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Measurements on heat transfer and critical heat flux of pool boiling cooling of the baseplate of an inverter power module are performed. A refrigerant with low global warming potential, FK-649, is used as coolant. Tests are done for heat fluxes up to 146 kW/m2, with refrigerant saturation temperatures of 36 °C, 41 °C and 46 °C and with refrigerant liquid heights of 1 cm, 6 cm and 17 cm. Both heat transfer rates and critical heat flux increase with increasing saturation temperature. In the range tested, the liquid height had no effect on both the boiling curve and the critical heat flux. The measured boiling curve can be divided in three regions: two regions with a lower slope at heat fluxes just above onset of nucleate boiling and just below the critical heat flux and a region with a higher slope at intermediate heat fluxes. The measured critical heat flux for FK-649 is predicted by the Lienhard-Dhir correlation within 10%. The highest critical heat flux measured is 146 kW/m2, which is lower than the heat fluxes in the most compact power modules. This indicates that methods to increase the critical heat flux are needed for enabling two-phase power module cooling with FK-649. [ABSTRACT FROM AUTHOR]

Ebullition is an important route of methane emission from aquatic ecosystems. Ebullitive CH4 emissions from the wetlands, particularly the mountain wetlands of Eastern Himalayan, are poorly understood. To gain insights into the role of ebullition in CH4 emissions and understand the factors influencing CH4 ebullition, we conducted field measurements of the spatial and temporal variation of ebullition in a freshwater wetland area in floating national park (40 sq. km, 780 m amsl, maximum depth < 4.5) in Northeast India. The average ebullitive CH4 flux ranged from 220.24 to 1889.35 mg m−2 d−1, while the overall CH4 fluxes varied widely ranging from 345.81 to 2240.56 mg m−2 d−1. Methane constituted 90.18% of the gas bubbles produced from the sediment, with CO2 comprising 8.82% of the total sediment gas in the wetland. This suggests that CH4 emission through ebullition plays an important role in transporting biogenic CH4 to the atmosphere. The ebullition rate was markedly higher during summer and lower during winter and exhibited a significant seasonal variation. At a spatial scale, the sites with dense aquatic vegetation growth increase CH4 emission where plants derived autochthonous sediment organic matter, substantiating the supply of carbon substrate for CH4 production. Linear mixed-effect models revealed that water temperature, organic matter, organic carbon and dissolved organic matter are the important factors affecting the ebullitive methane flux. Our results indicate that mountainous wetlands with organic-rich sediments may be potential hotspots for CH4 ebullition. However, the lack of information on these wetlands in the scientific literature emphasizes the need for further research. [ABSTRACT FROM AUTHOR]

Wetlands are active biogeochemical processing sites with conditions that promote carbon storage and the production and release of greenhouse gases (GHGs). Estimates of GHG release from wetlands, including small ponds, are still highly uncertain, and rarely consider diverse pathways of exchange, instead focussing primarily on diffusion. One way to resolve this uncertainty is to quantify and compare multiple pathways of GHG release and to consider specific wetland types. At four natural ponds in the Canadian Prairie Pothole Region (PPR), we investigated four flux pathways (diffusion, ebullition, exposed sediment, and vegetation-mediated) and found distinct differences between pathways for methane (CH4), carbon dioxide (CO2), and nitrous oxide (N2O). The highest magnitude effluxes were via exposed sediment for CO2 and N2O and ebullition for CH4, though ebullition was not the dominant CH4 efflux pathway in two ponds. For pathways with potential for high GHG efflux, we used generalized least squares (GLS) regression to investigate physicochemical predictors. We identified significant relationships between air temperature and exposed sediment fluxes of CO2 and N2O, and between sulphate and dissolved oxygen concentrations and diffusive CH4 fluxes. Water temperature may be linked to ebullitive CH4 fluxes, but this was not statistically significant. This research identifies hotspots and physicochemical predictors for GHG efflux in the first study to directly compare four key flux pathways for PPR ponds, highlighting that processes occurring in different parts of the wetland can greatly outweigh their areal extent. This analysis will inform future work to synthesize and upscale GHG fluxes for these ponds. [ABSTRACT FROM AUTHOR]

Subcooled flow boiling has important applications in cooling systems with high heat fluxes. Additionally, it has higher heat transfer efficiency and better performance in critical heat flux compared to saturated flow boiling. In this paper, subcooled flow boiling heat transfer of deionized (DI) water under varying heat fluxes was investigated experimentally, in a vertical tube with inner and outer diameters of 4.3 and 6.3 mm, respectively. The heat transfer coefficient (HTC) behavior was studied as the flow transitioned from forced convection in a single-phase state to subcooled flow boiling in a two-phase state, ultimately reaching the critical heat flux (CHF). The curve of subcooled flow boiling of deionized water was presented by explaining the heat transfer mechanism in various boiling regions. Investigation of the effects of various parameters, such as mass flux, pressure, subcooled temperature, the length of the heating tube, and output equilibrium vapor quality (Xe), indicated that CHF increased by 42% and 42.7% with increasing mass flux from 689 to 1148 kg m−2 s−1 and pressure from 1 to 3 bar, respectively. Meanwhile, the critical heat flux decreased by 5% and 24.2% with the increase in subcooling temperature and heating tube length, respectively. Moreover, increasing the mass flux, absolute pressure, and subcooling temperature enhanced the behavior of the heat transfer coefficient. However, as the length of the test section tube increased, the HTC decreased. [ABSTRACT FROM AUTHOR]

R134a was recognized as probably one of the most important refrigerants of the two past decades. Among the proposed alternative fluids, there are certainly isobutane (R600a) and R152a. This article presents about 200 new heat transfer coefficient and pressure drop data obtained during flow boiling of R152a and R600a inside a smooth copper tube having an internal diameter of 4 mm. Three saturation temperatures were considered for each refrigerant, from 5 °C to 20 °C. Furthermore, for each temperature studied, the heat flux was varied between 15 and 30 kW m−2 and the refrigerant mass flux from 100 to 400 kg m−2 s−1. After presenting the new data, a critical comparison was proposed between the performance of these refrigerants and R134a. Finally, some classic correlations available in the literature have been implemented. The deviations between the calculated and experimental values were reported and commented. [ABSTRACT FROM AUTHOR]

Compared with the traditional mechanical knitting needle, the tubular magnetic suspension knitting needle has the advantages of no friction and flexible control. But the highspeed reciprocating motion of the needle needs to consume a lot of power. The winding temperature is difficult to suppress. The heat dissipation performance becomes the main obstacle restricting the power improvement. In this paper, an integral tubular electric knitting needle is proposed and studied. The heat dissipation area of the needle is increased by the annular thermosyphon in the motor housing. The heat dissipation performance is carefully studied by experiments, and the results show that the heat dissipation performance is obviously improved compared with the original design. Under the power of 17 W, after the annulus thermosyphon is started, the maximum temperature of the winding can be suppressed at about 107 °C. Boiling occurs only at certain points on the surface of the winding, which is related to the structural asymmetry in the winding manufacturing and epoxy injection processes. The heat dissipation performance is best when the winding is located at the bottom of the motor. The axial temperature difference is within 15 °C while the circumferential temperature difference is within 4 °C. [ABSTRACT FROM AUTHOR]

Heat exchange on a heat-stressed surface and the critical heat flow from it in the process of cooling this surface by a system of distributed impact submerged microjets of a dielectric liquid, depending on the velocity of these jets, were investigated experimentally for the case where the initial subcooling of the liquid in the jets to the saturation temperature comprises 40 ± 2°C. The experiments were conducted for 36 jets of the HFE-7100 dielectric liquid with an initial diameter of 174 μm, outflowing from the nozzles positioned at a distance of 1 mm from a cooling surface. It was established that the heat transfer coefficients of this surface and the critical heat flow from it are determined by the velocity of the jets, acting on the surface, and the initial subcooling of the cooling liquid, and that they are much larger than those in the case of pool boiling of the cooling liquid on the surface and in the case of its cooling by a single jet of a liquid with a small subcooling to the saturation temperature. [ABSTRACT FROM AUTHOR]

The effect of biphilic surfaces on subcooled flow boiling in a horizontal rectangular duct was investigated. Biphilic surfaces were created on an aluminum alloy substrate in the form of juxtaposed Hydrophobic (HPo) and Hydrophilic (HPi) transverse strips. In this regard, two different testing samples with strip widths of 10 and 18 mm were prepared, named pattern I and pattern II, respectively. Using Deionized Water (DIW), the experiments were performed with the two mentioned biphilic patterns and a plain surface. Finally, different cases were compared, and the results were interpreted. The results showed that the biphilic surfaces improve the Heat Transfer Coefficient (HTC) and cause boiling to be initiated at a lower wall temperature. In this regard, pattern I and pattern II represent 22 and 40% improvement in HTC, and boiling initiates 31 and 33.5 °C sooner compared to the plain surface, respectively. In addition, the experiments were also conducted with an Ethylene Glycol/Water mixture (EG/W) in the same manner. The results revealed that EG/W represents smaller HTC values for all cases and shifts the boiling points to higher wall temperatures compared to DIW. It is worth mentioning that the major amount of this HTC reduction is occurred in the single-phase area, in lower wall temperatures. [ABSTRACT FROM AUTHOR]

Ebullition transports large amounts of the potent greenhouse gas methane (CH 4 ) from aquatic sediments to the atmosphere. River beds are a main source of biogenic CH 4 , but emission estimates and the relative contribution of ebullition as a transport pathway are poorly constrained. This study meets a need for more direct measurements with a whole-year data set on CH 4 ebullition from a small stream in southern Germany. Four gas traps were installed in a cross section in a river bend, representing different bed substrates between undercut and slip-off slope. For a comparison, diffusive fluxes were estimated from concentration gradients in the sediment and from measurements of dissolved CH 4 in the surface water. The data revealed highest activity with gas fluxes above 1000 ml m - 2 d - 1 in the center of the stream, sustained ebullition during winter, and a larger contribution of ebullitive compared to diffusive CH 4 fluxes. Increased gas fluxes from the center of the river may be connected to greater exchange with the surface water, thus increased carbon and nutrient supply, and a higher sediment permeability for gas bubbles. By using stable isotope fractionation, we estimated that 12-44% of the CH 4 transported diffusively was oxidized. Predictors like temperature, air pressure drop, discharge, or precipitation could not or only poorly explain temporal variations of ebullitive CH 4 fluxes. [ABSTRACT FROM AUTHOR]

A microwave discharge inside of a methane bubble in boiling water is modeled in a 0D approximation taking into account the change in the size of the plasma bubble. The process of quenching the reaction products after the bubble detaches from the electrode surface is also simulated. The working pressure is 1 atm. It is shown that the main reaction products are H2, CO2, and CO. The ratio of CO2 and CO concentrations depends on the ratio of the initial flows of water vapor and methane. The calculated concentrations of the main decomposition products of methane and water are in good agreement with experimental data. [ABSTRACT FROM AUTHOR]

Liver fibrosis is a hallmark of chronic liver disease which could lead to liver cirrhosis or liver cancer. However, there is currently lack of a direct treatment for liver fibrosis. Boiling histotripsy (BH) is an emerging non-invasive high-intensity focused ultrasound technique that can be employed to mechanically destruct solid tumour at the focus via acoustic cavitation without significant adverse effect on surrounding tissue. Here, we investigated whether BH can mechanically fractionate liver fibrotic tissue thereby exhibiting an anti-fibrotic effect in an animal model of liver fibrosis. BH-treated penumbra and its identical lobe showed reduced liver fibrosis, accompanied by increased hepatocyte specific marker expression, compared to the BH-untreated lobe. Furthermore, BH treatment improved serological liver function markers without notable adverse effects. The ability of BH to reduce fibrosis and promote liver regeneration in liver fibrotic tissue suggests that BH could potentially be an effective and reliable therapeutic approach against liver fibrosis. [ABSTRACT FROM AUTHOR]

This work conducts a numerical investigation of water jet impingement cooling during the steel quenching process. Although much of the simulation work in the literature relies on two-dimensional analyses, this study developed a three-dimensional CFD simulation model using Ansys-Fluent. The Eulerian mixture formulation with the volume of fluid (VOF) method was employed. It is shown that the developed model accurately simulates the boiling behavior in impingement cooling using circular water jets. The main parameters used in the simulation were: initial surface temperature of 700 °C, and jet velocity of 0.4 m / s impinging from a nozzle at 8 m m height from the heated surface. The 3D mesh has been refined in a way to maintain a y + value of 1 at the heated surface to capture the physics on the surface and to ensure that the viscous boundary layer is captured. Results such as temperature drop, boiling curve, and bubble frequency were presented and verified with the available experimental work in the literature. The developed mixture simulation using Ansys-Fluent has demonstrated its capability to numerically simulate the temperature history and boiling curves in the impingement process. This advancement will facilitate the study of numerous industrial parameters that are challenging to investigate experimentally. [ABSTRACT FROM AUTHOR]

High heat flux devices necessitate efficient heat dissipation systems, with pool boiling emerging as a promising method. Leveraging advancements in nanoscience, this study investigates the enhancement of heater surface characteristics for pool boiling through experimental means. Three bare copper surfaces are coated with a hybrid nanofluid comprising copper-based carboxylic functionalized multi-walled carbon nanotubes and distilled water at concentrations of 0.3, 0.6, and 1.0 mass% using the spin coating technique. Contact angle measurements reveal superhydrophilicity across all surfaces, ranging from 14° to 7°. The 1.0 mass% coated surface exhibits significant improvements in boiling heat transfer coefficient and critical heat flux, reaching 143 W m−2 K−1 and 2206 W m−2 K−1, respectively, representing increments of 324% and 204%. Visualization of bubble dynamics demonstrates enhanced surface roughness and active nucleation sites, leading to early bubble detachment under low heat flux conditions. Bubble sizes ranging from 0.6 to 1.6 mm indicate smaller diameters compared to bare copper surfaces, facilitating rapid heat dissipation due to more nucleation sites and proper nanofluid adhesion. The microporous surfaces prepared exhibit exceptional performance, offering potential applications in boilers, heat pipes, and various heat transfer systems. [ABSTRACT FROM AUTHOR]

This study investigates the vapor chemical composition, during the melting step of an electron beam powder bed fusion process using Ti–6Al–4V powder. A phenomenological model is proposed to analyze and discuss the vapor composition. The model focus on the heat dissipation of the molten powder. Vapor stream from the molten powder is compounded by vapor saturation pressure and rapid boiling (ebullition) of the molten pool. The model is based on post mortem results of condensed vapor (thin film), which were analyzed by X-ray photoelectron spectroscopy and glow discharge optical emission spectrometry, providing quantitative and in-depth profile data. It was found that the ratio of [Al] to [Ti] in the vapor stream is influenced by the melting conditions. As the e-beam current increases, the heat dissipation reaches the ebullition domains, and the [Al]/[Ti] ratio tends to the molar ratio of the precursor powder (Ti–6Al–4V), indicating the complete overheating of all the alloy elements. [ABSTRACT FROM AUTHOR]

In this study, pool boiling experiments were conducted using carbon nanotubes (CNTs)-Cu nanoparticle-coated porous surfaces. Applying a layer of CNTs-Cu nanoparticles on boiling surfaces resulted in the formation of porous structures, which led to a rise in the quantity of active nucleation sites. We fabricated three coated boiling test sections, namely 0.1CNTs-99.9Cu, 0.2CNTs-99.8Cu, and 0.3CNTs-99.7Cu in weight percentages. A bare copper surface and a surface coated only with Cu particles were tested as benchmarks. Distilled water was used in the pool boiling experiments. To investigate the bubble dynamics, a high-speed camera was employed, while scanning electron microscopy was utilized to analyze the morphologies of the surfaces that were coated. The objective of this research was to elucidate the impact of varying CNTs content on boiling inversion and pool boiling efficiency. Findings indicated that an increased content of CNTs improved the boiling heat transfer coefficient, with boiling inversions observed on the porous coated surfaces. [ABSTRACT FROM AUTHOR]

This study presents the pool boiling heat transfer performance of R-513A, a low-GWP alternative to R-134a, on a smooth tube at various saturation temperatures. The tests were carried out in the heat flux range of 10 to 90 kW/m2. The experimental results show that at low heat flux q ″ ≤ 30 kW/m2, the heat transfer coefficient (HTC) of R-513A is equivalent to R-134a, while at heat flux 30 ≥ q ″ ≥ 90 kW/m2, the average HTC of R-513A is nearly 14% lower than that of R-134a irrespective of all the saturation temperatures. While the average HTC of pure R-513A is nearly 13% higher than that of R-1234ze(E). Further, the HTC of R-513A is compared with other similar alternative low GWP refrigerants R-1234yf, R-1234ze(E), and R-450A. According to the literature review, R-513A and R-1234yf perform almost equally well in terms of heat transfer during pool boiling. Depending on the boiling surface and testing setup, R-1234yf's pool boiling heat transfer performance is either less than or equal to R-134a. [ABSTRACT FROM AUTHOR]

The influence of surface adhesion between the electrodeposited coating and the base material prepared by different modes of electrodeposition on pool boiling heat transfer is presented here. Electrodeposition modes, namely one-step, two-step, six-step, and inverted one-step, were applied to prepare the surface-modified copper substrate aimed at creating a microporous copper network. By implementing these methods, the copper deposit laden with numerous micropores and nano-dendrites that acts as nucleation sites for bubble generation. Among all the specimens, the sample prepared at the 1500 s of two-step deposition time reported the maximum heat transfer coefficient (h) and lowest wall superheat. The enhancement reported in all the cases was attributed to the substantial nucleation site density, interconnectivity among micropores, and superior adhesion between substrate and coating. The two-step electrodeposition time, the number of steps involved in electrodeposition, and the inverted one-step current density significantly affect the coating-base substrate adhesion, which guided for enhancement in pool boiling heat transfer. The synergic coordination between all these parameters is crucial for its ability to enhance pool boiling heat transfer. [ABSTRACT FROM AUTHOR]

Boiling is a phase change heat transfer process that transfers latent heat quickly, making it suitable for use in various heat transfer systems. An important worry for the boiling performance degradation is the durability of the artificial nano-/microporous interfaces concerning the bottom surface. This study therefore proposes a novel three-step surface creation process (chemical etching, electroplating, and sintering process). Wet/chemical etching is first used to form three distinct micro/nanostructured substrates (ES#1, 2, 3). The most effective etched substrate (ES#3) is again employed as a cathode for the electrochemical depositing process or next-of-surface manufacturing. To strengthen the link between the etched layer (ES#3) and the surface of the coating (copper-alumina), the electroplating produced substrate (ES#4) is sintered in a predetermined environment. The enhanced boiling efficiency obtained on ES#4 is attributable to the appropriate bonding among ES#3 and electroplated nanoparticles (Cu-Al2O3). By maintaining a consistent temperature across the heater's topmost layer and the fin tip, the reduction in resistance at the intermediate level brought on by appropriate binding increases the rate of heat transfer. The critical heat flux (CHF) and heat transfer coefficient (HTC) improvements for ES#4 over bare copper are 184% and 216%, respectively. Additionally, the impact of certain macro- and micro-scale restrictions on the occurrence of flow boiling heat transfer is examined. The ES#4 surface showed better stability during repeated thirty testing cycles, as seen by the much smaller decline in superheat temperatures (1.2 °C) and wettability (32° to 33.7°). [ABSTRACT FROM AUTHOR]

The effects of boiling water treatment on the physical properties of Quercus variabilis virgin cork (Qv VC) were examined and compared with those of Quercus suber reproduction cork (Qs RC). The water treatment was conducted at 100 °C for 1 h. Qv VC showed a significantly higher dimensional change in the three directions and lower weight loss than Qs RC by boiling water treatment. Untreated and boiled Qv VC showed higher density, air-dried moisture content, red/green (a*) and yellow/blue (b*) chromaticity, overall color change, shrinkage in all three directions, moisture adsorption on the entire surface, and swelling per 1% moisture content than untreated and boiled Qs RC. However, the lightness (L*) and water absorption on each surface were higher for Qs RC than for Qv VC. Moisture adsorption on each surface was comparable before and after heat treatment for both species. After boiling water treatment, the air-dried moisture content, dimensions, volume shrinkage, water absorption, and moisture adsorption on each surface and the entire surface increased, whereas L*, a*, b*, and swelling per 1% moisture content decreased. The results of the present study could be useful for further utilization of Qv cork growing in Korea. [ABSTRACT FROM AUTHOR]

We present the results of a pilot study demonstrating the feasibility of non-invasive non-thermal disintegration of human mucinous carcinoma of the breast ex vivo using sequences of high-intensity focused ultrasound pulses in boiling histotripsy regimen. The target volume was sonicated by focusing ultrasound pulses (n=20) of 1.5 MHz frequency, 10-msec duration and 1-sec pulse repetition period, 517 W acoustic power within the pulse, and 103 MPa shock front amplitude at the focus into each node of a volumetric grid 4×4×1 mm. Sonication was visualized and controlled using B-mode ultrasound imaging, total time of the treatment was 21 min. Histological hematoxylin and eosin and Masson's trichrome staining revealed the absence of tumor elements in the treated region confirming destruction of cancer cells and their nuclei after boiling histotripsy procedure. [ABSTRACT FROM AUTHOR]

A detailed study at the microscopic level of the transient behavior of boiling phenomena during quenching of an AISI 304 stainless steel, conical-end, cylindrical probe in flowing water at 60 °C was conducted using high-speed video recordings and cooling curve data acquisition. Two free-stream velocities (0.2 and 0.6 m/s) and two initial probe temperatures (850 and 950 °C) were investigated. It was complemented by video recordings at 60 fps to calculate the wetting front velocity. Surface heat flux histories at the thermocouple positions were estimated by solving the corresponding Inverse Heat Conduction Problem. As the water velocity increases the duration of the vapor film at each thermocouple position shortens and the difference among cooling curves at the thermocouple positions decreases. Increasing the initial temperature increases the duration of the vapor film stage. The wetting front velocity increased from 4 to 6 m/s. The time to reach the maximum surface heat flux at the position of the thermocouple closest to the probe tip ranged from 9.7 to 18 s. Undulations at the vapor-liquid interface that appear periodically and propagate in the direction of quenchant flow were observed early during the vapor film stage. Later, before the collapse of the vapor film, a kind of a shock wave was generated at the probe tip which modified the appearance of the film. Once the Leidenfrost temperature is reached, a wetting front (which consists of many small bubbles that coalesce rapidly in a very small area) is formed and travels in the direction of quenchant flow while fewer and larger bubbles nucleate and grow upstream. The nucleation, growth and detachment of the larger bubbles was studied; as the free-stream velocity decreases larger values of bubble maximum diameter and half-life time were observed, while the initial temperature has a marginal effect on these quantities. [ABSTRACT FROM AUTHOR]

This study investigates the comparative analysis performance of three environmentally friendly refrigerants, R1270, R290, and R600a, in the context of flow boiling heat transfer (FBHT) and pressure gradients. The experiments employ copper microfin and smooth tubes, operating under varying conditions, including saturation temperatures (Tsat) of 6 and 15 °C, heat fluxes (HF) ranging from 13 to 30 kW.m−2, mass fluxes (MF) spanning 187 to 427 kg.m−2.s−1, and vapor quality from 0.1 to 1.0. Both tube types share identical dimensions - an outer diameter, inner diameter, and length of 7 mm, 6.14 mm, and 500 mm, respectively - facilitating a focused investigation into the impact of microfins on flow boiling characteristics. The results highlight noteworthy differences among the refrigerants, with the microfin tube exhibiting substantial enhancements in heat transfer coefficient (HTC), particularly pronounced with R1270 and R290. At the same time, the R600a demonstrates more HTC improvements than the smooth tube. Additionally, the microfin tube increases pressure gradients. The average enhancement factor (EF) for R600a, R290, and R1270 are 2.15, 1.95, and 1.9, respectively, while the average penalty factor (PF) for R600a, R290, and R1270 are 1.25, 1.3, and 1.35, respectively. Comparative analyses with established literature correlations validate the experimental findings. [ABSTRACT FROM AUTHOR]

The recent advances in the growth of heat dissipation from microelectronic devices have led to the two-phase heat transfer method via nucleate boiling for better thermal management. In this study, the effect of surface wettability on the saturated pool boiling heat transfer performance is examined with deionized water. Three types of wettability surfaces are compared, i.e., superhydrophilic (SHPi), hydrophilic (HPi) and hydrophobic (HPo) surfaces. The SHPi surface is prepared by anodic oxidation of the copper surface, while the HPi and HPo surface is prepared by coating Cu–TiO2 and Cu–MWCNTs, respectively, on the copper surface using the electrochemical deposition method. The earliest incipience of nucleate boiling was observed with the HPo surface, while a most delayed onset of nucleation was obtained for the SHPi surface. The critical heat flux is found to be 1012 kW·m−2, 1251 kW·m−2, 1490 kW·m−2 and 1610 kW·m−2 corresponding to the plane copper, HPo, HPi and SHPi surfaces following the ascending order. The improved rewetting of the arid area underneath the formed vapour bubble caused a delay in the dry-out occurrence and resulted in a maximum critical heat flux for the SHPi surface. The maximum heat transfer coefficient of 88.42 kW·m−2·K−1, 64.7 kW·m−2·K−1 and 59.19 kW·m−2·K−1 have been observed for the HPi, HPo and SHPi surfaces, respectively, which translates to an increment of 60.2 %, 17.23 % and 7.25 %, respectively, as compared to plain surface. The SHPi surface induces the rightward shifting of the boiling curve as compared to the plane surface, which gives a lower heat transfer coefficient for a particular heat flux. [ABSTRACT FROM AUTHOR]

New linear hydrazinocarbonothioyl derivatives of maleopimarimides were synthesized in high yields by the interaction of acyl isothiocyanates of 2-allyl- and 2-benzylmaleopimarimides with acetohydrazide and hydrazide of 4-methoxybenzoic acid. 1,3,4-Thiadiazole derivatives were synthesized by boiling hydrazinocarbonothioyl derivatives of maleopimarimides with a catalytic amount of concentrated H2SO4 in ethanol. The structure of the synthesized compounds was determined using 1H,13C NMR, 1H–13C HSQC, 1H–13C HMBC, COSY, NOESY, and 1H-15N HMBC spectroscopy methods. [ABSTRACT FROM AUTHOR]

The paper considers the fragmentation of fluid films and, in particular, the used similarity numbers that characterize the process of fragmentation. Based on the analysis of a previously proposed mathematical model for a rotating fluid film evaporating in the Leidenfrost regime, the Sf criterion is proposed. It represents the relationship between the pressing inertial mass force acting on the fluid film and the dynamic effect of vapor from the heating wall. [ABSTRACT FROM AUTHOR]

Previous studies have demonstrated that altering the surface structure can enhance heat transfer. In this study, a square micropillar array with a homogeneous structure was designed for a long rectangular channel with a hydrodynamic diameter of 10 mm. Deionized water and HFE-7100 were used as working fluids for the study. The effect of flow rate and subcooling degree on flow boiling heat transfer performance is discussed. The bubble behavior of two different media was compared by visualization experiments. The results show that the square microcolumn array will delay the ONB point by increasing the heat transfer area and disturbing the main fluid, and improve the overall boiling heat transfer performance by 2–3 times. It was found that HFE-7100 boils better under low heat flow density, but its stable nuclear boiling time is shorter. Furthermore, the effects of volume flow and subcooling on heat transfer performance vary significantly at different stages of the boiling process. Before the ONB point, an increase in volume flow will increase the heat current density by 88.9% and reduce the boiling heat transfer stability. After the ONB point, the effect of fluid flow on the boiling process weakens. [ABSTRACT FROM AUTHOR]

This study aims to investigate the advantage of using flash boiling atomization as a new method of feedstock injection in suspension plasma spraying (SPS) and compare the results with continuous jet injection at ambient temperature that is currently used in SPS. In conventional methods, clogging is the main obstacle for the injection of suspension with concentrations beyond 40 wt.%. In this work, we demonstrate that flash boiling atomization enables the injection of suspensions with solid concentrations up to 70 wt.%. The chosen suspension was water based, and the average diameter for the dispersed titania particles was 500 nm. Coating characterization, phase composition, deposition efficiency, deposition rate and thickness per pass were investigated for different suspension concentrations. It was shown that using suspensions with high solid contents leads to a significantly higher deposition weight per pass and thickness per pass and results in a different coating microstructure. [ABSTRACT FROM AUTHOR]

The transportation of quick latent heat during phase change heat transfer (boiling) guides its prospective application in various heat transfer devices. The stability of the fabricated cavity/porous surfaces with the base substrate is a significant concern for the degradation of boiling performance. Therefore, a new three-step surface fabrication method (wet etching, electrochemical deposition, and sintering) is proposed in this work. Initially, the three micro/nanostructured surfaces (ES#3, ES#2, and ES#1) are fabricated by using wet/chemical etching. The best-performing wet/chemical etching surface (ES#3) is further used as a cathode for next-of-surface fabrication, i.e., electrochemical deposition. The electrochemically deposited surface (ES#4) is sintered in a predefined atmosphere to increase the bonding between the coated surface (copper-alumina) and the etching surface (ES#3). The higher boiling performance found on the final surface (ES#4) is due to the proper bonding between the ES#3 and electrodeposited copper-alumina nanoparticles. A decrease in the intermediate resistance due to proper binding boosts the percentage of heat transmission by keeping the temperature constant between the top surface of the heater and the tip of the fin. For ES#4, the critical heat flux (CHF) improvement over bare copper is 98%. Comparing the ES#4 coated surface to the bare copper surface results in a 260% increase in heat transfer coefficient (HTC). The effect of various macro and micro-scale constraints on pool boiling heat transfer phenomena is also investigated. Following multiple testing cycles, the decrease in superheat temperatures, surface morphology, and wettability for ES#4 is significantly lower, which indicates healthier stability of ES#4 surface. [ABSTRACT FROM AUTHOR]

Ultrasonic field and rib surfaces are very important factors that affect the thermal performance in pool boiling. The paper has investigated the significance testing of thermal performance of the rib arrangement, the distance of ultrasonic field and the ultrasonic power in pool boiling with ultrasonic field and ribs surfaces by the orthogonal experiment. The deionized water is used as the working coolant. Then, the synergistic heat transfers and bubble motion characteristics in pool boiling are carried out at different rib arrangement, distance of ultrasonic field and the ultrasonic power by the single factor experiment. It is obtained that, compared with the single heat transfer technology of rib surface or ultrasonic field in the pool boiling, the thermal performance of compound heat transfer enhancement can be improved more significantly by combining the rib surfaces and ultrasonic field as a result of the expanded areas of heat exchange surface of rib and the cavitation effect and acoustic streaming effect of the ultrasonic field. The most significant affecting factor on the thermal performance is the rib arrangement, followed by ultrasonic power and distance of ultrasonic field. The increasing rate of heat transfer coefficient (HTC) of the best optimal scheme combination A3B3C1 with the rib arrangement of Rib II, the distance of ultrasonic field of 50 mm and the ultrasonic power of 528 W is 29.9%, which is higher than those of all the other schemes. The research results can effectively optimize the pool boiling performance of the heat transfer enhancement and provide useful support for the development of heat dissipation in related fields. [ABSTRACT FROM AUTHOR]

In this paper, a multilayer perceptron (MLP)-type artificial neural network model with a back-propagation training algorithm is utilized to model the bubble growth and bubble dynamics parameters in nucleate boiling with a non-uniform electric field. The influences of the electric field on different parameters that describe bubble's behaviors including bubble waiting time, bubble departure frequency, bubble growth time, and bubble departure diameter are considered. This study models single bubble dynamic behaviors of R113 created on a heater in an inconsistent electric field by utilizing a MLP neural network optimized by four different swarm-based optimization algorithms, namely: Salp Swarm Algorithm (SSA), Grey Wolf Optimizer (GWO), Artificial Bee Colony (ABC) algorithm, and Particle Swarm Optimization (PSO). For evaluating the model effectiveness, the MSE value (Mean-Square Error) of the artificial neural network model with various optimization algorithms is measured and compared. The results suggest that the optimal networks in the two-hidden layer and three-hidden layer models for the bubble departure diameter improve MSE by 33.85% and 35.27%, respectively, when compared with the best response in the one-hidden layer model. Additionally, for bubble growth time, the networks with two hidden layers and three hidden layers have the 44.51% and 45.85% reduction in error, when compared with the network with one hidden layer, respectively. For the departure frequency, the error reduction in the two-layer and three-layer networks is 46.85% and 62.32%, respectively. For bubble waiting time, the best networks in the two hidden-layer and three hidden-layer models improve MSE by 52.44% and 62.27% compared with the best 1HL model response, respectively. Also, the two algorithms of SSA and GWO are able to compete well (comparable MSE) with the PSO and ABC algorithms. [ABSTRACT FROM AUTHOR]

Numerous energy systems, including distillation, power production, air conditioning, cooling, and purification, use evaporation and flow boiling in minichannels. In this study, we show noticeably higher heat transfer coefficients and critical heat flux of 182% and 114% during DI water flow boiling in ZnO-nano-thin-film nanostructured (∼110–423 nm), industrial-scale-heated copper bottom surface. By using a combination of the sol–gel spin coating and annealing methods, we produce durable and highly conformal nanostructured surfaces that enable scale nano-manufacturing. Flow boiling experiments were carried out in 1.5 mm height bottom surface-heated minichannel using DI water as the working fluid. In order to measure the effectiveness of present method and clarify how the structural length scale affects it, the present study ZnO-nano-thin-film structured surfaces are compared with previously published micro/nano-scale fabricated surfaces, demonstrating the necessity and importance of the nanoscale properties of ZnO-nano-thin films for improvement. The surfaces of the nano-thin film were subjected to durability testing utilizing a seven-day continuous flow boiling experiment, which revealed minor deterioration. The higher boiling performance is achieved on ZnO-TF-423 is due to the proper bonding between polished copper bare surface (BS) and deposited ZnO thin films. Additionally, the rough surface on BS allows the copper and ZnO thin films to bind properly. It can be concluded that surfaces made using an efficient sol–gel spin coating process possesses superior boiling heat transfer capabilities at comparatively lower surface temperatures, suggesting a smaller chance of damaging the surface from rising temperatures. [ABSTRACT FROM AUTHOR]

Boiling is known as an effective mode of heat transfer at low-temperature differences, due to the rapid vaporization of liquid. The performance of boiling heat transfer can be enhanced by reducing surface wettability and modifying surface structures. In this study, polished copper (bare) substrates were modified by composite coatings of TiO2 and SiO2 nanoparticles. Four different samples were prepared using electrophoretic deposition and by varying the coating duration to 5, 10, 15, and 20 min, which were named S5, S10, S15, and S20, respectively. The surface characteristics of bare and coated samples, such as morphology, wettability, surface roughness, and coating layer thickness, were investigated. The contact angle measurements of the bare surface were 65.7°, whereas the coated samples S5, S10, S15, and S20 were 112.9°, 103.6°, 100.3°, and 96.8°, respectively. The coating layer thickness of the samples S5, S10, S15, and S20 was 2.46, 4.76, 9.86, and 14.58 microns, respectively. The pool boiling performance was examined in demineralized (Milli-Q) water on bare and coated surfaces. The onset of nucleate boiling (ONB) temperature was reduced for all composite coated surfaces. The largest reduction in ONB was observed for S15, which was ~ 3.5 °C less than the bare surface. The maximum enhancements in the boiling heat transfer coefficient (BHTC) recorded for S10 and S15 were 38% and 62%, respectively. The optimum coating layer thickness was observed to be ~ 10 µm, up to which heat transfer performance was improved. [ABSTRACT FROM AUTHOR]

An experimental study of nucleate pool boiling is conducted on the GNP/Ni-Al2O3 (GNP-graphene nano particle) nano-composite coated copper surfaces at atmospheric pressure using distilled water (DI) as boiling fluid. The microporous coated surfaces are fabricated using hybrid method (electrochemical deposition of GNP and nano-composite coating of Ni-Al2O3). A modified surface structure is generated as a result of this deposition, and different surface morphological parameters of this modified structure, such as surface structure, roughness and wettability, are investigated. Results show the enhancement in boiling heat transfer coefficient (BHTC) and critical heat flux (CHF) in nano-composite coated surfaces compared to the bare Cu surface. The improvement in boiling performance is mostly attributable to the enhancement of roughness and wettability as well as the higher thermal conductivity of the GNP/Ni-Al2O3 nano-coating. The highest CHF of 2217 (kW/m2) and BHTC of 112.83 (kW/m2K) is found in case of composite nano-coated superhydrophilic (CNCS) surfaces, which are 104% and 123% more than the bare Cu surface. High-speed visualization is used to conduct a quantitative investigation of the dynamics of bubble, including active bubble site density, emission frequency of the bubble, bubble departure diameter and their impact on the performance of pool boiling heat transfer. [ABSTRACT FROM AUTHOR]

It is very important to accurately analyze the heat transfer characteristics of a working fluid in the cooling system based on subcooled flow boiling. In contrast to previous computational fluid dynamics (CFD) studies for the subcooled flow boiling of water or synthetic refrigerants in a vertical tube, we study the subcooled flow boiling characteristics of CO2 in a horizontal tube at -30 ℃. Our model is built based on Eulerian multi-phase model combined with the interfacial area concentration and wall heat flux partitioning models, and it is solved by the CFD solver, ANSYS FLUENT 19.3. This paper determines a reasonable bubble waiting time coefficient (CWT), critical Weber number (Wecri), and turbulence model (TM) for modelling of flow boiling heat transfer of CO2 by combining with uniform design (UD), Taguchi method, multiple quadratic regression (MQR) model and grid search method. As the result, the reasonable values of CWT and Wecri, and reasonable TM were determined as CWT = 0.8, Wecri = 0.7, and RNG k–ε model. This work has a significant contribution to study the subcooled flow boiling heat transfer characteristics of CO2 at low temperature. The proposed approach could be actively applied to improve the solution accuracy of the heat transfer of a working fluid in various heat transfer system. [ABSTRACT FROM AUTHOR]

The response surface methodology was used to optimize the hydrothermal treatment conditions of foxtail millet using the soak-boil or soak-steam method. The optimized hydrothermal treatment conditions for soak-boil method were, soaking time of 2 h at 50.5 °C and boiling time of 6.2 min, which resulted in a decortication yield of 82.91%, TPC (45.19 mg GAE/100 g), TAA (55.62%), peak viscosity (270 cP), trough viscosity (264 cP) and final viscosity (440 cP). In the case of soak-steam method, the optimized conditions were, soaking time of 2.05 h at 44 °C followed by steaming at 110 °C for 5 min, which resulted in the decortication yield of 86.89%, TPC (48.64 mg GAE/100 g), TAA (69.42%), peak viscosity (165 cP), trough viscosity (207cP) and final viscosity (297 cP). Both the hydrothermal treatments significantly increased decortication yield, TPC and TFC contents of decorticated millet kernel, however, lowered the pasting viscosities. The drying kinetics studies of optimized samples of both the treatments were performed at 40, 45 and 50 °C. The soak-steamed grain had shown lower effective diffusivity coefficient (Deff), whereas the soak boil millet samples had indicated lower activation energy (Ea). For soak-boil and soak-steam optimized samples, the highest values of R2 (0.99949 and 0.0051), the lowest chi-square (χ2) (3.24 × 10−5 and 0.99879) and lowest RMSE (0.0105 and 0.0001) respectively, were obtained for the Midilli model. While comparing the experimental and predicted values, a good agreement between the experimental and predicted values of moisture ratio with drying time curve confirms the suitability of Midilli model in describing drying behaviour of hydrothermally treated foxtail millet. [ABSTRACT FROM AUTHOR]

In current study, a flow boiling experimental examination has been performed on water, water-TiO2 nanofluid, and water-Al2O3 nanofluid and Gradient Boost Regression model was established to predict the Nusselt number of TiO2 and Al2O3 nanofluids. Nusselt number was calculated by varying heat flux, Reynolds number, and volumetric concentration. Good agreement was shown by water results acquired from experiments with the correlation of Chen and CFD. Results demonstrated that the Nusselt number of TiO2 and Al2O3 nanofluid was larger than water. Increment in Nusselt number was noticed with the increment in concentration, heat flux, and Reynolds number. It was seen that Al2O3 nanofluid was superior to TiO2 nanofluid. Highest improvement in the Nusselt number was 37% shown by Al2O3 nanofluid when compared to water. Correlations of Nusselt number were developed for both nanofluids. GBR-GSO machine learning model showed a good agreement with the experimental Nusselt number. [ABSTRACT FROM AUTHOR]

Boiling is an efficient mode of heat transfer and has important applications that use high heat flux systems. However, a single wettable boiling surface is not appropriate for the dual requirements of low superheat for nucleation and high critical heat flux. Here, we present a hydrophilic composite and a functional hydrophilic-hydrophobic partitioned porous structure that significantly improves boiling heat transfer performance via a double-sintering process. The superheat requirement for the onset of nucleate boiling decreased from 2°C on the single hydrophilic porous structure to 1°C on the hydrophilic-hydrophobic porous structure, the critical heat flux was reduced by 3.3% in the early stages of boiling (below 250 kW/m2), the heat transfer efficiency increased by 20%, and the heat transfer was comparable to that of the hydrophilic porous structure. Bubble dynamics were observed using a high-speed camera. The results demonstrate that the bubble nucleation sites mainly occur in the hydrophobic region and this is attributed to a decrease in the energy barrier for nucleation. The bubble dynamic statistics revealed that the product of the diameter of the bubble and the bubble escape frequency are similar for composite surfaces and hydrophilic porous surfaces, which is consistent with Zuber's conclusion. The synergistic effect of the hydrophilic-hydrophobic partitioned porous structure can promote nucleation in the hydrophobic region and retain capillary suction for liquid reflux in the hydrophilic region to enhance boiling heat transfer. This work enables the large-scale deployment of heat exchanger surface processing technology because of its low cost, availability, and reliability. [ABSTRACT FROM AUTHOR]

Effects of various physical mechanisms at the stage of vapor bubble collapse and the subsequent formation of a shaped-charge jet in the process of laser-induced boiling near the end of a thin waveguide immersed in a cold liquid is studied numerically. Depending on the evaporation intensity, three process modes are identified and described. [ABSTRACT FROM AUTHOR]

Objective and Methods: The reliable estimation of phase transition physicochemical properties such as boiling and melting points can be valuable when designing compounds with desired physicochemical properties. This study explores the role of external rotational symmetry in determining boiling and melting points of select organic compounds. Using experimental data from the literature, the entropies of boiling and fusion were obtained for 541 compounds. The statistical significance of external rotational symmetry number on entropies of phase change was determined by using multiple linear regression. In addition, a series of aliphatic hydrocarbons, polysubstituted benzenes, and di-substituted napthalenes are used as examples to demonstrate the role of external symmetry on transition temperature. Results: The results reveal that symmetry is not well correlated with boiling point but is statistically significant in melting point. Conclusion: The lack of correlation between the boiling point and the symmetry number reflects the fact that molecules have a high degree of rotational freedom in both the liquid and the vapor. On the other hand, the strong relationship between symmetry and melting point reflects the fact that molecules are rotationally restricted in the crystal but not in the liquid. Since the symmetry number is equal to the number of ways that the molecule can be properly oriented for incorporation into the crystal lattice, it is a significant determinant of the melting point. [ABSTRACT FROM AUTHOR]

In this study, deionized water pool boiling experiments were performed on austenitic stainless steel AISI 304 steel balls with different initial temperatures. The disturbance and rupture of the vapor film during the quenching process are obtained by a high-speed camera. The temperature profile of the steel ball center during cooling was obtained by thermocouple temperature measurement. Based on the inverse heat conduction method, the inverse heat transfer program was independently developed to solve the surface temperature of the steel ball, the interfacial heat transfer coefficient and the heat flux. The results show that there is no film boiling when the steel ball temperature is 650 °C. There are four stages of film boiling, transition boiling, nucleate boiling and natural convection when the steel ball temperature is between 700 and 1000 °C. The thickness of the vapor film increases with the increase of the initial quenching temperature. At an initial temperature of 1000 °C, the thickness of the vapor film in the equatorial direction is 3.5 to 3.6 mm. With the increase of the initial temperature, the duration and rupture time of the vapor film were prolonged, and the central and boundary LFP temperatures gradually decreased. When the initial temperature is between 700 ~ 1000 °C, the vapor film lasts about 6.5 ~ 32.1 s, and the LFP temperatures at the center are between 612.3 °C and 514.7 °C, respectively. When the initial temperature is 650 °C, the maximum IHTC value is about 11,700 W/(m2·℃), and the critical heat flux is 1545.85 kW/m2. As the initial temperature is 1000 °C, the maximum IHTC value is about 14,900 W/(m2·°C), and the critical heat flux is 1508.43 kW/m2. [ABSTRACT FROM AUTHOR]

This work reports the nucleate boiling heat transfer characteristics of n-pentane on smooth and enhanced surfaces. Surface modifications were carried out on stainless steel surfaces by fabricating microholes of diameter between 0.3 and 0.7 mm arrays using electric discharge machining. Pool boiling experiments were carried out at normal atmospheric pressure. Experiments have been performed for applied effective heat flux range between 1 and 10 W cm−2. An enhancement of 20–45% in heat transfer coefficient was observed on the enhanced surface compared to the smooth surface. The heat transfer improvement in the enhanced surface can be attributed to more active nucleation sites, better rewetting phenomenon, and favorable bubble growth and release mechanism. Further changing the material from steel to brass enhances the heat transfer coefficient by 20%. This will be a viable option as a cooling technology for high-power electronic industries. [ABSTRACT FROM AUTHOR]

The temperature rise characteristics of PMSM (permanent magnet synchronous motor) during operation were studied under the condition of BHT (boiling heat transfer) in cooling water. The subcooling boiling heat transfer model, RPI (Rensselaer polytechnic institute), was used to calculate and improve the computational accuracy of simulation results. The experiments have shown that, when the motor was tested and simulated after preheating, the temperature rise characteristics were similar to test data because the boiling heat transfer phenomenon of the motor was taken into account, with an error of 1.7%, which was more accurate than the error of 7.5% without boiling. Therefore, from the results obtained from the experiments, the phenomenon of boiling heat transfer in cooling system has a significant effect on the temperature rise characteristic of the motor, which should be regarded as an important factor. Due to the influence of two-phase flow boiling heat transfer, the temperature rise of the motor in the plain areas is 4–5 °C higher than that in the high altitude areas. Consequently, if the motor is operated in high altitude areas, its temperature rise characteristic has better effect compared with plain area. Additionally, when BHT in cooling water is considered, the temperature of the motor drops as the rate of flow increases. In the meantime, the temperature difference between the minimum flow rate and the maximum flow rate is about 1 °C, which means that the increase in rate of flow can enhance the boiling heat transfer effect. [ABSTRACT FROM AUTHOR]

This article provides a comprehensive overview of research conducted on heat transfer and crisis phenomena during boiling. It discusses the main stages and trends in the development of this research over the past 60 years, highlighting the increase in studies due to advancements in experimental and theoretical methods and materials science. The article covers topics such as heat transfer coefficient, critical heat flux, nucleate boiling, and heat transfer crisis under forced flow conditions. It also emphasizes the importance of future studies on nanofluid boiling. The text presents various experimental studies on heat transfer during boiling, exploring the effects of coatings and surface structures on heat transfer efficiency. It also discusses phenomena such as vapor films, heat transfer crisis, and vapor explosions. The studies offer valuable insights for researchers and engineers in fields such as microelectronics, power electronics, and energy systems. [Extracted from the article]

Vapor condensation is extensively used in applications that demand the exchange of a substantial amount of heat energy or the vapor-liquid phase conversion. In conventional condensers, the condensate removal from a subcooled surface is caused by gravity force. This restricts the use of such condensers in space applications or horizontal orientations. The current study demonstrates proof-of-concept of a novel plate-type condenser platform for passively removing condensate from a horizontally oriented surface to the surrounding wicking reservoir without gravity. The condensing surface is engineered with patterned wettabilities, which enables the continuous migration of condensate from the inner region of the condenser surface to the side edges via surface energy gradient. The surrounding wicking reservoir facilitates the continuous absorption of condensate from the side edges. The condensation dynamics on different substrates with patterned wettabilities are investigated, and their condensation heat transfer performance is compared. The continuous migration of condensate drops from a superhydrophobic to a superhydrophilic area can rejuvenate the nucleation sites in the superhydrophobic area, resulting in increased heat transport. The proposed condenser design with engineered wettability can be used for temperature and humidity management applications in space. [ABSTRACT FROM AUTHOR]

Epithermal bonanza-type ores, characterized by weight-percent contents of e.g., gold and silver in a few mm to cm, are generated by mixtures of magmatic-derived hydrothermal brines and external fluids (e.g., meteoric) that transport a variety of metals to the site of deposition. However, the low solubilities of precious metals in hydrothermal fluids cannot justify the high concentrations necessary to produce such type of hyper-enriched metal ore. Here we show that boiling metal-bearing brines can produce, aggregate, and accumulate metal nanomaterials, ultimately leading to focused gold + silver ± copper over-enrichments. We found direct nano-scale evidence of nanoparticulate gold- and/or silver-bearing ores formed via nonclassical growth (i.e., nanomaterial attachment) during boiling in an intermediate-sulfidation epithermal bonanza. The documented processes may explain the generation of bonanzas in metal-rich brines from a range of mineral deposit types. [ABSTRACT FROM AUTHOR]

A study of heat emission during the boiling of distilled water and isopropyl alcohol in a microchannel with a size of 12.5 × 3× 0.2 mm3 has been carried out. To calculate heat emission during boiling in the microchannel, the Kutateladze equation for a flat slot with one-sided heating was used, as well as the Kutepov–Sterman dependences for nucleate boiling under conditions of directional fluid motion and the Danilova dependence for calculating heat emission during boiling. It is established that the Kutepov–Sterman equation yields the minimum deviation from experimental data (no more than 25%). [ABSTRACT FROM AUTHOR]

The physical parameters exerting an effect on the density of the heat flux transported by vapor bubbles during nucleate boiling are considered. It is shown that this density depends on the radius of bubble departure from the substrate, the rate of formation of departing bubbles per unit area of the substrate, the thermophysical properties of the liquid, and the saturation temperature. It has been established that the density of the energy flux transported by bubbles increases exponentially with the saturation temperature and depends strongly on the bubble departure radius. It is shown that the thickness of the superheated liquid layer, inside which bubbles grow, does not exceed several hundred microns and depends on the total energy flux. In this case, if the average distance between the bubbles is comparable to the departure radius, bubble coagulation leads to a boiling crisis. [ABSTRACT FROM AUTHOR]

The authors have presented experimental data on the boiling of superfluid helium (helium II) on the surface of a cylindrical heater located in the volume of helium II. Observations of the process of heat and mass transfer in the experimental helium volume were carried out from the end of the cylindrical heater. The formation of a vapor film of finite thickness on the surface of the heater on applying thermal load to it, the existence of a noiseless regime of boiling of helium, and the development of oscillations of the phase boundary in its volume have been shown. [ABSTRACT FROM AUTHOR]

A wide range of industrial processes (i.e., evaporation and condensation in desalination process, steam power plant, solar plant, etc.) involve heat transfer among the fluids. During the process of evaporative and cooling heat transfer, undesirable materials from the fluids accumulate on the surfaces, which critically reduces the performance of heat exchangers and creates one of the biggest challenges in energy transfer. Though the various studies on prediction and removal of fouling was conducted by numerous scientists, this problem is still unresolved in industrial process and is responsible for huge environmental damage and economic losses. This investigation provides a comprehensive overview of crystallization fouling in heat exchangers. Various factors affecting the deposition of crystallization foulaning such as fluid temperature, flow velocity, surface material and roughness, concentration and boiling are systematically reviewed. Accuracy and uncertainty of different equipment and experimental studies are discussed. In addition, fouling modelling is comprehensively discussed from earlier fundamental model to recent computational fluid dynamic and artificial neural networks model. Furthermore, mitigation of fouling with off-line and online approaches are chronologically discussed. Finally, an overview from environmental and economic prospective of fouling in heat exchangers are discussed. The future directions for crystallization fouling in heat exchangers are emphasized, which will support the researchers and industries to retard fouling and achieve economic benefits. [ABSTRACT FROM AUTHOR]

The expansion and collapse of a cavitation bubble during laser heating and subcooled boiling of water in the vicinity of the tip of an optical fiber (laser heating element) installed in a water-filled glass tube with two open ends is studied experimentally and numerically. Cavitation, initiated by continuous laser radiation, is accompanied by the pushing and pulling movement of the heated liquid in the tube and outside it. For the first time, it has been shown that in a tube with an installed laser heating element in a liquid flow moving behind the walls of the bubble, when it collapses at the pole of the bubble surface remote from the end, a liquid jet appears, directed through the bubble to the end of the optical fiber. The jet speeds up the process of sucking liquid into the tube. [ABSTRACT FROM AUTHOR]