Problem Of Condensation Research Articles

Practical Use of Materials of Natural Origin as Loose-Fill Insulations in Open-Diffusion Constructions—Observation and Numerical Simulation

The increasing requirements concerning the consideration of the environmental impact of building materials, along with the simultaneous preservation and enhancement of building thermal parameters, have led to a surge in interest in insulations based on organic or recycled materials. Despite the growing interest in these materials, there remains a scarcity of scientific studies regarding their hygrothermal properties. Within the scope of the research described in the text, the insulation properties of loose-fill materials (hemp shives, cellulose fibers, loose wood wool, and mineral wool as a reference) in wooden frame walls were analyzed. The authors simulated walls with the same U value filled with these materials using Delphin 6.1 software. The simulation time was 3 years, considering the appropriate climatic conditions of Olsztyn and different microclimatic conditions inside the rooms. Insulations made of natural organic can absorb and reveal moisture to the internal environment, while mineral wool transports the moisture to the outside, which may cause condensation problems. Insulations made of hemp shives or wood wool do not increase the level of accumulated moisture over time, which results in thermal stability. In contrast, cellulose and mineral wool store more moisture, which in wet conditions increases the heat flux by 6.9% and 5.2%, respectively.

Robust and Superhydrophobic Polydimethylsiloxane/Ni@Ti3C2Tx Nanocomposite Coatings with Assembled Eyelash-Like Microstructure Array: A New Approach for Effective Passive Anti-Icing and Active Photothermal Deicing.

To solve the problem of ice condensation and adhesion, it is urgent to develop new anti-icing and deicing technologies. This study presented the development of a highly efficient photothermal-enhanced superhydrophobic PDMS/Ni@Ti3C2Tx composite film (m-NMPA) fabricated cost-effectively and straightforwardly. This film was fabricated utilizing PDMS as a hydrophobic agent, adhesive, and surface protector, while Ni@Ti3C2Tx as a magnetic photothermal filler innovatively. Through a simple spraying method, the filler is guided by a strong magnetic field to self-assemble into an eyelash-like microstructure array. The unique structure not only imparts superhydrophobic properties to the surface but also constructs an efficient "light-capturing" architecture. Remarkably, the m-NMPA film demonstrates outstanding superhydrophobic passive anti-icing and efficient photothermal active deicing performance without the use of fluorinated chemicals. The micro-/nanostructure of the film forms a gas layer, significantly delaying the freezing time of water. Particularly under extreme cold conditions (-30 °C), the freezing time is extended by a factor of 7.3 compared to the bare substrate. Furthermore, under sunlight exposure, surface droplets do not freeze. The excellent photothermal performance is attributed to the firm anchoring of nickel particles on the MXene surface, facilitating effective "point-to-face" photothermal synergy. The eyelash-like microarray structure enhances light-capturing capability, resulting in a high light absorption rate of 98%. Furthermore, the microstructure aids in maintaining heat at the uppermost layer of the surface, maximizing the utilization of thermal energy for ice melting and frost thawing. Under solar irradiation, the m-NMPA film can rapidly melt approximately a 4 mm thick ice layer within 558 s and expel the melted water promptly, reducing the risk of secondary icing. Additionally, the ice adhesion force on the surface of the m-NMPA film is remarkably low, with an adhesion strength of approximately 4.7 kPa for a 1 × 1 cm2 ice column. After undergoing rigorous durability tests, including xenon lamp weathering test, pressure resistance test, repeated adhesive tape testing, xenon lamp irradiation, water drop impact testing, and repeated brushing with hydrochloric acid and particles, the film's surface structure and superhydrophobic performance have remained exceptional. The photothermal superhydrophobic passive anti-icing and active deicing technology in this work rely on sustainable solar energy for efficient heat generation. It presents broad prospects for practical applications with advantages such as simple processing method, environmental friendliness, outstanding anti-icing effects, and exceptional durability.

Objective form: the brief story of a critical struggle

Amidst debates in the sixties regarding late modernisation in peripheral countries, Roberto Schwarz came to define objective form (1991) as a construct that provides the rhythmic and invisible links between the social-historical domain and the aesthetic. It consists, said Schwarz, of a form comprising ‘a practical and historical substance’ acting also as the ‘social core of the art form’ (1997). By connecting the preexistent social experience to the aesthetically built form, the objective form works as a social contract legitimating the aesthetic form. Socially and historically ordered by a collective and impersonal subject, such construct distinguishes itself from postmodern eclecticism disconnected from the historical process. The objective form offers critical intelligibility before the historical-social matter, but only if taken as a form that is intrinsic to the aesthetic sphere. Thus, the problem of the aesthetic condensation of the social rhythms is therefore concretely and ceaselessly reoccurring—in production and reception—whenever necessary to retrace the reciprocal links between social-historical and artistic forms. Accordingly, the exercise of aesthetic intuition and the critical act in the infighting with the art materials are required to synthesise the structures of the social-historical matter—otherwise inapprehensible in the intrinsic connections to the perception and reflexion about the historical objectivity and dynamics. There are things that only in art emerge and make it an indispensable tool for dialectical historical reflexion. In this sense, this paper will revisit some critical responses that Brazilian art (Antonio Dias, Amilcar de Castro, Mendes da Rocha) gave to the civil-military coup of 1964 and to the late accelerated economic modernisation that ensued. And finally, it will also revisit the contemporary installation Big Wheel (2019, Carmela Gross)—a negative architectural construct that totalised Brazil’s tragic moment with rare clarity and epic poignancy.

Study of the cooling performance of an anti-condensation radiant cooling unit with an infrared-transparent silicon wafer

Radiant cooling systems consume a low amount of energy and provide high thermal comfort; however, the risk of condensation in hot and humid areas limits their cooling capacity and is not conducive to their application. To solve the contradiction between condensation problems and the cooling demand, this study proposes a novel anti-condensation radiant cooling unit (RCU) that uses an infrared-transparent silicon wafer (ISW) with a good mechanical strength to separate the cooling radiant panel from the humid air, thus avoiding condensation. A heat transfer model of the anti-condensation RCU was established, and experimental tests were conducted under different indoor air temperatures, humidities, and vacuum degrees in the interlayer. At a temperature of 26 °C in 50 % relative humidity, the maximum cooling capacity of the anti-condensation RCU reached 103.66 W/m2, which was 60.88 % higher than the performance of conventional RCU. When the vacuum degree of the interlayer was 0.06 Mpa, the air-contacting surface outside the ISW was approximately 1.2 °C higher than that of atmospheric pressure. The results demonstrate that the anti-condensation RCU overcomes the limitation of the dew-point temperature on the cooling capacity to a certain extent and expands its applicability in high-humidity environments.

Prediction of Condensation in the Heat Exchangers of Engine Intake Systems according to External Environmental and Operating Conditions

Low-pressure exhaust gas recirculation (LP-EGR) systems are applied to diesel engines because they reduce nitrogen oxide emission by lowering the internal temperature of the cylinder by mixing the oxides with intake air. However, low-temperature ambient conditions include a large amount of vapor in the mixed gas flowing into the intercooler; when heat is exchanged, the water vapor condenses and is adsorbed on the surface of the intercooler fin to form a liquid film. Condensation occurs as the thermal resistance between the vapor and solid surface increases with the thickness of the liquid film and causing a corrosion due to condensation of the surface. In this study, the amount of condensation was predicted through calculations based on thermodynamic studies. Factors that can cause condensation inside the intercooler (fuel, air, and LP-EGR) were selected as variables. A mathematical formula was established to predict the convergence form of condensation or the amount of condensation over time at various temperature and relative humidity conditions. The formula predicted the condensation amount in the intercooler of the diesel engine, compared it to the actual amount of condensation in the test evaluation with an error of less than 4%. Additionally, because the formula can predict the amount of condensation by changing the heat exchange area of the intercooler, the application range of the formula was expanded to predict the condensation in the intercoolers of gasoline vehicles with different heat exchange areas and fuel types. The condensation error was within 2%, indicating a high consistency. Validation of the formula predicts a reliable amount of condensation under various operating and ambient temperature conditions, which means that both the time and cost of the test evaluation require the determination of the cause before solving the actual condensation problem.

Self-Similar Solution to the Problem of Unsteady Film Condensation on a Vertical Semi-Infinite Plate

Self-Similar Solution to the Problem of Unsteady Film Condensation on a Vertical Semi-Infinite Plate

Self-Similar Solution to the Problem of Unsteady Film Condensation on a Vertical Semi-Infinite Plate

Changes in the regimes of condensate film flow along the underlying surface in the presence of a body force are considered within the framework of a simplified physical and mathematical model of hydrodynamic and thermal processes occurring under unsteady film condensation on a vertical semi-infinite plate. The model is used to determine the applicability conditions of the zero-gravity approximation when considering film condensation. It is found that the validity of using the zero-gravity approximation to calculate the film thickness growth rate on any plate section depends not only on the magnitude of the body force, but also on time and distance between this section and the leading edge of the plate.

On paradoxical phenomena during evaporation and condensation between two parallel plates.

Kinetic theory has long predicted that temperature inversion may happen in the vapor-phase for evaporation and condensation between two parallel plates, i.e., the vapor temperature at the condensation interface is higher than that at the evaporation interface. However, past studies have neglected transport in the liquid phases, which usually determine the evaporation and condensation rates. This disconnect has limited the acceptance of the kinetic theory in practical heat transfer models. In this paper, we combine interfacial conditions for mass and heat fluxes with continuum descriptions in the bulk regions of the vapor and the liquid phases to obtain a complete picture for the classical problem of evaporation and condensation between two parallel plates. The criterion for temperature inversion is rederived analytically. We also prove that the temperature jump at each interface is in the same direction as externally applied temperature difference, i.e., liquid surface is at a higher temperature than its adjacent vapor on the evaporating interface and at a lower temperature than its adjacent vapor on the condensing interface. We explain the interfacial temperature jump and temperature inversion using the interfacial cooling and heating processes, and we predict that this process can lead to a vapor phase temperature much lower than the lowest wall temperatures and much higher than the highest wall temperature imposed. When the latent heat of evaporation is small, we found that evaporation can happen at the low temperature side while condensation occurs at the high temperature side, opposing the temperature gradient.

A perturbed averaging operator on finite graphs

On a finite random walk {X,p(x,y)}, an averaging operator A is defined by Au(x)=∑p(x,y)u(y) and its perturbation is Aφu(x)=Au(x)−φ(x)u(x), where φ(x) is a real-valued function on the states of X. The properties of the solutions and the supersolutions of Aφu(x)=0 are studied which fall into three categories depending on the greatest eigenvalue (a term made precise) of the non-symmetric matrix representing Aφ. Relative to the operator Aφ, the Dirichlet-Poisson solution, the Green function, the Equilibrium Principle and the Condenser problem are investigated.

Thermal impact of tourist visits on the microclimate in the Cap Blanc shelter, Dordogne, France

ABSTRACT Tourism is a growing concern for the conservation of heritage sites. In the Dordogne, the Cap Blanc shelter attracts many visitors and their presence may affect its parietal frieze by altering the thermal environment. To assess this impact, a study is carried out using numerical simulation, a non-intrusive conservation tool that can model the thermal behaviour of the cavity during tourist visits. We validate the numerical model with the temperature measurements taken inside the shelter during three tourist visits. We show that the heat emitted by the tourists is mostly absorbed by the walls, resulting in a small increase in air temperature (between 1°C and 2°C) and a large temperature gradient near the walls during the visits, which favours condensation and possible conservation problems.

Uncooled Tunable Laser Based on High-Density Integration of Distributed Feedback Semiconductor Lasers

Most types of tunable lasers are sensitive to the ambient temperature and require thermoelectric coolers (TECs) for temperature control. For conventional tunable laser modules, high power consumption of cooling is required for stabilizing the laser temperature and complex hermetic packages are normally used to avoid moisture condensation problems, which are expensive and difficult to manufacture. To overcome these drawbacks, we demonstrated an uncooled tunable laser via the monolithically integrated multi-wavelength distributed feedback (DFB) laser array based on the reconstruction-equivalent-chirp technique. Totally sixteen DFB semiconductor lasers are densely integrated with a 4-by-4 matrix laser array. To ensure the uncooled laser operates properly, the active material of the laser chip is designed to work at high temperatures without TEC cooling. Therefore, an uncooled wavelength-tuning range of 33.8 nm is achieved during the whole commercial operating temperature range from 0 °C to 70 °C.

5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a carbon dioxide binary mixture based compressed gas energy storage system: A comprehensive research and feasibility validation

Recently, the application of carbon dioxide binary working fluids in compressed carbon dioxide energy storage systems has been proposed to improve the system characteristics, especially for the condensation problem of carbon dioxide. Based on the previous research, a more comprehensive 5E (energy, exergy, energy level, exergoeconomic, and exergetic sustainability) analysis on a typical transcritical compressed carbon dioxide energy storage system using carbon dioxide binary working fluid is carried out. Propane, propylene, R32, R161, R1234ze, and R1234yf are chosen to compose the binary working fluid with carbon dioxide, respectively. The effect of changing parameters, including pump pressure ratio, compressor isentropic efficiency, and heat exahcnger1 outlet temperature on system performance, is also analyzed. In addition, the feasibility of applying carbon dioxide binary working fluid at high ambient temperature is investigated. According to the results, the performance of heat exchanger1, heat exchanger2, and pump decreases while the performance of the turbine is improved with a higher refrigerant mass fraction from the point of energy level. The compressor, pump, and turbine show potential for optimization according to their higher process energy level difference. The pump power and system operating pressure is reduced at the cost of reducing round trip efficiency when using carbon dioxide binary working fluid. A 1% improvement in compressor isentropic efficiency leads to an increase of nearly 0.4% in round trip efficiency, albeit with reduced turbine power. Increasing the heat exchanger1 outlet temperature from 305 K to 315 K results in a 1% increase in round trip efficiency but with a decrease in the performance of heat exchanger1. Both increasing compressor isentropic efficiency and heat exchanger1 outlet temperature benefit the system economy and exergetic sustainability. A noticeable decrease in system performance is observed when the ambient temperature shifts from 293 K to 303 K. However, this deterioration can be mitigated by raising the pressure of saturated working fluid gas at the compressor inlet. Propylene, R32, and R1234yf are suitable candidates to address the condensation issue, considering the system performance at high ambient temperatures. This paper extends research on the compressed carbon dioxide energy storage system based on carbon dioxide mixtures and provides a reference for the working fluid selection and system optimization for related research.

Robust direct solar water production by integrating interfacial evaporation and membrane distillation

Interfacial solar vapor generation (ISVG) is an important technique for producing water with a minimal carbon footprint. For customers who need a lot of water, the state-of-the-art ISVG devices are unbearable and unacceptable because of their low condensation capacity. This paper introduces a novel configuration that integrates ISVG and direct contact membrane distillation (DCMD) devices to increase the water yield. A carbon nanoparticle-based solar absorber that can collect 94.6 % of incident sunlight and has a substantial water supply capacity is employed for ISVG. For high vapor permeability, moreover, a hydrophobic polyvinylidene fluoride membrane with a moderate pore structure is adopted. The result shows that the ISVG-DCMD device has a water productivity of up to 2.71 kg m−2h−1 under 2 sun illumination. More importantly, the system has a sustainable water productivity of 2.08 kg m−2h−1 when operating in NaCl solution with a concentration of 3.5 % (w/w). This work effectively solves the problem of vapor condensation of the interfacial photothermal evaporator, offering a novel concept for scalable and robust direct solar water production.

Anti-Condensation Temperature Control Strategy of the Concrete Radiant Roof

Radiation cooling, as a new terminal mode that has been gradually emerging in recent years, has attracted more and more attention. However, the problem of condensation has become a vital bottleneck restricting the broad application of radiation-cooling technology. This paper used the numerical simulation method of Ansys Fluent to study the effect of different water supply parameters on the concrete radiant roof’s heat transfer performance, temperature uniformity analysis, and anti-condensation temperature control strategy. The accuracy of the simulation model was verified by comparing the numerical simulation values and measured values of temperature monitoring points. In thermal performance research, the inlet temperature significantly impacted the cooling capacity and radiant surface temperature compared with the inlet flow velocity. In the uniformity study, the distance between the serpentine pipes area and the concrete edge was easily neglected, which was also an important factor affecting the distribution of temperature uniformity. Regarding anti-condensation and performance improvement research, first supplying water at low temperatures and then dynamically adjusting high-temperature water could effectively avoid condensation and improve the radiant roof’s heat transfer performance. The research results could provide technical references for the practical application of radiation roof anti-condensation temperature control technology.

Development and modified implementation of Lee model for condensation simulation

Numerical oscillation is a non-physical phenomenon in which the interface temperature fluctuates around the saturation temperature. The simulation for condensation is more susceptible to the numerical oscillation caused by the phase change model. To suppress the numerical oscillation and reduce interface temperature deviation in condensation simulation, a developed model modified the Lee model is presented in this study. In the present model, the mass source terms and the energy source terms are added in the governing equations to calculate the condensate within the cell and the allocation of condensation energy between the interface cells. The mass and energy source transfer model is firstly compared with the original Lee model to simulate one-dimensional Stefan problem. Indicating that with the similar accuracy the developed model could increase computational efficiency by 40 times. Then the Nusselt condensation problem is verified with a reasonable selection of model parameters, and the average error of the film thickness was controlled below 2%, as the interfacial temperature deviation within 3%. Finally, verification is also attained on the forced convective condensation of R134a and the interfacial temperature deviation is below 0.1 K. Simulation results validate the feasibility of using this model to predict heat and mass transfer in condensation. The numerical oscillations are also significantly suppressed in the simulations.

Fluctuation-induced dispersion forces on thin DNA films.

In this work, the calculation of Casimir forces across thin DNA films is carried out based on the Lifshitz theory. The variations of Casimir forces due to the DNA thicknesses, volume fractions of containing water, covering media, and substrates are investigated. For a DNA film suspended in air or water, the Casimir force is attractive, and its magnitude increases with decreasing thickness of DNA films and the water volume fraction. For DNA films deposited on a dielectric (silica) substrate, the Casimir force is attractive for the air environment. However, the Casimir force shows unusual features in a water environment. Under specific conditions, switching sign of the Casimir force from attractive to repulsive can be achieved by increasing the DNA-film thickness. Finally, the Casimir force for DNA films deposited on a metallic substrate is investigated. The Casimir force is dominated by the repulsive interactions at a small DNA-film thickness for both the air and water environments. In a water environment, the Casimir force turns out to be attractive for a large DNA-film thickness, and a stable Casimir equilibrium can be found. The influences of electrolyte screening on the Casimir pressure of DNA films are also discussed at the end. In addition to the adhesion stability, our finding could be applicable to the problems of condensation and decondensation of DNA, due to fluctuation-induced dispersion forces.

Sepiolite based humidity-control coating specially for alleviate the condensation problem of radiant cooling panel

Sepiolite based humidity-control coating specially for alleviate the condensation problem of radiant cooling panel

Performance of a siphon-like water supplying solar distiller with helium gas enhancing the reverse film evaporation process

The multistage solar desalination method based on the interface local thermal method is an attractive and efficient desalination method. However, there are still problems such as the upward diffusion of water vapor in the air and the downward irradiation of solar light, which make the multistage device fail to effectively condense and interface salt crystallization cannot be effectively eliminated, hindering the development of large-scale and sustainable applications of this technology. Here, we use a cheap nanofiber super-hydrophilic material to promote the flow of seawater at the interface and promote the discharge of salt crystallization under the siphon-like effect. At the same time, the water vapor‑helium space is constructed by filling helium to promote the downward diffusion of water vapor in the space and solve the problem of insufficient multistage condensation. In this work, a two-stage and three-stage reverse mass transfer solar seawater desalination system with solar hot film evaporation was built, and the corresponding theoretical calculation and experimental verification were carried out. The experimental results show that under sunlight irradiation of 800 W m−2, the three-stage experimental system filled with helium can effectively enhance the condensation of water so that the GOR value of the system vapor is 1.54, the first-stage evaporation efficiency reaches 67.9 %, and the water productivity reaches 1.85 kgm−2h−1. In this study, injecting low molecular weight gas to achieve efficient condensation of the system to improve the performance of the interfacial evaporation desalination system provides a new method and reference.

Mannitol assisted oxalic acid pretreatment of poplar for the deconstruction and separation of hemicellulose

The effect of mannitol (MA) on the poplar separation using mannitol-assisted oxalic acid (M/OA) pretreatment was revealed. The effects of reaction parameters on the separation efficiency were studied. The optimized conditions were OA 7.0%, MA 7.0%, temperature 150 °C, and time 60 min. The hemicellulose separation was 79.08%. The separation of cellulose and lignin decreased from 12.43% and 21.82–8.58% and 16.11%, respectively, under hemicellulose separation similar to those of conventional OA pretreatment. Smooth fiber surfaces with less lignin deposition were observed. There were more β-O-4 and fewer β-β in lignin. Additionally, larger amounts of aliphatic hydroxyl groups and smaller amounts of phenolic hydroxyl groups were observed, which implies that MA addition prevented lignin from condensing. An effective and environmentally friendly separation of hemicellulose was achieved by M/OA pretreatment. This provides a practical approach for resolving the stubborn problems of lignin cleavage and condensation during organic acid pretreatment.

Efficient delignification of wheat straw for microbial lipid production enabled by a novel ternary deep eutectic solvent containing ethylene glycol

Lignocellulose pretreatment often faces the problem of lignin condensation with less attention to biofuel production from total sugars, which significantly hinders biomass fractionation and energy utilization efficiency. The aim of this work was to design a novel ternary deep eutectic solvent (DES) (citric acid: choline chloride: ethylene glycol in a molar ratio of 1:1:2) for pretreatment of wheat straw with a solid/liquid ratio (S/L) of 1:20 (w/w) to achieve non-condensed lignin and high-yield fermentable sugars at 100 °C for 12 h. The introduction of ethylene glycol into ternary DES could capture the formed benzyl carbocation to protect lignin structure, inhibit excessive degradation of hemicellulose but to fermentable sugars (e.g., xylose), and improve the enzymatic digestibility of cellulose (98.73%, w/w). The mechanisms of both lignin fractionation and the in-situ lignin protection during the pretreatment of wheat straw enabled by ternary DES were systematically elucidated. Importantly, Trichosporon cutaneum cultivated in undetoxified DES waste liquid (hemicellulose-rich) and residue hydrolysate (cellulose-rich) could totally afford 8.7 g microbial lipid per 100 g wheat straw, which is superior to previous reports. This green in-situ lignin protection and fractionation strategy provides a new avenue for upgrading lignocellulose to microbial lipids.