High-intensity Heat Research Articles

Heat wave resilience in open Spaces: A case study of a Self-Sufficient cooling shelter

Climate change intensifies urban uninhabitability due to increasingly frequent heat waves. To alleviate it, climatic shelters emerge as an initiative for the research community, which should deepen the integration of technologies that use natural resources for cooling. This work aims to evaluate a novel climatic shelter by characterizing its thermal behavior through an experimental study at a bus stop. It has the capacity to alleviate the thermal stress of its occupants thanks to cooling modules. The results allow to determine the capacity of the natural water-cooling system and the level of thermal storage, allowing to quantify the impact on the citizen by means of the COMFA comfort index. It is corroborated that the chilled water temperature reduces the surface temperature by 15 °C. The installation reduces overheating caused by solar radiation by 75 % compared to traditional shelters. It also demonstrates energy and electrical self-sufficiency even during high intensity heat waves. The shelter maintains daytime water temperature between 18 and 25 °C, even in heat waves exceeding 7 days and 45 °C air temperature. The COMFA index has been reduced to values between 70 and 120 W/m2 in 90 % of the worst weather conditions in Csa climates by Köppen Geiger, for the months of July and August 2023.

Performance assessment of firefighter protective clothing under different thermal environments: Impact of the variation of thickness in inter-layer airgap and microclimate

Personal protective equipment for firefighters can effectively prevent skin burns and ensure firefighters' safety. Considering a variety of fire environments faced by a firefighter, the present study is devoted to showing the role of the inter-layer fabric airgap and its variation in thickness on skin burns under high intensity heat flux. The present numerical model is formulated by considering a coupled conduction and radiation heat interaction in the porous fabric medium and the Pennes bioheat transfer model for the multi-layered skin. The study considers the effect of variation in airgap thickness, variation in heat transfer coefficient, and duration of exposure on the thermal damage of the firefighter's skin subjected to different harsh thermal environments. The results found that increasing the thickness of AG1 and AG2 does not yield a significant impact during the exposure time. Conversely, AG3 and AG4 lead to considerable temperature reductions at the basal layer, with AG3 causing a decrease of 2.6 °C to 2.9 °C and AG4 causing a decrease of 11.9 °C to 17.0 °C under all exposure conditions. Additionally, when the heat transfer coefficient increases during post-exposure, temperature drops of 9.17 °C to 10.72 °C, 9.81 °C to 11.46 °C, 10.0 °C to 11.64 °C, and 8.68 °C to 10.07 °C are observed for AG1, AG2, AG3, and AG4, respectively, across all exposure conditions. However, both the airgaps have a substantial effect on thermal protection during the post exposure period. In addition, the nature of the variation of stored and transmitted energy in fabric assembly shows an opposite trend during both the exposure and post exposure period in contrast to the third and fourth airgaps for all the considered thermal environments.

Flux Sensor Measurement and Calibration Requirements for High-Intensity Heat Flux Applications

Stakeholders of CSP and non-CSP high-intensity broadband flux measurements were surveyed and interviewed to obtain flux sensor design and calibration requirements. Existing sensor technologies and existing calibration facilities were then compared against this standard. Stakeholders require a flux sensor designed for >5,000 kW/m2 flux measurements, >1,000 life cycles, <500 ms response time, >60-minute exposure at maximum flux, and <5% measurement uncertainty. Stakeholders also require a sensor with minimal cost, short procurement lead time, and a high-intensity broadband flux calibration. Commercial CSP stakeholders primarily rely on infrared (IR) temperature measurements of receiver equipment to control CSP plant process operation, whereas CSP research and development (R&D) and non-CSP stakeholders rely on accurate flux gauge measurements for a variety of applications. It was determined that existing flux sensor technologies and calibration facilities do not comprehensively meet stakeholder needs. This study suggests a more robust circular foil gauge with a high-intensity solar flux calibration comprehensively meets stakeholder flux measurement needs. Improved circular foil gauge designs and an improved flux sensor calibration facility are discussed.

Numerical Study on the Heat Transfer of Confined Air-Jet Quenching of Steel Sheets

The high flatness quenching of ultra-high-strength steel sheets is a technical problem in the steel industry. In this study, the traditional water and spray quenching methods were abandoned, and the roller-constrained slot air-jet quenching method was proposed for steel sheets below 3 mm thickness, which provided a theoretical reference for producing thinner, wider, and higher-flatness steel sheets. A 2D roller-constrained slot air-jet numerical model was established to study the flow field and heat transfer characteristics under the conditions of Reynolds number 24,644–41,076, a dimensionless jet height of 16–24, and a jet angle of 45°–135°. The results showed that the average Nusselt number on the heat transfer surface was proportional to Rem. At the same time, high-intensity heat transfer was achieved when the dimensionless height and jet angle were properly combined. At the same Reynolds number, the heat transfer intensity could be increased by 289%. In addition, the position of the peak Nusselt number was affected by reducing the jet angle, which served as an effective strategy for adjusting the martensite ratio and obtaining ideal mechanical properties.

Experimental and numerical investigations into the fabrication of alumina ceramic surface microchannel by electrochemical discharge machining

The electrochemical discharge machining (ECDM) is an advanced and promising technology for fabricating micro structures. This method is effectively applicable for non-conductive hard and brittle materials micromachining, such as glass and ceramics. However, the ceramics high melting point and intense heat exchange effects during microchannel fabrication lead to the easy dissipation of thermal energy and the difficulty in processing. To address this issue and expanded the ECDM processing range. This paper dedicated to the investigation of the material removal mechanism and process characteristics for the alumina ceramic surfaces microchannels preparation. Firstly, this study explained the difference of the ECDM critical applied voltage and gas film generation mechanism by analyzing the volt-ampere characteristic curve of 20 wt% NaOH electrolyte with a tool immersed depth of 2 mm and 10 mm respectively. Then, a thermal removal finite element model (FEM) for ECDM was developed. The heat cumulative and intermittent cooling effects applied on the alumina ceramic surface dominated the materiel removal. Additionally, it can be found that the microchannel machining accuracy and bottom surface quality depended on the Gaussian heat source characteristics, gas film formation mechanism, heat accumulation effect, and temperatures spatial and temporal distribution. And a series of single factor experiments for evaluating the parametric studies such as the effect of discharge frequency, applied voltage, duty ratio and tool feed rate on the fabricated microchannel performance are executed. Finally, the complex three-dimensional structures of cross microchannel grid and zigzag microchannel array with variable depth were successfully fabricated on aluminum oxide ceramic surface. Notably, the results highlighted and enriched the ECDM stability, consistency and applicability for alumina ceramic surface microchannel fabrication.

Highly integrated smart mountaineering clothing with dual-mode synergistic heating and sensitive sensing for personal thermal management and human health monitoring

The development of multifunctional textiles is an effective strategy to improve the quality of human life. Normal single-mode heaters and strain sensors have been developed, but their low integration leads to multiple devices being installed on the garment, which greatly increases the weight of the garment and thus reduces its wearability. Here, bio-enzymatic polymerization and a simple shaking deposition method were used to prepare poly(3,4-ethylenedioxythiophene) (PEDOT) and copper(II) sulfide (CuS) onto the surface of the elastic nylon fabrics, which endowed the fabrics with excellent dual-mode heating properties and sensitive sensing properties, and used to develop highly integrated multifunctional and smart mountaineering clothing. In electro-driven heating mode, low-voltage (6 V) and high-voltage (12 V) heating can be used for joint heat therapy and active rapid deicing, respectively. In photo-driven heating mode, low intensity (0.3 sun) and high intensity (1.5 sun) heating can be used for joint heat therapy and rapid antibacterial, respectively. In addition, the fabric has the ability of dual-mode synergistic heating, and the surface temperature of the fabric can exhibit an ultra-high temperature of 137.9 °C under the external stimulation of 0.3 sun and 12 V. The fabric will greatly enhance the deicing and antibacterial efficiencies under the synergistic effect. This work provides a facile strategy for the fabrication of flexible and highly integrated multifunctional electronic devices, and therefore has great potential for the design and development of all-in-one multifunctional electronic devices such as personal thermal management, soft robotics, and human-computer interaction.

The crack behavior and delamination mechanisms of air plasma sprayed thermal barrier coatings under ultrasonic plasma jet at 1600 °C

In this contribution, the performance and delamination mechanisms of air plasma sprayed (APS) yttria stabilized zirconia thermal barrier coatings (YSZ TBCs) under high intensity heat flux at 1600 °C was investigated. The plasma jet was adopted as the heat source with a combination of high temperature and high-speed jet-stream erosion. It was found that the YSZ topcoat would exfoliate when the vertical crack connected to the interior (interfacial/shear) cracks to form a free edge, which turned the mixed-mode buckle delamination into a mode I cracking. The thermo-mechanical analysis indicated that energy release rate associated with the transient cooling was the driving force for the interfacial cracks, while the vertical cracks were developed by the tensile stress during cooldown. The findings obtained in this study implied that the YSZ TBCs can be used for the thermal protection of combustor in ramjet engines.

Heat transfer characteristics of tubular heat exchanger using reverse air injection flameless combustion

The heat transfer characteristics of a co-axial triple tube reformer using flameless combustion were studied herein. Methane steam reformers for hydrogen production have been developed with a long history, but as hydrogen has recently come into the limelight as a future energy, research on the development of more efficient reformers is being pursued. Flameless combustion has the advantage of being applicable for the high performance reformers, but studies to date have focused on the combustion phenomenon itself, and research on the heat transfer phenomenon is lacking. In this study, RAI (reverse air injection) flameless combustion, which generates high intensity combustion and heat transfer, was applied to the reformer and its heat transfer effect was analyzed in parallel with experiments and CFD analysis. In the experiment, it was confirmed that the RAI flameless combustion increased the heat transfer by up to 58% compared to the conventional flame type combustion, and the case of two air nozzles was found to have a better heat transfer enhancement effect than the case of four. However, the case using four air nozzles showed a more axisymmetric flow pattern. The heat transfer enhancement effect of RAI flameless combustion is caused by the high-speed air jet creating a highly recirculating flue gas to generate uniform temperature distribution and high convective heat transfer on the surface. As RAI flameless combustion is characterized by being mixed with fuel at the rear end of a strong air jet, which is a completely different configuration from these existing combustors, it is expected that the limitations of the EDC model, which has been widely used in previous studies, will become more prominent. The equilibrium-PDF model based on chemical equilibrium and tabulated chemistry gave a closer result to the experimental results.

Numerical study of the high-intensity heat conduction effect on turbulence induced by the ablative Rayleigh–Taylor instability

By adopting heat conduction of the Spitzer form in implicit large eddy simulations, the effect of high-intensity heat conduction on turbulence induced by the ablative Rayleigh–Taylor instability is studied in this paper. The height of the spike and bubble exhibit self-similar evolution with t2 dependence by the late stage of simulations, while heat conduction suppresses the coefficient of spike αs and slightly enhances that of the bubble αb. Heat conduction displays a strong damping effect for small-scale fluctuations of the temperature and density field, resulting in a much steeper slope for energy spectra in intermediate scales. The diffusion effect is responsible for the suppression of temperature fluctuations, and velocity dilatation is shown to be a possible route for heat conduction to affect density fluctuations. The impact of heat conduction on the velocity field is relatively weak, with vertical velocity spectra exhibiting classical Kolmogorov inertial range in intermediate scales. By comparing enstrophy profiles, it is found that vorticity tends to peak at the bubble side in cases with high-intensity heat conduction.

Comparison of high intensity ultrasound and heat treatment for extending shelf life of a fermented milk beverage

Application of high intensity ultrasound (HIUS) was compared with conventional heat treatment for extending shelf life of a fermented milk beverage. Beverage samples were subjected to HIUS (24 kHz, 400 W) at different power levels (25–100%) and temperature (20–60 °C) or conventional heat treatment (60–70 °C), each for 10 min. Acidity, serum separation, rheological, microbiological and sensory properties of the beverages were measured. HIUS at 20 °C was not sufficient for inactivation of lactic acid bacteria and moulds/yeasts; moreover, it lowered consistency and increased serum separation. HIUS at 60 °C resulted in similar levels of microbial inactivation, consistency and serum separation to those obtained by heat 60 °C treatment. Heat treatment at 70 °C yielded the highest microbial inactivation and the most stable structure in the beverage. HIUS treatment was found to reduce particle size but caused foreign odour and taste in the beverage in sensory analysis.

DETERMINATION OF THE CONTACT AREA UNDER CYCLIC LOADING OF CONTACT PAIRS OF ISOTROPIC MATERIALS ON THE BASIS OF 3D SURFACE MICRORELIEF MODELLING

The parameters of the surface microrelief are paramount in the problems of frictional interaction of parts, the flow of liquid and gas in channels, ensuring the required thermal conditions and the stress-strain state of the structure. The solution of the problem of ensuring the optimal thermal regime for a significant range of technical products often becomes decisive in the design of products operating under conditions of high-intensity heat flows. Transit heat fluxes flowing through the product, as well as heat fluxes from own heat sources, must be either accumulated or removed to the external space. In this case, the directions of the heat flux vectors are determined by the design features of the products, including through various contact connections. Obviously, a reliable determination of the parameters of the contact interaction of product parts is the basis for a reliable analysis of the stress-strain and thermal state of a wide range of structures operating under conditions of high-intensity heat flows. The operational characteristics of the contacting parts of the structure are directly determined by the properties of the contact of the mating surfaces. When solving many problems of thermal, mechanical and electrical contact interaction, surface roughness is a major factor. The processes of friction and wear occur precisely on the actual contact area and depend not only on the properties of the material, but also on the intercontact pressure on this area, since the magnitude of the actual pressure determines the destruction of surface films and the appearance of adhesive bonds in the contact. In the presented work, the change in the actual contact area under cyclic loading of contact pairs of materials based on digital twins of contact surfaces in a wide range of compressive pressures is considered.

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.).

Thermal management of power electronics using nanofluids and nucleate boiling heat transfer technique

Nucleate boiling is an efficient solution for thermal management of power electronics where high-intensity heat flux needs to be transferred in a compact space. Both micro surfaces and nanofluids are used in literature to enhance the performance of nucleate pool boiling heat transfer systems; however, the effect of nanofluids over the microporous surface still needs to explore in several phase change heat transfer applications. The study’s objective is to examine the performance of nanofluid over microporous surfaces in Nucleate Boiling Heat transfer (NBHT) and performs a comparative analysis with plain and micro-porous surfaces. The study analyzed three ceramic (Alumina) nanofluids for nucleate pool boiling heat transfer (NBHT) over plain and microporous surfaces. The literature reported enhanced performance of nanofluids over the plane surface is verified in the study before proceeding to the detailed analysis over the microporous surface. Three different concentrations of 0.005%, 0.0005%, and 0.00005% were tested for the nanofluid. For plane surface, the critical heat flux (CHF) has been increased to 1035 [kW/m2] for Alumina from 783 [kW/m2] for deionized water, with the average increase in heat transfer coefficient (HTC) being 46.5%. The maximum CHF has been reported for micro-porous surfaces with a value of 1110 kW/m2. Out of the tested surfaces and fluids combination, the micro-porous surfaces with deionized water have been concluded as the most efficient surface with the highest heat transfer capacity for thermal management of high-power electronics and other high heat flux applications.

Influence of cutting parameters on laser assisted machining of C103 Nb alloy

ABSTRACTC103 Nb alloy shows the good consistent microstructure that leads to better controlled properties of the material such as high strength, stress resistance, fabricability, and high temperature resistance. C103 Nb alloy shows the unique properties for challenging the aerospace, orbital rocket nozzles or chambers, and jet engine applications but they are costly and difficult to machine through traditional technique like single point cutting operation. Laser assisted heating plays a significant role in machining process due to easy and to develop very high intense heat energy in a precise region The generated energy leads to soften sample and smooth machining surfaces with crack free and superior quality. The present work deals with the influence of cutting parameters (laser power (LP) and depth of cut (DoC)) on the responses (surface roughness and cutting force (CF)) of C103 Nb alloy through laser assisted machining process at constant feed rate (0.02 mm/rev) and constant cutting speed (500 rpm). Based on the experimental results, LP shown the significance influence on surface roughness, CFs and decreases with increase of LP and increases with increase of DoC.

Characterization of laminar and turbulent supercritical carbon dioxide slot jet impingement heat transfer

Supercritical carbon dioxide (sCO2) has recently been proposed as a promising alternative to conventional fluids for thermal management because of its unique thermophysical properties near the critical point. Jet impingement is also recognized as one of the most effective configurations for high intensity heat transfer. Therefore, leveraging the favorable thermophysical properties of sCO2 in microscale jet impingement may lead to high performance thermal management solutions. However, the effects of thermophysical property variations in the pseudo-critical temperature range on the flow and heat transfer behavior in such configurations is not well understood. The present investigation seeks to address this need through computational simulations of laminar and turbulent slot sCO2 jet impingement. Large eddy simulations (LES) are validated and employed for turbulent cases. The studied range of conditions span reduced pressures of Pr=1.03−1.10, Reynolds numbers Re=225−11,000, dimensionless jet lengths H/W=2−4, jet inlet temperatures Tin=294−330K, and impingement plate temperatures Tplate=270−370K. The turbulent simulations reveal varying spatial distributions of heat transfer coefficient with different jet and plate temperatures, which can be explained in terms of the temperature-dependent properties of sCO2. Heat transfer deterioration (HTD) is observed for both laminar and turbulent flows. HTD is found to be most significant in the stagnation zone, and its relative magnitude decreases downstream more sharply for turbulent flows than laminar. Heat transfer enhancement (HTE) is observed when both the jet inlet and impingement plate temperatures are at opposite ends of the pseudo-critical temperature range. For cooling applications, HTD and HTE effects can be explained in terms of opposing temperature-dependent variations in boundary layer thermal conductivity and overall thermal boundary layer thickness with Prandtl number. Considering the dependence of thermophysical properties on Pr, a thermal management system control strategy is proposed in which Pr is adjusted depending on Tplate to achieve optimal performance over varying operating conditions.

Анализ погрешности измерения температуры образцов высокотемпературной керамики при различных способах заделки термопар

The evaluation of methodological errors in measuring the temperature of nitride ceramics under unilateral heating by high-intensity heat flow was carried out. Simulation of thermal processes in the temperature sensor — sample system was performed using the Siemens PLMNX program. Various methods of fixing platinum-rhodium thermocouples with a diameter of 0.1 mm on the surface and inside the samples have been investigated. The regularities of the influence of the size of the hot junction, the presence of thermal cement, the shape of the grooves for fixing thermocouples on the methodological error of temperature measurement were investigated. Significant errors were revealed when installing thermocouples on the surface of the sample without violating its integrity. Recommendations for the installation of thermocouples were given. The results of the paper can be useful in the preparation of experimental samples for thermal tests on radiation heating stands.

Study on adaptive heat transfer performance of high temperature heat pipe

High temperature heat pipe (HTHP) employs alkali metal or its alloy as working fluid. Due to the large latent heat of its working fluid during phase change heat transfer, HTHP has the advantages of high temperature uniformity, high working temperature and high intensity heat transfer capacity, which has broad application prospects in the field of HTHP cooled nuclear reactors and the thermal protection of hypersonic vehicles. In order to simplify the structure of heat transfer system in nuclear reactors, so that it can safely and reliably realize passive heat transfer without additional pump power under various operating conditions, HTHP must have adaptive heat transfer capacity. In this paper, several HTHPs with excellent heat transfer performance are designed and prepared. The test-bed for frozen startup and heat transfer performance of HTHP is set up, and the electromagnetic induction high frequency heater is used as high temperature heat source. The thermal performance of HTHP with different heating power, heating position and the length of evaporation section (adaptive heat transfer characteristics) is experimentally studied, and the theoretical model is used to validate the experimental result. The experimental and theoretical results show that high vacuum degree is the prerequisite for excellent heat transfer performance of HTHP; high capillary driving force and suction force, reasonable filling ratio of working fluid are the key factors for HTHP to have adaptive heat transfer capacity, and the diameter of HTHP also has important influence on adaptive heat transfer capacity.

Experimental and Computational Method for Determining Temperature Stresses in the Welding of Structures Made of Carbon and High-Alloy Structural Steels

A method for determining temperature stresses in a welded joint of a thin-walled pipe with a base is described. The method is based on experimental data of temperature measurement at reference points of the structure. The features of the elements of the welded joint made of carbon and high-alloy structural steels and the modes of electric arc welding were taken into account. The efficiency of using spline approximation of experimental data to obtain analytical dependences of the distribution of temperature fields and stresses, as well as to obtain a solution of the heat equation by numerical differentiation and integration for this case, is shown. Formulas for calculating temperature stresses for the case of an asymmetric temperature distribution in a cylinder under the action of a moving high-intensity heat source are obtained.

A novel investigation into the edge effect reduction of 4340 steel disc through induction hardening process using magnetic flux concentrators

Induction hardening serves as one of the best mass production processes used recently due to its ability to quickly generate high-intensity heat in a well-defined location of the part. Numerous advantages of this method make it a reliable technique to produce a thin martensite layer on the part surface that has compressive residual stresses. In this regard, the presented study is devoted to investigating utilizing induction heating for surface hardening of AISI 4340 steel disc. The purpose is to evaluate the performance of magnetic flux concentrators and the effects of the induction process parameter on the case-depth and edge effect in the surface hardening of the disc. Once the proper range of parameters is defined, Taguchi experimentation planning is used to frame comprehensive experimentation with the minimum possible trial. Then, the case-depth of discs is evaluated on their cross-sections (edge and middle plane) through hardness profile measurement of samples using a micro-indentation hardness machine. The results are then statistically analyzed using analysis of variance (ANOVA) and response surface methodology (RSM) to determine the best combination of parameters to achieve maximum case-depth yet minimum edge effect. The goodness-of-fit regression models are then developed to predict the case-depth profile as a function of machine parameters based on linear regression utilizing case-depth responses in the edge and middle planes of discs. Results imply that maximum case-depth with minimum edge effect can be produced by using the highest heating time along with the average amplitude of the power, axial gap, and radial gap. This study gives a good exploration of case-depths optimized by setting up process parameters when a magnetic flux concentrator is utilized; thus, a guideline to reduce discs edge effect in induction surface hardening application is given.

Is Social Status Linked to Pain Sensitivity Responses for Latinx-Americans? The Role of Social Mobility

Latinx Americans within the United States (U.S.) disproportionately experience significant chronic pain severity and lower social status. However, little is known about how social status interacts with pain sensitivity mechanisms to contribute to later pain severity for Latinx Americans. Therefore, the current study examined the relationship between social status and pain sensitivity among Latinx adults. Self-identified U.S. native Latinx and non-Hispanic White (NHW) university students without acute or chronic pain were recruited from a larger study examining Latinx American pain sensitivity. Participants completed self-report objective and subjective (i.e., perceived social standing in the U.S.) social status measures during adulthood and childhood. Social mobility was also calculated (i.e., change in social status across the lifespan). Participants completed an ascending thermal-heat laboratory pain assessment involving four heat pulses at low, moderate, and high intensities, verbally rating their pain on a 11-point numerical rating scale after each pulse. Among Latinx Americans, analyses revealed that neither income nor subjective social status during childhood or adulthood were significantly associated with pain responses. However, increases in subjective social mobility (i.e., upward changes in subjective social status across the lifespan from childhood to present day) correlated with lower pain responses to moderate and high intensity heat among Latinx Americans. No significant relationships were observed among NHWs. This study adds to the developing work bringing awareness to social status’ complexity and its role in chronic pain inequities. The current findings suggest that increases in subjective social mobility may be protective, while decreases in subjective social mobility may be a risk factor for future chronic pain severity. Though replication and longitudinal assessment is warranted, the present findings highlight the merit of focusing further attention on the interplay between social status, social mobility, and pain sensitivity to better understand and inform interventions to reduce pain severity concerns among Latinx Americans.