Search Results (36)

High-temperature heat pump systems are essential for industrial processes that usually require high-temperature and high-pressure steam. An efficient design of these systems is critical for minimizing fossil fuel consumption, thereby contributing to a significant reduction in carbon emissions. One of the key components of these systems is the horizontal falling film evaporator, which is commonly employed due to its high thermal efficiency and low refrigerant charge. This study presents a preliminary design of a falling film evaporator to meet the target of the heat duty value of 2.2 MW. The phase-change dynamics inherent to the falling film evaporation process were critically analyzed using ANSYS Fluent (2024 R2). The low-global warming potential refrigerant R1336mzz(Z) was incorporated as a refrigerant on the shell side, while hot water was used in the tubes. The study identified key regions of film flow to maximize vapor production and design optimizations. The discussed performance parameters and operational mechanisms of the evaporator are prevailing features, particularly with the adoption of environmental regulations. Overall, the simulation results offer valuable insights into heat transfer mechanisms and evaporator effectiveness for advancing heat pump technologies in industrial applications. Full article

Plasma–liquid reactions represent an emerging green chemical process for nitrogen fixation; however, these processes generally exhibit low selectivity for ammonium (NH₄⁺). This limitation highlights the need to explore simple methods to increase NH₄⁺; selectivity. In this study, a catalyst-free falling film dielectric barrier discharge plasma system was employed for the selective synthesis of NH₄⁺. By manipulating the flow state of the discharge gas, NH₄⁺ selectivity was found to increase by 138.4% in the sealed gas flow state compared to the flowing gas state. Furthermore, an increase in the discharge voltage positively influenced the NH₄⁺ selectivity. This phenomenon can be attributed to higher energy input and longer reaction times, which facilitate the formation of nitrogen molecular ions, a critical intermediate in ammonia synthesis. The reaction products were analyzed by UV spectrophotometry and emission spectroscopy to investigate the underlying mechanisms of ammonia synthesis. This study reveals the highest reaction rate reported to date for ammonia synthesis via single-system plasma gas–liquid reactions and offers a novel way to improve both the yield and selectivity of ammonium synthesis via non-thermal plasma gas–liquid interactions. Full article

Drying experiments with varying air temperature and humidity were conducted to investigate the influence of the drying process on the crystallization of thin sucrose films. For the first time, the effects of the nucleation onset, nucleation rate, and growth rate were investigated in situ and their differentiated influence on product crystallinity could be assessed. The growth rate was not influenced by air humidity but showed a strong dependence on temperature. It increased with drying temperature; however, at high temperatures, growth was inhibited when the water content falls below a critical level. Noticeable differences in nucleation behavior could be observed with regard to air humidity. Dry air led to crystallization onsets at lower levels of supersaturation, while moderately humid air retarded it. At higher temperatures, nucleation onset commenced at lower water contents but at a constant supersaturation level. The nucleation rate doubled in experiments with moderately humid air (15% RH), while an elevated drying temperature showed generally lower nucleation rates. The observed differences in the nucleation onset and rate could be explained by the film-internal concentration profile, which is strongly influenced by drying parameters. The insights therefore provide a differentiated understanding of the formation of the physical state and how it can be influenced during convective drying. Full article

The new technique of filming in autumn and planting directly through the plastic film in spring is an effective method for water-saving and drought-resistant commercial potato production. However, there are currently no supporting film-drilling seeders available. To address this, a new potato seeder machine has been specifically designed for planting potatoes in the dryland, hilly, and mountainous areas of northwest China. This machine can perform top mulching and hole planting in both the autumn and spring seasons. This innovative potato seeder accomplishes several tasks simultaneously: seeding, inoculation (if desired), hole punching through the mulch film, seed placement, and soil covering. The machine features an optimized spoon-chain seeder with an eccentric coupling mechanism that ensures the hole-punching device stays perpendicular to the ground throughout planting, minimizing damage to the mulch film. Additionally, a dedicated seeding valve opening and closing mechanism was designed to extend the opening time of the hole-forming device’s movable mouth beyond the potato’s falling time, guaranteeing successful seed placement. Furthermore, a soil-covering device specifically designed for use with mulch film ensures proper soil retention after seeding. Through computer-aided design (RecurDyn V9R5 software) analysis, the hole-punching device’s penetrating angle was optimized to minimize the tearing of the mulch film during entry into and exit from the soil. Rigorous field testing demonstrated the machine’s effectiveness. The seeder achieved a 92% success rate for proper planting depth, an 88% success rate for accurate seed potato spacing, a 98% success rate for avoiding overplanting, and a 99% success rate for eliminating missed planting spots. These field test results meet or exceed national and industry standards, validating the machine’s design goals. In essence, this innovative potato seeder, with its eccentric coupling mechanism, offers a one-pass solution for potato seeding, inoculation (optional), planting, and soil covering, significantly improving efficiency. Full article

We present a surface modification technique that turns CuNi foam films with a high contact angle and non-sticking property into a sticky surface. By decorating with mesh-like biaxially oriented polypropylene (BOPP) and adjusting the surface parameters, the surface exhibits water-retaining capability even when being held upside down. The wetting transition process of droplets falling on its surface were systematically studied using the finite element simulation method. It is found that the liquid filled the surface microstructure and curvy three-phase contact line. Moreover, we experimentally demonstrated that this surface can be further applied to capture underwater air bubbles. Full article

Rapid urbanization and industrialization have heightened concerns about air quality worldwide. Conventional air purification methods, reliant on chemicals or energy-intensive processes, fall short in open spaces and in combating emerging pollutants. Addressing these limitations, this study presents a novel water-film air purification prototype leveraging the adhesion between low-curvature liquid surfaces and air convection friction. Uniquely designed, this prototype effectively targets toxic gases (e.g., formaldehyde, SO₂, NO₂) and particulate matter (such as PM_2.5) while allowing continuous airflow. This research explores the adhesion and sedimentation capabilities of a low-curvature water solution surface under convection friction, reducing the surface energy to remove airborne pollutants efficiently. The prototype was able to reduce the initial concentration in a 30 m³ chamber within 180 min by 91% for formaldehyde, 78% for nitrogen dioxide (NO₂), 99% for sulfur dioxide (SO₂), and 96% for PM_2.5. Experimentally validated indicators—decay constants, CADR, and purification efficiency—enable a comprehensive evaluation of the purification device, demonstrating its efficacy in mitigating air pollution. This innovative design, which is cost-effective due to its use of easily accessible components and water as the primary medium, indicates strong potential for large-scale deployment. This study points to an environmentally friendly and economical approach to air purification, shedding light on a promising direction for enhancing indoor air quality. Further optimization and exploration of diverse pollutants and environmental conditions will propel the practical applications of this pioneering technology. Full article

In this paper, novel humidity sensors based on montmorillonite, kaolinite, and composite films coated on micro-cantilevers were prepared to measure the relative humidity (RH) values by the deflection of a micro-cantilever (MC) at room temperature. The humidity-sensing properties, such as response and recovery, sensitivity, repeatability, humidity hysteresis, and long-term stability, were investigated in the range of working humidity (10–80% RH). The humidity response in the close humidity range of 10% RH to 80% RH revealed a linear increase in water absorption of montmorillonite, kaolinite, and montmorillonite/kaolinite mixed dispersant (1:1) as a function of RH with linear correlation factors between the humidity change and deflection estimated to be 0.994, 0.991, and 0.946, respectively. Montmorillonite’s sensitivity was better than kaolinite’s, with the mixed-clay mineral film’s response falling somewhere in between. This research provides a feasible and effective approach to constructing high-performance MC humidity sensors that can be operated at room temperature based on clay minerals. Full article

Following up on a proof of concept, this publication presents a new method for mixing mapping on falling liquid films. On falling liquid films, different surfaces, plain or structured, are common. Regarding mixing of different components, the surface has a significant effect on its capabilities and performance. The presented approach combines marker-free and molecule-sensitive measurements with cross-section mapping to emphasize the mixing capabilities of different surfaces. As an example of the mixing capabilities on falling films, the mixing of sodium sulfate with tap water is presented, followed by a comparison between a plain surface and a pillow plate. The method relies upon point-by-point Raman imaging with a custom-built high-working-distance, low-depth-of-focus probe. To compensate for the long-time measurements, the continuous plant is in its steady state, which means the local mixing state is constant, and the differences are based on the liquids’ position on the falling film, not on time. Starting with two separate streams, the mixing progresses by falling down the surface. In conclusion, Raman imaging is capable of monitoring mixing without any film disturbance and provides detailed information on liquid flow in falling films. Full article

Understanding the mechanism of bubble growth is crucial to modeling boiling heat transfer and enabling the development of technological applications, such as energy systems and thermal management processes, which rely on boiling to achieve the high heat fluxes required for their operation. This paper presents analyses of the evaporation of “microlayers”, i.e., ultra-thin layers of liquid present beneath steam bubbles growing at the heated surface in the atmospheric pressure nucleate of boiling water. Evaporation of the microlayer is believed to be a major contributor to the phase change heat transfer, but its evolution, spatio-temporal stability, and impact on macroscale bubble dynamics are still poorly understood. Mass, momentum, and energy transfer in the microlayer are modeled with a lubrication theory approach that accounts for capillary and intermolecular forces and interfacial mass transfer. The model is embodied in a third-order nonlinear film evolution equation, which is solved numerically. Variable wall-temperature boundary conditions are applied at the solid–liquid interface to account for conjugate heat transfer due to evaporative heat loss at the liquid–vapor interface. Predictions obtained with the current approach compare favorably with experimental measurements of microlayer evaporation. By comparing film profiles at a sequence of times into the ebullition cycle of a single bubble, likely values of evaporative heat transfer coefficients were inferred and found to fall within the range of previously reported estimates. The result suggests that the coefficients may not be a constant, as previously assumed, but instead something that varies with time during the ebullition cycle. Full article

Corn straw incorporation in soil has been regarded as an environment-friendly approach for straw utilization. However, straw incorporation has been a challenge under a cold and dry climate due to slow decomposition. This field study was to use a novel approach to incorporate corn straw into the soil during the fall season with a plastic film cover in an effort to enhance the straw degradation, soil water use efficiency, and corn growth and yield. Two-year field experiments were conducted in northeast China to investigate the effects of four treatments on soil properties and corn growth: (1) straw incorporation with film cover, (2) straw incorporation only, (3) film cover only, and (4) control. Soils and corn plants were collected during the growing season and analyzed for soil temperature and moisture, straw degradation, corn biomass, grain yield, and water use efficiency. Results indicated that straw incorporation with film cover increased grain yield by 53% as compared to straw incorporation only and by 102% to control. The straw decomposition under film cover was 20% faster, significantly higher than that of the straw incorporation treatment. In all cases, soil water content before planting, corn water uptake, and corn water use efficiency under straw incorporation with film cover were significantly higher than straw incorporation and control. Surface film cover resulted in 10-day earlier corn tasseling in compared to treatments without film cover. This field study demonstrated that straw incorporation with film cover would enhance straw degradation in soil, improve soil properties, and increase corn yield and water use efficiency, which could be potentially used as a sustainable soil management practice in northeast China. Full article

Falling film evaporation processes involve high fluid velocities with continuous variations in local film thickness, fluid composition, and viscosity. This contribution presents a parallel and complementary film thickness and concentration mapping distribution in falling films using a non-invasive fluorescence and near-infrared imaging technique. The experiments were performed with a mixture of glycerol/water with a mass fraction from 0 to 0.65 $g_{glyc}{g}_{total}{}^{-1}$ and operating ranges similar to evaporation processes. The measurement system was designed by integrating two optical measurement methods for experimental image analysis. The film thickness was evaluated using a VIS camera and high-power LEDs at 470 nm. The local glycerol concentration $g_{glyc}{g}_{total}{}^{-1}$ was determined using a NIR camera and high-power LEDs at 1050, 1300, 1450 and 1550 nm. A multiwavelength analysis with all NIR wavelengths was implemented with a better correlation for falling films at low flow velocity. The results show an improvement in the analysis of falling films with high flow velocities up to almost 500 mm/s by using only the 1450 nm wavelength and the fluorescence measurement. Simultaneous imaging analysis of film thickness and concentration in falling films provides further insight into understanding mass and heat transport and thus supports the optimization of falling film evaporators. Full article

The closed evaporative cooling tower (CECT) is widely used in the field of industrial cooling. At present, most CECTs still mainly adopt the horizontal-tube falling-film cooling method. In this paper, a novel vertical CECT using 3D deformation tubes is developed. To investigate the vertical surface falling-film evaporative cooling effect of this novel cooling equipment, a traditional horizontal CECT was modified to produce a prototype of vertical non-packing CECT. The cooling performance of the novel vertical CECT has been investigated and compared to the previous traditional horizontal CECT by experimental method. The results show that the convective heat transfer coefficient of the water film outside the tube was increased by 5.87~12.95% and the overall cooling performance was increased by 7.31% on average. This indicates that the cooling load can be increased by changing the traditional horizontal-tube falling-film evaporative cooling method to the vertical falling-film evaporative cooling method. Moreover, the heat flux of the novel vertical CECT decreases by about 7% when the wet bulb temperature increases by 1 °C under the test range of wet bulb temperature, which indicates that the ambient wet bulb temperature has an obvious influence on the cooling load. The research results can provide reference for the optimization design of the CECT. Full article

Liquid nanofilm is used in industrial applications, such as heat exchangers, water desalination systems, heat pumps, distillation systems, cooling systems, and complex engineering systems. The present work focuses on the numerical investigation of the condensation of falling liquid film containing different types of nanoparticles with a low-volume fraction. The nanofluid film falls inside a heat exchanger by mixed convection. The heat exchanger is composed of two parallel vertical plates. One of the plates is wetted and heated, while the other plate is isothermal and dry. The effect of the dispersion of the Cu or Al nanoparticles in the liquid on the heat exchange, mass exchange, and condensation process was analysed. The results showed that the heat transfer was enhanced by the dispersion of the nanoparticles in the water. The copper–water nanofluid presented the highest efficiency compared to the aluminium–water nanofluid and to the basic fluid (pure water) in terms of the heat and mass exchange. Full article

The open spaces of cities have become hostile to citizens due to the high temperatures. Lack of thermal comfort hampers outdoor activities. It is imperative to combat these phenomena to bring life back to the streets and make spaces frequently used in the past more appealing to local citizens. The aim is to mitigate the severity of the outdoor climate to reach comfortable conditions in open spaces. For that, microclimate control based on natural cooling techniques is proposed to recover the habitability of these spaces of the cities. These techniques are characterised via experiments. Demostrando como es posible conseguir and integrated using simulation tools. Following this methodology, it is possible to design, size and define operation strategies for the ideal climate control system according to the type of need. This paper addresses a degraded and unused real space as a case study to demonstrate the feasibility of the methodology used. A system has been designed that stores water cooled at night by using the sky and night air and uses it during the day to produce cold air and cool cover. The experimental results test the efficiency of each solution that has been integrated into the complete system. The system operates every technology to keep the temperature radiant and the air of the occupants cool. For it, falling-film technology cools every night a volume of water below 18 °C and dissipation in a water pond by water sprinkler maintains a pond 10–15 °C below the outside air temperature. Also, results test how it is possible to guarantee thermal comfort conditions (operative temperature below of 28 °C) even when the environment surrounding the conditioned volume is at temperatures above 40 °C, and how the seismic allows maintaining these conditions during the worst summer hours. In conclusion, microclimate control allows for mitigating the severity of the outdoor climate to reach a degree of thermal comfort equivalent to that in enclosed venues. Full article

As one of the effective solutions to recover waste heat, absorption refrigeration systems are used in various industrial or refrigeration places. Flat-plate falling-film absorption is one of the newer types, and the lattice Boltzmann method (LBM) has certain advantages compared with the traditional numerical simulation method. In this work, an LBM is used to analyze flat-plate falling-film absorption. Using the additional calculation of the pressure by the pseudo-force model, a lithium bromide–water working fluid–heat and mass transfer model driven by steam partial pressure is realized. The results show that the turbulence generated in the surface wave has a favorable effect on the absorption process; the degree of turbulence gradually decreases with the increase in the Reynolds number, which weakens the increasing effect of the surface wave on the absorption. When the Reynolds number is moderate, the solitary wave flows forward relative to the front thin liquid film, which promotes concentration and temperature diffusion inside the liquid film and inside the solitary wave. The model of falling-film flow under vibration environment is realized by using the characteristic of imposing inertial force in the model by pseudo-force method. The results show that vibration has a favorable effect on liquid film absorption, increasing the amplitude can increase the gas–liquid contact area and obtain a lower average film thickness, while increasing the vibration frequency can promote the internal diffusion of the solution. Full article