Film Evaporation Research Articles

Insights Into Pool Boiling Heat Transfer on Minichannel Surfaces Through Point and Field Measurements

Abstract In this study, saturated pool boiling experiments were conducted on copper minichannel and flat surfaces at atmospheric pressure using water as the working fluid. The heat transfer performance was assessed through point measurements with a heater block, cartridge heaters, and thermocouples, as well as field measurements using a thin-foil heater and infrared thermography. Two copper minichannel surfaces with square cross sections of 1 mm (minichannel-1) and 2 mm (minichannel-2) side lengths were tested and compared to a flat surface. Minichannel-1 and minichannel-2 enhanced the critical heat flux (CHF) by 17% and 45%, respectively, and improved the heat transfer coefficient by 24–40% and 51–75%, respectively, compared to the flat surface. Minichannel-2 exhibited the lowest and most uniform boiling surface temperature, making it the best performer among the three. There was no significant change in departure frequency among the surfaces, and no significant change in departure diameter for the flat surface and minichannel-1. However, minichannel-2 had lower departure diameters due to its deeper channels, which prevented bubble coalescence and maintained low departure diameters. Additionally, minichannel-2 delayed vapor film formation by breaking it with its deeper fins, thereby improving CHF and slightly enhancing bubble dynamics. The enhancement in boiling heat transfer is primarily attributed to the increased surface area provided by the minichannels, with a minor contribution from improved bubble dynamics. However, the dominant factor in enhancing pool boiling heat transfer on minichannel surfaces is the increase in surface area.

Perfluorohexyloctane ophthalmic solution for dry eye disease: pooled analysis of two phase 3 clinical trials

BackgroundDry eye disease (DED) is commonly caused by excessive tear film evaporation due to Meibomian gland dysfunction (MGD). There is a need for DED treatment options that address tear evaporation and benefit patients across a broad range of demographic and disease characteristics. This study evaluated treatment effects of perfluorohexyloctane ophthalmic drop (formerly NOV03) in the pooled dataset from 2 pivotal clinical trials in patients with DED associated with MGD, both in the overall population and in patient subgroups based on sex, age, and baseline severity of eye dryness.MethodsPooled data from 2 similarly designed, phase 3, randomized controlled trials (GOBI, MOJAVE) were analyzed. Patients aged ≥18 years with DED administered perfluorohexyloctane (n=614) or hypotonic (0.6% solution) saline control (n=603) four times daily for 8 weeks. Primary endpoints were total corneal fluorescein staining (tCFS) score (National Eye Institute scale, 0-15) and eye dryness visual analog scale (VAS) score (0-100). Efficacy was evaluated using analysis of covariance among patient subgroups (male and female, older [≥65 years] and younger [18 to <65 years], tCFS score <7 and ≥7, VAS eye dryness score <70 and ≥70, MGD score <7 and ≥7, Schirmer I test <10 mm and ≥10 mm).ResultsReductions in tCFS and VAS eye dryness scores were greater for perfluorohexyloctane versus control. In the overall patient population, least-squares mean treatment difference was −1.1 (95% CI: −1.41 to −0.79; p<0.0001) for tCFS and −9.0 (95% CI: −11.90 to −6.00; p<0.0001) for VAS eye dryness. Treatment favored perfluorohexyloctane over control in all patient subgroup analyses of tCFS and VAS eye dryness. Overall, the most common adverse event with perfluorohexyloctane was blurred vision (2.1% of patients), which was mild and transient.ConclusionsCompared with a hypotonic saline control, perfluorohexyloctane improved both the signs and symptoms of DED, including in patients with greater self-reported severity of eye dryness.Clinical trial registrationThis study represents an integrated analysis of 2 previous clinical trials: GOBI (ClinicalTrials.gov, NCT04139798) and MOJAVE (ClinicalTrials.gov, NCT04567329).

Universal correlation for falling film evaporation heat transfer coefficients of water and seawater

Universal correlation for falling film evaporation heat transfer coefficients of water and seawater

The Nusselt number of a hot sphere levitated by a volatile pool

When placed at the surface of a volatile liquid, a sphere of hot dense non-volatile material remains suspended until it cools sufficiently. The duration of this ‘inverse Leidenfrost’ phenomenon depends on the Nusselt number $Nu$ of the sphere, itself determined by flow in the film of vapour separating particle and liquid. It is shown that provided the Nusselt number is large, it can be calculated numerically using only the Laplace relation and the equations governing the thin film; patching to a solution for the outer thick film is not necessary. This method is demonstrated by using it to determine $Nu$ for a sphere sufficiently small that in the governing equations, the acceleration due to gravity is negligible except where multiplied by the density of the sphere. Numerical results giving $Nu$ as a function of a dimensionless measure of sphere weight are supplemented with analysis showing that, when the weight is of the order of the maximum supportable by surface tension alone, the film consists of a spherical bubble cap bounded by its contact rim. The solutions for these regions are coupled: although the apparent contact angle $\chi$ for the cap is determined within the rim, its value depends on the flow rate arriving from the cap as well as on the additional evaporation from the rim. The latter acts to reduce $\chi$ from the value it would otherwise have, thereby reducing the thickness of the entire cap. For the example treated here, the value of $Nu$ is doubled by this mechanism.

A Comprehensive Review about Risks of Type-II Diabetes on Ocular Tear Film

Millions of people worldwide suffer from diabetes mellitus (DM), which can lead to systemic issues in a number of organs. Ocular problems, such as dry eye syndrome (DES), are among its less well-known side effects. This review delves into the interactions between diabetes and the composition of tear films, emphasizing alterations in the mucin, aqueous and lipid layer. Dry eye symptoms are exacerbated by induced changes in the components of the tear film in diabetes DM, which lead in decrement in tear production, increment in tear evaporation and tear film instability. Lipid layer is a lubricant, that reduces friction between the ocular surface and the eyelids which promotes high-quality, smooth refractive surface. The lacrimal function unit shields the tear film, preserves the normal function of the ocular surface. The mucin layer is secreted by the conjunctival goblet cells, in hyperglycemia the functionality of the cells are reduced thus, the mucin secretion is also altered which causes instability of the tear film. Diabetic patients can have their tear film integrity assessed with the help of diagnostic methods like Schirmer's Test and Tear Break- Up Time (TBUT). In order to relieve symptoms and maintain ocular health, there should be a complete management of diabetes and the induced tear film disorders.

An Experimental Study of Boiling Heat Transfer and Quench Front Propagation Velocity During Quenching of a Cylinder Rod in Subcooled Water

In this study, a quenching experiment was conducted at atmospheric pressure to investigate the flow and heat-transfer characteristics of cylindrical rods made from SS, FeCrAl, and Zr-4 under various subcooling degrees (ΔTsub). The inverse heat-conduction problem (IHCP) method and image-processing technique were utilized to determine the surface temperature and heat flux, vapor film thickness, and quench front propagation. The results show that smaller solid kρcp and larger ΔTsub result in relatively more efficient quenching boiling heat transfer, thinner vapor film thickness, and greater quench front propagation velocity. The quench front originates at the bottom of the test specimen and becomes progressively larger in velocity with time. It eventually converges with the downward-propagating quench front in the upper middle of the test specimen. Moreover, at the beginning of quench front propagation, the SS and FeCrAl test specimens have a constant velocity region. However, because the Zr-4 test specimen has a small kρcp, the velocities gradually increase from the onset of quench front generation. Furthermore, the measured average quench front velocities are consistent with the experimental datum from the literature. However, the predicted model proposed by Duffey underestimates the propagation velocity due to ignoring the cooling effect of film boiling.

How surface modifications enhance vertical falling film evaporation

How surface modifications enhance vertical falling film evaporation

Abnormalities of the Conjunctiva, Sclera, Cornea, and Anterior Chamber in Pathological Myopia

Pathological myopia is characterized by typical complications in the fundus resulting from the progression of high myopia. These complications include posterior staphyloma, myopic maculopathy, and widespread choroidal atrophy. This review aims to understand the abnormalities of the conjunctiva, sclera, cornea, and anterior chamber associated with pathological myopia.Patients with pathological myopia are found to be more prone to the dry eye syndrome. This condition is explained by increased axial length, increased proptosis, and rapid evaporation of the tear film. Children with allergic conjunctivitis are shown to have a higher risk of developing myopia and that finding is explained with induced retinal inflammation promoting myopia progression. Posterior staphyloma is one of the diagnostic features of pathological myopia, which can lead to the development of myopic maculopathy. It occurs due to changes in the curvature of the sclera. It is challenging to find a direct relationship between pathological myopia and corneal or anterior chamber abnormalities. Besides, searches for components of pathological myopia have not yielded sufficient results. Understanding the anterior segment abnormalities associated with pathological myopia can play a significant role in the treatment and management of the disease. Future researches should focus on the etiology of axial elongation and factors related to the formation of posterior staphyloma. If the pathogenesis of staphylomas can be elucidated, more specific treatment methods may be developed.

Insights into glass surface dynamics from fast scanning calorimetry studies of softening and vaporization of ultrathin molecular films.

Chemical and physical processes on the surfaces of amorphous solids have been the focus of many studies over the past decades. These studies have established that dynamics in a thin layer near a glass surface are often dramatically faster than those in the glass bulk. Nevertheless, recent advances also emphasize the need for new experimental techniques capable of characterizing the structure and dynamics of the near-surface regions in glassy materials at the molecular length scale. Using a quasi-adiabatic fast scanning calorimetry (FSC) technique, we have investigated softening and vaporization of pure amorphous methylbenzene films of moderately heightened kinetic stability with thicknesses ranging from 1 to 20nm. The analysis of the FSC thermograms reveals the existence of a high fictive temperature (liquid-like) layer on the surface of the solid glass with a thickness of 3.5 ± 0.5nm or seven molecular diameters. Furthermore, the width of the boundary between liquid-like and solid layers in the films is less than 1nm. These preliminary findings compliment and substantiate past determinations of the mobile surface layer thicknesses obtained by introduction of nanoparticles or spectroscopic molecular probes to near-surface regions of amorphous samples. The developed FSC methodology will advance the theoretical and computational research by providing calorimetric data on the enhanced interfacial dynamics phenomenon in a variety of low-molecular-weight amorphous materials.

Record-high heat transfer performance of spray cooling on 3D-printed hierarchical micro/nano-structured surface

Managing high-flux waste heat with controllable device working temperature is becoming challenging and critical for the artificial intelligence, communications, electric vehicles, defense and aerospace sectors. Spray cooling, which combines forced convection with phase-change latent heat of working fluids, is promising for high flux heat dissipation. Most of the previous studies on spray cooling enhancement adopted high spray flow rates to strengthen forced convection for high critical heat flux (CHF), leading to a low heat transfer coefficient (HTC). Micro/nanostructured surfaces can enhance boiling, but bubbles inside the structures tend to form a vapor blanket, which can deteriorate heat transfer. This work demonstrates simultaneous enhancement of CHF and HTC in spray cooling by improving both evaporation and liquid film boiling on three-dimensional (3D) ordered hierarchical micro/nano-structured surface. The hierarchical micro/nanostructured surface is designed to coordinate the transport of spray droplets, capillary liquid films, and boiling bubbles to enhance spray cooling performance. Boiling inversion where superheat decreases with increasing heat flux is observed, leading to an ultra-high HTC due to the simultaneous promotion of bubble nucleation and evaporation. Unprecedented CHF is obtained by overcoming the liquid-vapor counterflow, i.e., synergistically facilitating bubble escape and liquid permeation. A record-breaking heat transfer performance of spray cooling is achieved with a maximum heat flux of 1273 W/cm2 and an HTC of 443.7 kW/(m2 K) over a 1 cm2 heating area.

Liquid crystal gel-based acetone sensor using correlated laser speckles

Acetone, a common volatile organic compound (VOC), poses health risks even at low concentrations. Current acetone sensors are costly and require specialized equipment and expertise. This work develops a novel vapor sensor for determining acetone vapor concentration using the speckle patterns generated by liquid crystal gels (LCGs). The vapor sensor comprises a LCG film prepared by the phase separation of a mixture containing polystyrene microspheres and liquid crystals (LCs). The orientation of the LC molecules changes when the LCG film is exposed to an acetone vapor environment, altering the equivalent refractive indices of the LC domains. This leads to a change in the scattering state of the LCG film under laser illumination, forming different speckle patterns. The concentration of acetone vapor is determined by calculating the correlation coefficient of the speckle images, where the sensitivity and limit of detection of the sensor are 4×10-4 ppm-1 and 754.05 ppm, respectively. The developed correlated laser speckle-based optical system is simpler, less expensive, and more stable than traditional LC film vapor sensors. This acetone gas sensor has potential applications in industrial and indoor air quality testing.

Lubrication flow law and cooling mechanism considering cavitation in mechanical seals with Rayleigh step pattern

The purpose of this research is to obtain the cavitation cooling characteristics and flow law in mechanical seals with Rayleigh step pattern. A new cooling approach has been proposed, which is of great significance to preventing liquid film vaporization and limiting thermal deformation of sealing face. Based on the previous literatures focused only on cavitation or viscous heat, the thermohydrodynamic lubrication (THD) and hydrodynamic lubrication (HD) numerical models with cavitation in mechanical seals are developed to obtain the cavitation cooling characteristics and flow mechanism by FLUENT software. The results show that the liquid film cavitation occurs severely in the reverse Rayleigh step and generates a remarkable local cooling effect to the fluid film and sealing faces, which leads to a temperature rise reduction of up to 39.2% and a leakage rate reduction of up to 72.7%. Meanwhile, the high-temperature zone at downstream side migrates upstream, especially, forming temperature valley and peak zones at liquid film rupture and reformation boundaries. The cooling level is controlled by the intensity and area of cavitation. Moreover, the vapor phase block of cavitation, the pressure flow and the shear flow collectively generate a vortex flow behind the cavitation zone in the reverse Rayleigh step. The center and intensity of vortices are closely related to the cavitation area, viscous heat, shear flow and pressure flow. Under THD conditions, the vortex is enhanced due to the viscosity loss and the small cavitation area. The cavitation, viscous heat and vortex flow have important effects on the sealing performance.

On the Multi-Layered Adsorption of Alcanols in the Vicinity of Liquid–Vapor Transition at the Saturated Hydrocarbon–Water Interface

Structure of adsorption layer of long-chain monoatomic alcohols: 1-dodecanol and 1-tetracosanol at the interfaces n-hexane – water and n-hexadecane – water in the vicinity of “liquid – vapor” thermotropic phase transition is investigated by the method of X-ray reflectometry at synchrotron source. Model-independent structural data obtained on the adsorption layers under investigation deviate considerably from the structural parameters which have been proposed previously within a model-based representation and discussed in previous publications on said systems. It is shown that in the low-temperature mesophase the adsorption film consists of a Gibbs monolayer, a transitional liquid region with thickness of two to three monolayers ~50 Å and an extended (wide up to 200 Å) layer of micelles. Presence of a plane of the closest approach of micellar layer to the adsorption film at the interface is established. Transition to the high-temperature mesophase is followed by liquefying and partial evaporation of alcanol film along with observed depletion of micellar layer down to its complete disappearance.

Growth of CuO NPs layers on TiO2 NTs using vacuum thermal evaporation

CuO/TiO2 composites have been reported to exhibit higher potential for various applications (electronics, energy storage, and sensor technology…). This study investigates the impact of different film thicknesses on the properties of CuO NPs on TiO2 NTs. CuO NPs were deposited onto TiO2 NTs using vacuum thermal evaporation, with thicknesses ranging from 5 to 30 nm. A quartz crystal monitor measured evaporation rate and film thickness at a substrate temperature of 350 °C. Following the deposition process, the samples were thermally treated through air annealing at 400 °C for 1 h.XRD analysis showed that all films had an anatase phase. The annealed sample also had a confirmed CuO phase, indicating good crystallinity. Crystallite size and strain varied with film thickness, assessed using the Williamson-Hall method and Rietveld refinement. The deposition and distribution of CuO on TiO2 NTs were verified using Scanning Electron Microscopy (SEM) combined with energy dispersive spectroscopy (EDS). Optimizing the materials nanostructures requires controlling film thickness and annealing. Insights from this study can improve nanomaterial fabrication techniques, which could enhance their performance in technological applications.

Enhanced Peltier refrigerator using an innovative hot-side heat-rejection mechanism; Experimental study under both transient and steady-state conditions

Peltier refrigerators are an environmentally friendly cooling method, as they require no refrigerants and have no moving parts. However, effective cooling requires optimal-strong heat rejection from the hot side of the Peltier module. This research proposes and tests a self-capillary ultra-thin (0.1 mm) water-attracting coated PVC membrane (SCCP) as an innovative effective heat rejection mechanism. The SCCP cools the hot side of the Peltier module to temperatures even lower than ambient air, without external power. The cooling effect is achieved through the evaporation of a thin water film on the hot surface, driven by capillary action, which releases latent heat. This process can occur under natural or forced convection, both of which are investigated under various voltage and temperature conditions. The SCCP method was compared to traditional heatsinks and showed superior performance, with the hot side temperature being not only cooler than that in heatsink mode but also cooler than the ambient temperature in most cases. Additionally, the SCCP method demonstrated reduced sensitivity to ambient temperature changes, with only a 2–3° increase in the hot side temperature when the ambient temperature was raised by 10°. The findings suggest that SCCP is a promising technique, with further results discussed.

Impact of jute covered hemispherical cups on the performance augmentation of a single slope solar still; An experimental investigation

In this article, an experimental endeavour has been reported to enhance the performance of single slope solar still by placing jute-covered hemispherical plastic cups in the water. The logic behind the augmentation is that the jute causes capillary action, due to which a thin film of water forms on the surface of the jute. The plastic cups will act as heat insulation, which will try to block the heat from going to the basin water, hence resulting in heat localization and quick evaporation of thin water film. It has been observed that this adaptation has increased overall distillate output of the single slope solar still by 36.2%. The modified still performs best till 14:00 h due to high solar insolation. In the afternoon hours, the reduction of solar radiation adversely impacts its performance in comparison to the conventional single slope solar still. The overall cost of the distillate due to the augmentation of the jute-covered hemispherical plastic cups has been reduced by 24.34% in comparison to the conventional solar still.

Experimental study on the dynamic behaviors and spreading characteristics of a liquid nitrogen droplet impacting superheated wall

Liquid nitrogen droplets impacting superheated wall is a fundamental phenomenon in liquid nitrogen spray cooling. Its dynamic characteristics directly affect the cooling performance. In this paper, we design and build an experimental setup to investigate a cryogenic liquid nitrogen droplet impacting superheated wall. Using a high-speed camera, we capture the dynamic behaviors of the liquid nitrogen droplet upon impact. The effects of wall temperature and Weber number on the impacting dynamics and spreading characteristics of droplets are studied. The experimental results show that the droplets exhibit six regimes of dynamic behaviors under different wall temperatures and Weber numbers, namely, contact boiling, atomization boiling, film boiling with complete rebound, film boiling with retraction and breakup, film boiling with instantaneous splashing, and film boiling with crown splashing. The Leidenfrost temperature at which film boiling occurs is found to be independent of the Weber number. The spreading characteristics of droplet under different boiling regimes are summarized. During contact boiling, droplet spreading is affected by both wall temperature and Weber number. In contrast, for atomization boiling and film boiling, the spreading is solely affected by the Weber number and is insensitive to the wall temperature. But the underlying mechanisms are different. The former is due to the efficient boiling heat transfer making it insensitive to the wall temperature, while the latter is due to the near thermal isolation caused by the vapor film. Lastly, dimensionless fitting correlations for the maximum spreading coefficient of droplets under different boiling regimes are established. This study can provide guidelines for the design and development of liquid nitrogen spray cooling.

Pharmaceutical development of etodolac transfersomal gel for topical drug delivery system in rheumatoid arthritis

Background: Transferosomes provide delivery of the drug into systemic circulation via the skin as a topical delivery system. So, this study started with the objective of formulating Etodolac transfersomal gel to enhance its skin permeation. Methodology: A total of nine transferosomes (ET-1 to ET-9) containing lecithin, different grades of span and tween, were successfully prepared using a rotary film evaporator. Results and Discussion: After primary evaluation, results were as particle sizes ranged from 222 to 421 nm, zeta potential shows results from –18.50 to –62.53 mV with PDI values 0.254 to 0.303, and the entrapment efficiency (EE%) of Etodolac in the transferosomes ranged from 54.15% to 80.25%. Additionally, the transfersomes formulations were included in carbopol 940 gels (ETC-1 to ETC-9 and EC-0 without transferosomes) and assessed for various characteristics like color, pH, homogeneity, spreadability, viscosity, and in vitro drug release study. Optimized formulation (ET4 and ETC4) underwent further analysis using SEM, TEM, DSC, FTIR, XRD, ex vivo skin permeation, skin irritation and in vivo studies. The in vivo results were compared. % edema inhibition maximum was observed with optimized transfersomal gel formulation (ETC4) as compared to the marketed formulation and plain Carbopol gel when the study was completed after 8 hrs. Conclusion: After this research, it is suggested that Etodolac Transfersomal gel (ETC4) can be considered as an alternate drug carriers system for topical delivery and it could be used to treat Rheumatoid Arthritis

Phase change and fluid transport in porous evaporators

Porous evaporators have become the core component of energy systems such as thermal management of electronic equipment, solar steam power generation, and wet power generation by the advantages of their large specific surface area, high-efficiency heat transfer, and liquid self-transportation. How direct observation of the heat and mass transfer process inside the porous evaporator has always puzzled researchers, resulting in a lack of a theoretical foundation for the optimization of the porous structure. This limitation has significantly hindered improvements in the performance of energy systems. To address this challenge, this study proposes a novel visualization approach that integrates three-dimensional (3D) printing and Indium-Tin Oxide (ITO) glass observation of the phase change region in the evaporator. The key novel findings are that: (1) By controlling the pore size to match the bubble nucleation size, the phase change mode can transition from boiling to thin film evaporation, forming a continuous easy vapor escape channel and enhancing heat transfer. (2) The larger the capillary force of the porous structure, the stronger the locking force at the vapor–liquid interface, which ensured the stability of vapor escape and liquid transport at higher heat flux. (3) An ideal porous evaporator should possess strong liquid locking ability, feature pore structures at the phase change point within the size range of vapor nucleation, and simultaneously exhibit large pore size conducive to vapor escape. This investigation casts a new light on the fluid transport and phase change characteristics of porous evaporators, laying a theoretical foundation for the design of porous evaporators.

A quasi-dimensional model of multiple-cycle fuel film evaporation in a port fuel injection spark-ignition methanol marine engine

For a port fuel injection (PFI) spark-ignition (SI) methanol marine engine, the proportion of residual methanol (Xf) depending on the fuel film evaporation (FFE) plays a crucial role in the fuel-air mixing process, combustion performance and emissions. Therefore, a quantitative assessment method on quasi-steady-state FFE was proposed and implemented to calculate the Xf, which was utilized to develop a novel FFE model aimed at improving the predictability of engine simulation. Then, the impact mechanism of injection timing on the engine's performance and emissions under different intake pressure conditions was revealed utilizing the Xf. Delaying the end of injection timing from −400°CA to −180°CA resulted in an early decrease of Xf, and then began to increase after the Xf reversal point. The shortest combustion duration (CA10-90) and the largest brake thermal efficiency (BTE) were achieved at higher Xf levels. Furthermore, optimizing injection timing could reduce HC and NOx emissions by up to 42.38 % and 48.54 %, respectively, though such adjustments need to be carefully tailored to different loads. Finally, a 1-D engine simulation incorporating the FFE model has been constructed and successfully replicated the effects of fuel film evaporation on engine combustion.