimensional heat transfer models of crude oil transportation, respectively. Some numerical procedures, including grid generation, partial differential equation discretization, and algebraic equation solution, are combined to solve the two heat transfer models. Based on the designed cases with different pipeline parameters, the relative deviation between the numerical results from the two heat transfer models does not exceed 1%, and the two heat transfer models agree well. Furthermore, the nonuniform natural soil temperature field is designed, and its influence on the oil temperature and the deviation of the 1D heat transfer model is investigated. Under the condition of the nonuniform natural soil temperature field, the atmospheric temperature as the ambient temperature in the 1D heat transfer model causes an apparent deviation, whereas the soil temperature at the buried depth of the pipeline in the natural soil temperature field as the ambient temperature does not. This study can provide a reference for the reasonable selection and use of the heat transfer models of the buried hot oil pipeline.

Acoustic reconstruction of the vortex field in the nonuniform temperature field of a simulated furnace

The high-temperature thermal vortex flows generated by the tangential combustion of large-scale coal-fired power plant boilers represent a complex medium that causes acoustic ray bending. In this paper, nonlinear acoustic tomography is combined with particle swarm optimization as a means of reconstructing the two-dimensional thermal vortex field. The nonuniform and large-gradient temperature distribution is the main cause of acoustic ray bending. We establish curved paths of acoustic propagation that are closely related to the temperature distribution. Based on these curved paths, a set of radial basis functions combined with Tikhonov regularization is derived to achieve more accurate reconstruction of the temperature field. The nonuniform temperature field affects the reconstruction of the flow field information. Our model considers a variation in the angle between the direction vector of the acoustic curved paths and the horizontal and vertical components of the flow velocity, and incorporates a priori information and a six-parameter hypersurface into the flow field reconstruction scheme. Particle swarm optimization is applied to minimize the objective function and obtain the vortex velocity field. Numerical experiments show that the proposed mathematical model of acoustic ray bending improves the reconstruction accuracy of the temperature distribution and vortex flow field. The acoustic time-of-flight is experimentally measured through the generalized cross-correlation with different window functions. The temperature and vortex fields reconstructed based on the actual time-of-flight are compared with thermocouple and anemometer measurements to demonstrate the validity and robustness of the proposed reconstruction model.

Equivalent value of non-uniform temperature field for thermocouple measurement

The incoming flow is assumed to have a uniform temperature profile when the energy balance of a thermocouple bead is analyzed for the purpose of measurement corrections, which is hardly true in real applications. The incoming temperature is normally non-uniform and the temperature of the flow closer to the bead has a stronger influence on the bead temperature. Considering this, for the first time, a Gaussian probability density function is established to generate an equivalent temperature of the non-uniform temperature field, which can be used in the corrections. With the one-dimensional thermocouple heat transfer program, the bead temperatures are calculated with five non-uniform temperature profiles and compared with the bead temperatures with the uniform temperatures to find the variance correlation of the Gaussian function. The variance is correlated to the Nusselt number and the wire diameter and the bead diameter of the thermocouple. Many cases with different thermocouple sizes, velocities and temperature ranges and widths of the power function profile are simulated. For all the tested cases, the bead temperature differences between the real profiles and the equivalent profiles are less than 27K, demonstrating the good accuracy of the current method.

Thermo-hydro-mechanical behavior of energy barrettes: Field experiments and numerical simulations

Over the past two decades, the thermo-hydro-mechanical behavior of earth-contact structures such as piles, walls, slabs, and tunnels, which simultaneously provide structural support and energy supply, has been studied through various field experiments and numerical simulations. These endeavors have built an understanding of the behavior of so-called energy piles, energy walls, energy slabs, and energy tunnels. This paper explores the thermo-hydro-mechanical behavior of a novel class of earth-contact structures that has the specificity of providing structural support and renewable energy to tall buildings: energy barrettes. This study particularly presents the first field experiments and 3-D time-dependent numerical simulations of energy barrettes. The work investigates the thermo-hydro-mechanical behavior of energy barrettes for a comprehensive set of variables: geometric variables (i.e., pipe configuration, barrette aspect ratio, and barrette section ratio), site variables (i.e., barrette–soil stiffness ratio and ground effective thermal conductivity), and operational variables (i.e., flow rate of the fluid circulating in the pipes). The obtained results expand the current knowledge base to analyze the behavior of energy barrettes in multiple situations that are likely to be encountered in practice and highlight markedly non-uniform temperature, displacement, and stress fields within and around such foundations.

Active control of cure-induced distortion for composite parts using multi-zoned self-resistance electric heating method

High dimensional accuracy of the carbon fiber reinforced polymer (CFRP) composite parts has been a long-term challenge for manufacturers in the aerospace industry. Traditionally, the uneven curing temperature could aggravate the cure-induced distortion (CID) and should be avoided as much as possible. But even under an ideally uniform temperature field, the CID of curved parts still cannot be eliminated because of the anisotropic shrinkage nature of the CFRP laminate. In this work, a novel CID control method based on the multi-zoned heating methodology is proposed, which actively applies an optimized non-uniform temperature field in different zones of the part to counteract the CID influenced by geometric structures. The counteracting principle of the proposed method lies in that using the actively formed through-thickness temperature gradients in different zones generates numerous small local thermal deformations, and their combination can significantly reduce the overall CID of the CFRP part. A co-optimization framework combined with the numerical model and genetic algorithm is established to rapidly compute the optimized multi-zoned temperature field for the CFRP parts with arbitrary complex structures. A good agreement between the numerical and the previous experimental results shows the effectiveness of the numerical model, and the multi-zoned temperature field optimization case of a scaled air-intake CFRP part demonstrates the performance of the co-optimization framework. Finally, by using the multi-zoned self-resistance electrical heating method, the CID reduction of the proposed method is experimentally validated on a complex CFRP part, where the average displacement reduces by >60 % compared to that of the traditional oven process.

Stress-based topology optimization of thermoelastic structures considering self-support constraints

A thermoelastic topology optimization method considering stress and manufacturing constraints is developed for engineering structures under thermo-mechanical coupled field in this paper. A design dependent non-uniform temperature field is considered for the heat conduction and the thermoelastic analysis during the topology optimization. Based on the solid isotropic material with penalization (SIMP), a topology optimization model is formulated to minimize the structural compliance under stress and overhang angle constraints. The overhang angle constraint to achieve the self-support property in additive manufacturing is established by connecting the elemental density values between the printing element and the corresponding support elements in the lower layer. The stress aggregation function is built to approximate the maximum stress value and an improved adaptive normalization scheme is applied to deal with the highly nonlinearity of the optimization. The sensitivity of the objective function and constraints with respect to the design variables are derived by the adjoint method, and the design variables are updated by the gradient-based optimization method. Moreover, a robustness scheme is proposed for the thermoelastic topology optimization to eliminate possible manufacturing issues such as “single node connection” and “thin rod” phenomena. Several typical numerical examples are provided to demonstrate the effectiveness of the proposed method in stress value reduction and overhang angle control. Meanwhile, the topology optimization with robustness scheme is also proved to result in more robust designs for manufacturing.