Temperature-dependent Thermophysical Properties Research Articles

Exergy efficiency and exergy destruction assessment of heat transfer and fluid flow through spiral passages using source-sink model

Exergy efficiency and exergy destruction of forced turbulent convective fluid flow through spiral passages using sourcesink model are assessed. Constant and temperature dependent thermophysical properties of process fluid in sink regions have been considered, while in the source regions phase change material is kept at constant temperature. Moreover, the effect of a secondary flow phenomenon due to spiral motion of the fluid flow through narrowing spiral passages has been evaluated in the sink passage domain. It was found that this phenomenon plays an important role in decreasing the exergy destruction as a result of energy exchange between source and sink in this compact type of energy carrier or storage equipment. It was found that the De (Dean Number) whose magnitude is a measure of the secondary flow, has positive impact on exergy efficiency while decreasing along the spiral passage. The fluid properties that are temperature dependent have a significant influence on the enhancement of heat transfer process, exergy efficiency and exergy destruction. It is concluded that the source-sink model could be considered from engineering point of view as a good simple model for evaluating the thermodynamic performance of this type of thermal energy process device.

Numerical study on flow and heat transfer characteristics of R1233zd(E) cooled in horizontal circular tubes under supercritical pressure

Supercritical organic refrigerants have been widely used in energy conversion and waste heat recovery systems due to their excellent heat transfer characteristics. R1233zd(E), as a fourth-generation environmentally friendly alternative refrigerant, has extensive application prospects. However, there is a lack of research on the heat transfer of supercritical R1233zd(E). In this work, the flow and heat transfer characteristics of supercritical R1233zd(E) in horizontal cooling tubes, including a mini tube and three ordinary tubes, are numerically simulated. In the simulation, not only the wall thickness but also the temperature-dependent thermophysical properties of the tube wall material are considered. The simulated results indicate that the specific heat capacity distributions determine that the peak of the overall heat transfer coefficients appears at a temperature higher than the pseudo-critical temperature. The flow and heat transfer characteristics of supercritical R1233zd(E) in different tubes, especially in the mini tube, are different. The applicability of three typical buoyancy criteria to this study is discussed, and the results show that two of three typical buoyancy criteria can be used to predict the buoyancy effect of supercritical R1233zd(E) in this study, but the thresholds of mini tube and ordinary tubes are different. Finally, a new heat transfer correlation is developed for supercritical R1233zd(E) by using the piecewise fitting method with pseudo-critical temperature as the point of division. The average relative deviation of the correlation is 0.57 % and the root mean square deviation is 0.87 %.

Enabling Part-Scale Scanwise process simulation for predicting melt pool variation in LPBF by combining GPU-based Matrix-free FEM and adaptive Remeshing

• A highly efficient GPU-based matrix-free finite element modeling with adaptive remeshing framework is developed to overcome the high computational expense of l -PBF thermal process modeling, making it feasible to do detailed scanwise thermal simulation for part-scale within days. • The effects of the scanning strategy, geometrical features, and proximity to the turning points on the melt pool size variability and lack of fusion porosity are investigated for two different parts. • The predicted variation in melt pool size and lack of fusion porosity has good correlation with experimental measurements. This work proposes to combine matrix-free finite element modeling (FEM), adaptive remeshing, and graphical processing unit (GPU) computing to enable, for the first time, scanwise process simulation of the Laser Powder Bed Fusion (L-PBF) process with temperature-dependent thermophysical properties at the part scale. Compared to the conventional FEM using the global stiffness approach and a uniform mesh running on 10 CPU cores, l -PBF process simulation based on the proposed methodology running on a GPU card with 5,120 Compute Unified Device Architecture (CUDA) cores enables a speedup of over 10,000x. This significant speedup facilitates detailed thermal history and melt pool geometry predictions at high resolution for centimeter-scale parts within days of computation time. Two parts consisting of various geometric features are simulated to reveal the effects of scan strategy and local geometry on melt pool size variation, which correlate well with melt pool and lack-of-fusion porosity measurements obtained via experiment.

Theoretical Approach to Investigate Temperature Dependent Ultrasonic and Thermophysical Properties of Ti-Zr-Hf Ternary Alloy

Abstract: In this study, we have computed temperature dependent ultrasonic and thermophysical properties of hcp medium entropy alloy Ti-Zr-Hf in temperature range of 0K-900K. Second order and third order elastic constants (SOECs and TOECs) have been calculated using lattice parameters using the Lennard-Jones potential model. With the help of SOECs and TOECs, the elastic parameters such as bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio have been computed. SOECs were also utilized to determine the ultrasonic velocities at different angle along unique axis. Further, thermophysical properties such as Debye temperature, Debye heat capacity, energy density in temperature range of 0K-900K and thermal conductivity in temperature range of 300K-900K have also been theoretically estimated. Additionally, the ultrasonic attenuation due to phononphonon interaction in both longitudinal and shear mode and thermoelastic mechanism have been computed for chosen alloy in the temperature range 300K-900K and attenuation due to the phonon-phonon interaction was found to be dominating over that due to thermoelastic mechanism

Graded Longitudinal Fins Having Spatially Varying Temperature-Dependent Thermophysical Properties

This paper reports transient responses of graded longitudinal fins subject to step change in base temperature and base heat flux wherein the graded fin materials are theorized to have spatial- and temperature-dependent thermal conductivity. Microstructure variations in graded materials (GMs) are addressed by axially varying the thermal conductivity; because GMs are potentially high-temperature application materials, consequently, thermal conductivity and heat generation are, respectively, assumed as polynomial and linear functions of temperature. Additionally, most of the applicable pragmatic fluid regimes are accounted for using the power law convection coefficient. The numerical solution of a typical nonlinear governing differential equation is obtained by using a particle tracking-based method called the lattice Boltzmann method (LBM). The LBM is a mesoscopic-based simulation method centered around the principles of kinetic theory and statistical mechanics. The LBM formulation accompanied with the in-house MATLAB code of the aforesaid problem with varying parameters is reported; also, it is validated with a previously available solution. The foregoing analysis is carried out to enhance the performance of a fin by using the superior thermomechanical property of graded materials. Furthermore, the inclusion of temperature-dependent thermophysical properties and heat generation will provide more accurate design data. The reported graph reveals that, even though a linear GM fin tip possesses thermal conductivity that is 25% less in magnitude in comparison to the Type-II homogeneous material (HM-2), the GM fin always yields a higher fin tip temperature because of grading. In addition, the tip temperature deficits between GMs and HM-2 proportionally increase from 0.4 to 2.1% for values of increasing from 0.1 to 2.0, respectively, for step changes in temperature; whereas in the case of the step change base flux, the deficits increase from 8.72 to 12.1% for values of decreasing from 3.0 to 1.0, respectively.

Temperature dependence of thermophysical properties of carbon/polyamide410 composite

In this study, the temperature dependence of the carbon/polyamide 410 composite's heat capacity, thermal expansion, density, and thermal conductivity was investigated. The results demonstrated that the specific heat capacity of the C/PA410 composite increases with temperature, with major transitions observed at the glass transition (Tg) and melting (Tm) temperatures. Due to the presence of fibers, the CTE values in the fiber direction of C/PA410 specimens were one order of magnitude smaller than in the transverse direction. The density measurements reveal that as temperature rises, volume increases, causing density to decrease. The heat diffusivity of the C/PA410 composite was measured using the laser flash technique, which was then used to calculate thermal conductivity. The results show that the average thermal conductivity in the fiber direction increases linearly with temperature, while in the transverse direction it increases linearly with temperature up to 50 °C and then becomes constant between 50 °C and 100 °C.

Convective Heat Transfer in Magneto-Hydrodynamic Carreau Fluid with Temperature Dependent Viscosity and Thermal Conductivity.

This study is aimed to explore the magneto-hydrodynamic Carreau fluid flow over a stretching/shrinking surface with a convectively heated boundary. Temperature-dependent variable thermophysical properties are utilized to formulate the problem. The flow governing equations are obtained with boundary layer approximation and constitutive relation of the Carreau fluid. The shooting method is utilized to obtain graphical and numeric outcomes. Additionally, initial guesses are generated with the help of Newton's method. The effect of Weissenberg number, Magnetization, stretching ratio, Prandtl number, suction/blowing parameter, and Lewis number is obtained on velocity, temperature and species continuity profile and analyzed. Shear stress rates and Nusselt number outcomes under body forces influences are present in tabulated data and discussed. It is observed that in absence of magnetization force, B = 0 and strong mass suction 5≤S≤7.5 effect high rates of Nusselt number is obtained. It is concluded that under the influence of power law index and non-linearity parameter maximum heat transfer and reduced shear stress rates are obtained.

Thermo-physical properties of liquids and gases over a heated rotating disk

The motivation of this study arises due to huge occurrence of rotating disk in field of real-world processes like rotational air cleaner, turbomachinery, centrifugal pumps, aerospace engineering and chemical engineering. A numerical investigation is undertaken to study the thermo-physical properties of Newtonian fluid flow over a strongly heated rotating disk with temperature dependent viscosity. The solar radiative heat flux is considered in the heat equation. The temperature dependent viscosity and thermo-physical properties are assumed to explore the flow behavior. Numerical solutions of the converted boundary layer equations are then achieved by using fifth order Rung-Kutta Fehlberg integration approach with a shooting method. The attained results are discussed for mean flow profiles and physical interpretations of the problem are given through graphs and tables. It is observed that temperature dependence viscosity for liquids ranges to decrease the base flow profiles, whilst the gaseous viscosity nature has the opposite impact. The mass diffusion coefficient creates enhancement in concentration field. Moreover, correlations are plotted graphically in terms of temperature, concentration, and viscosity.

Heat Transfer Enhancement with Ni-Water Nanofluid Flowing through a Prismatic Glass Louver for Solar Energy Harvest and Illumination

Three-dimensional nickel-water nanofluid flow and heat transfer in a prismatic glass louver are analyzed under various solar irradiation conditions and different nanoparticle sizes. Our innovative louver serves for dual-purpose: solar energy harvest and illumination. To meet natural daylighting requirement, the nanofluid is extremely dilute. The solar radiation and illumination were analyzed by the Monte Carlo method and the acquired solar energy absorption distribution is input as a source in the conjugate heat convection and conduction modeling executed by COMSOL. Temperature-dependent thermophysical properties and various nanofluid models are considered. The temperature rise and distribution under various combinations of solar air-mass models, nanoparticle sizes, and flow conditions are scrutinized. It is found that the nanofluid properties are not appreciably affected by the different nanofluid models because the nanofluid considered is dilute. The harvested solar thermal power and its efficiency are strong functions of the nanoparticle diameter and the flow Reynolds number.

Anomalous thermal conductivity in amorphous niobium pentoxide thin films: A correlation study between structure and thermal properties

Niobium pentoxide (Nb2O5) based thin films are predominantly used in optical filters, solar cells, electrochromic devices, sensors and microelectronic devices. The temperature-dependent thermophysical properties of Nb2O5 films are crucial for the performance and reliability of such devices. Within this work, for the first time, the thermal properties of sputter deposited Nb2O5 films are correlated with their structural properties at different length scales. Thermal measurements were carried out by time-domain thermoreflectance, yielding a thermal conductivity of 3.0±0.3 W/mK at 25 °C for crystalline Nb2O5 films, which decreases to 2.6±0.2 W/mK at 450 °C. In contrast, amorphous Nb2O5 films had a thermal conductivity of 2.2±0.2 W/mK below 275 °C. Above 275 °C, an abrupt increase in thermal conductivity up to a maximum value of 2.8±0.2 W/mK at 325 °C was recorded. The average and local structure are determined by in-situ high-temperature X-ray diffraction and in-situ high-temperature Raman spectroscopy, respectively. These characterization techniques together enable to cross-correlate structural and thermal properties of Nb2O5 thin films highlighting the observed peculiarity of the thermal conductivity. This substantial increase in thermal conductivity cannot be linked to any macroscopic phase change but rather to a local phase rearrangement near the crystallization temperature, evidenced by temperature-dependent Raman spectra analysis. This study serves as a guide to engineering future Nb2O5 based thin film devices and for their reliability optimization.

Comparative performance analysis of a SF-CPV/T collector under Australian climatic conditions using CFD and radiation modelling techniques

A hybrid numerical modelling approach has been developed and applied to investigate the performance of a spectrally-filtered concentrated photovoltaic thermal (SF-CPV/T) collector under local climate conditions. The approach couples the single-phase model for spectrally-filtered nanofluids and discrete ordinate (DO) radiation modelling to solve the radiative transport equation (RTE) of the solar participating media. To increase model accuracy, temperature-dependent thermophysical properties of working fluid and heat loss-coefficient are employed using existing correlations. This article makes contributions in three areas. First, the model, which was validated using published experimental data, is capable of capturing the thermal distribution in the three-dimensional geometry of the collector, which consists of several physical components (i.e. glass, filter thickness, air gap, and PV cell). Second, the direct-irradiance value can be effectively calculated when the non-gray radiation boundary is accounted for. Finally, the comparative performance of the collector when employing the local ambient and solar radiation data helps determine the best region for installing the SF-CPV/T collector. The results show that the current model can accurately predict the thermal and electrical output at given atmospheric conditions. Future studies will include the influence of nanoparticle concentration allowing for the heterogeneity of the suspension to influence performance of the SF-CPV/T collector.

An in-depth investigation into high fluence femtosecond laser percussion drilling of titanium alloy

High fluence femtosecond laser percussion drilling has a potential to produce micro holes for cooling purpose in turbine blades made of titanium alloys due to its short interaction time with the material. For an in-depth investigation, numerical simulation is carried out using 2D axi-symmetric two-temperature and heat conduction models in tandem, mimicking the laser percussion drilling. Moving mesh approach in finite element based COMSOL Multiphysics software is used to arrive at the crater geometry during the ablation process. The heat conduction model provides the value of surface temperature after each pulse. Taking temperature-dependent thermo-physical and optical properties with intraband absorption effect, the simulations are carried out on a 2 mm thick Ti6Al4V plate for 1–15 pulses with fluence in the range of 0.84 to 8.4 J cm−2. For comparison, the simulation results based on room temperature properties are also included. Validation experiments are carried out and the crater morphology is measured using laser scanning confocal microscope. The overall average absolute deviations of the results for crater diameter and depth are within 20% and 40% respectively. The proposed simulation approach is robust and can be used to investigate multi pulses laser ablation process in any other applications.

Thermal Response of Magnetic Refrigerants: Combined Effect of Temperature Dependent Specific Heat and Thermal Conductivity

Device optimization plays a paramount role in current research on magnetic refrigeration. Solid state refrigerants have been characterized and numerical simulations assume a critical relevance in the development of magnetocaloric technology to have alternatives to vapour-compression systems whose operating elements have high global warming potential. Experimental studies have shown that the thermal properties of several magnetocaloric materials considerably change around their Curie temperatures (TC) and that this temperature dependency should not be dismissed. Current numerical research does not fully predict the complete thermal response of such materials, due to inaccuracies from neglecting the impact of combining both thermal conductivity (k) and specific heat (Cp) dependence on temperature. In this study, a simple unidimensional model includes k(T) and Cp(T) functions as input parameters, highlighting the relevance of considering temperature dependent thermophysical properties’ inputs when simulating the magnetic refrigerant’s heat transfer processes. The obtained results evidence that neglecting the temperature dependence of the magnetocaloric material thermophysical properties, namely its thermal conductivity and its specific heat, affects its temperature response, what may strongly affect the results after a succession of (hundreds or thousands) cycles.

Comparison of single-phase Newtonian and non-Newtonian nanofluid and two-phase models for convective heat transfer of nanofluid flow in backward-facing step

The aim is to investigate the application of nanofluids for improving the heat transfer in a backward-facing step channel. Numerical simulations are performed using single-phase models for both Newtonian and non-Newtonian fluids in the Reynolds number range 280–470. Constant and temperature-dependent thermo-physical properties of different volume fractions (0–4%) of nanoparticles are considered. The thermal enhancement of the nanofluids within the channel is analyzed and compared with the experimental data. A detailed comparison of different CFD models is established. Numerical results are obtained with two types of single-phase models (Newtonian and non-Newtonian) and three types of two-phase models (mixture, volume of fluid (VOF), Eulerian) and compared with experimental results obtained for the Nusselt number. The finite volume method is used to solve the system of governing partial differential equations describing the steady-state, two-dimensional, laminar, mixed convective flow in a micro backward facing step channel with uniform heat flux. The single-phase and two-phase models predict practically equivalent hydrodynamic fields, but significantly different thermal fields are observed in our results. The performance efficiency coefficient (PEC) is determined using single-phase and two-phase methods for Al2O3-water nanofluids at different Reynolds numbers to investigate their thermal performance.

Thermal rectification mechanism of composite cylinders with temperature and stress-dependent interface thermal resistance

Thermal rectifier behaves thermal rectification phenomenon if it exhibits asymmetric heat transfer characteristics along a given direction. The present paper established a theoretical model of the cylindrical thermal rectifier, and developed a Galerkin finite element method to numerically investigate the thermoelastic coupling response of the thermal rectifier. Initial interface gap is introduced here to manipulate the different contact statuses of the rectifier for forward and reverse cases to optimize the thermal rectification ratio. Temperature and stress-dependent interface thermal resistance as well as temperature-dependent thermophysical properties of the rectifier are considered in the analysis. Effects of initial interface gap, boundary conditions, geometry parameters and material pairs on thermal rectification ratio are given based on the numerical results. Results show that, the equivalent thermal conductance of the thermal rectifier is the key factor to optimize the thermal rectification ratio that can be utilized through different initial interface gaps, and the status switch of the interface gap for forward and reverse cases leads to the maximal thermal rectification ratio. The proposed numerical method as well as the thermal rectification mechanism could be guidance for the optimal design of the cylindrical thermal rectifier.

HIZLI VE ÖNGÖRÜLÜ ISI BORUSU TASARIM VE ANALİZ ARACI: H-PAT

For the assessment of the thermal performance of heat pipes, a wide range of modeling is available in the literature, ranging from simple capillary limit analyses to comprehensive 3D models. While simplistic models may result in less accurate predictions of heat transfer and operating temperatures, comprehensive models may be computationally expensive. In this study, a universal computational framework is developed for a fast but sufficiently accurate modeling of traditional heat pipes, and an analysis tool based on this framework, named Heat Pipe Analysis Toolbox, in short H-PAT is presented. As a diagnostic tool, H-PAT can predict the fluid flow and heat transfer from a heat pipe under varying heat inputs up to the onset of dryout. During the initial estimation of phase change rates, the solutions of particular thin film phase change models are avoided by specifying an appropriate pattern for the mass flow rate of the liquid along the heat pipe rather than using finite element/volume based methods for the computational domain. With the help of a modular structure, H-PAT can simulate heat pipes with different wick structures as long as an expression for the average liquid velocity and corresponding pressure drop can be introduced. H-PAT is also capable of analyzing heat pipes with variable cross-sections, favorable/unfavorable gravity conditions and utilizes temperature dependent thermo-physical properties at evaporator, condenser and adiabatic regions together with heat input sensitive vapor pressure. In addition, H-PAT performs the computation very fast which also makes it a perfect design tool for researchers and design engineers in the field of thermal management.

Prediction of Heat Transfer and Fluid Flow Effects on Entropy Generation in a Monolithic Catalytic Converter Using Large-Eddy Simulation.

In the present work, heat transfer and fluid flow and their effects on entropy generation in a realistic catalytic converter of a Lada Niva 21214 vehicle are studied using large eddy simulation. At first, the pressure drop over the catalytic converter is measured for dry air at constant temperature ( K), different volumetric flow rates, and extrapolated to large volumetric flow rates for dry air ( K) and for the exhaust gas under realistic engine conditions ( K) using the Darcy–Forchheimer relation. Then, coupled heat and fluid flow phenomena inside the catalytic converter are analyzed for nonreacting isothermal conditions and nonreacting conditions with conjugate heat transfer by using the large-eddy simulation. The predicted pressure drop agrees well with the measured and extrapolated data. Based on the obtained numerical results, the characteristic flow features are identified, namely: the impinging flow with stagnation, recirculation, flow separation and laminarization within the fine ducts of the monolith, which depends on the heat transfer through temperature-dependent thermophysical properties of exhaust gas. Moreover, due to high-velocity gradients at the wall of the narrow ducts in the monolith, entropy production by viscous dissipation is observed predominantly in the monolith region. In contrast, entropy production due to heat transport is relatively small in the monolith region, while it overwhelms viscous dissipation effects in the pipe regions.

An Iterative Algorithm for the Estimation of Thermal Boundary Conditions Varying in Both Time and Space

The presented survey of the up-to-date state of knowledge indicates that despite the great number of works devoted to the issue in question, there is no simple method that allows the use of commercial programs for the identification of the transient thermal state in elements with a simple or complex shape. This paper presents an inverse method developed to estimate the convective heat transfer coefficient varying both in time and space on a vertical plate during its cooling. Despite the smaller number of measurement points and larger disturbance of measured temperatures compared to the data presented in the available literature, comparable results are obtained. The developed iterative algorithm is also applied to estimate the time- and space-dependent heat flux and the convective heat transfer coefficient in the steam boiler membrane waterwall. The analysed component has the form of the non-simply connected and complex shape domain Ω. Temperature-dependent thermophysical properties are used. Calculations are performed for the unknown heat flux or heat transfer coefficient distribution on the domain boundary based on measured temperature transients disturbed with a random error of 0.5 °C. To reduce oscillations, the number of future time steps of NF = 20 is selected. The number of iterations in each time step ranges between 1 and 8. The estimated boundary conditions are close to the exact values. In this work, the ANSYS software using the FEM is applied.

A new microchannel heat exchanger configuration using CNT-nanofluid and allowing uniform temperature on the active wall

The present study presents a three-dimensional numerical analysis using the finite element method of nanofluid enhanced heat transfer in micro heat exchanger equipped with triangular fins. The new configuration based on an existent system where a jet impingement supplies a microchannel structure. A modification of the heat exchanger geometry in the z-direction is added allowing a uniform wall temperature profile. The micro heat exchanger is assumed to be well insulated. The hot fluid (water) flows in the lower channel with a fixed velocity (u w_in = 20 mm/s) and cold fluid (CNT-water nanofluid) flows in the upper channel which is equipped with triangular fins with a velocity (u nf_in ) ranged from 5 to 45 mm/s. The nanofluid is considered homogeneous with temperature-dependent thermophysical properties and the CNT nanoparticles volume fraction is varied from 0 to 5%. The results are presented in term of thermal and flow fields, heatlines, overall heat transfer coefficient, thermal effectiveness, and thermal performance factor (TPF). It was found that the performances of the heat exchanger are significatively improved using the CNT nanofluid and the triangular fins. But the TPF increase with the CNT volume fractions and decreases with the fin’s height.

Experimental validation of a continuum model for local heat transfer in shell-and-tube moving-bed heat exchangers

• Local heat transfer coefficients in shell-and-tube moving bed heat exchangers were simulated. • Local heat transfer coefficients were measured using a small heat exchanger mockup. • Experimental results were used to validate a comprehensive thermal model. • Simulation results were in good agreement with the experiments. Moving-bed heat exchangers with a horizontal tube arrangement offer a promising solution to exchange high-temperature heat with a particle stream. However, in order to guide the design of such heat exchangers, accurate and time-efficient simulation tools capable of capturing the complex heat transfer characteristics still need to be improved. In this article we present experimental results of the local heat transfer coefficients around the tube circumference of a heat exchanger mockup. To this end, specially prepared measuring probes were developed and a test campaign was conducted. A comprehensive thermal model was applied to the setup under consideration. This model takes into account the temperature-dependent thermophysical properties of the bulk, variable temperature boundary conditions, and the increased thermal resistance caused by the stagnation and void zones. To validate the model, calculated and experimental results were compared. It turns out that the predicted heat transfer coefficients well match the experimental data, albeit with slight deviations at the stagnation and void zones of the tubes. The prediction of a tube’s area-weighted heat transfer coefficient, which constitutes the most important factor for design purposes, yields results with errors of less than 3%. Therefore, it is concluded that the proposed thermal model is able to well predicts the heat transfer in shell-and-tube moving-bed heat exchangers.