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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.
Fire Protection and Prevention
Published in W. David Yates, Safety Professional’s Reference and Study Guide, 2020
The vapor pressure of a liquid is defined as the pressure exerted by the molecules that escape from the liquid to form a separate vapor phase above the liquid surface. The pressure exerted by the vapor phase is called the vapor or saturation pressure. Vapor or saturation pressure depends on temperature. As the temperature of a liquid or solid increases, its vapor pressure also increases. Conversely, vapor pressure decreases as the temperature decreases.
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.
Treatment of Simulated Radioactive Wastewater Using Reverse Osmosis and Membrane Distillation
Published in Nuclear Technology, 2022
Caishan Jiao, Hao Wang, Yaorui Li, Meng Zhang, Yang Gao, Mingjian He
The MD process took the RO concentrate as feed liquid. The effects of the feed temperature and feed flow rate on the permeate flux of the MD process were investigated (Fig. 5). It can be seen that the permeate flux increased approximately exponentially with increasing feed temperature (Fig. 5a). When the feed temperature varied from 50°C to 90°C, the permeate flux increased from 3.51 to 15.48 L/m2·h. The MD process is driven by the vapor pressure difference between the two sides of the membrane. According to the Antoine equation, the vapor pressure at the vapor-liquid interface exponentially increases with the increasing temperature. The vapor pressure on the hot side of the MD membrane module will increase exponentially when the feed temperature increases.20 Thus, the driving force of the MD process is enhanced, resulting in the increase of the permeate flux. In addition, the increase in feed temperature can reduce the viscosity of the feed liquid and weaken the concentration polarization, which leads to the increase of the permeate flux.21,22
Improved model structure of direct contact membrane distillation for saline water purification
Published in Chemical Engineering Communications, 2023
Emad Ali, Abdullah Najib, Jamel Orfi, Fahad Awjah Almehmadi
Figure 3(d) compares the water mass production for all dT’s. Obviously, the water production improves with dT which is intuitive because wider dT leads to wider temperature difference at the membrane interface (dTm), that is, wider driving force, as they are correlated. Specifically, at the water production of dT = 50 °C is 13% higher than that of dT = 40 °C and 30% higher than that of dT = 30 °C. Another interesting finding is that the water production for each dT increases with It is well known that mass flux increases with feed temperature due to the exponential relationship between the vapor pressure and temperature (Al-Anezi et al. 2012; Bouguecha et al. 2015; Kayvani Fard et al. 2015). However, here the performance is improved even that the inlet permeate temperature is also jointly increases. This means that improvement can still be obtained if warmer condenser stream is used. It is not clear whether dTm increases with at fixed dT unless the interface temperatures are computed by solving the model equations. Nevertheless, the interface temperature will increase for both channels since both inlet temperature increase. Since the vapor pressure is an exponential function of the temperature, the vapor pressure difference will continue to increase with temperature resulting in higher vapor flux. This situation can be further analyzed when the MD model is fitted to the data to examine the underlying physics of the operation. Nevertheless, Figure 3(d) confirms the superiority of operating at the highest dT and to attain the highest water production. In addition, operating at these conditions implies using as high as 30 °C.In this case, the cooling energy requirement can be reduced if the condenser circuit should be recycled to the MD system. Otherwise, the cooling energy requirement can be eliminated if waste process water available at 30 °C can be used continuously as the condenser stream.