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In this work, the condensation characteristics of droplets considering the non-condensable gas with different interaction effects are numerically studied utilizing a multicomponent multiphase thermal lattice Boltzmann (LB) model, with a special focus on the asymmetric nature induced by the interaction effect. The results demonstrate that for isolated-like growth with negligible interactions, the condensation characteristics, that is, the concentration profile, the temperature distribution, and the flow pattern, are typically symmetric in nature. For the growth regime in a pattern, the droplet has to compete with its neighbors for catching vapor, which leads to an overlapping concentration profile (namely the interaction effect). The distribution of the condensation flux on the droplet surface is consequently modified, which contributes to the asymmetric flow pattern and temperature profile. The condensation characteristics for droplet growth in a pattern present an asymmetric nature. Significantly, the asymmetric condensation flux resulting from the interaction effect can induce droplet motion. The results further demonstrate that the interaction strongly depends on the droplet's spatial and size distribution, including two crucial parameters, namely the inter-distance and relative size of droplets. The asymmetric condensation characteristics are consequently dependent on the difference in the interaction intensities on both sides of the droplet. Finally, we demonstrate numerically and theoretically that the evolution of the droplet radius

Purpose: Investigating the existence of inflammation in the distal outflow system posterior of the Schlemm's canal in primary open-angle glaucoma (POAG).Methods: Scleral biopsies (n = 62) from POAG...

A multi-component multi-phase thermal lattice Boltzmann model considering vapor-liquid phase change is developed to study droplet condensation with the presence of non-condensable gas. Some tests, including an isolated droplet evaporation, are conducted to verify the capability of this model in simulating multi-component multi-phase flow with vapor-liquid phase change. After that, single droplet condensation considering non-condensable gas is investigated with different mass fraction of non-condensable component and contact angles. The results show that the influence of the non-condensable gas upon droplet condensation heat transfer is depended on the growth stage and the amount of the non-condensable gas. The mass transfer of vapor and non-condensable component will tend to an equilibrium state with the droplet condensation going. Furthermore, for different contact angles, the dynamic behavior of the contact line plays a critical role in the accumulation effect of the non-condensable component. And the heat transfer of droplet condensation is enhanced by the hydrophilic substrate rather than the hydrophobic substrate as expected, no matter adding the non-condensable component or not. In different conditions, the power law, which fits the droplet radius with time, is used to define the growth rate mathematically.

A new facility feasible for the investigation of dropwise condensation at a vertical polymer surface (9 × 6 mm, L × H) is described in detail. The droplets are liquefied out of humid air, which flows through a rectangular channel (12 × 32 mm, W × H) and passes the sub-cooled surface of a sensor. The latter one is flush mounted into one of the vertical channel walls beyond a hydrodynamic entry length of 550 mm determining perpendicular heat fluxes by measuring temperature differences. Furthermore the droplet covered surface is observed through the opposite channel wall by an infrared camera. The variable experimental parameters include temperature, water content and flow velocity of the humid air, as well as the surface temperature of the sensor. The scope of the experimental study is to investigate the mean heat transfer resistance of the condensate droplets which form on the substrate surface. The procedure is based on the determination of heat fluxes and the evaluation of the temperature differences between the substrate surface and the liquid/gas interface by means of thermography, both of them carried out synchronously. The experimental droplet heat transfer coefficient, h d , is evaluated as an average value and it considers both heat conduction through the droplets and the augmentation of heat transfer due to inner convection. The parameter variation covers Reynolds numbers between 7900 and 21400, relative humidities between 56% and 95% and air temperatures between 30 °C and 46 °C for a broad range of cooling temperatures. The latter one influences the droplet surface temperature and together with the water content of the bulk, it determines the driving force for mass transfer. h d was found to increase with the Reynolds number and the driving force for mass transfer. However, increasing the latter one beyond a certain value causes massive accumulation of noncondensable gases at the liquid/gas interface inhibiting the vapour mass flux and leading to invariant droplet heat transfer coefficients. The experimental data is correlated providing the basis for the experimental investigation of the heat transfer at the liquid/gas interface which will be done in future.

The present paper, convective dropwise condensation flow over a cold spot is numerically investigated using a 2D hybrid thermal lattice Boltzmann (LB) model with vapor-liquid phase change. After validating the present LB model, dropwise condensation on a cold spot as the nucleation region is simulated so as to study the nucleation and growth of the isolated droplet. The well-known power law for the growth of a single condensing droplet is demonstrated. And then, both simulations of dropwise condensation and convective dropwise condensation are carried out to study the effect of forced convective flow on dropwise condensation. Aiming to consider the effect of contact angle, the droplet is growing in the constant contact radius (CCR) mode. The results indicate that the forced convectional flow complicates the internal flow of the droplet and the vapor flow. The detouring flow (including the lee-side vortex) around the droplet in an isothermal system is replaced by the suction flow owing to condensation. The interaction between the dragging force of the vapor flow and the surface tension gradient changes the size of two symmetric vortices within the droplet in dropwise condensation. The size of these two vortices inside the droplet depends on the velocity and direction of convective flow. By comparison, the heat transfer enhancement of the superimposed flow is not worth mentioning in spite of different flow mode. Not affected by the vapor flow, the heat transfer is weakened by increasing of the contact angle owing to the change of conduction resistance. The present study illustrates the mechanisms of convective dropwise condensation flow in detail.

The thermal accommodation coefficient α has been assumed, although lacking any experimental proof, to be near unity for most gases so far, which denotes no influence. However, it plays a contributing role in the field of the effective thermal conductivity of highly porous insulation materials based on S i O 2 or C a S i O 3 as it is shown in this work. Besides, this work investigates a possible influence on α for A r , N 2 , H e within parameters like temperature, roughness and contamination as this has not been examined on such materials so far. More importantly, it answers the question whether the assumption of α = 1 is valid. By using a parallel plates device, very similar to the guarded-hot-plate, following EN 12667 it was possible to determine α on a dense C a S i O 3 . It occured that the assumptions α = 1 (for A r , N 2 ) and α = 0.3 (for H e ) are valid for measurements near room temperature. Further, physical adsorption was found to increase α . The determination of the influence of roughness has been started showing an interesting effect, but it still remains an open topic. In a collaborative study molecular dynamics (MD) simulations were performed showing a strong equivalence of α between S i O 2 and C a S i O 3 . These results can be considered a lower limit of α as neither roughness nor adsorption processes have been included in the simulation. Therefore, any deviations between experiments and MD could be considered as an apperance of physical adsorption.

Aims: The diagnostic approach to idiopathic giant-cell myocarditis (IGCM) is based on identifying various patterns of inflammatory cell infiltration and multinucleated giant cells (GCs) in histologic sections taken from endomyocardial biopsies (EMBs). The sampling error for detecting focally located GCs by histopathology is high, however. The aim of this study was to demonstrate the feasibility of gene profiling as a new diagnostic method in clinical practice, namely in a large cohort of patients suffering from acute cardiac decompensation. Methods and Results: In this retrospective multicenter study, EMBs taken from n = 427 patients with clinically acute cardiac decompensation and suspected acute myocarditis were screened (mean age: 47.03 &plusmn, 15.69 years). In each patient, the EMBs were analyzed on the basis of histology, immunohistology, molecular virology, and gene-expression profiling. Out of the total of n = 427 patient samples examined, GCs could be detected in 26 cases (6.1%) by histology. An established myocardial gene profile consisting of 27 genes was revealed, this was narrowed down to a specified profile of five genes (CPT1, CCL20, CCR5, CCR6, TLR8) which serve to identify histologically proven IGCM with high specificity in 25 of the 26 patients (96.2%). Once this newly established profiling approach was applied to the remaining patient samples, an additional n = 31 patients (7.3%) could be identified as having IGCM without any histologic proof of myocardial GCs. In a subgroup analysis, patients diagnosed with IGCM using this gene profiling respond in a similar fashion to immunosuppressive therapy as patients diagnosed with IGCM by conventional histology alone. Conclusions: Myocardial gene-expression profiling is a promising new method in clinical practice, one which can predict IGCM even in the absence of any direct histologic proof of GCs in EMB sections. Gene profiling is of great clinical relevance in terms of a) overcoming the sampling error associated with purely histologic examinations and b) monitoring the effectiveness of therapy.

Aims Since December 2019, the novel coronavirus SARS‐CoV‐2 has spread rapidly throughout China and keeps the world in suspense. Cardiovascular complications with myocarditis and embolism due to COVID‐19 have been reported. SARS‐CoV‐2 genome detection in the heart muscle has not been demonstrated so far, and the underlying pathophysiological mechanisms remain to be investigated. Methods and results Endomyocardial biopsies (EMBs) of 104 patients (mean age: 57.90 ± 16.37 years; left ventricular ejection fraction: 33.7 ± 14.6%, sex: n = 79 male/25 female) with suspected myocarditis or unexplained heart failure were analysed. EMB analysis included histology, immunohistochemistry, and detection of SARS‐CoV‐2 genomes by real‐time reverse transcription polymerase chain reaction in the IKDT Berlin, Germany. Among 104 EMBs investigated, five were confirmed with SARS‐CoV‐2 infected by reverse real‐time transcriptase polymerase chain reaction. We describe patients of different history of symptoms and time duration. Additionally, we investigated histopathological changes in myocardial tissue showing that the inflammatory process in EMBs seemed to permeate vascular wall leading to small arterial obliteration and damage. Conclusions This is the first report that established the evidence of SARS‐CoV‐2 genomes detection in EMBs. In these patients, myocardial injury ischaemia may play a role, which could explain the ubiquitous troponin increases. EMB‐based identification of the cause of myocardial injury may contribute to explain the different evolution of complicated SARS‐CoV‐2‐infection and to design future specific and personalized treatment strategies.

A combustion front quenching technique is used to investigate the separation of reaction products during a fast self-propagating high-temperature synthesis (SHS) thermite reaction, which is applied to the aluminothermic welding of rails. Quenching of the reaction zone with a melt temperature at approximately 2400 K enables the possibility of analyzing intermediate stages during exothermic SHS type reactions and the prediction of a time duration for a complete separation of the products Fe, Al2O3, and intermetallics. An average separation time is then used to validate a 3D phase field solver phaseFieldFoam and solution parameters through application of the diffusive Cahn–Hilliard equation, also known as model B.

Open cell foams have desirable geometrical characteristics that make them a suitable choice in various heat exchanger applications. The objective of this study is to determine such volume-averaged key parameters that can characterize the complex thermal transportation process through open cell foams. These key parameters are represented by effective thermal conductivity, ke, volumetric heat transfer coefficient, hv, and dispersion conductivity, kd. In order to determine these parameters, detailed pore-scale simulations through the representative element volumes (REVs) of the actual foam structures are performed. Moreover, knowing the fact that the successful implementation of simplified foam structures as a suitable representative of the actual foam structures can simplify the complexity of the problem, it is also investigated. In the presented work, various microscopic pore-scale models are implemented for both simplified and actual foam structures to determine the key parameters. Subsequently, these key parameters are implemented into two different homogenized macroscopic models to predict the temperature fields of large-scale steady-state and transient forced convection processes. The numerical outcomes of homogenized macroscopic models are validated with the experimental data, which is available for a set of ceramic foams having different pore size (10–30 PPI) and porosity (79–87%). As a consequence of the validation process, the findings of this study reveal that the proposed methodology successfully predicts the values of the concerned key parameters. Further, it is observed that simplified foam structures cannot represent the actual foam structures, as the tortuous shape of open cell foams bound to enhance the advection and dissipation of heat due to recirculation and eddy formation.

A single droplet model is developed to describe the droplet growth during dropwise condensation of moist air on a cold substrate. The condensation process is divided by the droplet surface into two parts. The first step, i.e. the processes of mass transfer from the surroundings to the droplet surface, is modeled by the Kinetic theory and the laws of continuum fluid dynamics formulated using the two-region concept (Knudsen layer and continuum region) at any droplet size and at any concentration of non-condensable gas (NCG). The second step, i.e. the heat transfer across the droplet, is governed by Fourier’s law of heat conduction. These three regions (the continuum region, the Knudsen layer and the region inside the droplet) are incorporated by the matching both the mass flow rates and the energy flow rates. From these, the droplet growth rate, the nucleation size of droplet, the temperature at the droplet surface and Knudsen layer interface can be evaluated depending on different conditions. For this, a numerical algorithm is developed to reflect the droplet dynamics sufficiently detailed, including nucleation, growth/coalescence, slide-off/fall-off, re-nucleation. This is applied to the simulation of the entire condensation process by putting the growth rate and minimum radius from single droplet model into the growth algorithm. Additionally, dropwise condensation experiments of moist air in different relative humidity (RH) are carried out for validation of the simulation results. Good agreement is obtained which demonstrates that the present droplet growth model for dropwise condensation of moist air is credible. The current model and experiments also indicate that the diffusion resistance of water vapor in air from the free stream toward the droplet surface has a significant influence for the heat transfer performance of dropwise condensation of moist air.

Starting with an extensive literature review, in this study investigations of the film spreading of falling films inside smooth and structured tubes are presented in dependence of the tube inclination angle ( β = 0° til 20° from the vertical), mass flow rate and fluid temperature (263.15–293.15 K). Experiments are conducted at isothermal conditions and at partly film evaporation as well. The liquid film is observed visually with a camera which can be moved along the total flow length of the liquid without essential disturbance of the liquid respectively gas flow. The liquid used for the investigations is propane (Pr ≈ 3, Ka ≈ 20 · 10 10 , Re smooth tube = 20–950). The experiments reveal that the investigated helically structuring of the internal tube surface leads to an improvement of film spreading even for inclination angles up to β = 20°. Preliminary tests in an open air-water system clearly showed that the groove structure geometry has an influence on initial wetting and film spreading. Further, the results of the calculated capillary transport from two theoretical approaches are compared and adapted to each other.

This study investigates the particle size distribution's effect on the microstructure and effective thermal conductivity (ETC) of alumina castables. The ETC was measured by the transient plane source method and predicted numerically based on a two-scale model describing the structure on a fine and coarse scale. The prediction considered particle and pore size distributions, porosity (around 20%) and grain morphology. The microstructure was investigated by scanning electron microscopy. For a constant fines content, increasing the coarse grain fraction while decreasing the medium fraction enhanced sintering of the matrix. Small pores (≤250 nm) increased the sintering activity. The densest castable contained the most small pores. The particles’ and pores’ contributions to the sintering activity led to intensified microcracking and a decreased ETC. The numerical model did not consider constituents ≤500 nm like the small pores and microcracks and the calculated ETC values consequently deviated from the measured values.

As a ubiquitous vapor-liquid phase-change process, dropwise condensation has attracted tremendous research attention owing to its remarkable efficiency of energy transfer and transformative industrial potential. In recent years, advanced functional surfaces, profiting from great progress in modifying micro/nanoscale features and surface chemistry on surfaces, have led to exciting advances in both heat transfer enhancement and fundamental understanding of dropwise condensation. In this review, we discuss the development of some key components for achieving performance improvement of dropwise condensation, including surface wettability, nucleation, droplet mobility, and growth, and discuss how they can be elaborately controlled as desired using surface design. We also present an overview of dropwise condensation heat transfer enhancement on advanced functional surfaces along with the underlying mechanisms, such as jumping condensation on nanostructured superhydrophobic surfaces, and new condensation characteristics (e.g., Laplace pressure-driven droplet motion, hierarchical condensation, and sucking flow condensation) on hierarchically structured surfaces. Finally, the durability, cost, and scalability of specific functional surfaces are focused on for future industrial applications. The existing challenges, alternative strategies, as well as future perspectives, are essential in the fundamental and applied aspects for the practical implementation of dropwise condensation.

To simulate the non-uniform frost growth in flow direction for humid air flowing through a freezing channel, a 2D numerical frosting model based on dynamic meshes technique is developed in the current work via the secondary development of commercial ANSYS Fluent. The computation domain consists of both frost layer and humid air regions, and the local heat and vapor fluxes at the surface of frost layer are determined by numerical temperature and vapor fraction fields in the humid air region rather than by empirical correlations. The frost layer is treated as a growing packed bed with heat and mass transfer dominated by molecular diffusion, where local absorption coefficient of vapor desublimation and local vapor fraction are both determined by solving the pseudo steady vapor diffusion equation with a source term theoretically. The interface of frost layer and humid air regions is treated as two walls for the iteration of its temperature, of which the humid air side is specified with the temperature equal to the frost-side counterpart and the frost side takes the heat flux including the extra latent heat caused by vapor deposit. User-defined functions are compiled to implement the above treatments to ANSYS Fluent. Frosting experiments in the literature are simulated with the current model for validation. How the profile of frost layer evolves with time in the frosting process is explored. The contours and profiles of velocity, temperature and vapor fraction are presented to discuss the effects of heat and mass transfer on frost formation. Numerical results demonstrate that the proposed CFD model can predict the frost growth and densification with a relative deviation less than 5% compared with experiments. Besides, the computation load of current model is small due to no solution of complex multiphase flow. In addition, dynamic meshes help current model to capture the interface of frost layer and humid air regions accurately.

In this article, a reduced numerical model for the heat transfer in a commonly used Thermit rail welding procedure is presented. A geometrically reduced calculation domain was deduced from the weld...

Furnaces are frequently lined with low permeability refractory concrete. During the first heat-up process of a relined furnace, high vapour pressures inside the initially wet refractory concrete can result in an explosive destruction of the concrete structure. In this article, the first heat-up process of complex geometries is investigated by modeling and further by a large-scale experiment. The article bases on a previous one, concerning the first heat-up of a one-dimensional single layer wall. The simulation of the first heat-up process of a one-dimensional three-layer wall shows the occurrence of several drying fronts inside the wall. Even if the wall is heated only from one side, two drying fronts appear at both surfaces, moving deeper and deeper inside the wall. Four further drying fronts are arising at the two boundary surfaces, moving in contrawise directions. The simulation shows that the first boundary surface is drying even faster than the first concrete layer, although this layer is arranged in front of that boundary surface. Further the simulation predicts a constant temperature slightly below 100° C at the wall's unheated surface over a large period of time. The model is validated by a large scale experiment which confirms both observations. Further, two more complex geometries are investigated by the aid of a two-dimensional model. One of these geometries, a corner, needs much more time for drying compared with the drying process of a (multilayer-) wall or an exposed edge. This is mainly caused by the slow heat transfer into the corner's core. The second two-dimensional geometry, the (exposed) edge shows the highest pressure maximum of all investigated geometries, caused by the fast heat transfer into the geometry's exposed needle. For both two-dimensional geometries, optimized (pressure-driven) heat-up curves are calculated. These curves are effecting the fastest possible heat-up process without exceeding a given pressure limit. The curves of both geometires are differing significantly from each other and from those ones calculated for a single-layer wall of equal thickness.

The objective of the study is to compare skeletal and dental changes in class II patients treated with fixed functional appliances (FFA) that pursue different biomechanical concepts: (1) FMA (Functional Mandibular Advancer) from first maxillary molar to first mandibular molar through inclined planes and (2) Herbst appliance from first maxillary molar to lower first bicuspid through a rod-and-tube mechanism. Forty-two equally distributed patients were treated with FMA (21) and Herbst appliance (21), following a single-step advancement protocol. Lateral cephalograms were available before treatment and immediately after removal of the FFA. The lateral cephalograms were analyzed with customized linear measurements. The actual therapeutic effect was then calculated through comparison with data from a growth survey. Additionally, the ratio of skeletal and dental contributions to molar and overjet correction for both FFA was calculated. Data was analyzed by means of one-sample Student’s t tests and independent Student’s t tests. Statistical significance was set at p

Furnace walls and bottoms frequently consist of a refractory concrete, which has to be replaced from time to time due to abrasion. After relining, the furnace has to reach its operating temperature again. During this heat-up process, there is a risk of explosive spalling caused by the pore pressure build-up inside the wet concrete. These explosions may be very dangerous to the crew and the furnace-site. Those risks are reduced till today by the aid of empirically developed heat-up instructions (heat-up curves). The application of these curves doesn't really prevent explosive spalling and it is very time-consuming. To improve the first heat-up procedure, the empirically developed heat-up curves are replaced by optimized ones developed by the aid of numerical modeling. These curves are characterized by a constant maximum pressure during the heat-up drying period, and they bring a significant reduction of both, the heat-up time and the maximum pressure inside the concrete. Furthermore their dependency on wall thickness and pressure limit is investigated, as well as effects of previously not expected conditions which can occure during the heat-up of concrete under industrial conditions. Additionally, an optimized heat-up curve is used to dry a concrete brick in a laboratory experiment showing the practical applicability. Good agreement is obtained for the predicted pressure and temperature devolutions and the measured ones.

In the present article, the effective thermal conductivity (ETC) of 10 ppi open-cell ceramic foams is measured at temperatures ranging from 22 °C to 750 °C using the transient plane source (TPS) technique. The detailed morphology of the foam structures is reconstructed from 3D CT-scan images and their structural analysis is carried out using a volume image processing tool. The experimental results are compared with the predictions of directional ETC, obtained using a simplified 1D homogeneous model that considers coupled conduction–radiation heat transfer. The parameters, required by the model, are evaluated based only upon the information that could be extracted from 3D CT-scan images under certain simplifying assumptions. It can be concluded that the predictions of ETC for the present ceramic foam samples clearly correlate with the geometric parameters obtained from their structural analysis. It is also observed that the estimated microscopic porosity of the foam, which is not captured by 3D CT-scan images, has considerable influence on the reconstructed foam structure and hence on the predicted ETC. The predictions of ETC in the measured direction, obtained after the proposed directional averaging, compare extremely well with TPS measurements for the complete range of investigated temperatures. This suggests that the measurements of ETC, obtained employing TPS technique, are the directionally averaged representations of ETC in three perpendicular directions. The present investigation also clearly demonstrates the potential of the simplified modeling approach for characterizing even the directional ETC of open-cell ceramic foams, based primarily on their structural information.

In this study, the e ective thermal conductivity of a variety of materials is deter- mined using a TPS based HotDisk Analyzer. The performance of this method is illustrated by application of three di erent materials viz. SILCAL 1100, OM100 and 1.4841 (X15CrNiSi25-21), with SILCAL 1100 serving as a reference case, as it is well documented in the literature. Numerous experiments were conducted for SILCAL 1100 by means of the e ective thermal conductivity (ETC), and deviations were found to increase up to 35% compared to Ebert et al. [1]. An intensive analysis of the TPS system reveals two possible sources of de- viation of the ETC. The TPS measurement may be a ected by an initially steady-state non-homogeneous temperature eld, but the deviations may also be a consequence of inappropriate temperature coecient of resistance (TCR) settings. Thus, the present work addresses the problem in three steps: rstly, the in uence of an initially steady-state, non-homogeneous temperature eld is evaluated numerically by comparing mean temperature rises of the sensor. Therefore, various example scenarios, which include variations of temperature gradients and uni-axial material properties are simulated. Secondly, the TCR values are determined experimentally by a number of experiments to rule out a variety of possible in uencing parameters such as insulating material of the sensor and connection cables. Thirdly, the TPS measurements are recalculated using the revised TCR data. The obtained ETC is compared to those ones ob- tained by comparative measurements. The numerical calculations indicate that non-homogeneous temperature elds do not a ect the recorded mean tempera- ture rise of the sensor, and thus the thermophysical properties associated with it. On the contrary, the experimental part supposes that calibrating the TCR values seems almost mandatory for achieving trustworthy data by the use of a TPS system.

In modelling dropwise condensation, growth of the droplet is frequently assumed in an isolated form. However, for dropwise condensation of moist air the vapor diffusion from the surrounding to the droplet surface will be tremendously influenced by the blocking effect of the neighboring droplets. The influenced spatial distribution of water vapor totally determines a different condensation rate comparing with that by the isolated droplet model. In this work, a distributed point method (DPSM) as the methodof Green function is developed to capture the interaction effects of droplets without requiring solution of the diffusion equation and the numerical discretization. Due to its nature, the automaticallysatisfied boundary conditions make sure the solution accuracy based on the uniqueness theorem. The significant characteristics for the interaction effects between droplets are investigated by handling a series of droplet arrays. During dropwise condensation, a typical droplet array containing up to 1000 droplets is considered. The results indicate that the interaction effect between droplets is critical in accurately predicting the condensation behavior for dropwise condensation in the presence of non-condensable gas.

In the current work, the turbulent flow and heat transfer in divergent swirl cooling tubes is studied numerically by using the open source CFD code OpenFOAM. The k-ω SST turbulence model with curvature correction, i.e., the k-ω SSTCC model, is used to compute the strong turbulent swirling flow. The unsteady solver “rhoPimpleFoam” is adopted in the computation and a time-averaging operation is implemented for the pressure, velocity and temperature fields to cover the effect of large-scale, low-frequency deterministic fluctuations of the vortex breakdown phenomenon. To generate high-quality grids, different parts of the swirl tubes are meshed with different block structures in ICEM and the Arbitrarily Coupled Mesh Interface (ACMI) boundary condition is used to couple the neighboring segments with non-conformal grids. The current model is validated by comparing the numerical results of a swirl tube with constant diameter to experimental data and numerical results from literature. In this study we investigated the turbulent heat transfer enhancement in a divergent swirl tube that features two 180°-displaced tangential inlets and a divergence angle of 0.596°. Moreover, the influence of axially multiple tangential inlets is studied for the same divergence angle. The current work demonstrates that the computationally cheap k-ω SSTCC model can predict the flow and heat transfer performances in a swirl tube with reasonable accuracy. Additionally, it is found that the Nu number of the divergent swirl tube with 180°-displaced inlets (S2D), is about 3.57 times higher than the one in a smooth tube with axial flow, and it is slightly lower (by 13%) than that of constant-diameter swirl tube (S2C), while its decrement of pressure drop is notable (by40%) compared with S2C. Axially-displaced multiple inlets can result in a tremendous reduction of pressure drop for swirl tubes by over 90% at the cost of a limited decrease in the Nu number (by ˜10%) compared to the swirl tube S2D.

The CO2-neutral self-supply of heat and electric energy is an important objective for new and existing buildings in the future [1] , [2] . Therefor the energy autonomous house (EAH) as a new concept for single-family buildings in central Europe is presented. It represents a further development of the solar and efficiency house concepts based on full self-sufficiency in thermal (partly provided by a fireplace) and electrical energy (100%). Two occupied houses have been built in Germany and they are under an extensive scientific monitoring with real user behavior since 2014. This contribution is focused on thermal energy balances and the differences due to different user behavior and the influence of weather conditions. The evaluated solar fraction was fsol, th ≥ 71.4% and fsol, el ≥ 91.8% for both houses in 2014. So far the 100% autonomy in electricity could not be reached due to the unusual low irradiation in Jan. and Dec. 2014 (-24% / -37% compared to long term values). Nevertheless the planned low electricity consumption of ∼ 2000 kWh/year could nearly be achieved, whereby a self-consumption rate of electric energy gains of ≥ 31.8% were assumed. Further findings of 1 ½ years of monitoring of the two EAH are presented within the paper.

In the present paper, the dynamic thermo-hydraulic model ISENA is presented which can be applied for answering different questions occurring in design and operation of district cooling networks—e.g. related to economic and energy efficiency. The network model consists of a quasistatic hydraulic model and a transient thermal model based on tracking water segments through the whole network (Lagrangian method). Applying this approach, numerical errors and balance inaccuracies can be avoided which leads to a higher quality of results compared to other network models. Verification and validation calculations are presented in order to show that ISENA provides reliable results and is suitable for practical application.

The first heat-up of furnaces consisting of wet refractory concrete is a challenge due to the pore pressure build-up which can exceed the strength of the concrete. To extend understanding of the complex heat and mass transfer phenomena taking place during the first heat-up, two reproducible heat-up experiments are carried out. These are performed by using a new developed pore pressure sensor. The experiments exhibit an intense change of concrete's thermal conductivity during the process. Further, even in case of one sided heating, two drying fronts are found to occur. In addition to the experimental investigation the first heat-up is simulated using a physical model, based on the coupled balances of energy and the masses of liquid water, water vapour and air as well. By the aid of numerical simulation the first heat-up is further investigated and mass flow behaviour of air, vapour and liquid water is discussed. Within the scope of a sensitivity study the concrete's thermal conductivity and it's permeability are obtained as it's most important material properties and they are used for calibration of the model aiming well representation of the experimental data. The adjusted material properties are found to be in good agreement with refractory concrete properties reported in literature.

The present study investigates the use of sodium waterglass as an environmental friendly foaming agent to create fine porous foam glasses. The reactivity of the foaming agent was determined using thermogravimetrical measurements and difference scanning calorimeter analysis. The porosity of the foam glasses was measured and the pore morphology was evaluated using scanning electron microscopy. Phase formation caused by the addition of waterglass was studied using X-ray diffraction. Furthermore, thermal conductivity and splitting tensile strength of the materials were measured. Foaming by using only waterglass as foaming agent is possible. As a result, fine porous foam glasses with closed pores of 4 nm to 800 µm in diameter and mechanical strengths of 1.7 N/mm 2 could be obtained. Conventional foam glasses which are available on the market have bigger pore sizes up to 3 mm and achieve lower strength. For this reason the produced foam glass can be used as a promising light weight construction material.

Thermal transportation in case of open cell foams is a complex process that comprises of all the modes of heat transfer. In macroscopic numerical models the key parameters that govern these modes of heat transfer are stagnant effective thermal conductivity, k e , dispersion conductivity, k d , effective radiative conductivity, k r and volumetric heat transfer coefficient, h v . The purpose of this study is to determine these key parameters for the forced convection of air through open cell alumina foams. It is achieved by performing two different types of experiments on alumina foams having different PPI number (10, 20 and 30) and porosity (0.79–0.87). The first sets of experiments are based on the transient heat transfer and the aim of performing these experiments is to determine the volumetric heat transfer coefficient, h v . The second sets of experiments are based on the steady state heat transfer and they are the outcome of our previous study. The aim of implementing steady state experiments is to determine dispersion conductivity, k d by supplying the values of h v as an input parameter from the transient analysis. Further, to supply effective thermal conductivity data to both transient and steady state analyses, the Kelvin cell model is implemented. The findings of this study exhibit that the convection heat transfer in case of transient analysis and the thermal dispersion in case of steady state analysis are the dominant modes of heat transfer. Further, this study reveals that by employing the proposed combined analysis, it is possible to predict the values of key parameters rather accurately. But still, the accuracy of the results predicted through the macroscopic models largely depends on the accuracy of the experiments.

A healthy woman with acute onset of pulmonary oedema and severely depressed left ventricular function underwent endomyocardial biopsy under the clinical suspicion of fulminant myocarditis. While awaiting the results of biopsy, the situation deteriorated to Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) and extracorporeal membrane oxygenation was implanted. Finally, immunohistochemistry in biopsy specimen corresponded to fulminant lymphocytic myocarditis, although active myocarditis was excluded. Furthermore, gene expression profiling identified giant cell myocarditis although multinuclear cells were absent. This prompted the start of immunosuppression with cortisone and cyclosporine. The patient fully recovered.

In this investigation dropwise-condensation heat transfer of out of a turbulent flow of humid air is experimentally investigated. The test section consists of a horizontal channel, sized 12 × 32 × 750 mm. The condensation takes placed on a 9 × 6 mm sized section of the vertical channel wall. A model based on the analogy of heat and mass transfer - previously used in the context of filmwise condensation - is adopted in order to describe the data obtained for varying bulk Reynolds numbers (3000–22000), temperatures (36∘C–55∘C) and relative humidities (36%–55%). Modifications are made in order to capture the effect of fog formation within the mixture and the enhancement of the area available for heat transfer induced by the droplets on the substrate. The formulation of the model is intended to be easily adoptable to other geometries, boundary conditions, types and orientations of the substrates. Previous investigations of this group were focused on the thermal resistance of the condensate. Based thereon, the present modelling completes the former approach, resulting in a model capable of predicting the total heat transfer coefficients of dropwise condensation from humid air. The predictions are validated using own experimental data as well as external data.

In this work, experimental and modeling investigations of convective dropwise condensation from moist air are carried out for the mechanistic understanding of the influence of non-condensable gas. For modeling, different droplet growth models in the presence of non-condensable gas are firstly developed by treating the droplet as an isolated form. During dropwise condensation, the presence of non-condensable gas brings some specific condensation characteristics, including the interaction effect between droplets and convection mass transfer. However, those characteristics cannot be reasonably captured by the droplet growth model. In this work, the distributed point sink method and the droplet Sherwood number are used to evaluate the inter-droplet interaction and convection mass transfer, respectively. Combining those progresses, the droplet growth rate is predicted and the prediction is evaluated by the measurements. Based on the accurate prediction for the droplet condensation rate, a semi-analytical modeling method is released to predict convective dropwise condensation of moist air. It considers the latent heat by condensation and the sensible heat by forced convection. Finally, this work presents the direct comparisons of the overall heat flux measured in experiments and the prediction. Furthermore, mechanistic understanding is discussed simultaneously and conclusively. Throughout this work, we highlight the reduction (the diffusion resistance of water vapor and the inter-droplet interaction) and enhancement (convection mass transfer) factors for dropwise condensation in the presence of non-condensable gas. In addition, in the case of this work, large droplets are more beneficial for heat transfer of dropwise condensation.

Fur die Erdwarmegewinnung aus Grubenwasser im oberflachennahen Bereich stellen nicht verschlossene und geflutete Bergwerke (z. B. Erz- und Kohlebergwerke) auch nach ihrer ursprunglichen Nutzung z. T. sehr geeignete Standorte fur eine alternative und regenerative Energieversorgung dar. Geflutete Grubengebaude weisen aufgrund der grosen kunstlich geschaffenen warmeubertragenden Flachen mit hohen Wasserdurchlassigkeiten zwischen Kavernen, Schachten und Stollensystemen sehr grose Warmepotentiale auf. Dieses kann durch unterschiedlichste Nutzungsarten z.B. zur Beheizung und Kuhlung von Gebauden sowie Klimatisierung mit Grubenluft angewendet werden. Die ersten technischen Anwendungen von Grubenwasser im Bergwerk wurden zur Wasserhaltung und ab dem 19. Jahrhundert zur Elektroenergiegewinnung in sogenannten Kavernenkraftwerken realisiert. Getrieben durch steigende Energiepreise begann die thermische Nachnutzung der Wasser aus gefluteten Bergwerken gegen Ende der 1980er Jahre mit dem Einsatz von Warmepumpen zur Anhebung des Temperaturniveaus.

Fur die Nutzung der Oberflachennahen Geothermie als erneuerbare Energiequelle zur Bereitstellung von Heizwarme im Gebaudebereich existiert eine Vielzahl an unterschiedlichen Warmeentzugssystemen. Bei allen Systemen sind die thermophysikalischen als auch die materialspezifischen Parameter (Warmeleitfahigkeit, spezifische Warmekapazitat, Dichte etc.) u. a. des Erdreiches, des Bohrlochs, des Zementes und der Geothermiesonde oder des Kollektors wichtige Einflussgrosen und mussen in der Planung und Auslegung entsprechend berucksichtigt werden. Ein innovatives und zugleich sehr effizientes Prinzip fur den Warmeentzug aus dem Erdreich stellt eine Anwendung der Fallfilmverdampfung in einem geothermischen Thermosiphon (auch Phasenwechselsonde genannt) in Kombination mit einer Warmepumpe dar. Erste Anwendungen von Thermosiphons in oberflachennahen Erdschichten datieren aus der Zeit um 1960, z. B. in Alaska, wobei es sich vorwiegend um die Untergrundstabilisierung in Regionen mit Permafrostboden handelte. Das wohl bekannteste Projekt ist die 1977 fertiggestellte Trans-Alaska-Pipeline, welche auf ca. 730 km mit uber 122.000 Thermosiphons stabilisiert wird. Seit 1997 wird dieses einfache Prinzip auch in Kombination mit Warmepumpen zur Warmeversorgung von Gebauden genutzt. In diesem Beitrag werden hierzu die Funktionsweise und die Betriebsbedingungen von geothermischen Phasenwechselsonden mit den Vor- und Nachteilen gegenuber Flussigkeitszirkulationssonden auf dem neuesten Stand der Forschung sowohl fur Anwender als auch fur Wissenschaftler umfangreich dargelegt. Dabei werden die ablaufenden Prozesse fur verschiedene Betriebsphasen (Start, zyklischer oder dauerhafter Warmeentzug, Regeneration) u. a. hinsichtlich der Filmausbreitung, der Poolaktivitat und einer energetischen Bewertung beschrieben. Abschliesend werden kurz zukunftige Forschungsfelder geothermischer Phasenwechselsonden umrissen sowie relevante Perspektiven und Herausforderungen diskutiert.

Transparent heat insulation materials (TIMs) exhibit great potential for different solar applications. Despite this fact, they are not used widely, since they are either very expensive (aerogel) or made from organic materials and, thus, are not resistant to higher temperatures. Xerogel, obtained from silica gel by drying at ambient pressure, is a promising material for the production of TIMs. This study investigates different treatments applied during the production of silica gel and their influence on its optical and structural properties. To this end, silica sol was gelled and the resulting silica gel was aged before it was either hydrothermally treated or fired. Subsequently, radiation transmission measurements from 400 to 2700 nm as well as porosity, specific surface area, and scanning electron microscopic/transmissions electron microscopic measurements were conducted. It was found that under certain conditions, the transmittance can be improved by firing as well as by hydrothermal treatment. Firing at 600 °C with 10-min dwell time and hydrothermal treatment at 120 °C with 5-h dwell time resulted in the silica gels with the highest transmittance of 63 up to 66 %. The porosity (24–76 %), the pore radii (3–26 nm), and the specific light absorption by embedded water and SiOH molecules could be adjusted over a wide range.

Geothermal thermosyphons utilise the latent heat of a working fluid in order to extract heat from the sub-surface without the requirement of any further mechanical energy. Earlier visual observations showed that the inner pipe area is often not fully wetted by the liquid film. This fact raised the question of the influence on the overall heat transfer of the imperfect wetting in conjunction with the materials of borehole filling (grout) and thermosyphon, and the operational modes. In order to facilitate the discussion, a quasi-three-dimensional model has been developed and solved numerically. The results agree well with experiments and it can be discovered that the choice of the pipe and grout material becomes increasingly important for lower wetting ratios and shorter extraction times. Furthermore, it could be illustrated that a well-wetted polyamide plastic pipe with a thermal conductivity larger than 2 W/(m K) would be a possible alternative to steel pipes.

Thermal diffusivities of pyrochlore and fluorite phases in the Nd2Zr2O7–Y2O3 and Sm2Zr2O7–Y2O3 systems were measured using the laser flash method for the first time. Samples synthesized by co-precipitation were sintered by conventional sintering at 1600 °C or by spark plasma sintering/field assisted sintering technique (SPS). Thermal conductivity was calculated based on thermal diffusivity data, heat capacity data measured by differential scanning calorimetry (DSC) and densities measured using the Archimedes method. Thermal diffusivity and conductivity in the Nd2Zr2O7–Y2O3 system demonstrated similar dependencies on the Y2O3 content as were observed for the La2Zr2O7–Y2O3 system: the highest values were indicated for most ordered Nd2Zr2O4 pyrochlore whereas the lowest were observed for the disordered fluorite structure containing more Y2O3 than pyrochlore. However the thermal diffusivity and conductivity dependencies in the Sm2Zr2O7–Y2O3 were different – the highest values were measured for fluorite phase having higher Y2O3 content.

We propose a lattice Boltzmann approach for simulating contact angle phenomena in multiphase fluid systems. Boundary conditions for partially-wetted walls are introduced using the moment method. The algorithm with our boundary conditions allows for a maximum density ratio of 200000 for neutral wetting. The achievable density ratio decreases as the contact angle departs from 90°, but remains of the order O(102) for all but extreme contact angles. In all simulations an excellent agreement between the simulated and nominal contact angles is observed.

The Effective Thermal Conductivity (ETC) of open-cell porous foams can be predicted from the detailed numerical simulation, considering the complex foam structure obtained from three-dimensional (3D) Computed Tomography (CT)-scan images. An alternative approach could be to consider simplified models for a quick and accurate estimation of the ETC. A model for ETC of open-cell porous foams, using such a simplified approach, has been proposed recently which relies upon a single numerical prediction of the dimensionless ETC under vacuum condition, evaluated using the detailed foam structure obtained from 3D CTscan information. This model is applied in the present study in order to analyze the influence of different parameters, namely the microscopic porosity within the bulk solid material and the direction of heat transfer, on the ETC of open-cell ceramic foams. The present investigation demonstrates that the considered simplified modeling approach offers reasonable accuracy with reduced computational effort for the sensitivity analysis of ETC to different parameters. INTRODUCTION Porous foams are commonly used for a wide range of applications in numerous technological fields due to their special structural and thermo-physical properties. In this respect, the evaluation of their Effective Thermal Conductivity (ETC) has become a major requirement for the accurate prediction of heat transfer behavior of many systems, such as heat exchangers, thermal insulators, combustion systems, evaporators, etc., using homogenization approach [1-3]. The complex morphology of foam structures plays an important role in the overall heat transfer characteristics and hence the ETC can vary substantially among different foams of same material and porosity. Moreover, owing to the very high porosity of foams, total heat transfer can take place by both conduction as well as thermal radiation, particularly when the operating temperature as well as the applied temperature difference are relatively high [4]. The present investigation, however, is restricted only to the conduction heat transfer at room temperature, where the contribution of thermal radiation is seemingly small. The ETC of porous foams can be numerically predicted from simulations of conduction heat transfer through them due to imposed temperature gradient by considering their detailed morphology. The structural information of foams, required by these simulations, nowadays can be obtained from the high resolution 3D CT-scan images. Such detailed approach is generally quite accurate, as well as time consuming. Therefore, in order to achieve a reasonable compromise between the accuracy and the computational effort, an alternative approach is to use simplified models for quick and accurate evaluation of the ETC, ideally presenting a wide range of applicability. A review on models for the ETC, presenting different levels of complexity, has been presented by Coquad et al. [5]. Recently, a model for evaluating the ETC of opencell porous foams, using a simplified approach with one adjustable parameter, has been proposed by Mendes et al. [6]. This, parameter appearing in an explicit expression for the ETC, can be uniquely determined from a single numerical prediction of the dimensionless ETC under vacuum condition (made dimensionless with respect to the thermal conductivity of solid phase), based on the detailed geometry of foam. Quite obviously, evaluation of the dimensionless ETC under vacuum condition requires significantly reduced computational time, which scales at least to the order of porosity of foams and owing to the definition, the result is independent of the thermal conductivity of solid phase. Most importantly, as has been demonstrated by Mendes et al. [6], the dimensionless ETC under vacuum condition implicitly contains the relevant quantitative morphological