High Thermal Diffusivity Research Articles

Molten pool behaviors and printability of tungsten anti-scattering grids with extremely thin wall thickness fabricated via laser powder bed fusion

It is challenging for laser powder bed fusion (LPBF) technique to fabricate metal parts with a wall thickness below 100 μm. This work investigated the critical conditions for achieving extremely thin wall thickness in tungsten grids fabricated via LPBF. Specifically, the impact of low energy density on the printability of tungsten single tracks and grids via LPBF was comprehensively examined. A computational fluid dynamics approach was employed to develop a thermal fluid flow model for single tracks with multilayers in LPBF. The findings demonstrate that at low energy densities, single tracks exhibit four different morphologies, i.e., balling, discontinuity and winding, discontinuity but straightness, as well as continuity and straightness. The simulation model effectively elucidates the continuity of single tracks and provides insights into the governing mechanism of molten pool defects. Due to high thermal diffusion properties of tungsten, the continuity of its track relies on the connection of neighboring molten pools and is sensitive to scanning speed. The tungsten molten pools with low energy density can be categorized into shallow flows affected by surface morphology and deep flows influenced by internal voids of the powder bed. After multi-layer stacking, the track fluctuations and defects in single tracks accumulated into greater surface roughness and deteriorate thin-walled morphology. The critical conditions required for printing extremely thin walls were achieved, ensuring minimal merging of tracks between two layers by maintaining the energy density of 57J/mm3. Based on these findings, an ultra-thin-walled anti-scattering tungsten grid with a wall thickness of 86 μm and a wall roughness below 3.3 μm (Ra) was fabricated by LPBF. This work provides valuable theoretical insights and presents a viable methodology for determining the minimum energy density threshold and wall thickness essential for LPBF processing of thin-walled components.

Highly efficient multi-layer flexible heatsink for wearable thermoelectric cooling

Flexible thermoelectric cooler (fTEC), which interfaces well with curved human body surface and provides cooling functions, is an emerging candidate for personal thermal management and non-hospitalized medical treatment. Achieving efficient and long-term cooling performance of TEC requires high thermal conductivity and heat diffusion of the hot side, which has yet to achieve. In this study, we design and fabricate a highly thermally conductive and flexible heatsink with a multi-layered structure especially for wearable TEC wristband, which obtains a large temperature drop (8.8 °C) for imitated on-body test and the maxim 13.1 °C temperature decrease in air. Here, we demonstrate that a well-designed functional composite layer, including phase change material, thermally conductive fillers and metal foam, can establish an effective equilibration among cooling performance, thermal management capacity and mechanical property. Particularly, the heatsink with highly thermal conductive skeleton (k ∼ 2.7 W/mK) and effective heat dissipating fins can significantly improve heat conduction and dissipation, which improve the cooling performance by more than 55 %. With the help of theoretical simulation, we propose a promising strategy for heat management on thermoelectric device through a flexible multi-layered structure, paving the way for achieving practical applications of wearable thermoelectric coolers for personal thermal regulation or cooling therapy.

Additive effect of silicone resin on direct current arc quenching performance of a model electric fuse: electrical resistivity and thermal diffusivity of high-temperature Cu/SiO2 vapor mixed with C2H6SiO vapor decomposition

Concerning DC fuses equipped with silica sand (SiO2) as an arc quenching material, the authors have proposed an additive installation of silicone resin (C2H6SiO) on a fuse-element surface to improve the limitation and interruption ability of high DC. This paper describes the additive effect of the silicone resin on the transient resistance of the arc that has formed during the DC interrupting process in a model fuse, based on the measurement result that the arc resistance markedly rises with the silicone mass coated on the fuse element. This phenomenon is subsequently explained as resulting from a thermal diffusivity of high-temperature C2H6SiO/SiO2/Cu vapor. In other words, the mixing of C2H6SiO decomposition vapor into the arc can promote vapor temperature decay through the higher thermal diffusivity, resulting in a rapid increase in the electrical resistivity of the vapor during the DC interrupting process.

Impingement of vortex dipole on heated boundaries and related thermal plume dynamics

The profound influence of an externally induced vortex dipole on thermal plume dynamics is numerically studied for varying Rayleigh numbers (Ra) employing the Bhatnagar–Gross–Krook collision model-based lattice Boltzmann method with a double distribution function approach. This study is extended to vortex dipole impingement with different types of heated bottom boundaries of two-dimensional domain, such as flat, “V-shaped,” and “inverted-V-shaped.” The vortex dipole impingement with the heated boundaries generates secondary vortices, which in turn produce vortex-driven thermal plumes, thereby advancing plume generation. The subsequent merging of the plumes enhances heat transport and leads to a continuous plume ascent. The presence of convex corners facilitates flow separation and also gives rise to the formation of secondary vortex dipoles, thereby significantly impacting the continuous generation of jet-like plumes when compared to concave configurations. The lack of an external vortex in pure buoyancy-driven flows produces less pronounced jet-like plumes and a relatively low Nusselt number. The boundary types and Ra significantly influence the vorticity production, resulting in higher enstrophy and palinstrophy for convex boundaries compared to flat and concave ones. A lower Prandtl number increases secondary vortices and corner rolls, leading to larger velocity gradients, higher thermal diffusivity, resulting in increased kinetic energy and thermal dissipation rates. The increased cell height enhances heat transfer at the top boundary due to improved heat convection from the slanted boundary and influence of early dipole impingement. Furthermore, kinetic energy dissipates in the dipole-driven flows and increases in the buoyancy-dominated flows.

Supersonic hot jet ablative testing and analysis of boron nitride nanotube hybrid composites

Boron nitride nanotubes (BNNTs) are high-strength, high-modulus nanotubes with high thermal and oxidative stabilities. Two hybrid composites were prepared with satin weave carbon fiber (CF) and resole-type phenolic resin: one with surface layers of BNNTs and one with alternating interlayers of BNNTs. The samples were subjected to hot jet tests that simulate realistic high-pressure-temperature conditions to understand the behavior of BNNTs under high-pressure erosion. Adding BNNTs to CF/phenolic laminates enhanced the ablation resistance by reinforcing the char material and mitigated localized thermal damage. Hybrid laminates exhibited up to 14 % lower weight loss, 55 % increase in flexural modulus, higher thermal diffusivity, and improved char yield and microstructure compared to CF/phenolic samples. The surface layer hybrid had many surviving nanotubes reinforcing the char and crystalline oxide structures that could mitigate further oxygen diffusion. Various characterization methods were used to deduce possible mechanisms and their products, indicating that BNNTs could serve as growth templates for direct crystalline boron oxide formation. Overall, hybrid BNNT/CF/phenolic laminates displayed better ablation resistance and favorable microstructure evolution under high-pressure conditions.

Pressureless Welding of Temperature-Invariant Multifunctionality Body Based on Hydroxyl-Functionalized Boron Nitride Nanosheets and Bifunctional Monoethanolamine Cross-linker.

Bulk hexagonal boron nitride (h-BN) ceramics with structural integrity, high-temperature resistance and low expansion rate are expected for multifunctional applications in extreme conditions. However, due to its sluggish self-diffusion and intrinsic inertness, it remains a great challenge to overcome high-energy barrier for h-BN powder sintering. Herein, a cross-linking and pressureless-welding strategy is reported to produce bulk boron nitride nanosheets (BNNSs) ceramics with well-crystalized and dense B-N covalent-welding frameworks. The essence of this synthesis strategy lies in the construction of >B─O─H2C─H2C─H2N:→B< bond bridge connection structure among hydroxyl functionalized BNNSs (BNNSs-OH) using bifunctional monoethanolamine (MEA) as cross-linker through esterification and intermolecular-coordination reactions. The prepared BNNSs-interlaced ceramics have densities not less than 1.2gcm-3, and exhibit exceptional mechanical robustness and resiliency, excellent thermomechanical stability, ultra-low linear thermal expansion coefficient of 0.06ppm°C-1, and high thermal diffusion coefficient of 4.76mm2s-1 at 25°C and 3.72mm2s-1 at 450°C. This research not only reduces the free energy barrier from h-BN particles to bulk ceramics through facile multi-step physicochemical reaction, but also stimulates further exploration of multifunctional applications for bulk h-BN ceramics over a wide temperature range.

Experimental investigation of the effect of droplet size on the vaporization of butanol in turbulent environments at elevated pressure

This paper presents an experimental study of the effect of droplet size on the vaporization rate of butanol fuel under turbulent flow conditions at elevated pressure and room temperature. The butanol droplet is suspended at the intersection of two micro-fibers in the center of a spherical vessel. The initial size of the butanol droplet is varied in the range between 300 and 700 μm. A controlled turbulent flow field, characterized by quasi-zero mean velocity and turbulence intensity of up to 1.5 m/s, was generated by eight axial fans. The findings reveal an improvement in the vaporization rate of butanol droplet as the droplet size increases. This improvement is more pronounced under conditions of elevated pressure and turbulence intensity. The results show that turbulence begins to influence the vaporization process when the droplet diameter exceeds the Kolmogorov length scale. Butanol droplet vaporization rate is found to lie between heptane and decane, leaning towards decane under all explored test conditions. The results reveal that the vaporization rate of hydrocarbon fuels is more sensitive to the droplet size variations than butanol. Turbulence is found to exert greater impact on the vaporization of fuels that have lower gas-phase mass diffusivity and higher thermal diffusivity. Finally, the previously proposed correlations, expressed in terms of Damköhler and turbulent Reynolds numbers, are assessed and found capable of predicting the vaporization of butanol droplet over a wide range size.

Plasma sprayed K2Ti6O13 as thermal barrier coatings with high thermal swing for diesel piston enabled by inter-splat bonding and porosity tailoring

Thermal swing coatings with high thermal diffusivity but low thermal conductivity could increase the efficiency of diesel engines by minimizing the piston surface thermal gradient. However, the thermal diffusivity is usually positively related to the thermal conductivity and thus it is generally difficult to deposit thermal barrier coating with a low thermal conductivity but high thermal diffusivity by plasma spraying. In the present work, K2Ti6O13 with intrinsic low thermal conductivity and low melting point (1350 °C) was used as the coating material to prepare a coating with a high ratio of thermal diffusivity to thermal conductivity. Results revealed that due to the low melting point feature of K2Ti6O13 all plasma sprayed coatings have high inter-splat bonding quality which resulted in a high thermal diffusivity close to the sintered counterpart. K2Ti6O13 coatings of high porosity were plasma sprayed by optimizing powder structure, which leads to a low thermal conductivity but influences little the thermal diffusivity. It is also found that the preferential evaporation of potassium oxide from the K2Ti6O13 molten droplets leads to the formation of the TiO2 phase and generates global pores in the coating. At optimized spray conditions by using sintered porous powder, the K2Ti6O13 coating with a porosity of 21 % and single K2Ti6O13 phase reveals the lowest thermal conductivity of 0.85 W/m·K and a high diffusivity of 0.43 mm2/s. The coating exhibits the highest thermal swing of about 91 °C, having much higher performance than the conventional thermal barrier coatings used for enhancing the thermal swing effect.

Analytical solution model of heat transfer for energy soldier piles during excavation to backfilling

This paper presents a two-dimensional heat transfer model for energy soldier piles during excavation and after backfilling. Based on Green's function and separation of variables method, this model considers the heat transfer process from various angles during excavation and after backfilling, deriving a series of analytical solutions for the heat transfer processes. It is more suitable for solving the heat transfer problem of energy soldier piles. The accuracy of the analytical solution was verified by numerical simulation and classical analytical solutions. Then, the effects of air convection coefficient and backfill materials' thermal diffusivity on heat transfer are analyzed. The results show that the temperature rise of both the soil and the pile in the non-excavated case (ordinary energy pile) is lower than that of the various convective coefficient cases, and the convective heat transfer contributes to the heat transfer capacity of energy soldier piles. After backfilling, materials with higher thermal diffusivity have smaller temperature rise. Conversely, materials with lower thermal diffusivity have higher temperature rise. Under the long-term operation strategy, the heat flux within the soil and backfill is higher and favorable for heat transfer by selecting the backfill with lower thermal diffusivity.

Effects of thermal shocks on integrity of existing and newly-designed sealants for CCS applications

Sealants that can guarantee long-term wellbore sealing integrity are of great significance to the safe and sustainable storage of CO2 in carbon capture and storage (CCS). In this study, we investigate how abrupt cyclic thermal shocks affect the integrity of four sealants of different compositions. These sealants include two reference OPC-based blends (S1 and S2), one newly-designed OPC-based blend that contains CO2-sequestering additives (S3), and one calcium aluminate cement (CAC)-based blend designed for CCS applications (S4). We have measured the thermal properties of these samples, followed by quenching and flow-through experiments to apply strong cyclic thermal shocks on samples of the four sealants, where we heated the samples to 120 °C, and quenched them in, or flowed through water of 20 °C. Using X-ray tomography (32 µm/voxel) before and after the experiment showed that both S1, S2 (reference OPC-based) and S4 (CAC-based) broke after thermal-shocking experiments. Cracks and new voids developed in the samples. Post-treatment strength testing shows that thermal shocks reduce the unconfined compressive strength of these three sealants. This implies that these compositions may not be optimal materials for long-term wellbore sealing during CO2 injection and storage afterward. For all these three sealant compositions, quenching resulted in a greater reduction in strength (by 53 % on average) than flow-through experiments (by 29 % on average). On the contrary, we have not observed any cracks after either quenching or flow-through experiments in S3 sealant (OPC with CO2-sequestering additives). We attribute the intactness of this sealant after thermal shocks to its higher thermal diffusivity than the other three sealants. Heat transfers more rapidly in this sealant and the associated thermal stresses are mild and insufficient to cause any damage to its integrity, which makes this sealant a good candidate for wellbore sealing material that can effectively withstand strong thermal shocks encountered during CCS, though further studies are required.

PHOTOTHERMAL DEFLECTION ANALYSIS OF β-In2S3 THIN FILMS: THE EFFECT OF S/In MOLAR RATIOS

[Formula: see text]-In2S3 thin films ([Formula: see text], 2 and 4) were prepared using the pneumatic spray pyrolysis (PSP) route to analyze the effect of the S/In ratio on the physical properties. These properties were conducted using the photothermal deflection spectroscopy (PDS) method. The PDS signal amplitudes as a function of wavelength show multiple reflections which appear for all prepared In2S3 films. Such multiple reflections indicate homogeneity and high crystalline quality of the films. The deduced values of the optical band gap vary in the range 2.55–2.65[Formula: see text]eV. The highest thermal diffusivity is obtained for [Formula: see text]. The product ([Formula: see text]) is found in order of 10[Formula: see text][Formula: see text]cm[Formula: see text]/V. The estimated carrier diffusion lengths are 0.06, 0.11 and 0.09[Formula: see text][Formula: see text]m for films corresponding to [Formula: see text], 2 and 4, respectively. Defect absorption in [Formula: see text]-In2S3 films is also investigated by PDS. Five absorption peaks are observed. These absorption peaks contain defect information in the band gap. Hence, this work evidences that [Formula: see text]-In2S3 is a multi-functional material that can be used in optoelectronic, photovoltaic and visible-irradiation photocatalyst applications.

Compatibility of LaFe13−x−yMnxSiyH1.6 and Eutectic Liquid GaInSn Alloy

The heat transfer rate of magnetocaloric regenerators is a topic of extensive research and the cyclability of these regenerators is critical to the operation of systems with a high coefficient of performance (e.g., potentially &gt;22, significantly higher than typical vapor compression cooling technologies). To enable a high operating frequency that will result in a high specific cooling power, the heat transfer fluid should have high thermal conductivity and lower specific heat, i.e., higher thermal diffusivity. Eutectic metal alloys possess these qualities, such as gallium–indium–tin (Galinstan), whose thermal diffusivity has been found to be approximately an order of magnitude higher than water. For this study, the effects of eutectic liquid Galinstan exposure on the phase stability of LaFe13−x−yMnxSiyH1.6 magnetocaloric powders in an active magnetic regenerator device were investigated. The powders were characterized before and after exposure to Galinstan using X-ray diffraction, in which the phases were determined using the Rietveld refinement technique and X-ray fluorescence. It was found that after Galinstan exposure, hydrogen containing phases were present in the powder, suggesting that the hydrogen was lost from the magnetocaloric phase. The magnetocaloric phase degradation indicates that the powder was incompatible with the Galinstan metal in an environment with moisture.

Numerical heat transfer to LBE flow in a wire-wrapped 19-rod bundle using an OpenFOAM-based solver: fourParameterFoam

The LBE-cooled fast reactor (LFR) has received significant attention due to its diverse applications. However, numerical heat transfer simulations encounter challenges with lead-bismuth eutectic (LBE) due to its low Prandtl number and high molecular thermal diffusion, often resulting in an overestimation of heat transfer using the simple gradient diffusion hypothesis (SGDH). This study aims to improve the prediction accuracy of heat transfer to LBE in numerical models by developing a solver, named fourParameterFoam, based on the turbulent model SST k-ω and algebraic heat flux model (AHFM) kθ-ɛθ within the OpenFOAM framework. The performance of SGDH models and AHFMs is compared based on heat transfer experiments in vertical tube flow with LBE. The behavior of the turbulent Prandtl number (Prt) under various flow conditions is concluded based on the SST k-ω-kθ-ɛθ model. Additionally, the applicability of the SST k-ω-kθ-ɛθ model in complex flow is validated through heat transfer experiments in a wire-wrapped 19-rod bundle with LBE flow. Local temperature variations on the heated rod surface and sub-channels are analyzed to elucidate the thermal development process in the bundle. The impact of wire spacers on flow behavior is summarized using visualization techniques, and the suitability of corresponding empirical Nusselt number correlations in LBE flow is evaluated.

Cantilever enhanced fiber-optic photoacoustic microprobe for diffusion detection of sulfur dioxide

A cantilever enhanced fiber-optic photoacoustic microprobe with the cavity volume of only 119 μL is designed to detect SO2, which has the obvious advantages of passive sensing, anti-electromagnetic interference and low cost. A UV multi-mode fiber and a single-mode fiber are applied to transmit excitation light emitted by UV-LED and probe light, respectively. The lens assembly based on a collimating lens and a focusing lens is added to improve the light energy of UV-LED coupling into UV-fiber. Based on theoretical analysis and finite element method, a photoacoustic cavity with a radius of 1.5 mm and a length of 15 mm is designed, which is conducive to the realization of photoacoustic enhancement and rapid response at high frequencies. SO2 gas diffuses into the PA cavity through a hole with the diameter of 0.5 mm and a gap of the cantilever with the width of 0.5 µm. A fiber-optic cantilever based on F-P interference is adopted to detect sound pressure. The frequency characteristic and response time of the sensor in different backgrounds of SF6 and N2 are analyzed experimentally. Compared with N2, the photoacoustic microprobe operates in SF6 background with lower resonance frequency and longer response time, which is due to the high density and low thermal diffusivity of SF6 gas. With the flow rate of 250 SCCM in the external cavity, the response time of the photoacoustic microprobe to SO2/SF6 and SO2/N2 are 96 s and 40 s, respectively. The detection limits of SO2 in SF6 and N2 background are 35 ppb and 5 ppb, respectively.

Preparation and assessment of ionic liquid and few-layered graphene composites to enhance heat and mass transfer in adsorption cooling and desalination systems

Adsorption systems can utilise low-temperature renewable and waste heat sources, which have emerged as a feasible alternative to conventional water desalination and cooling systems. However, the material of poor heat and mass transfer performance stall their widespread utilisation. This article presents the development and investigation of new composites employing few-layered graphene platelets and ionic liquids, namely ethyl-methylimidazolium methane sulfonate ([EMIM][CH3SO3]) and Ethyl-methylimidazolium-chloride ([EMIM][Cl]) to address such challenges. The impact of the few-layered graphene platelets, thermal properties, water adsorption properties of the developed composites and their thermal diffusivity were experimentally investigated. Besides, the overall cyclic performance was studied experimentally at the material level and computationally at the component level by employing a previously validated 2D dynamic heat and mass transfer model. The experimental investigation indicated that pristine few-layered graphene has a surface area of 56.8978 m2/g and a relatively high thermal diffusivity of 22.23 mm2/s. The developed composites showed higher thermal diffusivity than the baseline adsorbent silica gel. The highest thermal diffusivity was 11.84 mm2/s for GP-CH3SO3-10, 394 times higher than silica gel. Water adsorption characteristics of the composites were carried out, and the Dubinin–Astakhov (D-A) model was employed to model the experimental isotherms with good accuracy. The cumulative advanced adsorption and thermal characteristics of the developed composites resulted in higher cyclic performance by up to 82 % and 85 % than that of the baseline silica gel.

Electrospinning fibrous membrane matrix ionic capacitive sensor for pressure value and distribution detection

Considering the practical applications of capacitive sensors, electrical sensing fibrous membranes should own high mechanical strength, elasticity, sensitivity, thermal diffusivity and biocompatibility, listing the basic design and preparation demands via electrostatic spinning. Polyvinylidene fluoride (PVDF) fibrous membrane matrix pressure ionic capacitive sensors were prepared via electrostatic spinning. The addition and dissolution of polyvinylpyrrolidone (PVP) particles realized porous structures of PVDF fibrous membrane, providing silver particles (Ag) dependence matrix for conductive Ag-porous PVDF fibrous membrane of electrode layer. The PVDF matrix capacitive sensor was composed of sandwiching dielectric layer of PVDF fibrous membrane with ionic liquid (IL-PVDF) between two electrode layers. The construction of electrical double layers at the interfaces between electrode layer and dielectric layer significantly enhanced capacitance sensing properties. After encapsulating by pure PVDF fibrous membranes, PVDF fibrous membrane matrix ionic capacitive sensor exhibited excellent stability, sensitivity and durability in pressure loading range of 0–8 kPa for 5000 cyclic experiments，which was suitable for real-time detection of multiple physiological bending signals. Based on pressure sensing array construction, the values and distribution of static and dynamic loads were reflected accurately and intuitively, providing feasible methods for practical applications of functional fiber matrix sensors in fields of healthcare and human-machine interaction.

Role of applying PCMs on thermal behavior of innovative unit roof enclosure

As a technical approach, using Phase Change Materials (PCM) can be an effective method to prevent energy losses through building enclosures. In the present paper, different roof structures containing PCM have been examined to analyze their thermal behavior. The governing equations were developed and solved for a sample unit extracted from a typical roof. The control volume based finite element method has been applied for solving coupled equations governing heat transfer through the roof and flow of melted PCM. The effect of key parameters including thermal diffusivity of the PCM and the wall, Prandtl number (Pr), Rayleigh number (Ra) and solid wall thickness to total thickness has been examined. The main results indicate an enhancement of heat transfer through the increase of the thermal diffusivity of the PCM with respect to the building material. Increasing the thermal diffusivity ratio from 1 to 25 doubles the heat transfer rate and decreases the full melting time by 80% for high Rayleigh. Pr affects the mode of heat transfer but has little impact on PCM melting rate. Raising Ra improves heat transfer under the condition of high thermal diffusivity in the PCM. Increasing Rayleigh number from 104 to 106 doubles the heat transfer rate and reduces the melting by 67% for high thermal diffusivity ratio. Finally, increasing the size of the wall thickness does not affect the fraction of melted PCM but reduces the heat transfer rate. The heat transfer rate can be increased by up to 75% when the non-dimensional thickness of the solid layer is reduced from 0.5 to 0.005.

MHD nonlinear natural convection from a uniformly moving porous vertical plate with constant heat and mass flux in the presence of thermal radiation, diffusion‐thermo, heat sink, and chemical reaction

AbstractAn attempt has been made to investigate the problem of nonlinear free convection heat and mass transfer flow past an infinite vertical porous plate embedded in a porous medium by taking into account thermal radiation and heat sink with constant heat and mass flux. Transversely oriented and of uniform strength , a magnetic field has been introduced to the fluid area. The nonlinear density variation with temperature as well as concentration are the basis for the current physical situation, which is explained by this mathematical model. Exact solutions are derived for momentum equation, energy equation, and species continuity equation under the relevant boundary conditions. The dimensionless governing equations are analytically solved. The influence of various physical parameters, such as Dufour number, Schmidt number, thermal Grashof number, magnetic parameter, mass Grashof number, heat sink, thermal radiation, Prandtl number, chemical reaction parameter on the flow, and transport characteristic, has been presented graphically and in tabular form. The novelty of the present investigation is that here both constant heat and mass flux at the plate are taken into account in addition to thermal radiation and heat sink. The findings of the mathematical study demonstrate that velocity, temperature, and skin friction intensify with a rise in the Dufour number this is due to the fact that the convection current becomes stronger as the Dufour number rises. Fluid's concentration declines as the Schmidt number grows, or the concentration rises as the mass diffusivity rises. Fluid temperature is enhanced with high thermal diffusivity. Frictional resistance on the plate hikes due to thermal buoyancy force.

Investigation of dissimilar metal (stainless steel and copper) joining and the effect of offsetting and other welding parameters

Dissimilar metal joining without additional preparation like preheating and grooving using conventional arc welding processes. The challenges related to dissimilar joints are overcome by using proper heat distribution according to the heat requirement of different plates. In the present study, GTAW is used to join SS and Cu, mode of joining is welding-brazing mode on the SS side. The heat distribution is done by offsetting the arc towards the Cu side because of the high thermal diffusivity of Cu compared to stainless steel (SS). For the complete joining, the 2nd pass is done without offset. A “beach” of unmixed Cu metal along the Cu fusion line and “peninsula” of an unmixed SS in the weld metal is observed in the microstructure. The grain size variation is observed in the different zones of the weldment due to the segregation of SS particles in weldment. The joint integrity is analyzed with an optical microscope image of the bead, and the detailed analysis of weldment is done using FESEM images in BSD mode. From the microstructure porosity and Cu, penetration is observed in the SS side mushy zone. The microhardness of the weld bead is utilized to see the effect of grain size and amount of SS particles on the mechanical property of weldment in the different zone of the weld bead. The tensile test is conducted to study the joint property of the test coupon. The joint strength of Joint-7 is 225 MPa and percentage elongation is 17 percent, efficiency obtained is around 85 per cent of the Cu plate.

Liquid-vapor interface behaviors during quenching and cooling of vials containing cryoprotectants immersed in liquid nitrogen

The vapor film layer during cryovials quenching in LN2 has been thought to severely impede heat transfer for cryopreservation of biomaterials. The current work mainly investigates both liquid–vapor interface behaviors and heat transfer characteristics when cryovials with CPAs immersed into LN2 by high-speed camera and data processing techniques. The results show that a shorter film boiling regime occurs for the vial with lower thermal effusivity, which implies that the vapor film was not the major obstacle to heat transfer for this case, but rather a result of the low thermal diffusivity of the vial. For example, the film boiling regime, for PP vial containing Vs55, lasted 1 s. Whereas for the case of Al vial containing Vs55, it lasted about 50 s, and the quenching time for Al vial to reach cryogenic temperature was 24.49 % faster than that for PP vial. For the vial with high thermal diffusivity, the solution inside the vial and its crystallization behaviors during quenching significantly affect the vapor film thickness and development of film boiling regime. For example, the heat released due to crystallization maintains the vapor film thickness stable over time for Al vial containing water. Vs55 in Al vials raise the Leidenfrost temperature by 22.3 °C compared to water. Based on the above experimental phenomena and results, further analysis shows that the vapor film of the vial filled with water is thicker than that of the vial containing Vs55 within 2 mm. For Al vials, the interfacial velocity and wavelength are higher than those of PP vials. This work is valuable for understanding the key issues in the quenching process of cryopreserved biomaterials.