Film Evaporation Research Articles

Solid-liquid phase equilibrium relationship of high salt wastewater of coal chemical industry and mechanism of crystallization and scaling process

Crystallization and scaling problem in the process of falling film evaporation was one of the key problems restricting the evaporation process in near-zero discharge of coal chemical wastewater. We studied the phase equilibrium data of the ternary system Na+, Mg2+//Cl--H2O at 303.15–373.15 K. And, the influencing factors of crystallization and scaling were investigated, the flow characteristics of high-salt wastewater descending film were analyzed and the scaling sites were predicted. Results showed the system was a simple ternary system. Both w(NaCl) and w(MgCl2) were linearly correlated with the temperature. The higher MgCl2 contents, the faster rates of crystallization and scaling; temperature and scaling rate showed a positive correlation; the fitted curve of scaling under different roughness was in accordance with y=ax+b. The flow characteristics in evaporation tubes of four high-salt wastewaters (10% NaCl+9, 11% CaCl2, 10% NaCl+9, 11% MgCl2) were simulated. The risk of precipitation scaling was obtained at 591 mm, 667 mm, 772 mm and 938 mm, which was also verified by falling film evaporation experiments. The phase equilibrium relationship was creatively combined with numerical simulation in this paper. Meanwhile, phase equilibrium data was introduced in the study of crystallization and scaling process. This study provided a theoretical basis for the reasonable control of salt scaling in evaporation process of coal chemical industry. It is benefit to ensure the efficient operation of the evaporator, achieve the recycling of inorganic salt products and maximize economic benefits. The goal of "near-zero discharge" would be achieved eventually.

Heat transfer in falling film evaporators during the industrial process of apple juice concentrate production

Heat transfer in falling film evaporators during the industrial process of apple juice concentrate production

Evaluation of Therapeutic Capability of Emustil Drops against Tear Film Complications under Dry Environmental Conditions in Healthy Individuals.

Background and Objectives: Dry eye disease (DED) is a multifactorial ailment of the tears and ocular surface. The purpose of this study was to assess the tear film physiology under controlled dry environmental conditions and compare the efficacy of oil-in-water emulsion drops on tear film parameters in protection and relief treatment modalities under low-humidity conditions. Emustil eye drops were used after exposure to a low-humidity environment in the relief method, whereas, in the protection method, the drops were applied before exposure to low humidity. Materials and Methods: 12 normal male subjects (mean age 34.0 ± 7.0 years) were exposed to ultra-dry environmental conditions. A number of tear film measurements were carried out under desiccating environmental conditions in a controlled environment chamber (CEC), where the chamber temperature sat at 21 °C with a relative humidity (RH) of 5%. Keeler's TearScope Plus and an HIRCAL grid were used to assess the tear break-up time and lipid layer thickness (LLT), and the evaporation rate was evaluated using a Servomed EP3 Evaporimeter. Results: LLT measurements showed that the dry environment affected LLT significantly (p = 0.031). The median grade of LLT dropped from grade 3 (50-70 nm) at 40% RH to grade 2 (13-50 nm) at 5% RH. A significant increase in LLT was seen after both modes of treatment, with a median LLT grade of 3 when the Emustil was used for both protection (p = 0.004) and relief (p = 0.016). The mean tear evaporation rate in normal environmental conditions (40%) was 40.46 ± 11.80 g/m2/h (0.11 µL/min) and increased sharply to 83.77 ± 20.37 g/m2/h (0.25 µL/min) after exposure to the dry environment. A minimal decrease in tear film evaporation rate was seen in relief; however, statistical tests showed that the decrease in tear film evaporation rate was not significant. Mean NITBUT dropped from 13.6 s at 40% RH to 6.6 s at 5% RH (p = 0.002). All NITBUT measurements at 5% RH (with or without the instillation of Emustil) were significantly lower than those at 40%. The instillation of Emustil at 5% RH resulted in a significant improvement in NITBUT for protection (p = 0.016) but this was not the case for relief (p = 0.0.56). Conclusions: A control environmental chamber (CEC) enables the analysis of tear film parameters comparable to those found in dry eye patients. This enables us to examine the capability of oil in emulsion drops to manage tear film disruption in healthy individuals. This study suggests that using Emustil oil-in-water emulsion before exposure to a dry environment should be advocated for people who work in dry environments.

Device‐Scale Nanochannel Evaporator for High Heat Flux Dissipation

AbstractHigh heat flux values in thin film evaporation experiments are typically attained based on short wicking distance, ranging from tens to hundreds of micrometers between the meniscus and the liquid reservoir, thus making such devices vulnerable to quick drying out while also limiting their real‐world applicability. Here, the performance of a nanochannel (122 nm depth and 10 µm width) based evaporator with FC72 is demonstrated as working fluid. FC72 is an ideal fluid for electronics cooling as it is nonpolar and dielectric with a low boiling point. The 1 mm thick evaporator consists of more than 1000 nanochannels connecting two micro‐reservoirs 4.8 cm apart. Thin film evaporation experiments are conducted for four different power inputs, and the steady‐state wicking distance varied from 21 to 8 mm depending on the evaporator's working temperature. Direct weight measurement of evaporated FC72 is used to estimate the interfacial evaporative heat flux. Such a technique mitigates the need for contact angle measurement in micro/nano confined space, a methodology commonly used in literature studies that is prone to error and uncertainties. The maximum evaporative heat flux is 0.93 kW cm−2 at ≈65 °C hot spot temperature. Interestingly, the product of wicking distance and evaporative heat flux remain constant for all power inputs. Numerical simulations are performed to quantify heat loss and effectiveness of the evaporator.

Experimental and computational studies of CCTS material: Novel design of solar cell for high efficiency

This paper focuses on the performance of Cu2CoSnS4 (CCTS)-based solar cell in the context of thin film technology, which has received less attention compared to its CZTS-based counterpart. The research work aims to bridge this knowledge gap by examining the efficiency of CCTS-based cell in an eco-friendly frame. Indeed, it reports on the thermal evaporation of CCTS thin film on glass substrate and numerical simulation of a CCTS-based solar cell using SCAPS 1D software. The basic characteristics of CCTS film are studied by UV–VIS and PL techniques revealing high absorption coefficient of 104 and bandgap energy of 1.4 eV which allow it to absorb a significant portion of the solar spectrum leading to an enhanced photon-to-electricity conversion. The next step suggests the modelling of new photovoltaic structure including such material as absorber: Ag/ZnO/In2S3/CCTS/Pt. The CCTS cell shows a promising conversion efficiency of 14.76% after an overall optimization of buffer and absorber layers. The upgraded efficiency is related to the improvement of short current density to 28.824 mA/cm2 and FF to 63.6% while open-circuit voltage remains unchanged. This positive impact is originated from the reduction of barrier at buffer/absorber interface with the increasing of absorber layer affinity resulting in the fall of cliff-like conduction band offset CBO, accordingly electrons can easily reach the front contact. The obtained values are compared withhigh-efficient solar cells which will motivate the manufacture of a similar device.

Efficient nondoped Deep-Blue electrofluorescence benefiting from structural hindrance and regular C-H···π stacking

Developing a high-performance nondoped deep-blue luminescent material that meets the substantial demand of high-definition organic light-emitting diodes (OLEDs) is significant and challenging. Herein, two highly efficient bar-like pure-blue and deep-blue materials, namely, PIPMePBO and PIPDMePBO, respectively, are designed and synthesized. Rigid planar phenanthroimidazole (PI) and benzoxazole (PBO) moieties are linked to construct a conjugated structure for a regulated aggregation pattern in both single crystals and evaporation films. This approach helps enhance and balance their carrier mobilities for excellent, stable OLED efficiency. Furthermore, different numbers of steric hindrance methyl groups are added to the π-conjugated bridge. This not only avoids potential conjugation quenching and aggregation redshift but also benefits the excited-state constructions for the regulation of blue purity. Results show that the double-methyl-substituted PIPDMePBO, with a moderate charge-transfer excited state, shows nondoped deep-blue electroluminescence with Commission Internationale de l’Eclairage coordinates of (0.156, 0.048). Its maximum luminescence is 12212 cd m−2. Remarkably, the nondoped OLED based on PIPDMePBO exhibits an excellent external quantum efficiency of 8.0%, with an efficiency roll-off of only approximately 12%, even at 10000 cd m−2. These findings are among the best for nondoped deep-blue fluorescent OLEDs with similar light colors.

Analysis of the Distortion of the Bearing Rings after Quenching

Bearings are usually used at high-speed and high-load conditions, so the bearing sleeve must be able to withstand large contact stress, which requires heat treatment. However, during the quenching process of the bearing sleeve, a vapor film is formed on the surface. Since the vapor film is not uniform along the axial direction during the process of boiling and breaking, it will cause uneven distortion of the bearing sleeve. This uneven distortion will cause the outer ring of the bearing to have elliptical distortion after heat treatment. However, the mechanism of this problem and how to reduce the elliptical distortion has not been completely solved. In this paper, two points on the inner wall and outer wall of the bearing sleeve in the orthogonal direction are measured by means of experiments, and the mechanism of the ellipticity distortion during the quenching process is revealed. Additionally, through its horizontal placement, oblique placement, and vertical placement, the cooling curve and cooling rate curve changes in the process of entering the quenching agent are studied; based on the cooling curve, the heat transfer coefficient of the bearing sleeve during quenching is obtained by the heat transfer equation. Input the heat transfer coefficient into the CAE heat treatment simulation software COSMAP, according to the Metallo-Thermo-Mechanics theory and the method of multi-field coupling, simulating the quenching process of GCr15 and 16MnCr5 materials. By comparison, the ellipticity value of the bearing placed at a 45° angle is smaller than that of the horizontally and vertically placed bearings, with the 16MnCr5 material having the smallest ellipticity value of 0.00016. The simulation results verified the distortion mechanism of the bearing sleeve during the quenching process and how to reduce the solution of elliptical distortion.

A numerical study of saturated pool film boiling over a sphere

A detailed numerical investigation of saturated pool film boiling over a sphere is presented in this work. The CLSVOF method was used for capturing the dynamic interface. Computations were performed to study the effect of dimensionless sphere diameter (D/λ0), the dimensionless wall superheat (Jav) and the external gravity field on the interface evolution and the associated heat transfer characteristics. The simulations were performed for D/λ0 varying in the range of 0.5-5.0, while Jav varies in the range of 6.36-19.07 for both normal and reduced gravity field. Under the normal gravity conditions, a periodic vapour bubble ebullition cycle is observed for D/λ0=0.5 and 1.0, whereas a stable vapour column is observed to develop for D/λ0=5.0. The vapour film thickness decreases as the D/λ0 increases for a constant Jav under normal gravity conditions. Furthermore, under the normal gravity conditions, vapour generation is observed to be asymmetrical in the thin vapour film for D/λ0=5.0. For D/λ0=0.5 and 1.0, vapour bubbles are released further downstream of the heated sphere as the dimensionless wall superheat increases under normal gravity. When compared to the normal gravity conditions, the interface evolution pattern changes significantly at low gravity. The space–time averaged Nusselt number is used to quantify the heat transfer in the present work. A Fast Fourier Transform (FFT) analysis of the temporal evolution of the space averaged Nusselt number reveals a complex interplay between different forces for saturated pool film boiling over a sphere for various flow and geometrical conditions.

Anomalously enhanced subcooled flow boiling in superhydrophobic graphene-nanoplatelets-coated microchannels

In boiling heat transfer, superhydrophobic surface is deemed to reduce the critical heat flux (CHF) due to the immediate formation of an insulating vapor film that inhibits effective heat transfer despite its smaller energy barrier for bubble nucleation than that of a superhydrophilic surface. Here, a subcooled flow boiling investigation is carried out in a microchannel heat sink at a low mass flux condition using the superhydrophilic and superhydrophobic graphene nanoplatelets (GNPs) composite coatings. Interestingly, the flow boiling performance of the superhydrophobic GNPs-coated microchannel significantly transcends that of its superhydrophilic counterpart. By benchmarking with the performance of an uncoated microchannel, the CHF and heat transfer coefficient of the superhydrophobic GNPs-coated microchannel are enhanced up to 134% and 135%, respectively. This anomaly is ascribed to the Cassie Baxter-to-Wenzel transition on the superhydrophobic GNPs-coated surface, which is infiltrated with liquid, restricting the nucleating bubbles from expanding into a vapor film and sustaining an efficient boiling. The initial Wenzel state of the superhydrophobic GNPs surface is primarily ascribed to the rapid intercalation of water molecules via the unique graphene nanostructure. This study sheds new light on the unique wetting behavior of graphene-nanostructured surfaces in the context of microscale flow boiling heat transfer.

Field trap effect on pool boiling enhancement in a non-uniform electric field: A numerical study

In this paper, the effect of a non-uniform electric field on pool boiling is investigated by using the pseudopotential lattice Boltzmann model and the leaky dielectric model. The focus of the study is on the field trap effect, which drives bubbles to migrate toward regions with a lower electric field intensity. Relevant results demonstrate that the non-uniform electric field effectively adjusts the distribution of dry and wet areas during boiling. Moreover, the field trap effect significantly delays the onset of film boiling by disrupting the vapor film through non-uniform electric field forces. Further, parameter analysis reveals a linear correlation between the critical heat flux and the electric capillary number (Cae). It is also determined that there exists an optimal electrode length that can achieve the best effect in delaying the Leidenfrost temperature (TL). To maximize the utilization of non-uniform effects in vapor film destruction, the hydrophilic strips are introduced to inhibit bubble coalescence and can further enhance the boiling heat transfer in this way.

Effect of evaporation on the limit of detection of explosive traces by active spectral imaging

When developing methods for standoff detection of explosive traces, an important issue is determination of the limit (minimum) amount of a substance available for detection. This limit depends on the features of the measuring complex realization, on the physicochemical properties of the substance, and on the dynamics of sublimation (evaporation) of the substance from the surface. In this work, we consider the problem of detection limit for a measuring complex based on the method of active spectral imaging. In realization of this method, the distance to the object and the measurement time after the appearance at the surface of a substance imprint are important. How long this trace amount of substance can be detected, taking into account its evaporation? An explosive imprint is a thin layer on a surface (usually considered as a fingerprint with traces of the substance). We theoretically consider the dynamics of the change in the area of this imprint on the basis of a mathematical model of evaporation of a thin layer. Based on mathematical modeling, we can estimate the amount of a specific substance available for detection under the given conditions and the availability time. We identified the main parameters that affect the rate of film evaporation and the range of parameter change and calculated the kinetic parameters of sublimation of thin films of some explosives. The performed calculations allowed us to draw conclusions about the detection limit of substances for the active spectral imaging method depending on the distance to the measurement object and the time after the appearance of a surface trace with an initial surface concentration and area specific to a fingerprint.

Molecular dynamics simulation of the evaporation of thin liquid sodium film on the conical nanostructure surface

Deeply understanding the evaporation of the nanoscale thin liquid film on the nanostructure substrates is significant for further constructing the novel wick structure with nanostructure surfaces, which would be used in the optimal design of the sodium heat pipe. For this purpose, this paper investigates the evaporation of thin liquid film on conical nanostructured surfaces by the molecular dynamics method. A cuboid evaporation system is constructed. It consists of the bottom solid substrate and thin liquid sodium film. A flat solid wall is set as the reference. By changing the nanoscale cone's number and height, five conical nanostructure surfaces are built. The number of gas atoms and the total energy of fluid atoms are observed respectively. The evaporation rate and the average heat flux (q) of six cases are compared. The conical nanostructure suppresses evaporation. With the roughness of the conical nanostructures, the evaporation rate decrement maximum can reach 83% and the q decrement maximum can reach 58%. Based on the thermal resistances in the solid-liquid contact region, the D (Self-diffusion coefficient), and the peak values of RDF (Radial distribution function), the mechanisms of the conical nanostructure surfaces are analyzed. The suppressing effects of the conical nanostructure surfaces are achieved by weakening the heat conduction in the solid-liquid contact region and mitigating the collision heat transfer of liquid atoms.

Improving the performance of indirect evaporative cooler for energy recovery from the perspective of nozzle configuration: A CFD model analysis

As a sustainable cooling technology, indirect evaporative cooling (IEC) has been widely recognized as an effective means of achieving carbon neutrality based on its low energy consumption and high efficiency in central air conditioning (AC) systems of buildings. In contrast to the conventional arrangement, IECs as heat recovery units are often arranged in a diamond shape inside the air handling units (AHUs) of data centers (DCs), an approach that facilitates the flexible use of space and integration within the units in a more compact form. The use of CFD simulations allows an integrated analysis of the coupling of hydrodynamic, thermal and mass properties helps to improve the evaporation performance of IECs. In this study, a 3D simulation model of a diamond-shaped IEC containing the water spray system was developed to compare and analyze the air-water arrangement options in IEC systems currently used in DCs, and the corresponding characteristics are explored from the perspective of CFD techniques to determine the effect of nozzle configurations on the formation and evaporation of water film within the wet channels. Then, parametric analysis of nozzle setup schemes based on performance metrics showed that the nozzle arranged in top-side configuration and paired with the air-water counterflow form had the best performance, with 59.2% and 27.4% improvement in water film coverage area and temperature drop, respectively, over the worst scheme (bottom configuration) at a water supply flow rate of 65 L/s. Finally, the effectiveness of the enhanced approach was simulated and analyzed for hydrophilic and fiber coatings, and it was found that the water film coverage increased by 14.5% and 31.6%, respectively, while the coefficient of performance (COP) increased by 7.4% and 16.1%.

Stability Analysis of Hydrodynamic Mechanical Seals in Multifrequency Excitation

The dynamic characteristics of the complex relationship among the sealing system, excitation, and response have a considerable impact on the operational reliability of hydrodynamic mechanical seals, which is a critical issue in the field of sealing theory and technology. Scholars at home and abroad have established dynamic models and calculated the displacement responses of dynamic and static rings in the time domain based on the force on these rings so that the response results can be used for system stability analysis. Neither are the excitation characteristics of cavitation load extracted, nor are the distance response and system leakage rate of the dynamic and static rings analyzed under coupled cavitation and random excitation. In this study, under different operating conditions of the hydrodynamic mechanical seal system, the liquid film evaporation load and seismic load are applied to study the frequency domain response of the distance between the dynamic and static rings and the system leakage rate. The following conclusions have been obtained: Assuming that the chamber pressure is 0.5 MPa and the spring specific pressure is 0.055 MPa, during stable operation, the distance between the moving and stationary rings at 1500 rpm~3000 rpm speeds is 1.12 μm~3.05 μm. For a specific spring pressure of 0.055 MPa, medium pressures of 0.2 MPa~1.0 MPa, and spindle speeds of 1500 rpm~3000 rpm, the excitation force is 30 N, and the frequency is 30 Hz, And the seismic load is assumed to be sinusoidal, the excitation force is 6 N, the fundamental frequency is 120 Hz, and the system leak rate is in 0.1 mL/min~1.3 mL/min. Under multi-frequency excitation coupling, the distance between the dynamic and static rings will decrease as the pressure of the medium in the sealing cavity increases, and this will increase with the increase in the rotating speed. The leakage rate of the system will increase with the increase in the rotating speed and the pressure of the medium, and the test value is largely consistent with the theoretical value.

An experimental study on quenching of metallic spheres in seawater

Motivated by quenching of melt droplets and debris particles in seawater during a hypothetical severe accident of light water reactors (LWRs), the quenching process of stainless-steel spheres in a seawater pool was investigated in the present study. The polished spheres were pre-heated up to 1000℃ in an induction furnace with inserted atmosphere, and then immersed into the subcooled water pool in a chamber made of transparent quartz. A thermocouple was embedded in the center of the sphere to measure the history of the sphere’s temperature, while a high-speed camera was employed to record the quenching process and vapor film dynamics. Quantitative data, e.g. film thickness and oscillation, of the vapor film evolution during the quenching process were obtained through an image processing program developed on the MATLAB platform.The experimental results indicated that the quenching rate was higher in seawater than in deionized water, and the vapor film collapsed at a temperature higher than the Leidenfrost temperature in deionized water. The trend appeared more significant with increasing subcooling of water. The comparison of the quenched spheres suggested the surface of the sphere in seawater achieved higher degree of discoloration and roughening than that in deionized water, probably due to the additives of salt which change water properties. The image processing and analysis revealed that the vapor film had different thickness profile along the upper and lower hemispheres, and the averaged film thickness was smaller in seawater than in de-ionized water during the stage of stable film boiling. The vapor film was thinning and oscillating with time, and its fluctuations appeared different frequencies and amplitudes at the upper and lower locations, which may explain the mechanism of the earlier collapse of vapor film in the quenching process of a high-temperature sphere in seawater.

Temperature-dependent wicking dynamics and its effects on critical heat flux on micropillar structures in pool boiling heat transfer

Boiling heat transfer is a vital process that needs to be incorporated into next-generation cooling systems due to its high heat transfer performance. The critical heat flux (CHF), which defines boiling performance, needs to be enhanced to expand the operating limits of heat transfer applications. The crucial factor enhancing CHF is wicking performance, i.e., liquid-supply capacity during the boiling process. This study investigated the relationship between wicking performance and CHF enhancement using micropillar structures of various roughness (diameter: 4–20 um and gap: 10–40 um). To measure wicking performance near the boiling condition, we increased the surface temperature from 20 °C to 95 °C. At the highest temperature (95 °C), the D04 G10 sample (i.e., highly-roughness) showed an enhanced wicking coefficient (6.8 mm/s0.5), 48% higher than the value measured at room temperature. For the boiling tests, the D04 G10 sample (∼164 W/cm2) showed a notable CHF enhancement of 85%, compared to the plain surface (∼89 W/cm2), owing to the strong liquid flow induced by wicking, which delayed vapor film formation. Based on these results, we proposed a new CHF correlation that accounts for the wicking performance near the boiling condition, which is accurate within an error of 9% with experimental results.

Effect of composition and structure of In-Te alloy on evaporation property and film of Te

Te (tellurium) film used for semiconductors and photocathode is prepared by a resistive heating evaporation system in this paper. The evaporation property is assessed by comparing the evaporation rate of In-Te alloy with different compositions and structures. The morphology and structure of Te films prepared by In5Te95, In10Te90, and In15Te85 alloy are characterized. The result shows that the In-Te alloy consists of the Te phase and the In2Te5 phase with a hexagonal and monoclinic structure. The primary Te phase and eutectic Te phase are obtained in In5Te95 alloy, and the eutectic Te phase is displayed in In10Te90 and In15Te85 alloy only. The content of Te is 100% in the primary Te phase and eutectic Te phase. Alloying has reduced the evaporation of Te effectively, while the evaporation rate is affected by the distribution of the Te phase. The Te films prepared with three alloys are consisting of the needle-shape Te grain. The Te film deposited from the eutectic Te phase has smaller grain size and the film thickness is affected by the evaporation rate. The composition of Te is confirmed by XPS. The peak value of XPS spectra matches the Te3d5/2 and Te3d3/2.

Enhancing industrial vertical falling film evaporation through modification of heat transfer surfaces – an experimental study

In this study we introduce and experimentally study modifications of heat transfer surfaces as a means to improve the heat transfer in evaporative vertical falling film units. We look at two modified tubular surfaces and compare the obtained results to those acquired using a similar smooth surface. We carry out experiments with two fluids of significantly different viscosities and work with a broad range of industrially relevant operating conditions, with Kapitza (Ka) and Reynolds (Re) numbers in the range of Ka = 500–10 000 and Re = 100–2 000, respectively. We find that the heat transfer rate in a pilot-scale unit can be improved by 50% to more than 100%, depending on geometrical features (e.g. sharpness) of the modified surface. Our results pave the way for increasing the overall efficiency of industrial evaporation plants by increasing the energy intensity of the evaporator per unit area through carefully tailored modifications of heat transfer surfaces.

Janus film evaporator with improved light-trapping and gradient interfacial hydrophilicity toward sustainable solar-driven desalination and purification

Solar-driven desalination and purification offers a promising approach to water treatment, while the clean water yields under natural sunlight can be further increased by developing well-designed evaporators. Herein, a TiN/GO//GO Janus film was fabricated to realize the synergetic effect of effective photothermal conversion and water transportation. The top TiN/GO hybrid layer possesses high solar absorption and thermal conversion efficiency, while the bottom GO layer promotes expeditious water transport. Moreover, the film maintains gradient interfacial hydrophilicity due to the reservation of oxygen-functional groups, which facilitate the formation of thin liquid film at water-film interface and increase heat utilization efficiency. Therefore, the Janus film is demonstrated to possess high evaporation rate of 1.70 kg m−2 h−1 for various non-conventional water resources under 1 solar illumination, which is comparable or better than most of the film evaporators. The excellent durability is demonstrated in a wide acid–base range (pH 2–11) and salinity range (0–250‰) over 30 cycles. The outdoor device with Janus film exhibits daily water yield of 7.44 kg m−2, indicating a potential application in efficient solar-driven desalination and non-conventional water treatment.

An Investigation into the Deterioration of Copper Surface Quality in Plasma Electrolytic Polishing

Plasma electrolytic polishing (PEP) is widely used in the finishing process of metallic parts. Some parts with narrow structures always suffer from surface quality deterioration in the PEP process. In this paper, the deterioration of surface quality was studied to reveal the vapor film evolution mechanism during the polishing. The conditions for the bump defects generation were investigated with the comparison of polished surface morphology under different voltages and immersion depths. The reasons for the bump defects generation were analyzed through the compositions, the chemical states of the elements, and the microstructure of bump defects. The relationship between the current density, the thickness of the vapor film, and the heat to maintain the vapor film was discussed. The vapor film was maintained by Joule heat generated by itself. During the PEP process, excessive current density on the anode surface made the vapor film thickness greater than the critical value of heat could maintain, leading to the collapse of the vapor film. The anode then came into partial contact with the electrolyte, resulting in bump defects. As a result, it is suggested that the thickness of the vapor film be reduced to prevent the surface quality of narrow structures from deteriorating.