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To assess the compliance of "integrated" continuous glucose monitoring (CGM) systems with U.S. Food and Drug Administration requirements, the calculation of confidence intervals (CIs) on agreement rates (ARs), that is, the percentage of CGM measurements lying within a certain deviation of a comparator method, is stipulated. However, despite the existence of numerous approaches that could yield different results, a specific procedure for calculating CIs is not described anywhere. This report, therefore, proposes a suitable statistical procedure to allow transparency and comparability between CGM systems. Three existing methods were applied to six data sets from different CGM performance studies. The results indicate that a bootstrap-based method that accounts for the clustered structure of CGM data is reliable and robust. We thus recommend its use for the estimation of CIs of ARs. A software implementation of the proposed method is freely available (https://github.com/IfDTUlm/CGM_Performance_Assessment). [ABSTRACT FROM AUTHOR]

Highlights • The liquid film formation during vapor bubble expansion was investigated. • The liquid film became thicker as time advanced by increment of interface velocity. • The front edge thickness of liquid film agreed with Taylor's law. • Contribution to heat transfer from wall to liquid film evaporation was evaluated. Abstract The evaporation of vapor bubbles inside a microchannel is important to realize a device with high cooling performance. The liquid film formed on the solid surface is essential for evaporative heat transfer from solid to fluid; its formation process and heat transfer characteristics need to be investigated. The expansion process of a single vapor bubble via evaporative heat transfer in microchannels was evaluated via a numerical simulation in this study. In the calculation model, the working fluid used was saturated FC-72 at 0.1013 MPa and the channel diameter was 200 µm. The superheat of the initial temperature field and wall were considered as parameters. To evaluate the heat transfer characteristics, the time variation of liquid film thickness was evaluated. The averaged liquid film thickness had a correlation with the capillary number. Additionally, the dominant heat transfer mode was estimated by decomposing the heat transfer rate into the heat-transfer rate through the liquid film, rear edge, and wake. When the superheat was low, the heat transfer mostly occurred via liquid film evaporation; the heat flux through the liquid film could be predicted using the liquid film thickness. On the other hand, in cases of higher superheat, owing to rapid expansion of the vapor bubble, no evaporative heat transfer occurred through the liquid film around the bubble head. It could be inferred from this study that the relationship between the thickness of the thermal boundary layer of the bubble and liquid film thickness is important for predicting the cooling effect of this phenomena. When the vapor bubble grows in the high superheat liquid, the rapid growth makes the liquid film thick, and the thick liquid film prevents the heat transfer between the liquid–vapor interface and heated wall. [ABSTRACT FROM AUTHOR]

The concept of Gross National Happiness (GNH) - or the idea that a nation’s development strategy should have as its goal the maximization of a people’s happiness, rather than the maximization of their economic output - is appealingly persuasive in its humanistic simplicity. When he first articulated the concept it in 1979, the 4th Druk Gyalpo (hereditary King) of Bhutan signaled to the world that Bhutan’s integration into the global community must not be premised on the blind acceptance of standard definitions of development ‘progress,’ but that instead the country should be allowed to insist on its own definition of success - focused not only on economic growth but also on environmental conservation, preservation of culture and communities, and good governance. In retrospect, Bhutan’s insistence on the latter course seems particularly prescient. Today, GNH is seen as one of a handful of so-called alternative visions of international development, and is attracting global attention from a growing number of policy makers, diplomats, scholars, tourists, journalists, and even religiously motivated truth-seekers. This article discusses the implications of GNH for Bhutan’s lawmakers, lawyers, legal academics, and foreign development partners. This article contributes to the literature on law and development, but flips the analysis to speculate not on how legal reforms do (or do not) promote economic development, but rather how a unique national development strategy might in turn influence the nature of the legal sector. [ABSTRACT FROM AUTHOR]

In this study we present an interferometric technique based on multiple wavelengths to capture the transient free surface contour of nanolitre drops spreading on a wettable surface, in particular close to the three-phase contact line. Various data analysis procedures are evaluated in terms of error and noise sensitivity. The technique allows an unambiguous determination of the local liquid film thickness for optical path differences up to Δ s ≈ 3.19 μ m without the need of a known reference height. Film thicknesses as low as 0.1 μ m can be measured with the present optical configuration. The entire three-dimensional droplet shape is investigated for different capillary numbers, allowing also reliable measurements of the time-resolved contact angle. [ABSTRACT FROM AUTHOR]

This paper examines the evolution and rupture of a thin liquid film evaporating on a structured wall and the concomitant heat and mass transport. The heat is supplied either from the side of the wall or from the hot ambient gas. An evolution equation for the film thickness is derived in the framework of the long-wave theory under the assumption that the film thickness is small compared to the length scale of film deformation. The resulting fourth order partial differential equation is solved numerically employing a finite difference scheme using a MATLAB code. The results show that, in the case of a hot wall, the film breakup may occur even in the absence of evaporation. The reason for this breakup is Marangoni convection driven by uneven temperature distribution at the liquid-gas interface due to the wall structure. With increasing evaporation rate the rupture time decreases and the position at which the rupture occurs is shifted towards the crests of the wall topography. Additionally, it is found that the wave length of the wall structure has a non-monotonous effect on rupture time. If the film is heated by the ambient gas, the liquid-gas interface tends to follow the wall topography shape. [ABSTRACT FROM AUTHOR]

Distributed mass balance models, which translate micrometeorological conditions into local melt rates, have proven deficient to reflect the energy flux variability on mountain glaciers. This deficiency is predominantly related to shortcomings in the representation of local processes in the forcing data. We found by means of idealized large-eddy simulations that heat advection, associated with local wind systems, causes small-scale sensible heat flux variations by up to 100Wm-2 during clear sky conditions. Here we show that process understanding at a few observation sites is insufficient to infer the wind and temperature distributions across the glacier. The glacier-wide hourly averaged sensible heat fluxes are both over- and underestimated by up to 16Wm-2 when using extrapolated temperature and wind fields. The sign and magnitude of the differences depend on the site selection, which is used for extrapolation as well as on the large-scale flow direction. Our results demonstrate how the shortcomings in the local sensible heat flux estimates are related to topographic effects and the insufficient characterization of the temperature advection process. [ABSTRACT FROM AUTHOR]

Highlights: [•] Establishing standardized irradiation conditions for photocatalytic tests. [•] Radiation sources and the measurement of irradiance for photocatalytic testings. [•] Solution for the fundamental problem of irradiating and measuring of irradiance in photocatalysis research. [•] Electromagnetic spectrum is split into several spectral colors specifically adapted for photocatalysis research. [•] Continuum source equipped with a smart setup of fitted filters. [ABSTRACT FROM AUTHOR]

We present reflection anisotropy spectroscopy (RAS) as a powerful optical technique for degradation studies of structurally changing thin organic films, here the case of porphyrin films. The measured optical anisotropy of a thin ( d = 16 nm) ZnTPP (Zinc tetraphenylporphyrin) film grown by thermal evaporation on silicon using reflectance anisotropy spectroscopy was studied before and after aging in ambient conditions. The observed absorption features, also found by standard transmission spectroscopy, are correlated with the π-π* electronic transitions of the Q and Soret bands of the molecule. Simulation of RAS spectra revealed blue-shifted resonances, which are in agreement with a preferential face-to-face (stacking) arrangement of the ZnTPP molecules. The findings are in agreement with atomic force microscopy studies of the surface morphology showing with aging a transition from a closed film to separated aggregates. [ABSTRACT FROM AUTHOR]

Abstract: Liquid jet impingement cooling technique is critical in many industrial processes, such as fuel bundle cooling post-loss-of-coolant-accident in nuclear reactors, heat treatment of metal parts post-hot-processing, etc. The ability of liquid jets to extract high heat flux from metal parts, with temperatures as high as 800–1000°C, at moderate flow rates has made them indispensable in these applications. The complex mechanism of flow boiling heat transfer during jet impingement cooling is not been well understood. This study presents a systematic methodology for the measurement and estimation of the temporospatial variation of heat transfer on the impingement surface during jet impingement cooling of extremely hot steel plate. The effect of jet impingement velocity and subcooling variations from 2.5 to 10m/s and 60 to 87K, respectively, on the temporospatial heat transfer variation on the impingement surface is reported. A gradually growing circular wetted region, with its periphery named as the wetting front, forms soon after the cooling starts but its velocity decreases as it grows in diameter. A local maximum in the surface heat flux closely follows the wetting front, with the local maximum heat flux reducing with distance from the stagnation point. The wetting front velocity and local maximum heat flux increase with both the jet velocity and subcooling. The enhancement in the local film velocity and subcooling result in a strong suppression of boiling activity and, resultantly, high heat transfer rates at plate surface temperatures in much excess of the critical temperature of the coolant is achieved. This observation confirms the industrial practice of using impinging jets for accelerated cooling of hot steel plates. [Copyright &y& Elsevier]

The heat transfer to water-based suspensions of microencapsulated phase change material (MEPCM) flowing laminarly through rectangulak copper minichannels was investigated both experimentally and numerically. The MEPCM-particles had an average size of 5 pm and contained as phase change material n-eicosane, which has a theoretical melting temperature of 36.4 °C. Water and suspensions with particle mass fractions of 10% and 20% were considered. While the experiments result in rather global values such as wall temperatures at certain points, suspension inand outlet temperatures, and the pressure drop, the numerical simulations allow additionally a more detailed insight, for example, into the temperature distribution in the flowing suspension. The results show that MEPCM suspensions are only advantageous in comparison to water in a certain range of parameter combinations, where the latent heat is exploited to a high degree. The available latent heat storage potential, which depends on the particle fraction in the suspension and on the mass flow rate, has to he in the same order of magnitude as the supplied heat. Moreover, the mean residence time of the particles in the cooling channels must not be considerably shorter than the characteristic time for heat conduction perpendicular to the flow direction. Otherwise, the particles in the center region of the flow leave the cooling channels with still solid cores, and their latent heat is not exploited. Furthermore, the benefit of the added MEPCM particles depends on the inlet temperature, which has to be slightly below the theoretical melting temperature, and on the subcooling temperature after the heat supply, which has to be sufficiently low to guarantee that the entire phase change material solidifies again before it re-enters the cooling channels. The suspensions showed Newtonian behavior in the viscosity measurement. The actual pressure drop determined in the experiments is smaller than the pressure drop estimation based on the measured viscosities. The difference between the two values increases with increasing particle mass fraction. This shows that the particles are not evenly distributed in the flowing suspension, hut that there is a particle-depleted layer close to the channel walls. This reduces the required pumping power, but makes it even more important to provide conditions, in which a sufficiently large amount of the supplied heat is conducted to the center region of the channels. [ABSTRACT FROM AUTHOR]

Heat pipes, loop heat pipes (LHP), and capillary pumped loops (CPL) have already proven their potential to remove high heat fluxes from a small electronic device and transport the heat to a heat sink that is large enough to transfer it into the ambient air. We introduce a novel two-loop system similar in design to CPLs but with an additional buoyancy-driven fluid loop. Non-degassed methanol is used as a working fluid. Key benefits compared to LHPs and CPLs are easy filling procedure, easy startup, and the tolerance toward noncondensable gases in the fluid. The amount of fluid in the system can be varied over a broad range without affecting the heat transfer performance. Three different inverted-meniscus-type evaporators have been employed in this study. A maximum evaporator heat transfer rate of 105 W has been obtained, which corresponds to a heat flux of 35 W/cm2 based on the projected surface area of the porous capillary structure (15 mm × 20 mm) inside the evaporators. A maximum heat transfer coefficient of 16.5 W/(cm2 K) has been achieved at a wall superheat as little as 0.45°C. Oscillations of pressure, temperature, and the liquid vapor interface occur for all experimental conditions. The analysis of different loop parameters indicates that the heat transfer coefficient is increased due to the periodical wetting/dewetting of the channel walls triggered by the interface oscillations. [ABSTRACT FROM AUTHOR]

TNF-α is postulated to play a significant role in regulating TGF-β expression. In lung fibroblasts, for example, TNF-α is supposed to induce TGF-β via AP-1 activation. TNF-α receptor, knock-out mice are resistant to induced fibrosis and over-expression of TNF-α causes increased TGF-β production in mice. Therefore, we investigated whether TNF-α mRNA levels are associated with the TGF-β mRNA levels of blood leucocytes in humans. Quantitative real-time PCR of TNF-α and TGF-β was performed in 118 Germans. Calculations of expression were made with the 2 method. When the investigated population was divided in two groups (TNF-α low and TNF-α high) by the median of the determined TNF-α expression, highly significant ( p < 0.0001) differences of TGF-β1 mRNA expression were revealed. Additionally, dividing the investigated population into quartiles of the determined TNF-α expression showed significantly different TGF-β1 mRNA expressions. Comparing the determined CT-values of TNF-α in context with these of TGF-β1, a coefficient of determination R = 0.4635 was calculated. In this study we demonstrated in vivo a significant association of the relative TNF-α/B2M mRNA expression and the relative TGF-β/B2M mRNA expression in 118 Germans. [ABSTRACT FROM AUTHOR]

Abstract: The objective of the government-funded research project “SiLat” (Simulation der instationären Lacktrocknung bei dreidimensionalen Objekten—simulation of paint drying processes on three-dimensionally shaped geometries) is the development of a CFD-software simulation add-on for the drying process of paints . The software is intended to be used in the automotive industry to predict the intermediate drying process of water based paints on car bodies in continuous convective dryers. To validate the software, several laboratory scale experiments, using industrial water-based paint systems and a model base paint system applied on a sheet of metal, were carried out. Conditioned air was used for the drying process. The experimental setup was varied in three different ways: paint on a flat sheet was dried in impinging jet and parallel flow conditions. Furthermore, a Z-shaped sheet was dried during parallel flow conditions. Additional experiments were performed varying the flow parameters. During all experiments, the sheet temperature and weight of the painted sheet were monitored with a rate of 1Hz. The evaporation of the organic solvents could be monitored using FTIR-spectroscopy. This contribution deals with the experimental investigations and simulation results, whereas the paint drying model is presented by Domnick et al. in detail. [Copyright &y& Elsevier]

Abstract: The transient heat transfer during nucleate boiling of refrigerant HFE-7100 is investigated numerically and the results are compared to experimental data. The Volume-of-Fluid solver of the OpenFOAM CFD package was modified and extended for the numerical simulation of single bubble boiling. The model tracks the bubble shape during growth, departure and vertical rise and incorporates evaporation at the liquid–vapor interface as well as microscale heat transfer at the 3-phase contact line. The simulation results give insight into the transient heat transfer between the solid wall, the superheated liquid layer and the growing vapor bubble. The boundary conditions have been chosen according to temporally and spatially highly resolved experimental investigations. Global parameters such as bubble size and mean wall superheat as well as local phenomena such as the cooling of the heater at the contact line are in good agreement to the experimental data. [Copyright &y& Elsevier]

This article describes the implementation and validation of a nucleate boiling model in the volume-of-fluid solver of OpenFOAM. Emphasis is put on the implementation of the contact line evaporation, which can typically not be resolved by the numerical grid, and on the conjugate heat transfer between solid and fluid. For validation, the sucking interface problem and the growth of a spherical bubble have been simulated successfully. In order to validate the contact line model and the conjugate heat transfer, the growth of a bubble from a heated steel foil has been calculated. [ABSTRACT FROM AUTHOR]

Abstract: Spray cooling experiments have been performed on a smooth heater surface. The working fluid water was atomized through a full cone nozzle into a low pressure spray chamber. Different coolant mass fluxes were studied by varying the distance between nozzle and heater. Observations obtained with an infrared camera indicated that the length of the three phase contact line increased as the heat flux in the experiments was raised. Motivated by this finding, the effect of different micro structured surfaces, which lead to an increase in the three phase contact line, on the spray cooling performance was studied. The micro structures consisted of micro pyramids with different heights. A significant enhancement in the heat transfer performance due to the surface structures could be observed, especially at low coolant fluxes. Additionally, high spatial resolution temperature measurements on a smooth heater using thermochromic liquid crystals were obtained. These measurements indicate high local temperature gradients for a regime where the coolant film on the heater is ruptured. [Copyright &y& Elsevier]

An interferometric measurement technique for determining accurately the temperature field around an axial symmetric vapor bubble that might be used for boiling investigations was developed. The specific setup of optical components and the fluid test cell for the generation of a single vapor bubble are described. The procedure and main steps to derive an accurate temperature field from the recorded interferograms are explained in detail. These are: wrapped phase calculation based on a four frames algorithm, phase unwrapping using Itoh algorithm, and Abe inversion for the calculation of the local temperatures. The results from interferometry are verified by point wise measurements using micro-thermocouples. Compared to formerly applied measurement techniques the presented phase shift interferometry leads to higher accuracy and higher spatial resolution. [ABSTRACT FROM AUTHOR]

Based on experimental and theoretical investigations the present paper evaluates heat and mass transfer phenomena in nucleate boiling of pure substances and binary mixtures. It is recognized that microscale phenomena can be very important for the understanding and prediction of macroscopic heat transfer. Modeling strategies are presented that include microscale heat and mass transfer. The nucleate boiling heat transfer coefficient can be well predicted using these models and the process can be better explained taking the microscale phenomena into account. Microscale evaporation experiments of the authors confirm the modeling results on this scale. On the microscale, governing phenomena are: intermolecular forces of adsorption, capillary forces, molecular interfacial phase change resistance, and change of phase equilibrium. In a binary mixture, the phase equilibrium temperature is influenced by the strong gradient of concentration and thus the microscale heat transfer is significantly reduced. The contributions of diffusive mass transfer and variable thermophysical properties are negligible in microscale heat and mass transfer. On the macroscale, the influence of free and forced convection, transient heat conduction, and latent heat depends on the geometry of the evaporator and the boiling conditions. In a binary mixture, parameters are identified that are responsible for the characteristic reduction of heat transfer coefficients at intermediate mole fractions. [Copyright &y& Elsevier]

High performance heat pipes are widely used for the thermal control of electronic devices. Concerning heat transport limitations, typical wick or capillary structures show advantages in some aspects and disadvantages in others. An advanced capillary structure was developed with high thermal effectiveness, low axial pressure drop, high capillary pressure, and a high boiling limit. It combines open minichannels with open microchannels that are manufactured perpendicular on top of the minichannels. The heat transfer coefficient in the evaporator zone, which is a characteristic value for the thermal effectiveness, was up to 3.3 times higher compared to a similar structure without microchannels. A model that combines micro- and macroscopic phenomena was developed. It predicts the heat transfer coefficient with quite good accuracy as long as the microchannels are at least 300 μm. [ABSTRACT FROM AUTHOR]

A model is presented to calculate nucleate boiling heat transfer coefficients of binary mixtures. The model includes the governing physical phenomena, such as the variation of the phase interface curvature, the adhesion pressure between wall and liquid, the interfacial thermal resistance as well as the local variation of composition and liquid- vapor equilibrium. Marangoni convection is considered, too. The theoretical background of these phenomena is described and their implementation is explained. The model is verified by comparing calculated heat transfer coefficients of hydrocarbon mixtures with experimental data. Computational and experimental data are in good agreement. In the examples a considerable amount of the total heat flow passes through a tiny thin film area, called micro region, where the liquid-vapor phase interface is attached to the wall. Very high spatial gradients of heat flux and mixture concentration occur interacting with overall heat transfer performance. [ABSTRACT FROM AUTHOR]

In the present paper an attempt is made to clarify the influence of mixture effects upon heat transfer in nucleate boiling of binary mixtures. The studies are based on a theoretical model that is briefly summarized. Evaluating heat and mass transfer around a single vapor bubble emphasizes a strong influence of the so-called micro region where the liquid-vapor phase interface approaches the wall. Due to the preferential evaporation of one component of the mixture, strong concentration gradients occur in the micro region. These microscale composition effects cause diffusive mass transfer, Marangoni convection, and a variation of the liquid-vapor phase equilibrium as well as a variation of the thermophysical properties. From a macroscopic point of view the bubble site density and the departure diameter vary with the composition of the liquid. By means of parameter studies decisive mixture effects are identified and their relevance in the nucleate boiling process is stated. The heat transfer coefficient crucially depends on the bubble site density and departure diameter. For increasing bubble site density, the influence of microscopic concentration gradients increases. But only the variation of liquid-vapor phase equilibrium becomes important, while diffusive mass transfer and Marangoni convection can be neglected. [ABSTRACT FROM AUTHOR]

• Novel numerical model for deposit formation from evaporating urea-water drops. • Detailed analysis of heat and mass transfer in evaporating drop, deposit, and gas. • Deposit shape affects contact line temperature and evaporation rate. • Impact of temperature, composition, and radius on deposit formation quantified. • Deduction of characteristic time scale and of a correlation for start of deposition. Evaporation and deposit formation of a pinned urea-water drop on an initially smooth surface is modeled. Water evaporates from the two-component drop into the surrounding gas phase. This leads to an increase of the urea concentration inside the drop. At the three-phase contact line, high evaporation rates lead to a maximum of the urea concentration. As a result, heterogeneous nucleation and growth of urea crystals takes place in the vicinity of the three-phase contact line. The model resolves the deformation of the liquid–gas interface using a moving mesh and an arbitrary Lagrangian–Eulerian method (ALE). The deposit shape and the influence of the deposit on the transport processes in the drop are accounted for. The drop evaporation agrees quantitatively with a correlation, and the deposit shape matches qualitatively with experimental investigations from the literature. A parametric study reveals that the wall temperature, initial drop composition, and drop radius influence the deposit formation process. The time instant of deposit nucleation and the deposit shape depend on the choice of these parameters. A characteristic time scale is identified and a correlation to predict the beginning of deposit formation is derived. Once the deposit formation has started, the deposit growth rate increases with time. [ABSTRACT FROM AUTHOR]

Liquid jet impingement is used in industries for cleaning or cooling the surfaces, since this process is characterized by high heat or mass transport rates. The impinging jet spreads radially outwards and creates a wall film flow, which is bounded by a hydraulic jump. The existing models describing the extent of the radial flow zone and the position of hydraulic jump are only applicable for small nozzle-to-target distances and low flow rates. In this work, the model is extended to include the effect of splattering liquid, which may reduce the extent of the radial flow zone considerably. The splattering in combination with the hydraulic jump position is investigated experimentally for a liquid jet impinging horizontally onto a vertical wall. In addition, the high-speed images of the jet and of the impingement region provide further insight into the splattering mechanisms. It is found that for large nozzle-to-target distances the splattered mass fraction is determined only by the jet Weber number. The hydraulic jump position can be predicted using the extended model with deviations of less than 20% in this region. [ABSTRACT FROM AUTHOR]

Impinging droplets on a hot surface is a significant phenomenon in many industrial applications, such as spray cooling. Previous studies reported various morphological behaviours affecting the droplet's wetting, heat transfer, and evaporation characteristics. However, there is an ambiguity in understanding the influence of the surrounding medium on the resulting boiling regimes. The present work aims to study this aspect through an experimental investigation using high-speed photography and infrared thermography. During the experiments, the degassed FC-72 liquid droplets have impinged onto a heated chromium-plated calcium fluoride (C a F 2) surface with a constant impact velocity. Three ambient conditions, such as saturated vapour (heated vapour), air at liquid saturation temperature (heated air), and air at room temperature (ambient air), are used. The surface temperature is varied in each ambience until the complete droplet dewetting, i.e., the Leidenfrost phenomenon has appeared. In this study, the stages of boiling are perceived as film evaporation, excessive and nominal bubbly boiling, transition, and Leidenfrost. With different surrounding media, the onset of a regime and its boiling morphology are distinct. During the film evaporation regime, the droplet heat transfer is high for the impact in ambient air, and the contact line evaporation is dominant in the vapour medium. In contrast, heat transfer is improved in a vapour medium during the bubbly boiling process, reaching up to 30% enhancement compared to the droplets in air surroundings. It is attributed to increased nucleation sites and excessive bubbling compared to air media. Correlations from the literature are also revisited to understand the onset of bubbly boiling and the droplet breakup at the Leidenfrost point. An overall comparison of droplet heat transfer during the boiling regimes in surrounding media is discussed in this paper. • The effect of surrounding media on boiling regimes is experimentally investigated. • Boiling regimes are categorised into film evaporation, bubbly boiling, transition, and Leidenfrost point. • In each regime, the droplet's spreading and heat transfer are analysed using shadow photography and infrared thermometry. • The significance of contact line evaporation in various surroundings during the film evaporation regime is presented. • Correlations related to the onset of bubbly boiling and droplet breakup at Leidenfrost point are revisited. [ABSTRACT FROM AUTHOR]

In this work, we present an extended Discontinuous Galerkin method for simulating transient, incompressible two-phase flows, which include heat transfer and thermally driven evaporation at the interface of single-component systems. This expands our previous work to include the consideration of non-material interfaces and a coupling between velocities and temperature gradients at the interface. The phase boundary is represented by the zero-set of a level set function, while effects due to surface tension are treated by the Laplace-Beltrami formulation. This sharp interface model allows for a sub-grid accurate representation of the solution fields. By using compactly supported polynomial solutions, discontinuities at the interface can be sharply represented without employing additional reconstruction schemes. The approach is validated through well-known evaporation test cases. This includes two 1D test cases, known as Stefan and Sucking problem, a 2D film boiling and finally the 3D growth of a vapor bubble, known as Scriven test case. • Extended DG method for two-phase flow with phase transition. • Discretization of interfacial conditions at the interface position. • High-order Ansatz functions resolve the solution fields up to the interface. • No reconstruction of values and gradient values at the interface necessary. [ABSTRACT FROM AUTHOR]

High-performance computing systems are needed in advanced computing services such as machine learning and artificial intelligence. Consequently, the increase in electron chip density results in high heat fluxes and requires good thermal management to maintain the servers. Spray cooling using liquid offers higher heat transfer rates and is efficient when implemented in electronics cooling. Detailed studies of fundamental mechanisms involved in spray cooling, such as single droplet and multiple droplet interactions are required to enhance the process's knowledge. The present work focuses on studying a train of two FC-72 droplets impinging over a heated surface. Experimental investigation using high-speed photography and infrared thermography is conducted. Simultaneously, numerical simulations using opensource CFD package, OpenFOAM are carried out, emphasizing the significance of contact angle hysteresis. The surface temperature is chosen as a parameter, and different boiling regimes along with dynamic Leidenfrost point for the present impact conditions are identified. Spreading hydrodynamics and heat transfer characteristics of these consecutively impinging droplets till the Leidenfrost temperature are studied and compared. [ABSTRACT FROM AUTHOR]

Storing electrical energy in the form of thermal energy, pumped heat electricity storage (PHES) systems are a location‐independent alternative to established storage technologies. Detailed analyses, considering the transient operation of PHES systems based on commercially available or state‐of‐the‐art technology, are currently not publicly accessible. In this work, numerical models that enable a transient simulation of PHES systems are developed using the process simulation software EBSILON®Professional. A PHES system based on a Joule/Brayton cycle is designed, considering commercially available and state‐of‐the‐art components. Employing the developed models and an exergoeconomic analysis, the transient operation of the PHES system is simulated and evaluated. The analyzed PHES system reaches a round‐trip efficiency of 42.9%. The exergoeconomic analysis shows that PHES systems have higher power‐specific costs than established storage technologies. They can currently not be economically operated at the day‐ahead market for Germany and Austria, which is predominantly resulting from high purchased equipment costs. However, PHES systems have the advantage of being location‐independent. [ABSTRACT FROM AUTHOR]

The rising share of renewable energies leads to increased fluctuations in electrical power supply. One possibility to shift the surplus energy based on demand is a Carnot battery (CB). A CB uses a heat pump or resistance heater to convert and store thermal energy into electrical energy. Later, the stored thermal energy is converted back into electrical energy using a heat engine. This study investigates a CB with a two-zone tank for thermal energy storage. A transcritical process with CO 2 is applied for charging, while discharging employs a transcritical process with CO 2 and six refrigerants operating in a subcritical process. The transcritical process with CO 2 and the four most promising subcritical processes are compared regarding round trip efficiency and levelized cost of electricity (LCOE) depending on the pinch points 5 K and 1 K in the heat exchangers. Additionally, the technology readiness level (TRL) is determined for these configurations. The results show round-trip efficiencies between 11.3% and 33.5% and LCOEs ranging from EUR 0.95 (kWh) − 1 to EUR 2.09 (kWh) − 1 for the considered concepts with TRLs of up to six. [ABSTRACT FROM AUTHOR]

Pumped thermal energy storage (PTES) is a technology for intermediate storage of electrical energy in the form of thermal energy. In this work, PTES systems based on a transcritical CO2 charging process are investigated. A two‐zone water storage tank with a storage temperature of 115°C is used as thermal energy storage. For discharge, an Organic Rankine Cycle (ORC) and, alternatively, a transcritical CO2 heat engine are investigated. The considered concepts are modelled and simulated as stationary processes using the EBSILON Professional software. The scaling is based on an electrical input power of 5 MW. Using an ORC with the working fluid R1234yf for the discharging process results in the highest round‐trip efficiency of 36.8%. The component costs of the different configurations are estimated using cost functions. On the basis of this, the levelized cost of storage (LCOS) is calculated. The configuration with the ORC as the discharging process has the lowest LCOS of 59.2 €cents (kWh)−1. In addition, the technological maturity is determined using the technology readiness level scale. There are no prototypes of the investigated PTES systems yet. Therefore, further investigations must be carried out to implement the technology in the future. [ABSTRACT FROM AUTHOR]

Energy and mass-balance modelling of glaciers is a key tool for climate impact studies of future glacier behaviour. By incorporating many of the physical processes responsible for surface accumulation and ablation, they offer more insight than simpler statistical models and are believed to suffer less from problems of stationarity when applied under changing climate conditions. However, this view is challenged by the widespread use of parameterizations for some physical processes which introduces a statistical calibration step. We argue that the reported uncertainty in modelled mass balance (and associated energy flux components) are likely to be understated in modelling studies that do not use spatio-temporal cross-validation and use a single performance measure for model optimization. To demonstrate the importance of these principles, we present a rigorous sensitivity and uncertainty assessment workflow applied to a modelling study of two glaciers in the European Alps, extending classical best guess approaches. The procedure begins with a reduction of the model parameter space using a global sensitivity assessment that identifies the parameters to which the model responds most sensitively. We find that the model sensitivity to individual parameters varies considerably in space and time, indicating that a single stated model sensitivity value is unlikely to be realistic. The model is most sensitive to parameters related to snow albedo and vertical gradients of the meteorological forcing data. We then apply a Monte Carlo multi-objective optimization based on three performance measures: model bias and mean absolute deviation in the upper and lower glacier parts, with glaciological mass balance data measured at individual stake locations used as reference. This procedure generates an ensemble of optimal parameter solutions which are equally valid. The range of parameters associated with these ensemble members are used to estimate the cross-validated uncertainty of the model output and computed energy components. The parameter values for the optimal solutions vary widely, and considering longer calibration periods does not systematically result in better constrained parameter choices. The resulting mass balance uncertainties reach up to 1300 kg m -2 , with the spatial and temporal transfer errors having the same order of magnitude. The uncertainty of surface energy flux components over the ensemble at the point scale reached up to 50 % of the computed flux. The largest absolute uncertainties originate from the short-wave radiation and the albedo parameterizations, followed by the turbulent fluxes. Our study highlights the need for due caution and realistic error quantification when applying such models to regional glacier modelling efforts, or for projections of glacier mass balance in climate settings that are substantially different from the conditions in which the model was optimized. [ABSTRACT FROM AUTHOR]

• Numerical predictions generally agree well with experimental data. • A wide heat flux peak can be observed during the spreading phase. • A wavy fluid flow causes several rings of high heat flux at the drop footprint. • Successive drop impact during the spreading phase enhances heat transfer. In this work, hydrodynamics and heat transport during the vertical coalescence of multiple drops impacting successively onto a hot wall are studied numerically and experimentally. The numerical model uses the volume of fluid method within the OpenFOAM library and takes evaporation into account. The significant heat transfer at the three-phase contact line is considered in a subgrid model. FC-72 is used as working fluid in a pure, saturated vapor atmosphere at ambient pressure. For the case of a drop chain of low impact frequency, numerical results are compared with experimental data. In particular, temperature and heat flux fields at the drop footprint as well as drop shape are compared between experiments and simulations. During the impingement of the second drop, several rings of high heat flux are observed in experiment and predicted by simulations, and the physical reasons of their appearance are elucidated by the analysis of simulated velocity and temperature fields. Furthermore, the impact of a drop chain consisting of five drops impacting at a high frequency is studied numerically. The drop chain configuration enhances both spreading and heat transport compared to the case of a single drop impact with a five-fold volume. [ABSTRACT FROM AUTHOR]

A new test rig has been designed to investigate the effect of carbon based deposit layer formation on the hydrodynamics and heat transfer of a thin evaporating methylnaphthalene film, which builds deposits at a hot wall under thermal stress in an oxidative environment. The liquid film is shear driven by a preconditioned air flow, spread on a foil heater (joule heating) and evaporates. With a black and white camera the hydrodynamics of the moving film is visualized, whereas the temperature field below the foil is qualitatively measured with an IR camera. Prior to conducting the measurements the foil is wetted and dried periodically multiple times to form an initial deposit layer. For the main investigations the deposit layer is removed locally. The presented recordings show a direct effect of the deposit layer on wetting and heat transfer, and thus the ongoing deposit formation. Deposit layers are preferably wetted and act as thermal barriers leading to local higher wall temperatures and thus to a reduced foil cooling. [ABSTRACT FROM AUTHOR]

The heat and mass transfer close to the apparent three-phase contact line is of tremendous importance in many evaporation processes. Despite the extremely small dimensions of this region referred to as the microregion compared to the macroscopic length scale of a boiling process, a considerable fraction of heat can be transferred in this region. Due to its small characteristic length scale, physical phenomena are relevant in the microregion, which are completely negligible on the macroscopic scale, including the action of adhesion forces and the interfacial heat resistance. In the past, models have been developed taking these effects into account. However, so far these models are based on the assumption of one-dimensional (1D) heat conduction, and the flow within the thin liquid film forming the microregion near the apparent three-phase contact line is modeled utilizing the lubrication approximation. Hence, the application of existing models is restricted to small apparent contact angles. Moreover, the effects of surface structures or roughness are not included in these lubrication models. To overcome these limitations, a direct numerical simulation (DNS) of the liquid flow and heat transfer within the microregion is presented in this paper. The DNS is employed for validation of the existing lubrication model and for investigation of the influence of surface nanostructures on the apparent contact angle and in particular on the heat transfer within the microregion. [ABSTRACT FROM AUTHOR]

This study presents a reanalysis of the glaciologically obtained annual glacier mass balances at Hintereisferner, Ötztal Alps, Austria, for the period 2001- 2011. The reanalysis is accomplished through a comparison with geodetically derived mass changes, using annual high-resolution airborne laser scanning (ALS). The grid-based adjustments for the method-inherent differences are discussed along with associated uncertainties and discrepancies of the two methods of mass balance measurements. A statistical comparison of the two datasets shows no significant difference for seven annual, as well as the cumulative, mass changes over the 10-year record. Yet, the statistical view hides significant differences in the mass balance years 2002/03 (glaciological minus geodetic records = +0.92mw.e.), 2005/06 (+0.60mw.e.), and 2006/07 (-0.45mw.e.). We conclude that exceptional meteorological conditions can render the usual glaciological observational network inadequate. Furthermore, we consider that ALS data reliably reproduce the annual mass balance and can be seen as validation or calibration tools for the glaciological method. [ABSTRACT FROM AUTHOR]

[Display omitted] During the evaporation of urea water solution (UWS), the wall temperature and surface properties influence the dynamics of deposit formation by affecting the internal mass transport. These effects are expected to be reflected in the resulting deposit morphology and allow different deposit regimes to be distinguished. The temperature of metallic substrates is varied for three different surface treatments to analyze the wetting, evaporation behavior and the crystallization process of single UWS droplets in situ using a high-speed camera. The deposit morphology is captured by confocal microscopy and analyzed via the power spectral density method (PSD). PSD is used to extract the height of different surface features for each deposit, providing valuable information about the local crystallization history. A significant influence of the surface properties on the crystallization process as well as on the morphology of the final deposit is found. The influence of wettability is described by the resulting internal mass transport, which determine the urea distribution. PSD analysis quantified distinct trends in the scaling tendencies of the deposit aggregates under different wall conditions. The local crystal growth history extracted by PSD agrees well with proposed crystallization mechanisms, which is further supported by high-speed and SEM imaging. [ABSTRACT FROM AUTHOR]

In a special boiling cell, vapor bubbles are generated at single nucleation sites on top of a 20 μm thick stainless steel heating foil. An infrared camera captures the rear side of the heating foil for analyzing the temperature distribution. The bubble shape is recorded through side windows with a high-speed camera. Global measurements were conducted, with the pure fluids FC-84 and FC-3284 and with its binary mixtures of 0.25, 0.5, and 0.75 mole fraction. The heat transfer coefficient (HTC) in a binary mixture is less than the HTC in either of the single component fluid alone. Applying the correlation of Schlünder showed good agreement with the measurements (1982, "Über den Wärmeübergang bei der Blasenverdampfung von Gemischen," Verfahrenstechnik, 16(9), pp. 692-698). Furthermore, local measurements were arranged with high lateral and temporal resolution for single bubble events. The wall heat flux was computed and analyzed, especially at the three-phase-contact line between liquid, vapor, and heated wall. The bubble volume and the vapor production rate were also investigated. For pure fluids, up to 50-60% of the latent heat flows through the three-phase-contact region. For mixtures, this ratio is clearly reduced and is about 35%. [ABSTRACT FROM AUTHOR]

Surfaces with topography promote rivulet flow patterns, which are characterized by a high cumulative length of contact lines. This property is very advantageous for evaporators and cooling devices, since the local evaporation rate in the vicinity of contact lines (microregion evaporation) is extremely high. The liquid flow in rivulets is subject to different kinds of instabilities, including the long-wave falling film instability (or the kinematic-wave instability), the capillary instability, and the thermocapillary instability. These instabilities may lead to the development of wavy flow patterns and to the rivulet rupture. We develop a model describing the hydrodynamics and heat transfer in flowing rivulets on surfaces with topography under the action of gravity, surface tension, and thermocapillarity. The contact line behavior is modeled using the disjoining pressure concept. The perfectly wetting case is described using the usual h-3 disjoining pressure. The partially wetting case is modeled using the integrated 6-12 Lennard-Jones potential. The developed model is used for investigating the effects of the surface topography, gravity, thermocapillarity, and the contact line behavior on the rivulet stability. We show that the long-wave thermocapillary instability may lead to splitting of the rivulet into droplets or into several rivulets, depending on the Marangoni number and on the rivulet geometry. The kinematic-wave instability may be completely suppressed in the case of the rivulet flow in a groove. [ABSTRACT FROM AUTHOR]

In nucleate boiling two specific models are used to describe wall heat transfer to single bubbles: (i) The contact line model, in which evaporation close to the three-phase contact line is the dominating effect, and (ii) the microlayer model, in which evaporation of a thin liquid film below the bubble is the dominating effect. These models are discussed controversially in literature. In this work high speed IR thermography is used to investigate influence factors onto the development of such a thin, evaporating liquid film at a single receding meniscus. FC-72 is used as working fluid. From the time-dependent temperature field the evolution of the local heat flux is derived numerically. Both situations could be observed, contact line, as well as microlayer evaporation, depending on the experiment parameters. Through comparative analysis, the velocity of the interface, the wall superheat and the latent heat of evaporation are found to have a major influence. Furthermore the wetting characteristics of the heated wall have an influence onto the incipience of thin film deposition. From a stationary mass and energy balance at an infinitesimal short segment of the thin evaporating film an equation for the local gradient of the film thickness is obtained. Integration of the dimensionless form of this equation results in a description of the film thickness and the local heat transfer at such a thin evaporating film. Three dimensionless groups are found to have an influence onto the film thickness profile. A comparison of the model to experimentally determined values shows good agreement. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, a numerical investigation of the phase change characteristics of Taylor-Bubbles (T-B) during flow boiling of FC-72 in a square minichannel is carried out. Multiple Taylor-Bubbles starting from their nucleation, growth and coalescence along with the associated heat transfer mechanisms have been modeled. The temporal variation of bubble coalescence pattern is found to exhibit a good agreement with the in-house experimental measurements conducted in microgravity environment. A detailed parametric study is conducted to understand the effects of Reynolds number (Re), wall superheat ( ), bubble nucleation radii, and the surface tension expressed in terms of Capillary number (Ca) on the T-B nucleation and coalescence characteristics. The parametric study reveals that the nucleating bubbles tend to grow and coalesce faster at Re =500 compared to Re =50 due to higher temperature gradients leading to enhanced evaporation rates. The phenomenon of bubble ‘roll-off’ is observed when the wall and liquid are both superheated to 2K due to absence of heat transfer between the top wall of the channel and the T-B. Also it is observed that the bubble coalescence time is reduced nearly by a factor of two for the coalescence of unequal bubble sizes. At higher values of Ca, both coalescence and break-up of T-B occur in succession while at lower values no coalescence is observed. The heat flux contours in the vicinity of the T-B contact line region predicted by the numerical model is found to exhibit a good qualitative agreement with the experimental measurement. It is inferred that of the parameters studied, Re and are the two most significant factors that influence wall heat transfer during T-B coalescence. [Copyright &y& Elsevier]

The formation of liquid microlayers during the dewetting of a hot surface has significant effects on heat transfer in boiling and evaporation processes. Understanding the criteria for the formation of such microlayers is crucial for explaining the heat transfer characteristics, in particular the heat transfer coefficient (HTC). Research in this area has been almost exclusively concerned with the study of pure liquids, but not with the specific behavior of binary mixtures used in numerous boiling processes. As an example, we investigate the formation of microlayers in ethanol water mixtures, whose global boiling behavior has been widely studied. We conducted dewetting experiments during evaporation with pure ethanol as the reference case and with ethanol/water mixtures with ethanol fractions of 90 % w/w and 70 % w/w. Using high resolution infrared thermography, two evaporation regimes were identified depending on the process conditions and fluid composition: contact line evaporation (CLE) and microlayer evaporation (MLE). The transition from CLE to MLE in pure ethanol was observed at a critical dewetting velocity that depended on wall superheat. Interestingly, for an ethanol water mixture containing 90 wt% ethanol, MLE was observed at all wall superheats and dewetting velocities tested. This can be explained by two specific mixture effects: First, Marangoni convection leads to a flow toward the contact line, and second, the locally increased water concentration near the contact line reduces the evaporating mass flux, which favors film formation and thus MLE. However, with the further increase in water concentration, as with the 70 % ethanol water mixture, MLE was observed only transiently for a few milliseconds, followed by a rapid shift to CLE at all wall superheats and dewetting velocities. These results provide valuable insight into the formation of microlayers in binary mixtures, and thus into the heat transfer characteristics observed in the nucleate boiling studies with binary mixtures. [ABSTRACT FROM AUTHOR]

As the urgency for decarbonization of economies around the world is becoming more pressing, green energy carriers synthesized with renewable energy are emerging as tradable commodities for connecting regions with abundant renewable energy to those with high energy demand. Among the various options, metals – especially iron – have been identified by the scientific community as promising green fuels due to their high volumetric energy densities. However, there persists a gap in comprehensive thermodynamic analyses despite the growing interest. This study provides a rigorous thermodynamic assessment of an iron-based circular energy economy for carbon-free power supply. The circular system encompasses the storage of renewable energy through the thermochemical reduction of iron oxide powder to metallic iron powder, intermediate storage, energy release in iron-fired power plants via thermochemical oxidation of the iron powder, and long-distance inter-regional transport. Each sub-process of the iron-based energy cycle is described and evaluated using comprehensive thermodynamic models, addressing technical implications and thermodynamic limitations. Two technological options for the hydrogen direct reduction of iron oxides – namely, the shaft furnace and the flash reactor hydrogen direct reduction – are compared. The thermodynamic assessments reveal that the flash reactor is superior to the shaft furnace concept, primarily due to the elimination of additional process steps for particle size adjustments. Moreover, the study underscores the feasibility of iron-fired power plants as a means to retrofit and decarbonize existing coal-fired power plants. The analysis shows that iron-fired power plants attain higher efficiency levels than coal-fired power plants, even under non-ideal conditions. Regarding transport, industrial practices and regulations for handling iron and its oxides are well established globally, providing further confidence in the feasibility of the approach. The findings indicate that integrating an iron-based circular energy economy with the repurposing of existing infrastructure presents a compelling option. This approach effectively addresses the temporal and spatial mismatch between energy demand and supply serving as a critical enabler for renewable energy transport and long-term storage, which is essential for a successful energy transition. • Iron can significantly contribute to a sustainable and reliable energy future. • Using green iron for decarbonizing coal-fired power plants enhances efficiency. • Iron (oxide) can be handled on a global scale with established protocols. • Power-to-power efficiencies can approach or exceed 30 %. • Improvement potential peaks in new reduction concepts and electrolyzer efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

The flow of thin falling liquid films is unstable to long-wave disturbances. The flow insta-bility leads to development of waves at the liquid-gas interface. The effect of the waves on heat and mass transfer in falling liquid films is a subject of ongoing scientific discus-sion. In this work, numerical investigation of the wave dynamics has been performed using a modified volume-of-fluid (VOF) method for tracking the free surface. The surface tension is described using the continuum surface force (CSF) model. With low disturb-ance frequency, solitary waves of large amplitude are developed, which are preceded by low-amplitude capillary waves. With high disturbance frequency, low amplitude sinusoi-dal waves are developed. The waveforms dependent on the Reynolds number and disturb-ance frequency are summarized in a form of a regime map. A correlation describing the separation curve between the sinusoidal waves regime and solitary waves regime is pro-posed. The wave parameters (peak height, length, and propagation speed) are computed from the simulation results and compared with available experimental correlations in a wide range of parameters. The effects of the disturbance frequency and the plane inclina-tion angle on the wave dynamics have been studied. The interaction of waves initiated by simultaneous disturbances of two different frequencies has been investigated. The heat transfer in the wavy film has been simulated for the constant wall temperature boundary condition. The effects of Prandtl number and disturbance frequency on local and global heat transfer parameters have been investigated. It has been shown that the influence of waves on heat transfer is significant for large Prandtl numbers in a specific range of disturbance frequencies. [ABSTRACT FROM AUTHOR]

Abstract: The cooling effectiveness of spray cooling is strongly influenced by droplet size and velocity as well as by the fluid properties. To enhance the understanding of the entire process, first of all basic processes occurring in the spray have to be addressed. Therefore, in this study the heat transfer during a single drop impingement onto a dry, superheated wall is investigated numerically, and the effects of the dominating dimensionless parameters on the convective and evaporative heat transfer are analyzed. In order to be able to distinguish between the influences of the individual dimensionless groups, each parameter is varied individually. The study is performed using fluid properties of the refrigerant FC-72. The droplet is surrounded by a saturated vapor atmosphere. The numerical model accounts for the complex two-phase flow, the transient conductive heat transfer within the solid domain and the evaporative mass transfer. Special attention is paid to the local heat and mass transfer close to the moving three-phase contact line. The spreading phase appears to be dominated by the Reynolds number, while in the receding phase the Weber number has the strongest influence on heat transfer. For the evaporation of a sessile droplet, which is the final stage of the impact process, the heat transfer is governed by the Bond number. [Copyright &y& Elsevier]

One of the most commonly used methods of liquid atomization is spinning disk atomization. This technique makes use of centrifugal forces to create a thin liquid film spreading radially over a disk. The film flowing along the disk is mostly wavy. The waves have a negative influence on the drop size distribution in the atomization process. It is known that the waves on falling films can be suppressed by using walls with longitudinal grooves. Due to the similarity of the physical mechanisms governing the wave development on falling films and on films flowing over spinning disks, we suggest using grooved surfaces for suppressing the waves in spinning disk atomizers. We develop a mathematical model for description of the film dynamics on a spinning disk with wall topography using the long-wave theory. It takes into account the centrifugal force, inertia, surface tension, and heat transfer. The wall surface topography induces a thermocapillary flow in the liquid film, which significantly affects the film thickness distribution. We develop an experimental method for high-speed measurements of film dynamics on a spinning disk. The average film thickness qualitatively agrees with the basic theoretical solution. Quantitative discrepancies can be attributed to the film waviness. [ABSTRACT FROM AUTHOR]

Abstract: Heating wall temperature distribution and bubble shapes were measured during nucleate boiling of FC-72 in microgravity in the presence of an electric field. The presented results are part of the results obtained during the 50th ESA parabolic flight campaign and focused on the electric field experiments. A 25μm stainless steel foil served as heated wall for the boiling process. The temperature distribution of the foil was measured via infrared thermography at a frame rate of 1000Hz and with a resolution of 30μm/pixel. The bubbles were observed by a synchronized high speed camera. A washer shaped electrode was located parallel to the heated wall. The electrode was charged to up to +10kV while the heating foil served as ground potential. The effect of the electric field created by this configuration on the boiling process was investigated for different boiling states. Due to the absence of buoyancy in microgravity the bubbles generally do not detach from the heating foil with the given heat fluxes. The electric force on the bubbles generated by the field gradient sucked the vapor through the center hole of the electrode. Thereby, a reliable bubble detachment and re-wetting mechanism could be established and allowed the implementation of a nucleate boiling process in microgravity. [Copyright &y& Elsevier]