Heat Flux Source Research Articles

Dynamic characterization measurement of the circular foil heat flux sensor based on laser method

In order to make the circular foil heat flux sensor meet the growing demand for dynamic heat flux monitoring in extreme environments such as hypersonic wind tunnels, a dynamic calibration platform with a high-power semiconductor laser as heat flux source is built. Combining Finite Element Analysis (FEA) and experiments to carry out relevant studies. Our findings indicate a negative correlation between the time constant and laser power/pulse width, whereas the rise time is positively correlated with the laser pulse width. And they are all positively correlated with the coating thickness. Importantly, FEA revealed the independence of laser parameters from the time constant. Additionally, when the laser pulse width is approximately one order of magnitude less than the time constant of the sensor, it can be deemed an ideal pulse excitation. In the experiment, the maximum heat flow density was applied up to 3.49 MW/m2, the minimum ideal pulse laser width can reach 1ms, the minimum time constant was measured to be 63 ms, and the minimum rise time was 12 ms. This research serves as a valuable reference for dynamically calibrating sensors using the laser method.

Evaluations of ground surface heat fluxes and its potential vegetation effects in the permafrost region of northeastern China

Ground surface-air temperature difference (GATD) is the primary source of sensible heat flux from the ground surface, and vegetation inevitably affects it by altering the ground surface characteristics. However, the relationship between vegetation and GATD in the permafrost region has not been well-elucidated. Using meteorological station data, National Oceanic and Atmospheric Administration Climate Data Record Normalized Difference Vegetation Index (NOAA CDR NDVI) data, and some auxiliary data, this study aims to investigate the patterns of GATD in the Northeast China permafrost region and quantify the response of GATD to vegetation changes. The study employs trend analysis, Geodetector, and correlation analysis methods. The results show that the GATD in the Northeast China permafrost region decreased from west to east and the annual mean GATD exhibited an upward from 1982 to 2020. The relationship between NDVI and GATD trend is non-linear, in areas with low vegetation, vegetation changes amplify the GATD trend, while in areas with high vegetation, vegetation changes inhibit the GATD trend. Furthermore, the rate of GATD increase is higher in the discontinuous permafrost (DP) region than in the sporadic permafrost (SP) and isolated permafrost (IP) regions, suggesting that the DP region may have experienced a faster ground surface state change process. The findings of this study will provide new insights for evaluating permafrost degradation and studying the resulting ecological environmental effects in the permafrost region.

Damage of Nickel-coated glass/epoxy foam-core composites induced by artificial lightning strikes

In the field of composite materials, many reports have shown that catastrophic structural damage is caused by lightning strikes. In this study, new design concepts were proposed for the lightning-strike protection of nickel-coated glass/epoxy foam-core composites. Instead of using a neat metal mesh, glass fibers were modified with nickel particles via a plating technique to improve their thermal and electrical conductivities. In addition, a thin Invar plate was inserted at the middle of the structure and a foam core was introduced to reduce damage to the structure. Three models with different materials and stacking sequences were used in this study. Severe damage was experimentally observed following artificial lightning at a peak current of approximately 150 kA when considering a waveform A. Furthermore, numerical prediction was performed to identify the damage mechanisms of the structures. Besides the heat flux source, a mechanical source known as the shock wave overpressure was investigated separately as a new factor for dielectric materials. These two sources of lightning were determined as minor reasons for the structural damage. The failure modes were analyzed for further discussion about the failure mechanism in this study.

Effect of Cattaneo–Christov heat flux model and elastic deformation on Walters'B viscoelastic fluid flow with porosity

In the current work, flow of 2-D MHD Walters'B viscoelastic fluid is discussed in the existence of elastic deformation, Cattaneo–Christov Heat Flux Model (CCHFM), heat source, Newtonian heating, viscous dissipation and porous medium. Dimensionless equations that are in charge of the problem's analysis are produced by using the suitable similarity transformation, and Optimal Auxiliary Functions Method (OAFM) is employed to solve them. In the ongoing investigation, the main results are decreasing behavior of temperature profile for the thermal relaxation parameter and elastic deformation parameter, while the reverse effect is noticed while increasing the Weissenberg number and porosity parameter. Our findings reveal significant insights into the fluid dynamics and heat transfer characteristics. Integrating the Cattaneo–Christov heat flux model and elastic deformation analysis in Walters'B viscoelastic fluid flow having its importance in polymer processing, aerospace engineering and waste treatment systems.

Numerical and experimental analysis of the sinusoidal heat flux source of heat transfer in laminar flow in a tube for single phase flow

Numerical and experimental analysis of the sinusoidal heat flux source of heat transfer in laminar flow in a tube for single phase flow

Computational assessment of flow and heat transfer characteristics through Cu + Al2O3 + TiO2 ternary hybrid nanomaterial host-water with shape effect

ABSTRACT Solar energy stands out as a vital source of thermal power derived from the sun. Its capacity finds applications across various technological domains, including photovoltaic panels, solar vehicles, solar lighting infrastructure, and solar water pumps. The contemporary landscape emphasizes the integration of solar energy in industries, notably exemplified by the prevalence of solar-powered charging stations. This article proposes a new perspective on heat transport analysis, incorporating the shape effect on the ternary hybrid nanofluid model along with considerations of thermal radiation, Cattaneo–Christov heat flux factor, heat source, and sink. For the evaluation, three differently shaped ternary hybrid nanoparticles are taken into account including platelet-shaped Cu , cylindrical-shaped A l 2 O 3 , and disc-shaped Ti O 2 . Through boundary layer approximations, the contributions of radiation, heat source, and sink variables are implemented into the regulating equations. The redesigned ordinary differential equations are numerically solved employing the NDSolve method after treating similarity variables. In the case of physical quantities, multiple linear regression is introduced to discover solutions for the flow elements. Augmentation in the momentum of dissimilarly shaped Cu , A l 2 O 3 and Ti O 2 nanoparticles enhance the velocity of ternary hybrid nanofluid flow more than that of spherical-shaped nanoparticles. The significant heat transfer is observed in mono, hybrid and ternary nanofluids with the existence of radiation and heat source phenomena. The multiple linear regression precisely forecasted the physical quantities with the error 10 − 3 . An application of a ternary hybrid nanofluid in a solar powered charging station can efficiently perform and successfully address an energy crisis by exhibiting an acceptable amount of power. This capability contributes to the reliable charging of electronic devices. Also, the machine learning technique can reliably and accurately perform the heat transfer analysis.

Experimental research on cooling performances of radial expanding-channeled heat sinks applied for multiple heat sources

Intrinsic two-phase flow instability using multiple parallel boiling channels hinders the actual implementation of flow boiling cooling techniques in high heat flux and multiple heat source applications. Recently, we proposed a radial expanding-channeled heat sink (ECHS) to realize a high two-phase flow stability under extreme conditions. In the present work, the cooling performances of two heat sinks connected in series or in parallel were investigated with the heat load adjusted individually. The results indicated that when two ECHS were connected in parallel, the inlet flowrate was evenly distributed into the two heat sinks, and their heat transfer performance was identical. At a sudden change in the heat load of one path, the flowrate of the other heat sink may change by 10% to 30% without inducing flow instability or heat deterioration. The thermal resistance for both heat sinks was lower than 0.025 °C/W, and no instability or dry-out was observed as long as the initial flowrate was larger than 0.28 kg/min. With the proposed ECHS, multiple heat sources such as central processing unit, server, rack, etc. can be connected in series or in parallel to construct an integrated cooling system for large-scale data center applications.

Three-dimensional transient CFD modeling of multiple finned aluminum foam heat sinks in a horizontal channel

Finned metal foam heat sinks are well-known because of their excellent performance in cooling of powered electronics. In this study, three-dimensional transient numerical simulations of finned aluminum foam heat sinks in a forced convection of air were carried out using commercial COMSOL. The geometry under consideration consists of an array of finned aluminum foam heat sinks mounted on heater blocks and placed on a plate in a horizontal channel. Heat sink aluminum foam regions were considered as porous media with a local non-equilibrium thermal model to evaluate thermal characteristics, while the Forchheimer-Brinkman extended Darcy model is considered for the flow analysis. Our main concern in the present study is to evaluate the transient thermal–hydraulic behavior and the cooling performance under constant flux heat sources while varying the Reynolds number and variable morphological parameters of the aluminum foam, i.e., porosity (ε) varied from 0.85 to 0.95. The thermal performance ratio and the average Nusselt number of the finned aluminum foam heat sinks are 23.14% and 30%, respectively, larger than the finned aluminum heat sinks. As the Reynolds number increases, the thermal characteristics are enhanced, and the pressure drop is increased. An increase in porosity causes a reduction in heat transfer rate and an elevation of pressure drop.

The Macolod Corridor (Philippines)–A passive rift compensated by ponded magmas?

The Macolod Corridor is a zone of active volcanism situated at the junction of different tectonic elements (i.e., arc-continent collision, arc volcanism, bounded by two major faults). Contentions regarding its formation arise due to its tectonic characteristic and the lack of subsurface data in the region. Its shallow and deep crustal configuration is investigated by processing novel ground gravity data and existing gravity datasets. Regional-residual separation and forward and inverse modeling of the gravity data indicate the existence of high-density bodies. These might reveal the shallow and deep magmatic bodies in the area. The shallow subsurface features reflect the trends of the reported fractures in the area, implying structurally controlled volcanic complexes. Three forward gravity models are created to evaluate the crustal structure of the region: 1) thinned arc crust, 2) normal arc crust, and 3) normal arc crust with an anomalous zone of high-density material. The forward response of the third model has the lowest error. The anomalous zone identified from the model is characterized by high-density (low-velocity and high temperature) material, possibly due to a shallower mantle material or ponded partially molten magmatic materials. The geophysical signature of the shallow crust exhibits extension-related features, as shown by the trends of the shallow high-density bodies. However, the deep crust does not indicate crustal thinning typical of extensional settings; instead, the model shows a relatively thick crust (∼34 km). This phenomenon is reconciled by the compensation of ponded magmatic materials, which act as the source of volcanism and elevated heat flux in the Macolod Corridor. This ponded material is attributed to subduction-related magmatism. The eventual crustal extension led to the formation of the arc-perpendicular volcanism in the Macolod Corridor by tapping the ponded materials in the lower crust.

CFD Analysis of the Forced Airflow and Temperature Distribution in the Air-Conditioned Operator’s Cabin of the Stationary Rock Breaker in Underground Mine under Increasing Heat Flux

The exploitation of natural resources is associated with many natural hazards. Currently, the copper ore deposits exploited in Polish mines are located at a depth of about 1200 m below the surface. The primary temperature of the rocks in the exploited areas reaches 48 ∘C, which constitutes a major source of heat flux to the mine air. However, another important source of heat is the machine plant, which mainly consists of machines powered by diesel engines. Following the results of in situ measurements, boundary conditions for a simulation were determined and a geometric model of the cabin was created. Furthermore, an average human model was created, whose radiative heat transfer was included in the analysis. Three cases were studied: the first covering the current state of thermal conditions, based on the measurement results, and two cases of forecast conditions. In the second case, the temperature of the conditioned air was determined, and in the third, the flow velocity required to ensure thermal comfort was found. The results of the simulation indicated that for the microclimatic conditions established based on the measurements (ambient air temperature in the excavation 35.0 ∘C, air-conditioned airflow 2.4 × 10−2 m3/s, and temperature 10.0 ∘C), the temperature of the air inside the air-conditioned operator’s cabin would be 20.4 ∘C. Based on the personal mean vote (PMV) index, it was concluded that the thermal sensation would range from neutral to slightly cool, which confirmed the legitimacy of the actions taken to reduce the adverse impact of the microclimatic conditions on workers in the workplace. However, for the case of predicted conditions of enhanced heat flux from strata and machinery, resulting in an average ambient temperature increased to 38.0 ∘C, it would be necessary to lower the temperature of air from the air conditioner to 8.00 ∘C or increase the flow rate to 3.14 × 10−2 m3/s to maintain thermal comfort at the same level of PMV index.

Flow and radiation modeling over a Martian entry vehicle

The high-temperature shock layer around re-entry vehicles strongly emits radiation through atomic lines and molecular bands. Radiative heat transfer strongly affects boundary layer flow and heat transfer. A novel spectral model based on k-distribution is implemented and coupled with a hypersonic flow solver in OpenFOAM to simulate heat transfer over a Martian entry vehicle. The Navier-Stokes equations with finite rate chemistry are used to model hypersonic chemically reacting flows. The convective terms in the governing equations are treated with various flux schemes (HLL, AUSM+, Kurganov, and Tadmor). The non-gray radiative properties of shock layer gases were modeled with the Emission-weighted Full Spectrum k-distribution (EFSK) method. The Radiative Transfer Equation (RTE) is solved with the P1 radiative solver to calculate the wall heat flux and radiative heat source term. At a high Mach number, the radiative heat flux is dominant compared to the convective heat flux. The numerical results for Mach number 26 are compared with published data and are found to be in good agreement. All the flux schemes provided results in close agreement, with minor differences, especially near the wall for the AUSM+ flux scheme.

A wide-band based weighted-sum-of-gray-gases model for participating media: Application to [formula omitted]-[formula omitted] mixtures with or without soot

The presence of participating gases and soot in combustion processes often makes the thermal radiation the main mechanism of heat transfer due to the elevated temperatures involved. The accurate solution of the radiative transfer equation (RTE) through the line-by-line (LBL) integration in engineering applications is in general still impracticable due to the high computational effort required to account for the millions of spectral lines that characterize the absorption coefficient of a gas. Global spectral models, such as the weighted-sum-of-gray-gases (WSGG) model, are attempts to replace the LBL integration with low computational cost and satisfactory accuracy. In the present study, an improvement of the WSGG model through a partition of the spectrum is proposed. The spectrum is divided into a set of ranges in which the standard methodology of the WSGG model is applied to determine the gray gases coefficients in these bands. This is the central aspect of what is named here a wide-band based WSGG (WBW) model, which consists firstly of determining the emittance of each band from the HITEMP 2010 database, then obtaining the pressure-absorption coefficients and the temperature-dependent coefficients. The total radiative heat flux and radiative heat source are obtained by the summation of the contribution of each band individually. For soot, a gray gas approach is considered for each band via Planck-mean absorption coefficients. A set of 1D problems consisting of two infinite parallel black walls, filled with a non-isothermal and non-homogeneous gaseous mixture of water vapor, carbon dioxide and soot, is solved. The results show that, especially in cases where the thermal radiation of soot is dominant, the maximum deviations obtained with the proposed method in relation to the LBL solution reduce by almost three times compared to other global WSGG models in the literature, in addition to decreasing by 40% the number of equations that need to be solved.

Experimental study on plasma generated by a tapered coaxial accelerator and its damage effects on a tungsten target at different angles

Plasma wall interaction inevitably occurs during the operation of tokamaks. The coaxial gun device has low operation cost and the parameters of plasma produced by the gun are close to those of type I edge localized mode (ELM); therefore, the coaxial gun is suitable in simulation experiments as a heat flux source of transient events such as type I ELM under the condition of H-mode in the International Thermonuclear Experimental Reactor. In this paper, the plasma generated by the discharge of a tapered coaxial accelerator thermal shock on a tungsten target is used to simulate the damage effect of the divertor. The plasma parameters are measured in the experiment. The velocity of the plasma is 41.7 km s−1, and the kinetic energy of a single hydrogen ion is 9.2 eV. The energy density at the center of the plasma can reach 1.5 MJ m−2, and the density can reach about 2.78 × 1015 cm−3. The reflection of plasma in the process of exposure at different angles is observed. It is observed that droplets of millimeter size splash from the target. Traces of liquid flow are observed on the surface of the target, which shows that there is a melting process on the surface of the target. The mass loss of the target is of the order of milligrams after 20 pulses. The ablation and residual stress of the target surface both decrease with a decrease in the angle. This is because the accumulated energy per unit area of the target surface decreases with a decrease in the angle. The results of the simulation experiment help us to understand the working state around the divertor target in tokamak devices.

On prescribed thermal distributions of bioconvection Williamson nanofluid transportion due to an extending sheet with non-Fourier flux and radiation

Bio-convection, Cattaneo-Christov, and thermal radiation fluxes are accompanied by mixed convection flow of Williamson nano-fluids. The dynamics of the fluid occur due to an extendable surface with two thermal boundary constraints; the prescribed heat flux and surface temperature. The objective of this exploration pertains to effective and efficient thermal distributions. Theoretical layout is formulated in the form of a partial differential format. In order to attain the numerical resolution of this non-linear formulation, similarity transforms are employed to modify them into ordinary differential forms. The computational code for the Runga-Kutta procedure is developed in a MATLAB script. The temperature of fluids enhances with mounting strength of prescribed heat flux, thermophoresis, thermal radiation, magnetic field, Brownian motion and heat source but it descends against thermal relaxation time. The speed of fluids undergoes retardation against exceeding inputs of Williamson parameter λ, parameters of porosity, and magnetic body force. The range of distinct parameters while computing graphically is taken as , , , , , , , , , , , , , , and .

Conductive Heat Transfer in Materials under Intense Heat Flows

The paper presents the solution of the spatial transient problem of the impact of a moving heat flux source induced by the laser radiation on the surface of a half-space using the superposition principle and the method of transient functions. The hyperbolic equation of transient thermal conductivity accounting for the relaxation time is used to model the laser heating process. It is assumed that the heat flux is distributed symmetrically with respect to the center of the heating spot. The combined numerical and analytical algorithm has been developed and implemented, which allows one to determine the temperature distribution both on the surface and on the depth of the half-space. In this case, the principle of superposition is used with the use of a special symmetric Gaussian distribution to describe the model of a source of high-intensity heat flux. The use of such a symmetric distribution made it possible to calculate the integrals over the spatial variables analytically. The results of the work could be used to estimate the contribution of the conductive component in the overall heat transfer of materials exposed to intense heat flows (laser surface treatment, laser additive technologies, streamlining and heating of materials by high-enthalpy gases, etc.).

Mathematical analysis about influence of Lorentz force and interfacial nano layers on nanofluids flow through orthogonal porous surfaces with injection of SWCNTs

The effort is presented to numerical examine the flow behavior of non-Newtonian fluid through orthogonal porous surfaces. A two-phase model of nanofluids simulations is considered which represents speculative features of materials that are obliged in biomechanics,lubricantsformation,polymer solution, suspension, etc. The mechanism of interfacial nano layer at surfaces is deliberated through thermal conductivity. Numerical sculpting of non-Newtonian CNT fluid including the impact of chemical reaction, heat flux and mass transfer source is manifested in the form of partial differential equations. Similarity variables are capitalized to transmute governing modeled conservation laws into ordinary non-dimensional expressions. Assessment of flow attributing profiles is disclosed by implementing the Runge-Kutta procedure in collaboration with the shooting method. The numerical stability with convergence rate is also discussed here. Graphical visualization and numerical data about surface drag coefficients and heat and mass transfer rates are also presented. The effect of expansion and contraction (−2 <α < 2) on boundary layer thickness is discussed in detail. The rate of heat transfer increases with the increase of boundary layer thickness in the presence of single-wall carbon nanotubes (SWCNT) is observed. An increase in heat transfer profile due to the presence of SWCNTs with the variation of thickness and radius of sustainable particles is perceived. The nano layer thickness is a significant effect related to the heat transfer rate.

Experimental study on dynamic behavior of mechanically pumped two-phase loop with a novel accumulator in simulated space environment

Mechanically pumped two-phase loop (MPTL) which is a prominent two-phase heat transfer technology presents a promising prospect in thermal control for space payload. However, transient behavior of MPTL caused by phase-change and heat sources load-on/off in simulated space environment is rarely reported. In the present study, one MPTL setup was designed and constructed, and experimentally studied. Particularly, a novel two-phase thermally-controlled accumulator integrated with passive cooling measure and three capillary structures was designed as the temperature-control device. Dynamic behavior of the start-up, temperature control, and temperature adjustment were monitored; meanwhile, thermodynamic behavior within the proposed accumulator, the operating behavior as well as the heat and mass transfer behavior between the main loop and the accumulator were revealed. The results show that the fluid management function of the capillary structures for the novel accumulator is verified. The working point of the MPTL system can be adjusted by changing the temperature control point of the accumulator and it is little influenced by external heat flux and heat sources on/off. Pressure-drop oscillations which are manifested as fluctuations of temperature and pressure can be observed after phase changing due to the compressible volume within the accumulator and the negative-slope portion of the internal pressure.

Experimental determination of effective thermal properties of soils in situ

The report presents a description of an attempt to create a measuring device for determining the thermal properties of soils in situ (in situ). The method of determining soils thermal properties consists in creating by linear source of constant radial heat flux and measuring temperature by two electrical cable (wich is parallel to the heater and locate at distances of 5 (1st cable) and 10 (2 th cable) cm from the heater) with 7 soldered temperature sensors with 20 cm from each other. The measurements were taken on November 1, 2021 before the onset of frost and after frost on April 11, 12, 2022. The thermal state of the soil in a certain place and time is characterized by the ambient temperature, the presence of solar radiation, the ability of the soil to absorb solar radiation, the presence of sources/sinks of heat, and the ability of the soil to absorb and transfer heat, which in the mathematical description corresponds to its thermal properties, which we want to determine.

Estimation of anthropogenic heat release in Mexico City

The urban heat island (UHI) is a phenomenon that appears in cities due to the alteration of the energy balance caused by the drastic land use change. A factor that can contribute to its development is the energy generated by the city inhabitants, or the anthropogenic heat flux (QF). Therefore, the determination of this component can improve the predictability of UHI development and variability. The objective of this work was to estimate the main sources of anthropogenic heat flux, based on a vehicle classification (taxis, cars, minibuses and buses), surveys of electricity consumption and population density in Mexico City. The anthropogenic heat determination is based on a simple distribution of heat generated by vehicles, buildings and people. Vehicle classification was made through video analysis and the vehicle flow was also accounted for with sensors at the road level, within a radius of 1 km. The consumer surveys were applied to businesses and homes, and with the support of basic geostatistical areas the population density was determined. The analysis showed that the highest heat emission occurs from 15:00 to 21:00 h. This heat flux in average was not significant when compared to net radiation. However, anthropogenic heat flux generation in dense areas of Mexico City, can exceed 75 W·m−2 for certain times of the day, while the inventory carried out QF averaged 24.7 W·m−2 at San Agustin, in the historical center. With the obtained results, also a standard car was idealized, and the electricity consumption profiles of some sectors were generated, which will allow obtaining the heat flux more easily and quickly. According to the results, it is advisable to integrate the anthropogenic heat flux component into the energy balance for future studies of the UHI.

Analytical Model of Heating an Isotropic Half-Space by a Moving Laser Source with a Gaussian Distribution

This study presents the solution of the transient spatial problem of the impact of a moving source of heat flux induced by laser radiation on the surface of a half-space using the superposition principle and the method of transient functions. The solution is based on the Green’s function method, according to which the influence function of a surface-concentrated heat source is found at the first stage. The influence function has axial symmetry and the problem of finding the influence function is axisymmetric. To find the Green’s function, Laplace and Fourier integral transforms are used. The novelty of the obtained analytical solution is that the heat transfer at the free surface of the half-space is taken into account. The Green’s function that was obtained is used to construct an analytical solution to the moving heat-source problem in the integral form. The kernel of the advising integral operator is the constructed Green’s function. The Gaussian distribution is used to calculate integrals on spatial variables analytically. Gaussian law models the distribution of heat flux in the laser beam. As a result, the corresponding integrals on the spatial variables can be calculated analytically. A convenient formula that allows one to study the non-stationary temperature distribution when the heat source moves along arbitrary trajectories is obtained. A numerical, analytical algorithm has been developed and implemented that allows one to determine temperature distribution both on the surface and on the depth of a half-space. For verification purposes, the results were compared with the solution obtained using FEM.