Excessive Heat Accumulation Research Articles

Influence of scan line spacing on nanosecond pulse laser welding of 6063 Al to steel thin sheets

Nanosecond pulsed laser welding of 316L stainless steel and 6063 aluminum alloy thin sheets was performed. The influence of scan line spacing on the joining process was clarified. Large explosive hole and hot cracking defects including radial cracks and arc-shaped cracks occurred in the joint caused by excessive heat accumulation when the line spacing was 0.02 mm. The joints without oxidation were obtained. The thermal-induced penetration increment (TIPI) decreased with the increase of line spacing and reached the maximum value of about 162.24% with the line spacing of 0.02 mm. Fe2Al5 and FeAl phases probably were produced at all the line spacings. However, FeAl and α-Fe phases in the form of banding structures were possibly generated only with the line spacing of no less than 0.06 mm. The shear force test results indicated that the maximum shear load of 158.8 N was achieved at the line spacing of 0.06 mm due to the large bonding area and fewer defects. Three fracture paths, namely, button pullout failure (BPF), interfacial failure (IF) and mixed fracture (MF) mode of BPF and IF were produced. The heat affected zone was the origin of BPF mode. Local deformation, pores and Fe-Al brittle phases led to the fracture paths of IF and MF.

EVALUATION ON THE REDUCED GRAPHENE OXIDE THERMAL INTERFACE MATERIAL AND HEAT SPREADER FOR THERMAL MANAGEMENT IN HIGH-TEMPERATURE POWER DEVICE

Thermally conductive reduced graphene oxide (rGO) is desirable for removing generated heat during the operation of a power device. Excessive heat accumulation results in device failure. In this article, the performance of rGO as a thermal interface material (TIM) and heat spreader on Si substrate was evaluated using a custom build thermal test setup. By a simple drop-casting of graphene oxide (GO) on Si followed by 700 oC thermal reduction, a hybrid film of GO (electrical insulator) and rGO (thermal conductor) was obtained. This was verified by Raman spectra and surface morphological image. Approximately 300 nm-thick rGO film prepared from 4-times drop-casting of GO exhibited the highest performance as a TIM and heat spreader. The heating rate of Si increased from 14.85 oC/W to 18.37 oC/W due to the improved heat transfer from the heater into the Si substrate. The experimental results endorsed the effectiveness of rGO as a thermal solution and verified the capability of the thermal test setup as a thermal simulation of a high-power device.

Heat Storage of Paraffin-Based Composite Phase Change Materials and Their Temperature Regulation of Underground Power Cable Systems.

Excessive heat accumulation in backfill materials causes thermal fatigue damage in underground power cable systems that significantly affects the cable carrying capacity. To improve the thermal conditions of the system, two types of composite phase change materials (CPCMs) were prepared by incorporating paraffin into porous ceramsite (CS)/expanded graphite (EG) in this study. EG and CS can carry 90 and 40 wt.% paraffin, respectively. The phase change temperature of paraffin/CS and paraffin/EG CPCMs was approximately 65 °C, and the corresponding latent heats were 63.38 J/g and 156.4 J/g, respectively. Furthermore, the temperature regulation by CPCMs was evaluated experimentally by designing a setup to simulate the underground power cable system. The reduction in the maximum temperature of the backfill materials with paraffin/CS CPCM and paraffin/EG CPCM was approximately 7.1 °C and 17.1 °C, respectively, compared to reference samples. A similar conclusion was drawn from the heat flux curves. Therefore, the prepared CPCMs could significantly alleviate temperature fluctuations, where the paraffin/EG CPCM provided better temperature regulation than paraffin/CS CPCM. Both materials have potential applications for use in backfill materials for underground power cable systems.

Estimation Method of Interpass Time for the Control of Temperature during a Directed Energy Deposition Process of a Ti-6Al-4V Planar Layer.

Directed energy deposition (DED) provides a promising additive manufacturing method to fabricate and repair large metallic parts. However, it may suffer from excessive heat accumulation due to a high build rate, particularly during a wire feeding-type DED process. The implementation of interpass time in between two depositions of beads plays an important process role to passively control the interpass temperature. In this study, a method to estimate the proper interpass time using regression analysis from heat transfer finite element analysis is proposed for maintaining the interpass temperature during a wire feeding-type DED deposition of a planar layer. The overlapping beads of a planar layer are estimated using a polygonal-shaped bead profile in the finite element model. From the estimated proper interpass time, a selected proper interpass time scheme (PITS) is suggested for practical implementation. The selected PITS is applied in a thermo-mechanical finite element model to evaluate the temperature distribution and its effects on the depth of the melt pool, the depth of the heat-affected zone (HAZ), displacement, and residual stresses. By comparing the predicted results with those using a constant interpass time scheme (CITS), the selected PITS shows better control in reducing the depths of the melt pool and HAZ without severely inducing large displacement and residual stresses.

Achieving a 3D Thermally Conductive while Electrically Insulating Network in Polybenzoxazine with a Novel Hybrid Filler Composed of Boron Nitride and Carbon Nanotubes.

To solve the problem of excessive heat accumulation in the electronic packaging field, a novel series of hybrid filler (BN@CNT) with a hierarchical “line-plane” structure was assembled via a condensation reaction between functional boron nitride(f-BN) and acid treated carbon nanotubes (a-CNTs). The reactions with different mass ratios of BN and CNTs and the effect of the obtained hybrid filler on the composites’ thermal conductivity were studied. According to the results, BN@15CNT exhibited better effects on promoting thermal conductivity of polybenzoxazine(PBz) composites which were prepared via ball milling and hot compression. The thermally conductive coefficient value of PBz composites, which were loaded with 25 wt% of BN@15CNT hybrid fillers, reached 0.794 W· m−1· K−1. The coefficient value was improved to 0.865 W· m−1· K−1 with 15 wt% of BN@15CNT and 10 wt% of BN. Although CNTs were adopted, the PBz composites maintained insulation. Dielectric properties and thermal stability of the composites were also studied. In addition, different thermal conduction models were used to manifest the mechanism of BN@CNT hybrid fillers in enhancing thermal conductivity of PBz composites.

Finite-Element Modeling of Landfills to Estimate Heat Generation, Transport, and Accumulation

In North America, temperatures nearing 100°C have been reported in several municipal solid waste landfills. However, the temporal and spatial-dependent processes that result in excessive heat accumulation are not well understood. The objective of this study was to develop a transient finite-element three-dimensional model that incorporates gas-liquid-heat reactive transfer in a landfill with biotic and abiotic reactions and spatially dependent heat transfer processes to better understand heat generation, accumulation, and propagation. The model incorporates gas-liquid-heat reactive transfer with aerobic and anaerobic biological reactions, anaerobic metal corrosion, and ash hydration and carbonation. Increasing boundary temperature, biological reaction rates, and landfill height increase the maximum temperature in the central region of a landfill, whereas the impact of thermal properties of municipal solid waste (MSW) is small. Simulation results predict that placement of ash near the corner of a landfill reduces the size of the elevated temperature region relative to placement in the landfill center. Mixing heat-generating wastes (ash or Al) with MSW decreases maximum temperatures but results in elevated temperatures over a larger fraction of the landfill volume relative to segregated ash disposal.

WAAM system with interpass temperature control and forced cooling for near-net-shape printing of small metal components

In an attempt to find a solution similar to the FDM 3D printers which would allow cost-effective and reliable additive manufacturing of metal components, this paper proposes a three-axis WAAM system capable of reliably printing small, near-net-shape metal objects. The system consists of gas metal arc (GMA) process equipment, a three-axis CNC positioning system, the interpass temperature control and forced cooling of the base plate and the deposit. The main challenge addressed is the minimisation of shape distortions caused by excessive heat accumulation when printing small objects. The interpass temperature control uses an IR pyrometer to remotely measure the last deposited layer and a control system to keep the interpass temperature below the predefined value by stopping the deposition after each layer in order to allow the deposit to cool. This results in a stable and more repeatable shape of the deposit, even when the heat transfer conditions are changing during the build-up process. The combination of adaptive interlayer dwell time and forced cooling significantly improves system productivity. Open-source NC control and path generation software is used, which enables fast and easy creation of the control code. Different control methods are evaluated through the printing of simple walls, and the printing accuracy is evaluated by printing small shell objects. As the results show, the interpass temperature control allows small objects to be printed at near-net shape with a deviation of 2%, which means that successful printing of 3D shapes can be achieved without trial and error approach.

Effect of laser power and deposition environment on the microstructure and properties of direct laser metal-deposited 12CrNi2 steel

Direct laser metal deposition was used for preparing blocks of steel 12CrNi2 using four different laser powers under two different deposition environments including atmospheric environment and Ar-protected chamber. The results showed that microstructures and mechanical properties were significantly affected by different laser powers. Increasing laser power and deposition in Ar chamber will lead to a decrease in the quantity and size of the voids, which brings more elongation to the samples. Bainitic microstructure was replaced by Widmanstatten ferrite and pearlite, and the amount of proeutectoid ferrite increased with increasing laser power. Moreover, microstructures of previous layers were completely altered in high laser power. Excessive heat accumulation by using high heat input can produce equiaxed ferritic grains with the pearlites in previously deposited layers. Hardness of deposited samples increased from the bottom layer toward the top layer. By using a diode laser with a spot diameter size of 2 mm, the 900-W laser power is suitable for producing crack- and void-free samples. However, post-deposition heat treatment is necessary for obtaining homogeneous desired microstructure and grain size in the manufactured samples.

Expert consensus statement on Pudilan Xiaoyan Oral Liquid in clinical practice

Pudilan Xiaoyan Oral Liquid has effects in clearing away heat and detoxifying,and is used to treat pharynx and throat swelling caused by the syndrome of excessive heat and toxin accumulation. Its efficacy is to relieve swelling and pain( redness,swelling and hot pain). It is included in the Chinese Pharmacopoeia of 2015 Edition,and has been listed in provincial health insurance directories of Shaanxi,Jiangsu,Liaoning,Hunan,Tianjin,Xinjiang and Hebei. It has been recommended by health departments of Beijing,Chongqing and other provinces as a preferred drug for the prevention and treatment of H1 N1 and HFMD,and listed in the diagnosis and Treatment Guide of HFMD by the Ministry of Health,the Clinical Application Guide of Chinese Patent Medicine edited by the Lung Department Disease Branch of China Association of Chinese Medicine,and the Clinical Practice Guide of Single Administration/Combined Administration of Antibiotics in Treatment of Common Infectious Diseases by China Association of Chinese Medicine. To further improve the clinician's understanding of drugs and better guide the rational clinical application,we invited front-line clinical experts from respiratory department,infectious department and dermatology of traditional Chinese and Western medicine to develop and compile the expert consensus. The consensus fully considered the clinical evidence and the expert clinical experience to give recommendations for clinical problems with evidence support and consensus suggestions for clinical problems without evidence support by the nominal group method.This consensus is based on clinical research evidence and expert experience in a simple and clear format,which provides a preliminary reference for the clinical use of the drug.

Enhanced resistance-welding hybrid joints of titanium alloy/thermoplastic composites using a carbon-nanotube lamina

The joining of titanium (Ti) alloy and composite parts with weight reduction and cost saving is being developed to improve aircraft performance. The high-efficiency resistance welding technology was explored for joining Ti alloy plate and glass fabric reinforced polyetherimide (GF/PEI) laminate in this work and a carbon nanotube (CNT) reinforced laminae was embedded into the interface of the welding region to enhance the strength of the hybrid joints of Ti -GF/PEI. The CNTs were in-situ grown on the surface of the Ti alloy plate, and their structures and morphologies were characterized by Raman spectrum, scanning electron microscope (SEM) and transmission electron microscope (TEM). The single lap shear strength (LSS) of the hybrid joints was evaluated with tensile tests. The LSS values first increased and then decreased with welding time (tw) due to the combined effects of the improving molten state of PEI resin and its local thermal degradation induced by excessive heat accumulation. The optimum LSS of the hybrid joint with CNT reinforced lamina is increased by 146% to 17.28 MPa in comparison with that of the hybrid joint without CNTs. The failure modes shift from interlayer debonding of the Ti alloy plate and the implant to the cohesive fracture of the implant and the delamination of the GF/PEI laminate with increasing tw. The ultrasonic C-scan images also show an increase of the number of internal defects of GF/PEI laminates with tw.

Warming in the Agulhas Region during the Global Surface Warming Acceleration and Slowdown

The Agulhas Region gains more heat during the global surface warming slowdown than acceleration period. Yet, mechanisms that cause excessive heat accumulation in this region remain largely unknown. We investigate the underlying physical processes and examine their influence on ocean heat changes in the last three decades. Heave is found to drive the increasing ocean heat content in the last three decades whereas elevated heat accumulation rate in slowdown compared than acceleration period is mainly attributed to spice. During the acceleration period, pure heaving of Subtropical Mode Water induced by wind stress change and pure warming caused by heat flux, leading to a strong heave component and relatively weak spice, drive the increases in ocean heat content. During the slowdown period, increasing salinity strengthens the spice, resulting in a higher heat accumulation rate compared to the acceleration period.

Self‐judgement flip coding for resistive random access memory

A novel low-energy write scheme, self-judgement flip coding (SJFC), for resistive random access memory (RRAM) is proposed. Lots of energy will be consumed in the write process of RRAM, especially in the reset process. Owing to RRAM being sensitive to heat, excessive heat accumulation will lead to thermal crosstalk. Through reading original data, SJFC analyses and computes the Joule heat produced in the write data flow and further judges whether to make flip coding on the write data flow. The result is that between the original write data flow and flip coding data flow, the one producing lesser energy will be transmitted to the write circuit to produce lesser energy in the RRAM write process. The stimulation result shows that SJFC could reduce energy consumption by 39% on average in the write process.

Cushion plant morphology controls biogenic capability and facilitation effects of Silene acaulis along an elevation gradient

Summary The stress‐gradient hypothesis (SGH) predicts that the balance of plant–plant interactions shifts along abiotic environmental gradients, with facilitation becoming more frequent under stressful conditions. However, recent studies have challenged this perspective, reporting that positive interactions are, in some cases, more common at the intermediate level of environmental severity gradients. Here, we test whether and how neighbour effects by Silene acaulis cushions vary along a 700 m wide altitudinal transect, in relation to cushion morphological traits and environmental severity. Field measurements along the gradient, within and outside cushions, included (i) species richness and cover of coexisting vascular plants; (ii) cushion morphology; (iii) above‐ and below‐ground microclimate; and (iv) soil quality. We used the relative interaction index to decouple neighbour trait effects and environmental severity effects on plant diversity at different elevations. The ability of the cushion plant to facilitate heterospecifics shifts considerably along the elevation gradient, being greatest at the intermediate level. On the other hand, Silene morphological traits steadily change along the gradient, from lax, soft and flat‐shaped cushion habits at low elevation to tightly knit and dome‐shaped habits at high elevation. Cushion morphological changes are associated with mitigating effects on microclimate, indicating that cushions effectively act as a heat‐trap at medium and high elevations, while at low elevations the soft and flat cushions avoid excessive heat accumulation by tight coupling with the surrounding atmosphere. At the upper end of the gradient, cushion cespitose–pulvinate compactness and high stem density appear to be critical traits in modulating the net effect of plant–plant interaction, since the space available for hosting other vascular species is considerably reduced. In conclusion, this work provides a mechanistic link between plant morphological traits, associated biogenic microclimate changes and variation in net plant–plant interactions along the explored severity gradient. Our findings support an alternative conceptual model to SGH, with plant facilitation collapsing at the upper extreme of the abiotic stress gradient.

Experimental investigation and numerical modeling of the thermal behavior of a micro-heater

In micro-heater, heat flux is generated by Joule effect thanks to short electric pulses. This leads to a rapid increase of the micro-heater temperature that reaches a few hundreds degree Celsius in a few microseconds. In addition to this, the cyclic nature of the energizing signal may cause an excessive heat accumulation and hence a reduction of the device life expectancy. It is thus of utmost importance to accurately model heat transfer in the whole device. This work focuses on a 200 dots per inch printing head system which consists of a row of micro-heaters. Structure and chemical composition of a single micro-heater are determined by scanning electron microscopy coupled to an EDX analyzer (energy dispersive X-ray spectrometry). These data are used to build a two dimensional numerical model which represents a micro-heater cross-section. This model gives the spatiotemporal evolution of the temperature field which highlights clearly the thermal loading phenomenon in the micro-heaters. In parallel, electric measurements are performed during the printing process to access to the actual power supplied to the micro-heaters. Infrared thermography was used to measure the thermal response of the micro-heaters to the electrical solicitation. The comparison of experimental and numerical results shows that the numerical model correctly predicts the thermal behavior of micro-heaters.

Fabrication of novel bundled fiber and performance assessment for clinical applications.

During laser vaporization of benign prostate hyperplasia (BPH), high precision of optical fiber handling is pivotal to minimize any post-operative complications. The aim of the study was to evaluate the feasible applications of a bundled fiber to treat BPH by directionally and selectively manipulating laser light onto the targeted tissue. A bundled optical fiber, consisting of four side-firing fibers, was fabricated to selectively emit laser beams in from one to four directions. Both transmission efficiency and light distribution were qualitatively and quantitatively characterized on the bundled fiber. In terms of interstitial application of the proposed fiber with 1064 nm on porcine liver tissue, the extent of thermal denaturation was estimated and compared at various laser parameterizations and for different directions of light. From the laser source to the fiber tip, the fabricated fiber device demonstrated a total light transmission of 52%. Due to internal light reflection, a secondary beam was emitted backward from the fiber tip and was responsible for 25% of the transmission loss. According to tissue testing, the extent of tissue denaturation generally increased with laser power, irradiation time, and number of light directions. The geometrical shape of thermal coagulation correlated well with the direction of light emission. Thermal damage to the glass tube occurred during excessive heat accumulation generated by continuous irradiation. The proposed fiber can be beneficial for laser vaporization of BPH by providing a selective light direction irradiation along with minimal thermal damage. Further studies will extend the applicability of the bundled fiber to treat tubular tissue structure.

Optical feedback-induced light modulation for fiber-based laser ablation.

Optical fibers have been used as a minimally invasive tool in various medical fields. However, due to excessive heat accumulation, the distal end of a fiber often suffers from severe melting or devitrification, leading to the eventual fiber failure during laser treatment. In order to minimize thermal damage at the fiber tip, an optical feedback sensor was developed and tested ex vivo. Porcine kidney tissue was used to evaluate the feasibility of optical feedback in terms of signal activation, ablation performance, and light transmission. Testing various signal thresholds demonstrated that 3 V was relatively appropriate to trigger the feedback sensor and to prevent the fiber deterioration during kidney tissue ablation. Based upon the development of temporal signal signatures, full contact mode rapidly activated the optical feedback sensor possibly due to heat accumulation. Modulated light delivery induced by optical feedback diminished ablation efficiency by 30% in comparison with no feedback case. However, long-term transmission results validated that laser ablation assisted with optical feedback was able to almost consistently sustain light delivery to the tissue as well as ablation efficiency. Therefore, an optical feedback sensor can be a feasible tool to protect optical fiber tips by minimizing debris contamination and delaying thermal damage process and to ensure more efficient and safer laser-induced tissue ablation.

Application of air cooled pipes for reduction of early age cracking risk in a massive RC wall

The construction of massive concrete structures is often conditioned by the necessity of phasing casting operations in order to avoid excessive heat accumulation due to cement hydration. To accelerate construction and allow larger casting stages (usually increasing lift height), it is usual to adopt internal cooling strategies based on embedding water pipes into concrete, through which water is circulated to minimize temperature development. The present paper reports the use of horizontally placed ventilated prestressing ducts embedded in a massive concrete wall for the same purpose, in line with a preliminary Swedish proposal made in the 1990s. The application herein reported is a holistic approach to the problem under study, encompassing extensive laboratory characterization of the materials (including a technique developed for continuous monitoring of concrete E-modulus since casting), in situ monitoring of temperatures and strains, and 3D thermo-mechanical simulation using the finite element method. Based on the monitored/simulated results, it is concluded that the air-cooling system is feasible and can effectively reduce early cracking risk of concrete, provided adequate planning measures are taken.

Failure investigation of a boiler bank tube from a 77 × 2 MW coal based thermal power plant in the northwest region of India

The failure of industrial boilers has been a prominent feature in fossil fuel fired power plants. The contri-bution of one or several factors appears to be responsible for failures, culminating in the partial or complete shutdown of the plant. The use of high sulfur and ash containing fuel, exceeding the design limit of temperature and pressure during operation, and poor maintenance are some of the factors, which have a detrimental effect on the performance of materials of construction[1-4]. Among the many forms of corrosion mechanisms operating in tube failures in different parts of the boiler, ash corrosion and galvanic corrosion were the prime failure mechanisms predominantly found in bank tubes which arise due to use of low quality feed coal as fuel and poor cleaning proc-edures, respectively [5,6]. These types of failures are manifested by the accumulation of ash deposits on the fireside, which impart excessive fireside heat input and accumulation of corrosion products on the waterside of the tube [7], which induce localized corrosion. In the present paper, a comprehensive analysis of a boiler bank tube failed in one of the captive power plant of 77 x 2 MW capacity located in the northwest region of INDIA is presented.

Rapid and selective removal of composite from tooth surfaces with a 9.3 µm CO2 laser using spectral feedback.

Dental composite restorative materials are color matched to the tooth and are difficult to remove by mechanical means without excessive removal or damage to peripheral enamel and dentin. Lasers are ideally suited for selective ablation to minimize healthy tissue loss when replacing existing restorations, sealants, or removing composite adhesives such as residual composite left after debonding orthodontic brackets. In this study, a carbon dioxide laser operating at 9.3-µm with a pulse duration of 10-20-microsecond and a pulse repetition rate of ∼200 Hz was integrated with a galvanometer based scanner and used to selectively remove composite from tooth surfaces. Spectra of the plume emission were acquired after each laser pulse and used to differentiate between the ablation of dental enamel or composite. Microthermocouples were used to monitor the temperature rise in the pulp chamber during composite removal. The composite was placed on tooth buccal and occlusal surfaces and the carbon dioxide laser beam was scanned across the surface to selectively remove the composite without excessive damage to the underlying sound enamel. The residual composite and the damage to the underlying enamel was evaluated using optical microscopy. The laser was able to rapidly remove composite from tooth buccal and occlusal surfaces with minimal damage to the underlying sound enamel and without excessive heat accumulation in the tooth. This study demonstrated that composite can be selectively removed from tooth surfaces at clinically relevant rates using a CO(2) laser operating at 9.3-µm with high pulse repetition rates with minimal heat deposition and damage to the underlying enamel.

High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage

CO(2) lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO(2) laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO(2) lasers with minimal peripheral thermal and mechanical damage and without excessive heat accumulation.