Water Film Evaporation Research Articles

Experimental study on the removal of PM2.5 using modified carbon steel collectors with hydrophilic properties in wet ESPs

Along with the increasingly stringent dust emission concentration standards for the thermal power plants and the challenge of market competition, wet electrostatic precipitators (ESPs) have been widely used as terminal equipment for the flue gas treatment. The wet ESPs pilot test platform using the modified carbon steel collectors with hydrophilic properties was established in this paper and the experimental research on PM2.5 removal characteristics were carried out. The mechanism of the particles removal efficiency enhancement by water film on the surface of modified collectors was studied. The effect of gas temperature, residence time, working voltage, inlet concentration and flushing water flowrate on the particles removal efficiency was investigated. The results indicated that the fibrous layer over the surface of the modified collectors could reduce the effect of the airflow recoil and the electromigration resistance of particles. The surface of the modified collectors could also maintain a uniform and stable water film with a lower amount of water consumption. The water film could restrain the back corona and the re-entrainment of dust. And the evaporation of water film increased the humidity of the flue gas, meanwhile, the particles charge capacity and electromigration velocity increased. Those all could improve the particles removal efficiency. The particles removal efficiency increased with the increase of the flue gas residence time and the applied voltage, but the particles removal efficiency improved less with the increase of the particles inlet concentration and flushing water flow rate after maintaining uniform and stable water film. The modified rigid collector provided high removal efficiency for particles with diameters of 0.04～0.48 μm under lower energy and water consumption. Implications: The wet electrostatic precipitators (ESPs) have been widely used as terminal equipment of the flue gas treatment to purify the flue gas deeply. The surface of the modified carbon steel collectors with hydrophilic properties could maintain a uniform and stable water film with a lower amount of water consumption. The evaporation of water film improved the particle charge capacity and electromigration velocity. The wet ESPs using the modified rigid collector exhibited significantly higher removal efficiency of particles than using the conventional rigid collector especially to the particles with diameter of 0.04～0.48 μm.

Effects of solid/liquid interface on size-dependent specific heat capacity of nanoscale water films: Insight from molecular simulations

The thermophysical properties of an evaporative thin water film that is near the triple line may change because of the effects of size, geometry, interface, temperature, etc. However, the factor-dependence of the properties was seldom considered for the corresponding nanoscale transport phenomena or processes. In this work, the effects of the interface and temperature on the thickness-dependent specific heat capacities of nanoscale water films are investigated by comparing the values of the freestanding film between vacuum, the sessile film on a copper plate, and the confined film between two copper plates. It is found that the specific heat capacities of the thin water films decrease exponentially with reducing thickness, with the confined film having the highest value, followed by the sessile film and the freestanding film, at the same film thickness. The solid/liquid interface presents a substantial impact on the increase in the specific heat capacity, demonstrated by the analysis of density profile, vibration density of state of hydrogen atoms of water molecules, radial distribution function, and interface energy, compared between the films of different types. The analysis of the temperature effect by comparing the vibration densities of state in different regions of the films at different temperatures shows that the temperature has a negligible influence as compared to the size and interface effects. Therefore, the form of a thin water film will greatly affect its thermophysical properties, including specific heat capacity, which should be considered in applications such as evaporation of thin water film, nanoconfinement transfer in membrane, and interface separation of porous media.

Simulating heat and mass transfer processes during water film evaporation in a horizontal channel

This paper is devoted to the numerical study of heat and mass transfer at evaporative cooling of a stream of a moist air in the horizontal channel, taking into account the final thickness of a film of water. Heat and mass transfer simulation is based on solving a system of differential equations for the laminar flow regime of air flow in a two-dimensional setting in the boundary layer approximation. Numerical studies are performed in a wide range of input parameters changes: temperature T0=10÷50 °C, relative humidity φ0 = 0÷100 %, and Reynolds number Re = 50÷2000. The geometric dimensions of the channel are taken for height H = 6 mm and length L = 50H. Calculations are performed at atmospheric pressure.

Heat and mass transfer during water film evaporation in a horizontal channel with a cocurrent flow of moist air

In this paper, we consider the issues of modeling of joint processes of heat and mass transfer during evaporative cooling of a laminar flow of moist air in a flat horizontal channel, taking into account the finite thickness of the water film. Numerical simulation of processes is based on solving the system of differential equations in boundary layer approximation and in two-dimensional formulation. The research is conducted in the range of input parameters: temperature T 0 = 10 ÷ 50 °C, relative humidity φ0 = 0 ÷ 100 %, and Reynolds number Re = 50 ÷ 1000 at atmospheric pressure. The influence of the Reynolds number and relative humidity on the change of local and average thermodynamic and thermohydraulic parameters of flows along the channel length is shown.

The influence of transient evaporation and geometric characteristics on shale gas transmission in inorganic nanopores

Transient evaporation characteristics of water film in inorganic nanopores play an important role in the shale gas storage and transmission. Meanwhile, Inorganic nanopores in shale minerals exhibit complex geometric characteristics. In this work, TESCAN MAIA3 is used to observe the pore shape and size of inorganic nanopores. The pore shapes of rectangular or wedge-shaped are frequently occurred in inorganic nanopores. Water distribution characteristic influenced by surface wettability and disjoining pressure in slit-like nanopores is then analyzed in detail. We divide the water film attached to the surface of the inorganic nanopores into two layers: the high-viscosity water film and the bulk water film. The Moving Mesh Method is used to simulate the evaporation of water film and a mass flow prediction model synthetically considering the pore shape, evaporation, water film slip and layering is established in a single inorganic nanopore. Based on this model, the influence of four different parameters including pressure gradient, water-methane diffusivity coefficient, pore size and wedging coefficient on the shale gas production are investigated. The results show that the presence of water film and its evaporation have significant influence on the production of shale gas. This phenomenon can be interpreted by the increase of pore size caused by evaporation. However, the water film slip and layering have little effect on the shale gas flow rate. With the increase of pressure gradient, the mass flow rate increases significantly. The water-methane diffusion has a considerable influence on the time to reach the steady state. Lower wedging coefficient and larger pore size contribute to higher mass flow rate. Meanwhile, as the wedging coefficient increases from 1.0 to 1.8, the contribution of evaporation increases from 39.34% to 45.33%. Generally, the effective migration space of shale gas directly determines the amount of gas production.

A meshfree analysis of the thermal behaviors of hot surface glass pane subjects to down-flowing water film via smoothed particle hydrodynamics

Glass cooling using water film depends on several parameters such as heat flux, down-flowing velocity, and thickness of water film. The efficiency of glass protection with water film can be significantly enhanced through a proper combination of the fire and water film parameters. This study aims to present an in-depth investigation into the influence of the heat flux, down-flowing velocity and thickness of water film parameters on the thermal behavior of glass panes during a fire and to propose new guidelines to enhance the efficiency of the water film glass protection system. Smoothed particle hydrodynamics (SPH) method is used here to simulate glass cooling with a down-flowing water film. Based on several SPH simulation scenarios of glass cooling at a different fire and water film working conditions, new empirical equations are derived to describe the effects of heat flux, down-flowing velocity, and thickness of water film on the temperature drop in glass and water film. Furthermore, these empirical equations were employed to study the evaporation of water film and to compare the efficiency of the cooling mechanism with different down-flowing velocity and thickness of water film. The simulation results confirm that increasing down-flowing velocity is more efficient in glass cooling than increasing water film thickness.

Using water wall like air humidifier

Abstract This paper presents experimental results of the study of falling water film evaporation from water wall. The contribution is divided into several parts. The introduction is devoted to the theoretical part of the use, then the prototype of the water wall is presented and its most important parts are described. In order to verify the humidification performance of the water wall, experimental verification under laboratory conditions (climate chamber) was chosen. One task for the definition of water wall evaporation potential is to determine and develop the measuring system, which is clearly defined in article. The present document describes the methodology and boundary conditions during experiments. Plate heat exchanger ensured a water temperature in the system approximately 23 °C hot during all measurements. A total of 4 measurements were performed at different air temperatures and relative humidity. The results showed that at different temperatures and relative humidity of air, the water wall has a different humidification performance.

Investigation of water spray evolution process of port water injection and its effect on engine performance

In this study, a 1.5L turbocharged gasoline direct injection (GDI) engine was modified by installing a port water injection (PWI) system adjacent to the intake valve to simulate the “quasi-direct” water injection. Experiments was performed at 1500 rpm wide throttle open (WOT) condition to investigate the effect of PWI on knock suppression, and 4850 rpm WOT condition to test the removal of fuel enrichment through PWI. Then, numerical simulation was conducted to investigate the water spray evolution process and subsequent influence on mixture formation. The experimental results showed that PWI could effectively suppress knock and decrease combustion temperature. Therefore, at 4850 rpm WOT condition, the engine was able to operate at a stoichiometric air/fuel ratio with moderate advancement of spark timing. The combined effect finally resulted in nearly 6% thermal efficiency improvement. At 1500 rpm WOT, 3.8% efficiency gain was achieved solely due to knock mitigation. Nitrogen oxides (NOx), soot and hydrocarbon (HC) emissions also showed a decreasing trend with the increase of water injection amount. The simulation results indicated that about 80% of total injected water collided on the inner surface of the intake port which became the major source of water vapor. The portion of water vaporized in the air is small. Sufficient time was important for intake port water film evaporation. PWI also resulted in in-cylinder wall wetting. The in-cylinder water wall wetting in 4850 rpm was sober than that at 1500 rpm due to stronger intake air motion and higher cylinder temperature. Although port water injection imposes limited impacts on the whole in-cylinder equivalent ratio, it can induce part fuel-rich zones inside the combustion chamber.

Numerical Investigation of Water Film Evaporation with the Countercurrent Air in the Asymmetric Heating Rectangular Channel for Passive Containment Cooling System

Passive containment cooling system (PCCS) is an important passive safety facility in the large advanced pressurized water reactor. Using the physical laws, such as gravity and buoyancy, the water film/air countercurrent flow is formed in the external annular channel to keep inside temperature and pressure below the maximum design values. Due to the large curvature radius of the annular channel, one of the short arc segments is taken out, as a rectangular channel, to analyze the main water film evaporation heat transfer characteristics. Two numerical methods are used to predict the water film evaporative mass flow rate during the heat transfer process in the large-scale rectangular channel with asymmetric heating when the water film temperature is not saturated. At the same time, these numerical simulation results are validated by the experiment which is set up to study water film/air countercurrent flow heat transfer on a vertical back heating plate with 5 m in length and 1.2 m in width. It is shown that the maximum deviation between numerical simulation and experiment is 30%. In addition, the influences on these parameters, such as heat flux, evaporative mass flow rate, and water film thickness, are evaluated under the different tilted angles of the rectangular channel and horizontal plane, water/air inlet flow rates, water/air inlet temperatures, heating surface temperatures, and air inlet relative humidities. All these results can provide a good guidance for the design of PCCS in the future.

Experimental study of wet porous sand layer air-drying characteristics

An experimental study has been carried out to investigate the convective air-drying characteristics of a wet sand layer. The experimental setup allows dynamic measurements of both sand layer weight and temperature, with hot air flowing towards the sand layer surface to ensure a uniform drying of it. Experiments are conducted for a 4 mm thick sand layer for three air temperatures of 45, 60 and 75 °C. The lumped parameter method is used to analyze the sand layer heat transfer. The results show that the sand layer temperature continuously increases throughout the drying process, which can be divided into three stages, i.e. the initial rapid, intermediate slow, and final rapid increase stages. There is no constant temperature stage that is often observed in water film evaporation experiment. The drying process can also be divided into three stages according to the sand layer drying rate variation, they are the increasing, constant, and decreasing rate stages, which roughly correspond to the three temperature rise stages. The lumped parameter analysis result supports that the convective heat from the hot air is used mainly for the water evaporation.

Heat and mass transfer of combined forced convection and thermal radiation within a channel: Entropy generation analysis

The present paper deals with a numerical modelling of thermal and mass transfer coupled by thermal radiation and forced convection in a semi-transparent medium during the evaporation of a thin water film used for wall protection within a channel. Particular attention is paid to the analysis of the entropy generation due to heat transfer and mass diffusion. The governing equations are solved numerically using the Finite Volume Method. Furthermore, the resolution of the Radiative Transfer Equation was carried out by the “Ray-Tracing” method according to a symmetric quadratic scheme of SN (S4) whereas the radiative properties of the non-grey gas were deduced by the application of the “Statistical Narrow Band Correlated-K” (SNB-CK) model. The effect of several parameters on entropy generation due to conduction, thermal radiation and mass diffusion are analysed in this paper. The results clearly demonstrate the major dominance of the wall radiative entropy generation in all the studied cases. The results also prove that for high values of drywall temperature and emissivity, the entropy generation due to mass diffusion augmented.

Mass flow rate prediction of shale gas considering gas diffusion and water film evaporation

The difference between organic and inorganic matters in shale matrix has significantly influence on the transport capacity of shale gas and the total production of shale gas further. Previous studies have demonstrated that the organic pores are hydrophobic and the inorganic pores are hydrophilic. Therefore, the water film can be adsorbed on the walls of the inorganic pores. However, the evaporation of water film in inorganic pore is often overlooked due to the analytical challenge and the effect of the water film evaporation on gas transport capacity is rarely discussed. Thus, it is important to accurately predict mass flow rate of the shale gas through a single nanopore whether it is organic or inorganic. In this article, the mass flow rate prediction model of the organic pore is developed firstly, which considers the interactions of slip flow, gas adsorbed at pore walls, surface diffusion for adsorbed gas and gas diffusing from the kerogen which contains dissolved shale gas in organic pores at nanoscale. This model is then used to investigate the influences of initial pressure, pressure gradient, and thickness of kerogen on the gas mass flow rate. For inorganic pores, the mass flow rate prediction model is developed secondly and the interactions of water film and the evaporation of water film have been considered. The influence of evaporation, initial humidity, water–methane diffusivity is investigated on the gas mass flow rate. Results show that diffusion from kerogen plays an important role in the transport capacity of shale gas. Both higher pressure gradient and thicker kerogen can contribute to higher gas mass flow rate and higher diffusion from kerogen. Higher initial pressure and thicker kerogen can contribute to the lower shale gas desorption. The thicker kerogen can contribute to the higher surface diffusion. The evaporation in inorganic pore should not be ignored, because it impacts gas mass flow rate and can contribute to the higher flow rate. Experimental data was compared with our prediction model, which proves the correctness and validity of our model.

Molecular dynamics simulation on evaporation enhancement of water and aqueous nano-films by the application of alternating electric field

In this work, molecular dynamics simulation has been adopted to investigate the influence of square-wave alternating electric field on the evaporation of pure water and aqueous nano-films. The evaporation of the films with 3360 water molecules and 0, 1.11 and 2.18 mol L−1 NaCl on a hot gold (1 0 0) surface was analyzed. The results showed that both the evaporation of water and aqueous films were enhanced by applying the alternating electric field. Compared with the liquid films at the absence of the electric field, the maximum evaporation rates increased 1.71, 1.70 and 1.66 times for water film and aqueous films with 1.11 and 2.18 mol L−1 NaCl for the frequency of 500 GHz, respectively. The reasons were inferred that the water film subjected to the time-varying electrical force resulted in increasing of the rotational and translational kinetic energy of water molecules. Thus applying the alternating electric field accelerated the temperature rise of the water film and enhanced thermal volume expansion of the water film. In addition, the interaction between water molecules became weaker and the water molecules escaped from the water film more easily. The MD simulation also showed that the evaporation enhancement was more significant for the alternating electric field parallel to the films surface than in the perpendicular direction.

Experimental investigations and analysis of wet porous sand layer air-drying process

Experimental studies have been conducted to investigate the wet porous material convective air-drying characteristics. An experimental setup is designed and constructed to examine the air-drying process of a wet sand layer, and it allows dynamic measurements of both the sand layer weight and temperature. Hot air flows down towards the sand layer upper surface to realize a uniform drying of it and multiple thermocouples are embedded in the sand layer to evaluate its temperature distribution. Experiments are carried out for three sand layer thicknesses of 2, 4 and 8 mm and for three hot air temperatures of 45, 60 and 75 °C. Water film evaporation experiments are also performed to obtain the convective heat and mass transfer coefficients, which are then used for the lumped parameter analysis of the sand layer heat and mass transfer. The results show that in the water film evaporation experiment, the water temperature initially increases and then remains constant at the air wet-bulb temperature for a long period of time until the water all evaporates. In the sand layer drying experiment, however, the sand layer temperature continues to increase throughout the drying process, which can be divided into three stages, i.e. the initial rapid, intermediate slow, and final rapid increase stages. The lumped parameter method is employed to analyze the sand layer heat transfer because of the small sand layer thickness. Such analysis uses the heat transfer coefficient obtained in the water film evaporation experiment and the sand layer temperature increasing rate to calculate the sand layer moisture content and drying rate. The obtained results agree well with the experimental data. The evolution of water film cover fraction on the sand layer upper surface during drying is also discussed by assuming that the water evaporation occurs mainly at the sand layer upper surface at the drying stage at which the sand layer upper surface is fully wet or partly wet.

Deciphering the heat and mass transfer behaviors of staggered tube bundles in a closed wet cooling tower using a 3-D VOF model

This article presents a three-dimensional CFD model to describe the counter-current air-water flow across the staggered tube bundles in a bench-scale closed wet cooling tower by combining VOF multiphase method and SST k-ω turbulence model. The proposed model can investigate the interfacial heat-mass transfer and complex interaction mechanisms among multiple tubes. Through adding the shear force term and water evaporation in the model, the circumferential distribution of the falling film and air humidity fields are obtained, and the effects of the spray density and the air velocity on the falling film flow mode, air humidity, and transfer process are studied. The results show that, the thinnest water film and maximum evaporation rate are obtained when the circumferential angle is 75° and the spray density is 0.048 kg m−1 s−1, respectively; the air Reynolds number has a greater influence on multiphase heat and mass transfers than that of the spray water Reynolds number.

흡수식 냉동기의 증발기에 사용되는 전열촉진관에서 물의 유하 액막 증발 열전달에 대한 실험적 연구

Thin film evaporation of water using enhanced tubes is one of the most common mode of heat transfer in absorption chillers evaporators. Proper design of the evaporators require adequate knowledge of evaporation heat transfer coefficient. In this study, seven enhanced tubes with different enhancement geometries were tested at a saturation temperature of 12℃, 15℃ tube-side water inlet temperature and a film flow rate of . The results indicated that the evaporation heat transfer coefficient of the Floral tube was lower than that of the smooth tube, while the Corrugated tube yielded almost the same heat transfer coefficient as the smooth tube. Notched Floral tube yielded a heat transfer coefficient of 72%, which is higher than that of smooth tube. It was found that Notched geometry was better than the End-cross geometry. Moreover, addition of Floral and Corrugated geometry formations to tubes having threedimensional protrusions, such as Notched or End-cross tubes further enhanced the evaporation heat transfer. As for the overall heat transfer coefficient, which accounts for both evaporation and tube-side heat transfer, End-cross Corrugated tube yielded the highest heat transfer coefficient at 57% as compared to smooth tube.

Interaction of shale gas recovery and moisture transport in post two-phase flowback stage

In the post two-phase flowback stage of shale gas recovery, the residual water in fractures no longer forms a stable continuous flow but mitigates through moisture transport. How this residual water affects gas production is still not clear. This paper studies the motion of this residual water during shale gas recovery. Following three aspects are mainly studied: First, the residual water forms a water film on the surface of fractures and makes Darcy flow in fractures no longer applicable. A new empirical formula for threshold pressure gradient is proposed and directly related to residual water saturation. Second, moisture transports through diffusion, convection and evaporation reaction. Especially, the evaporation of water film depends on surrounding humidity, water activity, and gas flow rate. This evolution of water film is a dynamic equilibrium process and impacts fracture permeability. Third, residual water in matrix interacts with clay minerals to form bonded water. This part of water modifies the Langmuir isotherm adsorption and changes the adsorption capacity of shale gas. Thus the moisture transport significantly affects the shale gas recovery, which should be carefully considered.

Characteristics of the high-temperature water film evaporation with countercurrent turbulent air flow in the duct

Passive containment with high design pressure often has high evaporation temperature. The evaporation mass transfer with high evaporation temperature along with countercurrent turbulent airflow in a long duct was experimentally investigated. The experiments were performed for a wall surface temperature range of 71–90 °C. The experimental data showed that the high evaporation temperature significantly enhanced evaporation. By comparison, it reveals that the significant prediction deviation of the correlation from Kang and Park (Nuclear Engineering and Design, Vol. 204, pp 347–359, 2001) is mainly due to the cubic power modification. HMTA from Huang and Yang (Annals of Nuclear Energy, Vol. 76, pp 237–242, 2015) also underestimates the Sherwood number at high evaporation temperature but it could be applicable when the modification of the wavy interface and the advective mass transfer are included. A modified correlation for falling water film evaporation with high evaporation temperature is finally developed.

Mathematical modeling of ignition of coal-water slurries particles coated with water film

The results of the mathematical modeling of heat and mass transfer processes occurring jointly with ignition of coal-water slurries particles covered with a water film are presented. It is shown that water film thickness can have a significant effect on the ignition dynamics. In addition, it was found out that the main fuel layer is heated to the evaporation temperature during water film evaporation. As a result, following processes of thermal preparation (evaporation of moisture, thermal decomposition) occur faster.

Evaporation of water film in a three-dimensional vertical rectangular channel by laminar mixed convection

This study conducts the numerical analysis of heat and mass transfer with film evaporation by laminar mixed convection in a vertical three-dimensional rectangular channel. Purposely, the study investigates the outcome of inlet dry nitrogen temperature, temperature of wetted wall, Reynolds number and aspect ratio on the heat and mass transfer of thin water film along the isothermal walls. The induced laminar downward flow consists of dry nitrogen and water vapor, which is treated as ideal gases. The thermo-physical properties were connected with the 3-D steady-state and elliptical flow model in view of thin liquid film assumptions. This model’s governing equations are solved by implementing the finite volume approach. Also, the velocity pressure fields are connected by the PISO (Pressure Implicit Split Operator) algorithm. The results, which include velocity, temperature and concentration contours, as well as axial evolutions of Nusselt number and Sherwood number were displayed so as to investigate the results for inlet and wall temperatures, Reynolds numbers and aspect ratios. Besides, the influences of buoyancy forces on developing combined thermo-solutal convection are discussed. For the predominated latent heat transfer, the mass transfer with film evaporation augments the heat transfer along the wetted walls tremendously. The different combinations of the opposing thermal and solutal buoyancy forces bring about various flow structures and the flow reversal will occur when Richardson number is large enough.