Transient Heat Flux Research Articles

Numerical analysis of fatigue behaviors for tungsten armor of ITER divertor

Abstract Thermal responses and fatigue behaviors of the tungsten armor of monoblock divertor under steady-state and transient high heat flux (HHF) loads as well as the coupling of the two were simulated and analyzed by the finite element method. It was found that, under the action of thermal cycle loads, the earliest fatigue failure area of tungsten armor is on the surface, and with the increasing of HHF load, the damage area of the armor extends also, while the transient load only causes damage on surface of the armor. The fatigue lifetime of tungsten armor decreases rapidly with the increase of load, whether under steady-state load or transient load. Different transient load under the same steady-state load is researched. When two loads are coupled, the fatigue life is shorter as the load value is high, while the fatigue lifetime is basically unchanged when the transient load is the same under different steady-state loads, that is to say, the steady-state load has little influence on the results, and the transient load during ELMs is the leading factor for the fatigue lifetime.

Decadal coupling between storm tracks and sea surface temperature in the Southern Hemisphere midlatitudes

The relationships between the seasonal mean storm-track anomalies and sea surface temperature anomalies (SSTAs) in the midlatitude Southern Hemisphere (SH) on the decadal time scale are investigated using the lagged maximum covariance analysis (MCA). It shows that the coupling between storm-track anomalies and SSTAs is most prominent in austral summer (January–March, JFM). Firstly, large cold SSTAs in the western South Indian Ocean (SIO), corresponding to the strengthened SST front on the equator side, substantially intensify the storm-track activity manifested by the increased low-level poleward transient eddy heat flux over the entire SH. The coherent intensification of the atmospheric baroclinicity and the subtropical jet associated with such strengthened SST front provides baroclinic energy for the growth of synoptic eddies. Further, the intensified storm-track activity induces large cold SSTAs in the South Atlantic (SA), the SIO and the subtropical South Pacific (SP), primarily via anomalous net surface heat fluxes. The mean SST advection by the anomalous Ekman current also contributes to the cold SSTAs in the SA, which is related to the anomalous westerlies induced by the anomalous storm-track activity.

Numerical Analysis of Bowing Phenomenon Due to Thermal Stresses in Marble Slabs.

Bowing is a pathology known by the deformation experienced in some external covering systems in ornamental stones, especially in marble, and thermal action is one of the key factors that lead to this degradation. Previous studies presented remarkable contributions about the mechanical behavior of bowing but they were based on classical beam’s theory and improper assumptions might mislead the evaluation of internal stresses. This study proposes to evaluate internal stresses in bowing due to thermal loading considering the true deformed shape in continuum media. Finite displacement concepts are proposed to calculate stress-strain relationship and comparison with linear elastic theory is also addressed. Internal stresses not predictable in the Euler-Bernoulli beam were found in parametric analyses. Moreover, the numerical analysis accomplished in this paper indicates that transient heat flux should induce higher stresses than just considering higher gradients of temperature in steady flux which could explain the larger decohesion through width in bowing tests.

Climatological patterns of subseasonal eddy flux transfer based on the co‐spectral analysis over the Indian region and the derivation of an index of eddy transfer for operational tracking

AbstractThe heat and momentum flux transfer by transient eddies from the extratropical to the tropical (E2T) region causes a significant variation of weather and climate in the tropical region. Such transports also cause a regional departure from zonally symmetric large scale circulation patterns caused by the Hadley type transports. During boreal summer monsoon season, the zonally symmetric Hadley type circulation is typically considered in theoretical as well as modelling studies. The current study introduces a method based on the calculation of the E‐vector components and co‐spectra analysis to diagnose the zonally asymmetric climatological patterns of E2T transport and its subseasonal variability. The spectral analysis identifies the climatological as well as low and high frequency patterns of the transient eddy heat and momentum flux transfer over the Indian region and compares the result with traditional Eliassen‐Palm (EP) Flux based stationary eddy patterns. The study identifies the zonal, seasonal, and vertical asymmetries in the transport of transient eddy heat and momentum flux. The study also clearly categorizes the seasonality and frequency dependence of northeast to the southwest tilt of transient eddies transporting momentum and heat flux. Based on the climatological patterns, the wavelet transform approach is used to study the subseasonal variability of the eddy transport indices. We define a set of indices, which identify the subseasonal temporal variation of the E2T transfer mechanism. These indices could be used to operationally track the E2T eddy flux transfer both in observation and in forecast models.

Active Radiative Liquid Lithium Divertor for Handling Transient High Heat Flux Events

The extreme heat flux anticipated in fusion reactor divertor plasma facing components (PFCs) is perhaps the most challenging technology issue for fusion energy development. Most divertor PFCs are designed based on the maximum steady-state operational limits. Application of lithium (Li) in NSTX resulted in improved H-mode confinement, H-mode power threshold reduction, and reduction in the divertor peak heat flux while maintaining essentially Li-free core plasma operation even during H-modes. These promising Li results in NSTX and related modeling calculations motivated the passive and active radiative liquid lithium divertor concepts (RLLD and ARLLD) (Ono et al. in Nucl Fusion 53:113030, 2013; Fusion Eng Des 89:2838, 2014). This radiative process has the desired effect of spreading the localized divertor heat load to the rest of the divertor chamber wall surfaces, facilitating divertor heat removal with relatively small amount of lithium ~ few moles/s to handle the expected steady-state high divertor heat load. However, in addition to the high steady-state heat flux, the fusion reactor divertor PFCs could also experience significant transient heat flux such as ELMs and/or other magnetic reconnection events which can deposit large transient heat flux onto the divertor PFCs. If unprotected, it could damage the divertor PFC surfaces which could lead to a highly undesirable unplanned shutdown for PFC repair and/or replacement. In this paper, we explore feasibility of LLD and ARLLD concepts in handling such transient heat flux to protect the divertor PFCs from the extreme transient heat flux while maintaining the normal plasma operations. We also suggest a possible implementation technique using inductive pellet injector for the reactor PFC protection from transient heat flux which can be tested on NSTX-U.

Experimental study of transient liquid nitrogen jet impingement boiling on concrete surface using inverse conduction problem algorithm

There is a shortage of research in the literature on the evaporation rate of the liquid pool under instantaneous conditions, which is important for the risk assessment of the liquid hazard leakage accidents. Previous perfect thermal contact model and typical pool boiling could not completely represent the boiling process in the spreading liquid pool. In this work, the spreading liquid pool was characterized as a free-surface jet impingement on the plate surface. Liquid nitrogen (LN2) was adopted to simulate liquid hydrogen (LH2) and liquid natural gas (LNG) leakage, and a series of transient jet impingement boiling experiments were conducted on the concrete surface. Liquid jetted upon the stagnation region, and the transient heat flux from the concrete surface was estimated by transfer function method.The boiling curve obtained in the present study appears significantly different from the typical pool boiling, which indicate that large deviation will occur when the typical pool boiling correlations are used for instantaneous leakage, at least for the stagnation region. A point between the onset of nucleate boiling point and fully developed nucleate boiling point was recognized, which represents the turn of forced convection dominated to nucleate boiling dominated. It is confirmed that the heat transfer was enhanced with increased jet height z, and the peak values were found at z/d = 8.

A mechanistic model for nucleate pool boiling including the effect of bubble coalescence on area fractions

A mechanistic model that includes the effect of the bubble coalescence on nucleate pool boiling heat transfer is developed through experimental and theoretical investigations. Transient temperature and heat flux distributions on the boiling surface are obtained using a high-speed infrared imaging technique. According to the temperature and heat flux distributions, the boiling surface is classified into three regions: natural convection, quenching, and evaporation regions. By observing how the heat flux on each region and the corresponding area fraction change as the bubble coalescence occurs, the effect of the bubble coalescence on nucleate pool boiling is investigated. It is found that the bubble coalescence does not affect the heat fluxes on the three regions but affects the area fractions: As the bubble coalescence occurs, the rates of increase in quenching and evaporation area fractions with respect to the wall superheat decrease, while the natural convection area fraction remains the same. By accounting for the effect of the bubble coalescence on quenching and evaporation area fractions, a new correlation of the boiling heat flux is developed and presented. To validate the proposed model, boiling curves for saturated water and FC-72 are reproduced and compared to experimental data. The most distinguishing feature of the model is that it accurately predicts the rate of change of the heat flux with respect to the wall superheat as well as the location of the inflection point at which the slope of the boiling curve begins to decrease. As a result, the error between the reproduced boiling curve and experimental data is reduced by 94% compared to the previous model, which does not include the effect of the bubble coalescence for both water and FC-72.

Quasi-steady and transient study of heat transfer during sub-cooled flow boiling in a small aspect ratio microchannel

Owing to the transient nature of microchannel flow-boiling, gaining an in-depth understanding of the associated trends in time-averaged heat transfer variables as well as mechanisms of heat transfer is quite challenging. This work studies sub-cooled flow-boiling of de-ionized water in a microchannel. The micro-channel heights studied are 0.14, 0.28 and 0.42 mm while the tested mass fluxes range from 200 to 1000 kg/(m2s). Slug flow regime is observed under most of the tested conditions. Transient wetted surface heat flux and temperature as well as heat transfer coefficient are evaluated from the wall temperature data captured at a high data-logging frequency (synchronously with flow-visualizations). Heat transfer mechanisms as well as the trends observed in plots associated with time-averaged heat transfer variables are explained from the perspective of transient data correlated to the observed flow-boiling phenomena. Thin-film evaporation emerges as the prominent heat transfer mechanism. Two-way coupling between transient heat transfer variables and the boiling phenomena is evident.

Flow Structure and Heat Flux Distribution of a Backswept Fin Induced Flow Field at M = 6

Transient flow structures and surface heat flux distribution of the interfered flow field induced by a backswept fin were obtained by Nano-tracer-based Planar Laser Scattering and temperature sensitive paints under M = 6. Meanwhile, the Reynolds-averaged Navier–Stokes equations with k-ω Shear-Stress Transport turbulence model were solved to simulate the flow field. The numerical results were compared and analyzed with the experimental results. Typical flow structures in interference areas of the swept fin were observed in experiment, including the detached bow shock wave, separation zone, thin boundary layer around the fin and horseshoe vortex, etc. The numerical results were in good agreement with flow visualization images. For heat flux distribution, the experiment observed the high heat flux region near the side of the fin leading edge caused by separated flow and the region with heat flux increase caused by bow shock. The numerical results of the heat flux caused by bow shock were pretty good, but the results of the high heat flux region near leading edge due to reattachment had much difference with the experimental results, which still need further improvement.

Performance analysis of coaxial thermocouples for heat flux measurement of an aerodynamic model on shock tube facility

The K, E and J-types of coaxial thermo-sensors have been used to measure surface heat flux at the nose, spatial position-1 and spatial position-2 over an aerodynamic model subjected to a homemade shock tube flow facility. The high pressure shock has been applied to the aerodynamic model for 60 ms subsequently their variation in transient temperatures have been recorded for four experimental shots. The surface heat flux has been predicted from the transient temperatures by using one-dimensional heat transfer theory in a semi-infinite solid body. The average errors have been found between four experiments for transient temperature and surface heat flux are less than ±0.2% and ±4% respectively. A two-dimensional numerical model has been developed by using commercial software Ansys to solve the high enthalpy flow facility as exists in shock tube arrangement to validate the experimental results. The accuracy found in transient temperatures and surface heat fluxes are ±0.51% and ±0.633%. These coaxial thermo-sensors will help the design and development of aerodynamic vehicles in terms of measurement of heating rate on different inclined surfaces, missile nose, hypersonic aircraft technology, gun barrel test, advanced production technology, engine measurements etc.

Experimental on thermal performance of bridge deck with hydronic heating system

Hydronic heating systems with geothermal heat exchangers are one of the innovative methods for bridge deck deicing in winter, which avoids infrastructure corrosion and environmental pollution caused by chemical methods. This paper focused on field tests of the thermal performance of a bridge deck with a hydronic heating system under heating conditions. The inlet fluid temperatures were kept constant to study the transient heat flux through outlet fluid temperatures under different ambient temperature conditions. Three different inlet fluid temperatures of 30.5 °C, 35.5 °C, and 41.0 °C were considered in the field test. The objective of this paper is to study the influences of the air temperature, slab temperature, and inlet fluid temperature on the heat exchange flux and the thermally induced stresses due to heating. The results indicate that the inlet fluid temperature should be controlled above 2.3 times the absolute value of the air temperature to keep the slab surface temperature above 0 °C when the air temperature is below 0 °C. The thermally induced stresses caused by operating the system are smaller than 5% of the strength of the concrete, which are negligible.

Flow transient critical heat flux in a narrow rectangular channel under downward flow

Flow transient critical heat flux (CHF) in a narrow rectangular channel has not been studied adequately, and the same is currently predicted using steady-state CHF correlations. To address this gap in research, experiments were performed in this study to investigate the flow transient CHF in a narrow rectangular channel of a research reactor under downward flow. The experiments cover a wide range of flow conditions, including mass fluxes in the 950–4,700 kg/m2s range, inlet temperature of 37 °C, outlet pressure of 170 kPa, and transient time parameters in the 8.7–485 range. Evaluation of previous correlations applicable to flow transient CHF in a tube revealed they could not reasonably predict experimental data obtained in this study. Consequently, the present experimental data and Celata R-12 database were used to deduce a new correlation. The CHF ratio (the ratio of transient CHF to steady-state CHF under same mass flux) was observed to increase up to 1.6 for water and 2.7 for R-12 under the flow transient condition. As observed, the proposed correlation is applicable to both downward flow of water in a narrow rectangular channel and upward flow of R-12 in a tube. The correlation shows average and root-mean-square error values 0.04% and 3.46%, respectively, under a flow reduction rate of 0.1–2.5 s−1.

A building unit decomposition model for energy leakage by infrared thermography image analysis

A quantitative energy leakage model was developed based on the thermography image data measured for both external and internal building surfaces. The infrared thermography images of both surfaces of doors, windows, and walls of an office building in the Hengqin Campus of University of Macao were taken at various times in a day for four seasons. The transient heat flux for sample units were obtained based on measurements of the seasonal transient local temperature differences and calculations of the effective thermal conductivity from the multiple-layer porous medium conduction model. Effects of construction unit types, orientations, and seasons were quantitatively investigated with unit transient orientation index factors. The corresponding electric energy consumption was calculated based on the air conditioning system coefficient of performance of heat pump and refrigerator cycles for different seasons. The model was validated by comparing to the electric meter records of energy consumption of the air conditioning system. The uncertainties of the predicted total building energy leakage are about 14.7%, 12.8%, 12.4%, and 15.8% for the four seasons, respectively. The differences between the predicted electric consumption and meter values are less than 13.4% and 5.4% for summer and winter, respectively. The typical daily thermal energy leakage value in winter is the highest among the four seasons. However, the daily electric energy consumption by the air conditioning system in summer and autumn is higher than that in winter. The present decomposition model for energy leakage is expected to provide a practical tool for quantitative analysis of energy leakage of buildings.

Inverse Estimation of Heat Transfer Coefficient and Reference Temperature in Jet Impingement

Abstract Applications of impinging jets are wide-ranging from cooling to heating in industrial as well as domestic field. Most of the reported heat transfer distribution data to and from impinging jets have been found from steady-state measurements. This study utilizes the solution to three-dimensional (3D) inverse heat conduction problem to estimate transient temperatures on the impingement side. Then, the temperature gradient is determined near the impingement wall (∼0.01 mm inside) with which transient heat flux is estimated on the impingement side. Instead of steady-state values, transient heat flux and corresponding wall temperatures are utilized in a thin foil technique to find out heat transfer coefficient and reference temperature simultaneously. The scope of the present technique is examined through its application to impinging jets with various configurations such as laminar jet, turbulent jet, hot jet, cold jet, and multiple jets. In all cases, estimations are reasonably close. The application of this inverse technique can be extended to any configuration of jet impingement irrespective of geometry of nozzle (circular/rectangular), the orientation of nozzle (orthogonal/inclined), the temperature of a jet (hot/cold), Reynolds numbers (laminar/turbulent), the nozzle-to-plate spacing (any Z/d), and roughness of the plate surface. The effect of plate thickness on the accuracy of the present technique is also studied. Up to 5 mm thick plates can be used in impinging jet applications without worrying much on accuracy. The use of the present technique significantly reduces the experimental cost and time since it works on transient data of just a few seconds.

Thermal shock resistance of tungsten with various deformation degrees under transient high heat flux

Tungsten (W) is considered as the most promising plasma facing material in fusion device, which will be exposed to steady and transient heat loads. Usually, the deformation degree of W influences its thermal shock properties. So we evaluated the thermal shock resistance of rolled pure tungsten (PW) with 60%, 90% deformation degrees and W-1.0wt%La2O3 (WL10) with 52%, 88% deformation degrees using electron beam at an absorbed power density of 0.22 GW m−2 for 5 ms and further discussed the relationship between the thermal shock resistance and microstructures, thermal-mechanical properties. The absorbed beam current (30 mA), electron beam acceleration voltage (120 kV) and loaded area (4 × 4 mm2) is used to estimate the absorbed power density. The results indicated that PW-90%, LW-88% exhibited smaller grain size, higher relative density, microhardness but lower strength, thermal conductivity compared to PW-60%, LW-52%. The cracking threshold was <0.22 GW m−2 for PW-60%, LW-52% and >0.22 GW m−2 for PW-90%, LW-88%. Elliptic left pores in PW-60% and LW-52% aggravated the effect of stress concentration cracking during the transient high heat flux test and decreased the cracking threshold altough they exhibited high strength and thermal conductivity.

Experimental Investigation of Heat Flux Characteristics on the Thermally Induced Vibration of a Slender Thin-Walled Beam

The spacecraft with large flexible space structures may be subject to the thermally induced vibration (TIV) due to the rapidly changed solar heat flux when it enters and leaves the eclipse, which would lead to certain spacecraft failure. This paper reports a laboratory experiment that aims to study the impact of transient characteristics of heat flux on the ground experiment of TIV. In the experiments on the TIV of a slender thin-walled beam, two different methods of providing transient heat flux were considered, and the process of entering and leaving eclipse was simulated, respectively. The experimental results demonstrate that different transient characteristics of heat flux will have large impact on the TIV of the specimen, and the ideal theoretical estimation of thermal characteristic time has limitations in practical engineering. In addition, it is found that the traditional way of simulating solar heat flux by turning on/off infrared heat lamps is not suitable for the TIV ground experiment. Instead, a transient heat flux simulation method by moving the baffle is recommended.

Reprocessed waste sunflower cooking oil as quenchant for heat treatment

The growing concern to minimize the use of petroleum derived mineral oil in heat treatment industries has led to the search for alternative eco-friendly quenchants. Although vegetable oils seem to be a viable option, the higher cost and inferior thermal and oxidation stability have limited their application in the heat treatment industry. The reuse of waste cooking oils for industrial heat treatment would not only make quenchants cost-efficient but also environment friendly. In this study, the cooling performance of waste sunflower cooking oil was assessed and compared with that of unused sunflower cooking and mineral oils. The waste sunflower oil was made suitable for quenching by cleaning and chemical treatment. The experiment to assess the suitability of reprocessed oil for quenching was conducted using an Inconel 600 standard probe according to ISO 9950 and ASTM D 6200 standards. The thermal history acquired while quenching of the probe was used to estimate the surface heat flux transients. The results indicated that the chemically treated waste sunflower cooking oil had a higher cooling performance than that of unused sunflower and the mineral oils. A good agreement was found between the heat flux transients and hardness data obtained with the quenched AISI 4140 steel probe. The simulation of temperature and hardness distribution indicated more uniformity along the length of the probe indicating more uniform cooling with chemically treated waste sunflower cooking oil.

The effect of using nanofluid flow into a porous channel in the CPVT under transient solar heat flux based on energy and exergy analysis

Concentrator photovoltaic thermal system is one of the heat and power generation systems that have received special attention in recent decades. In this paper, concentrator photovoltaic thermal cell with the effect of Al2O3 nanofluid flow in porous channel has been investigated under transient heat flux. The system is analyzed from energy and exergy viewpoint, and also the first and second laws of thermodynamics efficiencies are calculated. The governing equations are continuity, Brinkman momentum and energy conservation equations considering the transient solar flux using parabolic dish concentrator over a day in Mashhad city. The numerical modeling is based on the finite element method. The numerical results show that the Nusselt number, normalized temperature and electrical efficiency of the presented model have an acceptable agreement with experimental data. Efficiency of the photovoltaic cell increases with increasing the Reynolds number as the difference between the highest and the lowest efficiency value is 5% at 12 p.m. In addition, with increasing Reynolds number, the first law of thermodynamics efficiency increases due to porosity and permeability effects of the porous channel cooling. The maximum difference between highest and the lowest value for first law efficiency is 49.4% at Re = 110. The second law of thermodynamics efficiency decrease as Reynolds number increases as the highest value is 4.2% and the lowest is 2.8% at Re = 20 and Re = 10, respectively.

Transient heat flux estimation during the baking of cereal batter by contact heating

In many applications, it is essential to evaluate the heat flux transferred by contact between two materials. Heat flux sensors must be properly designed to reduce sources of measurement bias while maintaining a high sensitivity without disrupting the flux itself. The aim of this study is to estimate the heat flux exchanged between two materials in contact at different temperatures. When materials are rapidly brought into contact (less than one second) the heat flux exchanged presents large variations. In this study, the heat fluxes transferred are computed using an inverse heat conduction problem. Initially, a particular attention is focused on the numerical analysis of the method and its reliability. A first experimental study is conducted on a prototype where an elastomer plate is suddenly placed on a hot iron disk. Based on temperature measurements recorded in each medium, the heat flux exchanged is estimated by two ways and the results are compared with each other. These first results show the efficiency of the method and its ability to extract information from temperature measurements. Then, a second experimental study is carried out with a cereal batter spread on the iron disk. The estimation of the heat flux from cast iron temperatures is compared with that deduced from an energy balance performed on the batter. The energy balance takes into account the sensible heat, the mass losses and the heat flux exchanged by radiation and convection with ambiance.

Further Experiments on the Effect of Bulk In-Cylinder Temperature in the Pressurized Motoring Setup Using Argon Mixtures

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Mechanical friction and heat transfer in internal combustion engines have long been studied through both experimental and numerical simulation. This publication presents a continuation study on a Pressurized Motoring setup, which was presented in SAE paper 2018-01-0121 and found to offer robust measurements at relatively low investment and running cost. Apart from the limitation that the peak in-cylinder pressure occurs around 1 DegCA BTDC, the pressurized motoring method is often criticized on the fact that the gas temperatures in motoring are much lower than that in fired engines, hence might reflect in a different FMEP measurement. In the work presented in SAE paper 2019-01-0930, Argon was used as the pressurization gas due to its high ratio of specific heats. This allowed to achieve higher peak in-cylinder temperatures which close further the gap between fired and motored mechanical friction tests. In 2019-24-0141, Argon was mixed in different proportions with Air to synthesize gases with different ratios of specific heats in the aim of observing any abrupt transitions in the FMEP with different peak in-cylinder temperatures. In this publication, a higher loading test matrix to that published in 2019-24-0141 is presented, with an engine speed ranging from 1400 rpm to 3000 rpm and ratios of specific heats varying from that of Air (&lt;b&gt;&lt;i&gt;γ&lt;/i&gt;&lt;/b&gt; = 1.4) to that of Argon (&lt;b&gt;&lt;i&gt;γ&lt;/i&gt;&lt;/b&gt; = 1.67). The peak in-cylinder pressure was kept at a constant 103 bar. Results obtained in this work strengthen further the observations made in 2019-24-0141; where the measured FMEP is found to be insensitive to the different peak in-cylinder temperatures. In this study, a fast-response thermocouple of the eroding type was also fitted in the combustion chamber and gas-wall interface temperature histories were recorded. The transient heat flux was also computed through a spectral analysis and reported in this publication.&lt;/div&gt;&lt;/div&gt;