Melt Depth Research Articles

Effect of layer thickness on the melt pool behavior and pore defects evolution of selective laser melting CuCrZr alloy

Despite the great potential of selective laser melting technology, the low build rate has become a major reason limiting its large-scale use. Thick layer thickness can significantly increase the build rate, but an unlimited increase in layer thickness can easily lead to defects which can seriously affect the mechanical properties of the part. To date, the correlation between powder layer thickness and melt pool dynamics behavior and its influence on defect evolution in the production of copper-based alloys by selective laser melting remains unclear. Therefore, in this paper, a high-fidelity computational fluid dynamics (CFD) model combined with a ray-tracing algorithm is developed to investigate the effect of layer thickness on melt pool dynamics and the evolution of pore defects. The results show that as the powder layer thickness increases, the melt track width and depth rise, reaching a maximum of 169.8 µm and 177.2 µm at 60 µm layer thickness, which is probably attributed to the growth of global absorptivity. Besides, the increased instability of melt flow under thick layer thickness resulted in undulations in the solidification track surface and accompanying slag phenomena. It is worth noting that the generation of pores was observed at 45 µm and 60 µm layer thickness. Both the number and dimension of pores increase with thicker layer thickness, which are caused by the multiple reflection behavior of the laser rays in the keyhole. In addition, the elimination of pore defects under thick layer thickness was also explored, and it was found that remelting could effectively reduce the pores generated by previous layers.

Effect of thermophysical properties on porosity and microstructure of laser welded cast and wrought aluminum alloy dissimilar lap joints

The influence of thermophysical properties of materials on the porosity and microstructure of dissimilar lap joints between laser-welded Al–Si–Mg cast and Al–Mg–Si–Cu wrought aluminum alloys was investigated. The low thermal conductivity and viscosity of the weld would promote bubble escape, while the high electrical conductivity of the base material would increase the melt depth and reduce the convection intensity in the melt pool, thus increasing the difficulty of bubble escape. The variation in thermophysical properties did not significantly impact the distribution of elements, the type of precipitated phases, and the dislocation density, however, it did affect grain morphology. Differences in thermal diffusion coefficients between base materials created conditions for constitutional supercooling, increasing the likelihood of a columnar-to-equiaxed transition. Moreover, the temperature difference between the liquid phase lines of the weld and base materials facilitated the liquid base material flushed into the weld to solidify before mixing, resulting in an “island” formation. This “island” acted as a heterogeneous nucleation site, leading to equiaxed grain layer formation in the lowest zone of the weld. The variations in thermophysical properties exerted an influence on the tensile strength by impacting both the melt depth and the grain morphology of the weld but did not yield a significant impact on the average microhardness.

Optimization of laser spiral welding using Response surface methodology and genetic algorithms

In the laser spiral welding (LSW) process, the welding parameters have a significant impact on the weld quality. In this paper, experiments were conducted and experimental data were collected on galvanized steel sheets using the LSW process, and mathematical models were developed using response surface methodology (RSM) and genetic algorithm (GA) to verify the specific effects of each process parameter on the weld and to perform process optimization. Laser power, welding speed, gap and focal length were selected as the influencing factors, and melt depth, melt width and concave as the output results. In the RSM model we found that the laser power was positively correlated with the weld depth and width, while the welding speed was inversely correlated with the weld depth and width, the gap was positively correlated with the amount of concave, and the focal length had no significant effect on the weld. In the GA model we use a large amount of experimental data for BP neural network training and iterative optimization using a genetic algorithm. Validation experiments were conducted on two models, and the results indicated that the two models had higher accuracy in predicting the welding depth and width compared to predicting the concave. The GA model had an 8% increase in tensile strength and a 25% increase in plasticity of the weld joint obtained from the optimal process compared to the RSM model. The GA model has higher accuracy in optimizing the LSW process.

Numerical and experimental study on keyhole dynamics and pore formation mechanisms during adjustable-ring-mode laser welding of medium-thick aluminum alloy

Keyhole induced-pore is one of the biggest challenges in laser welding of aluminum alloys. A shaped laser controlling strategy, ring-mode laser, has shown the possibility of reducing porosity in welding due to its potential to enlarge keyhole openings and improve the stability of the keyhole. However, few attempts have been made to reveal the influence of ring-mode laser on keyhole dynamics and pore formation. This paper quantitatively investigated porosity improvement during adjustable-ring-mode laser welding (ARM-LW) of aluminum alloys and analyzed keyhole dynamics and porosity formation mechanisms using a validated model. Experimental results indicate that porosity can be dramatically reduced when compounding a ring laser beam over the Gaussian beam. As the core/ring power ratio adjusts from 10:0 to 5:5, the porosity decreases significantly and remains lower (1.73%∼2.58%) while ensuring a similar melt depth (5∼6 mm). Simulation results demonstrate that two mechanisms work synergistically to suppress porosity: (1) The ring-mode laser contributes to decreasing keyhole collapse and regulating melt pool flow, hence reducing pores created at the Gas-Liquid interface (G/L-pore); (2) The ring-mode laser facilitates reducing the frequency and depth of keyhole into the melt pool, thus minimizing pores created at the Liquid-Solid interface (L/S-pore). This work can guide the porosity suppression during laser welding of aluminum alloys and is of significant theoretical meaning and application value.

Feasibility study on natural cold energy utilization in negative temperature underground space rock mass in permafrost region of northeast China

This study aims to investigate the possibility of using natural cold energy to establish a negative temperature space in northeast China by combining previous studies on natural cold energy and the ground temperature data obtained in northeast China. The temperature field changes of different rock masses after joining different depths of the subsurface space were simulated and analyzed by the finite element software COMSOL, exploring the feasibility of establishing underground spaces that maintain a temperature below 0 °C. The numerical simulation results show that the maximum melting depths of granite, limestone and basalt rocks are −6.4 m, −7.85 m and −5.34 m after adding underground space in the Genhe area under the proposed conditions. The temperature in the underground space is lower than the initial setting temperature after a year of temperature change influence, this indicates a surplus of cold energy, Therefore, the goal of maintaining negative temperature in the underground space year-round with zero energy consumption in the Genhe region is feasible. This paper provides new ideas for the utilization of cold resources in China and helps to better achieve the goal of sustainable development.

Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

The failure mechanism of plasma-facing components (PFCs) under extreme plasma conditions relevant for fusion reactors were investigated. Here, edge-localized mode (ELM)-like transient thermal shock irradiation experiments were performed on tungsten and molybdenum using compressed plasma flow, and combined with thermal–mechanical analysis by means of finite element simulations to discuss the grain structure evolution, cracking behavior and variations of hardness. When ELM-like thermal shock irradiation was sufficient to melt tungsten and molybdenum, a submicron-sized cellular sub-grain structure was created on their surface due to the high temperature gradient of the molten layer under the effect of Bénard–Marangoni instability. Rapid directional solidification from the bottom of the molten layer to the surface induced the formation of columnar grains dominated by the <200> orientation. While the formation of cellular sub-grains increased hardness, the thermal effect of irradiation and the formation of columnar grains led to softening. The high thermal stress induced by the ELM-like thermal shock produced macro-cracks and micro-cracks on the surface of tungsten and only micro-cracks on the surface of molybdenum. Macro-cracks were generated due to the intrinsic brittleness of tungsten. As a result of stress evolution, longitudinal macro-cracks extending perpendicular to the surface experienced transverse transformation within the material. Micro-cracks formed due to the embrittlement of the re-solidification zone, and their width increased with the melting depth. These results help us to understand failure mechanisms in PFCs under extreme operating conditions and are valuable for developing future fusion reactors.

Study on the coupling thermal effect of thermokarst lake and high sunny slope on permafrost embankment

Sunny-shady slope and thermokarst lake are widely distributed along the Qinghai-Tibet highway (QTH), and their thermal influence on permafrost embankment can induce serious engineering diseases and affect its long-term service performance. This study aims to reveal the coupling thermal impact mechanism of roadside thermokarst lake and high sunny-slope on permafrost embankment. Firstly, an in-situ ground temperature monitoring site at K2952 + 300 section of QTH has been built and temperature distribution characteristic of observed embankment are investigated. Then, three numerical models are established and spatial–temporal characteristics of asymmetric temperature filed of permafrost embankment have also been analysed and compared. The results show that: (1) Permafrost artificial upper limit of observed embankment has a large fluctuation with the synergy of high sunny slope and thermokarst lake, and severe unilateral thermal erosion leads to the aggravation of subgrade disease despite heat pipes treatment has been adopted. (2) Thermalkarst lake has a certain degree of lateral thermal influence on permafrost embankment, while the magnitude of its thermal impact is related to the distance from embankment. (3) Significant endothermic effect of 5.3 m height sunny slope accelerates the melting depth of embankment underlying permafrost, and triggers off asymmetry morphology of permafrost temperature field. (4) Under the action of ipsilateral thermokarst lake and high sunny slope, the maximum melting depth and thawing plate deviation of embankment underlying permafrost can be exacerbated simultaneously, and the lateral thermal erosion caused by these two factors becomes more intensive as the thermokarst lake gradually approaches the roadbed.

U–Pb geochronology and geochemistry of dikes in the Changbaishan Tianchi volcanic field (NE China) and their relations with the coeval Jingbohu and Longgang monogenetic volcanic fields

ABSTRACT The plain around the intraplate Changbaishan Tianchi volcano in NE China includes monogenetic cones whose shallowest plumbing system consists of dikes, and three main phases of activity are recognized since 2.8 Ma. The monogenetic volcanism mainly developed in the shield-forming phase (2.8–0.3 Ma), but the age and geochemical features of many of these vents remain poorly known. Here, we present geochemical, Sr‒Nd‒Pb isotopic and zircon trace element data from two dikes feeding monogenetic vents located north and northwest of the Changbaishan Tianchi volcano. Our aim is to constrain the emplacement age, the magma evolution processes, and the mantle source. We compare our results with those from the Jingbohu and Longgang monogenetic vents located north and west of the Changbaishan Tianchi volcano to investigate possible mantle heterogeneities in the recent NE China volcanism. The two Changbaishan dikes have 230Th disequilibrium-corrected ages of 1.27 and 1.00 Ma and show a basaltic composition with a potassic affinity. The Mg# values are 35.48–34.27 and 66.09–65.79. The whole-rock compositions, trace element compositions, and Sr‒Nd variations are consistent with fractional crystallization and minor contamination with lower crustal material, indicating an OIB-like mantle source with an EMI component possibly related to fluids released from the underlying Pacific flat slab. The melting depth determined from Na/Ti and Sm/Yb is between 140 and 180 km, i.e. the asthenospheric mantle. The dikes are characterized by (K2O+Na2O)/δEu, La/Ba, Ba/Nb, La/Sm, and La/Nb values similar to those of the Jingbohu and Longgang basaltic rocks. We conclude that the NE China volcanism at approximately 1 Ma was related to a single, relatively homogeneous OIB-like mantle source modified by ascending slab-derived fluids. According to the available geophysical data, the ascending magmas stopped at the mantle/lower crust interface and experienced limited crustal contamination.

Lithosphere tearing and foundering during continental subduction: Insights from Oligocene−Miocene magmatism in southern Tibet

The distribution of Oligo−Miocene magmatic rocks from southern Tibet in space and time yields critical information on the geometry and deformation of the subducted Indian lithosphere which impacts on plateau growth following the India and Eurasia collision. A growing body of geophysical evidence has shown that the subducted Indian lithosphere beneath the Tibetan Plateau has been torn apart. However, the spatiotemporal distribution and cause of the tearing remain enigmatic. Timing of the post-collisional magmatic rocks in southern Tibet exhibits four patterns of decreasing ages; magmatism began earlier in the west and east Himalayan syntaxis and evolved to two age undulations in the central southern Tibet. Seismic images show that regions of slab window (both 90°E and 84°E) and flattened subducted lithosphere (both 86°E and 81°E) are present at depth of 135 km. Correspondingly, increasing mineral crystallization temperatures (absolute value of 50 °C) were recorded in the Oligo−Miocene ultrapotassic-potassic rocks at 90°E and 84°E, while opposing trends were shown by coeval ultrapotassic-potassic rocks at 86°E and 81°E. Besides, the melting depth of the Oligo−Miocene ultrapotassic-potassic primitive melts decreases from nearly 100 km to 70 km between 81°E and 90°E, probably indicating progressive rising of the lithosphere-asthenosphere boundary. Such variations were possibly the results of the focused flow and upwelling of asthenosphere, which advanced rapidly but diachronously through weakened and torn sectors within the overlying Indian slab. The upwellings probably induced diachronously upward bending of the residual Indian slab and its flattening, which accelerated the tearing of the Indian lithosphere during continental subduction.

Influence of Novel Beam Shapes on Laser-Based Processing of High-Strength Aluminium Alloys on the Basis of EN AW-5083 Single Weld Tracks

The commonly used Gaussian intensity distribution during the laser-based processing of metals can negatively affect melt pool stability, which might lead to defects such as porosity, hot cracking, or poor surface quality. Hot cracking is a major factor in limiting production rates of high-strength aluminium alloys in laser-based processes such as welding or the powder bed fusion of metals (PBF-LB/M). Going away from a Gaussian intensity distribution to ring-shaped profiles allows for a more even heat distribution during processing, resulting in more stable melt pools and reduced defect formations. Therefore, the aim of this study is to investigate the influence of different laser beam profiles on the processing of high-strength aluminium alloys by using a multicore fiber laser, allowing for in-house beam shaping. Single weld tracks on the aluminium alloy EN AW-5083 are produced with varying laser powers and weld speeds, as well as different beam profiles, ranging from Gaussian intensity distribution to point/ring profiles. The molten cross sections are analyzed regarding their geometry and defects, and the surface roughness of the weld tracks is measured. By using point/ring beam profiles, the processing window can be significantly increased. Hot cracking is considerably reduced for weld speeds of up to 1000 mm/s compared to the Gaussian beam profile. Furthermore, the melt pool width and depth are more stable, with varying parameters for the point/ring profiles, while the Gaussian beam tends to keyhole formation at higher beam powers. Finally, a strong decrease in surface roughness for the point/ring profiles, accompanied by a significantly reduced humping effect, starting even at lower beam powers of 200 W, can be observed. Therefore, these results show the potential of beam shaping for further applications in laser-based processing of high-strength aluminium alloys.

A Spectral Study of the Caloris Basin on Mercury and the Origin of Associated Volcanic Smooth Plains

AbstractResults from the NASA/MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission showed that 27% of Mercury's surface is covered by smooth plains mostly produced by extensive effusive volcanism. The Caloris impact basin is associated with two, mostly volcanic, smooth plains, one in its interior and one surrounding the basin. Previous studies have shown that it is difficult to estimate the relative ages of the interior and exterior plains and to explain their spectral and compositional differences. We perform an exhaustive spectral analysis of the basin based on data obtained by the Mercury Atmospheric and Surface Composition Spectrometer spectrometer onboard MESSENGER between 300 and 1,450 nm with a 5 nm resolution. Unlike previous results based on crater counts, we found that the exterior plains were emplaced before the interior plains although both postdate the formation of the basin. We propose a decrease in the partial melting degree and/or partial melting depth over time to explain the spectral and compositional differences. The study highlights spectrally heterogeneous exterior plains associated with a compositional heterogeneity and the presence of low reflectance material (LRM) deposits. This heterogeneity in the exterior plains could be related to the formation of the basin and asymmetry of the ejecta deposits or to a heterogeneous distribution of LRM present at depths before the formation of the basin.

Transition mechanism of melt depth in vacuum during laser powder bed fusion using in-situ X-ray and thermal imaging

Transition mechanism of melt depth in vacuum during laser powder bed fusion using in-situ X-ray and thermal imaging

Microstructure Formation and Mechanical Properties of Metastable Titanium-Based Gradient Coating Fabricated via Intense Pulse Ion Beam Melt Mixing.

The unique flash heating characteristics of intense pulsed ion beams (IPIB) offer potential advantages to fabricate high-performance coatings with non-equilibrium structures. In this study, titanium-chromium (Ti-Cr) alloy coatings are prepared through magnetron sputtering and successive IPIB irradiation, and the feasibility of IPIB melt mixing (IPIBMM) for a film-substrate system is verified via finite elements analysis. The experimental results reveal that the melting depth is 1.15 μm under IPIB irradiation, which is in close agreement with the calculation value (1.18 μm). The film and substrate form a Ti-Cr alloy coating by IPIBMM. The coating has a continuous gradient composition distribution, metallurgically bonding on the Ti substrate via IPIBMM. Increasing the IPIB pulse number leads to more complete element mixing and the elimination of surface cracks and craters. Additionally, the IPIB irradiation induces the formation of supersaturated solid solutions, lattice transition, and preferred orientation change, contributing to an increase in hardness and a decrease in elastic modulus with continuous irradiation. Notably, the coating treated with 20 pulses demonstrates a remarkable hardness (4.8 GPa), more than twice that of pure Ti, and a lower elastic modulus (100.3 GPa), 20% less than that of pure Ti. The analysis of the load-displacement curves and H-E ratios indicates that the Ti-Cr alloy coated samples exhibit better plasticity and wear resistance compared to pure Ti. Specifically, the coating formed after 20 pulses exhibits exceptional wear resistance, as demonstrated by its H3/E2 value being 14 times higher than that of pure Ti. This development provides an efficient and eco-friendly method for designing robust-adhesion coatings with specific structures, which can be extended to various bi- or multi-element material systems.

Research on Coordinated Control Strategy of Thermal Heating and Melting Depth of Steam Heating and Melting Salt Reservoir

The implementation of the upgrading of the national coal electric power unit has provided a clear proposal to promote the clean and low-carbon transformation of the power industry. With the power of large-scale intermittent renewable energy and power generation, the electric crew should be flexible enough to adjust resources to achieve a depth of 35% THA. This article aims to propose a heat extracting and heat storage system for fire power plants, to realize the coordinated control strategy of the deep peak, and to explore the coordinated control strategy of the steam–molten salt heat exchanger, molten salt and water exchanger, and the turbine’s main control. The simulation results reveal that the coordinated control of the steam–molten salt heat exchanger, molten salt and water heat exchanger, and steam turbine control could reduce the depth of the fire power unit by 10% THA. The output power response speed of the thermal power unit is enhanced by utilizing the heat turbine, which could effectively enhance the output power response speed of the thermal power unit and increase the output power response speed pertinent to 302.55 s by 75.60%.

Origin of Alkaline Basaltic Intrusive Rocks in an Exhumed Accretionary Complex: Implications for Past Petit‐Spot Volcanism in the Ocean

AbstractAccreted basaltic rocks are expected to provide information on intraplate volcanism in the oceans. Basaltic rocks, originating from mid‐ocean ridges, plateaus, and seamounts, have been reported from exhumed accretionary complexes. However, basaltic rocks related to petit‐spot volcanism remain poorly documented. We examined basaltic intrusive rocks in an exhumed accretionary complex on Amami‐Oshima Island, Ryukyu Arc. Basaltic sills intruded mélange composed of seamount‐derived micritic limestone and basaltic rocks, which deformed together with the mudstone‐dominated mélange in the subduction zone. A separate basaltic sill intruded pelagic chert before being incorporated as a mélange block in the mudstone matrix during deformation in the subduction zone. Geochemical discrimination diagrams and trace element patterns indicate that the accreted dolerites and nonintrusive basalts likely originate from mid‐ocean ridges and hotspots, respectively. On the other hand, the geochemical characteristics of basaltic sills are compatible with alkaline basalt with enriched in incompatible trace elements relative to other basaltic rocks of hotspot origin and may represent a low degree of partial melting from a deeper mantle source (&gt;90 km). A higher ratio of gadolinium to ytterbium in the basaltic sills relative to hotspot or mid‐ocean ridge‐related basalt indicates both a deeper melting depth, and a magma source which upwelled through thick oceanic lithosphere far from the mid‐ocean ridge. Based on the timing of basaltic intrusion and geochemical features, we suggest that the basaltic intrusive rocks could record past petit‐spot volcanism in the oceanic plate.

Effects of melt depth on oxygen transport in silicon crystal growth by continuous-feeding Czochralski method

The continuous-feeding Czochralski method (CCz) is an effective and promising way for the high-quality and large-weight monocrystalline silicon growth. In the CCz technology, the inner crucible is employed to prevent unmelted silicon granules from being transported to the melt-crystal interface, which introduces a new source of oxygen impurities and makes the temperature and flow distribution in the melt complicated. So it is challenging to regulate the oxygen impurities at the m-c interface in the CCz process. The melt depth stays constant during the CCz process, and it determines the crucible area where oxygen impurities are dissolved. Therefore, in order to manage and minimize the oxygen impurities at the m-c interface, controlling the melt depth may be a good way. In the study, the influence of melt depth on oxygen impurity distribution at the melt-crystal interface is investigated using a series of global simulations coupled with the transport of oxygen and carbon impurities. The findings indicate that as melt depth increases, the temperature of the crucible wall inside the inner crucible drops, and oxygen impurities transported from the melt between the inner and outer crucibles to the interior of the inner crucible likewise decrease in content. However, the rate of SiO evaporation at the free melt surface inside the inner crucible essentially stays the same. Therefore, the oxygen impurity content at the melt-crystal (m-c) interface decreases with the increase of melt depth. The paper also suggests that while constructing the scheme for lowering oxygen content, it is necessary to take into account the position relation between the heater and the crucible, the height of the crucible above the free melt surface, and the rotation of the inner crucible.

Discussion on “Stinging News: ‘Dickinsonia’ discovered in the Upper Vindhyan of India not worth the buzz” by Meert, et al. (2023)

Widespread orogenesis associated with supercontinent assembly generates extensive collisional mountain chains with high elevations that are crucial for modulating the interaction between the atmosphere and lithosphere. However, not all supercontinents formed over Earth's history shared the same topography. This study investigates the temporal variation over the last 1.5 Ga in La/Zr ratio of continental-arc mafic volcanic rocks. We show that 0.6–0.5 Ga rocks related to Gondwana assembly are characterized by much higher La/Zr ratios compared with 1.2–0.9 Ga rocks formed during Rodinia assembly. Thermodynamic modeling reveals that the La/Zr ratios of continental-arc magmas are predominantly controlled by melting depth, which is directly tied to the thickness of the overlying arc crust. Thick continental arc decreases the extent of melting in the mantle wedge, leading to an increase in La/Zr ratios. Higher La/Zr ratios of continental-arc rocks during Gondwana vs. Rodinia assembly thus imply thicker continental arcs for the younger supercontinent. We suggest that the secular La/Zr ratio of continental-arc mafic magmas is an effective geochemical indicator of topography difference between the Rodinia and Gondwana supercontinents, with implications for coupling between the evolution of the lithosphere and atmosphere.

Imaging the magmatic plumbing of the Clear Lake Volcanic Field using 3-D gravity inversions

The Quaternary Clear Lake Volcanic Field (CLVF) in the Northern California Coast Range is the youngest of a string of northward-younging volcanic centers in the state. The CLVF is located within the broad San Andreas Transform Fault System and has been active intermittently for ∼2 million years. Heat beneath the CLVF supports The Geysers, one of the largest producing geothermal fields in the world.Previous geophysical studies proposed the existence of a magma reservoir beneath Mount Hannah, which is northeast of The Geysers, near the geographic center of the CLVF. The lateral extent, depth, and presence of melt within this reservoir are poorly constrained, as is the relationship between this body and the broader magmatic plumbing of the CLVF. To gain a clearer and more comprehensive picture of the CLVF magma source region, a gravity dataset was compiled and the first 3-D gravity inversions of the CLVF were completed.Field and synthetic model inversions from the current study both indicate that the gravity low roughly centered on Mount Hannah is not accurately explained by a 5–7 km thick lens of Mesozoic Great Valley Sequence (ρ=2.58g/cm3) as proposed by Stanley et al. (1998). The observed gravity low is more accurately described by one or more silicic, partial melt bodies between The Geysers and Mount Hannah. Although our inversions cannot constrain the exact depth and geometry of these bodies, the recovered models indicate the existence of a partial melt zone between 6 and 13 km depth.The prolonged eruption history of the CLVF, coupled with the compositional variation of erupted rocks over time and space, is consistent with the existence of several, potentially ephemeral, melt-bearing bodies as opposed to one large melt body. Given the density and location of the recovered anomaly, rhyolite-MELTS thermodynamic modeling suggests the existence of 10–30% rhyodacitic melt within the proposed silicic magma reservoir at about 700 °C and 8 km depth (210 MPa). Independent petrologic, geochemical, and seismic evidence indicates that this silicic partial melt zone is underlain by basaltic melt in the lower to middle crust (13 to 21 km depth), which is fed by a mantle source.Eruptions in the past ∼8.5–13.5 thousand years; high regional heat flow; 3He enrichment of hydrothermal fluids; and our modeling, which suggests the presence of a mid-crustal, silicic partial melt zone, point to a still-active CLVF. The relatively low estimates of partial melt (10–30%) predicted by thermodynamic modeling indicates that an injection of new magma into the imaged partial melt zone is needed to generate sufficient melt to incite future eruptions. Despite the low percent melt estimates within the proposed silicic partial melt zone the potential for future volcanic eruption remains. Due to the proximity of the CLVF to cities surrounding Clear Lake and the densely populated San Francisco Bay Area, continued research and monitoring of the volcanic field are warranted. The geophysical and petrologic modeling presented here improves our understanding of the CLVF magma plumbing system and allows us to better characterize its associated volcanic hazards.

Design and performance analysis of solar air heater with phase change materials

A novel solar air heater (SAH) with provision of integrating phase change material (PCM) was designed and developed in the Department of Energy, Tezpur University located in (26.7003°N and 92.8308°E). A code was developed in MATLAB platform to estimate design parameters of the PCMSAH viz., (i) air mass flow rate (0.018 kg/s), (ii) length of the absorber plate (1.57 m) and thickness of PCM cavity (1 cm) based on energy analysis. Required quantities of selected PCMs viz., acetamide (14.56 kg), stearic acid (12.12 kg) and paraffin wax (11.30 kg) were also assessed based on the PCM melting depth. Close agreement between the simulated and experimental outlet temperature was obtained and the mean relative error between experimental and theoretical outlet temperature for three different PCMs are 4.50 % (paraffin wax), 2.32 % (stearic acid) and 2.63 % (acetamide). Performances of the SAH with various PCMs (including acetamide, stearic acid, and paraffin wax) were compared to those of an identical SAH without PCM during both charging and discharging periods of operation. According to the outlet temperature profile of SAH with PCM compared to SAH without PCM, use of PCM becomes advantageous in terms of higher and smoother outlet temperature during the low sunshine period. The absorbed, useful, loss and stored heat for all the three PCMs were estimated, and paraffin wax was found to be highest as 36.56 kW, 14.13 kW, 0.83 kW and 21.59 kW. In terms of efficiency the paraffin wax (52.83 %) based SAH ranked first followed by stearic acid (52.31 %) and acetamide (47.25 %). During performance comparison between SAH with PCM and without PCM, efficiency of SAH with acetamide is found to be 15.09 % higher to the SAH without acetamide, similarly for SAH with paraffin wax is 8.18 % and acetamide is 6.67 % higher to the SAH without PCM respectively. The uncertainty analysis was carried out for thermal efficiency of the SAH is determined to be ±2.02 %. The novel PCM integrated SAH will be useful in space heating and solar drying of the local perishable agricultural products. It is also possible to carry out detail technique for selection of PCM for solar drying application along with the exergy, economy, and environmental analysis of the PCMSAH.

Numerical insight into heat transfer in surface melting and ablation subject to femtosecond laser processing aluminum

In the present work, the heat transfer in surface melting and ablation subject to femtosecond laser processing aluminum is investigated by a proposed algorithm concentrating on the energy consumed by latent heat of melting. The electron temperature-dependent material optical and thermophysical properties are employed in solving the two-temperature model (TTM). The evolutions of electron temperature and ion temperature pave a spatiotemporal way for evaluating the surface melting and ablation. The validation of proposed model is carried out by comparing the numerically calculated ablation depth with the experimentally measured ablation depth. The fraction of liquid by taking the latent heat of melting into account is put forward to describe the surface melting. A mushy zone characterizing the surface melting is identified. The electron-ion coupled heat transfer is found to trigger the rapid expansion of the mushy zone and melting depth in ultrafast surface melting. The energy consumed by latent heat of melting accounts for the delay of melting initiation moment and smaller melting depth, but it is inappreciable to ablation. Moreover, the energy loss through thermal radiation is numerically proved to have a neglectable impact on surface melting and ablation.