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Laser Machining of Metals
Published in V. K. Jain, Advanced Machining Science, 2023
Vaporization refers to the passage from condensed phase (solid or liquid) to vapor by virtue of the emission of particles (atoms or molecules) from the top surface of the target. The rate of vaporization can be calculated using the Hertz-Knudsen equation. According to this, the flux (Φ) of particles (atoms or molecules) leaving the surface due to vaporization can be written as [8], Φ=µps(2πmkBT)−1/2
Risk Assessment Techniques and Methods of Approach
Published in D. Kofi Asante-Duah, Hazardous Waste Risk Assessment, 2021
Vapor pressure — Vapor pressure is the pressure exerted by a chemical vapor in equilibrium with its solid or liquid form at any given temperature. It is a relative measure of the volatility of a chemical in its pure state and is an important determinant of the rate of volatilization. It is used to calculate the rate of volatilization of a pure substance from a surface or in estimating a Henry’s law constant (c.f.) for chemicals with low water solubility. Numerous estimation procedures exist in the technical literature; Lyman et al. (1990), among others, elaborate some estimation methods for this parameter. The higher the vapor pressure, the more likely a chemical is to exist in significant quantities in a gaseous state; thus, constituents with high vapor pressure are more likely to migrate from soil and groundwater to be transported in air.
Characteristics and Behavior of Fire
Published in Peter M. Bochnak, Fire Loss Control, 2020
With this in mind, it is important to know some of the chemistry and physics of fire. For flammable liquids, we start with an explanation of vapor pressure and boiling point. As liquid molecules leave the surface of an open container, they form a vapor. Since the container is open, the liquid evaporates. With a closed container, the vapor is limited to the space above the liquid. At the point of equilibrium (equal amount of vapor leaving and entering the liquid), the pressure exerted is the vapor pressure, measured in psia (pounds per square inch atmospheric) or kPa (kiloPascals). As the temperature of a liquid increases, the vapor pressure increases. The boiling point of a liquid is the temperature at which vapor pressure equals atmospheric pressure. The percentage of vapor is directly proportional to the relationship between the vapor pressure and the total pressure of the vapor-air mixture above the liquid.
A critical overview of thin films coating technologies for energy applications
Published in Cogent Engineering, 2023
Mohammad Istiaque Hossain, Said Mansour
The vapor pressure is the equilibrium pressure of the material (the density of molecules in the gas phase) above an evaporating surface. A uniform film cannot be achieved unless the chamber is first cleared of excess atmospheric particles. These particles can be trapped on the substrate surface by the condensing thin film, leaving “pinholes” or other surface distortions. Since the thermal process generally takes places at pressures around 10−4 Torr, it is desirable to have pumping systems capable of achieving base pressures, which are several orders of magnitude below this range, usually 10−6 Torr or less. Most metals reach their normal melting point before the vapor pressure is high enough to achieve a significant evaporation rate. Two exceptions are chromium and manganese, which sub-lime; they evaporate rapidly while still a solid. Other materials, called refractory metals and compounds, are difficult to evaporate since they have low vapor pressures even at high temperatures. Some materials that leave the surface can be scattered back. The amount that is scattered depends on the molecular weight of the evaporating atoms and the vapor density above the evaporant surface.
Estimating evaporation rates and contaminant air concentrations due to small spills of non-ideal aqueous organic solvent mixtures in a controlled environment
Published in Journal of Occupational and Environmental Hygiene, 2023
Spéro Franck Abattan, Patrick Eddy Ryan, Jérôme Lavoué, Stéphane Hallé, Ali Bahloul, Daniel Drolet, Maximilien Debia
In general, the volatility of a liquid chemical depends on its saturated vapor pressure (Ishidao et al. 2016). The vapor pressure of the chemical corresponds to the pressure that the liquid exerts as it moves to the vapor phase (tendency of molecules and atoms to escape from the liquid chemical) (Keil 2009). The higher the pressure, the faster the liquid evaporates. For solvent mixtures, the equilibrium vapor pressures of the chemicals that constitute the solution are different from those of pure compounds. Therefore, estimating the partial vapor pressures of the constituents of the mixture is of great interest for predicting emission rates (Reinke 2009). Three approaches are available for estimating partial vapor pressures for solvent mixtures: Raoult’s Law, Raoult’s Law adjusted by the activity coefficient, and Henry’s Law (Popendorf 2006, 2019).
Experimental investigation of a novel micro-channel flat loop heat pipe (MC-FLHP) for data center cooling and heat recovery
Published in International Journal of Green Energy, 2022
Jinwei Xiang, Liang Luo, Xupeng Wang, Samson Shittu, Zhangyuan Wang, Xudong Zhao, Chuangbin Weng
The working principle of the MC-FLHP could be summarized as follows: part of the heat generated from the IT equipment is absorbed by the working fluid flowing across the evaporator, and the remainder is dissipated into surroundings. As a result, the liquid inside the evaporator is converted into vapor. The vapor will be collected at the upper vapor header and is transported into the condenser through the vapor transportation line. The vapor entering the condenser is gradually condensed by the cooling water in the heat exchanger. At the bottom end of the condenser, the vapor is completely condensed, and the condensed liquid falls into the header of the condenser under the force of gravity and capillary. The liquid returns to liquid distribution tube of the evaporator through the liquid transportation line. The cooling water of the heat exchanger could be from the ground water or surface water and the heat from the IT equipment in the data center racks is continuously transmitted to the outdoor condenser for heat dissipation, which creates a loop that keeps the temperature of the data center IT equipment within the set range without consuming additional power.