Pure Condensation Research Articles

THE CONDENSATION OF WATER VAPOUR IN A MIXTURE CONTAINING A HIGH CONCENTRATION OF NON-CONDENSABLE GAS IN A VERTICAL TUBE

This paper deals with the condensation of water vapour possessing a content of noncondensable gas in vertical tubes. The condensation of pure steam on a vertical surface is introduced by the Nusselt condensation model. However, the condensation of water vapour in a mixture with non-condensable gas differs from pure vapour condensation and is a much more complex process. The differences for the condensation of water vapour in a mixture containing a high concentration were theoretically analysed and evaluated. In order to investigate these effects, an experimental stand was built. Experiments were carried out in regards to the case of pure steam condensation and the condensation of water vapour with a non-condensable gas mixture to evaluate the influence of the variable non-condensable gas content during the process. A non-condensable gas in a mixture with steam decreases the intensity of the condensation and the condensation heat transfer coefficient. A gradual reduction of the volume and partial pressure of steam in the mixture causes a decrease in the condensation temperature of steam, and the temperature difference between steam and cooling water. The increasing non-condensable gas concentration restrains the transportation of steam towards the tube wall and this has a significant effect on the decrease in the condensation rate.

Key Atmospheric Signatures for Identifying the Source Reservoirs of Volatiles in Uranus and Neptune

We investigate the enrichment patterns of several delivery scenarios of the volatiles to the atmospheres of ice giants, having in mind that the only well constrained determination made remotely, i.e. the carbon abundance measurement, suggests that their envelopes possess highly supersolar metallicities, i.e. close to two orders of magnitude above that of the protosolar nebula. In the framework of the core accretion model, only the delivery of volatiles in solid forms (amorphous ice, clathrates, pure condensates) to these planets can account for the apparent supersolar metallicity of their envelopes. In contrast, because of the inward drift of icy particles through various snowlines, all mechanisms invoking the delivery of volatiles in vapor forms predict subsolar abundances in the envelopes of Uranus and Neptune. Alternatively, even if the disk instability mechanism remains questionable in our solar system, it might be consistent with the supersolar metallicities observed in Uranus and Neptune, assuming the two planets suffered subsequent erosion of their H-He envelopes. The enrichment patterns derived for each delivery scenario considered should be useful to interpret future in situ measurements by atmospheric entry probes.

Effect of Surface Inclination on Filmwise Condensation Heat Transfer During Flow of Steam–Air Mixtures

Abstract Empirical/semi-empirical correlations are available in the literature to quantify the effect of several major parameters, like bulk pressure, non-condensable gas mass fraction, and wall subcooling, on condensation heat transfer coefficient (HTC). However, despite numerous applications of condensation on inclined flat plates, there is a lack of understanding of the effect of surface inclination on condensation heat transfer. Accordingly, a dedicated experimental program was undertaken to investigate the effect of surface inclination angle on filmwise steam condensation. Experiments were performed at different bulk pressures (1.7–4.2 bar absolute) and steam-air mass fractions (ranging from pure steam, i.e., 0% to 40% w/w air), with the steam-air mixture flowing over a flat test plate (Re range, 4200–4800). In each run, the inclination angle of the test surface was varied from −90 deg (condensation underneath the horizontal surface, facing downward) to +90 deg (condensation over the horizontal surface, facing upward) in increments of 15–20 deg (inclination angle θ measured from vertical). The results reveal an intriguing trend: for pure steam condensation, the HTCs decrease as the plate is inclined in either direction from the vertical, and the variation is nearly symmetric for both upward- and downward-facing configurations. On the other hand, for steam condensation in the presence of air, the HTCs decrease monotonically for upward-facing configurations, while they increase slightly (10–20%), and decrease subsequently (for θ < −70 deg) for downward-facing cases. Finally, the HTCs for inclined orientations are compared with the HTC in the standard vertical configuration to quantify the effect of inclination angle.

Experimental Study of Lubricating Oil Effect on R600a Condensation inside Micro-Fin Tubes

In this study, the effect of lubricating oil on the heat transfer characteristics of R600a condensing flow inside a horizontal micro-fin tube is experimentally investigated. The results are presented in three parts, including the characteristics of pure R600a condensation inside a smooth tube, the impact of using a micro-fin tube, and the effect of adding lubricating oil on the condensing heat transfer inside a micro-fin tube. The test condensers are smooth and micro-fin copper tubes of 14.18 mm inner diameter which are installed in a 6 cm polyethylene pipe to form double-pipe heat exchangers. The test conditions include mass velocity of 54 to 90 kg/m2s and vapor quality of 0.03 to 0.78, while condensation pressure is between 550 to 700 kPa. The results show that in the case of pure R600a, using the micro-fin tube may enhance the local heat transfer coefficients up to 79%. In addition, for the refrigerant-oil mixture condensing flow, by increasing the vapor quality, the heat transfer coefficient increases up to a critical value after that it starts to decrease due to the effect of oil on the condensation liquid film.

Monitoring of Ammonia in Biogas

AbstractAmmonia content is an important factor, which has to be considered when optimizing the processes in a biogas plant. A measurement system for a continuous monitoring of ammonia has been constructed, which can be placed in the gas room above the digester. The monitoring is based on the measurement of the electrical impedance. In this system, a condensate is generated on the surface of an interdigital electrode so that the whole stray field is covered by the condensate. For determining the ammonia content, impedance spectroscopy of these drops is performed. The ammonia of the biogas causes a decrease in the impedance in comparison to a pure aqueous condensate. A first evaluation of this measurement system using artificial slurries has been performed.

Cold dilute nuclear matter with α -particle condensation in a generalized nonlinear relativistic mean-field model

We explore the thermodynamic properties of homogeneous cold (zero-temperature) nuclear matter including nucleons and $\alpha$-particle condensation at low densities by using a generalized nonlinear relativistic mean-field (gNL-RMF) model. In the gNL-RMF model, the $\alpha$-particle is included as explicit degree of freedom and treated as point-like particle with its interaction described by meson exchanges and the in-medium effects on the $\alpha$ binding energy is described by density- and temperature-dependent energy shift with the parameters obtained by fitting the experimental Mott density. We find that below the dropping density $n_{\rm{drop}}$ ($\sim 3\times 10^{-3}$ fm$^{-3}$), the zero-temperature symmetric nuclear matter is in the state of pure Bose-Einstein condensate (BEC) of $\alpha$ particles while the neutron-rich nuclear matter is composed of $\alpha$-BEC and neutrons. Above the $n_{\rm{drop}}$, the fraction of $\alpha$-BEC decreases with density and vanishes at the transition density $n_t$ ($\sim 8\times 10^{-3}$ fm$^{-3}$). Above the $n_t$, the nuclear matter becomes pure nucleonic matter. Our results indicate that the empirical parabolic law for the isospin asymmetry dependence of nuclear matter equation of state is heavily violated by the $\alpha$-particle condensation in the zero-temperature dilute nuclear matter, making the conventional definition of the symmetry energy meaningless. We investigate the symmetry energy defined under parabolic approximation for the zero-temperature dilute nuclear matter with $\alpha$-particle condensation, and find it is significantly enhanced compared to the case without clusters and becomes saturated at about $7$ MeV at very low densities ($\lesssim 10^{-3}$ fm$^{-3}$). The critical temperature for $\alpha$-condensation in homogeneous dilute nuclear matter is also discussed.

Visualization experiment and numerical simulation of nitrogen-neon mixture condensation

The condensation at cryogenic temperatures is rich in physics and challenging to explore, in particular for mixtures. The flow pattern evolution of liquid film for both pure nitrogen and nitrogen-neon mixture condensation is visualized. An improved mass transfer model is proposed to simulate the mixture condensation process, and the diffusion coefficient of nitrogen-neon mixed vapor and saturation temperature of nitrogen are modified. The new model agrees well with the experimental data. The complete transition process of three typical flow patterns, namely, laminar flow, two-dimensional wave flow and three-dimensional wave flow, is observed for the pure nitrogen condensation, while the Reynold number of liquid film decreases greatly during the condensation of nitrogen-neon mixture at the same condensation heat, and the fluctuation effect of interfacial waves shows attenuation. The simulation illustrates that the neon has an accumulation effect near the wall and greatly reduces the mass transfer rate of nitrogen vapor. Besides, it indicates that liquid film is the main thermal resistance for pure condensation, while the non-condensable gas layer at gas-liquid interface becomes a crucial factor affecting the mass transfer performance for mixture condensation. The mechanism of mixture condensation process is revealed through liquid film flow pattern analysis and CFD simulation results.

Impact of non-uniform wettability in the condensation and condensation-liquid water intrusion regimes in the cathode gas diffusion layer of proton exchange membrane fuel cell

The impact of variations in the wettability properties of the gas diffusion layer substrate on the liquid water distribution and the reactant gas access is studied from pore network simulations considering two main cases: a degradation case where the fraction of hydrophilic pores increases and a case where the spatial distribution of the hydrophobic agent is non-uniform with hydrophobic surfaces and a central region of mixed wettability. Contrary to previous works, this impact is assessed for various regimes of liquid water occurrence. The latter notably include the condensation regime and the mixed regime where the occurrence of liquid water in the gas diffusion layer results from both condensation under the rib and the ingress of liquid water from the catalyst layer or the microporous layer. The study shows that the wettability variation impact is highly dependent on the regime, i.e. on the operating conditions. Whereas this impact is minor when the conditions correspond to the occurrence of the pure condensation regime where the liquid water is confined in the region below the rib, it can be quite significant in the mixed regime when the conditions are such that liquid water is present also in the region below the channel.

Ground state of weakly repulsive soft-core bosons on a sphere

We study a system of penetrable bosons embedded in a spherical surface. Under the assumption of weak interaction between the particles, the ground state of the system is, to a good approximation, a pure condensate. We employ thermodynamic arguments to investigate, within a variational ansatz for the single-particle state, the crossover between distinct finite-size "phases" in the parameter space spanned by the sphere radius and the chemical potential. In particular, for radii up to a few interaction ranges we examine the stability of the fluid phase with respect to a number of crystal-like arrangements having the symmetry of a regular or semi-regular polyhedron. We find that, while quantum fluctuations keep the system fluid at low density, upon compression it eventually becomes inhomogeneous, i.e., particles gather together in clusters. As the radius increases, the nature of the high-density aggregate varies and we observe a sequence of transitions between different cluster phases ("solids"), whose underlying rationale is to maximize the coordination number of clusters, while ensuring at the same time the proper distance between each neighboring pair. We argue that, at least within our mean-field description, every cluster phase is supersolid.

Effects of stagnant air on condensation heat transfer over a horizontal tube

The effects of stagnant air on the condensation heat transfer of vapor over a horizontal tube were investigated by experiments. The condensation wall temperatures along the circumference and the cooling water temperature were measured at various cooling water and vapor mass fluxes as well as vapor pressures. The heat transfer coefficients and Nusselt number were calculated, and the effects of stagnant air on several parameters, including the wall temperature of the condensation tube, Nusselt number, heat transfer coefficient, and flow pattern transition point of liquid film, were analyzed. Results showed that stagnant air was a main factor that affected the heat and mass transfer uniformity of vapor. Unlike in pure vapor condensation, the temperature difference between the top and bottom parts of the condensation tube increased when the mole fraction of stagnant air was less than 0.17, whereas it decreased when the mole fraction of stagnant air was larger than 0.47. The increment in the mole fraction of stagnant air reduced the temperature difference along the circumference of the condensation tube wall. As the mole fraction of stagnant air increased, the heat transfer coefficient and Nusselt number decreased. However, Nusselt number was insensitive to the effect of air when the mole fraction of stagnant air was larger than 0.25. As the circumferential angle of horizontal condensation tube increased from 0° to 180°, the Reynolds number of liquid film transformed from the laminar state to the turbulence state and then changed into the laminar state. Reynolds number reached a maximum value within the circumferential angles of 45°–90°. As the circumferential angle changed from 90° to 180°, a large amount of condensate fell, and the liquid film attached to the condensation tube wall became thinner, which resulted in an intensive reduction in the Reynolds number of the liquid film. As the mole fraction of stagnant air increased, a transition point of liquid film moved to a larger circumferential angle, which delayed the transition of liquid film from laminar flow to turbulence. The present experimental results were compared with the data from Sherkriladze and Gomelauri (1966), Rose (1984), Fujii et al. (1972), and Nusselt (1916).

Rapid production of large Li7 Bose-Einstein condensates using D1 gray molasses

We demonstrate the production of large $^7$Li Bose-Einstein condensates in an optical dipole trap using $D_1$ gray molasses. The sub-Doppler cooling technique reduces the temperature of $4\times10^9$ atoms to $25~\mu{}$K in 3~ms. After microwave evaporation cooling in a magnetic quadrupole trap, we transfer the atoms to a crossed optical dipole trap, where we employ a magnetic Feshbach resonance on the $|F=1,m_F=1\rangle$ state. Fast evaporation cooling is achieved by tilting the optical potential using a magnetic field gradient on the top of the Feshbach field. Our setup produces pure condensates with $2.7\times10^6$ atoms in the optical potential for every 11~s. The trap tilt evaporation allows rapid thermal quench, and spontaneous vortices are observed in the condensates as a result of the Kibble-Zurek mechanism.

CFD model and simulation of pure substance condensation on horizontal tubes using the volume of fluid method

Surface structured tubes show a significant increase in efficiency of condensers, which can decrease the power consumption and CO2 emission of chemical plants. However, no generalized condensation model for surface structured tubes is developed so far, due to their complex structure. In future works, we aim to use computational fluid dynamics for the investigation of surface structured tubes. Therefore, in this study, we introduce a pure substance condensation model without heuristic or empirical parameters, by means of a new iteration scheme. We show the validation of the newly developed model using the Stefan problem and different simulation approaches for pure substance condensation on a horizontal smooth tube, which are compared to Nusselt’s film theory and measurements. The developed model shows a very good simulation stability, even for high temperature gradients. The simulation results of the Stefan problem stand in excellent agreement with the analytic solution. The horizontal smooth tube simulation results give slightly lower heat transfer coefficients compared to Nusselt’s film theory, but are in very good agreement to experimental data.

Numerical study of condensation flow regimes in presence of non-condensable gas in minichannels

A numerical research on flow regime of R134a in horizontal minichannels was conducted. The model was on the basis of the volume of fluid approach, and inserted user-defined routines which cover condensation mass and heat transfer. The observed annular flow, injection flow and intermittent flow of pure steam condensation, and annular (annular-wavy) flow, injection flow, annular-intermittent flow and intermittent flow of gas mixture condensation were qualitatively compared against experimental data. Flow patterns of lower non-condensable gas mole concentration show similar with that of pure steam, while the fluctuation of gas-liquid interface in annular flow and the noticeable annular-intermittent flow of higher non-condensable gas mole concentration were noted. Besides, injection flow characters with larger head volume and longer neck, and intermittent flow characters with larger slug sizes in existence of non-condensable gas were found. Furthermore, the influence of mole concentration of non-condensable gas and operating conditions on flow pattern transition lines were analyzed after validating the flow pattern transition. The results showed that the injection flow transition point has a relative fixed point at pure vapor condensation, while various in presence of NCG. Besides, lower non-condensable gas mole concentration, smaller inlet gas mass flux and larger wall heat flux could lead to earlier flow pattern regime.

Condensation heat transfer enhancement using steam-ethanol mixtures on horizontal finned tube

Condensation of steam-ethanol mixtures was investigated experimentally on instrumented, finned copper tube. The tube had length 70 mm, fin root diameter 12.7 mm. Height, thickness and inter-fin space was of rectangular fins was 1.6 mm, 0.5 mm and 0.6 mm. Concentration of ethanol by mass in the boiler when cold prior to the start-up were 0.025, 0.05, 0.1, 0.5 and 1.0%. Experiments were conducted over a range of vapor-to-surface temperature difference at three pressures of 14 kPa, 55 kPa and atmospheric. Maximum upstream vapor velocity on condensing finned test tube at atmospheric pressure and 14 kPa was 7.5 and 15.0 m/s respectively. Heat transfer enhancement as compared to pure steam of around 3 times was obtained over a range of vapor to surface temperature difference. Results have been compared with the available data for pure steam condensation on finned tube and steam-ethanol condensation on the smooth tube under same conditions of pressure, vapor velocity and vapor to surface temperature difference. Photographs showing increase of retention angle due to ethanol are included in the paper.

Analysis of the impact of different scenarios on the simulation results of unauthorized dilution of boric acid in the coolant of the primary circuit of the NPP-2006

Abstract Unauthorized dilution of boric acid in the reactor coolant due to improper operation of the chemical and volume control system (KBA) is a project mode with the violation of normal operation. The operator is obliged to identify unauthorized dilution within half an hour and stop feeding with pure condensate. The power unit has automation, which stops feeding on EP (emergency protection) and ATWS (Anticipated transient without scram) signals. The situation without the intervention of the operator and the failure of automation to stop dilution can be considered as a beyond design basis accident. The article presents an analysis of unauthorized boric acid dilution process in the primary circuit coolant of the NPP-2006 power unit up to the controlled state, either considering the operator's intervention after a 30-minute period of process, i. e. with a forced cessation of dilution, or without the operator's intervention until the tanks with pure condensate are completely emptied.

Noble Gas Abundance Ratios Indicate the Agglomeration of 67P/Churyumov–Gerasimenko from Warmed-up Ice

Abstract The origin of cometary volatiles remains a major open question in planetary science. Comets may have either agglomerated from crystalline ices condensed in the protosolar nebula (PSN) or from amorphous ice originating from the molecular cloud and interstellar medium. Here, based on the recent argon, krypton, and xenon measurements performed by the ROSINA mass spectrometer on board the European Space Agency’s Rosetta spacecraft in the coma of 67P/Churyumov–Gerasimenko, we show that these noble gas relative abundances can be explained if the comet’s building blocks formed from a mixture of gas and H2O grains resulting from the annealing of pristine amorphous ice (i.e., originating from the presolar cloud) in the PSN. In this scenario, the different volatiles released during the amorphous-to-crystalline ice phase transition would have been subsequently trapped at lower temperatures in stoichiometric hydrate or clathrate hydrate forms by the crystalline water ice generated by the transition. Once crystalline water was completely consumed by clathration in the ∼25–80 K temperature range, the volatile species remaining in the gas phase would have formed pure condensates at lower temperatures. The formation of clathrates hydrates and pure condensates to explain the noble gas relative abundances is consistent with a proposed interstellar origin of molecular oxygen detected in 67P/Churyumov–Gerasimenko, and with the measured molecular nitrogen depletion in comets.

Research on film condensation heat transfer of the shell side of the spiral coil heat exchanger

The theoretical basis for the calculation of shell side condensation of the spiral coil heat exchanger is weak. In order to solve the problem of pure steam film condensation heat transfer of the shell side of the spiral coil heat exchanger, the theoretical model of the homogeneous flow was established. Considering the centrifugal force, two different mathematical models were established and the heat transfer characteristics were studied. The solution formula of the heat transfer coefficient and thickness of first layer liquid film, meanwhile, was obtained. The theoretical formula of the membrane-like condensation heat transfer of the heat exchanger was worked out, based on the calculation model of the heat transfer coefficient of one-component working fluid outside the tube bundle, considering the effect of tube bundle. The two calculated results in this paper and the theoretical result of Bays and McAdams were compared with experimental values respectively. The results show that the relative error between the calculated values obtained by the two theoretical models and experimental values is 7.48% (ignoring centrifugal force), 3.05% (considering centrifugal force), while the relative error between Bays and McAdams’s result and the experimental value is 61.3%. The correctness of the theoretical models proposed in this paper are verified. The theoretical models can be used to calculate the film condensation heat transfer of the spiral coil heat exchanger.

Nano-structured aluminum surfaces for dropwise condensation

Superhydrophobic surfaces represent a promising strategy to consistently promote dropwise condensation, which can lead to an important increase of the heat transfer coefficient as compared to filmwise condensation. To get superhydrophobicity, it is necessary to reduce the surface energy and to modify the surface structure by achieving superficial micro-roughness.In this work, aluminum surfaces were modified via chemical methods to promote dropwise condensation due to superhydrophobic behavior. The metal substrates were etched using three different strategies to impart nanoscale roughness; a fluorosilane film was subsequently deposited over them to decrease the surface energy in two different modes (spin coating and immersion). In the end, four different surfaces were investigated. Experimental tests of pure steam condensation on the resulting substrates showed that dropwise condensation was successfully achieved on the superhydrophobic surfaces, measuring heat transfer coefficients as high as 100 kW m−2 K−1. Although the dropwise condensation moves soon to hybrid and filmwise condensation, the performance during pure dropwise condensation appears to be clearly linked to the different chemical procedures used in the sample preparation.

Pore-scale analysis of steam-solvent coinjection: azeotropic temperature, dilution and asphaltene deposition

Steam assisted gravity drainage is the main technologically and economically feasible method for in situ bitumen extraction. However, SAGD is energy intensive with economic and environmental challenges. Steam-solvent coinjection has proposed to improve SAGD performance, where hydrocarbon solvent is simultaneously injected with steam to increase the production rate and lower the steam-oil-ratio. The addition of solvent, however, complicates an already complex multicomponent thermal-chemical process. Microfluidics is well suited to quantify the pore-scale of steam-solvent coinjection with a tight control over experimental parameters. In this study, a high-pressure high-temperature micromodel combined with optical and thermal imaging is used to probe the pore-scale of steam-solvent coinjection process at relevant reservoir conditions. The effects of butane and hexane, as well as two industrial solvents, condensate and naphtha, on the pore-scale mechanisms are quantified and compared. The in situ thermal data is used to profile and analyze the condensation zone behavior and steam-solvent azeotropic temperature for all steam-solvent cases. We find that overall performance depends on the difference between steam-solvent azeotropic temperature and steam saturation temperature, the degree of solvent-bitumen dilution, and the degree of asphaltene precipitation in the condensing zone. In contrast with pure solvents and condensate, naphtha results in the highest recovery due to a higher steam-solvent azeotropic temperature, effective dilution, with minimal asphaltene deposition.

Effect of flow velocity on the process of air-steam condensation in a vertical tube condenser

This article describes the influence of flow velocity on the condensation process in a vertical tube. For the case of condensation in a vertical tube condenser, both the pure steam condensation process and the air-steam mixture condensation process were theoretically and experimentally analyzed. The influence of steam flow velocity on the value of the heat transfer coefficient during the condensation process was evaluated. For the condensation of pure steam, the influence of flow velocity on the value of the heat transfer coefficient begins to be seen at higher speeds, conversely, this effect is negligible at low values of steam velocity. On the other hand, for the air-steam mixture condensation, the influence of flow velocity must always be taken into account. The flow velocity affects the water vapor diffusion process through non-condensing air. The presence of air significantly reduces the value of the heat transfer coefficient. This drop in the heat transfer coefficient is significant at low velocities; on the contrary, the decrease is relatively small at high values of the velocity.