Temperature Dependence Of Thermal Parameters Research Articles

Thermal analysis of in-situ laser assisted diamond cutting of fused silica and process optimization

Fused silica is typically a difficult material to machine using conventional methods due to its high brittleness and hardness, despite its significance in optical systems such as high-power lasers and astronomical telescopes. Laser assisted diamond cutting has emerged as a promising and cost-effective alternative for machining fused silica. This study investigated the machinability and thermal response of fused silica during in-situ laser assisted diamond cutting through finite element analysis and cutting experiments. The temperature dependence of thermal parameters, identified by Beetle Antennae Search, was taken into consideration in the thermal model. To minimize surface roughness and determine the optimal machining parameters, various methods were employed, including analysis of variance, signal-to-noise ratio, and Particle Swarm Optimization coupled with Artificial Neural Network. The results indicated that various factors involved in in-situ laser assisted diamond cutting had a significant impact on the thermal response of fused silica, resulting in different surface roughness. Among these factors, spindle speed, feed speed, cutting depth, and laser power contributed to surface roughness by 17.34 %, 12.28 %, 12.03 %, and 48.31 %, respectively. By utilizing the optimal combination of parameters, which comprised a spindle speed of 2700 rpm, feed speed of 1.7 mm/min, cutting depth of 2.7 μm, and laser power of 12.5 W, a smooth surface finish of Sa 12.9 nm could be obtained.

A Nonclassical Stefan Problem with Nonlinear Thermal Parameters of General Order and Heat Source Term

The analytic solution for a general form of the Stefan problem with nonlinear temperature-dependent thermal parameters and a heat source the term is obtained. We prove the existence and uniqueness of the solution to the problem in the absence of a heat source (β=0), and in the presence of a heat source β(x)=exp(−x2). Then, we establish lower and upper bounds for the solutions of the homogeneous equation and the nonhomogeneous equation, for different values of δi and γi. It was found that the lower bounds exhibit an excellent alignment with the numerical solutions of the homogeneous and nonhomogeneous equations, so the lower bounds can serve as approximate analytic solutions to the problem. This is a generalization to the open problem proposed by Cho and Sunderland in 1974 and also generalizes the problem proposed by Oliver and Sunderland in 1987, in addition to the problems investigated recently.

The effect of temperature-dependent material properties on simple thermal models of subduction zones

Abstract. To a large extent, the thermal structure of a subduction zone determines where seismicity occurs through controls on the transition from brittle to ductile deformation and the depth of dehydration reactions. Thermal models of subduction zones can help understand the distribution of seismicity by accurately modelling the thermal structure of the subduction zone. Here, we assess a common simplification in thermal models of subduction zones, i.e. constant values for the thermal parameters. We use temperature-dependent parameterisations, constrained by lab data, for the thermal conductivity, heat capacity, and density to systematically test their effect on the resulting thermal structure of the slab. To isolate this effect, we use the well-defined, thoroughly studied, and highly simplified model setup of the subduction community benchmark by van Keken et al. (2008) in a 2D finite-element code. To ensure a self-consistent and realistic initial temperature profile for the slab, we implement a 1D plate model for cooling of the oceanic lithosphere with an age of 50 Myr instead of the previously used half-space model. Our results show that using temperature-dependent thermal parameters in thermal models of subduction zones affects the thermal structure of the slab with changes on the order of tens of degrees and hence tens of kilometres. More specifically, using temperature-dependent thermal parameters results in a slightly cooler slab with e.g. the 600 ∘C isotherm reaching almost 30 km deeper. From this, we infer that these models would predict a larger estimated seismogenic zone and a larger depth at which dehydration reactions responsible for intermediate-depth seismicity occur. We therefore recommend that thermo(-mechanical) models of subduction zones take temperature-dependent thermal parameters into account, especially when inferences of seismicity are made.

An Analysis of the One-Phase Stefan Problem with Variable Thermal Coefficients of Order p

Approximate solutions are obtained in implicit forms for the following general form of the nonlinear Stefan problem ddx(1+δ1yp)dydx+2x(1+δ2yp)dydx=4Steβ(x),0<x<λ, with y(0)=1,y(λ)=0, where λ>0 is a solution to the nonlinear equation y′(λ)=−2λSte, where δi>−1,i=1,2,p>0, and Ste is the Stefan number, which represents a phase-change problem with a nonlinear temperature-dependent thermal parameters (i.e., thermal conductivity and specific heat) on (0,λ).

Temperature-Dependent Thermal Parameter Identification of Ceramic Nanorod Aerogels Composite in the Ultrahigh Temperature Environment

The identification of the thermal properties of advanced materials is of great importance in engineering application. In this work, an inverse scheme is proposed to identify the temperature-dependent thermal parameters of ceramic nanorod aerogels (CNRAs) composite in the ultrahigh temperature environment up to 1873 K. The feasibility of the proposed method is successfully tested by an analytical solution for CNRAs with known material properties. Furthermore, the temperature-dependent thermal properties of CNRAs are successfully obtained using the experimental data acquired from the heat conduction experimental testing for a CNRAs plate. Lastly, the obtained thermal properties are used to simulate an arc-heated wind tunnel (AHWT) test of a receiving satellite antenna assembly using the FEM method. The simulated temperature at measured data has a very good agreement with the experimental data. This further demonstrates the strong capability of the proposed inverse method. In summary, the proposed approach provides an important approach for the identification of nonlinear and temperature-dependent thermal properties of advanced materials.

Effect of temperature-dependent rock thermal conductivity and specific heat capacity on heat recovery in an enhanced geothermal system

The modeling of heat recovery from an enhanced geothermal system (EGS) requires rock thermal parameters as inputs such as thermal conductivity and specific heat capacity. These parameters may encounter significant variations due to the reduction of rock temperature during heat recovery. In the present study, we investigate the effect of temperature-dependent thermal conductivity and specific heat capacity on the thermal performance of EGS reservoirs. Equations describing the relationships between thermal conductivity/specific heat capacity and temperature from previous experimental studies were incorporated in a field-scale single-fracture EGS model. The modeling results indicate that the increase of thermal conductivity caused by temperature reduction accelerates thermal conduction from rock formations to fracture fluid, and thus improves thermal performance. The decrease of specific heat capacity due to temperature reduction, on the contrary, impairs the thermal performance but the impact is smaller than that of the increase of thermal conductivity. Due to the opposite effects of thermal conductivity increase and specific heat capacity decrease, the overall effect of temperature-dependent thermal parameters is relatively small. Assuming constant thermal parameters measured at room temperature appears to be able to provide acceptable predictions of EGS thermal performance.

A Temperature-Dependent Cauer Model Simulation of IGBT Module With Analytical Thermal Impedance Characterization

In pursuit of high power density and high reliability of power converters, the junction temperature of power devices becomes an essential indicator for heath condition monitoring and thermal management. Particularly under high-temperature operating conditions, the temperature-dependent thermal properties of the chip and ceramic materials must be incorporated to enhance the prediction accuracy. In this article, an improved temperature-dependent Cauer-type thermal network of insulated-gate bipolar transistor (IGBT) module is established. The temperature dependence of thermal parameters for the chip layer and ceramic layer is meticulously considered. More importantly, finite-element method (FEM) simulation is used to yield the heat flux curve of the power module at the center line in order to better imitate the real heat-spreading scenario. In this way, the effective heat transfer area of each layer can be calculated accurately and analytically. By this analytic method, the temperature-dependent thermal impedance can be efficiently determined. Compared with prior-art fully FEM-based temperature-dependent thermal impedance characterization method, the method proposed in this article reduces the FEM simulation time cost approximately 20 times under the same computing hardware facilities and considerably simplifies the parameter extraction process. Finally, experimental results based on two commercial IGBT modules successfully validate the usefulness, effectiveness, and accuracy of the proposed thermal network model.

Thermophysical Model for Realistic Surface Layers on Airless Small Bodies: Applied to Study the Spin Orientation and Surface Dust Properties of (24) Themis from WISE/NEOWISE Multiepoch Thermal Light Curves

Abstract This work proposes a thermophysical model for realistic surface layers on airless small bodies (RSTPM) for the use of interpreting their multiepoch thermal light curves (e.g., WISE/NEOWISE). RSTPM considers the real orbital cycle, rotation cycle, rough surface, temperature-dependent thermal parameters, as well as contributions of sunlight reflection to observations. It is thus able to produce a precise temperature distribution and thermal emission of airless small bodies regarding the variations on orbital timescales. Details of the physics, mathematics, and numerical algorithms of RSTPM are presented. When used to interpret multiepoch thermal light curves by WISE/NEOWISE, RSTPM can give constraints on the spin orientation and surface physical properties, such as the mean thermal inertia or the mean size of dust grains, the roughness fraction, and the albedo via a radiometric procedure. As an application example, we apply this model to the main-belt object (24) Themis, the largest object of the Themis family, which is believed to be the source region of many main-belt comets. We find multiepoch (2010, 2014–2018) observations of Themis by WISE/NEOWISE, yielding 18 thermal light curves. By fitting these data with RSTPM, the best-fit spin orientation of Themis is derived to be (λ = 137°, β = 59°) in ecliptic coordinates, and the mean radius of dust grains on the surface is estimated to be b ˜ = 140 − 114 + 500 ( 6 ∼ 640 ) μm, indicating that the surface thermal inertia varies from ∼3 Jm−2 s−0.5 K−1 to ∼60 Jm−2 s −0.5 K−1 due to seasonal temperature variation. A more detailed analysis found that the thermal light curves of Themis show a weak feature that depends on the rotation phase, which is indicative of heterogeneous thermal properties or imperfections of the light-curve inversion shape model.

Temperature Dependence of Tissue Thermal Parameters Should Be Considered in the Thermal Lesion Prediction in High-Intensity Focused Ultrasound Surgery

This study considers the temperature-dependent thermal parameters (specific heat capacity, thermal diffusivity and thermal conductivity) used when predicting the temperature rise of tissue exposed to high-intensity focused ultrasound (HIFU). Numerical analysis was performed using the Khokhlov–Zabolotskaya–Kuznetsov equation coupled with a bioheat transfer function. The thermal parameters were set as the functions of temperature using experimental data. The results revealed that, for liver tissue exposed to HIFU with a focal intensity of 3000 W/cm2 for 10 s, the predicted focal temperature rise was 23% lower and the thermal lesion area 41% smaller than those predicted without considering the temperature dependence. The prediction was validated by experimental observations on thermal lesions visualized in a tissue-mimicking phantom. The present results suggest that temperature-dependent thermal parameters should be considered in the prediction of HIFU-induced temperature rise to avoid lowering ultrasonic output settings for HIFU surgery. The aim of the present study was to investigate how significantly the temperature dependence of the thermal parameters affects the thermal dose imposed on the tissue by a typical clinical HIFU device. A numerical simulation was performed using a thermo-acoustic algorithm coupling the non-linear Khokhlov–Zabolotskaya–Kuznetsov (KZK) equation (Meaney et al. 1998; Filonenko and Khokhlova 2001) and a bio-heat transfer (BHT) equation (Pennes 1948). Thermal parameters of liver tissue were modeled in the present study as functions of temperature and were incorporated into the BHT equation to compensate for the variations in thermal parameters with temperature. Experimental validation was achieved by comparing the predictions with the thermal lesions formed in the tissue-mimicking phantoms.

TEMPERATURE-DEPENDENT THERMOMECHANICAL MODELING OF SOFT TISSUE DEFORMATION

Modeling of thermomechanical behavior of soft tissues is vitally important for the development of surgical simulation of hyperthermia procedures. Currently, most literature considers only temperature-independent thermal parameters, such as the temperature-independent tissue specific heat capacity, thermal conductivity and stress–strain relationships for soft tissue thermomechanical modeling; however, these thermal parameters vary with temperatures as shown in the literature. This paper investigates the effect of temperature-dependent thermal parameters for soft tissue thermomechanical modeling. It establishes formulations for specific heat capacity, thermal conductivity and stress–strain relationships of soft tissues, all of which are temperature-dependent parameters. Simulations and comparison analyses are conducted, showing a different thermal-induced stress distribution of lower magnitudes when considering temperature-dependent thermal parameters of soft tissues.

Study on thermal effects of InSb infrared focal plane arrays irradiated by pulsed laser

To learn thermal effects of InSb infrared focal plane arrays (IRFPAs) detector irradiated by pulsed laser, basing on ANSYS software, and considering temperature dependent thermal parameters of InSb, a three dimensional temperature field analysis model of InSb IRFPAs detector by 1064 nm Gauss laser irradiation is built. The characteristics of temperature rise and temperature distribution in InSb IRFPAs detector are studied. The results show that the maximum temperature always occurs in InSb chip, locating at the top layer of InSb IRFPAs detector, the temperature rises in each layer are different, and the temperature distribution in InSb IRFPAs detector is quite different from that in single-layer material. The temperature distribution of InSb chip in InSb IRFPAs reduces from center to outside, while it shows not a smooth decrease, but a concentric-ringed ripple decrease with non-consecutive high temperature extremum regions. The temperature distribution patterns in underfill, Si readout integrated circuits are similar to that in InSb chip, but the discontinuous high temperature areas in InSb chip, underfill locate at the regions between indium bumps, and the discontinuous high temperature areas in Si readout integrated circuits locate at the contact area with indium bumps. This different temperature distribution phenomenon in each material is mainly due to its multi-layer architecture and quite different thermal properties of the middle layer, which is an interlacing layout of underfill and indium bumps. Besides, the influences of indium bump structure size on the temperature rise are also discussed. All these results qualitatively reflect the disciplines of temperature rise in InSb IRFPAs detector, providing a theory support for thermal analysis of detectors irradiated by laser.

Investigation on the effects of temperature dependency of material parameters on a thermoelastic loading problem

The present work is concerned with the investigation of thermoelastic interactions inside a spherical shell with temperature-dependent material parameters. We employ the heat conduction model with a single delay term. The problem is studied by considering three different kinds of time-dependent temperature and stress distributions applied at the inner and outer surfaces of the shell. The problem is formulated by considering that the thermal properties vary as linear function of temperature that yield nonlinear governing equations. The problem is solved by applying Kirchhoff transformation along with integral transform technique. The numerical results of the field variables are shown in the different graphs to study the influence of temperature-dependent thermal parameters in various cases. It has been shown that the temperature-dependent effect is more prominent in case of stress distribution as compared to other fields and also the effect is significant in case of thermal shock applied at the two boundary surfaces of the spherical shell.

Numerical Simulation and Experiment of Hardening Behaviors in Unsaturated Polyester Resin Artificial Marble Blocks Under Microwave Radiation

A high-power continuous microwave hardening system at the frequency of 915 MHz and the maximum output power of 60 kW is established to harden unsaturated polyester resin (UPR) artificial marble blocks of typical size $1600 \times 900\times 600$ mm3 in the industrial production. The microwave hardening system contains three major sections, including a $2000 \times 1300 \times 900$ mm3 multimode cavity, microwave generators, and three groups of feeding-waveguide systems from microwave generators to the multimode cavity. An optimum hardening method by adjusting the value of incident power and processing time is found on the basis of study of UPR properties and can promote products qualities. A numerical coupled electromagnetic and heat transfer model has been built to simulate microwave hardening process and to predict temperature profiles of artificial marble blocks successfully. The result that there is no significant change in temperature profiles between fixed and temperature-dependent thermal parameters indicates thermal conductivity K and specific heat capacity $C_{P}$ , which are not sensitive to temperature. The effect of height between artificial marble block and cavity bottom on electromagnetic field, absorption power, and temperature distribution is also discussed in this paper. The contrast results between the two hardening methods prove that the microwave hardening can achieve better comprehensive characteristics than natural hardening. The establishment of the high-power microwave hardening system has improved the industrial production efficiency of UPR artificial marble 300 times.

Thermal Properties of Mannitol Derivative

Mannitol is an alcoholic sugar that is commonly used in the food industry. It is a white, odorless crystalline powder. Its melting temperature is about 168 °C. It is possible to be used also for the accumulation of energy in the heat exchangers based on oils. On its basis is sold a product PlusICE A164 of company PCM Products Ltd. (T = 164 °C, cp = 2.42 kJ.K-1 kg-1). Thermal properties of the material in both, solid and liquid phase were investigated for this purpose in terms of potential applications. Temperature dependence of thermal parameters (thermal diffusivity, thermal conductivity, and specific heat) were determined using a transient (step-wise) method. Fractal model of heat transport was used for the determination of thermal parameters. This model is independent on the geometry and on the type of the sample heating, and includes heat losses too. The experiment confirms the phase change temperature about 168 °C.

Influence of Temperature-Dependent Thermal Parameters on Temperature Elevation of Tissue Exposed to High-Intensity Focused Ultrasound: Numerical Simulation

High-intensity focused ultrasound (HIFU) has been used successfully as a non-invasive modality in treating solid tumors. The temperature rise HIFU irradiation causes in a tissue depends on the thermal properties of the tissue. This study was motivated by our observation that the thermal properties of a tissue vary significantly with temperature (Guntur SR, Lee KI, Paeng DG, Coleman AJ, Choi MJ. Ultrasound Med Biol 2013;39:1771–1784). This research investigated how significantly the alteration of tissue thermal parameters, in the ranges of values measured at 25°C–90°C, affects prediction of the temperature elevation of tissue under the same HIFU exposure. The numerical simulation was performed by coupling a non-linear Khokhlov–Zabolotskaya–Kuznetsov equation with a bio-heat transfer function. In the conventional method of prediction, the thermal parameters were set as constants measured at room temperature (25°C). This study compared the conventional prediction with those predicted with different thermal parameters measured at the various temperatures up to 90°C. The results indicated that the conventional method significantly overestimated the rise in focal temperature in the liver tissue exposed to a clinical HIFU field, compared with the prediction made using thermal parameters measured at temperatures that cause thermal denaturation. This finding suggests that temperature-dependent thermal parameters should be considered in predicting the temperature rise in a tissue to avoid use of an insufficient thermal dose in treatment planning for HIFU surgery.

Estimation of Cooling Rate and Its Effect on Temperature Dependent Properties in GTA Welded High Carbon Steel Joints

An elaborate study has been conducted in this article to estimate the cooling rate of the Gas Tungsten arc (GTA) welded steel butt joints of grade AISI 1090. The temperature dependent thermal parameters has been investigated in connection with developed rate of cooling. Experiment has been carried out ffto determine the thermal cycle formed along the longitudinal direction from weld bead. Implementing experimental temperatures, Adams empirical cooling rate correlation has incorporated to analyze rate of cooling. A correlation has been suggested in this study, derived from thick plate temperature distribution model. To find out the heat loss from the joint, Vinokurov’s empirical combined heat transfer coefficient has been utilized and with it has verified with conventional heat transfer coefficient based on convection and radiation. Cooling rate has been found out to be very rapid at z = 36mm to z = 108mm based on thick plate model and it has completely agreed with the variation of Adams correlation. At higher temperatures above 800ºC, heat loss due to radiation completely dominates the convection and lower temperatures convection heat loss influences much than radiation. Heat loss due to convection and radiation fully justified with the results produced based on cooling rate and rapid cooling near the fusion boundary exists only for 5s-10s.

Heating process simulation for a body subjected to an intensive thermal effect on its surface

An approximate method of calculating the nonstationary temperature fields for the case of rapid and intensive heating of bodies is considered. The fast heating of a body is simulated by various boundary conditions at its heated surface. An approximate method is proposed in a one-dimensional formulation to solve the unsteady-state heat conduction equation with these boundary conditions. The applicability of this method in practice is confirmed by comparing the approximate temperature fields with the exact solution. An approximate temperature field is constructed for a particular case with consideration of a temperature dependence of thermal parameters, which allows one to describe the heat localization in a heated zone.

Ultrafast temperature relaxation evolution in Au film under femtosecond laser pulses irradiation

Ultrafast temperature relaxation processes in Au film including two temperature relaxation and thermal diffusion relaxation with femtosecond laser pulse excitation were investigated numerically by Finite Element Method (FEM). With the temperature dependent thermal parameters, the full 2D temperature field evolution in picosecond and nanosecond domains were obtained. It is proposed that the heat transfer depth can be alternatively localized or enhanced by the distinct temperature relaxation mechanisms. Moreover, the effect of laser parameters and Au film thickness and surface reflectivity on the two temperature relaxation time were analysed.

Quench Development in Superconducting Fault Current Limiters Based on YBCO Films

We measured and analyzed quench development in superconducting fault current limiters (SFCLs) based on Au/YBa <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Cu <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sub> thin films, taking temperature dependence of thermal parameters into consideration. The SFCLs were fabricated by patterning Au/YBCO films grown on 100 mm-diameter sapphire substrates. They were subjected to simulated AC fault currents for quench development measurement. The samples were immersed in liquid nitrogen during the experiment. The quench resistance increased rapidly first and then moderately fast. The increase slowed down afterwards. Data were analyzed quantitatively with the concept of heat transfer within the SFCLs. A heat balance equation was derived and solved, taking into consideration temperature dependence of thermal parameters of sapphire substrates. The solutions agreed with data well. They explained the quench behavior both prior to and after completion of quench propagation. Dependence of quench development on applied voltages could be also understood quantitatively.

Investigation of the 3D ANNNI Model by Monte Carlo Methods

The results for 3D anisotropic Ising model with competing interactions (ANNNI) investigated by the Monte Carlo methods are presented. The temperature dependence of thermal parameters is calculated. The character of all possible phase transitions in the model is analyzed.