End Of Evaporation Research Articles

Effect of small inclination angle on heat transfer performance of Ω-grooved bending heat pipe

Grooved bending heat pipe may operate at small inclination angle caused by practical installation errors. Previous researches mainly focused on large inclination angles of straight heat pipes, but fewer experiments were conducted at small inclination angle of bending heat pipe where liquid accumulation and gravity effect on liquid-vapor transport varies along the pipe. This paper experimentally studied the effect of small inclination angle (±3°) on heat transfer of aluminum-ammonia Ω-grooved bending heat pipe with total length of 650mm, vapor chamber diameter of 4mm and grooved wick diameter of 1.24mm. The results showed that small inclination angle significantly affect the heat transfer performance of bending heat pipe with heat transfer limit changed by 9 times form 20W to 180W and thermal resistance changed by 8 times from 0.04 K/W to 0.32 K/W. Effect of negative and positive angles in bending heat pipe is complex than that in straight heat pipe. Positive condensation end inclination enhances heat transfer due to gravity-driven liquid reflux. Negative condensation end inclination inhibits heat transfer due to anti-gravity reflux and liquid accumulation suppressing gas condensation. Positive evaporation end inclination weakens heat transfer due to anti-gravity reflux. Negative evaporation end inclination also weakens heat transfer due to thick liquid film, increasing thermal resistance and potentially blocking vapor channels. Attributed to coupling effect of liquid accumulation at bending section and capillary force dominant at tiny incline, maximum heat transfer limit of 180 W is achieved at both end inclination of -0.5°.

Numerical analysis of tapered wick configurations in cylindrical heat pipes

Heat pipes are essential devices in thermal engineering due to their ability to transport heat with remarkable efficiency. They are crucial for heat distribution and control in a variety of applications, such as aircraft systems and electronics cooling. This paper presents a numerical analysis on the performance characteristics of a cylindrical heat pipe featuring a novel tapered wick geometry. A two-dimensional numerical model incorporating non-Darcian liquid transport is formulated and solved at steady state. To investigate the effect of the tapered wick geometry, major characteristics such as axial distribution of vapor pressure, liquid pressure and wall temperature are evaluated and analyzed. Based on the direction of taper, three configurations viz., THPE (Tapering wick heat pipe from evaporator end), THPC (Tapering wick heat pipe from condenser end) and THPA (Tapering wick heat pipe at adiabatic center) are studied. A novel non-dimensional parameter termed as Temperature Pressure Index (TPI) is proposed to signify the extent to which an HP can reduce its evaporator temperature relative to increase in pressure drop. Initially a parametric study is performed. Results showed a superior performance of THPE and THPC designs over THPA in terms of output parameters. The numerical findings demonstrate that when compared to a uniform wick heat pipe, both the THPE and THPC configurations exhibit a notable enhancement of 58 % in effective thermal conductivity under a maximum load of 455 W. Further, by conducting a variance-based (Sobol) sensitivity analysis, the THPC design is found to be marginally better as compared to THPE. Finally, the BOBYQA optimization algorithm is employed to find optimum taper angle for THPC design that maximizes the output parameters. The optimum taper angle of the wick is found to be 0.0372° for minimum average evaporator temperature in the present case. For this optimized THPC design, a reduction in average evaporator temperature of 6.51 K is obtained compared to uniform wick heat pipe. Additionally, the obtained TPI value is about 1.86 times than that of a uniform wick heat pipe.

The doomsday of black hole evaporation

Abstract By assuming simultaneously the unitarity of the Hawking evaporation and the universality of Bekenstein entropy bound as well as the validity of cosmic censorship conjecture, we find that the black hole evaporation rate could evolve from the usual inverse square law in black hole mass into a constant evaporation rate near the end of the Hawking evaporation before quantum gravity could come into play, inferring a slightly longer lifetime for lighter black holes.

Experimental investigation of the oscillation threshold to limit state operation of a single branch pulsating heat pipe

The study investigates the characteristics of oscillations and associated thermo-hydrodynamic phenomena for startup, limit state, and intermediate transitional behavior of a pulsating heat pipe (PHP) with the help of its single branch. Experiments are performed on a transparent single branch PHP (SBPHP) at different orientations, evaporator and condenser section temperatures using n-pentane as the working fluid. The entire two-phase flow behavior is recorded with the help of shadowgraph based high speed imaging synchronized in real-time domain with pressure data acquisition at evaporator end. Instability threshold is determined in terms of evaporator temperature at different tube orientations and condenser temperatures. The oscillation startup mechanism along with the associated intermittency is studied in detail. The SBPHP is found to have characteristic variations in oscillation amplitude and frequency as it undergoes a gradual transition from its oscillation threshold to limit state. The mechanism by which the limit state creeps-in and intumesces further is an intrinsic function of liquid-vapor distribution in SBPHP, which in turn depends on the applied boundary conditions. The operational limit is governed by evaporator dryout exceeding permissible limits marked by the steep rise in the dry length of evaporator. As SBPHP approaches or operates at its limit state, evaporator is found to have different regimes across its length, viz., mild convective evaporation combined with subcooled nucleate boiling, saturated nucleate boiling, forced convective boiling, film breakdown and permanent dryout. The liquid film distribution, pressure fluctuations, and heat transfer components in evaporator at the limit state have also been studied.

Dual-species Bose-Einstein condensates of Na23 and K41 with tunable interactions

We report the creation of dual-species Bose-Einstein condensates (BECs) of Na23 and K41. Favorable background scattering lengths enable efficient sympathetic cooling of K41 via forced evaporative cooling of Na23 in a plugged magnetic trap and an optical dipole trap. The 1/e lifetime of the thermal mixture in the stretched hyperfine state exceeds 5 s in the presence of background scattering. At the end of evaporation, we create dual BECs in the immiscible phase, with about 3×105 Na23 atoms surrounding 5×104 K41 atoms. To further enable the tuning of the interspecies interaction strength, we locate multiple Feshbach resonances at magnetic fields up to 100 G. The broadest s-wave resonance located at 73.4(3) G features a favorable width of 1.8(2) G. This work sets the stage for the creation of ultracold gases of strongly dipolar bosonic Na23K41 molecules as well as the exploration of many-body physics in bosonic Na23−K41 mixtures. Published by the American Physical Society 2024

Prediction of transmission routes of respiratory infectious diseases in indoor environment: Based on droplet evaporation and sedimentation analysis

Many respiratory infectious diseases are believed to be transmitted from person to person through droplet nuclei in the air or contact with droplet-contaminated surfaces. Most studies related to droplet evaporation only focus on the evaporation process, without dividing the transmission routes of diseases caused by droplet evaporation. In this paper, the actual size of droplet nuclei was analyzed, and droplet evaporation and the changes in component content were predicted. Especially considering the dynamic effect of evaporation on droplets size change, a more realistic sedimentation model was established, and the probability of pathogen transmission through different routes and the corresponding droplet size distribution range were analyzed. The results showed that the size of droplet nuclei and the rate of the evaporation process together determined the time required for droplet evaporation. The number of droplets still suspended in the air after the end of evaporation is much higher than the number of droplets settling on the ground. In addition, the differences in component content during the evaporation process may affect the inactivation of pathogens in droplets. This study provided a reference for the prevention and control strategies of respiratory infectious diseases in indoor environments.

A Numerical and Experimental Investigation on a Gravity-Assisted Heat-Pipe-Based Battery Thermal Management System for a Cylindrical Battery

A thermal management system for lithium-ion batteries is an essential requirement for electric vehicle operation due to the large amount of heat generated by these cylindrical batteries during fast charging/discharging. Previously, researchers have focused mostly on pouch and prismatic cells with heat pipes arranged in the horizontal direction. The current study introduces a novel vertically-oriented heat-pipe-based hybrid cooling battery thermal management system (BTMS) that numerically evaluates the thermal performance of the cylindrical batteries and the flow pattern within the cooling channel at C rates as high as 8C. The model was experimentally validated using five round heat pipes in a vertical orientation utilizing the effect of gravity to assist condensate flow through the heat pipe. The heat pipes were arranged in a staggered pattern to improve the overall heat transfer performance by means of forced convective cooling. This design allowed for maximizing the heat transfer process despite the lack of contact between the cylindrical-shaped batteries and round-shaped heat pipes. During this study, the temperatures of the evaporator end and the condenser end of the heat pipes and battery surfaces were monitored, and the thermal performances of the system were determined at varying inlet cooling liquid temperatures (15, 20, 25 °C) and high rates of 4C and 8C. Representatively, the proposed hybrid BTMS could maintain a maximum battery surface temperature of around 64 °C and a temperature difference between cells under 2.5 °C when the inlet velocity was 0.33 L/min and the cooling liquid temperature was 25 °C. The high temperatures reached the fourth and fifth heat pipes because they are part of the backflow design and are affected by backflow temperature. Nevertheless, the current design shows that the proposed system can maintain battery surface temperatures well within 5 °C.

Experimental and simulation study on heat transfer performance of a high-concentrating photovoltaic system coupled with gravitational heat pipe

A hybrid high-concentrating photovoltaic system coupled with a specific gravitational heat pipe is proposed in this study for heat transfer research both experimentally and numerically, aiming to identify one innovative and promising cooling method for high-concentrating solar cells. The experimental platform is built first to test the average temperature of the evaporation end and is then compared with the simulation result to corroborate the reliability and applicability of numerical models. Based on the above verification, the effects of concentration ratio, liquid filling rate and saturation temperatures are studied, drawing a crucial conclusion that a liquid filling rate of 55% and a saturation temperature of 312.15 K help achieve the lowest cell temperature of 325 K and highest electrical efficiency of 30.9% when the concentration ratio exceeds 300. With experimental data, this study further fits the empirical formula of the heat transfer coefficient hfe at the evaporation end, hfe=C0⋅Tsat−3.863⋅VL0.0252⋅(CR⋅Sun)0.724, where C0=21.165(w0.276/m0.448⋅k4.683). At the condensation end, the error between the calculated heat transfer coefficient and values from Nusselt Theory is only 7%, demonstrating the rationality of simulation results in this study and the reliability of Nusselt Theory simultaneously.

Fluid model of a black hole-string transition

A fluid model of self-gravitating strings is proposed. It is expected that black holes turn into strings around the end of black hole evaporation. The transition will occur near the Hagedorn temperature. After the transition, strings would form a bound state by the self-gravitation. Horowitz and Polchinski formulated a model of self-gravitating strings by using winding strings wrapping on the Euclidean time circle [arXiv:hep-th/9707170]. In this paper, we first show that winding strings in the Horowitz-Polchinski model approximately behave as a perfect fluid. Then, we solve the Einstein equation for the fluid of winding strings. Our solution reproduces behaviors of the self-gravitating string solution in the Horowitz-Polchinski model near the Hagedorn temperature, while it approaches the Schwarzschild black hole at low temperatures. Thus, our fluid model of self-gravitating strings gives a description of the transition between black holes and strings.

Generality of Evaporative Crystal Liftoff on Heated Hydrophobic Substrates

Scaling or mineral fouling occurs due to the presence of dissolved minerals in water. Scaling is problematic in numerous industrial and household plumbing applications where water is used. The current methods of scale removal often utilize harsh chemicals that are not environmentally friendly. The evaporation of a saline droplet provides a platform to study the role of the substrate in the dynamics of crystallization during scaling. In the present work, we show out-of-plane growth of crystal deposits during the evaporation of saline droplets of aqueous potassium chloride on a heated smooth and microtextured hydrophobic substrate. These out-of-plane deposits, termed as "crystal legs", are in minimal contact with the substrate and can be easily removed from the substrate. The out-of-plane evaporative crystallization of saline droplets of different initial volumes and concentrations is observed irrespective of the chemistry of the hydrophobic coating and the crystal habits investigated. We attribute this general behavior of crystal legs to the growth and stacking of smaller crystals (size ∼10 μm) between the primary crystals toward the end of evaporation. We show that the rate at which the crystal legs grow increases with an increase in the substrate temperature. A mass conservation model is applied to predict the leg growth rate, which agrees well with the experiments.

Experimental study on sodium Screen-Wick heat pipe capillary limit

Heat pipes continuously transport the latent heat of vaporization from the evaporator to the condenser in the heat pipes due to the capillary pressure created by the menisci in the wick pumping the condensed fluid back to the evaporator. The heat pipe heat transfer capacity is then limited by the capillary limit. However, fewer capillary limit experiments were conducted to investigate the transient temperature variations and physical mechanism at the capillary limit for liquid metal wick heat pipes. This work presents capillary limit transient measurements on a sodium screen-wick heat pipe for high heat fluxes, high heating rates during frozen startup, and negative and positive inclination angles. It also investigates the special behavior before and after dryout, including dryout oscillations and the recovery process to understand the cause and physical mechanism at the capillary limit. The direct cause of the capillary limit is that the evaporation rate exceeds the capillary-driven liquid supply to the evaporator. The experiments show that the capillary limit creates a rapid temperature increase of about 5 °C/s at the evaporator end, while the condenser and adiabatic section temperatures decrease. Dryout oscillations were observed with positive inclinations before the capillary limit. After the capillary limit, reducing the power to just below the limit does not lead to heat pipe recovery, but the power needs to be reduced by about 30% of the critical heat flux to make the heat pipe return to its normal operating state.

Complete Evaporation of Black Holes and Page Curves

The problem of complete evaporation of a Schwarzschild black hole, the simplest spherically symmetric vacuum solution of the Einstein field equation, posed by Hawking, is that when the black hole mass M disappears, an explosion of temperature T=1/8πM takes place. We consider the Reissner–Nordstrom black hole, a static spherically symmetric solution to the Einstein–Maxwell field equations, and show that if mass M and charge Q<M satisfy the bound Q>M−CM3, C>0 for small M, then the complete evaporation of black holes without blow-up of temperature is possible. We describe curves on the surface of state equations such that the motion along them provides complete evaporation without temperature explosion. In this case, the radiation entropy follows the Page curve and vanishes at the end of evaporation. Similar results for rotating Kerr, Schwarzschild–de Sitter and Reissner–Nordstrom-(Anti)-de Sitter black holes are discussed.

Investigation of self-assembly and topological changes in the sessile droplets of Klebsiella oxytoca by Chronological study

The infectious droplet from the patient self-assembles into a novel pattern depending on bacterial interaction with substrate and liquid. The spatial location of bacteria inside the droplet fluctuates depending on the non-covalent forces. The deformation and dehydration induced stress on bacteria in evaporating contagious-fluid droplets alters the viability and infectivity. The self-assembly of Klebsiella oxytoca (KO) in contagious sessile droplets was studied by natural evaporation. KO forms novel patterns as the droplets exsiccate, thus revealing the unexplored topological changes that govern its survival and infection strategies. The droplets of both bacterial suspension in Milli-Q and SRF of volume 0.95 ± 0.1 μl were placed on the glass material for assessment of the self-assembly. The bacterial suspension was stained before allowing them to desicate. The bacterial chemotaxis and deposition near the end of evaporation are recorded using the bright and dark field optical method. The random time interval is also measured to track the bacterial movement. The investigation shows that the majority of the bacterial population moves toward the rim of the droplet because of edge closely packing, leading to enhanced viability and pathogenesis on the famously known “coffee ring” and few bacteria are present at the centre of the droplet which represents chemotaxis of bacteria. The mechanistic insight gained via our study can have far-reaching implications for bacterial infection through droplets e.g., through open wounds.

Avalanche Coalescence of Liquid Metal Particles for Uniform Flexible and Stretchable Electrodes

AbstractSelf‐sinterable gallium‐based liquid metal (LM) ink for a handy drop‐casting coating method is developed. The fabricated LM electrode is coffee‐ring‐free and bilayer‐free, which guarantees high electrical conductivity, wettability, flexibility, and stretchability. The ink consists of Galinstan, ethanol‐water mixture, hydrochloric acid, and polyvinylpyrrolidone. The binary mixture provides excellent wetting conditions and suppresses a coffee‐ring stain from Marangoni mixing. The acid removes an oxide layer on the LM interface. The colloidal interaction forces by self‐assembled polyvinylpyrrolidone induce avalanche coalescences of the particles at the end of evaporation, which produces a thin and uniform dried conductive layer. The acid and polymer provide a bilayer‐free structure and electrification without any post sintering. The drop‐casted self‐transformed LM electrode showed excellent electrical resistance of O (0.1–1 Ω) on folding and stretching conditions. It is believed that this method can serve as flexible and stretchable electrodes, on various substances for soft robots and wearable devices, without any complicated post‐process.

Entanglement entropy of a near-extremal black hole

We study how the entanglement entropy of the Hawking radiation derived using island recipe for the Reissner-Nordstr\"om black hole behaves as the black hole mass decreases. A general answer to the question essentially depends not only on the character of decreasing of the mass but also on decreasing of the charge. We assume the specific relationship between the charge and mass $Q^2=GM^2[1-\left(\frac{M}{\mu}\right)^{2\nu} ]$, which we call the constraint equation. We discuss whether it is possible to have a constraint so that the entanglement entropy does not have an explosion at the end of evaporation, as happens in the case of thermodynamic entropy and the entanglement entropy for the Schwarzschild black hole. We show that for some special scaling parameters, the entanglement entropy of radiation does not explode as long as the mass of the evaporating black hole exceeds the Planck mass.

Effects of attapulgite addition on soil evaporation and crack characteristics

Water is one of the most important factors limiting vegetation recovery and agricultural development in arid and semi-arid areas. The reduction of ineffective soil evaporation can improve soil water use efficiency. As a kind of clay mineral, attapulgite (ATP) plays a critical role in limiting soil evaporation due to its hydrophilicity and adsorption. In this study, three typical soils with different textures (dark loessial soil, cultivated loess soil, and sandy soil) were selected from the arid and semi-arid area of the Loess Plateau, and five ATP additions (0%, 1%, 2%, 3% and 4%) were set for conducting soil evaporation experiments under natural conditions using micro-evaporators to investigate the effects of ATP addition on different soil evaporation processes and the characteristics of evaporation surface cracks. The results showed that the cumulative evaporation and evaporation loss ratio of the same soil decreased with the increases of ATP addition when the ATP addition was <3%. When ATP was added at 3%, the cumulative evaporation and evaporation loss ratio of dark loessial soil and sandy soil decreased, while those of cultivated loess soil increased. When ATP was added at 4%, the cumulative evaporation decreased and the evaporation loss ratio increased for dark loessial soil, the cumulative evaporation increased and the evaporation loss ratio decreased for sandy soil, and the cumulative evaporation and evaporation loss ratio decreased for cultivated loess soil. The average cumulative evaporation of different soils followed an order of dark loessial soil > cultivated loess soil > sandy soil. Soil water content of ATP treatment was consistently higher than that of control throughout the whole evaporation process in the same soil. Simulations of cumulative evaporation versus the square root of time indicated that the amount of water released from the ATP-treated soil samples at the end of evaporation was higher than that of the control. After the addition of ATP, the crack area density of dark loessial soil and cultivated loess soil increased significantly, and the crack area density of sandy soil increased with the increase of ATP addition. The crack area density of all three soils reached the maximum at 4% of ATP addition. In summary, ATP addition of 3% could minimize the ineffective evaporation of soil water.

Fate and distribution of mercury during the desulfurization wastewater evaporation process

The wastewater evaporation technology was a promising method for desulfurization wastewater zero-liquid discharge. However, there is a risk of mercury release during wastewater evaporation, which may cause severe environmental issues. This work investigated the fate and distribution of mercury in the wastewater evaporation process. In the typical working conditions, 93.6% of Hg in the wastewater was released, and the rest part would retain in the final evaporation product. The gaseous Hg release process could be divided into three stages. The gaseous Hg0 was the primary Hg released source in the initial evaporation process. Subsequently, due to the hydrolysis of chloride, the chlorine oxidizing atmosphere was generated, which induced the homogeneous oxidation of Hg0. At the end of evaporation, the pyrolysis of HgS and HgO would release a small amount of Hg. Besides, the effect of evaporation temperature, Cl- and SO32- content on Hg release was investigated. The higher evaporation temperature was adverse to Hg stability. The proportion of gaseous Hg0 and Hg2+ was highly sensitive to the SO32- and Cl- content. In addition, obtained from the risk assessment, the Hg release from the wastewater evaporation would not affect either total Hg content in main flue gas or solid-phase comprehensive utilization.

Desiccation cracking of soil subjected to different environmental relative humidity conditions

Relative humidity (RH) is among key environmental and climatic factors that affect the evolution of soil desiccation cracking. This study aims to investigate how RH variations influence soil desiccation cracking, addressing an overlooked aspect in prior studies. A set of laboratory tests were performed to examine a fat clay undergoing desiccation cracking at various controlled RH levels of 15.0%, 44.0%, 66.0%, 76.0%, 83.5% and 93.7%. During testing, all samples were weighed and photographed simultaneously to monitor evaporation and surface cracking. The evolution of the surface crack network was quantitatively analyzed by an image processing technique. Results highlight the strong dependence of soil desiccation cracking on RH conditions. Increasing RH is found to decrease the overall evaporation rate and increase the water content at which cracking starts. Under high RH levels, the formation of surface cracks exhibits an evident hierarchical process with wide primary cracks developing first followed by fine sub-cracks propagating from the primary ones. Different cracking developing rates between a primary crack and sub-crack give rise to the remarkable multi-stage growth of crack length. Besides, owing to an increase in RH, desiccation cracks at a given water content tend to be wider and the width distribution of the final crack network changes from a unimodal to a bimodal feature. Lowering RH causes a faster cracking rate and makes the hierarchical process invisible, resulting in the formation of a longer total crack length at the end of evaporation. This study is expected to help analyze the underlying formation mechanisms of desiccation cracking-inducing geohazards and assess the long-term performance of earth structures under future climate changes.

Температурная динамика карбонизации хлопковых волокон микроволновым излучением на воздухе

Spectral pyrometry was used to determine the dynamics of microwave heating in air of samples (3 g samples) of cotton fibers pretreated with 2, 5, 7, and 10 % aqueous H3PO4 solution. Microwave heating was carried out in an open quartz reactor. The processing of the recorded radiation spectra and the calculation of the temperature were carried out using the “Spectral pyrometry” program. It has been established that the graph of the change in the temperature of the sample during heating has three characteristic regions — low-temperature, the region of unstable temperature, and the region of temperature stabilization. In the low-temperature region, free moisture is removed from the sample. The region of unstable temperature is associated with the process of cellulose combustion, which begins after the end of moisture evaporation at a temperature above 600 K. Under the influence of microwave radiation, all chemical processes intensify in the sample. Video filming during microwave heating showed that in the process of irradiation, sinuous slit-like cavities are formed on the surface of the sample, inside which electrical discharges and ignitions form “hot spots”, from which heat spreads to the entire volume of the sample and additionally heats it, which leads to significant temperature fluctuations. The combustion process continues until all the material is carbonized. After that, a relative stabilization of the temperature occurs, the value of which lies in the range of 1000 – 1200 K. It has been established that the higher the concentration of the H3PO4 solution used for pretreatment of the samples, the lower their temperature in the given area. It has been shown that the carbonization process begins in 70 – 75 s from the start of heating in the local areas of the sample. The results of comparative studies of the structure and elemental composition of samples before and after microwave exposure are presented. It is shown that after 180 s of heating, the fibers become significantly thinner, while maintaining integrity along the length. Carbonized fibers contain a significant amount of phosphorus, the concentration of which is maximum in the outer layers of the sample and is 15 – 20 %. The total weight loss of the samples depends on the concentration of the H3PO4 solution used to pre-impregnate the samples and ranges from 94 % for 2 % H3PO4 to 82 % for 10 % H3PO4.

End of a black hole’s evaporation. II.

We derive an explicit expression for the transition amplitude from black to white hole horizon at the end of Hawking evaporation using covariant loop quantum gravity.