Transfer Mode Research Articles

Maintaining a proper droplet transfer state in electron beam directed energy deposition via absorbed current-sensed control

Electron beam directed energy deposition (EB-DED) holds immense promise for the fabrication of large, intricate, and high-value metal components. However, with the synchronized nature of material feeding and melting, EB-DED introduces substantial challenges to the stability of the process. This affects both part consistency and repeatability. The droplet transfer process has a crucial part in shaping the stability of EB-DED, with the maintenance of the liquid bridge transfer assuming critical importance in ensuring optimal forming quality. Consequently, we present a cutting-edge closed-loop control system built with absorbed current as a solution to this conundrum. This system harnesses absorbed current signals as the sensory source for droplet transfer states. The droplet transfer state serves as the control objective and the droplet transfer distance acts as the regulated variable. We performed a series of experiments, that corroborated the efficacy of this control system in preserving the desired liquid bridge transfer across diverse scenarios while providing a comprehensive elucidation of its operational principles. By capitalizing on the electron products engendered during the forming process, our control system enabled convenient and reliable monitoring and control of droplet transfer states. The system revealed substantial potential in upholding a well-preserved droplet transfer mode, with significant ramifications for enhancing part consistency and repeatability within EB-DED.

Numerical Simulation and Experimental Research on Heat Transfer Characteristics Based on Internal Meshing Screw

The mixing and processing of high-viscosity materials play a pivotal role in composite material processing. In this context, the internal meshing screw mixer, rooted in volume extensional rheology, offers distinct advantages, including heightened mixing efficiency, exceptional material adaptability, and favorable thermomechanical properties. This research endeavors to advance our understanding of these qualities by presenting an in-depth exploration of internal meshing screw mixing. To facilitate this, an internal meshing screw mixing experimental apparatus was meticulously constructed, accompanied by extensive numerical simulations and experimental investigations into its heat transfer characteristics. Two distinct heat transfer modes are established: Mode 1 entails the transfer of the high temperature from the outer wall of the stator to the interior, while Mode 2 involves the transmission of the high temperature from the inner wall of the rotor to the exterior. The ensuing research yields several notable findings: 1. It is evident that higher rotational speeds lead to enhanced heat transfer efficiency across the board. However, among the three rotational speeds examined, 60 rpm emerges as the optimal parameter for achieving the highest heat transfer efficiency. Furthermore, within this parameter, the heat transfer efficiency is superior in Mode 1 compared to Mode 2. 2. As eccentricity increases, a corresponding decline in comprehensive heat transfer efficiency is observed. Moreover, the impact of eccentricity on heat transfer efficiency becomes increasingly pronounced over time. 3. A lower gap dimension contributes to higher heat transfer within the system. Nevertheless, this heightened heat transfer comes at the expense of reduced stability in the heat transfer process. 4. It is demonstrated that heat transfer in Mode 1 primarily follows a convection heat transfer mechanism, while Mode 2 predominantly exhibits diffusion-based heat transfer. The heat transfer efficiency of Mode 1 significantly surpasses that of Mode 2. This research substantiates its findings with the potential to enhance the heat transfer efficiency of internal meshing screw mixers, thereby making a valuable contribution to the field of polymer engineering and science.

Photocatalytic degradation of benzotriazole through synergy of electron donor–acceptor units and Au clusters in covalent organic frameworks

Covalent organic frameworks (COFs) have attracted great attention in photocatalysis, but the high recombination rate of photo-induced electron − hole pairs limits their photocatalytic performance. We report a synergy strategy based on the donor − acceptor (D-A) effect and Au clusters to enable the effective transfer and separation of photogenerated electrons to rationally fabricate visible light driven photocatalyst (MT-COF-Au) for the degradation of benzotriazole (BTA). MT-COF-Au displayed superior photocatalytic activity. The degradation efficiency of BTA was 93 % within 110 min, which was significantly improved 6.7 times than COF. For BTA degradation, O2− played a prominent role based on reactive species trapping experiments. The products of the last stage of the reaction were ketone, imidazole, acetamide, and nitrogen, which were formed via ring opening and isomerization reactions. MT-COF-Au could be reused for at least 5 cycles without significantly deteriorating its catalytic activity. Experiments and theory calculations confirmed the electron transfer mode and photocatalytic mechanism. This work provides new prospects for the design and synthesis of high-efficiency photocatalyst photocatalysts.

TRANSLATE - a Monte Carlo simulation of electron transport in liquid argon

The microphysics of electron and photon propagation in liquid argon is a key component of detector design and calibrations needed to construct and perform measurements within a wide range of particle physics experiments. As experiments grow in scale and complexity, and as the precision of their intended measurements increases, the development of tools to investigate important microphysics effects impacting such detectors becomes necessary. In this paper we present a new time-domain Monte Carlo simulation of electron transport in liquid argon. The simulation models the TRANSport in Liquid Argon of near-Thermal Electrons (TRANSLATE) with the aim of providing a multi-purpose software package for the study and optimization of detector environments, with a particular focus on ongoing and next generation liquid argon neutrino experiments utilizing the time projection chamber technology. TRANSLATE builds on previous work of Wojcik and Tachiya, amongst others, introducing additional processes, including ionization, thus modeling the full range of drift electron scattering interactions. The simulation is validated by benchmarking its performance with swarm parameters from data collected in experimental setups operating in gas and liquid. Program summaryProgram Title:TRANSLATECPC Library link to program files:https://doi.org/10.17632/v3tr6xp53h.1Developer's repository link:https://github.com/davidc1/TRANSLATELicensing provisions: GNU General Public License 3.0Programming language: C▪, pythonExternal routines/libraries used: make, cmake (required), ipython notebook (optional)Nature of problem: Simulation of electron-argon scattering events at energies of 10−3−103 eVSolution method: Monte Carlo time-domain transport of electrons simulating momentum transfer, excitations, and ionization interaction modes utilizing input single and double-differential cross sections.Additional comments including restrictions and unusual features: Effects of ion space-charge or recombination with positive argon ions are not included.

Distribution and Implications of Haloarchaeal Plasmids Disseminated in Self-Encoded Plasmid Vesicles.

Even though viruses and plasmids are both drivers of horizontal gene transfer, they differ fundamentally in their mode of transfer. Virus genomes are enclosed in virus capsids and are not dependent on cell-to-cell contacts for their dissemination. In contrast, the transfer of plasmids most often requires physical contact between cells. However, plasmid pR1SE of Halorubrum lacusprofundi is disseminated between cells, independent of cell-cell contacts, in specialized membrane vesicles that contain plasmid proteins. In this study, we searched for pR1SE-like elements in public databases and a metagenomics dataset from Australian salt lakes and identified 40 additional pR1SE-like elements in hypersaline environments worldwide. Herein, these elements are named apHPVs (archaeal plasmids of haloarchaea potentially transferred in plasmid vesicles). They share two sets of closely related proteins with conserved synteny, strongly indicating an organization into different functional clusters. We find that apHPVs, besides transferring themselves, have the potential to transfer large fragments of DNA between host cells, including virus defense systems. Most interestingly, apHPVs likely play an important role in the evolution of viruses and plasmids in haloarchaea, as they appear to recombine with both of them. This further supports the idea that plasmids and viruses are not distinct but closely related mobile genetic elements.

Numerical simulation of fluid flow and heat transfer in steady state laminar natural convection in horizontal circular cylindrical enclosures

Heat transfer by natural convection often occurs in a closed enclosure in various applications. Different geometries of the cross section of a two-dimensional enclosure, such as triangle, rectangle, and trapezoid have already been investigated. In this research, a regular polygon with twelve sides is considered. The study focuses on the rate of heat transfer through the enclosure, using one side of the polygon as the hot surface and another side as the cold surface. The dodecagon can serve as a model for circular cylindrical enclosures under constant temperature boundary conditions over a specified length. The Nusselt number of the enclosure is obtained for each side as the hot surface. Both the lowest and highest Nusselt numbers are evaluated based on the position of the cold side. The findings reveal that the highest Nusselt number does not necessarily correspond to configurations where the hot and cold sides are directly opposite each other. In situations where convection heat transfer through the enclosure is the predominant mode of heat transfer, the Nusselt number is a power function of the Rayleigh number. Conversely, a logarithmic relationship is observed in cases of conduction heat transfer within the enclosure.

Electrochemical surface-enhanced Raman spectroscopy analysis of malachite green on gold substrates

The pH-sensitivity and electroactivity of malachite green (MG), a cationic dye, can potentially affect the surface-enhanced Raman spectroscopy (SERS) profile during electrochemical SERS (EC-SERS) analysis. An EC-SERS investigation was performed by acquiring dynamic SERS profiles of MG on Au SERS substrates at various applied potentials to elucidate the electrochemistry of MG at the molecular level. The appropriate EC-SERS potential window of MG, mass and electron transfer modes, and the number of electrons and protons in the redox process were determined by cyclic voltammetry. The EC-SERS parameters (pH and type of supporting electrolyte) were optimized. The highest SERS signal was achieved by chronoamperometry SERS (CA-SERS) and CV-SERS at an applied potential of 0.6 V (vs. Ag/AgCl) using 0.1 M phosphate buffer at pH 4 as the supporting electrolyte. Plausible mechanisms for electrooxidation and SERS signal enhancement were proposed. The oxidized form of MG, conformational changes, and evolution of the adsorption orientation were successfully elucidated using CV-SERS. This study provides molecular-level insight into the adsorption orientation of MG and its oxidized form, which involves aromatic rings with a tilted upright orientation at positive applied potentials. The mechanism of SERS signal enhancement is expounded, which is valuable for developing EC-SERS-based MG sensing.

Thermal Modeling of Photovoltaic Panel for Cell Temperature and Power Output Predictions under Outdoor Climatic Conditions of Jodhpur

The rise in the temperature severely affects photovoltaic cell efficiency and hence its power output. Moreover, it also causes the development of thermal stresses that may reduce their life span. Thus, there is a need for an accurate estimation of the cell’s working temperature. In this paper, a detailed thermal model based on various heat transfer modes involved and their governing equations has been presented to estimate the cell temperature of a PV module using MATLAB software under different climatic and solar insolation conditions. In order to validate the presented model, an experimental setup has been built and operated under actual outdoor conditions of Jodhpur, a city in the Thar Desert of Rajasthan. For the peak summer month of June, the predicted glass cover outer surface temperature has been found to be within 0.2–4.5°C of experimentally measured values and the back sheet temperature is found to be within 0.5–5.5°C. The predicted and measured power outputs have been found to be within 0.85–1.2 W while the efficiency values are within 0.17–0.38%. For the early summer month of April, the variations are 0.13–4.1°C, 0.2–4.1°C, 0.44–1.65 W, and 0.1–0.5% for glass cover temperature, back sheet temperature, power output, and efficiency, respectively. Thus, the predictions of the developed thermal model have exhibited a good agreement with the experimental results. The maximum glass cover temperatures recorded were 60°C and 65.5°C when the ambient temperatures were 35°C and 42°C near the noon for the early summer and peak summer day experiments, respectively. The presented model can be used to generate a year-round cell temperature data for the known environmental data of a location, which can help in the selection or development of appropriate cooling technology at the planning stage of the installation of a solar PV plant.

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.

Nomination Vs. Succession - Dispute Regarding Mode of Inheritance of Shares

A company is said to have perpetual succession, meaning that a company continues to function for time immemorial and its working would not be affected by any change in membership, death of the owner or insolvency. Collaborating with the same thoughts, the shares of a company will also not have any expiry period insofar as the company remains to be a publicly listed entity. However, the current fad of trading in the open market depicts shares as a movable property that may be transferred from one person to another. Section 44 of the Companies Act, 2013 agrees that "the shares or debentures or other interest of any member in a company shall be movable property and transferable in the manner provided by the articles of the company. The Act legalizes the act of transferring shares in cases of them being bought, or sold in general. However, considering that shares and debentures are movable property, they can be considered familial property that can be inherited by one’s children. The problem of inheriting shares and debentures arises due to the mode by which the parent/guardian chooses to transfer his shares. Section 109A discusses the mode of Nomination of shares where a holder may nominate a person to whom his shares can be vested after his death. However, the problem arises when the person has stated in his will that particular people in his family will inherit his property and the shares under his name are also included as transferable property under his will. This paper will delve, into these modes of transfer of shares and which one will prevail over the other.

Assessment of Thermal Runaway propagation in lithium-ion battery modules with different separator materials

The current work aims to understand and model thermal runaway (TR) events in lithium-ion (LIB) 18650 cells within the context of aircraft battery applications. The primary goal is to comprehend the phenomenon and discuss strategies for mitigating its consequences during aircraft operation. TR is modeled using Arrhenius kinetic equations and is implemented in both lumped parameters (Matlab SimulinkTM), and 3D CFD simulations (Ansys FluentTM) using User Defined Functions. To validate the thermochemical model, cells are initially simulated in an oven test, where a cell is exposed to a temperature-controlled atmosphere, triggering exothermic reactions. With a strong correlation between lumped parameters and 3D models, the latter is simulated under battery module installation conditions. An internal short-circuit is then implemented within the cell to observe how thermal runaway is triggered by an internal heat source. The trigger cell is subsequently placed in a battery module assembly to assess the dominant heat transfer modes and the likelihood of TR induction from one cell to its neighbors. This work’s main objective and innovation are to compare different materials in which cells are immersed while observing the main heat transfer parameters for each material. Three conditions are tested: ceramic paper fiber and G7 as solid separators, and no separator material, where air fills the gaps between cells. The analysis of heat transfer modes reveals radiation’s dominance in the case of air interstice, suggesting the possibility of using a special coating to reduce the cell surface emissivity as an alternative to decrease the likelihood of TR propagation. Thus, two values of surface emissivity were tested in the case of air. Considering a cell triggered by an internal short-circuit, a thermal runaway temperature spike is not observed in any of the four cases. However, the air interstice case with regular emissivity is the most critical one, with the closest cell reaching peak temperatures as high as 136 °C in 490 s. The ceramic paper fiber is considered the best separator material, as it postpones the temperature increase in the closest cell while also being lighter than G7. The results and discussions concerning heat propagation presented herein can serve as guidelines for developing strategies to mitigate thermal runaway in battery modules.

DEPLOYMENT OF SENSOR NETWORKS FOR EFFICIENT POWER CONSUMPTION MONITORING APPLICATION

This paper presents a wireless monitoring system implemented using a wireless sensor network and the XCTU software. The existing monitoring systems for tracking alternating current utilization in various devices face limitations in terms of real-time data acquisition and seamless wireless transmission to a central computer for comprehensive analysis. This hinders the ability to accurately measure electric current consumption, impeding the development of efficient energy management strategies. Therefore, the primary focus of this monitoring system is to wirelessly track the utilization of alternating current in various devices. The wireless monitoring system relies on the integration of the XBEE device and the SCT 013 current sensor. The SCT 013 current sensor accurately measures electric current consumption, exhibiting a mere 0.03 variation, while the XBEE device is employed to transmit this data wirelessly to a computer for subsequent data analysis. In this configuration, the XBEE operates in AT mode for seamless data transfer to the computer.

Mesoporous TiO2 matrix embeded with Cs2CuBr4 perovskite quantum dots as a step-scheme-based photocatalyst for boosting charge separation and CO2 photoconversion

Halide perovskite quantum dots (PQDs) have shown great promise for the photochemical conversion of CO2. However, the fast carrier recombination rates and inadequate adsorption/activation for CO2 molecules have seriously restricted their practical application. Herein, an innovative step-scheme-based Cs2CuBr4/TiO2 (CCB/TiO2) photocatalyst was prepared by embedding Cs2CuBr4 PQDs in a mesoporous TiO2 matrix, which exhibits considerable potential as candidates for CO2 photoreduction under simulated sunlight. Remarkably, the optimised CCB/TiO2 photocatalyst delivered an impressive CO2 reduction activity, which was 3.1 and 16.0 times higher than those achieved by pure Cs2CuBr4 and TiO2, respectively. Furthermore, the S-scheme charge transfer mode was comprehensively corroborated by density functional theory (DFT) calculations, photo-assisted Kelvin probe force microscopy (KPFM), in situ irradiated X-ray photoelectron spectra (XPS), and electron spin resonance spectroscopy (ESR). On basis of theoretical calculations and in situ diffuse reflectance spectra (DRIFTS), the CCB/TiO2 exhibited a reduced energy barrier of the rate-determining step, which facilitated the CO2 photoreduction reaction.

Controllable construction of direct Z-scheme Mo2C-CdxZn1−xIn2S4 heterojunction via defect-mediated modulation for enhanced visible-light photocatalysis

Direct Z-scheme semiconductor heterostructures possess fascinating merits for solar photocatalysis, including increased light harvesting, spatially isolated photogenerated charge carriers, and well-preserved strong redox capability. However, steering Z-scheme charge transfer of semiconductor heterojunction in a controllable manner is still a challenging task. In this work, unique direct Z-scheme Mo2C-CdxZn1−xIn2S4 heterojunction is constructed via a defect-mediated modulating strategy, where Cd-doping switches the charge transfer mode of Mo2C-CdxZn1−xIn2S4 heterojunction from type-I to Z-scheme through increasing S vacancies, up-shifting conduction band level, and narrowing bandgap of CdxZn1−xIn2S4 component. Moreover, the defect-induced Mo-S bond affords fast channels for built-in electric field-induced Z-scheme photo-electrons transporting from Mo2C conduction band to CdxZn1−xIn2S4 valence band, supporting by X-ray photoelectron spectroscopy, surface photovoltage spectroscopy, and radical testing results. Noticeably, under irradiation of visible light (λ > 400 nm), Mo2C-CdxZn1−xIn2S4 Z-scheme heterojunction displays an excellent and stable photocatalytic H2-evolving activity, reaching an outstanding H2 generation rate of 28.12 mmol·g−1·h−1 with the corresponding high apparent quantum efficiency of 21.1% at 400 nm, far surpassing that of Pt-loaded C0.25ZIS and most documented ZnIn2S4-containing photocatalysts. The present work could inspire the crafty design of efficient Z-scheme photocatalysts through defect-mediated heterostructure construction and energy band engineering.

Thermal safety boundary of lithium-ion battery at different state of charge

Thermal runaway (TR) is a critical issue hindering the large-scale application of lithium-ion batteries (LIBs). Understanding the thermal safety behavior of LIBs at the cell and module level under different state of charges (SOCs) has significant implications for reinforcing the thermal safety design of the lithium-ion battery module. This study first investigates the thermal safety boundary (TSB) correspondence at the cells and modules level under the guidance of a newly proposed concept, safe electric quantity boundary (SEQB). A reasonable thermal runaway propagation (TRP) judgment indicator, peak heat transfer power (PHTP), is proposed to predict whether TRP occurs. Moreover, a validated 3D model is used to quantitatively clarify the TSB at different SOCs from the perspective of PHTP, TR trigger temperature, SOC, and the full cycle life. Besides, three different TRP transfer modes are discovered. The inter-conversion relationship of three different TRP modes is investigated from the perspective of PHTP. This paper explores the TSB of LIBs under different SOCs at both cell and module levels for the first time, which has great significance in guiding the thermal safety design of battery systems.

Study on the effect of partial filling of foam metal on the solidification performance of ice storage spheres

Ice storage sphere systems are favored in the field of energy storage, however, the poor thermal conductivity of phase change materials (PCM) seriously weakens their wide application. Metal foam has been shown to enhance its heat transfer. In this paper, we investigate the impact of varying the filling radius ratio of foam metal to further improve energy storage performance and reduce costs in ice storage spheres. Computational fluid dynamics are employed to analyze the heat transfer and solidification processes. The enthalpy-porosity method is used to describe PCM solidification, while the local equilibrium thermal (LET) model characterizes heat transfer between the PCM and foam metal. The study explores temperature field variations, solid phase fraction changes, solidification times, and cold storage volumes, accounting for natural convection. By comparing solidification rates and other relevant parameters, the effect of foam metal filling on the solidification process is explored. Moreover, a new evaluation index is proposed, which can assess the overall performance of ice storage systems in real-time, considering market prices. The results show that natural convection is the primary heat transfer mode in pure PCM-ffild ice storage spheres, whereas smaller foam metal filling radii significantly inhibit natural convection, resulting in heat conduction as the dominant mode. Without specific requirements, an optimal fill radius ratio of 9/13 is determined. This paper offers a comprehensive understanding of cold storage employing various foam metal filling radios, contributing to advancements in efficient thermal energy storage systems.

Research on particle retention in continuous horizontal fluidized bed based on CFD-DEM method

Horizontal fluidized beds are widely used in continuous production lines due to their efficient heat and mass transfer mode. Continuous production goals require stabilized reaction systems, which can be achieved by controlling particle retention. But there is a lack of an effective means of controlling particle retention. In this paper, Computational Fluid Dynamics - Discrete Element Method (CFD-DEM) method is applied to investigate the particle retention in different air inlet angles, which is characterized by the particle back-mixing degree, spatial and residence time distribution. The results show that at low air inlet angles, the system is effective in controlling particle retention. This is achieved through stronger particle back-mixing and more concentrated residence times, which are essential for maintaining reaction system stability. These findings provide guidance for controlling particle retention and enhancing continuous fluidization equipment efficiency.

Perovskite Cathodes for Aqueous and Organic Iodine Batteries Operating Under One and Two Electrons Redox Modes.

Although conversion-type iodine-based batteries are considered promising for energy storage systems, stable electrode materials are scarce, especially for high-performance multi-electron reactions. The use of tin-based iodine-rich 2D Dion-Jacobson (DJ) ODASnI4 (ODA: 1,8-octanediamine) perovskite materials as cathode materials for iodine-based batteries is suggested. As a proof of concept, organic lithium-perovskite and aqueous zinc-perovskite batteries are fabricated and they can be operated based on the conventional one-electron and advanced two-electron transfer modes. The active elemental iodine in the perovskite cathode provides capacity through a reversible I- /I+ redox pair conversion at full depth, and the rapid electron injection/extraction leads to excellent reaction kinetics. Consequently, high discharge plateaus (1.71V vs Zn2+ /Zn; 3.41V vs Li+ /Li), large capacity (421 mAh g-1 I ), and a low decay rate (1.74mVmAh-1 g-1 I ) are achieved for lithium and zinc ion batteries, respectively. This study demonstrates the promising potential of perovskite materials for high-performance metal-iodine batteries. Their reactions based on the two-electron transfer mechanism shed light on similar battery systems aiming for decent operational stability and high energy density.

Enhanced pool boiling of refrigerants R-134a, R-1336mzz(Z) and R-1336mzz(E) on micro- and nanostructured tubes

Pool boiling of refrigerants is a primary heat transfer mode in flooded evaporators, as well as a promising solution in electronics cooling applications. In this work, the pool boiling performance of R-134a, R-1336mzz(E), and R-1336mzz(Z) on the external side of round tubes are reported and compared to Cooper's heat transfer coefficient (HTC) model. Modification of Cooper's correlation is found to be necessary for R-1336mzz(Z) at low reduced pressure. Micro- and nanostructured tubes are tested using the three different refrigerants and are shown to enhance the boiling HTC. Specifically, three various structures consisting of: boehmite (AlO(OH)) nanostructures, etched aluminum microstructures, and copper oxide (CuO) micro-nanostructures are fabricated on the external sides of aluminum and copper tubes. The surface structures have characteristic length scales of 100 nm, 1 µm, and 10 µm for boehmite, CuO, and etched aluminum, respectively. While the boiling HTC is enhanced up to 250% (compared to smooth tubes) using R-134a with etched aluminum, it shows a 15% decrease in HTC when boehmite structures are used. For CuO, higher heat fluxes showed a 25% HTC enhancement, while lower heat fluxes showed negligible effects when compared to smooth copper tubing. Different refrigerants showed various relations between structure and HTC enhancements. To take account of both structure length scale and refrigerant properties, we introduce a normalized structure size (Rn) and conclude that HTC enhancement ratio increases non-linearly with Rn. Our study not only provides valuable data on refrigerant pool boiling of recently developed low global warming potential and ozone depleting potential fluids, it also provides valuable design guidelines for the development and application of micro- and nanostructured surfaces in chiller and electronics cooling applications.

On the mechanics of thermal collapse of a vapor bubble translating in an isothermal subcooled liquid

In this work, we numerically simulate bubble radius and velocity in a thermal collapse of a vapor bubble translating in an isothermal subcooled liquid based on solving the equations of energy and motion simultaneously. The mechanics of the collapse in the thermal regime plays a significant role in the thermal convection from the vapor-liquid interface of a translating bubble. In our mathematical model, the equation of motion considers the added mass force due to phase change and shape change, while the equation of energy includes thermal conduction and convection. The simulations include both spherical and non-spherical bubbles, the effect of initial bubble diameter and degree of subcooling. The simulations have been performed in three modes of heat transfer (conduction, convection and combined conduction-convection) to observe their effect on the bubble dynamics. The numerical results have been compared with the two classes of thermal collapse experiments (Type A and B) and CFD analysis reported in literature. They agree well with the experiments and CFD-analysis. We have seen a remarkable effect of the initial shape of the bubble in terms of aspect ratio on the time scale and modes of the heat transfer and the collapse time. An interesting concern is that the mechanism of the collapse and the modes of heat transfer depends on how the collapse is initiated in the experiments. Type A and B thermal collapses are mainly classified based on the bubble motion and the modes of thermal transport from the interface.