Condensation Regime Research Articles

Experimental investigation on pressure oscillation induced by steam injection into subcooled water through an opposite nozzle

The pressure oscillation characteristics induced by steam jet condensation through an opposite nozzle were experimentally studied. Four condensation regimes, namely Chugging-I (Chug-I), Chugging-II (Chug-II), Condensation Oscillation-I (CO-I), and Condensation Oscillation-II (CO-II), were identified based on interfacial behaviors and corresponding pressure signals in the pipe and the water tank. In the Chug-I and Chug-II regimes, the probability density function (PDF) of the pressure signals in the pipe was highly asymmetric, while the PDF in the water tank was sharp unimodal distribution. The PDF in the CO-I regime was sharp unimodal distribution, symmetrical to 0 kPa. The PDF in the CO-II regime was asymmetrical dumpy distribution. In addition, the variations of pressure oscillation intensity in the pipe and the water tank were investigated. Finally, a modified correlation was proposed for predicting the dominant frequency of pressure oscillation, with the maximum deviation of ± 10 %.

Influence of heat transfer and wetting angle on condensable fluid flow through nanoporous anodic alumina membranes.

The flow of isobutane and of freon 142b (1-chloro-1,1-difluoro-ethane) through anodic alumina membranes with pore diameters between 18 and 60 nm in a capillary condensation regime is experimentally and theoretically explored. The capillary condensation effect increases the membrane permeance for condensable gases from 25 to 150 m3(STP) m-2 bar-1 h-1 at certain conditions. To describe the experimental results, a model is suggested accounting for heat transfer from the condensing to the evaporating meniscus, different boundary conditions for the heat transfer between the environment and the membrane, and wettability of the pore wall. The proposed model indicates a large influence of heat supply from the environment to the membrane on the permeance in the capillary condensation regime and a moderate influence of condensate contact angle in the range of 0-60°. Measuring the temperature of the permeate side of the membrane allows to find a suitable boundary condition to describe heat transfer. The obtained boundary condition yields an excellent fit of experimental results of condensate flow through membranes with different pore diameters for the two utilized fluids. Also, confocal Raman spectroscopy gave evidence on the fraction of pores filled with condensate.

Numerical simulation of the condensation of R-113 in an inclined tube using the VOF method

This paper presents the results of the numerical simulation of R-113 condensation in an inclined 32 mm inner diameter tube 4 m long, using the VOF method. The dimensions of the tube correspond to the dimensions of the test section in the CJSC NPVP «Turbokon» test facility, where a series of experimental studies are to be carried out. The R-113 condensation regime is examined at a pressure of 0.33 MPa, a total mass flowrate of 180 kg/(m2s), and a tube inclination angle of 20°. Data are presented on the distribution of local heat transfer characteristics along the length and over the inner surface of the channel.

Condensation regimes inside a vapor chamber with transparent hollow fins of circular, triangular or fluted cross section

A vapor chamber with integrated hollow fins was manufactured and tested, with the aim of identifying the optimal fin geometry to prevent liquid hold-up and flooding at the condenser. In particular, the influence of the transverse cross section was experimentally investigated. Circular, triangular and fluted cross sections were compared, with inscribed diameters ranging from 1.3 to 2.6 mm. The air-cooled fins were made of polymer in order to visualize the condensation regimes. When operating with HFE-7100, three regimes were identified with increasing heat load (up to 95 W): filmwise condensation, plug condensation and flooding, which significantly deteriorates the heat transfer performance. The triangular cross section is the most interesting shape among those tested because flooding occurs at higher heat load and/or smaller diameter than in other shapes thanks to drainage into the corners. Circular fins have the worst performance and fluted ones are in-between. The critical diameter below which flooding occurs even at low heat load is around 2.0 mm for a triangular section and 2.5 mm for a circular one. Consequently, with an optimum fin placement, the total convective surface area at the condenser could be increased by about 15% when using triangles instead of circles.

Route toward classical frustration and band flattening via optical lattice distortion

We propose and experimentally explore a method for realizing frustrated lattice models using a Bose-Einstein condensate held in an optical square lattice. A small lattice distortion opens up an energy gap such the lowest band splits into two. Along the edge of the first Brillouin zone for both bands a nearly flat energy-momentum dispersion is realized. For the excited band a highly degenerate energy minimum arises. By loading ultracold atoms into the excited band, a classically frustrated $XY$ model is formed, describing rotors on a square lattice with competing nearest and next nearest tunnelling couplings. Our experimental optical lattice provides a regime, where a fully coherent Bose-Einstein condensate is observed, and a regime where frustration is expected. If we adiabatically tune from the condensate regime to the regime of frustration, the momentum spectra shows a complete loss of coherence. Upon slowly tuning back to the condensate regime, coherence is largely restored. Good agreement with model calculations is obtained.

Temperature-Dependent Decay of Quasi-Two-Dimensional Vortices across the BCS-BEC Crossover.

We systematically study the decay of quasi-two-dimensional vortices in an oblate strongly interacting Fermi gas over a wide interaction range and observe that, as the system temperature is lowered, the vortex lifetime increases in the Bose-Einstein condensate (BEC) regime but decreases at unitarity and in the Bardeen-Cooper-Schrieffer (BCS) regime. The observations can be qualitatively captured by a phenomenological model simply involving diffusion and two-body collisional loss, in which the vortex lifetime is mostly determined by the slower process of the two. In particular, the counterintuitive vortex decay in the BCS regime can be interpreted by considering the competition between the temperature dependence of the vortex annihilation rate and that of unpaired fermions. Our results suggest a competing mechanism for the complex vortex decay dynamics in the BCS-BEC crossover for the fermionic superfluids.

Lieb–Robinson bounds and growth of correlations in Bose mixtures

For a mixture of interacting Bose gases initially prepared in a regime of condensation (uncorrelation), it is proved that in the course of the time evolution observables of disjoint sets of particles of each species have correlation functions that remain asymptotically small in the total number of particles and display a controlled growth in time. This is obtained by means of ad hoc estimates of Lieb–Robinson type on the propagation of the interaction, established here for the multi-component Bose mixture.

Optomechanical response of a strongly interacting Fermi gas

We study a Fermi gas with strong, tunable interactions dispersively coupled to a high-finesse cavity. Upon probing the system along the cavity axis, we observe a strong optomechanical Kerr nonlinearity originating from the density response of the gas to the intracavity field and measure it as a function of interaction strength. We find that the zero-frequency density response function of the Fermi gas increases by a factor of two from the Bardeen-Cooper-Schrieffer to the Bose-Einstein condensate regime. The results are in quantitative agreement with a theory based on operator-product expansion, expressing the density response in terms of universal functions of the interactions, the contact and the internal energy of the gas. This provides an example of a driven-dissipative, strongly correlated system with a strong nonlinear response, opening up perspectives for the sensing of weak perturbations or inducing long-range interactions in Fermi gases.

Condensation of subsonic and supersonic gas flows on a flat surface

Intense heat-mass transfer in a gas flow to a condensation surface is studied with the consistent atomistic and kinetic theory methods. The simple moment method is utilized for solving the Boltzmann kinetic equation (BKE) for the nonequilibrium gas flow and its condensation on the surface, while molecular dynamics (MD) simulation of a similar flow is used for verification of BKE results and boundary conditions applied at the surface. We demonstrate that BKE can provide the flow profiles close to those obtained from MD simulations in both subsonic and supersonic regimes of steady gas flows. In particular MD confirms that the surface at a particular temperature condenses completely a steady supersonic flow with a shock front standing in reference to this surface. Hence it can be interpreted as a permeable condensating piston, which compresses and absorbs completely the incoming gas in contrast to a common nonabsorbing impermeable piston. The shock front divides the vapor flow on the supersonic and subsonic zones, and condensation of shocked gas happens in a subsonic regime. Conditions required for the complete, partial, and ceased condensation regimes are determined. It is shown that a runaway shock front can stop an inflow gas and condensation is ceased if the surface temperature is above some critical threshold determined by a saturation line of gas and its shock Hugoniot. We also demonstrate that the elementary theory of condensation has a good accuracy in a surprisingly wide range of flow parameters.

Conversion of combined heat and power coal-fired plants to Carnot batteries - Prospective sites for early grid-scale applications

Repurposing fossil fuel-fired plants to electricity storage systems known as Carnot batteries (CB) has been proposed before. This technology provides a prospect of high-power, high-capacity systems for medium and long duration storage. Significant benefits on capital cost from second use of the existing infrastructure and low cost per added MWh are expected to outweigh low round-trip efficiency. Retrofitting large coal plants is still demanding in terms of absolute capital, lack of previous experience and uncertain business. This work proposes smaller coal-fired combined heat and power plants with 50 MWe output as a suitable prospective site for conversion to CB instead of large power plants. Higher overall efficiency with heat providing an additional stream of revenue, plant flexibility, or smaller system size make such application more beneficial, especially for first-of-a-kind installations.Therefore, this paper illustratively investigates the techno-economic prospects of the conversion of a cogeneration coal plant to a CB. The proposed system is described. It is based on direct electrical heating for the power to heat process, thermal energy storage based on either molten salts or gravel packed bed and finally, heat exchangers integrated to operate as steam generators. The sizing of major components is followed by costing. In case of a backpressure turbine, packed bed storage and discharge duration of 5 h the specific cost of electrical storage system is around 200 €/kWhe, while in the case with no heat production and condensing turbine (full condensation regime), it is around 100 €/kWhe. The operation regimes and expected revenue streams from both electricity and heat are evaluated. A comparison with existing technologies is performed and the levelised cost of storage in presented cases varies from 35 to 179 €/MWhe for the fully condensing regime and 35 to 291 €/MWhe for the backpressure cogeneration regime.

Numerical investigation of phase change heat transfer in a confined micro-space by lattice Boltzmann method

Phase-change heat transfer has attracted wide attention in thermal management of electronic infrastructures, such as the data center and 5G base station antenna. It possesses the characteristics of high equivalent thermal conductivity, rapid heat diffusion and good temperature uniformity. However, the existing thermal solution to advanced high-performance devices becomes more challenging with high heat flux and small heat dissipation area. Current surface modification technology has been applied for enhancing phase-change means in energy-related fields. In this paper, the hybrid lattice Boltzmann (LB) method was utilized to explore vapor-liquid phase-change mechanism and its enhancement in a confined micro-space. Different modified surfaces’ effects on bubble growth behavior and interfacial phase-change heat transfer were respectively discussed. Based on the pseudopotential LB approach and energy equation, the boiling and condensation regimes were quantitatively evaluated with the heat transfer coefficient and transient heat flux. The numerical results indicated that the wettability possessed significant impacts on the primary characteristics of phase-change heat transfer. It was found that hydrophilic contact angle promoted the initial boiling, while hydrophobic one helped to facilitate drop-wise condensation. The hybrid surfaces possess the best performance for the boiling heat transfer enhancement. Both the modified hybrid and wettability gradient surfaces have positive contributions to the condensation heat transfer enhancement. This study is expected to provide a reference for improving phase-change heat transfer technology for sustainable energy applications.

Experimental investigations of water droplet transient phase changes in flue gas flow in the range of temperatures characteristic of condensing economizer technologies

The heating and phase changes of water droplets in 140 °C air flow humidified up to water vapor volumetric fraction of 0.3 were investigated experimentally in the context of heat recovery from flue gases with condensing economizers. The experiments were performed in experimental set-up, where atmospheric air of certain temperature and humidity passed over a water droplet suspended on thermocouple ball. It was demonstrated that initial temperature of droplet and humidity of gas flow are defining factors in transitional phase changes. However, initial droplet temperature had no effect on the equilibrium evaporation regime. The experiments performed confirmed that humidification of atmospheric air flow causes changes in magnitude of heating and phase change process of water droplets suspended in the air flow. These changes translate into increased temperature of equilibrium evaporation of the droplet, formation of favorable conditions for the condensation regime, and a change in dynamics of the droplet's geometrical parameters in initial stage of phase changes. In additionally humidified air flow, the droplet volume increased by three percent, and evaporation temperature of the droplet increased by 17 °C. Practical recommendations for water injection were produced to ensure optimal heat recovery from wet exhaust gases in a condensing economizer.

Influence of surface wettability on the transient characteristics of vapor condensation from humid air

ABSTRACT The initial transient behavior of condensation of water vapor from humid air plays vital roles in a large variety of engineering applications. Although such influences on the steady-state attributes of dropwise and filmwise condensations have been widely investigated in the literature, description of their initial transient behaviors is rather limited. Herein we have characterized the initial transient regimes of condensation from humid air under varying NCG fractions on condenser plates of four different wettability. Results of the experiments provide the droplet size distribution on the condensing surface, condensate collection rate, and transient life of condensation for selected parametric conditions.

Superfluid transition temperature and fluctuation theory of spin-orbit- and Rabi-coupled fermions with tunable interactions

We obtain the superfluid transition temperature of equal Rashba-Dresselhaus spin-orbit- and Rabi-coupled Fermi superfluids, from the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) regimes in three dimensions for tunable $s$-wave interactions. In the presence of Rabi coupling, we find that spin-orbit coupling enhances (reduces) the critical temperature in the BEC (BCS) limit. For fixed interactions, we show that spin-orbit coupling can convert a first-order (discontinuous) phase transition into a second-order (continuous) phase transition, as a function of Rabi coupling. We derive the Ginzburg-Landau free energy to sixth power in the superfluid order parameter to describe both continuous and discontinuous phase transitions as a function of spin-orbit and Rabi couplings. Lastly, we develop a time-dependent Ginzburg-Landau fluctuation theory for an arbitrary mixture of Rashba and Dresselhaus spin-orbit couplings at any interaction strength.

Comprehensive correlation for the prediction of the heat transfer through a single droplet in dropwise condensation regime

Numerical simulations have been performed to determine the conduction heat transfer in a sessile droplet for a large range of dynamic contact angle θ and Biot number B i . The substrate is set at a constant and uniform temperature, while a convective heat transfer is set at the liquid–vapor interface. In such a configuration, the heat flux is concentrated in the triple line region, so that numerical results can become inaccurate as the Biot number increases. A reference case in which the heat flux can be determined analytically has thus be established to derive an empirical criterion on the local mesh refining needed to obtain accurate numerical results. To consolidate the results obtained with a finite elements code, calculations have been performed with a completely independent tool using Monte Carlo method on a set of cases. A correlation has then been derived from the numerical results data with a maximum deviation of less than 4% in the considered range of θ and B i , that covers conditions encountered in all the studies dealing with dropwise condensation of pure vapor. Comparisons with other laws available in literature have then been performed, evidencing some important discrepancies. • Available correlations lead to huge discrepancies when they are compared to each other. • Elements of the mesh must be smaller than the inverse of the local Biot number. • An unbiased correlation is provided to calculate the conduction thermal resistance. • In dropwise condensation this law is valid whatever the Biot number and contact angle.

Experimental study on steam plume shape characteristics for bevelled spray nozzles exhausting into quiescent water

Steam-water direct contact condensation phenomenon is being widely used in many industries including chemical, thermal and especially in nuclear industry due to its efficient heat and mass exchange capabilities. The present experimental study explores the underlying physics of the steam cavity/plume shapes by condensing supersonic steam exhausting from five different bevelled nozzles into quiescent water tank. Based on the high speed image capturing methodology, the effects of steam pressure, water temperature and nozzle exit inclination angle on the cavity shape characteristics have been studied. Existence of six different plume shapes (oscillatory, conical, expansion–contraction, double expansion contraction, cylindrical and divergent) have been identified. The results show that for a fixed nozzle geometry, with the increase in water temperature and steam pressure, the steam jet becomes lengthy. However, under the same steam pressure and water temperature conditions, the plume shortens with the increase in nozzle exit inclination angle. The dimensionless jet length has been found in the range of 1.26–5.64. Furthermore, it has been observed that steam plume exhausting from bevelled nozzle undergoes deflection from its nozzle symmetry axis possibly due to the pressure difference between upper and lower lip of nozzle. This deflection may either be upward oriented at high steam pressure or downward deflected at lower steam pressure. Additionally, on the basis of findings from 175 No’s of experiments, condensation regime maps have also been developed for bevelled spray nozzle.

Effect of non-condensable gas in steam condensation at sub-atmospheric pressure condition

In the International Thermonuclear Experimental Reactor (ITER), a postulated Loss Of Coolant Accident (LOCA) in the Vacuum Vessel (VV) has to be managed with a pressure suppression system working at sub-atmospheric pressure. The operating conditions considerably differ from those experienced in the fission nuclear power plants such as BWR, since the ITER Tokamak works at very low pressure conditions and can withstand a maximum pressure of 0.15 MPa. For this reason, the pressure value must not exceed 10 kPa for a water temperature of 30 °C inside the Vapour Suppression Tanks (VSTs) that are the fundamental components of the Vacuum Vessel Pressure Suppression System (VVPSS). During a LOCA some non-condensable gases (mainly hydrogen and oxygen gases due to the water radiolysis or thermolysis) may be mixed in the steam and this could impair the condensation efficiency. In order to investigate the effects of non-condensable gas on DCC, we conducted a research program funded by ITER Organization at the laboratory of the University of Pisa: we designed and built a small-scale experimental rig to study the steam Direct Contact Condensation (DCC) with the presence of non-condensable gas and simulate the behaviour of a VST. Since DCC can occur with different characteristics, we ran 12 closed mode tests exploring all condensation regimes injecting a certain mass of air with the steam discharged in the subcooled water. The tests started at the saturation pressures corresponding to water temperatures ranging from 40 °C to 80 °C and ended when the free space volume reached the atmospheric pressure. From the analysis of the data acquired during the tests we observed that the condensation efficiency remained higher than 95%. We observed that despite this, the presence of a certain quantity of non-condensable gas has negative aspects on condensation: the condensation regime never reaches stability (the regimes quickly shift towards instability). Furthermore, the presence of air triggers a turbulence of the flow which interferes with the transfer of heat from the steam to the water. Not only the introduction of air into the flow increases linearly the pressure above the water head but its high temperature further contributes to the pressure increase. The air mixed with the flow also forms eddies that can trap the steam and transport it out of the water, preventing it from condensing. Apart from condensation, the most noticeable problem is the rapid increase in pressure inside the condensation tank.

Entraining of dust and steam flux in water pool: experimental and numerical simulations of vapor condensation and dust deposition

This paper deals with experimental tests of steam condensation in a water pool at atmospheric pressure and temperature in the range 15-100 °C. The activity is performed in the frame of a research program, funded by the ITER organization, for the study of dust deposition, produced in the ITER Vacuum Vessel and entrained by the steam and non condensable gas into the Pressure Suppression Tanks in the case of a Loss of Coolant Accident. The steam condensation into a subcooled water pool has been investigated to characterise the condensation regimes occurring during dust deposition tests. The dust distribution on the tank walls strongly depends on the steam jet length and on the effective heat transfer coefficient. Few grams of dust reduce the water transparency, therefore separated tests without dust overcome this drawback. Measurements of the lengths and surfaces of the steam jets (which permit to calculate effective average heat transfer) have been performed by means of image analyses and have been compared with theoretical correlations. The comparison showed a good agreement between the experimental data and theoretical correlations. Useful data have been obtained for implementing numerical models of dust deposition and for understanding the dust distribution on the tank wall obtained in the experimental tests.

Experimental Analysis of Steam Condensation Heat Transfer Coefficient in Water Pool at Sub-Atmospheric Pressure

The experimental analysis of steam direct contact condensation in a water pool at sub-atmospheric condition was carried out in relevant configurations for the International Thermonuclear Experimental Reactor (ITER) Vacuum Vessel Pressure Suppression System, during a postulated Ingress of Coolant Event category IV accidental scenario. This transient accident was experimentally simulated in a reduced scale (1:22) facility at University of Pisa, adopting a defined scaling law. The steam jet plumes were video recorded and image analysis was performed at stable and interfacial oscillation condensation regimes, providing steam plume average length and interfacial area. The average heat transfer coefficient was therefore computed and correlated to the condensation driving potential. Also, the steam jet length divided by orifice diameter (L/D) was characterised as function of driving potential. Empirical correlations available in literature at atmospheric conditions were modified for evaluating vacuum conditions peculiarities. The remarkable higher dependence of heat transfer coefficient (HTC) to driving potential parameter, at vacuum conditions, was highlighted by the driving potential exponent equal to 1.2 instead of 0.04 at ambient pressure. The obtained L/D and HTCcorrelations are able to predict with ± 15% and ± 30% of error the corresponding experimental data, respectively.

Photoinduced dynamics of a quasicrystalline excitonic insulator

We study the photoinduced dynamics of the excitonic insulator in the two-orbital Hubbard model on the Penrose tiling by means of the time-dependent real-space mean-field approximation. We show that, with a single-cycle electric-field pulse, the bulk (spatially averaged) excitonic order parameter decreases in the Bardeen-Cooper-Schrieffer (BCS) regime, while it increases in the Bose-Einstein condensate (BEC) regime. This behavior is in common with the excitonic insulator in the square lattice reported previously. To explore the dynamics peculiar to the Penrose tiling, we examine the coordination number dependence of observables and analyze the perpendicular space. In the BEC regime, characteristic oscillations of the electron number at each site are induced by the pulse, which are not observed in normal crystals with single coordination number. On the other hand, the dynamics in the BCS regime is characterized by drastic change in the spatial pattern of the excitonic order parameter. Our results imply that potentially interesting nonequilibrium physics is caused by rich local structural patterns involved in quasicrystals.